Injection molding system having offset valve pin biasing mechanism

Abstract: A center entry valve gated injection molding system having a heated nozzle (14) secured in front of a heated manifold (18) with at least a pair of valve member biasing mechanisms (94) extending radially outward from a reciprocating elongated valve member. The melt passage (88) splits into two branches (92) which extend through a manifold (18) outwardly around a rear portion (56) of the valve member (10). The two branches (92) of the melt passage (88) and the two biasing mechanisms (94) are alternatively evenly angularly spaced around the valve member (10) which considerably reduces the space required. The valve member has an enlarged forward end (62) which opens forwardly into the cavity and is closed in a retracted position in which it seats in the matching mouth (50) of a gate (48) in a nose portion (32) of the nozzle (14). Each biasing mechanism (94) includes a compression spring (96) which engages a lever member (100) to continuously urge the valve member (10) rearwardly. When injection pressure is applied it overcome the force of the springs (96) and moves the valve member (10) forwardly to the open position. When the cavity is filled, the combination of the back pressure of the melt and the force of the springs (96) with a mechanical advantage from the lever members (100) withdraws the valve member (10) to the closed position. In an alternate embodiment, only a single biasing mechanism (94) is utilized.

Description: This invention relates to a valve gated center entry hot runner injection molding device, according to the preamble of claim 1. Spring loaded elongated valve member actuators are well known in the art. An early example is shown in U.S. patent number 2,940,123 to Beck et al. which issued June 14, 1960. With the trend to higher injection pressures and reduced component size, providing sufficient space to locate the spring is a serious problem, particularly with a center entry system whre the melt passage extends through the manifold out around the rear portion of the valve member. Center entry systems having a radially offset pivotal acutating mechanism are known as shown in the applicant's U.S. patent number 4,286,941 which issued September 1, 1981. Another way of dealing with this problem is shown in U.S. patent number 4,380,426 to Wiles which issued April 19, 1983 which discloses a center entry system with a pneumatically actuated piston connected to the driven end of the valve member. It is also known to provide an injection molding nozzle with a nose portion extending forward into the cavity plate to form the gate as shown in the applicant's U.S. patent number 4,579,520 which issued April 1, 1986. A valve member which extends into the cavity and closes in the rearward direction is shown in the applicant's U.S. patent number 4,521,179 which issued June 4, 1985. Valve members which provide flexing gates are described in U.S. patent number 4,380,422 to Von Holdt which issued April 19, 1983 and "Hot-Runner Flex Gate Fills Large Parts Fast with Low Stress", Plastics Technology, July 1988, p 21-23. Thus, the previous actuating mechanisms either have relatively costly piston actuators, are too cumbersome for the space available, or do not provide sufficient force to close a large diameter gate. An injection molding system as indicated in the preamble part of claim 1 is known from GB-A-1 125 727. In that case a central valve stem is operated by a forked lever operated manually or mechanically or said forked lever can be used to indicate the movement of the stem. Accordingly, it is an object of the invention to provide a valve gated center entry hot runner injection molding device having an improved valve member operating system. In order to perform said objective, the present invention, according to claim 1, comprises a biasing mechanism mounted in the manifold, the biasing mechanism including biasing means mounted in the manifold and lever means extending to receive a force from the biasing means and apply a force to the valve member in the rearward direction. Preferred embodiments of the present invention are laid down in the sub-claims. In the following the present invention is explained in greater detail by means of a preferred embodiment thereof in conjunction with the accompanying drawings wherein: Figure 1 is a sectional view of a portion of an injection molding system according to one embodiment of the invention showing the configuration of the melt passage, Figure 2 is a split section view at a right angle to Figure 1 showing the biaising mechanisms in the open and closed positions, Figure 3 is a cut-away isometric view showing the relationship of the melt passage and the biasing mechanisms in more detail, and Figure 