DE102015109566B4 - Process for the production of tubular or tubular products by means of an extrusion device - Google Patents

Abstract

Process for the production of tubular or tubular products (2) by means of an extrusion device (1) with an extruder (4) with a mandrel (12) which is arranged coaxially to a central longitudinal axis (11) of a hollow body (9) and delimits an annular channel (7) , the melt being fed into the annular channel (7) between the hollow body (9) and the mandrel (12) by means of the extruder (4), the hollow body (9) and the mandrel (12) being driven rotatably relative to one another, thereby characterized in that over the width (b) of the melt between the mandrel (12) and the inner wall surface (8), a velocity profile (19) with a flow direction (17) in the circumferential direction of the mandrel (12) is set, in which the flow direction (17 ) in an area (20) adjacent to the inner wall surface (8) opposite to an area (21) adjacent to the mandrel (12) for aligning the polymer chains of the plastic material or the added reinforcing materials in the product llt, so that in the course of the main flow direction (13) in the annular channel (7) there is a velocity profile (19) over the width (b) of the melt between the mandrel (12) and the inner wall surface (8) with two areas (20, 21 ), which show an opposite negative or positive curve over the wall thickness of the melt between the mandrel (12) and the inner wall surface (8), with the integral of the respective velocity profile between the neutral phase ( 22) and the inner wall surface (8) or the mandrel (12) is of the same size, so that the associated components of the rotary movement cancel each other out, and the product (2) emerges from the outlet (14) without a recognizable external twist.

Description

The invention relates to a method for producing tubular or tubular products by means of an extrusion device with an extruder with a mandrel which is arranged coaxially to a central longitudinal axis of a hollow body and delimits an annular channel, the melt being fed into the annular channel between the hollow body and the mandrel by means of the extruder , wherein the hollow body and the mandrel are driven rotatably relative to one another.

An extrusion device with an extruder is already widely used in practice for the production of tubing, but also for the sheathing of wires or fibers for electrical or optical lines, and is therefore part of the state of the art due to its prior art. Due to the extrusion, the alignment of the material structure, in particular the polymer structure and optionally the fillers, is essentially parallel to the main extension in the longitudinal direction of the hose during hose production. The resulting anisotropy means that the hoses have a higher mechanical strength in the direction of their main extent than in the radial direction. In contrast, there is the load on the product in practice, which is many times higher in the radial direction than in the longitudinal direction, for example in the case of pressure-loaded, fluid-carrying hoses.

In practice, various measures are already known to effectively compensate for the radial forces caused by the fluid pressure. For example, reinforcing fabrics or layers made of plastic or metal, which can absorb the radial load, are incorporated for this purpose.

Further possibilities for reinforcement consist in the use of at least one further layer made of synthetic materials or rubber, which are applied for the purpose of increasing strength. As a result, the hoses have a comparatively large wall thickness overall. This makes the processing and also the winding or laying of such products in systems or in components more difficult.

Another method for producing hoses with particularly resilient properties is the winding of hoses in layers, consisting of different materials. Such processes are complex and, moreover, cannot be used for all hose dimensions.

Methods are also known for reinforcing elongated profiles by wrapping the profile with intersecting fiber layers. A plastic hose is covered with a hose braided from threads and then wrapped with another plastic hose.

The DE 38 24 757 A1 describes a process with which endless profiles can be reinforced in several dimensions by inserting threads through a rotating quill. For this purpose, the hollow body has an opening for supplying the melt, which opens into a concentric annular channel which extends in the axial direction. The annular channel is delimited by the hollow body and the quill rotatably mounted in the hollow body. The inside of the quill is essentially hollow. On the circumference of the quill, bores are provided as thread guide holes through which the threads are guided from the inside to the outside in order to feed the threads to the extruded profile. The threads are guided through the rotatable quill and inserted into the supplied melt.

Furthermore, through the DE 29 51 399 A1 a method for producing a fiber-reinforced profile is known. In this process, the profile is created by bringing together fiber strands that have previously been soaked in a plastic matrix in immersion baths.

In addition, the DE 37 09 009 A1 a cross-head in which the material to be extruded, for example a thermoplastic or an elastomer, is fed from an extruder perpendicular to the direction of passage of the conductor or cable and deflected so that it can be distributed concentrically around the conductor or core. As a result, the cross-head is suitable for sheathing wires or optical fibers for electrical or optical lines or cables. The cross-head is equipped with movable deflection and distribution devices in order to distribute the melt over the circumference and to improve the centricity of the tubular product with respect to the quill, which can only be moved axially. By adjusting rotatable elements, a different distribution and thus a concentric design is achieved.

