HK1111938A - A check valve with a spiral coil seal - Google Patents

Abstract

A seal for a check valve for a metal molding machine. The seal is provided by the combination of a peripheral groove in an outer surface of the check valve and a helically wound core in the groove. The helically wound coil is expandable into sealing engagement with a cylindrical wall of the molding machine. The helically wound coil may be movable laterally in the groove between a melt channel open position and a melt channel closed position to open or seal the melt channel.

Description

Check valve with spiral coil seal

Technical Field

The present invention relates generally to lock rings and seals for injection molding machines, and more particularly, but not by way of limitation, the present invention relates to lock rings and seals for metal injection molding machines and die casting machines.

Background

The prior art includes U.S. patent No. 3,578,803 to Huhn, 1971, 5-18, which describes the use of a coil spring to urge a seal ring against a counter ring to form a seal on a shaft.

United states patent No. 3,655,206 to Durametallic, 1972, 4-11, describes the use of a spiral seal ring that is pressed against a wedge-shaped surface to provide a radially inward and axial compressive force to the seal ring to form a seal around a shaft. The seal ring is composed of multiple layers of graphite material. The seal ring is designed for holding a seal around the shaft.

Us patent application 2002/0100507 to Hauser et al, published 2002, 8/1, describes a check valve for a piston pump in an automatic braking system. The check valve is formed as a single piece comprising a helical coil with a base ring on one end and a closure disc on the other end. Movement of the base ring provides opening and closing of the check valve. The coil spring provides the opening and closing mobility of the valve. The outer surface of the coil spring does not act as a closing or sealing surface.

U.S. patent application No. 2004/0001900 to Dominka, published on 1/2004, describes a check valve for an injection system. The valve includes a shear pin, a spring guide member, and a coil spring. The coil spring is compressed by the guide member to force the pin to close the flow path and decompressed by the guide member to enable the flow path to open. The surface of the coil spring is in contact with the flow path but does not provide any closing or sealing surface.

The prior art has not suggested the use of a helical coil to actually seal a flow path.

In injection molding machines, there is a need for a wear resistant, reliable seal for sealing a flow path through a check valve.

Disclosure of Invention

In the injection molding of plastics, check valves without any seals are generally employed and rely on the considerable clearance of the melt and high viscosity to form a complete seal. The metal used in metal injection molding does not have the high viscosity of plastic and will therefore leak back through the voids that are typically used in plastic injection molding. Furthermore, the high corrosiveness of metals and the high temperatures required for injection also impair the use of plastic injection molding sealing arrangements in metal injection molding. Thus, there is a need for an effective seal for metal injection molding that has tight clearances and tolerances and must withstand high temperatures and corrosive environments. The present invention provides such a seal using a spiral coil.

The present invention provides a seal for an injection molding machine that prevents backflow of melt in a check valve, reduces wear of the barrel and check valve, and operates reliably even when significant wear occurs. The invention is achieved by providing a spiral coil to seal the channel. The spiral coil may also serve as a check ring to open and close the melt path.

The present invention provides a seal for a check valve of a metal molding machine. The seal includes a peripheral groove in the outer surface of the check valve and a spiral core within the groove. The helical coil is expandable into sealing engagement with a cylindrical wall of the molding machine.

The present invention further provides a check valve for a metal molding machine. The valve includes a helical coil. The coil seals the check valve and slides over the cylinder of the check valve to open and close a flow path through the valve. The first turn of the coil has a surface that mates with a mating surface on the cylinder to close the valve when in contact with the mating surface. The outer peripheral surface of the coil cooperates with a cylindrical wall surrounding the check valve to provide an axial seal for the check valve.

The present invention further provides an injection unit for an injection molding machine comprising an injection screw, a nozzle body on one end of the injection screw, and a check valve on the nozzle body. The check valve includes a sealing ring. The sealing ring includes a helical coil that encircles the nozzle body and is slidable between a first position in which the nozzle is open and a second position in which the nozzle is closed. The first bead of the coil sealingly engages a shoulder on the nozzle body when the coil is in the closed position.

Drawings

Exemplary embodiments of the invention will now be described with reference to the accompanying drawings, in which:

FIG. 1 is an end view of a barrel assembly for a metal injection molding machine.

FIG. 1A illustrates a barrel assembly of a typical injection molding system to which the present invention may be used.

FIG. 2 is a cross-sectional view of the barrel assembly of FIG. 1 taken along section line 2-2 of FIG. 1 showing the spiral seal provided by the present invention.

