Stack mold linkage with unequal strokes

Abstract: The present invention relates to stack mold linkages for creating unequal strokes for use in an injection molding machine for making different sized molded parts. The stack mold linkages comprise linkages for moving each of at least two mold assemblies between a mold closed position and a mold open position and for separating the mold halves forming the mold assemblies by unequal stroke lengths.

Description: BACKGROUND OF THE INVENTION The present invention relates to an injection molding machine for producing different parts that has a linkage for producing unequal strokes during the opening and closing of the mold sections. The present invention also relates to a method for fabricating molded articles of different sizes using a single molding machine. A multi-level stack mold typically uses a linkage system to open and close the mold sections while maintaining equal spacing between all sections. U.S. Patent No. 3,669,601 to Lainesse shows an early two level stack mold which is opened by the motion of a platen. As the platen moves, a first mold station nearest the platen opens, while a second mold station remains closed. Pins, fastened to a center section, slide through a pair of plates until their heads contact the underside of one of the plates, thus limiting the opening stroke of the first mold station. As the platen continues to move, the center section is now caused to move via the pins. Other pins, fastened to the center section, slide through a second pair of plates until their heads contact the underside of an ejector plate causing it to move and compress springs which cause the second mold station to open. Motion of the platen continues until the heads, already bottomed out on the ejector plate, fully compress the springs thereby ejecting the parts from the second mold station. This mechanical system thereby causes a two level stack mold to open sequentially, first one side, then the other. U.S. Patent No. 3,941,548 to Bruder shows a two level stack mold which uses pairs of cylinders hydraulically connected to each other such that the opening motion of a movable platen causes an upper rod of an upper cylinder to move inside the cylinder and displace oil that is conducted via a pipe to a lower cylinder acting on its piston and causing a lower rod to extend and push against a fixed platen, thereby causing the center section of the stack mold to separate from the fixed platen. In this way, both mold stations are opened simultaneously by equal amounts at equal speeds. U.S. Patent No. 4,400,341 to Sorensen shows a two level stack mold in which a center section is opened independently of the moving platen by means of a cylinder. Each mold station is opened sequentially according to the stroke of the cylinder. One mold is opened while the others remains closed. U.S. Patent No. 4,207,051 to Wright shows a two level stack mold in which pairs of racks acting with a central pinion cause the mold stations to open simultaneously and equally in both stroke and speed. U.S. Patent No. 4,929,166 to DiSimone shows a two level stack mold carrier in which machine mounted castings for holding the center section of a stack mold are moved by means of pairs of racks and pinions having different diameters, and both mounted on the moving platen, such that the center section of the mold remains equally spaced between the fixed and moving platens of the machine. U.S. Patent No. 5,458,843 to Brown shows a four level stack mold linkage system in which all mold stations are opened equally in both stroke and speed via the opening motion of the moving platen. U.S. Patent Nos. 5,578,333 and 5,707,666, both to Schad, show multilevel stack mold carriers for four level stack molds in which nested castings mounted in the machine, support various sections of the stack mold and are moved by nested drive means such that the centermost section is driven first by the moving platen motion. Mounted to the center carrier are secondary drive means to cause the motions of the remaining mold sections that all mold stations are open-closed equally both in speed and distance. None of the above mentioned patents describe a linkage mechanism for opening and closing the various sections of a stack mold by unequal distances between the various mold sections. Nor are there any descriptions of linkage mechanisms for facilitating such unequal motions in an adjustable manners such that a stack mold carriers so equipped can be used to accommodate installations of different stack mold configurations requiring different unequal strokes. SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a stack mold having a linkage mechanism for opening and closing the various sections of the mold by unequal strokes between the various mold sections. It is a further object of the present invention to provide a stack mold as above having an adjustable linkage mechanism. It is yet a further object of the present invention to provide a method for fabricating molded parts of different