What all processes have in common is the time-consuming and cost-intensive manufacture of products that are subject to particularly high mechanical loads.

The generic U.S. 4,151,242 A refers to the processing of polyvinyl chloride (PVC), which has a high impact resistance, a high modulus of elasticity and a high tensile strength as well as a high melt viscosity, which lead to poor processability. During processing, rotating shear rings in Combination with spiral grooves, a pumping and shearing action acting on the material and thereby a uniform mixing effect and melt are generated, which lead to a smooth extrudate. The polymer is thus kept at a low temperature until it passes through the shear rings, where the pumping and shearing action causes a rapid temperature rise to bring the polymer to its optimal exit temperature.

The EP 0 499 025 A1 relates to an extrusion tool for the production of tubular hollow bodies or sheaths from polymeric materials, comprising a housing with an inlet for the supply of the polymeric material and an extruder nozzle, which are connected to one another via a cavity inside the housing. A cylindrical mandrel is rotatably arranged in the rotationally symmetrical housing on which several inlets for the material supply are arranged. An extruder nozzle with an, for example, annular extruder opening is arranged at one axial end of the housing.

The invention is based on the object of creating a possibility of being able to adjust the texturing of the product in a targeted manner during manufacture in order to be able to do without additional reinforcing means or reinforcing layers.

The object is achieved according to the invention with a method according to the features of claim 1. The further embodiment of the invention can be found in the subclaims.

According to the invention, a method for producing tubular or tubular products by means of an extrusion device is provided in which a velocity profile with a flow direction in the circumferential direction of the mandrel is set over the width of the melt between the mandrel and the inner wall surface, in which the flow direction is in one of the inner wall surface adjacent area opposite to an area adjacent to the mandrel for aligning the polymer chains of the plastic material or the added reinforcing materials in the product, so that in the course of the main flow direction in the annular channel there is a velocity profile across the width of the melt between the mandrel and the inner wall surface with two areas sets, which show an opposite negative or positive curve over the wall thickness of the melt between the mandrel and the inner wall surface, the integral of the respective speed in the two areas Ability profile between the neutral phase and the inner wall surface or the mandrel is the same size, so that the associated components of the rotary movement cancel each other out and thereby the product emerges from the outlet without a recognizable external twist.

This makes it possible, in a surprisingly simple manner, to specifically influence the alignment of the preferred direction of the polymer chains in the melt, which takes place between an inlet opening of the extruder and an outlet from the annular channel. As a result, the melt does not flow essentially along the shortest connecting line in the annular channel between inlet and outlet, as in the prior art. Rather, according to the invention, the melt is impressed with a rotary movement or a twist, by means of which the melt additionally winds around the mandrel during the flow movement between the inlet and the outlet, i.e. preferably flows around it several times. Due to this changed flow direction of the melt in the ring channel, two vector components of the flow are superimposed on one another, namely on the one hand a flow direction component in the circumferential direction of the mandrel and on the other hand a flow direction component in the direction of the main extent of the ring channel between inlet and outlet. As a result, the polymer chains of the plastic material or the reinforcing materials contained in the product are not aligned parallel to the main extent of the annular channel, as in the prior art, but deviating from this with a preferred direction with a considerable inclination, which is adjusted by the extrusion parameters, for example the flow rate of the melt can be. In tests, a preferred alignment of the polymer chains at an angle of approximately 45 ° to the longitudinal extension of the product has already proven to be particularly practical. The alignment of the polymer chains in the product is not only similar to the arrangement of the reinforcing threads known from the prior art, but comparable improvements in the load-bearing capacity of the product are also observed without the need for additional reinforcing material. Thus, according to the invention, without additional reinforcing layers or reinforcing materials, a substantial increase in the load-bearing capacity of the product can be achieved without changing the material used, merely by changing the orientation of the polymer chains in the product. According to the invention, the term melt should also be understood to mean those flowable substances which, after exiting the outlet, for example also solidify under a suitable atmosphere, to form a shaped body.

Since the hollow body has an inner wall surface and / or the mandrel has a circumferential surface which is equipped with a profile having a gradient, this leads to a particularly efficient deflection of the flow of the melt.