FIG. 3 is a detailed view of a portion of FIG. 2 showing the check valve with the spiral seal in a tightly sealed position taken along section line 3-3 in FIG. 4.

Fig. 3A is a detail view of the circular portion a of fig. 3, showing more clearly the relationship between the spiral geometry and the grooves.

Fig. 4 is an end view of the check valve of fig. 3.

Figure 5 is a perspective view of the locking ring of the present invention.

Figures 5A and 5B are a cross-sectional view and an end view, respectively, of the locking ring shown in figure 5.

FIG. 6 is a perspective view of a helical coil assembled on the check ring of FIG. 5 to seal the check ring.

Fig. 6A and 6B are a cross-sectional view and an end view, respectively, of the spiral coil shown in fig. 6.

FIG. 7 is a cross-sectional view of a check valve taken along section line 7-7 of FIG. 8 with a helical coil acting as a seal and check ring.

Fig. 8 is an end view of the check valve shown in fig. 7.

FIG. 9 is another embodiment of the present invention wherein the spiral coil assembly acts as a lock ring and seal.

FIG. 10 is a cross-sectional view of another embodiment of the present invention taken along section line 10-10 in FIG. 11, including a wear ring positioned between the helical coil check valve and the seal.

Fig. 11 is an end view of the check valve shown in fig. 10.

Detailed Description

The structure and operation of the present invention will be explained below within the scope of improving the function and durability of a check valve configured for use in a barrel assembly of an injection molding system for the molding of metal alloys such as magnesium in a semi-solid (e.g., thixotropic) state. A detailed description of the structure and operation of several such injection molding systems can be found in U.S. patent nos. 5,040,589 and 6,494,703. While described above, the general utility of the check valve of the present invention or its compatibility with other metal alloys (i.e., aluminum, zinc, etc.) is not limited by the foregoing.

The barrel assembly of a typical injection molding system is shown with reference to FIG. 1A.

The illustrated barrel assembly 138 includes an elongated barrel 140 with an axial cylindrical bore 148A configured to extend therethroughA cylinder. The barrel assembly shown is connected to a stationary platen 16 (not otherwise shown) of a clamping unit. The bore 148A is configured to cooperate with a screw 156 disposed therein for handling and conveying the metal feedstock and as a means for accumulating and subsequently directing a melt of molding material during injection thereof. The screw 156 includes a thread 158 disposed about an elongated cylindrical body portion 159. According to an embodiment of the invention, the rear portion (not shown) of the screw is configured for coupling with a drive assembly (not shown), and the front portion of the screw 156 is configured for receiving a check valve 160. The operative portion of the check valve 160 is disposed forward of the forward mating face or shoulder 32 of the screw 156. The barrel assembly 138 includes a barrel head 2A located intermediate the forward ends of the machine nozzles 144 and 140. The cartridge head 2A includes a melt channel 10 disposed therethrough, the melt channel 10 connecting the cylindrical bore 148A with an auxiliary melt channel 148C disposed through the machine nozzle 144. The melt channel 10 through the barrel head 2A includes an inwardly tapering portion that transitions the diameter of the melt channel to the much narrower melt channel 148C of the machine nozzle 144. The central bore 148A of the barrel 140 may be formed, for example, by Stellite^TMTo protect the can substrate material (typically made of, for example, Inconel @)^TMNickel-based alloys) from the corrosive properties of the high temperature metal melt. Other portions of the barrel assembly 138 that come into contact with the melt of molding material may also include similar protective linings or coatings. The barrel 140 is further configured for communication with a source of powdered metal feedstock through a feed throat (not shown) located through a top rear portion (not shown) of the barrel 140. The feed throat directs the feedstock into the bore 148A of the barrel 140. The feedstock is then processed into a molding material by its mechanical processing, by the cooperative action of the screw 156 and the cylindrical bore 148A, and by its controlled heating. Heat is provided by a series of heaters (not shown) disposed along a substantial portion of the length of the barrel assembly 138, and a heater 150 disposed along the machine nozzle 144.