sizes using a single molding machine. The foregoing objects are attained by the machine and the method of the present invention as claimed. According to a first aspect of the present invention there is provided an injection molding machine comprising: a stationary platen, a movable center section carrier movable relative to the stationary platen and a moving platen also movable relative to the stationary platen, the movable center section carrier having: a first face facing a first complementary face of the stationary platen; and a second face facing a second complementary face of the moving platen; the injection molding machines further comprising: a linkage mechanism for moving said movable center section carrier and said moving platen between respective first positions and second positions, the first positions being where a separation between the stationary platen and a respective one of the movable center section carrier and said moving platen corresponds, in use, to a mold open position and the second position being where a separation between the stationary platen and the respective one of the movable center section carrier and said moving platen corresponds, in use, to a mold closed position; the injection molding machine characterized in that: the linkage mechanism includes means for separating the movable center section carrier and the moving platen from the stationary platen by unequal stroke distances such that separations attained, in use, at the mold open positions between the first face and the first complementary face and between the second face and the second complementary face are different from each other. In another aspect of the present invention there is provided a method of fabricating molded articles using a stack mold machine having a stationary platen and at least two movable members movable relative to said stationary platen, the stack mold machine further having at least two mold assemblies formed by mold halves attached to said stationary platen and said at least two movable members, the method comprising: while said at least two mold assemblies are in a mold closed position, forming said molded articles by injecting melt into at least one cavity formed within each of said mold assemblies; separating the mold halves of said at least two mold assemblies by moving the least two movable members relative to the stationary platen, the at least two movable members moved to a mold open position where said molded articles are to be ejected; the method characterized in that: separating the mold halves to respective mold open positions results in the mold halves of the first mold assembly being separated by a first stroke distance and the mold halves of the second mold assembly being separated by a second stroke distance larger than the first stroke distance. In a further aspect of the present invention there is provided a linkage assembly for mounting, in use, to a center-section carrier of a stack mold, the center section carrier arranged to be positionable and movable between a stationary platen and a moving platen of an injection molding machine, the linkage assembly comprising: a central link member centrally rotatably mountable to the center section carrier, the central link member having a first end and a second end; a first link arm pivotally coupled to the first end of the central link member, the first link arm arranged to be connectable, in use, to the stationary platen to effect relative displacement of the central section carrier with respect to stationary platen by a first distance; and a second link arm having a first end and a second end, the first end of the second link arm pivotally coupled to the second end of the central link member; the linkage assembly characterized by: a linkage sub-assembly coupled to the second end of the second link arm, the linkage sub-assembly configured to be connectable, in use, to the moving platen, the linkage sub-assembly providing means for allowing the moving platen to be displaced from the center-section carrier by a second distance greater than the first distance, thereby permitting an injection molding machine fitted with the linkage assembly to operate with differing opening stroke distances. In yet another aspect of the present invention there is provided a stack mold assembly for mounting, in use, between a stationary platen and a moving platen of an injection molding machine, the stack mold assembly comprising: a center-section carrier having a first face and a second face each arranged to receive, in use, a mold half; a central link member rotatably mountable to the center section carrier, the central link member having a first end and a second end; a first link arm pivotally coupled to the first end of the central link member, the first link arm arranged to be connectable, in use, to the stationary platen to effect relative displacement of the first face central section carrier with respect to stationary platen by a first distance; and a second link arm having a first end and a second end, the