Valve pin guide for a valve-gated nozzle Number:6,921,259 from the United States Patent and Trademark Office (PTO) owispatent

Title: Valve pin guide for a valve-gated nozzle

Abstract: A valve pin guide is provided for guiding a valve pin from a nozzle into a gate of a mold cavity in an injection molding apparatus. The valve pin guide defines a guide aperture therethrough. The guide aperture is adapted to receive and guide the valve pin into alignment with the gate. The valve pin guide is positioned downstream from said nozzle and upstream from said gate.

Patent Number: 6,921,259 Issued on 07/26/2005 to Sicilia,   et al.

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Inventors:	Sicilia; Rob (Etobicoke, CA); Babin; Denis (Georgetown, CA)
Assignee:	Mold-Masters Limited (Georgetown, CA)
Appl. No.:	369564
Filed:	February 21, 2003

Current U.S. Class:	425/562; 425/564
Intern'l Class:	B29C 045/23
Field of Search:	425/549,562-564

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References Cited [Referenced By]

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U.S. Patent Documents

2865050	Dec., 1958	Strauss.
3488810	Jan., 1970	Gellert.
3716318	Feb., 1973	Erik et al.
3741704	Jun., 1973	Beasley.
3952927	Apr., 1976	Schaumburg et al.
4004871	Jan., 1977	Hardy.
4010903	Mar., 1977	Sakuri et al.
4013393	Mar., 1977	Gellert.
4043740	Aug., 1977	Gellert.
4173448	Nov., 1979	Rees et al.
4306852	Dec., 1981	Mateev et al.
4368028	Jan., 1983	Grish et al.
4412807	Nov., 1983	York.
4652230	Mar., 1987	Osuna-Diaz.
4768283	Sep., 1988	Gellert.
4768945	Sep., 1988	Schmidt et al.
4771164	Sep., 1988	Gellert.
4781572	Nov., 1988	Boring.
4832593	May., 1989	Brown.
4875848	Oct., 1989	Gellert.
4911636	Mar., 1990	Gellert.
4925384	May., 1990	Manner.
4945630	Aug., 1990	Gellert.
4981431	Jan., 1991	Schmidt.
5015170	May., 1991	Gellert.
5028227	Jul., 1991	Gellert et al.
5053271	Oct., 1991	Mori et al.
5208052	May., 1993	Schmidt et al.
5254305	Oct., 1993	Fernandez et al.
5299928	Apr., 1994	Gellert.
5334008	Aug., 1994	Gellert.
5421716	Jun., 1995	Gellert.
5443381	Aug., 1995	Gellert.
5492467	Feb., 1996	Hume et al.
5501594	Mar., 1996	Glozer et al.
5505613	Apr., 1996	Krummenacher.
5545028	Aug., 1996	Hume et al.
5554395	Sep., 1996	Hume et al.
5652003	Jul., 1997	Gellert.
5658604	Aug., 1997	Gellert et al.
5686122	Nov., 1997	Huntington et al.
5695793	Dec., 1997	Bauer.
5700499	Dec., 1997	Bauer.
5707667	Jan., 1998	Galt et al.
5804228	Sep., 1998	Kofsman et al.
5811140	Sep., 1998	Manner.
5834041	Nov., 1998	Sekine et al.
5848343	Dec., 1998	Takahashi et al.
5849343	Dec., 1998	Gellert et al.
5879727	Mar., 1999	Puri.
5895669	Apr., 1999	Seres, Jr. et al.
5941837	Aug., 1999	Amano et al.
6003182	Dec., 1999	Song.
6009616	Jan., 2000	Gellert.
6017209	Jan., 2000	Gellert et al.
6030202	Feb., 2000	Gellert et al.
6050806	Apr., 2000	Ko.
6089468	Jul., 2000	Bouti.
6164954	Dec., 2000	Mortazavi et al.
6227461	May., 2001	Schroeder et al.
6234783	May., 2001	Shibata et al.
6245278	Jun., 2001	Lausenhammer et al.
6264460	Jul., 2001	Wright et al.
6273706	Aug., 2001	Gunther.
6309208	Oct., 2001	Kazmer et al.
6358038	Mar., 2002	Rozenberg.
6358039	Mar., 2002	Manner et al.
6419116	Jul., 2002	Eigler et al.
2003/0008034	Jan., 2003	Niewels.
2004/0071817	Apr., 2004	Fischer et al.
Foreign Patent Documents
3245571	Jun., 1984	DE.
19608676	Jan., 1997	DE.
29602484	Mar., 1997	DE.
0638407	Apr., 1996	EP.
0750975	Jan., 1997	EP.
0873841	Oct., 1998	EP.
0962296	Aug., 2001	EP.
1188537	Mar., 2002	EP.
2537497	Jun., 1984	FR.
5-177664	Jul., 1993	JP.
05309695	Nov., 1993	JP.
05261770	Dec., 1993	JP.
07148786	Jun., 1995	JP.
8090598	Apr., 1996	JP.
10264222	Oct., 1998	JP.
10-296798	Nov., 1998	JP.
11254488	Sep., 1999	JP.
2002/-307492	Oct., 2002	JP.
2003-11173	Jan., 2003	JP.
2003-11174	Jan., 2003	JP.
2003-11176	Jan., 2003	JP.
WO 84/0092/2	Mar., 1984	WO.
WO 01/078961	Oct., 2001	WO.
WO 03/004243	Jan., 2003	WO.
WO 03/070446	Aug., 2003	WO.
WO 2004/012923	Feb., 2004	WO.