4 is a similar split section view showing another embodiment of the invention. Reference is first made to Figure 1 which shows a valve member 10 which is received in a central bore 12 in a nozzle 14 which is secured by bolts 16 to a manifold 18. The manifold 18 has a locating flange 20 which is seated against a circumferential shoulder 22 of a cavity plate 24 to locate the nozzle 14 in a well 26 in the cavity plate 24 with an insulative air space 28 between the heated nozzle 14 and the cooled cavity plate 24. The locating flange 20 has openings 30 through it to reduce heat loss to the surrounding cavity plate 24. The nozzle 14 and manifold 18 are also located laterally by a forward nose portion 32 of the nozzle 14 being received in a matching cylindrical opening 34 through the cavity plate 24 and by the rear end 36 of the manifold 18 being received in a matching opening in a locating collar 38. The locating collar 38 is held securely in place by bolts 40 which extend through the back plate 42 into the cavity plate 24. The central bore 12 through the nozzle 14 has a rear portion 44 and a larger diameter forward portion 46 which extends through the nose portion 32 of the nozzle to form a gate 48 with a forward mouth 50. The valve member 10 has a forward portion 52, a central portion 54 which extends through the rear portion 44 of the central bore 12, and a rear portion 56 which extends into a central opening 58 in the manifold 18. As can be seen, the forward portion 52 of the valve member 10 is smaller in diameter than the surrounding forward portion 46 of the central nozzle bore 12 which provides a melt flow space 60 between them, expect that the forward portion 52 of the valve member has an enlarged forward end 62 which seats in the mouth 50 of the gate 48 in the retracted closed position. The enlarged end 62 of the valve member 10 has a flat forward face 64 which aligns with the same side 66 of the cavity 68 in the closed position. The central portion 54 of the valve member 10 has a number of spaced ridges 70 which fit in the rear portion 44 of the central nozzle bore 12 through the nozzle 14 to prevent leakage of pressurized melt around the reciprocating valve member 10. In this embodiment, the nozzle 14 is heated by plate heaters 72 which are secured on opposite sides as seen in Figure 2. The manifold 18 is heated by an electrical heating element 74 which is integrally cast into it. The cavity plate 24 is cooled by pumping cooling water through cooling conduits 76. In this large volume application with the forward face 64 of the valve member extending to the cavity 68, it is desirable to provide more cooling to the enlarged end 62 of the valve member 10. Thus, a twisted partition 78 is mounted in the hollow valve member 10, and a circulation of cooling water is provided between inlet and outlet pipes 80,82 which extend laterally from the rear portion 56 of the valve member 10 through lateral openings 84,86 in the manifold 18. Thus, cooling water flows into the valve member 10 through the inlet pipe 80, forward along one side of the twisted partition 78 to the enlarged end 62 where it crosses over and flows rearwardly along the other side of the twisted partition and back out through outlet pipe 82. As seen in Figure 1, a melt passage 88 extends to convey pressurized melt from a central inlet 90 at the rear end 36 of the manifold 18 to the gate 48. The passage 88 splits into two branches 92 which extend around the opening 58 in the manifold and join the space 60 around the forward portion 52 of the valve member 10. While the forward portion 52 of the valve member 10 is shown in this embodiment as being smaller in diameter than the central portion 54, this is not necessarily the case. The important thing is that the forward portion 46 of the central nozzle bore 12 must be sufficiently larger than the forward portion 52 of the valve member 10 to provide the space 60 with a sufficient cross-sectional area to convey the melt received through the split branches 92 of the melt passage 88. When the injection pressure of the melt forces the valve member 10 to the forward open position, the melt then flows through the gate 48 outwardly around the enlarged head 62 of the valve member 10 into the cavity 68. Reference will now be made to Figure 3 in describing the two valve member biasing mechanisms 94 which are located on opposite sides of the central opening 58 in the manifold which receives the rear portion 56 of the valve member 10. In this embodiment of the invention the two biasing mechanisms 94 and the two branches 92 of the melt passage 88 are equally angularly spaced in an alternating arrangement around the valve member 10. This balances the lateral forces on the valve member and the branches 92 of the melt