Injection molding nozzle manifold

Abstract: Hot tip injection molding apparatus having a heated melt distribution manifold (12,18) for conveying melt to a number of gates (10). A number of nozzle manifolds (20) are closely mounted to the front surface (24) of the heated manifold (12,18). Each nozzle manifold (20) has a number of spaced nozzle portions (66) extending from a rear manifold portion (68). A melt channel (38) branches from an inlet (86) on the rear surface (70) of the rear manifold portion (68) to an outlet (90) on the conical surface (80) of each nozzle portion (66). The rear surfaces (70) of the nozzle manifolds (20) are rectangular rather than round to improve the efficiency of heat transfer from the heated manifold (12,18) to the nozzle manifolds (20).

Description: This invention relates generally to injection molding and more particularly to an injection molding apparatus comprising a heated melt distribution manifold having a melt passage, and a plurality of indirectly heated nozzle manifolds mounted on a front surface of said melt distribution manifold, wherein each nozzle manifold has a rear manifold portion for abutment of the entire rear surface thereof against said front surface of the melt distribution manifold, and a plurality of spaced nozzle portions extending frontwardly from said rear manifold portion, wherein each of the nozzle manifolds has a melt channel extending therethrough from an inlet on said rear surface to receive pressurized melt from said melt passage in the melt distribution manifold, the melt channel branching in the rear manifold portion. Multi-gate injection molding apparati are well known in which a melt passage branches in a melt distribution manifold, then each branch extending through a heated nozzle secured to the manifold. As seen in the applicant's U.S. Patent No. 4,094,447, it is also known to provide a heated nozzle in which the melt passage branches outwardly to several edge gates. While this is suitable for edge gating, each of the front portions of the nozzle has a flat face which is not suitable for hot tip gating. The applicant's U.S. Patent No. 4,921,708 further shows a multi-gate application with hot tips provided by four elongated probes mounted around a heated nozzle. Other arrangements of multi-tip nozzles are presented by DE-39 33 281 A1 and US-A-5,464,343. However, they all have a generally cylindrical shape with a circular rear surface which limits the surface contact with the adjacent manifold. In a system with a large number of gates, it is usually preferable to reduce overall size by having the gates as close together as possible. On the other hand, it is also desirable to maximise heat transfer from and thus surface contact with the adjacent manifold. Accordingly, it is an objective of the present invention to improve a conventional injection molding apparatus to have high thermal efficiency so that additional heating elements on the nozzle manifolds will become redundant. For an injection molding apparatus of the above kind this objective is solved in an inventive manner in that each nozzle portion has a conical front surface extending to a pointed tip to be mounted in alignment with an injection gate, wherein a respective one of the branches of said melt channel extends to an outlet on the conical surface of each of the nozzle portions, and wherein said nozzle manifolds are mounted closely and the rear manifold portion of each nozzle manifold has a [rectangular] cross-section of constant rectangular outer shape to provide maximum surface contact between the rear surfaces of said nozzle manifolds and the front surface of the melt distribution manifold. Further objects and advantages of the invention are laid down in the sub-claims and will appear from the following description taken together with the accompanying drawings. Therein: Figure 1 is a sectional view of a portion of a multi-gate injection molding system or apparatus having a number of nozzle manifolds according to a preferred embodiment of the invention, Figure 2 is an isometric view of one of the nozzle manifolds seen in Figure 1, Figure 3 is a plan view of the nozzle manifold seen in Figure 2, Figure 4 is a sectional view along line 4-4 in Figure 3, and Figure 5 is a sectional view along line 5-5 in Figure 3. Reference is first made to Figure 1 which shows a portion of a hot tip gated injection molding system or apparatus having ninety-six gates 10. In this case, a main manifold 12 is secured by screws 14 to the rear surface 16 of a sub-manifold 18 and twenty-four nozzle manifolds 20 according to the invention are in turn secured by screws 22 to the front surface 24 of the sub-manifold 18. However, in other configurations the nozzle manifolds 20 can be secured directly to a manifold without requiring a sub-manifold and thus in this case the sub-manifold 18 can be considered part of the manifold. While the main manifold 12 and the sub-manifolds 18 are made of steel, the nozzle manifolds 20 are made of a more thermally conductive material such as AMCO 940 copper alloy. Pressurised melt is conveyed to each gate 10 leading to a cavity 26 through a melt passage 28 which extends from a central inlet 30 in an inlet portion 32 of the main manifold 12. The melt passage 28 branches into six different branches 34 