Other References

Ewikon product catalogue and product illustration. Kunststoffe 85 (1995) 2 p. 166 "NadelverschluBdüsen für kurze Zykluszeit". "Mold Hotrunner Solutions" Product Illustration of a Guided Mechanism. "Kona Bushing for Sprueless Molding" pp. 2-24. PCT Search Report for WO 03/70446 (Application No. PCT/CA03/00244), dated May 16, 2003. Images and information from "Gunther Hot Runner Technology" taken from Gunther website Aug. 2003. Press Release entitled "Mold-Masters Introduces The New Accu-Gate Virtually Eliminating Gate Wear" (Dec. 12, 2002).

Primary Examiner: Heitbrink; Tim
Attorney, Agent or Firm: Sterne, Kessler, Goldstein & Fox P.L.L.C.

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Claims

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1. A valve pin guide positioned downstream from a nozzle for receiving and guiding a valve pin into a gate for a mold cavity in an injection molding apparatus, the valve pin guide comprising:

a guiding portion in which a guide aperture is defined therethrough, wherein said guiding portion is made from a guiding portion material having a first thermal conductivity and said guiding portion is adapted to contact the nozzle; and

an insulating portion, wherein said insulating portion is made from an insulating portion material having a second thermal conductivity, wherein said second thermal conductivity is lower than said first thermal conductivity and said insulating portion is adapted to contact a mold cavity block.

2. The valve pin guide as claimed in claim 1, wherein the gate is defined in a mold component, and said valve pin guide has a sealing surface, wherein said sealing surface is adapted to cooperate with the mold component to seal against melt leakage around the gate.

3. The valve pin guide as claimed in claim 1, wherein said valve pin guide is removably positionable downstream from the nozzle and upstream from the gate.

4. The valve pin guide as claimed in claim 1, wherein said valve pin guide is adapted to slidably contact the nozzle, to accommodate thermal expansion and contraction of the nozzle during an injection molding operation.

5. The valve pin guide as claimed in claim 1, wherein the nozzle has a nozzle tip that is made from a nozzle tip material having a thermal conductivity that is less than said first thermal conductivity of said guiding portion of said valve pin guide.

6. An injection molding apparatus, comprising:

at least one nozzle having a nozzle melt passage therethrough for receiving a melt from a melt source;

a nozzle tip secured to a downstream end of said nozzle by a nozzle tip retainer, wherein said nozzle tip receives the melt from said nozzle melt passage;

a mold cavity block defining at least one mold cavity and a gate into said at least one mold cavity, wherein said gate is positioned downstream from said nozzle tip;

a valve pin, wherein said valve pin is movable in said nozzle tip and said nozzle melt passage to open and close said gate; and

a valve pin guide positioned downstream from said nozzle tip and upstream from said gate, wherein said valve pin guide defines a guide aperture therethrough that is adapted to receive and guide said valve pin into alignment with said gate.

7. The injection molding apparatus as claimed in claim 6, wherein said valve pin guide is in contact with said mold cavity block.

8. The injection molding apparatus as claimed in claim 6, wherein said valve pin guide is connected to said mold cavity block.

