WO2026010751A1

WO2026010751A1 - High speed pultrusion system

Info

Publication number: WO2026010751A1
Application number: PCT/US2025/034739
Authority: WO
Inventors: Guido Bramante; Chi-Wei TSANG; Yuan Yao; Quan Yuan
Original assignee: Dow Global Technologies LLC; Rohm and Haas Co
Current assignee: Dow Global Technologies LLC; Rohm and Haas Co
Priority date: 2024-07-04
Filing date: 2025-06-23
Publication date: 2026-01-08
Anticipated expiration: 2027-01-04

Abstract

Embodiments of the present disclosure are directed towards a pultrusion system for forming a continuous fiber-reinforced polyurethane (CFRP) composite structure at a high rate of manufacture while reducing the amount of air trapped in the composite material. The pultrusion system includes an injection box comprising an entry region, an expansion dome region, and an end region. The entry region comprising a first tapered section and a second tapered section, the expansion dome region comprising at least a first, a second, and a third expansion dome, wherein each expansions dome is connected by a tapered section and each expansion dome exhibits a cross section having a tear drop shape. The end region comprising a tapered section and a flat section.

Description

HIGH SPEED PULTRUSION SYSTEM

Field of Disclosure

[0001] The present disclosure relates generally to a pultrusion system for preparing a continuous fiber-reinforced polymer composite structure and more specifically to an injection chamber of the pultrusion system designed for proper wetting of reinforcement fibers at high manufacturing speeds.

Background

[0002] Pultrusion is a manufacturing process used to create continuous lengths of composite materials with a constant cross-sectional shape. Pultrusion involves preparing continuous reinforcing fibers, such as fiberglass (glass fibers) or carbon fiber, among other materials, which are pulled through a series of guides and tensioning devices to ensure they are aligned and free from entanglements. The prepared fibers are then wetted with a resin by passing them through a resin bath or a resin injection system. The resin used is usually a thermosetting polymer such as polyester, polyurethane, vinyl ester, or epoxy. Unlike epoxy or vinyl ester resins, which can be processed using a resin bath, polyurethanes require a resin injection system. This is due to the fact that the polyol and isocyanate start to react immediately after being mixed together, even at ambient temperature. The resin-saturated fibers then pass through a shaping die, which determines the cross-sectional shape of the final composite product.

[0003] Once shaped, the composite structure enters a curing die assembly that provides the necessary heat and pressure to continue the curing process of the resin. Curing can be achieved through heat, ultraviolet (UV) light, or a combination of both, depending on the resin system used. This stage allows the resin to harden and form a rigid composite structure. As the composite structure cures, it is continuously pulled through the die by a pulling mechanism. This pulling mechanism ensures uniformity and helps in maintaining the desired shape and dimensions of the final product. Once the composite structure has fully cured, it is cut into desired lengths using a saw or other cutting methods.

[0004] Composite structures are typically used for structural applications. For example, composite structures made with carbon fibers and epoxy resins are being used commercially to make spar caps on modem wind turbine blade designs. The growing wind turbine blade market, however, requires a fast and efficient pultrusion system where linear production speeds of composite structures is an important consideration. While multiple factors can affect the pultrusion processing speed, it is currently accepted that epoxy resins are limited to a production speed of only around 0.6-0.8 m/min due to its intrinsic low conversion rate and high pulling force. On the other hand, polyesters and vinyl esters have good resin conversion degree and low pulling forces at high speeds, but mechanical properties are not at the level of epoxy resins or polyurethanes. So, there is need in the art to increase production speed with a focus on polyurethane.

[0005] Increasing production speed, however, brings substantial processing challenges. One challenge is that a closed injection system requires proper wetting of the reinforced fibers within the resin. A satisfactory impregnation of reinforcement fibers requires all the fiber filaments to be fully saturated by the resin. The presence of residual air, such as air bubbles, in the final composite product corresponds to manufacturing defects such as dry fibers and or/voids that can initiate and propagate cracks and therefore reduce mechanical performance. Therefore, there is a need for an improved injection box design for a closed injection pultrusion system to enable proper wetting and degassing of the fiber/resin system at high pultrusion manufacturing speeds.

Summary

[0006] The present disclosure provides various embodiments, including addressing the above shortcomings by addressing the reduction of air entrapment in a continuous fiberreinforces polyurethane (CFRP) composite structure in a pultrusion system and pultrusion process. Embodiments of the present disclosure provide for a CFRP composite structure that uses polyurethane as a thermoset resin in a high-speed pultrusion system and process. The CFRP composite structure can be used as a component of wind blade spar caps, among other applications. The pultrusion system and process of the present disclosure allows for the reduction of air entrapment within the CFRP composite structure while maintaining high manufacturing speeds.

[0007] The embodiments of the present disclosure provide for, among other things, a pultrusion system including an injection box for forming a continuous fiber-reinforced polyurethane (CFRP) composite structure. In some embodiments, the injection box comprises a wall defining an elongate body having a first surface defining a feed opening, a second surface defining an end opening distal to the feed opening and an elongate axis extending therebetween, where the wall defines a contiguous fluid tight conduit extending from the feed opening to the end opening. The wall has a third surface defining an entry region, a fourth surface defining an expansion dome region, and a fifth surface defining an end region of the elongate body. [0008] The third surface defining the entry region has a first tapered section having a first predetermined length taken along the elongate axis and a second tapered section having a second predetermined length taken along the elongate axis. The second tapered section is positioned between the first tapered section and the fourth surface defining the expansion dome region, where the first tapered section has a first taper angle taken relative to the elongate axis and the first surface defining the first tapered section. The second tapered section has a second taper angle taken relative to the elongate axis and the first surface defining the second tapered section. [0009] The fourth surface defining the expansion dome region positioned between the entry region and the end region. In some embodiments, the expansion dome region has at least a first expansion dome, a second expansion dome, and a third expansion dome, a third tapered section connecting the first expansion dome and the second expansion dome, and a fourth tapered section connecting the second expansion dome and the third expansion dome.

[0010] A cross-section of the wall taken longitudinally along the elongate axis through the expansion dome region, the fourth surface defining for each of the first expansion dome, the second expansion dome, and the third expansion dome have a teardrop shape with a dome entrance and a dome exit distal to the dome entrance relative to the feed opening. In some embodiments, the dome entrance has an entrance area, taken perpendicularly relative to the longitudinal axis, the dome exit has an exit area, taken perpendicularly relative to the longitudinal axis, and between the dome entrance and the dome exit there is a maximum area, taken perpendicularly relative to the longitudinal axis. Each of the first expansion dome, the second expansion dome and the third expansion dome has a dome area reduction ratio, calculated by dividing the dome exit area by the dome entry area and subtracting from 1, between 0.10 and 0.75.

[0011] In some embodiments, the third expansion dome has a 1.2 to 3 times larger dome area reduction ratio than the first expansion dome.

[0012] In some embodiments, each expansion dome has a dome taper angle taken relative to the elongate axis and the fourth surface extending from a location of the maximum area to a location of the exit area, where the dome taper angle is between 0.5 and 5 degrees.

[0013] In some embodiments, a third dome area reduction ratio value is 0.07 to 0.25 larger than a second dome area reduction ratio value.

[0014] In some embodiments, the second dome area reduction ratio value is 0.01 to 0.10 larger than a first dome area reduction ratio value. [0015] In some embodiments, each expansion dome has an expansion ratio, calculated by the maximum area divided by the entry area of each corresponding expansion dome, the expansion ratio for each expansion dome being between 1.10 and 2.

[0016] In some embodiments, a second dome expansion ratio value is between 0.05 and 0.2 larger than a first dome expansion ratio value, and a third dome expansion ratio value is between 0.1 and 0.30 larger than a second dome expansion ratio value.

[0017] In some embodiments, the second expansion dome is configured to be injected with a liquid polyurethane resin.

[0018] In some embodiments, a total area reduction ratio of the injection box, measured by a perpendicular cross-sectional area of the end opening, taken relative to the elongate axis and the second surface, divided by a perpendicular cross-sectional area of the feed opening, taken relative to the elongate axis and the first surface, the total area reduction ratio being between 0.05 and 0.25.

[0019] In some embodiments, the fifth surface defining the end region positioned between the dome region and the end opening, where the end region has a fifth tapered section and a flat section, the fifth tapered section connection the third expansion dome to the flat end section. [0020] In some embodiments, the second tapered section, the third tapered section, the fourth tapered section, and the fifth tapered section have a taper angle of 0.01 to 0.3 degrees, where each taper angle is taken relative to the elongate axis and the fourth surface defining each tapered section.

[0021] In some embodiments, the second tapered section, the third tapered section, the fourth tapered section, and the fifth tapered section have the same taper angle.

[0022] In some embodiments, the fifth tapered section is between 1.1 and 2 times longer than the fourth tapered section.

[0023] In some embodiments, the entry region, the first expansion dome, and the second expansion dome are under atmospheric pressure, and the third expansion dome and the end region are under pressure greater than atmospheric pressure.

[0024] In some embodiments, the second tapered section is 3 to 6 times longer than the third tapered section.

[0025] In some embodiments, the first taper angle of the first tapered section is 10 to 50 times larger than the second taper angle of the second tapered section and the second predetermined length of the second tapered section is 2 to 4 times larger than the than the first predetermined length of the first tapered section. [0026] In some embodiments, the immediate disclosure relates to a pultrusion system for forming a continuous fiber-reinforced composite structure, comprising continuous reinforcement fibers, a polyurethane dispensing unit configured to dispense a liquid polyurethane resin, an injection box of one of the embodiments of the immediate disclosure fluidly coupled to the polyurethane dispensing unit, where the injection box receives the reinforcement fibers and the liquid polyurethane resin to form wetted out reinforcement fibers, a curing die assembly coupled to the injection box, where the wetted-out reinforcement fibers of the injection box are cured, and a pulling system to pull the continuous fiber-reinforced polyurethane composite structure at a predefined rate.

[0027] In some embodiments, the pultrusion system is capable of operating at a speed between 2 and 4 m/min with less than 5% air trapped in a produced fiber-reinforced structure.

