Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C45/00—Injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould; Apparatus therefor
  • B29C45/17—Component parts, details or accessories; Auxiliary operations
  • B29C45/26—Moulds
  • B29C45/32—Moulds having several axially spaced mould cavities, i.e. for making several separated articles
  • B29C45/322—Runner systems for distributing the moulding material to the stacked mould cavities

Definitions

• This invention relates to injection molding and, in particular, to the distribution of melt through a multi-level stack mold.
• Stack molding advantageously permits molding machine output to be multiplied without appreciably increasing the overall size of the machine.
• stack molding has the disadvantage that a more extensive melt runner system is required to extend through the moving platens to reach the cavities.
• melt distribution arrangement for multi-level stack molds which has generally equal length melt paths for each mold level. Furthermore, there is a need for a melt distribution arrangement for a multi-level stack mold which does not require a centrally-located sprue bar, thereby allowing single parts to be molded which extend across the central mold axis. There is yet a further need for a melt distribution arrangement for a multi-level stack mold which utilizes a minimal number of sprue bars to minimize interference with the molding process. There is also a need for an improved drool control apparatus for use in multi-level stack molds. Summary Of The Invention
• the present invention provides a multi-level stack mold comprising a stationary platen, a first, second and third moving platens, the moving platens being moveable between an "open” and “closed” position in a longitudinal direction generally parallel to a generally centrally disposed mold axis, a plurality of mold cavities defined between the stationary and moving platens, a first mold cavity manifold disposed in the first moving platen in communication with at least one of said mold cavities, a second mold cavity manifold disposed in the third moving platen in communication with at least one of said mold cavities and a sprue bar assembly extending through the first platen for selectively providing a flow of pressurized melt from the stationary platen to the second platen for distribution to the first and second mold cavity manifolds.
• the present invention provides a multilevel stack mold comprising a stationary platen, a first, second and third moving platens, the moving platens being moveable between an "open” and “closed” position in a longitudinal direction generally parallel to a generally centrally disposed mold axis, a plurality of mold cavities defined between the stationary and moving platens, a first mold cavity manifold disposed in the first moving platen in communication with at least one of said mold cavities, a second mold cavity manifold disposed in the third moving platen in communication with at least one of said mold cavities, a bifurcated sprue bar assembly extending through the first platen for selectively providing a flow of pressurized melt from the stationary platen to the second platen, the sprue bar assembly having a first portion and a second portion in flow communication, the second portion separably matable with the first portion, the sprue bar assembly being disposed eccentrically from the central mold axis and a distribution manifold disposed in the second platen
• the present invention provides a multi- level stack mold, the stack mold comprising a stationary platen, a first, second and third moving platens, the moving platens being moveable between an "open” and “closed” position in a longitudinal direction generally parallel to a generally centrally disposed mold axis, a plurality of mold cavities defined between the stationary and moving platens, a first mold cavity manifold disposed in the first moving platen in communication with at least one of said mold cavities, a second mold cavity manifold disposed in the third moving platen in communication with at least one of said mold cavities, a distribution manifold in one of said moving platens and a bifurcated sprue bar assembly connected to, and in communication with, the distribution manifold for providing a flow of pressurized melt to the distribution manifold, the sprue bar assembly being disposed eccentrically from the central mold axis, whereby the sprue bar assembly and the distribution manifold are arranged to be non-coaxial.
• the present invention provides a method of distributing pressurized to a melt in a multi-level stack mold having a stationary platen, a first, second and third moving platens, the moving platens being moveable between an "open” and “closed” position in a longitudinal direction generally parallel to a generally centrally disposed mold axis, a plurality of mold cavities defined between the stationary and moving platens, a first mold cavity manifold disposed in the first moving platen in communication with at least one of said mold cavities, and a second mold cavity manifold disposed in the third moving platen in communication with at least one of said mold cavities, the method comprising the steps of transferring the pressurized melt from the stationary platen to a distribution manifold in the second moving platen and distributing the pressurized melt to the first and third moving platens via the first and second mold cavity manifolds for delivery to a plurality of mold cavities.