9. The injection molding apparatus as claimed in claim 6, wherein said valve pin guide is removably connected to said mold cavity block.

10. The injection molding apparatus as claimed in claim 6, wherein said valve pin is movable to an open position to permit melt flow into said mold cavity, and wherein in said open position said valve pin is spaced from said guide aperture.

11. The injection molding apparatus as claimed in claim 6, wherein said valve pin has a sealing surface, wherein said sealing surface is adapted to form a seal with said gate to prevent melt flow therebetween, and said valve pin has a guide surface, wherein said guide surface is adapted to cooperate with said guide aperture on said valve pin guide to align said valve pin with said gate prior to said sealing surface contacting said gate.

12. The injection molding apparatus as claimed in claim 11, wherein said sealing surface on said valve pin is a separate surface from said guide surface.

13. The injection molding apparatus as claimed in claim 6, wherein said gate is defined in a separate gate insert component from said surrounding portion of said mold cavity block.

14. The injection molding apparatus as claimed in claim 6, wherein said nozzle tip is made from a nozzle tip material having a first thermal conductivity, and said valve pin guide is made from a valve pin guide material having a second thermal conductivity and said second thermal conductivity is less than said first thermal conductivity.

15. The injection molding apparatus as claimed in claim 14, wherein said nozzle has a nozzle body and said nozzle tip is attached to said nozzle body.

16. The injection molding apparatus as claimed in claim 6, wherein said valve pin guide has a sealing surface, that is adapted to cooperate with said mold cavity block to seal against melt leakage around said gate.

17. The injection molding apparatus as claimed in claim 6, wherein said valve pin guide is adapted to slidably contact said nozzle to accommodate thermal expansion and contraction of said nozzle during an injection molding operation.

18. The injection molding apparatus as claimed in claim 6, wherein said valve pin guide comprises,

a guiding portion in which said guide aperture is defined, wherein said guiding portion is made from a guiding portion material having a first thermal conductivity, said guiding portion is adapted to contact said nozzle, and

an insulating portion, wherein said insulating portion is made from an insulating portion material having a second thermal conductivity, wherein said second thermal conductivity is lower than said first thermal conductivity and wherein said insulating portion is adapted to contact said mold cavity block.

19. The injection molding apparatus as claimed in claim 18, wherein said valve pin guide is adapted to slidably contact said nozzle, to accommodate thermal expansion and contraction of said nozzle during an injection molding operation.

20. The injection molding apparatus as claimed in claim 6, further comprising: a resilient member that is positioned between said nozzle and said valve pin guide.

21. The injection molding apparatus as claimed in claim 6, wherein said valve pin guide is attached to said nozzle.

22. An injection molding apparatus, comprising:

a mold cavity block, wherein said mold cavity block defines a mold cavity therein, said mold cavity has a gate, wherein said mold cavity block has a first bore and a second bore, wherein said gate is positioned in said second bore and wherein said first bore is larger in diameter than said second bore;

an injection nozzle having a nozzle tip secured thereto by a tip retainer, wherein a melt channel is defined in said injection nozzle and said nozzle tip to convey melt towards said gate;

a valve pin, wherein said valve pin is positioned at least partially in said melt channel and is movable to control melt flow into said gate; and

a valve pin guide, wherein said valve pin guide is adapted to receive and guide said valve pin into alignment with said gate, and wherein said valve pin guide is positioned in said first bore downstream from said nozzle tip.

23. The injection molding apparatus according to claim 22, wherein said second bore is in fluid communication with said melt channel so that said second bore substantially fills with melt during an injection molding operation.

24. The injection molding apparatus according to claim 22, wherein a shoulder separates said first and second bores and said valve pin guide is adapted to seal against said shoulder.

25. The injection molding apparatus according to claim 22, wherein said nozzle includes a sealing surface that is adapted to cooperate with said first bore to inhibit melt leakage therebetween.

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Description

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FIELD OF THE INVENTION

This invention relates to an injection molding apparatus, and more particularly to a guide for a valve pin in a valve-gated nozzle.

BACKGROUND OF THE INVENTION

It is known for a nozzle in a hot runner injection molding apparatus to include a valve pin gating mechanism at each gate into each mold cavity. The valve pin is typically moved in a melt channel of the nozzle towards or away from the gate, to control the flow of melt into the melt cavity. In order to provide a good seal at the gate, both the tip portion of the valve pin and the corresponding sealing surface on the gate must typically be machined to very close tolerances.