The profiling can be designed similar to a screw thread, the course can be made continuous or discontinuous. In a corresponding manner, the circumferential surface of the mandrel can also be equipped with a corresponding or differently configured profiling.

A particularly advantageous embodiment of the invention is also achieved in that the mandrel is rotatably driven with a direction of rotation opposite to the direction of rotation of the slope of the profiling. In that on the one hand a rotational movement of the melt is achieved through the profiling of the inner wall surface, along which the melt flows between the inlet opening and the outlet in the annular channel and, on the other hand, the rotational movement of the mandrel causes a further, second rotational movement opposite to the first rotational movement to act on the melt the product produced in this way from the outlet without an external twist, i.e. without the tendency of continued rotation outside the annular channel. Thus, the rotational movement of the mandrel with respect to the product leads to a cancellation of the angular momentum, while within the material in the annular channel the efficiency of the desired alignment of the polymer chain deviating from the axial direction is further increased. In other words, the product in the area of the outlet has a speed profile with positive and negative areas which correspond in terms of amount and therefore cancel each other out in total.

For this purpose, according to a particularly preferred embodiment of the invention, the speed of rotation of the mandrel is set in such a way that it essentially corresponds to the speed in the circumferential direction of the melt in the annular channel in order to be able to set the desired, overall neutral speed profile without any problems. For this purpose, for example, a swirl that may be present can be detected by means of a sensor at the outlet from the ring channel and a control signal for a changed rotational speed of the mandrel can be determined from this by means of a control unit.

For this purpose, according to a particularly promising embodiment of the invention, a speed profile is set via the material thickness of the melt between the mandrel and the inner wall surface, the vector of which can be set in a first area adjacent to the inner wall surface opposite to a second area adjacent to the mandrel, preferably the neutral phase lies between the areas near the geometric center between the inner wall surface and the mandrel. In this way, homogeneous material properties of the product can be ensured over the entire material thickness of the wall of the tubular or tubular product.

Furthermore, the mandrel can have a profile on the circumferential side which has a slope which is opposite to the slope of the profile of the inner wall surface. In this way, according to the principle of opposite thread pitches of the profiles of the mandrel on the one hand and the inner wall surface on the other hand, a particularly effective increase in the shear forces acting during transport in the annular channel is achieved, through which the desired texturing of the polymer chains is achieved. Here, the profiling preferably extends over the entire length of the annular channel between the inlet opening for the melt up to the outlet from the annular channel.

The profiling can be designed as an integral part of the mandrel, or it can be part of a correspondingly profiled sleeve, which is also arranged, for example, interchangeably, on the circumference of the mandrel.

A particularly practical embodiment of the invention is also achieved in that the mandrel is tempered, in particular heated, in order to ensure that no undesired premature cooling of the melt occurs on the mandrel, which could adversely affect the flow behavior of the melt in the annular channel. An electrical heating element, for example, is suitable for this purpose. Furthermore, the mandrel can also be designed, at least in sections, as a hollow body and through which a heat transfer fluid can flow, in order to be able to supply the desired amount of heat. Of course, sensors for detecting the surface temperature of the mandrel can be assigned to the mandrel for this purpose.

The annular channel can have a constant width along the central longitudinal axis, i.e. in particular a hollow cylindrical shape, in order to achieve that the distance between the mandrel and the inner wall surface is constant along the central longitudinal axis and only deviates in sections due to the regular profiling.

In contrast, it also proves to be particularly promising if the annular channel has a decreasing width along the central longitudinal axis, in that the hollow body and / or the mandrel are at least partially conical in order to increase the flow rate of the melt accordingly. Due to the increase in the flow rate in the annular gap, the shear stress also increases proportionally, which has an advantageous effect on the alignment of the polymer chains in the preferred preferred direction.

Particularly preferably, the hollow body or the mandrel are driven in an alternatingly movable manner relative to one another, axially parallel to the central longitudinal axis, so that a reversing stroke movement can be generated and the rotation can be superimposed. This further improves the deflection of the melt flow.

The mandrel preferably has an end face which faces the outlet and which, in particular, has an adjustable distance from the plane of the outlet. Since the mandrel already ends in front of the outlet, the desired neutral speed profile can be generated in a simple manner through the preferably adjustable distance and can be adapted with little effort in the event of changed process or material parameters.