• Figure 1 is a sectional view of a four-level stack mold apparatus according to a first embodiment of the invention, shown in the closed position;
• Figure 2 is a sectional view of the apparatus of Figure 1, shown in the open position;
• Figure 3 is a sectional view of a three-level stack mold apparatus according to a second embodiment of the invention, shown in the closed position;
• Figure 4 is a sectional view of the apparatus of Figure 3, shown in the open position;
• Figure 5 is a sectional of view of a melt control valve for use in the present invention, shown in a open position
• Figure 6 is a sectional view of a melt control valve of Figure
• Figure 7 is a not-to-scale sectional view of a drool control apparatus for use in the present invention, shown in a first position;
• Figure 8 is a not-to-scale sectional view of the drool control apparatus of Figure 7, shown in a second position;
• Figure 9 is a not-to-scale sectional view of the drool control apparatus of Figure 7, shown in the third position;
• Figure 10 is a not-to-scale sectional view of the drool control apparatus of Figure 7, shown in a fourth position
• Figure 11 is a not-to-scale sectional view of the drool control apparatus of Figure 7, shown in a fifth position
• Figure 12 is a sectional view of the drool control apparatus of Figure 8, taken along the line 12-12.
• FIG. 1 a stack mold embodying an improved melt distribution system in accordance with the present invention is shown generally at 10.
• Stack mold 10 comprises a stationary platen or back plate 12, a first moving platen 14, a second moving platen 16, a third moving platen 18 and a fourth moving platen 20. Platens 12, 14, 16, 18 and 20 are selectively matable at a first parting line 22, a second parting line 24, a third parting line 26 and a fourth parting line 28, respectively.
• An injection molding machine (not shown) has an injection nozzle 32 which communicates with a heated runner system 34 via a sprue bushing 36.
• Heated runner system 34 comprises a back plate runner passage 38, a sprue bar assembly 40, a central distribution manifold 42, a first platen manifold 44 and a third platen manifold 46.
• First platen manifold 44 and third platen manifold 46 communicate with a plurality of mold cavities (not shown), defined between the platens at the parting lines, via a plurality of mold cavity gates 48.
• Sprue bar assembly 40 comprises a first portion 40' and a second portion 40" selectively joined by a first melt flow control valve assembly 49.
• a first runner passage 50 communicates with a second runner passage 60, via control valve 49.
• First flow control valve assembly 49 comprises a first runner gate 52, selectively closeable by a first valve pin 54 actuated by a first actuator 56, and a second runner gate 62, selectively closeable by a second valve pin 64 actuated by a second actuator 66.
• First flow control valve assembly 49 is preferably of the construction more particularly described in United States Patent No. 4,212,626 to Gellert, and further described below.
• Second flow control valve assembly 69 is preferably constructed identically to first flow control valve assembly 49, and comprises a third runner passage 70, having a third runner gate 72, a third valve pin 74 and a third actuator 76, communicating with a fourth runner passage 80, having a fourth runner gate 82, a fourth valve pin 84 and a fourth actuator 86.
• Central distribution manifold 42 also communicates with third platen manifold via a third flow control valve assembly 89.
• Third flow control valve assembly 89 is preferably constructed identically to the first and second flow control valve assemblies, and comprises a fifth runner passage 90, having a fifth runner gate 92, a fifth valve pin 94 and a fifth actuator 96, communicating with a sixth runner passage 100, having a sixth runner gate 102, a sixth valve pin 104 and a sixth actuator 106.
• Sprue bar assembly 40 is disposed substantially parallel to injection axis 30, along a sprue bar axis 110. Sprue bar assembly 40 passes through first moving platen 14 via a first platen through-pass 112 (see Figure 5).
• First platen through-pass 112 permits sprue bar assembly 40 to deliver pressurized melt directly to central distribution manifold 42 disposed in second platen 16.
• Central distribution manifold 42 communicates at an angle (preferably 90°, although almost any angle less than 180° is possible) with sprue bar 40 to transfer pressurized melt to a central portion of second platen 16. Melt is transferred to first platen manifold 44 and third platen manifold 46 for delivery to the mold cavities, as described above.
• the angle between distribution manifold 42 and sprue bar assembly 40 is required to permit actuator 66 to avoid interference with the flow of pressurized melt in runner system 34.
• first flow control valve assembly 49 preferably comprises first runner gate 52 sealable by a tip 58 of first valve pin 54. In its "open" position ( Figure 5), first valve pin 54 is withdrawn from gate 52, by first actuator 56 (see Figure 1), to permit a flow of pressurized melt to exit first runner passage 50 via gate 52.