When a misaligned valve pin is moved to close a gate, the valve pin collides with the gate and can cause scoring of the sealing surfaces on the valve pin and/or the gate. This can ultimately result in poor quality parts with blemishes around the gate, and can cause other problems with the molding operation. Furthermore, a damaged valve pin or gate can be expensive and time consuming to replace. The damage may happen immediately, or alternatively it may happen gradually, over many cycles of opening and closing the valve pin.

Solutions that have been proposed for this problem, have typically included a guide means positioned towards the bottom of the nozzle melt channel to capture and align the free end of the valve pin. Because melt is required to flow past the alignment means/valve pin interface when the valve pin is in the open position, a plurality of circumferentially spaced slots are typically provided in either the valve pin or the alignment means. In doing so, these slots create the potential for weld lines to appear in the molded product, as a result of the melt flow in the nozzle melt channel separating to pass around the guide means, and subsequently reuniting downstream from the guide means. Furthermore, the presence of such guide means in the nozzle melt channel typically renders more difficult a cleanout of the nozzle melt channel, hampering for example the changeover of a machine to run a new melt.

Other solutions have provided an offset nozzle melt channel which has a main portion that is offset from the center of the nozzle, and a lowermost portion that is aligned with the gate. The valve pin passes through the nozzle body and extends only into the lowermost portion of the nozzle melt channel. In this way, the valve pin is captured along a substantial portion of its length, which makes it less susceptible to misalignment. However, because a substantial portion of the nozzle melt channel is offset from the center of the nozzle, the heat distributed to the melt flowing therethrough is uneven, which can cause difficulties in controlling melt temperature. Reference is made to U.S. Pat. No. 5,834,041 (Sekine et al) and U.S. Pat. No. 5,895,669 (Seres, Jr et al), which disclose embodiments of this genre of proposed solution.

Other problems also exist, which originate from the manufacture of the nozzles themselves instead from the properties of the melt flow. Manufacturing errors may exist in the nozzles, which can introduce a misalignment between the valve pin and the gate that is 'built-in'. The guide means that are described above, which are built into the nozzle itself, do nothing to correct this particular cause of misalignment.

Thus, a need exists for a nozzle having an improved guide for guiding the valve pin into the gate.

SUMMARY OF THE INVENTION

In a first aspect the invention is directed to a valve pin guide for guiding a valve pin from a nozzle into a gate of a mold cavity in an injection molding apparatus. The valve pin guide defines a guide aperture therethrough. The guide aperture is adapted to receive and guide the valve pin into alignment with the gate. The valve pin guide is positioned downstream from said nozzle and upstream from said gate.

In a second aspect, the invention is directed to an injection molding apparatus that incorporates at least one of the valve pin guide described above.

In a third aspect, the invention is directed to an injection molding apparatus. The injection molding apparatus includes a mold cavity block, an injection nozzle, a valve pin and a valve pin guide. The mold cavity block defines a mold cavity therein. The mold cavity has a gate. The mold cavity block has a first bore and a second bore. The gate is positioned in the second bore. The first bore is larger in diameter than the second bore. A melt channel is defined in the injection nozzle to convey melt towards the gate. The valve pin is positioned at least partially in the melt channel and is movable to control melt flow into the gate. The valve pin guide is adapted to receive and guide the valve pin into alignment with the gate. The valve pin guide is positioned in the first bore.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference will now be made by way of example to the accompanying drawings, showing articles made according to preferred embodiments of the present invention, in which:

FIG. 1 is a sectional view of an injection molding apparatus having a plurality of valve-gated nozzles and a plurality of valve pin guides in accordance with a first embodiment of the present invention;

FIG. 2 is a sectional side view of one of the nozzles shown in FIG. 1;

FIGS. 2a, 2b, 2c and 2d are magnified sectional side views of a valve pin guide shown in FIG. 2 aligning a valve pin entering a gate;

FIG. 2e is a magnified sectional side view of the valve pin guide and a bore in the mold cavity block shown in FIG. 2;

FIG. 3a is a cross-section view of a plurality of cutouts that are optionally included on a portion of the valve pin shown in FIG. 2;