Brief Description of the Drawings

[0028] These and other features of the disclosure will become more apparent from the following description in which reference is made to the appended drawings where:

[0029] FIG. 1 shows a schematic diagram of an injection box of a closed injection pultrusion system;

[0030] FIG. 2 shows a schematic diagram of a domed region of the injection box;

[0031] FIG. 3 shows a schematic diagram of a closed injection pultrusion system;

[0032] FIG. 3 shows a schematic diagram of an entry region of an injection box;

[0033] FIG. 4 shows a schematic diagram of an inventive example injection box and comparative example injection boxes.

Detailed Description

[0034] The present disclosure provides various embodiments that address efficient wetting of reinforcement fibers with a polyurethane resin in an injection box of a pultrusion process for the production of a continuous fiber reinforced polyurethane (CFRP) composite structure. Embodiments of the present disclosure provide for a CFRP composite structure that uses, for example, polyurethane as a thermoset resin in a high speed pultrusion system and process. The CFRP composite structure can be used as a component of wind blade spar caps, among other applications. The injection box of the closed injection pultrusion system and process of the present disclosure allows for efficient wetting of reinforcement fibers at high-speed production rates without manufacturing defects, such as voids or air entrapment in the composite structure. [0035] As mentioned throughout this disclosure, the terms “comprising,” “including,” “having,” and their derivatives, are not intended to exclude the presence of any additional component, step or procedure, whether or not the same is specifically disclosed. To avoid any doubt, all objects, components, or devices claimed through use of the terms “comprising,” “including,” “having,” and their derivatives may include any additional element, part, feature, or characteristic, unless stated to the contrary. In contrast, the term, “consisting essentially of’ excludes from the scope of any succeeding recitation any other component, step or procedure, excepting those that are not essential to operability. The term “consisting of’ excludes any component, step or procedure not specifically delineated or listed.

Injection Box

[0036] Referring now to FIG. 1, an injection box 100 of a pultrusion system for forming a CFRP composite structure is illustrated. The injection box 100 is configured to facilitate the controlled injection of a polyurethane reaction mixture into reinforcement fibers 136 to form wetted out the reinforcement fibers (not shown) prior to their entry into the curing die assembly (not shown) in a pultrusion system for forming a CFRP composite structure.

[0037] The injection box 100 comprising a wall 106 defining an elongate body having a first surface defining a feed opening 102, a second surface defining an end opening 104 distal to the feed opening and an elongate axis extending therebetween. The wall defines 106 a contiguous fluid tight conduit extending from the feed opening 102 to the end opening 104. The wall 106 of injection box 100 has a third surface defining an entry region 108, a fourth surface defining an expansion dome region 110, and a fifth surface defining an end region 112 of the injection box 100.

Entry Region of Injection Box

[0038] The entry region 108 of the injection box 100 receives reinforcement fibers 136 through the feed opening 102 of an entry section 114. In one embodiment, the entry section 114 is flat with a continuous cross-sectional area perpendicular to the elongate axis and does not taper. The entry section 114 and has a predetermined length taken along the elongate axis. In some embodiments, the entry section 114 has a length of between 50 and 200 mm. In some embodiments, the entry section 114 has a length of between 50 and 150 mm. In some embodiments, the entry section 114 has a length of between 75 and 150 mm. In some embodiments, the predetermined length of the entry section 114 is 100 to 250 % the length of the fourth tapered section 128. In some embodiments, the predetermined length of the entry section 114 is 110 to 175 % the length of the fourth tapered section 128. In some embodiments, the predetermined length of the entry section 114 is 75 to 150 % the length of the fifth tapered section 130. In some embodiments, the predetermined length of the entry section 114 is 80 to 120 % the length of the fifth tapered section 130.

[0039] In some embodiments, the entry section 114 comprises an observation window 138 for viewing the reinforcement fibers 136 entering the injection box 100. In some embodiments, the observation window 138 is made of a transparent material to provide suitable viewing of the interior of entry section 114. In some embodiments, a sensor 140 is mounted to the observation window 138 to detect the presence of a liquid polymer dispensed from a polyurethane mixing and dispensing unit 134. In some embodiments, the sensor 140 is an infrared sensor.

[0040] In some embodiments, the sensor 140 is configured to aid in regulating a feeding flow of the polymer mixture dispensed from the polyurethane mixing and dispensing unit 134. The sensor 140 is configured to monitor the entry section 114 to determine the presence of back flow of the dispensed polymer. In an embodiment, when the sensor 140 detects dispensed polymer backflow in the entry section, the sensor 140 generates a control signal which is sent to the polyurethane mixing and dispensing unit 134 to adjust a dispensing flow rate of the dispensed polymer from the polyurethane and dispensing unit 134.

[0041] The entry region 108 further comprises a first tapered section 116 adjacent and coupled to the entry section 114. The first tapered section 116 is interposed between the entry section 114 and a second tapered section 118. The first tapered section 116 having a predetermined length taken along the elongate axis. In some embodiments, the first tapered section 116 has a predetermined length of between 50 and 200 mm. In some embodiments, the first tapered section 116 has a length of between 50 and 150 mm. In some embodiments, the first tapered section 116 has a length of between 75 and 150 mm. In some embodiments, the predetermined length of the first tapered section 116 is 100 to 250 % the length of the fourth tapered section 128. In some embodiments, the predetermined length of the first tapered section 116 is 110 to 175 % the length of the fourth tapered section 128. In some embodiments, the predetermined length of the first tapered section 116 is 75 to 150 % the length of the fifth tapered section 130. In some embodiments, the predetermined length of the first tapered section 116 is 80 to 120 % the length of the fifth tapered section 130.

[0042] The first tapered section 116 has a first taper angle taken relative to the elongate axis and the first surface defining the first tapered section. The taper angle of the first tapered section 116 results in the gradual reduction of cross-sectional area of the first tapered section 116 from an entry area of the first tapered section 142 proximal the feed opening 102 to an exit area of the first tapered section 144 proximal the end opening 104. In some embodiments, the taper angle of the first tapered section 116 relative to the elongate axis and the first surface defining the first tapered section is between 1 and 5 degrees. In some embodiments, the taper angle of the first tapered section 116 relative to the elongate axis and the first surface defining the first tapered section is between 1.5 and 4 degrees. In some embodiments, the taper angle of the first tapered section 116 relative to the elongate axis and the first surface defining the first tapered section is 3.5 degrees. In some embodiments, the taper angle of the first tapered section 116 is 10 and 50 times larger than a taper angle of the second tapered section 118. In some embodiments, the taper angle of the first tapered section 116 is 20 and 40 times larger than a taper angle of the second tapered section 118.

[0043] The entry region 108 further comprises a second tapered section 118 adjacent and coupled to the first tapered section 116. The second tapered section 118 is interposed between the first tapered section 116 and a first expansion dome 120. The second tapered section 118 having a predetermined length taken along the elongate axis. In some embodiments, the second tapered section 118 has a length of 100 and 500 mm. In some embodiments, the second tapered section 118 has a length of between 200 and 450 mm. In some embodiments, the second tapered section 118 has a length of between 250 and 250 mm. In some embodiments, the predetermined length of the second tapered section 118 is 300 to 600 % the length of the fourth tapered section 128. In some embodiments, the predetermined length of the second tapered section 118 is 350 to 500 % the length of the fourth tapered section 128. In some embodiments, the predetermined length of the second tapered section 118 is 200 to 500 % the length of the fifth tapered section 130. In some embodiments, the predetermined length of the second tapered section 118 is 250 to 400 % the length of the fifth tapered section 130.

[0044] The second tapered section 118 has a first taper angle taken relative to the elongate axis and the first surface defining the first tapered section. The taper angle of the second tapered section 118 results in the gradual reduction of cross-sectional area of the second tapered section 118 from an entry area of the second tapered section 146 proximal the feed opening 102 to an exit area of the second tapered section 148 proximal the end opening 104. In some embodiments, the taper angle of the second tapered section 118 relative to the elongate axis and the first surface defining the first tapered section is between 0.01 and 0.2 degrees. In some embodiments, the taper angle of the second tapered section 118 relative to the elongate axis and the first surface defining the first tapered section is between 0.05 and 0.15 degrees. [0045] The entry region 108 is a low-pressure zone and operates at atmospheric pressure. The entry region 108 therefore may be made of materials that do not require high pressure or vacuum pressure ratings reducing the cost of manufacture for the entry region 108 and the injection box 100 as a whole. The lack of high pressure in the entry region 108 also reduces the potential for leaks and maintenance costs. In some embodiments, the entry region 108 is made of plastic materials, such as Teflon®, high density polyethylene (HDPE), or polypropylene (PP).

Dome Region of Injection Box

[0046] The injection box 100 of the present disclosure includes the dome expansion region 110 interposed between the entry region 108 and the end region 112. FIG. 2 illustrates a detailed view of the dome region 110. In some embodiments, the dome entry region 110 is defined by the fourth surface of the wall 106 and includes at least a first expansion dome 120, a second expansion dome 122, and a third expansion dome 124, a third tapered section 124 connecting the first expansion dome 120 and the second expansion dome 122, and a fourth tapered section 128 connecting the second expansion dome 122 and the third expansion dome 124.

[0047] The first expansion dome 120 is interposed between the second tapered section 118 and the third tapered section 126. The first expansion dome 120 has an entry 202 having a first expansion dome entry area, an exit 204 having a first expansion dome exit area, and a maximum expansion section 206 having a first expansion dome maximum expansion area with each area being taken perpendicularly relative to the elongate axis.