The injection mold includes at least one molding cavity (not shown) formed in close cooperation between secondary molding inserts shared between a cold mold half (not shown) and a hot mold half 125. The cold mold half includes a core plate assembly having at least one core molding insert disposed therein. The hot mold half 125 includes a cavity plate assembly 127 having at least one auxiliary cavity molding insert disposed therein, the cavity plate assembly being mounted to a face of the runner system 126. The runner system 126 provides a means of connecting the melt channel 148C of the machine nozzle 144 with at least one molding cavity for filling the molding cavity. As is generally known, the runner system 126 may be a branched or multi-branched hot runner, a cold sprue, or any other commonly known melt distribution means. In operation, the core and cavity molding inserts cooperate in a mold closed and clamped position to form at least one mold cavity for receiving and shaping a melt of molding material received from the runner system 126.

In operation, as the melt is injected into the mold, the machine nozzle 144 of the barrel assembly 138 is engaged in a sprue bushing 55 of the injection mold (i.e., against the reaction force generated by the injection of the melt).

The molding process generally includes the steps of:

i) flowing the metal raw material into the rear end portion of the barrel 140;

ii) working (i.e. shearing) and heating the metal feedstock into a thixotropic melt of molding material by:

a. operation (i.e., rotation and retraction) of the screw 156, which functions to convey the feedstock/melt along the length of the barrel 140 through the check valve 160 and into an accumulation zone defined in front of the check valve 160, through cooperation of the screw threads 158 with the axial bore 148A;

b. heating the feedstock material as it travels along a substantial portion of the barrel assembly 138;

iii) closing and clamping the injection mold halves;

iv) injecting the accumulated melt through the machine nozzle 144 and into the injection mold by forward translation of the screw 156;

v) optionally, filling at least any remaining space in the molding cavity (i.e., full) by applying a continuous injection pressure;

vi) opening the injection mold once the molded part is solidified by cooling the injection mold;

vii) removing the molded part from the injection mold; and

viii) optionally, adjusting the injection mold (e.g., applying a release agent) for a subsequent molding cycle.

The steps of preparing a mass of melt for subsequent injection (i.e., steps i) and ii)) are generally referred to as "reconstitution", while the steps of filling and filling at least one mold cavity (i.e., steps iv) and v)) are generally referred to as "injection".

The check valve 160 serves to allow forward transport of the melt into an accumulation zone in front of the barrel 140, but on the other hand prevents backflow of the melt during injection of the melt. Proper operation of the check valve 160 relies on a pressure differential between the melt on both sides thereof (i.e., greater pressure behind the valve during recovery and greater pressure in front of the valve during injection). The structure and operation of a typical check valve used in metal injection molding is described in U.S. Pat. No. 5,680,894.

Referring to fig. 1 and 2, a spiral coil used in accordance with a preferred embodiment of the present invention is generally shown. Fig. 1 shows the coil used as a seal.

In fig. 2, the barrel 2 with barrel liner 4 supports a screw (not shown) having a check valve 20 attached thereto by threads 28. Bolts (not shown) connect the barrel head 6 to the barrel 2 through the bolt holes 8. A sprue bushing (not shown) or the like is attached to the barrel head 6 by means of bolt holes 9. When the check valve 20 is in the open position as shown in FIG. 2, the screw is rotated and melt is fed through the check valve into the melt channel 10 in front of the check valve 20 in a manner well known in the art of metal molding.

A force is applied to ramp 32 as melt channel 10 is filled with melt to move check ring 24 forward and open a flow path between ramps 32 and 34. Surface 40 prevents forward movement of ring 24. During forward movement, the spiral coil is only under slight pressure of the melt and will create little resistance to forward movement of the ring.

When the melt channel 10 is filled with melt, rotation of the screw is stopped and injection of melt into a mold cavity (not shown) begins. The forward movement of the screw during injection results in a force being applied to the forward surface of the check ring, returning the check ring so that the inclined surfaces 32 and 34 contact and thereby seal the melt path.

In addition, an opening 12 (shown in FIG. 3) in the sidewall of ring 24 allows the melt to press against the inner wall of the spiral coil and push it into sealing contact with the barrel liner 4, thereby sealing along the length of the barrel during the injection cycle to prevent leakage.

As shown in FIG. 3, the check valve 20 is comprised of a main stem 22, a check ring 24, and a helical coil 26. The rod 22 is attached to the end of the injection screw by means of a thread 28. A shoulder 30 is fixed to the end of the injection screw.

In the closed position as shown in FIG. 3, the chamfer 32 on the check valve 20 and the chamfer 34 on the shoulder 30 are squeezed into sealing engagement by the back pressure exerted on the ring 24 by the melt in the melt channel 36 in a manner well known in the art.