FIG. 3b is a cross-sectional view of a plurality of cutouts that are optionally included on the valve pin guide shown in FIG. 2;

FIG. 3c is a cross-sectional view of a plurality of cutouts that are optionally included on the tip of the nozzle shown in FIG. 2;

FIG. 4 is a sectional side view of a valve pin guide in accordance with another embodiment of the present invention;

FIG. 4a is a sectional side view of a variant of the valve pin guide shown in FIG. 4;

FIG. 5 is a sectional side view of a combination of the valve pin guide shown in FIG. 2, with a variant of the nozzle shown in FIG. 2, in accordance with yet another embodiment of the present invention;

FIG. 6 is a sectional side view of a combination of the valve pin guide shown in FIG. 2, with another variant of the nozzle shown in FIG. 2, in accordance with yet another embodiment of the present invention;

FIG. 7 is a sectional side view of a combination of the valve pin guide shown in FIG. 2 with yet another variant of the nozzle shown in FIG. 2, in accordance with yet another embodiment of the present invention;

FIG. 8 is a sectional side view of a combination of the valve pin guide shown in FIG. 2 with yet another variant of the nozzle shown in FIG. 2, in accordance with yet another embodiment of the present invention;

FIG. 9 is a sectional side view of a combination of the valve pin guide shown in FIG. 2 with yet another variant of the nozzle shown in FIG. 2, in accordance with yet another embodiment of the present invention;

FIG. 10 is a sectional side view of a combination of the valve pin guide shown in FIG. 2 with yet another variant of the nozzle shown in FIG. 2, in accordance with yet another embodiment of the present invention;

FIG. 11 is a sectional side view of a combination of the valve pin guide shown in FIG. 2 with yet another variant of the nozzle shown in FIG. 2, in accordance with yet another embodiment of the present invention;

FIG. 12 is a sectional side view of a combination of the valve pin guide shown in FIG. 2 with yet another variant of the nozzle shown in FIG. 2, in accordance with yet another embodiment of the present invention;

FIG. 13 is a sectional side view of a combination of the valve pin guide shown in FIG. 2 with a variant of the mold cavity block shown in FIG. 2, in accordance with yet another embodiment of the present invention;

FIG. 14 is a sectional side view of a valve pin guide in accordance with yet another embodiment of the present invention, in combination with a variant of the valve pin shown in FIG. 2;

FIG. 15 is a sectional view of an injection molding machine having a plurality of valve pin guiding and alignment systems in accordance with the prior art; and

FIGS. 16a, 16b, 16c and 16d are magnified sectional side views showing the operation of a valve pin and mold plate of the prior art.

DETAILED DESCRIPTION OF THE INVENTION

Reference is made to FIG. 15, which shows an injection molding machine 1010 of the prior art. The injection molding machine 1010 includes one or more runners 1012, that transfer melt from an inlet 1014 to one or more nozzles 1016. The runners 1012 are defined within one or more molding machine plates, such as, for example, a manifold 1018. The inlet 1014 is adapted to be fluidly connected to a melt source (not shown).

The nozzles 1016 transfer melt from the runners 1012 through one or more gates 1020 and into one or more mold cavities 1022 defined in a mold plate 1024. A heater 1025 may heat each nozzle 1016. Each nozzle 1016 defines a nozzle melt channel 1026 which is in fluid communication with a runner 1012 and thus, with the melt source.

A valve pin 1028 is movable within each nozzle melt channel 1026 to open and close one of the gates 1020, permitting or restricting the flow of melt into the mold cavity 1022. The configuration of the end portion of the valve pin 1028 and the gate 1020 and their engagement are shown in more detail in FIGS. 16a, 16b, 16c and 16d. The valve pin 1028 typically includes a generally cylindrical body 1030, a cylindrical sealing surface 1031, which is typically on the endmost portion of the body 1030, and an end face 1032. The edge between the end face 1032 and the sealing surface 1031 is shown at 1034 and is typically chamfered to facilitate the introduction of the valve pin 1028 into the gate 1020.

Due to the fact that the end face 1032 and chamfered edge 1034 will ultimately make up a portion of the surface of the mold cavity 1022, there may be design restrictions on the angle of the chamfered edge 1034. For example, the chamfered edge 1034 may be limited to having a relatively shallow angle with respect to the end face 1032 so as to provide a certain shape in the molded part.