Furthermore, the mandrel can be designed as a hollow body with a passage opening for strand-like products. If necessary, strand-like products for applying a coating can be fed through this passage opening, for example in a tandem or coextrusion process. In this way, several layers with opposing, intersecting preferential directions can be applied in order to further increase the load-bearing capacity of the product.

In a cross-head of the extrusion device for the production of hose-shaped or tubular products with a mandrel that is arranged coaxially to a central longitudinal axis of a hollow body and delimiting an annular channel, the hollow body and the mandrel are designed to be rotationally movable relative to one another, with the hollow body being a hollow cylinder can be designed with an inner wall surface which is equipped with a profile having a slope for generating a flow of the melt in the circumferential direction of the mandrel. This makes it possible to increase the load-bearing capacity of the product produced in this way without changing the material composition of the melt, by using the rotary movement to align the polymer chains present in the melt at an incline relative to a central longitudinal axis of the product corresponding to the main conveying direction. By creating an additional movement component of the melt in the circumferential direction of the mandrel, various currents act on the melt up to the outlet from the annular channel, which cause the polymer chains to align, for example, at a 45 ° angle to the central longitudinal axis of the product.

• 1 eine perspektivische Darstellung der Extrusionsvorrichtung mit einem Extruder und einem Ringkanal;
• 2 einen Querschnitt durch den Extruder und den Ringkanal;
• 3 einen Längsschnitt durch den Ringkanal;
• 4 einen Längsschnitt durch den Ringkanal mit konischem Dorn;
• 5 einen Längsschnitt durch den Ringkanal mit konischem Hohlkörper;
• 6 ein mit der Extrusionsvorrichtung hergestelltes Erzeugnis in einer Vorderansicht und in einer Seitenansicht.

The invention allows various embodiments. For further clarification, the basic principle is shown in the drawing using an extrusion device and is described below. This is shown in a schematic diagram in

• 1 a perspective view of the extrusion device with an extruder and an annular channel;
• 2 a cross section through the extruder and the annular channel;
• 3rd a longitudinal section through the annular channel;
• 4th a longitudinal section through the annular channel with a conical mandrel;
• 5 a longitudinal section through the annular channel with a conical hollow body;
• 6th a product produced with the extrusion device in a front view and in a side view.

An extrusion device 1 is explained below using the 1 to 3rd explained in more detail. The extrusion device 1 is used for hose production and enables the production of an in 6th tubular product shown as an example 2 , its material structure 3rd , in particular the polymer structure and optionally the structure of the fillers, not parallel to the main extent in the longitudinal direction of the product 2 runs, but at an angle to this. As a result, the product produced in this way has 2 compared to the products known from the prior art 2 With an alignment of the material structure in the direction of the main extent, a much higher mechanical strength in the radial direction, which corresponds optimally to the load on such products in practice, especially as a pressure-loaded, fluid-carrying hose and therefore enables higher loads without additional reinforcement measures.

The extrusion device 1 is to do this with an extruder 4th equipped for feeding the melt, not shown, its conveying direction 5 tangentially into an inlet 6th of a ring channel 7th flows out. The ring canal 7th is on the one hand by an inner wall surface 8th a hollow body designed as a hollow cylinder 9 , on the other hand by a peripheral surface 10 one coaxial with a central longitudinal axis 11 of the hollow body 9 arranged thorn 12th limited. The melt thus occurs in a transverse plane to the central longitudinal axis 11 of the hollow body 9 tangentially and flows around the mandrel 12th , being a main flow direction 13th of the melt parallel to the central longitudinal axis 11 towards an outlet 14th of the ring channel 7th trains. At the same time, a further flow direction is impressed on the melt flow, which is brought about by the fact that the mandrel 12th is set in rotation while the inner wall surface 8th of the hollow body 9 with a profile having a slope 15th Is provided. This causes the melt to flow around the mandrel 12th helical. This developing melt flow is thus from a first translational flow direction 16 and a direction of flow 17th towards the circumference of the mandrel 12th composed. The direction of flow is used 17th towards the circumference of the mandrel 12th the alignment of the polymer chains in a preferred direction, which in practice essentially corresponds to the superimposed flow direction 18th with an angle between 30 ° and 60 ° to the central longitudinal axis 11 in the product to be manufactured 2 align.

The direction of flow 17th the thorn becomes opposite 12th in turn driven to rotate in the direction of arrow n, the speed of rotation of the mandrel 12th essentially the speed of the melt flow in the circumferential direction in the annular channel 7th and can be set based on the measured values determined. By the thorn 12th has a profile with a slope that corresponds to the slope of the profile 15th the inner wall surface 8th is opposite, the previously described effect of aligning the polymer chains is reinforced by the introduction of shear forces.