• Second valve pin 64 operates in a similar fashion, and cooperates with first valve pin 54 to allow the flow of pressurized melt to enter gate 62 when tip 68 is withdrawn therefrom.
• pins 54 and 64 are moved by their respective actuators such that tips 58 and 68 seal gates 52 and 62, respectively. With the runner gates sealed in this manner, the platens of the mold may then be parted (as shown in Figure 2) without fear of melt drooling from gates 52 or 62.
• first flow control valve assembly 49 has “open” ( Figure 5) and “closed” ( Figures 6) positions.
• the actuation of the valve pins is timed and synchronized such that the flow control valve assembly is “open” when the platens of the mold are closed, and the valve pins of the control valve assembly are moved to their "closed” position upon, or prior to, the opening of stack mold 10.
• the reference marker "P/L” in the Figures represents the nominal parting line upon which the flow control valve assembly is parted.
• first flow control valve assembly 49 it will be understood, with reference to Figures 1 and 2, that control valve assembly 49 does not part along one of the mold parting lines 22, 24, 26 or 28, but rather its own individual "parting line” within first platen 14.
• Second flow control valve assembly 69 and third flow control valve assembly 89 are preferably constructed and operated in a manner similar to as first flow control assembly 49. Second and third flow control valve assemblies will have a parting line ("P/L") which coincides with parting lines 24 and 26, respectively.
• the flow control valve assemblies may also optionally provide a cavity anti-drool means shown at 170, 170' and 170", as will be described in more detail below.
• the molding machine may then be actuated to force a flow of pressurized melt via nozzle 32 into back plate runner passage 38.
• the pressurized melt is transferred, via heated runner system 34, to the plurality of mold cavities in stack mold 10.
• the valve pins of the flow control valve units are actuated by their respective actuators to close the flow control valve units.
• Stack mold 10 may then be opened, as shown in Figure 2, to eject the molded parts from stack mold 10.
• the bifurcated sprue bar assembly 40 Upon opening of mold 10, the bifurcated sprue bar assembly 40 separates into its first and section portions 40' and 40", which are withdrawn from first platen through-pass 112 as the mold opens. Once the mold is open, the molded parts may be ejected from their respective cavities. The mold may then be closed, and the flow control valve assemblies opened in preparation for the next molding cycle.
• First platen through-pass 112 advantageously permits sprue bar assembly 40 to directly communicate with central distribution manifold 42 in second platen 16. This configuration permits the more central distribution of pressurized melt to the first and third platen manifold, thereby facilitating a more balanced runner length design throughout the runner system. It will be understood, however, that through-pass 112 strictly need not be provided, but rather sprue bar 40 may pass around first platen 14 instead.
• the bifurcated sprue bar assembly design according to the present invention may be equally applied to other multi-level stack mold configurations, such as a three-level stack mold 10'.
• Three-level stack mold 10' has platens 12, 14 16 and 18, in a similar configuration as described above.
• Distribution manifold 42 communicates with first and third manifolds 44 and 46, respectively, as described above, although manifold 44 now has halves 44 and 44', to match the modified configuration of the 3-level mold, as will be understood by one skilled in the art.
• Figures 7-12 a cavity anti-drool mechanism for use with the melt distribution system of the present invention will now be described.
• Figures 7- 11 are not shown on the same scale as Figures 1-4.
• the length of second runner passage 60, between, by-pass 174 and distribution manifold 42 has been shortened for convenience of illustration.
• Figures 7-11 show the cavity anti-drool system combined with a flow control valve system of the type described above with reference to Figures 5 and 6. It will be apparent to one skilled in the art that the anti- drool mechanism described herein need not be limited to such combination, but may also be used alone, or in conjunction with another flow control valve configuration.
• drool control assembly 170 which comprises a piston 172 and a by-pass chamber 174, being an enlarged section of second runner passage 60.
• Piston 172 is integrally incorporated in the second valve pin 64 and positioned on the stem of valve 64 such that piston 172 is positionable, in a first position, in a restricted section 176 of second runner passage 60 and, in a second position, in by-pass chamber 174.
• piston 172, restricted section 176 and by-pass chamber 174 are shaped and sized to substantially block second runner passage 60 in its first position but permit melt flow therearound when piston 172 is in its second position in by-pass chamber 174, as described below.
• drool control assembly 170 is synchronized with mold injection as will now be described.