[0048] In some embodiments, a cross-section of the wall 116 taken longitudinally along the elongate axis through the first expansion dome 120 is a tear drop shape. The first expansion dome entry area is larger than the first expansion dome exit area, but smaller than the first expansion dome maximum expansion area. The tear drop shape provides a cambered increase in cross-sectional area proximal the entry 202 of the first expansion dome 120 to the maximum expansion section 206. From the maximum expansion section 206 to the exit 204 of the first expansion dome 120, the cross-sectional area of the first expansion dome 120 reduces along a dome taper angle taken relative to the elongate axis and the fourth surface defining the first expansion dome 120. In some embodiments, the dome taper angle between the maximum expansion section 206 and the exit 208 is uniform. In some embodiments, the dome taper angle of the first expansion dome 120 is between 0.5 and 5 degrees taken relative to the elongate axis and the fourth surface defining the first expansion dome 120. In some embodiments, the dome taper angle of the first expansion dome 120 is between 1.5 and 3 degrees taken relative to the elongate axis and the fourth surface defining the first expansion dome 120. [0049] The first expansion dome 120 has a predetermined length relative to the elongate axis. In some embodiments, the predetermined length of the first expansion dome 120 is between 20 and 100 mm. In some embodiments, the first expansion dome 120 has a length of between 25 and 75 mm. In some embodiments, the predetermined length of the first expansion dome 120 is 40 to 100 % the length of the fourth tapered section 128. In some embodiments, the predetermined length of the first expansion dome 120 is 60 to 90 % the length of the fourth tapered section 128. [0050] The expansion dome region 110 further comprises a third tapered section 126. The third tapered section 26 is interposed between the first expansion dome 120 and the second expansion dome 122. The third tapered section 126 having a predetermined length taken along the elongate axis. In some embodiments, the third tapered section 126 has a length of between 25 and 150 mm. In some embodiments, the third tapered section 126 has a length of between 25 and 100 mm. In some embodiments, the third tapered section 126 has a length of between 25 and 75 mm. In some embodiments, the predetermined length of the third tapered section 126 is 75 to 125 % the length of the fourth tapered section 128. In some embodiments, the predetermined length of the third tapered section 126 is 90 to 110 % the length of the fourth tapered section 128. In some embodiments, the predetermined length of the third tapered section 126 is 50 to 150 % the length of the fifth tapered section 130. In some embodiments, the predetermined length of the third tapered section 126 is 50 to 100 % the length of the fifth tapered section 130.

[0051] The third tapered section 126 has a first taper angle taken relative to the elongate axis and the fourth surface defining the third tapered section. The taper angle of the third tapered section 126 results in the gradual reduction of cross-sectional area of the third tapered section 126 from an entry 208 area of the third tapered section 126 proximal the feed opening 102 to an exit 210 area of the third tapered section 126 proximal the end opening 104. In some embodiments, the taper angle of the third tapered section 126 relative to the elongate axis and the first surface defining the first tapered section is between 0.01 and 0.2 degrees. In some embodiments, the taper angle of the third tapered section 126 relative to the elongate axis and the first surface defining the first tapered section is between 0.05 and 0.15 degrees.

[0052] The second expansion dome 122 is interposed between the first expansion dome 120 and the second expansion dome 124, more specifically between the third tapered section 124 and the fourth tapered section 126. The second expansion dome 122 has an entry 212 having a second expansion dome entry area, an exit 214 having a second expansion dome exit area, and a maximum expansion section 216 having a second expansion dome maximum expansion area with each area being taken perpendicularly relative to the elongate axis. [0053] In some embodiments, a cross-section of the wall 116 taken longitudinally along the elongate axis through the second expansion dome 122 is a tear drop shape. The second expansion dome entry area is larger than the second expansion dome exit area, but smaller than the second expansion dome maximum expansion area. The tear drop shape provides a cambered increase in cross-sectional area proximal the entry 212 of the second expansion dome 122 to the maximum expansion section 216. From the maximum expansion section 216 to the exit 214 of the second expansion dome 122, the cross-sectional area of the second expansion dome 122 reduces along a dome taper angle taken relative to the elongate axis and the fourth surface defining the second expansion dome 122. In some embodiments, the dome taper angle between the maximum expansion section 216 and the exit 218 is uniform. In some embodiments, the dome taper angle of the second expansion dome 122 is between 0.5 and 5 degrees taken relative to the elongate axis and the fourth surface defining the second expansion dome 122. In some embodiments, the dome taper angle of the second expansion dome 122 is between 1.5 and 3 degrees taken relative to the elongate axis and the fourth surface defining the second expansion dome 122.

[0054] The second expansion dome 122 has a predetermined length relative to the elongate axis. In some embodiments, the predetermined length of the second expansion dome 122 is between 20 and 100 mm. In some embodiments, the second expansion dome 122 has a length of between 25 and 75 mm. In some embodiments, the predetermined length of the second expansion dome 122 is 40 to 100 % the length of the fourth tapered section 128. In some embodiments, the predetermined length of the second expansion dome 122 is 60 to 90 % the length of the fourth tapered section 128.

[0055] In some embodiments, the second expansion dome 122 is fluidly coupled to the polyurethane mixing and dispensing unit 134. In some embodiments, the second expansion dome 122 comprises axial ports (located at the top and bottom of the second expansion dome 122), wire ports, ring ports, or other similar port configurations. The ports of the second expansion dome 122 being configured to dispense liquid polymer from the polyurethane mixing and dispensing unit 134 into the injection box 100. The liquid polymer may be dispensed in the second expansion dome 122 axially or laterally. In an axial injection, the liquid polymer is injected from at least the top, bottom, and sides of the second expansion dome 122. In a lateral injection, the liquid polymer is injected from the top and bottom of the second expansion dome 122. The second expansion dome 122 is therefore an “active” dome as it is the dome that dispenses liquid polymer into the injection box 100 for the wetting of reinforcement fibers 136. [0056] The expansion dome region 110 further comprises a fourth tapered section 128. The fourth tapered section 128 is interposed between the second expansion dome 122 and the third expansion dome 124. The fourth tapered section 128 having a predetermined length taken along the elongate axis. In some embodiments, the fourth tapered section 128 has a length of between 25 and 150 mm. In some embodiments, the fourth tapered section 128 has a length of between 25 and 100 mm. In some embodiments, the fourth tapered section 128 has a length of between 25 and 75 mm. In some embodiments, the predetermined length of the fourth tapered section 128 is 75 to 125 % the length of the third tapered section 126. In some embodiments, the predetermined length of the fourth tapered section 128 is 90 to 110 % the length of the third tapered section 126. In some embodiments, the predetermined length of the fourth tapered section 128 is 50 to 150 % the length of the fifth tapered section 130. In some embodiments, the predetermined length of the fourth tapered section 128 is 50 to 100 % the length of the fifth tapered section 130.

[0057] The fourth tapered section 128 has a first taper angle taken relative to the elongate axis and the fourth surface defining the fourth tapered section. The taper angle of the fourth tapered section 128 results in the gradual reduction of cross-sectional area of the fourth tapered section 128 from an entry 218 area of the fourth tapered section 128 proximal the feed opening 102 to an exit 220 area of the fourth tapered section 128 proximal the end opening 104. In some embodiments, the taper angle of the fourth tapered section 128 relative to the elongate axis and the first surface defining the first tapered section is between 0.01 and 0.2 degrees. In some embodiments, the taper angle of the fourth tapered section 128 relative to the elongate axis and the first surface defining the first tapered section is between 0.05 and 0.15 degrees.

[0058] The third expansion dome 124 is interposed between the fourth tapered section 128 and the fifth tapered section 130. The third expansion dome 124 has an entry 222 having a third expansion dome entry area, an exit 224 having a third expansion dome exit area, and a maximum expansion section 226 having a third expansion dome maximum expansion area with each area being taken perpendicularly relative to the elongate axis.

[0059] In some embodiments, a cross-section of the wall 116 taken longitudinally along the elongate axis through the third expansion dome 124 is a tear drop shape. The third expansion dome entry area is larger than the third expansion dome exit area, but smaller than the third expansion dome maximum expansion area. The tear drop shape provides a cambered increase in cross-sectional area proximal the entry 222 of the third expansion dome 124 to the maximum expansion section 226. From the maximum expansion section 226 to the exit 224 of the third expansion dome 124, the cross-sectional area of the third expansion dome 124 reduces along a dome taper angle taken relative to the elongate axis and the fourth surface defining the third expansion dome 124. In some embodiments, the dome taper angle between the maximum expansion section 226 and the exit 228 is uniform. In some embodiments, the dome taper angle of the third expansion dome 124 is between 0.5 and 5 degrees taken relative to the elongate axis and the fourth surface defining the third expansion dome 124. In some embodiments, the dome taper angle of the third expansion dome 124 is between 1.5 and 3 degrees taken relative to the elongate axis and the fourth surface defining the third expansion dome 124.

[0060] The third expansion dome 124 has a predetermined length relative to the elongate axis. In some embodiments, the predetermined length of the third expansion dome 124 is between 20 and 100 mm. In some embodiments, the third expansion dome 124 has a length of between 25 and 75 mm. In some embodiments, the predetermined length of the third expansion dome 124 is 40 to 100 % the length of the fourth tapered section 128. In some embodiments, the predetermined length of the third expansion dome 124 is 60 to 90 % the length of the fourth tapered section 128.

[0061] Each of the first expansion dome 120, the second expansion dome 122, and the third expansion dome 124 has a dome area reduction ratio, calculated by dividing the respective dome exit area by the respective dome entry area and subtracting from 1. Each of the first expansion dome 120, the second expansion dome 122 and the third expansion dome 124 has a dome area expansion ratio, calculated by dividing the dome maximum area by the dome entry area.

[0062] In one embodiment, the dome area reduction ratio of the first expansion dome 120 is between 0.05 to 0.75. In one embodiment, the dome area reduction ratio of the first expansion dome 120 is between 0.05 to 0.5, or 0.1 to 0.4, or 0.15 to 0.3, or any number within the provided ranges.

[0063] In one embodiment, the dome area reduction ratio of the second expansion dome 122 is between 0.05 to 0.75. In one embodiment, the dome area reduction ratio of the second expansion dome 122 is between 0.1 to 0.6, or 0.1 to 0.5, or 0.2 to 0.4, or any number within the provided ranges.

[0064] In one embodiment, the dome area reduction ratio of the third expansion dome 124 is between 0.05 to 0.75. In one embodiment, the dome area reduction ratio of the third expansion dome 124 is between 0.1 to 0.75, or 0.3 to 0.7, or 0.4 to 0.6, or any number within the provided ranges.

[0065] In one embodiment, each expansion dome area reduction ratio value is between 0.10 and 0.75. In one embodiment, the second dome area reduction ratio value is 0.01 to 0.10 larger than a first dome area reduction ratio value. In one embodiment, a third dome area reduction ratio value is 0.07 to 0.25 larger than a second dome area reduction ratio value.

[0066] In one embodiment, the dome area expansion ratio of the first expansion dome 120 is between 1.1 and 2. In one embodiment, the dome area expansion ratio of the first expansion dome 120 is between 1.1 and 1.5. In one embodiment, the dome area expansion ratio of the first expansion dome 120 is between 1.1 and 1.4.