The outer diameter of the helical coil 26 has sufficient clearance to facilitate assembly. The openings 12 allow the melt to flow into the space 14 adjacent the inner circumference of the spiral coil 26. During injection, the melt in space 14 subjects coil 26 to injection forces in the axial and outward radial directions that urge the highly compliant structure of the helical coil 26 to readily compress axially and expand radially until all voids are eliminated and a seal is formed. Once the injection pressure is removed, the forces that promote compression and expansion are no longer present and the helical coil 26 is released. When the plasticizing screw begins to rotate (not shown) for the purpose of conveying new material in front of the screw, any contact between the check ring 24 and the helical coil 26 will cause an applied torque that causes the helical coil 26 to twist so that the outer seal diameter becomes smaller and forces the seal diameter to disengage from the wall of the barrel liner, thus reducing wear.

As shown in fig. 4, the end of the primary stem 22 is bifurcated to form fingers 38 that create slots 42 in the melt channel 36. When the injection screw is withdrawn and rotated in a manner known in the art, the screw provides melt that moves the check ring 24 forward to open the valve 20 and allow the melt channel 36 to receive melt from the rotating screw. As the melt channel 36 fills with melt, the pressure within the channel slowly moves the plasticizing screw back to its full shot position. When the injection stroke begins, the closed volume of melt in front of the check ring moves the check ring 24 back to the closed position shown in FIG. 3. When the check ring 24 reaches the sealing position shown in FIG. 3, sufficient melt is provided in the melt channel 36 to enable the next injection of melt into the cavity. The screw stops rotating and translates forward to force the melt into the mold cavity. The translational movement of the screw increases the pressure generated by the melt to ensure that melt path 36 is sealed at ramps 32 and 34 and along the barrel surface adjacent coil 26.

As shown more clearly in fig. 3A, the coil 26 is substantially rectangular in cross-section. The outer circumferential surface of the coil is machined to a high tolerance so that it closely interfaces with the wall of an associated barrel liner. The inner circumferential surface may be other shapes, such as convex or concave. The only limitation on the shape of the inner circumferential surfaces is that they need to have sufficient surface to ensure that sufficient force is transmitted to move the coil into sealing engagement with the barrel liner surface. The radial surface of each turn of the coil is also machined to a high tolerance to ensure that adjacent turns of the coil effectively seal against each other. The outer radial surface of the outer coil and its surface in contact with the lock ring should also be machined to high tolerances to ensure a good seal.

The locking collar 24 is more clearly shown in figures 5, 5A and 5B. The ring 24 has a circular groove 44 on its periphery. The slot 44 is shown located near the middle of the ring 24 but could be located closer to either end if desired. The only limitation is that the wall portions 46 and 48 adjacent the slot should be strong enough to withstand the pressure exerted by the coil 26 when installed in the slot 44.

Fig. 6, 6A and 6B show the helical coil 26 more clearly. As shown in these figures, the outer circumferential surface 66 is machined to a high tolerance. The radial surface 68 is also machined to a high tolerance. The inner circumferential surfaces 70 need not be made to high tolerances because they contact the melt during operation.

FIG. 7 shows a check ring coil 50 that combines the actions of opening and closing the check valve 52 and sealing the melt channel 54. As shown, in this embodiment, the outer coil surface 56 of the coil 50 engages the ramp 34 to close the valve. The circumferential surface of the turns of the coil 50 engage the wall of the barrel to seal the wall against any backflow of melt. The flexibility in the turns of the coil 50 ensures that the coil 50 will continue to provide a reliable seal even if there is wear in the barrel, as the pressure of the melt against the inner wall of the coil 50 will force the outer wall of the coil against the barrel. Thus, the seals along the wall will only begin to corrode if the barrel is worn so severely that the expansion of the coil is insufficient to cover the wear gap.

For metal molding, the spiral coil must be made of a material that is stable and not susceptible to corrosion at high operating temperatures (e.g., 600 ℃ for magnesium molding). For example, when magnesium is molded, nickel should not be present.

The lever 22 shown in figure 7 is substantially identical to the lever 22 shown in figure 3 and therefore like reference numerals have been used to identify like parts of the lever. The rod 22 need not be described further herein.

Fig. 7A more clearly shows the machined surface of the coil 50.

FIG. 8 is an end view of the check valve 52 shown in FIG. 7 and includes a groove 42 for allowing melt to flow into the injection cavity.