first end of the second link arm pivotally coupled to the second end of the central link member; the stack mold characterized by: a linkage sub-assembly coupled to the second end of the second link arm, the linkage sub-assembly configured to be connectable, in use, to the moving platen, the linkage sub-assembly providing means for allowing the moving platen to be displaced from the second face of the center-section carrier by a second distance greater than the first distance, thereby permitting an injection molding machine fitted with the stack mold to operate with differing opening stroke distances between the first face and the stationary platen and the second face and the moving platen. BRIEF DESCRIPTION OF THE DRAWINGS FIGs. 1A-1C illustrate a two-level stack mold having a first linkage mechanism for opening the mold stations by different stroke lengths; FIGs. 2A-2D illustrate a two-level stack mold having a second linkage mechanism for opening the mold stations by different stroke lengths; FIGs. 3A-3D illustrate a two-level stack mold having a third linkage mechanism for opening the mold stations by different stroke lengths; FIGs. 4A-4H illustrate a two-level stack mold having a fourth linkage mechanism for opening the mold stations by different stroke lengths; FIGs. 5A-5D illustrate a two-level stack mold having a fifth linkage mechanism for opening the mold stations by different stroke lengths; FIGs. 6A and 6B illustrate a linkage mechanism for opening the mold stations of a four-level stack mold by unequal stroke lengths; FIGs. 7A and 7B illustrate an alternative linkage mechanism for opening the mold stations of a four-level stack mold by different stroke lengths; FIGs. 8A and 8B illustrate another embodiment of an adjustable linkage mechanism in accordance with the present invention for opening a molding station of a stack mold; and FIGS. 9A and 9B illustrate still another embodiment of an adjustable linkage mechanism in accordance with the present invention for opening a molding station of a stack mold. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S) Referring now to the drawings, FIGS. 1A - 1C illustrate a portion of an injection molding machine having a two level stack mold arrangement 10 for molding different sized parts having a linkage mechanism 12 for allowing the mold stations A and B to be opened by unequal distances or strokes. The two level stack mold 10 is shown mounted in a clamp and comprises a stationary or fixed platen 14, a moving platen 16, four tiebars 18, and a movable center section carrier 20. The tiebars 18 extend between the stationary platen 14 and a clamp block (not shown). The moving platen 16 and the movable center section carrier 20 are slidable along the tiebars 18. Alternatively, the moving platen 16 and the movable center section carrier 20 could be slidable on a clamp base (not shown) with the tiebars 18 passing through or around them. The stack mold has two mold sections A and B. Mold section A is formed by a mold core plate or mold half 22 and a mold cavity plate or mold half 24. The mold core plate 22 is mounted to the stationary platen 14, while the mold cavity plate 24 is mounted to one side of the center section carrier 20. Plate 22 and plate 24 may be mounted to the platen 14 and the carrier 20 using any suitable means known in the art. When closed together (a mold closed position), the two plates 22 and 24 define a first mold cavity space into which a material to be molded is injected. Similarly, stack mold section B is formed by a mold core plate or mold half 26 and a mold cavity plate or mold half 28. The mold core plate 26 is mounted to one side of the moving platen 16, while the mold cavity plate 28 is mounted to one side of the center section carrier 20. As before, plate 26 and plate 28 may be mounted to the platen 16 and the carrier 20 using any suitable means known in the art. When closed together (the mold closed position), the plates 26 and 28 define a second mold cavity space into which a material to be molded is injected. The mechanism for injecting the material to be molded into the first and second mold cavity spaces does not form part of the present invention and therefore has not been shown. Any suitable molten material injection system known in the art may be used to inject molten material, such as molten plastic material, into the cavity spaces. The mold sections A and B move between the mold closed positions shown in FIG. 1A and the mold open positions shown in FIG. 1C as a result of the movable platen 16 being moved away from the stationary platen 14. This may be accomplished by applying an opening force to the platen 16 via a column 30. Any suitable actuation means known in the art, such as a piston-cylinder arrangement (not shown), may be used to move the platen 16 relative to the platen 14. The actuation means (not shown) is also used to move the mold sections A and B from the open position to the closed position. In the machine shown in FIGS. 1A - 1C, the mold station A is forming a lid and