[0067] In one embodiment, the dome area expansion ratio of the second expansion dome 122 is between 1.1 and 2. In one embodiment, the dome area expansion ratio of the second expansion dome 122 is between 1.1 and 1.6. In one embodiment, the dome area expansion ratio of the second expansion dome 122 is between 1.2 and 1.5. In one embodiment, the dome area expansion ratio of the second expansion dome 122 is between 1.3 and 1.5.

[0068] In one embodiment, the dome area expansion ratio of the third expansion dome 124 is between 1.1 and 2. In one embodiment, the dome area expansion ratio of the third expansion dome 124 is between 1.3 and 1.9. In one embodiment, the dome area expansion ratio of the third expansion dome 124 is between 1.4 and 1.8. In one embodiment, the dome area expansion ratio of the third expansion dome 124 is between 1.5 and 1.7.

[0069] In one embodiment, the second dome expansion ratio value is between 0.05 and 0.2 larger than the first dome expansion ratio value. In another embodiment, the second dome expansion ratio value is between 0.05 and 0.15 larger than the first dome expansion ratio value. [0070] In one embodiment, the third dome expansion ratio value is between 0.1 and 0.40 larger than the second dome expansion ratio value. In another embodiment, the third dome expansion ratio value is between 0.1 and 0.30 larger than the second dome expansion ratio value.

[0071] In one embodiment, the third dome expansion ratio value is between 0.15 and 0.6 larger than the first dome expansion ratio value. In another embodiment, the third dome expansion ratio value is between 0.2 and 0.40 larger than the first dome expansion ratio value.

[0072] In some embodiments, the term “injection box,” as used in the art, is considered the entry region 108, the expansion dome region 110, and the end region 112. In other embodiments, the term “injection box,” as used in the art, is considered only the entry region 108 and the expansion dome region 110. In other embodiments, the term “injection box,” as used in the art, is considered only the entry region 108 and portions of the expansion dome region 110 including the first expansion dome 120, the third tapered section 126, the second expansion dome 124, and portions of the fourth tapered section 128. End Region of In jection Box

[0073] The injection box 100 of the present disclosure includes the end region 112 downstream of the dome expansion region 110. In some embodiments, the dome entry region 110 is defined by the fifth surface of the wall 106 and includes at least a fifth tapered section 130 and a flat end section 132.

[0074] The end region 112 further comprises a fifth tapered section 130. The fifth tapered section 130 is interposed between the third expansion dome 120 and the flat end section 132. The fifth tapered section 130 having a predetermined length taken along the elongate axis. In some embodiments, the fifth tapered section 130 has a length of between 25 and 200 mm. In some embodiments, the fifth tapered section 130 has a length of between 50 and 150 mm. In some embodiments, the fifth tapered section 130 has a length of between 75 and 125 mm. In some embodiments, the predetermined length of the fifth tapered section 130 is 100 to 300 % the length of the third tapered section 126. In some embodiments, the predetermined length of fifth tapered section 130 is 120 to 200 % the length of the third tapered section 126. In some embodiments, the predetermined length of fifth tapered section 130 is 100 to 300 % the length of the fourth tapered section 128. In some embodiments, the predetermined length of the fifth tapered section 130 is 120 to 200 % the length of the fourth tapered section 128.

[0075] The fifth tapered section 130 has a first taper angle taken relative to the elongate axis and the fifth surface defining the fifth tapered section 130. The taper angle of the fifth tapered section 130 results in the gradual reduction of cross-sectional area of the fifth tapered section 130 from an entry 228 area of the fifth tapered section 130 proximal the feed opening 102 to an exit 230 area of the fifth tapered section 130 proximal the end opening 104. In some embodiments, the taper angle of the fifth tapered section 130 relative to the elongate axis and the first surface defining the first tapered section is between 0.01 and 0.2 degrees. In some embodiments, the taper angle of the fifth tapered section 130 relative to the elongate axis and the first surface defining the first tapered section is between 0.05 and 0.15 degrees.

[0076] The end region 112 further comprises a flat end section 132. flat end section 132 downstream and adjacent to the fifth tapered section 130. The flat end section 132 having a predetermined length taken along the elongate axis. In some embodiments, the flat end section 132 has a length of between 25 and 200 mm. In some embodiments, the flat end section 132 has a length of between 50 and 150 mm. In some embodiments, the flat end section 132 has a length of between 75 and 125 mm. In some embodiments, the predetermined length of the flat end section 132 is 75 to 125 % the length of the fifth tapered section 130. In some embodiments, the predetermined length of the flat end section 132 is 100 to 300 % the length of the third tapered section 126. In some embodiments, the predetermined length of the flat end section 132 is 120 to 200 % the length of the third tapered section 126. In some embodiments, the predetermined length of the flat end section 132 is 100 to 300 % the length of the fourth tapered section 128. In some embodiments, the predetermined length of the flat end section 132 is 120 to 200 % the length of the fourth tapered section 128.

[0077] In some embodiments, the flat end section is coupled to a curing die assembly and therefore connects the injection box 100 to a curing die. In other embodiments, the flat end section is a part of a curing die assembly.

[0078] The end region 112 is under pressure greater than atmospheric pressure. The end region 112 is made of material capable of withstanding pressure greater than atmospheric pressure. In some embodiments, the end region 112 is made of metal or metal alloys.

[0079] For the various embodiments, the injection box 100 is fluidly coupled to a polyurethane mixing and dispensing unit 134. The injection box 100 receives the reinforcement fibers 136 and a reaction mixture from the polyurethane mixing and dispensing unit 314 under pressure. For the various embodiments, the injection box 100 facilitates the controlled injection of the reaction mixture into the reinforcement fibers 136 to form wetted out the reinforcement fibers (not shown) prior to their entry into the curing die assembly (not shown). Such controlled injection of the reaction mixture into the reinforcement fibers 136 helps to ensure a thorough impregnation and consistent distribution of the reaction mixture throughout the reinforcement fibers 136 and the CFRP composite structure.

[0080] For the various embodiments, the injection box 100 enables for high-speed production of the CFRP composite structure. In one embodiment, the injection box 100 can operate at a speed to produce the CFRP composite structure at a rate of 0.1 to 6 m/min. In one embodiment, the injection box 100 can operate at a speed to produce the CFRP composite structure at a rate of 1 to 5 m/min. In one embodiment, the injection box 100 can operate at a speed to produce the CFRP composite structure at a rate of 2 to 4 m/min.

Closed Injection Pultrusion System

[0081] Referring now to FIG. 3, a pultrusion system 300 for forming a CFRP composite structure is illustrated. The pull system 300 includes reinforcement fibers 302, an injection box 304, a pulling system 306 configured to pull reinforcement fibers 302 through the injection box 304 and a curing die 308, the curing die assembly 308 is coupled to the injection box 304, a cutting mechanism 312, and a polyurethane mixing and dispensing unit 314 configured to inject a polyurethane resin into the injection box 304 for wetting of the reinforcement fiber 302.

[0082] The reinforcement fibers 302 are located upstream from the injection box 304 and curing die assembly 308 and can be supplied by one or more spools (not shown). For the various embodiments, the reinforcement fibers 302 are pulled from the one or more spools and can pass through one or more carding plates and/or tensioning mechanisms, as are known in the art, to arrange and/or position the reinforcement fibers 302 in a desired orientation and arrangement. [0083] For the various embodiments, the reinforcement fibers 302 constitute about 55 to 85 percent by weight (wt.%) of the CFRP composite structure. All individual values and subranges from about 55 to 85 wt.% are included; for example, the reinforcement fibers 302 can constitute from a lower limit of 55, 60 or 65 wt.% to an upper limit of 85, 80 or 75 wt.% of the CFRP composite structure. For the various embodiments, the reinforcement fibers 302 can be formed from glass, carbon, or polyaramid, however there are a variety of other reinforcement fibers, which can be used for the reinforcement fibers 302. For example, these include, but are not limited to, synthetic and natural fibers or fibrous materials, for example, but not limited to polyester, polyethylene, nylon, quartz, boron, metal, basalt, ceramic and natural fibers such as fibrous plant materials, for example, jute and sisal. Combinations of the above discussed reinforcement fibers can also be used for the present disclosure. For the various embodiments, the reinforcement fibers 302 can have a diameter on the order of 5 to 25 pm.

[0084] The pultrusion system 300 further includes the polyurethane mixing and dispensing unit 314, having and supplying both an A-part and a B-part (the isocyanate reactive component) to form a polyurethane resin. Both the A-part and the B-part are individually dispensed from their respective vessels under pressure and at predetermined flow rates to a mixer of the polyurethane mixing and dispensing unit 314. For the various embodiments, the A-part includes, among other things, at least one of an isocyanate containing compound, while the B-part includes at least one of a polyol containing compound, among other things. For the various embodiments, the predetermined flow rates can be based on the desired isocyanate index for the reaction mixture. As known in the art, the isocyanate index is the ratio of the number of isocyanate functional groups present in a formulation (e.g., the reaction mixture) to the number of hydroxyl functional groups (Isocyanate Index = (NCO groups) / (OH groups)), which determines the stoichiometry of the reaction between isocyanates and hydroxyl-containing compounds during the polyurethane formation process. [0085] The mixer of the polyurethane mixing and dispensing unit 314 can be a static or active mixer as are known in the art. In the mixer, the A-part and a B-part mix to form a reaction mixture for the polyurethane resin of the CFRP composite structure. The polyurethane mixing and dispensing unit 314 pumps and delivers the reaction mixture from the mixer under pressure to the injection box 304 for wetting out the reinforcement fibers 302 prior to them entering the curing die assembly 308. As used herein, “wetting”, “wetting out”, “wet” and “wetter” means to saturate the voids and interstices within and between the reinforcement fibers 302 with the reaction mixture for the polyurethane resin as provided herein.

[0086] For the various embodiments, the A-part may comprise the polyisocyanate component and the B-part may comprise the polyol component. By the term “polyol” means a composition that contains a plurality of active hydrogen groups that are reactive towards the polyisocyanate component under the conditions of processing (e.g., hydroxyl groups, amine groups, etc.).

[0087] Examples of such polyols include polyether polyols that may be prepared by polyaddition of alkylene oxides (alkoxylation) onto an initiator (i.e., a polyhydroxy functional starter compound) in the presence of catalysts known in the art that can shape the proportion of primary and secondary hydroxyls in the resulting polymer or oligomer.