The gate 1020 typically includes a cylindrical sealing surface 1036 adjacent the mold cavity 1022, and also includes a chamfered inlet surface 1038. The sealing surface 1036 receives and cooperates with the sealing surface 1031 of the valve pin 1028 to seal the gate 1020 against melt flow into the mold cavity 1022. The chamfered inlet surface 1038 cooperates with the chamfered edge 1034 on the valve pin 1028 to facilitate the introduction of the valve pin 1028 into the gate 1020.

The movement of the valve pin 1028 will now be described. In FIG. 16a, the valve pin 1028 is shown spaced from the gate 1020. The valve pin 1028 may be misaligned with the gate 1020 to any degree. When the valve pin 1028 is moved to close the gate 1020, if there is any misalignment of the valve pin 1028 and gate 1020, the valve pin 1028 first contacts the gate 1020 in the manner shown in FIG. 16b. The first contact is made by the chamfered edge 1034 and the chamfered inlet surface 1038. As the valve pin 1028 moves forward to close the gate 1020, the chamfered edge 1034 slides off the chamfered inlet surface 1038 thereby guiding the valve pin 1028 into alignment with the gate 1020. The valve pin 1028 then moves forwardly in the sealing surface 1036 of the gate 1020, as shown in FIG. 16c until arriving at the 'closed' position, as shown in FIG. 16d. It will be appreciated that the 'closed' position of the valve pin 1028 need not be as shown in FIG. 16d. After a number of molding cycles, the repeated contact between the valve pin 1028 and the inlet surface 1036 of the gate 1020 can eventually result in one or both of the sealing surface 1031 of the valve pin 1028 and the sealing surface 1036 of the gate 1020 being scored, worn away or otherwise damaged.

The portions of the valve pin 1028 and the gate 1020 that can be damaged are shown at 1039a and 1039b respectively. This damage can result in melt leaking past the gate 1020 after the gate 1020 is closed, and can also result in blemishes on the molded part. Thus, depending on the needs of the molding operation, the valve pin 1028 and the gate 1020 may require repair or replacement. It will be noted that the scoring or damage shown at 1039a and 1039b can occur almost immediately, depending on the nature of the molding operation, and thus poor quality parts can result virtually immediately. This problem is exacerbated if the angle of the chamfered edge 1034 on the valve pin 1028 is shallow, because the contact forces between the valve pin 1028 and the gate inlet surface 1038 can further promote wear, scoring or other damage.

Reference is made to FIG. 1, which shows an injection molding apparatus 10, having a manifold 12, a plurality of nozzles 14, valve pins 16, valve pin actuators 18, a plurality of valve pin guides 20 in accordance with a first embodiment of the present invention, and a mold cavity block 22.

Manifold 12 includes a plurality of runners 23 (also known as melt channels), which have an inlet 24, which receives melt from a melt source (not shown), and transport the melt to the nozzles 14. Manifold 12 may be heated by a heater 25.

Reference is made to FIG. 2. Each nozzle 14 has a nozzle body 26. The nozzles 14 may have a separate tip 27, and may further have a separate tip retainer 28. The nozzles 14 each have a nozzle melt channel 29 that extends therethrough to transport melt from the manifold 12 to an outlet 30. Each nozzle 14 may have a heater 31, which may be any suitable type of nozzle heater. For example, the heater 31 may be a wrapped wire heater, such as is shown in FIG. 2.

The tip 27 may be made from a thermally conductive material to facilitate the conduction of heat from the heater 31 to any melt flowing through the tip 27. Furthermore, the tip 27 may also be made from a wear-resistant material. For example, the tip 27 may be made from Tungsten Carbide. The tip 27 may alternatively be made from a thermally insulative material to reduce heat transfer out of any melt flowing therethrough.

The tip retainer 28 may further seal against a first bore 40 in the mold cavity block 22. The tip retainer 28 may be made of a thermally insulative material, such as titanium, mold steel, or chrome steel, to reduce heat transfer to the mold cavity block 22.

The mold cavity block 22 has a plurality of mold cavities 32, which may be cooled by a cooling fluid flowing through a plurality of cooling channels 33. Each mold cavity 32 has an inlet 34, which is commonly referred to as a gate 34. An axis 36 extends along the centerline of the gate 34 and the nozzle melt channel 29. The valve pin 16 is generally centered along axis 36, and is movable along axis 36 by the actuator 18, to open and close the gate 34 into the mold cavity 32. The valve pin 16 is shown in the Figures in the open position on the left side of axis 36, and in the closed position on the right side of axis 36.