the mold station B is forming a bucket. The opening stroke LA of mold station A required to eject or release the lid can be much less than the opening stroke LB of mold station B required to release or eject the bucket. As used herein, the term "opening stroke" refers to the distance between the mold plates when a particular mold section is in an open position. In this embodiment, the stack mold 10 is provided with a linkage mechanism 12 to cause the mold stations A and B to have different or unequal opening strokes LA and LB respectively. The linkage mechanism 12 includes a central link member 32 pivotably connected to the center section carrier 20 and a link arm 34 which is connected at one end to the central link member 32 and at the second end to the stationary platen 14. The link arm 34 is preferably connected to the central link member 32 by a pin so that the angular relationship between these two structures can be changed. The linkage mechanism 12 further includes a second link arm 36 and a third link arm 38, which pivots about a boss 40 fastened to the moving platen 16 by a member 41. The link arm 36 is mounted to pivot point 42 on the third link arm 38 which can be moved to one of several available positions 44, 46, and 48, each offering a different radius of motion, and thereby a different distance for the motion of the end of the link arm 36. A cylinder 50 is mounted to the moving platen 16, which cylinder moves or actuates the second link arm 36. In operation, as the moving platen 16 opens the mold (see FIG. 1B), the linkage mechanism 12 causes both molds to begin opening. When the moving platen 16 reaches a preselected position, the cylinder 50 is actuated by a programmed controller (not shown) to cause the third link arm 38 to rotate through a preselected arc, thereby altering the end position of the second link arm 36. This, in turn, causes mold section B attached to the moving platen 16 to continue opening further than mold section A attached to the stationary platen 14. Mold section B opens at a different speed than mold section A because of the additional motion of the third link arm 38. The procedure is reversed to cause the molds to close. The structure of the programmed controller does not form part of the present invention and therefore has not been described in detail. In fact, any conventional programmable controller known in the art may be used to actuate cylinder 50. Both the timing of the actuation and the speed of motion of cylinder 50 can be programmed to occur at any time during the open stroke of the moving platen 16, thereby causing the two mold sections A and B to open differing or unequal distances at differing speeds as required. Any suitable ejection means (not shown) known in the art may be provided to eject or remove the molded articles from the mold stations A and B when the mold stations reach the position shown in FIG. 1C. FIGS. 2A - 2D illustrate another embodiment of a linkage mechanism 112 for causing the mold stations A and B of a two level stack mold 110 to open with different or unequal stroke lengths. The basic components of the stack mold 110 are the same as in FIGS. 1A - 1C. For example, a column 30 is provided to move the moving platen 16 relative to the stationary platen 14 and thereby open and close the mold stations A and B. Further, the linkage mechanism 112 includes a central link member pivotably connected to the central section carrier 20 and a link arm 34 which is connected to the stationary platen 14 at one end and to the central link member 32 at its opposite end. As shown in FIG. 2A, shoes 35 are mounted to both sides of the carrier 20 by brackets 37. The shoes 35 facilitate sliding along the lower tiebars and prevent tipping and rocking. The brackets 37 may be attached to the carrier 16 by any suitable means known in the art such as bolts or screws. A similar shoe arrangement may be provided on platen 16 if desired. In this alternative embodiment however, a frame 114 is supported by, and slides on, the tiebars 18. The frame 114 carries the end of the link arm 36 in a bracket 116. The bracket 116 is selectively gripped or released by a clamp 118 mounted on the moving platen 16. In operation, the mold is operated so that movement of the platen 16 in a direction away from the platen 14 causes the mold stations A and B to open, initially by an identical stroke (See FIG. 2B). The controller (not shown) is programmed however so that when the moving platen 16 reaches a preselected position as it moves from the mold closed to the mold open position, the bracket 116 is released from the clamp 118, thus freeing the link arm 36 and allowing the mold section B to continue opening further while mold section A stops opening. When the moving platen 16 reaches a preselected position as it moves from the mold open position to the mold closed position, the bracket 116 is automatically reengaged by the clamp 118 so that the link arm 36 operates normally during the closing stroke. The clamp 118 may comprise any suitable clamping