[0088] The initiator includes one or more compounds having a low molecular weight and a numerical hydroxyl functionality of at least 2. The initiator can be an organic compound that is to be alkoxylated in the polymerization reaction. The initiator may contain as many as 10 hydroxyl groups. For example, the initiator may be a diol or triol. Mixtures of initiators may be used. The initiator will have a hydroxyl equivalent weight less than that of the polyether product, e.g., may have a hydroxyl equivalent weight of less than 500 g/mol equivalence, less than 300 g/mol equivalence, greater than 20 g/mol equivalence, from 20 to 300 g/mol equivalence, from 20 to 200 g/mol equivalence, or from 30 to 150 g/mol equivalence by way of example. Exemplary, initiator compounds such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, 1,4-butanediol, 1,6-hexanediol, 1,8-octanediol, cyclohexane dimethanol, bisphenol A, glycerin, trimethylolpropane, trimethylolethane, pentaerythritol, sugars and sugar alcohols such as sorbitol and sucrose, and/or alkoxylates of any of these that have a weight average molecular weight less than that of the product of the polymerization.

[0089] The polyether polyols may have a functionality of at least 2 or more such as ranging from 2 to 6, or 2 to 4. The preferred polyether polyols has 100% secondary OH groups. [0090] Polyurethane compositions may include an isocyanate-reactive component containing at least one poly ether polyol, and optionally one or more hydroxy functionalized (meth)acrylates. As used herein, use of “(meth)” in conjunction with various acrylate species indicates that the scope of the specification covers both the acrylate or methacrylate variations of the referenced compound . As such the isocyanate-reactive component or B-part may include one or more hydroxy functional (meth)acrylate monomers that react with the isocyanate component and/or polymerize in the presence of a free radical initiator to produce a polyurethane acrylate hybrid composition. Hydroxy functional (meth)acrylate monomers may have the general structure:

O R, ₀^ _n ^H

[0091] where Ri is selected from hydrogen, methyl or ethyl; R2 is selected from alkylene groups having 2-6 carbon atoms, 2,2-bis(4-phenylene) propane, l,4-bis(methylene)benzene, 1,3- bis(methylene)benzene, l,2-bis(methylene) benzene; and n is an integer selected from 1-6.

Hydroxy functional (meth)acrylate monomers may include hydroxy Cl-10 alkyl (meth)acrylate monomers, such as hydroxyethyl acrylate, hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate monomer, and the like.

[0092] Hydroxy functional (meth)acrylates may be added at a percent by weight (wt.%) of the polyurethane acrylate hybrid composition in a range of 15 wt.% to 40 wt.%, from 20 wt.% to 38 wt.%, from 25 wt.% to 35 wt.%, or from 27 wt.% to 32 wt.%.

[0093] The described polyether polyols and hydroxy functional methacrylate monomer may be used in the polyurethane resin compositions described herein. The term “polyisocyanate” means a composition that contains a plurality of isocyanate or -NCO groups that are reactive towards the polyol component under the conditions of processing. Examples of such polyisocyanates can include di- or polyisocyanate compounds, as are known in the art. Compositions disclosed herein may be substantially free of water (i.e., max content in the formulation is 0.1 % or less) and produce negligible amounts of foam upon combination of the reactant components.

[0094] Examples of other polyurethane resins that are useful with the present disclosure include, but are not limited to, those provided in WO 2023/035262, incorporated herein by reference.

WO 2023/035262 provides examples of what is referred to as hybrid polyurethane compositions, where such compositions include at least one of (a) a first polyisocyanate compound; (b) a first prepolymer that is formed by reacting a second polyisocyanate compound and a first polyol having an average equivalent weight of 30 to 200 g/eq and an average functionality of 2 to 3 and where the first prepolymer has an NCO content of 21 to 25 % based on the weight of the first prepolymer; and (c) a second prepolymer prepolymer formed by reaction of a third polyisocyanate compound and a second polyol, where the second polyol has an average equivalent weight of from 250 to 3000 g/eq and an average functionality of 2-3 and the second prepolymer has a NCO content of 10 to 20 % based on the weight of the second prepolymer. The total amount of the first prepolymer and the second prepolymer can be 10 to 70 wt.% based on the total weight of the isocyanate component. The hybrid polyurethane composition further includes an isocyanate-reactive component comprising a third polyol, an isocyanate reactive (meth) acrylate monomer and a free radical initiator. Other polyurethane compositions can include those polyether and polyester-based compositions seen in, for example, U.S. Pat. No. 11,142,616 B2 and U.S. Pat. Pub. 2018/214914A1, both of which are incorporated herein by reference.

[0095] Isocyanate components may contain one or more isocyanate compounds, such as polymeric isocyanates, aromatic isocyanates, or carbodiimide-modified isocyanates. Isocyanate compounds may be monomeric, oligomeric, prepolymers, and the like. The isocyanate component can include, for example, one or more isocyanate and/or polyisocyanate compounds. Isocyanate components may include isocyanate compounds having a nominal functionality of 1.5 or greater, or > 2.0 or greater, more precisely 2.2 to 2.8.

[0096] The isocyanate component may include an isocyanate compound having a number average molecular weight of 150 g/mol to 750 g/mol. In some cases, the isocyanate compound can have a number average molecular weight from a low value of 150 g/mol, 200 g/mol, 250 g/mol or 300 g/mol to an upper value of 350 g/mol, 400 g/mol, 450 g/mol, 500 g/mol or 750 g/mol. The number average molecular weight values reported herein are determined by end group analysis, gel permeation chromatography, and other methods as is known in the art. The isocyanate compound can be monomeric and/or polymeric, as are known in the art.

[0097] The isocyanate component may include on or more of aliphatic polyisocyanate, cycloaliphatic polyisocyanate, araliphatic polyisocyanate, aromatic polyisocyanate, and the like. Examples of isocyanates include, but are not limited to, polymethylene polyphenylisocyanate; toluene 2,4-/2,6-diisocyanate (TDI); methylenediphenyl diisocyanate (MDI, including its isomers); polymeric and prepolymeric MDI; triisocyanatononane (TIN); naphthyl diisocyanate (NDI); 4,4’-diisocyanatodicyclohexyl-methane; 3-isocyanatomethyl-3,3,5-trimethylcyclohexyl isocyanate (isophorone diisocyanate, IPDI); tetramethylene diisocyanate; hexamethylene diisocyanate (HDI); 2-methyl-pentamethylene diisocyanate; 2,2,4-trimethylhexamethylene diisocyanate (THDI); dodecamethylene diisocyanate; 1,4-diisocyanatocyclohexane; 4,4’- diisocyanato-3,3’-dimethyl-dicyclohexylmethane; 4,4’-diisocyanato-2,2-dicyclohexylpropane; 3- isocyanatomethyl- 1 -methyl- 1 -isocyanatocyclohexane (MCI) ; 1 ,3-diisooctylcyanato-4- methylcyclohexane; 1,3 -diisocyanato-2-methylcyclohexane; and combinations thereof, among others. In addition to the isocyanates mentioned above, partially modified polyisocyanates including uretdione, isocyanurate, carbodiimide, uretonimine, allophanate or biuret structure, and combinations thereof, among others, may be utilized.

[0098] Isocyanate compounds may include isocyanate prepolymers resulting from reaction of an isocyanate-reactive compound with a molar excess of an isocyanate compound or polymeric isocyanate compound under conditions that do not lead to gelation or solidification. Isocyanate prepolymers disclosed herein may have an isocyanate index, defined as the equivalents of isocyanate divided by the total equivalents of isocyanate-reactive hydrogen containing materials, multiplied by 100) in a range of from 30 to 400, 40 to 300, or 40 to 200. Isocyanates components disclosed herein may include one or more isocyanate compounds having an NCO content at a percent by weight of above 20 wt.%, such as in a range of 20 wt.% to 75 wt.%, or 20 wt.% to 60 wt.%.

[0099] PU compositions disclosed herein may include an isocyanate component at a percent by weight (wt.%) ranging from 15 wt.% to 80 wt.%, 20 wt.% to 80 wt.%, or 20 wt.% to 70 wt.%.

[00100] An example of suitable polyol and isocyanate combination for the reaction mixture of the present disclosure includes VORAFORCE™ TP1270EU/1300 (DOW), which is a blend of polyols and isocyanate that can achieved a low initial viscosity.

[00101] The two component polyurethane resin once the A-part and the B-part are mixed together has a viscosity at 25 °C of about 200 to 800 cP. The time to triple that initial viscosity at 25 °C is in about 15 minutes or more. This allows for a thorough mixing of the A-part and the B-part in the mixer of the polyurethane mixing and dispensing unit 314, and wetting the fibers in the injection box 304, before substantial polymerization occurs. Other additives may also be included in the A-part, and/or B-part, such as fillers, pigments, plasticizers, curing catalysts, UV stabilizers, internal mold release agents, antioxidants, microbiocides, algicides, dehydrators, thixotropic agents, wetting agents, water scavengers, antifoaming agents, antistatic agents, flow modifiers, matting agents, deaerators, extenders, molecular sieves for moisture control, dyes, UV absorber, light stabilizer, fire retardants and smoke suppressants.

[00102] For the various embodiments, the injection box 304 is fluidly coupled to the polyurethane mixing and dispensing unit 314. The injection box 304 receives the reinforcement fibers 302 and the reaction mixture from the polyurethane mixing and dispensing unit 314 under pressure. For the various embodiments, the injection box 304 facilitates the controlled injection of the reaction mixture into the reinforcement fibers 302 to form wetted out the reinforcement fibers 316 prior to their entry into the curing die assembly 308. Such controlled injection of the reaction mixture into the reinforcement fibers 302 helps to ensure a thorough impregnation and consistent distribution of the reaction mixture throughout the reinforcement fibers 302 and the CFRP composite structure. To achieve this, the injection box 304 includes one or more of an inlet port through which the reaction mixture is injected. In addition, the injection box 304 can include distribution channels or pathways that help to guide the reaction mixture from the intake port to various sections where the reinforcement fibers are introduced into the injection box 304. The channels can help ensure an even and controlled flow of the reaction mixture into and on to the reinforcement fibers 302 so as to wet out the reinforcement fibers 302. In some embodiments, the injection box 304 is the injection box 100 of FIG. 1 and FIG. 2.