The valve pin 16 has a body 43 and a tip 37. The tip 37 is sized to mate with the gate 34. When the tip 37 is inserted into the gate 34, a sealing surface 37a on the tip 37 cooperates with the gate 34 to seal against melt flow therebetween into the mold cavity 32. The tip 37 has a bottom face 37b. The bottom face 37b meets the sealing surface 37a along an edge 37c. The edge 37c may be a simple edge (as shown), or may alternatively be chamfered, depending on the specific requirements of the molding operation. It will be appreciated that having a simple edge 37c (ie. having substantially no chamfer on the edge 37c) provides better aesthetics on the molded part that is formed in the mold cavity 32. This is because the unchamfered bottom face 37b can be made to be substantially flush with the surrounding surfaces of the mold cavity 32. By contrast, a chamfered edge cannot be made flush, and will therefore leave a mark of some kind on the molded part, such as an indent or a vestige of some kind.

Upstream from the tip 37, the valve pin 16 may have a guide surface 38, which may have a larger diameter than the tip 37. A shoulder 35, which may be coned, transitions from the guide surface diameter down to the tip diameter. The shoulder 35 and the guide surface 38 are discussed further below.

Each valve pin guide 20 is positioned between one of the nozzles 14 and the mold cavity block 22. The valve pin guide 20 cooperates with the valve pin 16 to align the valve pin 16 with the gate 34. This inhibits damage to the gate 34 upon entry of the valve pin 16 therein.

In the embodiment shown in FIG. 2, the valve pin guide 20 cooperates with the guide surface 38 and the shoulder 35 to align the valve pin 16 with respect to the gate 34. By aligning the valve pin 16 on these surfaces and not on the sealing surface 37a and the bottom face 37b, the sealing surface 37a and the bottom face 37b are at least somewhat protected from wear during entry into the gate 34.

Furthermore, aligning the valve pin 16 on the guide surface 38 and the shoulder 35 permits the use of the unchamfered bottom face 37b, which provides improved aesthetics in the molded parts (not shown).

The valve pin guide 20 may be made, for example, from a single piece. Alternatively, however, the valve pin guide 20 may be made from two or more pieces as is discussed in more detail further below. Each valve pin guide 20 includes a peripheral edge 39 that cooperates with the first bore 40 in the mold cavity block 22 to align the valve pin guide 20 relative to the axis 36. Valve pin guide 20 may fit tightly in the first bore 40, by means of, for example an interference fit, to prevent the inadvertent movement of valve pin guide 20 in the first bore 40. The valve pin guide 20 may be made to be removable and replaceable once it is worn too much to align the valve pin 20 suitably. Thus, the guide 20 may be replaced, saving the time and expense of repairing the gate 34, or replacing the molding apparatus component containing the gate 34.

The valve pin guide 20 has a guide body 21a, which has a guide aperture 21b therethrough, which guides the valve pin 16 for entry into the gate 34. The guide aperture 21b may be centered along the axis 36.

The guide aperture 21b may have an upstream portion 21c and a downstream portion 21d. The upstream portion 21c may be coned to facilitate the insertion of the valve pin 16 therein and to inhibit the valve pin 16 from jamming against the valve pin guide 20 if the tip 37 of the valve pin 16 is offset from the axis 36.

The valve pin guide 20 may optionally have a sealing face 48, which cooperates with a bottom shoulder 50 in the first bore 40 to inhibit melt leakage therebetween. The peripheral edge 39 may also be a sealing face, inhibiting melt leakage between it and the first bore 40. The sealing face 48 and the peripheral edge 39 may seal in any suitable way, such as by a mechanical seal.

A second bore 51 may extend from the bottom shoulder 50 further into the mold cavity block 22. The gate 34 may be positioned in the second bore 51, as shown. The second bore 51 may be concentric with the first bore 40.