passage 88 extend between the biasing mechanisms 94 so as to not unduely increase the necessary diameter of manifold 18 and the nozzle 14. Each biasing mechanism 94 includes a coiled compression spring 96 which is seated in a cylindrical opening 98 in the manifold 18 and a lever member 100 which extends radially inward from the spring 96. As can be seen, the lever member 100 has an outer end 102 with a locating tit 104 which receives the spring 96 and an inner end 106 which extends into a notch 108 in a split ring 110 which extends around the rear portion 56 of the valve member 10. The lever member 100 extends radially in a slot 112 in the manifold and is shaped to provide a fulcrum 114 near the inner end 106 which abuts against the rear end 116 of the nozzle 14. The split ring 110 has an inner portion 118 which is seated in a channel 120 which extends around the rear portion 56 of the valve member 10. Thus, when the spring 96 forces the outer end 102 of the lever member 100 forward, the lever member 100 pivots around the fulcrum 114 and retracts the split ring 110 and the valve member 10 to which it is engaged. The position of the fulcrum 114 provides a mechanical advantage to the force transmitted from the spring 96 to the valve member 10. Consequently, the travel of the valve member 10 is considerably less than that of the outer end of the lever member 100 which receives the spring. Of course, the springs 96 and lever member 100 on opposite sides of the split ring 110 are of equal sizes so as to apply balanced forces to the valve member. In use, the system is assembled as shown and electrical power is applied to the plate heaters 72 and the terminal 122 of the heating element 74 to heat the nozzle and manifold 18 to a predetermined operating temperature. Pressurized melt from a molding machine (not shown) is introduced into the melt passage 88 through the central inlet 90 according to a predetermined cycle. When injection pressure is applied, the force of the melt on the enlarged end 62 of the valve member overcomes the spring force and drives the valve member 10 forward until the forwardly facing shoulder 124 of the split ring 110 stops against the rear end 116 of the nozzle 14 in the open position. The melt then flows through the melt passage 88 and the gate 48 until the cavity 68 is filled. When the cavity 68 is filled, the combination of the back pressure of the melt in the cavity 68 and the force of the springs 96 drives the valve member 10 to the retracted closed position in which the enlarged forward end 62 is seated in the matching mouth 50 of the gate 48. The injection pressure is then released and after a short cooling period, the mold is opened to eject the molded products. After ejection, the mold is closed, injection pressure is reapplied which reopens the gate 48. This cycle is repeated continuously with a frequency dependent upon the size of the cavity and the type of material being molded. As can be seen, the travel of the valve member 10 is relatively short, but large cavities can be filled quickly because of the large diameter of the enlarged end 62 of the valve member and the mouth 50 of the gate 48. The shape of the enlarged end 62 and the mouth causes the pressurized melt to flare outwardly as it enters the cavity 68. This produces a radial molecular orientation of the melt which is advantageous in increasing the strength of products having certain configurations. Figure 4 shows an alternate embodiment of the invention having only a single biasing mechanism 94. It has been found that during normal continuous operation, when the cavity 68 fills up with pressurized melt, the back pressure of the melt in the cavity against the forward face 64 of the valve member 10 is sufficient to drive the valve member 10 to the retracted closed position without the additional force of the biasing mechanism 94. However, the biasing mechanism 94 is necessary to avoid the valve member 10 being frozen in the open position when the system is shut down. This would cause considerable difficulty in getting the system operational again. Otherwise, this embodiment is the same as the embodiment described above and the description need not be repeated. While the description of the injection molding system with offset valve member biasing mechanisms has been given with respect to a preferred embodiment, it is not to be construed in a limiting sense. Variations and modifications will occur to those skilled in the art. For instance, it is apparent that the shape of the springs 96 and lever members 100 can be changed. Also the shape of the valve member 10, the central bore 12 and the opening 58 in the manifold 18 in which it is received can be varied. Reference is made to the appended claims for a definition of the invention.