[00103] The injection box 304 can further include a pressure control unit to control and regulate the pressure of the reaction mixture being injected into and wetting out the reinforcement fibers 302. Such pressure control helps to prevent either over-saturation or undersaturation of the reinforcement fibers 302. In addition, the injection box 304 can be temperature controlled (e.g., heated or cooled) to maintain the reaction mixture at a desired temperature to better achieve a desired viscosity and/or curing behavior for the reaction mixture. The wetted out reinforcement fibers 302 then exit the injection box 304 and proceed to the curing die assembly 308. Residence time for the reinforcement fibers 302 in the injection box 304 can be typically less than one minute.

[00104] In some embodiments, the curing die assembly 308 includes a heating die having a predefined temperature to provide heat to promote a curing process of the A-part and the B-part of the reaction mixture, and surfaces defining a cross-sectional shape through which the wetted out reinforcement fibers from the injection box pass to provide a predefined shape to the wetted out reinforcement fibers (e.g., a die). In some embodiments, the curing die assembly 308 includes multiple heating dies with predefined temperatures and surfaces. In some embodiments, the curing die assembly 308 includes one, two, three, four, or five heating dies. In some embodiments, one or more of the heating dies may have the same predetermined temperature. In some embodiments, the one or more heating dies have different predetermined temperatures. For the various embodiments, the cross-sectional shape of each die provides the eventual cross- sectional shape of the CFRP composite structure. In other words, the die(s) of the curing die assembly 308 impart the cross-sectional shape or geometry to the CFRP composite structure. [00105] For the various embodiments, the predetermined temperature of each one or more heating dies can independently be from 150 °C to 250 °C. All individual values and subranges from 150 °C to 250 °C. are included; for example, the predetermined temperature of each of the heating dies can have a lower limit of 150 °C, 160 °C, 170 °C or 180 °C to an upper limit of 250 °C, 240 °C, 230 °C, or 220 °C. For the various embodiments, the residence time of the wetted out reinforcement fibers 316 passing through the curing die assembly 308 can be from about 2 minutes to about 30 seconds.

[00106] In some embodiments, the curing die assembly 308 further includes a cooling element. For the various embodiments, the cooling element does not add heat to the curing process of the A-part and the B-part of the reaction mixture but provides surfaces defining the cross-sectional shape through which the wetted out reinforcement fibers from the injection box pass to provide the predefined shape to the wetted out reinforcement fibers (e.g., a die).

[00107] For the various embodiments, curing die assembly 308 with each one or more heating dies, and optionally the cooling element can be formed from a heat-resistant material, such as steel, stainless steel or other alloys, that can withstand the high temperatures required for the pultrusion process. The curing die assembly 308 along with each one or more of the heating dies and optionally the cooling element can consist of one or more portions (e.g., two halves) that are joined together so as to provide the cross-sectional shape that aligns and encase the reinforcement fibers wetted out with the reaction mixture 316. For the various embodiments, curing die assembly 308 can also include one or more mandrels depending on the geometry of the cross section being pultruded. For example, a mandrel may be used to produce a hollow cross-section.

[00108] According to the present disclosure, the wetted out reinforcement fibers 316 are compressed into the cross-sectional shaped as they pass through the curing die assembly 308 (e.g., the first heating die and, when present, the second heating die, the third heating die, and/or the cooling element). The compressive force applied in the curing die assembly 308 (e.g., the first heating die and, when present, the second heating die, the third heating die, and/or the cooling element) helps to further force the reaction mixture into and between the reinforcement fibers 302 during the curing process. This action helps to ensure that the reinforcement fibers 302 conform precisely to the desired shape, resulting in a CFRP composite structure that mirrors the die's intricate configuration. [00109] For the various embodiments, the surfaces defining the cross-sectional shape discussed herein can include cylindrical shapes, such as rods, tubes, beams, rectangular (including square) or other geometric cross-sectional shapes are known. For example, the cross- sectional shape discussed herein can be used to provide the predefined shape of the CFRP composite structure with a rectangular cross section having a thickness of 2 to 6 millimeters and a width of 50 to 300 millimeters. The curing die assembly 308 can have a length from 0.5 to 2 meters. Other dimensions and shapes are of course possible as will be appreciated by one skilled in the art.

[00110] In some embodiments, upon exiting the curing die assembly 308, the wetted out reinforcement fibers 316 in the predefined shape and undergoing the curing process enter one or more of a post curing heating block. The one or more of the post curing heating block act to provide additional heat to the curing process of the reaction mixture to form the CFRP composite structure and not as a die to provide the predefined shape of the CFRP composite structure. [00111] At the exit of the curing die assembly 308, the CFRP composite structure is pulled through the pultrusion system 300 at a predefined rate using the pulling system 306. The pulling system 306 can be one of either a caterpillar puller or a reciprocating puller, both as are known in the art. In some embodiments, the pulling system 306 can pull the CFRP composite structure from the cooling block at the predefined rate of 0.5 to 6 meters/minute. In some embodiments, the pulling system 306 can pull the CFRP composite structure from the cooling block at the predefined rate of 2 to 4 meters/minute.

[00112] The pulling system 306 maintains the continuous movement of the CFRP composite structure through the various stages of the pultrusion system 300, as discussed herein, while maintaining the desired tension and speed. For the various embodiments, the pulling system 306 can include a set of motorized puller wheels or grippers that grip the CFRP composite structure and exert a controlled pulling force. The pulling force is regulated to maintain consistent tension on the CFRP composite structure as it moves through the system 300. Tension control units, including tension sensors, can be used to maintain consistent and uniform properties of the CFRP composite structure. The motorized puller wheels or grippers and the tension sensors can adjust the pulling force on the CFRP composite structure in realtime, which helps to ensure uniformity in the CFRP composite structure dimensions and properties. The pulling system 306 can also be synchronized with the other stages of the pultrusion system 300, as discussed herein. Proper coordination ensures that the continuous fiber-reinforced polyurethane composite structure enters each stage at the right time and with the appropriate tension. For instance, the pulling speed might need to be adjusted to accommodate the curing time required for the specific polyurethane resin being used.

[00113] For the various embodiments, the number and design of the puller wheels of the pulling system 306 can vary depending on the specific requirements of the pultrusion process. The puller wheels or grippers used in the pulling system 306 can be formed from a variety of materials to ensure effective grip, durability, and resistance to wear and heat. Examples of suitable materials for the puller wheels or grippers include rubber or elastomeric materials such as polyurethane, and other polymeric materials such as nylon, polyether ether ketone (PEEK), or acetal. The puller wheels or grippers can also include metal or metal-coated materials, such as the ones discussed herein.

[00114] In some embodiments, at the exit of the pulling system 306 there is a cutting mechanism 312. The cutting mechanism 312 can also be coordinated with the pulling speed to ensure that the CFRP composite structure is cut into individual pieces of the desired length. The cutting mechanism 312 can include saws, blades, or other cutting tools as are known in the art. [00115] The produced CFRP composite can be cut to desired length through a proper cutting saw system, as discussed herein, or coiled at certain coil lengths as for example 50 meter (m), 100 m, 200 m, 300 m up to 400 m for each single coil. The advantage of producing coils is that they can be shipped as is to the end user where it can then be uncoiled and cut to the desired length, for example in the production of spar caps for wind blades.

Examples

[00116] The Inventive Examples (IE) and Comparative Examples (CE) are based on computational model predictions. The design of the injection box was varied to observe the effect of the injection box geometry on the amount of air trapped in the final product of the pultrusion system. In the model studies, a flat sheet of fiber reinforced polymer (FRP) of a rectangular cross-section having a width of 15 times to 40 times that of the thickness was used. However, the same injection box design 100/400A may be configured to be used in any constant pultrusion cross-section. Various speeds of production were also modeled to determine the effectiveness of various injection box designs at higher manufacturing speeds.

[00117] Referring to FIG 4., the Inventive Example (IE) 400A illustrates an embodiment of the novel injection box 100, as discussed herein, that was used in a computational model. IE is an injection box 400A comprising a wall defining an elongate body having a first surface defining a feed opening 402A, a second surface defining an end opening 404A distal to the feed opening and an elongate axis extending therebetween. The wall defines a contiguous fluid tight conduit extending from the feed opening 402A, having a first height as found in Table 1, to the end opening 404A, having a second height as found in Table 1. The injection box 400A has an overall area reduction calculated by dividing the second height by the first height as found in Table 1. The injection box 400A further has an overall length as found in Table 1. The wall has a third surface defining an entry region, a fourth surface defining an expansion dome region, and a fifth surface defining an end region of the elongate body.

[00118] The entry region of the injection box 400A has an entry section 414A that is flat and does not have an angled taper. The entry section 414A is adjacent and coupled to the first tapered section 416A. The first tapered section 416A has a first taper angle taken relative to the elongate axis and the third surface defining the first tapered section 416A, the first taper angle being 3.25 degrees. The first tapered section 416A is adjacent and couples to the second tapered section 418A. The second tapered section 416A has a second taper angle taken relative to the elongate axis and the third surface defining the second tapered section 418A, the second taper angle being 0.1 degrees. The second taper angle of the second tapered section 418A is smaller in magnitude than the first taper angle of the first tapered section 416A.

[00119] The expansion dome region of the injection box 400A has a first expansion dome 420A, a second expansion dome 422A, and a third expansion dome 424A. The first expansion dome 420A and the second expansion 422A dome are connected by a third tapered section 426A. The second expansion dome 422A and the third expansion dome are connected by a fourth tapered section 428A. The third tapered section 426A and the fourth tapered section 428A each have a taper angle taken relative to the elongate axis and the fourth surface defining each taper section. The taper angle of the third tapered section 426A and fourth tapered section 428A being 0.1 degrees. Each expansion dome 420A, 422A, and 424A has a cross section, taken along the elongate axis, of a teardrop shape. A taper angle of a portion of the teardrop shape of each expansion dome 420A, 422A, and 424A taken relative to the elongate axis and the fourth surface defining each dome section being 2.5 degrees. Each dome 420A, 422A, and 424A has a dome entrance and dome exit.