The valve pin guide 20 may be made from any suitable material, such as, for example, steel, Tungsten Carbide, Beryllium-Copper, and Tungsten-Zirconium-Molybdenum. Any material from which the tip 27 or the tip retainer 28 are made can be used for the valve pin guide 20. The valve pin guide 20 may be thermally insulative, or thermally conductive, or may be made from more than one material, depending on the requirements of the molding operation. For example, the valve pin guide 20 may include an outer piece made from a thermally insulative material, such as titanium, mold steel, or chrome steel, or Vespel™, and may include an inner piece made from a thermally conductive material, or from a wear-resistant material, such as Tungsten Carbide.

In use, melt flows from a melt source (not shown), through the manifold runners 23, through the nozzle melt channel 29, through aperture 21b, through the gate 34 and into the mold cavity 32. The nozzle 14 is heated by the heater 31, to heat the melt flowing therethrough. As the nozzle 14 is heated, it undergoes thermal expansion, during which time it may or may not contact the valve pin guide 20.

Reference is made to FIG. 2e. In the embodiment shown, melt is permitted to accumulate in the second bore 51 around the valve pin guide 20. The melt can act as a thermal insulator between the valve pin guide 20 and the mold cavity block 22. In an embodiment not shown, it is alternatively possible for the valve pin guide 20 to contact the mold cavity block 22 immediately adjacent the gate 34, so as to form a closed conduit from the guide aperture 21b into the gate 34, and thus prevent melt from leaking into the second bore 51. While this would provide an insulative air gap between substantially all of the guide 20 and the mold cavity block 22, this would provide some heat loss from the guide 20 into the mold cavity 22 proximate the gate 34.

Due to the layout of the runners 23 and other factors, the melt flowing through the nozzle 14 may have varying properties across its cross-section, and may thus push the tip 37 of the valve pin 16 so that it is offset from the axis 36.

As the valve pin 16 is extended by the actuator 18 (FIG. 1), the valve pin guide 20 realigns the tip 37 with the axis 36, so that the tip 37 is suitably aligned prior to contacting the gate 34. Once the valve pin 16 closes the gate 34, the mold cavity block 22 is cooled in order to solidify the melt in the mold cavity 32, thereby forming a molded part (not shown). The mold cavity block 22 is then opened; the molded part is ejected from the mold cavity 32, and the mold cavity block 22 is closed again. The valve pin 16 is withdrawn from the gate 34 and the cycle is started again.

Reference is made to FIGS. 2a, 2b, 2c and 2d, which illustrate the alignment of the valve pin 16 by means of the valve pin guide 20 prior to contact with the gate 34. The shoulder 35 and valve pin guiding surface 38 cooperate with the upstream and downstream portions 21c and 21d of the guide aperture 21b, to bring the valve pin 16 into alignment with the gate 34.

As the valve pin 16 moves from the position shown in FIG. 2a towards the gate 34, if there is any misalignment between the valve pin 16 and the gate 34, the first contact occurs between the valve pin shoulder 35 and the upstream portion 21c, as shown in FIG. 2b.

The shoulder 35 and the upstream portion 21c may be provided with any selected cone angles. The cone angles can be selected to reduce the risk of scoring or otherwise damaging one or both of the valve pin 16 or the valve pin guide 20, upon first contact or upon any subsequent sliding contact.

It will be noted that the valve pin shoulder 35, the valve pin guide surface 38, and the upstream and downstream portions 21c and 21d of the guide aperture 21b are larger in diameter than the valve pin tip 37 and the gate 34. By having the contact and sliding occur on these larger diameter surfaces 35, 38, 21c and 21d, a longer service life can be achieved before requiring repair or replacement of the valve pin 16 and the valve pin guide 20.

One or both of valve pin shoulder 35 and the upstream portion 21c on the guide 20 may be hardened by any suitable surface treatment means, to further reduce the risk of scoring. One of the surfaces 35 and 21c may be selected to be harder than the other, so that the softer of the two may be 'sacrificed' during the repeated contacting and sliding that occurs during an injection molding campaign. The surface 35 or 21c that is selected to be sacrificed may be, for example, on the part that is the less expensive of the two, the easier of the two or the less time consuming of the two to replace.

As the valve pin 16 is moved towards the gate 34, the shoulder 35 and upstream portion 21c of the guide aperture 21b cooperate to bring the valve pin 16 into alignment with the gate 34. Once the shoulder 35 is moved past the upstream portion 21c, the valve pin guiding surface 38 and the downstream portion 21d of the guide aperture 21b contact each other to maintain the valve p