As in 3rd to be recognized, is thus in the course of the main flow direction 13th in the ring channel 7th a speed profile 19th across the width b of the melt between the mandrel 12th and the inner wall surface 8th with two areas 20th , 21st one that has an opposite negative or positive curve over the wall thickness of the melt between the mandrel 12th and the inner wall surface 8th demonstrate. By the two areas 20th , 21st i.e. the integral of the respective speed profile between the neutral phase 22nd and the inner wall surface 8th or the mandrel 12th are the same size, the associated components of the rotary movement cancel each other out, so that the product 2 without a recognizable external swirl from the outlet 14th exit. While the melt in the direction of the outlet 14th migrates, this is sheared tangentially. This leads to the preferred direction. The mandrel rotates to avoid product twist as it exits 12th opposite to the peripheral speed of the melt.

In the 4th and 5 is still another variant of the extrusion device 1 shown in which the ring channel 7th towards the outlet 14th has a decreasing width b ₁ , b ₂ by as in 4th depicted the thorn 12th or as in 5 shown the hollow body 9 are designed at least partially conical or conical. As a result, the flow rate of the melt can be increased accordingly in order to achieve a particularly efficient alignment of the polymer chains in the preferred direction due to the likewise increased shear stress.

As in 2 recognizable is the thorn 12th tubular with a concentric bore 23 executed during the operation of the extrusion device 1 is acted upon with a heat transfer fluid and so an adjustment of the temperature of the mandrel 12th the temperature of the melt in the annular channel 7th enables. This results in undesirable cooling of the melt on the circumferential surface 10 of the thorn 12th and the associated impairment of the melt flow is avoided.

Claims (7)

Process for the production of tubular or tubular products (2) by means of an extrusion device (1) with an extruder (4) with a mandrel (12) which is arranged coaxially to a central longitudinal axis (11) of a hollow body (9) and delimits an annular channel (7) , wherein the melt is fed into the annular channel (7) between the hollow body (9) and the mandrel (12) by means of the extruder (4), the hollow body (9) and the mandrel (12) being driven rotatably relative to one another, thereby characterized in that over the width (b) of the melt between the mandrel (12) and the inner wall surface (8), a velocity profile (19) with a flow direction (17) in the circumferential direction of the mandrel (12) is set, in which the flow direction (17 ) set in an area (20) adjacent to the inner wall surface (8) opposite to an area (21) adjacent to the mandrel (12) for aligning the polymer chains of the plastic material or the added reinforcing materials in the product is ellt, so that in the course of the main flow direction (13) in the annular channel (7) a velocity profile (19) across the width (b) of the melt between the mandrel (12) and the inner wall surface (8) with two areas (20, 21 ), which show an opposite negative or positive curve over the wall thickness of the melt between the mandrel (12) and the inner wall surface (8), with the integral of the respective velocity profile between the neutral phase ( 22) and the inner wall surface (8) or the mandrel (12) is of the same size, so that the associated components of the rotary movement cancel each other out, and the product (2) exits the outlet (14) without a discernible external twist. Procedure (1) according to Claim 1 , characterized in that the melt enters tangentially in a transverse plane to the central longitudinal axis (11) of the hollow body (9) and flows around the mandrel (12). Procedure according to Claim 1 , characterized in that the mandrel (12) with one direction of rotation (n) is driven in a rotationally movable manner in particular opposite to the pitch of the profiling (15) designed as a screw thread. Method according to at least one of the preceding claims, characterized in that the mandrel (12) is tempered, in particular heated. Method according to at least one of the preceding claims, characterized in that the hollow body (9) and / or the mandrel (12) are driven to be movable in an alternating manner relative to one another, parallel to the central longitudinal axis (11). The method according to at least one of the preceding claims, characterized in that the mandrel (12) has an end face facing the outlet (14), which has an in particular adjustable distance from the plane of the outlet (14) and that the distance is set such that a neutral speed profile is generated. The method according to at least one of the preceding claims, characterized in that the melt by means of the extruder (4) with a conveying direction (5) in a cross-sectional plane of the hollow body (9), in particular tangential to a central longitudinal axis (11) of the hollow body (9) in the Annular channel (7) between the hollow body (9) and the mandrel (12) is fed.

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