[00120] The dome entrance has an entrance area, taken perpendicularly relative to the longitudinal axis, the dome exit has an exit area, taken perpendicularly relative to the longitudinal axis, and between the dome entrance and the dome exit there is a maximum area, taken perpendicularly relative to the longitudinal axis. Each of the first expansion dome 420A, the second expansion dome 422A and the third expansion dome 424A has a dome area reduction ratio, calculated by dividing the dome exit area bv the dome entry area and subtracting from 1. The values of each dome area reduction ratio can be found in Table 1. Each of the first expansion dome 420A, the second expansion dome 424A and the third expansion dome 426A has a dome area expansion ratio, calculated by dividing the dome maximum area by the dome entry area. The values of each dome area expansion ratio can be found in Table 1. The overall area reduction and the area reduction ratio is calculated by using area measurements of each respective section in the calculations. However, for simplicity in a design with a constant width, the calculation may be used with only the height as width measurements cancel out, as provided here.

[00121] The second expansion dome 422A is fluidly coupled to a polyurethane mixing and dispensing unit 434A, where the second expansion dome 422A is configured to be injected with polyurethane resin from the mixing and dispensing unit 434A for wetting of reinforcement fibers.

[00122] The end region of the injection box 400A has a fifth tapered section 430A and a flat end section 432A. The fifth tapered section 430A is adjacent and connected to the third expansion dome 424A and interposed between the third expansion dome 424A and the flat end section 432A. The fifth tapered section 430A has a taper angle taken relative to the elongate axis and the fifth surface defining the fifth tapered section 430A. The taper angle of the fifth tapered section 430A being 0.1 degrees. The flat end section 432A is adjacent and connected to the fifth tapered section 430A. The flat end section 432A has a length of 100mm taken along the elongate axis and a taper angle taken relative to the elongate axis and the fifth surface defining the flat end section of 0 degrees resulting in no taper.

[00123] The injection box 400B of CE A is also shown in FIG. 4. The injection box 400B, comprising a wall defining an elongate body having a first surface defining a feed opening 402B, a second surface defining an end opening 404B distal to the feed opening and an elongate axis extending therebetween. The wall defines a contiguous fluid tight conduit extending from the feed opening 402B, having a first height as found in Table 1, to the end opening 404B, having a second height as found in Table 1. The injection box 400B has an overall area reduction calculated by dividing the second height by the first height as found in Table 1. The injection box 400B further has an overall length as found in Table 1. The wall has a third surface defining an entry region, a fourth surface defining an expansion dome region, and a fifth surface defining an end region of the elongate body.

[00124] The entry region of the injection box 400B has an entry section 414B having a length of 200mm and a taper angle taken relative to the elongate axis and the third surface defining the entry section 414B of 0 degrees resulting in no taper. A first expansion dome 420B is adjacent and connected to the entry section 414B.

[00125] The dome region of the injection box 400B has the first expansion dome 420B has a cross section, taken along the elongate axis, of a teardrop shape. A taper angle of a portion of the tear drop shape of the first expansion dome 420B is taken relative to the elongate axis and the fourth surface defining each dome section being 1.125 degrees. The first expansion dome 420B has a dome entrance and dome exit. The dome entrance has an entrance area, taken perpendicularly relative to the longitudinal axis, the dome exit has an exit area, taken perpendicularly relative to the longitudinal axis, and between the dome entrance and the dome exit there is a maximum area, taken perpendicularly relative to the longitudinal axis. The first expansion dome 420B has a dome area reduction ratio, calculated by dividing the dome exit area by the dome entry area and subtracting from 1. The values of the first expansion dome 420B area reduction ratio can be found in Table 1. The first expansion dome 420B has a dome area expansion ratio, calculated by dividing the dome maximum area by the dome entry area. The values of each dome area expansion ratio can be found in Table 1.

[00126] The first expansion dome 420B is fluidly coupled to a polyurethane mixing and dispensing unit 434B, where the first expansion dome 420B is configured to be injected with polyurethane resin from the mixing and dispensing unit 434B for wetting of reinforcement fibers. [00127] The end region of the injection box 400B has a flat end section 432B. The flat end section 432B is adjacent and connected to the first expansion dome 420B. The flat end section 432A has a length of 100mm taken along the elongate axis and a taper angle taken relative to the elongate axis and the fifth surface defining the flat end section of 0 degrees resulting in no taper. [00128] The injection box 400C of CE B is also shown in FIG. 4. The injection box 400C, comprising a wall defining an elongate body having a first surface defining a feed opening 402C, a second surface defining an end opening 404C distal to the feed opening and an elongate axis extending therebetween. The wall defines a contiguous fluid tight conduit extending from the feed opening 402C, having a first height as found in Table 1, to the end opening 404C, having a second height as found in Table 1. The injection box 400C has an overall area reduction calculated by dividing the second height by the first height as found in Table 1. The injection box 400C further has an overall length as found in Table 1. The wall has a third surface defining an entry region, a fourth surface defining an expansion dome region, and a fifth surface defining an end region of the elongate body. [00129] The entry region of the injection box 400C has a first tapered section 416C having a taper angle taken relative to the elongate axis and the third surface defining the entry section 414C of 1 degrees. A first expansion dome 420C is adjacent and connected to the first tapered section 416C.

[00130] The dome region of the injection box 400C has the first expansion dome 420C has a cross section, taken along the elongate axis, of a hemispherical shape. The first expansion dome 420c has a dome entrance and dome exit. The dome entrance has an entrance area, taken perpendicularly relative to the longitudinal axis, the dome exit has an exit area, taken perpendicularly relative to the longitudinal axis, and between the dome entrance and the dome exit there is a maximum area, taken perpendicularly relative to the longitudinal axis. The first expansion dome 420C has a dome area reduction ratio, calculated by dividing the dome exit area by the dome entry area and subtracting from 1. The values of the first expansion dome 420C area reduction ratio can be found in Table 1. The first expansion dome 420C has a dome area expansion ratio, calculated by dividing the dome maximum area by the dome entry area. The values of each dome area expansion ratio can be found in Table 1.

[00131] The first expansion dome 420C is fluidly coupled to a polyurethane mixing and dispensing unit 434C, where the first expansion dome 420C is configured to be injected with polyurethane resin from the mixing and dispensing unit 434C for wetting of reinforcement fibers. [00132] The end region of the injection box 400A has a fourth tapered section 428C, a, fifth tapered section 430C, and a flat end section 432C. The fourth tapered section 428C is adjacent and connected to the first expansion dome 420C and interposed between the first expansion dome 420C and the fifth tapered section 430C. The fourth tapered section 428C has a taper angle taken relative to the elongate axis and the fifth surface defining the fourth tapered section 428C. The taper angle of the fourth tapered section 428C being 1 degrees. The fifth tapered section 430C is adjacent and connected to the fourth tapered section 428C and interposed between the fourth tapered section 428C and the flat end section 432C. The fifth tapered section 430C has a taper angle taken relative to the elongate axis and the fifth surface defining the fifth tapered section 430C. The taper angle of the fifth tapered section 430A being 0.85 degrees. The flat end section 432C is adjacent and connected to the fifth tapered section 430C. The flat end section 432C has a length of 100mm taken along the elongate axis and a taper angle taken relative to the elongate axis and the fifth surface defining the flat end section of 0 degrees resulting in no taper. [00133] The injection box 400D of CE C is also shown in FIG. 4. The injection box 400D, comprising a wall defining an elongate body having a first surface defining a feed opening 402D, a second surface defining an end opening 404D distal to the feed opening and an elongate axis extending therebetween. The wall defines a contiguous fluid tight conduit extending from the feed opening 402D, having a first height as found in Table 1, to the end opening 404D, having a second height as found in Table 1. The injection box 400D has an overall area reduction calculated by dividing the second height by the first height as found in Table 1. The injection box 400D further has an overall length as found in Table 1. The wall has a third surface defining an entry region, a fourth surface defining an expansion dome region, and a fifth surface defining an end region of the elongate body.

[00134] The entry region of the injection box 400D has an entry section 414D that is flat and does not have an angled taper. The entry section 414D is adjacent and coupled to the first tapered section 416D. The first tapered section 416D has a first taper angle taken relative to the elongate axis and the third surface defining the first tapered section 416D, the first taper angle being 1 degrees. The first tapered section 416D is adjacent and couples to a first expansion dome 420D.

[00135] The expansion dome region of the injection box 400D has a first expansion dome 420D, a second expansion dome 422D, and a third expansion dome 424D. The first expansion dome 420D and the second expansion 422D dome are connected by a third tapered section 426D. The second expansion dome 422D and the third expansion dome are connected by a fourth tapered section 428D. The third tapered section 426D and the fourth tapered section 428D each have a taper angle taken relative to the elongate axis and the fourth surface defining each taper section. The taper angle of the third tapered section 426D and fourth tapered section 428 AD being 1 degrees. Each expansion dome 420D, 422D, and 424D has a hemispherical cross section, taken along the elongate axis. Each dome 420D, 422D, and 424D has a dome entrance and dome exit.

[00136] The dome entrance has an entrance area, taken perpendicularly relative to the longitudinal axis, the dome exit has an exit area, taken perpendicularly relative to the longitudinal axis, and between the dome entrance and the dome exit there is a maximum area, taken perpendicularly relative to the longitudinal axis. Each of the first expansion dome 420D, the second expansion dome 422D and the third expansion dome 424D has a dome area reduction ratio, calculated by dividing the dome exit area by the dome entry area and subtracting from 1. The values of each dome area reduction ratio can be found in Table 1. Each of the first expansion dome 420D, the second expansion dome 424D and the third expansion dome 426D has a dome area expansion ratio, calculated by dividing the dome maximum area by the dome entry area. The values of each dome area expansion ratio can be found in Table 1.

[00137] The second expansion dome 422D is fluidly coupled to a polyurethane mixing and dispensing unit 434D, where the second expansion dome 422D is configured to be injected with polyurethane resin from the mixing and dispensing unit 434D for wetting of reinforcement fibers.

[00138] The end region of the injection box 400D has a fifth tapered section 430D and a flat end section 432D. The fifth tapered section 430D is adjacent and connected to the third expansion dome 424D and interposed between the third expansion dome 424D and the flat end section 432D. The fifth tapered section 430D has a taper angle taken relative to the elongate axis and the fifth surface defining the fifth tapered section 430D. The taper angle of the fifth tapered section 430D being 0.85 degrees. The flat end section 432D is adjacent and connected to the fifth tapered section 430D. The flat end section 432D has a length of 100mm taken along the elongate axis and a taper angle taken relative to the elongate axis and the fifth surface defining the flat end section of 0 degrees resulting in no taper.