in the main manifold 12 and each branch 34 branches into four different branches 36 in the sub-manifold 18. Each of these branches 36 extends to a melt channel 38 in one of the nozzle manifolds 20 as described below. The manifolds 12, 18 and the nozzle manifolds 20 are heated by an electrical heating element 40 integrally embedded in the front surface 42 of the main manifold 12 as well as by ambient heat from the melt received from the molding machine and shear heat generated in the pressurized melt being injected during the injection cycle. While the mold 44 normally has a greater number of plates depending upon the application, in this case only a cavity plate 46, spacer plate 48, and a back plate 50 with a locating ring 52 secured to it by screws 54 are shown for ease of illustration. The cavity 26 in the mold 44 is cooled by pumping cooling water through cooling conduits 56. The manifolds 12, 18 and the nozzle manifold 20 are securely located in place by insulative and resilient spacer members 58 between the main manifold 12 and the back plate 50 and by sealing and locating sleeves 60 which fit around each nozzle portion 66 of each nozzle manifold 20. In this embodiment the sealing and locating sleeves 60 are made of a titanium alloy and each of them is seated in a circular seat 62 in the cavity plate 46. This provides an insulative air space 64 between the heated manifolds 12, 18 and the nozzle manifolds 20 and the surrounding cooled mold 44. As best seen in Figures 2-5, each nozzle manifold 20 has a number of spaced nozzle portions 66 extending frontwardly from a rear manifold portion 68. The rear manifold portion 68 has a rear surface 70 which abuts against the front surface 24 of the sub-manifold 18. The nozzle manifolds 20 are secured in this position by two screws 22 (shown in Figure 1) extending from the sub-manifold 18 into threaded holes 76 in the rear manifold portions 68 of each nozzle manifold 20. In the embodiment shown, each nozzle manifold 20 has four equally spaced nozzle portions 66 and the rear manifold portion 68 has a square cross-section with one of the nozzle portions 66 extending forwardly from each quadrant 78 of the square rear manifold portion 68. In other embodiments, the nozzle manifolds 20 can have a different number of nozzle portions 66. However, it is critical that the rear manifold portion 68 have a rectangular cross-section to maximize surface contact between its rear surface 70 and the front surface 24 of the sub-manifold 18. The maximum surface contact provided by this rectangular shape ensures maximum heat transfer between the sub-manifold 18 and the closely mounted nozzle manifolds 20. Each of the nozzle portions 66 has a conical front surface 80 extending from a cylindrical portion 82 to a pointed tip 84. The cylindrical portion 82 fits in a sealing and locating sleeve 60 which locates the pointed tip 84 in alignment with one of the gates 10. As best seen in Figures 3-5, each nozzle manifold 20 has a melt channel 38. The melt channel 38 extends through the nozzle manifold 20 from an inlet 86 on the rear surface 70 and branches diagonally outwardly and forwardly in the rear manifold portion 68 with a branch 88 extending to an outlet 90 on the conical front surface 80 of each of the nozzle portions 66. The inlet 86 to the melt channel 38 in each nozzle manifold 20 is aligned with a respective outlet 92 from the melt passage 28 in the sub-manifold 18. In use, electrical power is applied to the electrical heating element 40 embedded in the main melt distribution manifold 12 and this heats the main manifold 12, the sub-manifold 18, and each of the attached nozzle manifolds 20 to a predetermined operating temperature. As mentioned above, the rear surface 70 of each nozzle manifold 20 being square rather than round provides maximum efficiency of heat transfer by conduction from the sub-manifold 18 to the closely mounted nozzle manifolds 20. Pressurized melt is supplied from a molding machine (not shown) to the melt passage 28 extending through the main manifold 12 and sub-manifold 18 according to a predetermined injection cycle. The melt from each branch 36 of the melt passage 28 flows through the melt channel 38 in a respective nozzle manifold 20 into a space 94 in the mold 44 around the conical front surface 80 and then through the gate 10 into the cavity 26. As seen in Figure 1, the sealing and locating sleeves 60 prevent leakage of the melt from this space 94 as well as locate the pointed tip 84 in exact alignment with the respective gate 10. After the cavity 26 is filled and a suitable packing and cooling period has expired, the injection pressure is released and the melt conveying system is decompressed to avoid stringing through the open gate 10. The mold 44 is then opened to eject the molded product. After ejection, the mold 44 is closed and the cycle is repeated continuously with a cycle time dependent upon the size of the cavity or cavities and the type of material being molded. While the description of the injection molding nozzle manifold 20 has been given with respect to a preferred embodiment, it will be evident that various other modifications are possible without departing from the scope of the invention as understood by those skilled in the art and as defined in the following claims.