Fig. 9 illustrates another embodiment of the present invention. In this embodiment, a melt channel 60 extends from the periphery of the check valve to the interior of the barrel (schematically indicated at 64). The helical coil 66 functions as a check ring and seal for the check valve in a manner similar to that described above with reference to fig. 7 and 8.

Fig. 10 and 11 show another embodiment of the present invention. In this embodiment, a ring 72 is located between a seat 74 on a screw (not shown) and a helical coil 76. The ring 72 allows for the use of a thinner coil 76 while maintaining the desired flow path. The ring 72 moves back and forth with the coil 76.

It will of course be understood that the above description has been given by way of example only and that modifications in detail can be made within the scope of the invention.

Claims (17)

1. A seal for a check valve of a metal molding machine, said seal comprising a peripheral groove in an outer surface of said check valve and a helically wound core in said groove, said helically wound coil being expandable into sealing engagement with a cylindrical wall of said molding machine.

2. The seal of claim 1, wherein each turn of the coil comprises flat radial walls, and adjacent turns of the coil contact each other to radially seal the coil.

3. A check valve for a metal molding machine, said valve comprising a peripheral groove in an outer surface of said check valve and a helically wound coil in said groove, said coil being expandable into sealing engagement with a cylindrical wall of said molding machine.

4. The check valve of claim 3, wherein the helically wound coil is laterally movable between a melt channel open position and a melt channel closed position.

5. The check valve of claim 3, wherein the turns of the coil are substantially rectangular in cross-section.

6. The check valve of claim 4 wherein adjacent surfaces of the turns of the coil are machined to a high tolerance to ensure a seal between adjacent turns when the coil is compressed.

7. The check valve of claim 4 wherein the outer surface of the coil turns are machined to a high tolerance to seal against the wall as the coil expands.

8. A check valve for a metal molding machine, said valve including a helically wound coil, said coil sealing said check valve and being slidable on a cylinder of said check valve to open and close a flow path through said valve, a first turn of said coil having a surface that mates with a mating surface on said cylinder to close said valve when in contact with said mating surface, an outer circumferential surface of said coil mating with a cylinder wall surrounding said check valve to provide an axial seal to said check valve.

9. The check valve of claim 8 wherein each turn of said coil other than a first turn has flat radial walls that provide a radial seal when pressed together.

10. An injection unit for an injection molding machine comprising an injection screw, a nozzle body on one end of said injection screw, and a check valve on said nozzle body, said check valve including a sealing ring comprising a helically wound coil surrounding said nozzle body and slidable between a first position in which said nozzle is open and a second position in which said nozzle is closed, a first turn of said coil sealingly engaging a shoulder on said nozzle body when said coil is in said closed position.

11. The injection unit of claim 10, wherein each turn of the coil other than the first turn has a flat radial surface and is in sealing engagement with a flat radial surface of an adjacent turn to provide radial sealing of the check valve.

12. A seal for a check valve of a metal molding machine, said seal comprising a helical coil insertable into a peripheral groove in said valve, said coil having an outer radial surface expandable into sealing engagement with a cylinder wall when subjected to pressure on an inner radial surface of said ring, and a first turn of said coil having an axial surface mating with an axial surface on said groove and providing an axial seal when said coil is subjected to an axial force.

13. The seal of claim 12, wherein each turn of the coil other than the first turn has a flat axial surface and is in sealing engagement with a flat axial surface of an adjacent turn to provide axial sealing of the coil.

14. A helical coil for use in a check valve of a metal molding machine, said coil sealing said check valve and being axially translatable to open and close a flow path through said valve, a first turn of said coil having a surface mating with a mating surface on said check valve body to close said valve when in contact with said mating surface, and outer radial surfaces of said coil mating with a cylindrical wall surrounding said check valve to provide a radial seal for said check valve.

15. The coil of claim 14 wherein each turn of the coil other than the first turn has a flat axial wall that provides an axial seal between each turn when subjected to an axial force.

16. An injection unit for a metal molding machine comprising an injection screw, a check valve on one end of said injection screw, said check valve including a seal, said seal containing a helically wound coil surrounding said check valve body and axially translatable to open and close a flow path through said valve, a first turn of said coil having a surface mating with a mating surface on said check valve body to close said valve when in contact with said mating surface, and outer radial surfaces of said coil mating with a cylindrical wall surrounding said check valve to provide a radial seal for said check valve.

17. The injection unit of claim 16, wherein each turn of the coil, except for the first turn, has a flat axial surface and is in sealing engagement with a flat axial surface of an adjacent turn to provide axial sealing of the check valve.