[00139] Table 1 presents relevant measurements, characteristics, and results of the computational modeling of Inventive Example 1 (IE1 ), Inventive Example 2 (IE2), Comparative

Example A (CE A), Comparative Example B (CE B), and Comparative Example C (CE C). [00140] CE A is illustrative of a single dome, tear drop injection box design, with an end flat section and a dome taper angle of 1.125 degrees. In view of the amount of air trapped at the exit of the box in the composite product, the injection box of CE A performs poorly as compared to IE1 at the same operating speed.

[00141] CE B is illustrative of a single hemispherical dome with a first tapered section 416C and fourth tapered section 428C having a 1 degrees convergence angle and the fifth tapered section 430C having a 0.85 degrees convergence angle. In view of the amount of air trapped at the exit of the box in the composite product, the injection box of CE B performs poorly as compared to IE 1 at the same operating speed.

[00142] CE C is illustrative of a three hemispherical cavity chamber with a constant taper angle of 1 degrees through the first tapered section 416D, third tapered section 426D, and fourth tapered section 428D followed by a 0.85 degrees taper angle in the fifth tapered section 430D. In view of the amount of air trapped at the exit of the box in the composite product, the injection box of CE B performs poorly as compared to IE1 at the same operating speed. The teardrop shape of the expansion domes of IE1 enables a higher compaction factor in the expansion dome than that of CE C, which is a key factor for successful degassing of the resin/fiber system. The teardrop shape also enables improved resin mixing within the expansion dome.

[00143] IE1 and IE2 have the same injection box 400A design but are tested at different production speeds. IE1 is tested at a speed of 1 m/min and IE2 is tested at a speed of 3 m/min. The production speed of IE 1 of 1 m/min is the same production speed used for CE A, CE B, and CE C. Regarding IE 1, the degassing present in the example is ideal as there are no traces of bubbles at the exit of the injection box 400A. The degree of resin mixing and homogeneity of the example is also ideal. The production speed of IE1 was increased from Im/min to 3 m/min for IE2. IE2 similarly showed no traces of bubbles at the exit of the injection box 400A. IE2, in view of IE1, similarly showed ideal degassing and resin homogeneity illustrating the robust design of the inventive example. The injection box 400A of the IE provides more cavities via the expansion domes 410A, 422A, and 422C with a gradual compaction profile resulting in efficient wetting and degassing of a fiber/resin system.

Air Trapped Measurement

[00144] The air trapped (%) at the exit of the injection box as shown in Table 1 was determined as follows. In CFD simulation, a number of bubbles with a diameter of 10 pm were uniformly seeded in a low-pressure region of the injection box and then the trajectory of the bubble was tracked. The low-pressure region in which the bubbles were seeded exhibited pressure less than 0.2 bar. The bubbles will be transported to either the resin near the feed opening 402A-D or the resin near the end opening 404A-D of the injection box 400A-D. Bubbles considered trapped are bubbles that are transported to the end opening 404A-D of the injection box 400A-D. Bubbles that are trapped in the resin/fiber system negatively affect the quality of the final product.

[00145] The air trapped (%) at the exit of the injection box is defined as: 100(%)

[00146] A smaller percentage of air trapped at the exit of the box correlates to a better degassing performance of the injection box 400A-D.

Claims

Claims What is claimed:

1. An injection box for a pultrusion system for forming a fiber-reinforced composite structure, comprising: a wall defining an elongate body having a first surface defining a feed opening, a second surface defining an end opening distal to the feed opening and an elongate axis extending therebetween, wherein the wall defines a contiguous fluid tight conduit extending from the feed opening to the end opening, and wherein the wall has a third surface defining an entry region, a fourth surface defining an expansion dome region, and a fifth surface defining an end region of the elongate body, wherein: the third surface defining the entry region has a first tapered section having a first predetermined length taken along the elongate axis and a second tapered section having a second predetermined length taken along the elongate axis, wherein the second tapered section is positioned between the first tapered section and the fourth surface defining the expansion dome region, wherein the first tapered section has a first taper angle taken relative to the elongate axis and the first surface defining the first tapered section, and wherein the second tapered section has a second taper angle taken relative to the elongate axis and the first surface defining the second tapered section; the fourth surface defining the expansion dome region positioned between the entry region and the end region, wherein the expansion dome region has at least a first expansion dome, a second expansion dome, and a third expansion dome; and wherein for a cross-section of the wall taken longitudinally along the elongate axis through the expansion dome region the fourth surface defining for each of the first expansion dome, the second expansion dome, and the third expansion dome a teardrop shape having a dome entrance and a dome exit distal to the dome entrance relative to the feed opening, wherein the dome entrance has an entrance area, taken perpendicularly relative to the longitudinal axis, the dome exit has an exit area, taken perpendicularly relative to the longitudinal axis, and between the dome entrance and the dome exit there is a maximum area, taken perpendicularly relative to the longitudinal axis, and where each of the first expansion dome, the second expansion dome and the third expansion dome has a dome area reduction ratio, calculated by dividing the dome exit area by the dome entry area and subtracting from 1, between 0.10 and

2. The injection box of claim 1, wherein the third expansion dome has a 1.2 to 3 times larger dome area reduction ratio than the first expansion dome.

3. The injection box of claim 1, wherein each expansion dome has a dome taper angle taken relative to the elongate axis and the fourth surface extending from a location of the maximum area to a location of the exit area, wherein the dome taper angle is between 0.5 and 5 degrees.

4. The injection box of claim 1, wherein a third dome area reduction ratio value is 0.07 to 0.25 larger than a second dome area reduction ratio value.

5. The injection box of claim 4, wherein the second dome area reduction ratio value is 0.01 to 0.10 larger than a first dome area reduction ratio value.

6. The injection box of claim 1, wherein each expansion dome has an expansion ratio, calculated by the maximum area divided by the entry area of each corresponding expansion dome, the expansion ratio for each expansion dome being between 1.10 and 2.

7. The injection box of claim 6, wherein a second dome expansion ratio value is between 0.05 and 0.2 larger than a first dome expansion ratio value, and a third dome expansion ratio value is between 0.1 and 0.30 larger than the second dome expansion ratio value.

8. The injection box of claim 1, wherein the second expansion dome is configured to be injected with a liquid polyurethane resin.

9. The injection box of claim 1, wherein a total area reduction ratio of the injection box, measured by a perpendicular cross-sectional area of the end opening, taken relative to the elongate axis and the second surface, divided by a perpendicular cross-sectional area of the feed opening, taken relative to the elongate axis and the first surface, the total area reduction ratio being between 0.05 and 0.25.

10. An injection box for a pultrusion system for forming a fiber-reinforced composite structure, comprising: a wall defining an elongate body having a first surface defining a feed opening, a second surface defining an end opening distal to the feed opening and an elongate axis extending therebetween, wherein the wall defines a contiguous fluid tight conduit extending from the feed opening to the end opening, and wherein the wall has a third surface defining an entry region, a fourth surface defining an expansion dome region, and a fifth surface defining an end region of the elongate body, wherein: the third surface defining the entry region has a first tapered section having a first predetermined length taken along the elongate axis and a second tapered section having a second predetermined length taken along the elongate axis, wherein the second tapered section is positioned between the first tapered section and the fourth surface defining the expansion dome region, wherein the first tapered section has a first taper angle taken relative to the elongate axis and the third surface defining the first tapered section, and wherein the second tapered section has a second taper angle taken relative to the elongate axis and the third surface defining the second tapered section; the fourth surface defining the expansion dome region positioned between the entry region and the end region, wherein the expansion dome region has at least a first expansion dome, a second expansion dome, a third expansion dome, a third tapered section connecting the first expansion dome and the second expansion dome, and a fourth tapered section connecting the second expansion dome and the third expansion dome; and wherein for a cross-section of the wall taken longitudinally along the elongate axis through the expansion dome region the fourth surface defining for each of the first expansion dome, the second expansion dome, and the third expansion dome a teardrop shape having a dome entrance and a dome exit distal to the dome entrance relative to the feed opening.

11. The injection box of claim 10, the fifth surface defining the end region positioned between the dome region and the end opening, wherein the end region has a fifth tapered section and a flat section, the fifth tapered section connection the third expansion dome to the flat end section.

12. The injection box of claim 11, wherein the second tapered section, the third tapered section, the fourth tapered section, and the fifth tapered section have a taper angle of 0.01 to 0.3 degrees, wherein each taper angle is taken relative to the elongate axis and the fourth surface defining each tapered section.

13. The injection box of claim 12, wherein the second tapered section, the third tapered section, the fourth tapered section, and the fifth tapered section have the same taper angle.

14. The injection box of claim 11, wherein the fifth tapered section is between 1.1 and 2 times longer than the fourth tapered section.

15. The injection box of claim 10, wherein the entry region, the first expansion dome, and the second expansion dome are under atmospheric pressure, and the third expansion dome and the end region are under pressure greater than atmospheric pressure.

16. The injection box of claim 10, wherein the second tapered section is 3 to 6 times longer than the third tapered section.

17. The injection box of claim 10, wherein the first taper angle of the first tapered section is 10 to 50 times larger than the second taper angle of the second tapered section and the second predetermined length of the second tapered section is 2 to 4 times larger than the than the first predetermined length of the first tapered section.

18. A pultrusion system for forming a continuous fiber-reinforced composite structure, comprising: continuous reinforcement fibers; a polyurethane dispensing unit configured to dispense a liquid polyurethane resin; an injection box of claim 1 fluidly coupled to the polyurethane dispensing unit, wherein the injection box receives the reinforcement fibers and the liquid polyurethane resin to form wetted out reinforcement fibers; a curing die assembly coupled to the injection box, wherein the wetted-out reinforcement fibers of the injection box are cured; and a pulling system to pull the continuous fiber-reinforced polyurethane composite structure at a predefined rate.

19. The pultrusion system of claim 18, wherein the pultrusion system is capable of operating at a speed between 2 and 4 m/min with less than 5% air trapped in a produced fiber-reinforced structure.

20. The pultrusion system of claim 18, wherein the liquid polyurethane resin is a polyurethane resin.