• actuator 66 moves second valve pin 64 to its "open" position, as shown in Figure 8.
• piston 172 is position in by-pass chamber 174.
• tip 68 of second valve pin 64 withdrawn from second gate 62 and tip 58 of first valve pin 54 withdrawn from first gate 52 to permit flow through flow control valve assembly 49, although as discussed above, these flow control valve assembly components do not necessarily form part of the anti-drool control apparatus.
• melt is permitted to flow from the molding machine through first runner passage 50 and into second runner passage 60, around piston 172 through by-pass chamber 174 and into distribution manifold 42, for delivery to the mold cavities.
• the molding pressure is maintained to apply a packing pressure, as is known in the art.
• actuator 66 move second valve pin 64 and piston 172 "upstream" (ie. away, fluidly speaking, from the mold cavities), thereby causing piston 172 to enter restricted section 176.
• piston 172 moves second valve pin 64 and piston 172 "upstream" (ie. away, fluidly speaking, from the mold cavities), thereby causing piston 172 to enter restricted section 176.
• the melt material in second melt passage 60 on the upstream side of piston 172 is forced back into restricted section 176, along second melt passage 60 in the upstream direction.
• piston 172 travels upstream through restricted section 176, a pressure drop is created in the melt material immediately behind (ie "downstream” from) piston 172, which pressure drop is correspondingly transmitted to distribution manifold 42 and, ultimately, to gates 72 and 92.
• second valve pin 64 moves to its full-stroke or "closed” position, the flow control valve assembly 49 partially closes by tip 58 of second valve pin 64 seating in gate 62 to close the downstream half of flow control valve assembly 49.
• the stroke length of piston 172 is chosen to obtain the desired pressure drop in the runner system of first moving platen 14 to achieve the intended anti-drool performance.
• first valve pin 54 is closed, with tip 58 fully seated in gate 52.
• Flow control valve assembly 49 is now fully closed.
• Mold 10 may now be opened, along first parting line 22, (see Figure 2 or 4) to permit the molded parts to be ejected from mold 10.
• the decompressed melt in distribution manifold 42 advantageously reduces the tendency of the melt to drool from the gates 72 and 92.
• the mold may be closed and the molding machine readied for the next molding cycle.
• piston 172 has a substantially identical, but slightly smaller, cross-section to second melt passage 60, but also has a longitudinal cutout 180 through its thickness. Cutout 180 permits some melt to flow past piston 172 as it is stroked upstream during its decompression cycle, thereby reducing the resistance pressure the upstream melt exerts on piston 172.
• cutout 180 advantageously allows the size of piston 62 to be reduced.
• the size and shape of cutout 180 can be tuned to a particular molding application to optimize decompression performance in the stack mold manifold, as will be apparent to one skilled in the art.
• anti-drool assembly 170 is preferably substantially the same as is used for anti-drool control assemblies 170' and 170".
• Anti-drool assemblies 170' and 170" may be used advantageously in fourth and sixth runner passages 80 and 100 to inhibit drool at gates 48 in thermally gated molding applications.
• drool control assembly 170 may also be configured to actuate contemporaneously with the parting of the mold, provided that a suitable bleed arrangement, as will be understood by one skilled in the art, is made for the upstream melt displaced by the stroke of piston 172 in second runner passage 60. While the above description constitutes the preferred embodiment, it will be appreciated that the present invention is susceptible to modification and change without parting from the fair meaning of the proper scope of the accompanying claims.

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• Engineering & Computer Science (AREA)
• Manufacturing & Machinery (AREA)
• Mechanical Engineering (AREA)
• Moulds For Moulding Plastics Or The Like (AREA)

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• 2000
  • 2000-05-09 WO PCT/CA2000/000535 patent/WO2000067985A1/en not_active Ceased
  • 2000-05-09 JP JP2000616990A patent/JP2002544004A/ja active Pending
  • 2000-05-09 AU AU45315/00A patent/AU4531500A/en not_active Abandoned
  • 2000-05-10 US US09/568,130 patent/US6575731B1/en not_active Expired - Lifetime
• 2003
  • 2003-04-23 US US10/420,921 patent/US6852265B2/en not_active Expired - Lifetime
• 2004
  • 2004-07-16 US US10/892,397 patent/US7122145B2/en not_active Expired - Lifetime

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