Claims: A valve gated center entry hot runner injection molding device having a heated nozzle (14) which is secured to a heated manifold (18), the heated nozzle (14) being received in a cavity plate (24), said nozzle (14) having a forward nose portion (32) which extends through an opening (26) in the cavity plate (24) to the cavity (68), the nozzle (14) having a central bore (12) with a rear portion (44) and a forward portion (46) which extends through the nose portion (32) of the nozzle (14) to form a gate (48) having a forward mouth (50), an elongated valve member (10) which extends through the central bore (12) in the nozzle (14) and reciprocates longitudinally between a retracted closed position and a forward open position, the valve member (10) having a forward portion (52), a central portion (54) which extends through the rear portion (44) of the central bore (12), and a rear portion (56) which extends into a central opening (58) in the manifold (18) and a melt passage (88) to convey pressurized melt from a central inlet (90) in the manifold (18) to the gate (48) which extends through the manifold (18) and nozzle (14) around the rear portion (58) of the valve member (10) to join a space around the forward portion (52) of the valve member (10) in the forward portion (46) of the central bore (12) which leads to the gate (48), the central portion (54) of the valve member (10) fitting in the rear portion (44) of the central bore (12) to prevent substantial leakage of the pressurized melt around the reciprocating valve member (10), wherein the valve member (10) has an enlarged forward end (52) which seats in the mouth of the gate (48) in the retracted closed position, characterised in that a biasing mechanism (94) is mounted in the manifold (18), the biasing mechanism (94) including biasing means (96) mounted in the manifold (18) and lever means (100) extending to receive a force from the biasing means (96) and apply a force to the valve member (10) in the rearward direction. A valve gated center entry hot runner injection molding device as claimed in claim 1, characterised by at least two valve member biasing mechanisms (94) being mounted in the manifold (18) to extend radially outward from the rear portion (58) of the valve member (10), the biasing mechanisms (94) being substantially equally angularly spaced around the valve member (10) without interfering with the melt passage (88) extending through the manifold (18), each biasing mechanism including biasing means (96) mounted in the manifold (18), and lever means (100) extending radially to receive a force from the biaising means (96) and apply a force to the valve member (10) in the rearward direction. An injection molding device as claimed in claims 1 or 2, characterised in that the lever means (100) engages a split ring (110) which is received between the rear portion (56) of the valve member (10) and the manifold (18), the split ring (110) engaging the rear portion (56) of the valve member (10) to urge the valve member (10) to the rearward closed position. An injection molding device as claimed in at least one of the preceding claims 1-3, characterised in that the biasing means are compression springs (96). An injection molding device as claimed in at least one of the preceding claims 1-4, characterised in that there are two valve member biasing mechanisms (94) and the melt passage (88) splits into two branches (92) which extend around the rear portion (56) of the valve member (10), the two valve member biasing mechanisms (94) and the two branches (92) of the melt passage (88) being located to alternate angularly around the valve member (10). An injection molding device as claimed in at least one of the preceding claims 1-5, characterised in that the forward end of the valve member has a forward face (64) which is in alignment with and forms a portion of a side of the cavity (68) when the valve member (10) is in the retracted closed position. An injection molding device as claimed in at least one of the preceding claims 1-6, characterised in that cooling water is circulated longitudinally through the valve member (10). An injection molding system as claimed in claim 7, characterised in that the cooling water flows forwardly and rearwardly on opposite sides of a partition. An injection molding system as claimed in claim 8, characterised in that the partition is twisted.

Inventors: GELLERT JOBST ULRICH, GELLERT, JOBST ULRICH
Applicants: GELLERT JOBST U, GELLERT, JOBST ULRICH
Application year: 1989
Main classification: B29C45
IPC codes: B29C45