Claims: Injection molding apparatus comprising: a heated melt distribution manifold (12,18) having a melt passage (34,36), and a plurality of indirectly heated nozzle manifolds (20) mounted on a front surface (42) of said melt distribution manifold (12,18), wherein each nozzle manifold (20) has a rear manifold portion (68) for abutment of the entire rear surface (70) thereof against said front surface (42) of the melt distribution manifold (12,18), and a plurality of spaced nozzle portions (66) extending frontwardly from said rear manifold portion (68), wherein each of the nozzle manifolds (20) has a melt channel (38) extending therethrough from an inlet (86) on said rear surface (70) to receive pressurized melt from said melt passage (34,36) in the melt distribution manifold (12,18), the melt channel (38) branching in the rear manifold portion (68), characterized in that each nozzle portion (66) has a conical front surface (80) extending to a pointed tip (84) to be mounted in alignment with an injection gate (10), wherein a respective one of the branches (88) of said melt channel (38) extends to an outlet (90) on the conical surface (80) of each of the nozzle portions (66), and wherein said nozzle manifolds (20) are mounted closely and the rear manifold portion (68) of each nozzle manifold (20) has a rectangular cross-section of constant rectangular outer shape to provide maximum surface contact between the rear surfaces (70) of said nozzle manifolds (20) and the front surface (42) of the melt distribution manifold (12,18). Injection molding apparatus according to claim 1, wherein heating elements (40) are provided in the front surface (42) of the melt distribution manifold (12,18). Injection molding apparatus according to one of claims 1 or 2, wherein insulating sleeves (60) are fitted around each nozzle portion (66) on the nozzle manifolds (20) for providing insulating seals between the nozzle manifolds (20) and a mold (44). Injection molding apparatus according to one of claims 1 to 3, wherein the nozzle manifolds (20) are made of a material more thermally conductive than the melt distribution manifold (12,18). Injection molding apparatus according to claim 1, wherein the rear manifold portion (68) of each nozzle manifold (20) has a plurality of threaded holes (76) to receive screw means (22) to allow secure attachment of each nozzle manifold (20) to the melt distribution manifold (12,18). Injection molding apparatus according to claim 2, wherein the branches (88) of the melt channel (38) of each nozzle manifold (20) extend diagonally outwardly and frontwardly from the inlet (86) on the rear surface (70) of the rear manifold portion (68). Injection molding apparatus according to claim 3, wherein the cross-section of the rear manifold portion (68) of each nozzle manifold (20) is square. Injection molding apparatus according to claim 4, wherein each nozzle manifold (20) has four equally spaced identical nozzle portions (66), each of the nozzle portions (66) extending frontwardly from a different quadrant of the rear manifold portion (68).

Inventors: GELLERT JOBST ULRICH, GELLERT, JOBST ULRICH
Applicants: GELLERT JOBST U, GELLERT, JOBST ULRICH
Application year: 1996
Main classification: B29C45
IPC codes: B29C45