means known in the art. For example, the clamp 118 may have fluid actuated surfaces which grip the bracket 116. A third embodiment of a linkage mechanism 212 for allowing the mold stations A and B of a two level stack mold 210 to be opened with unequal stroke lengths is shown in FIGS. 3A - 3D. The basic components of the stack mold 210 are identical to those shown in FIGS. 1A -1C. For example, a column 30 is provided to move the platen 16 relative to the stationary platen 14 from the mold closed position shown in FIG. 3A, through the mold open position in FIG. 3B, to the final mold open position in FIG. 3C where the mold stations A and B have been opened by unequal stroke lengths. The linkage mechanism 212 includes a central link member 32 pivotably connected to the central section carrier 20 by a central pinion 33 and a first link arm 34 connected at one end to the stationary platen 14 and at the other end to an end of the central link member 32 by a conventional pivot bearing. In this embodiment however, the linkage mechanism 212 is different in that it includes a slide bar 214 slidably mounted to the moving platen 16 and pivotally attached to the second link arm 36 by a conventional pivot bearing. The slide bar 214 may be slidably mounted to the moving platen using any suitable means known in the art and is preferably restrained to slide only in a horizontal motion. As shown in FIG. 3D, a block 702 is bolted to either the mold platen 26 or the machine platen 16. The block contains a plurality of bearing pads 704 which allow the slide bar 214 to move freely horizontally through the block 702. The bearing pads 704 may comprise bronze wear plates. A cover 706 is provided to protect the slide bar 214 and the bearing pads 704. A cylinder 50, controlled by a programmable controller (not shown), is connected to the slide bar 214 by two links 216 and 218. Actuation of the cylinder 50 extends and retracts the slide bar relative to the moving platen 16. In operation, the cylinder 50 is actuated during the opening stroke when the moving platen 16 reaches a preselected position such as that shown in FIG. 3B. The cylinder 50 then retracts the arm 220 causing the slide bar 214 to extend and thereby increase the opening stroke of mold station B without increasing the opening stroke of the mold station A. When the moving platen 16 is moved by the column 30 to the mold closed position, the cylinder 50 is again actuated when the platen 16 reaches a preselected position. The actuated cylinder 50 extends the arm 220 causing the links 216 and 218 to retract the slide bar 214. Referring now to FIGS. 4A - 4F, a fourth embodiment of a linkage mechanism 312 for permitting the mold stations of a two level stack mold 310 to open with different stroke lengths is illustrated. Here again, the basic components of the two stack mold 310 are identical to those shown in FIGS 1A - 1C. The mold 310 includes a stationary platen 14, a central section carrier 20 and a moving platen 16 which is caused to be moved by column 30 from a mold closed position (See FIG. 4A) to a position where the mold stations A and B are opened by the same distance (FIG. 4B) to a final mold open position (FIG. 4C) where the mold stations A and B have been opened by different or unequal stroke lengths. The linkage mechanism 312 includes a central link member 32 pivotably connected to the central section carrier 20, a first link arm 34 connected at one end to the stationary platen 14 and at the other end to the central link member 32, and a second link arm 36 connected to the opposite end of central link member 32. In this embodiment, the link arm 36 is connected to one end of a bar 314. The bar 314 slides through a bracket 316 mounted to the moving platen 16. The bar 314 has a recess 318 which is engaged by a locking unit 320. The locking unit 320 includes a block 322 which engages the recess 318 and an actuator 324 to move the block 322 between an engaged position (See FIG. 4A) and a disengaged position (See FIG. 4C). As shown in FIGS. 4D - 4H, a cylinder 50 is mounted to the moving platen 16. As before, the cylinder is actuated by a programmable controller (not shown). The cylinder 50 may be connected to the bar 314 by any one of the linkages 326, 326' or 326". As shown in FIGS. 4D and 4G, the linkage 326 comprises two pivotally connected first and second link arms 328 and 330 mounted within an end portion of the bar 314.The first and second link arms 328 and 330 are connected to the cylinder 50 via the arm 332. As shown in FIG. 4E and 4H, the linkage 326' includes two pairs of links 334 and 336 attached to opposite sides of the bar 314. Each pair of links 334 and 336 is connected by a bracket 338 and an arm 340 to the cylinder 50. As shown in FIG. 4F, the linkage 326" comprises two links 342 and 344 mounted to an upper surface of the bar 314. The links 342 and 344 are connected to the cylinder 50 by a bracket 346 and the arm 348. The machine may be programmed so that during the opening stroke, when the moving platen 16 reaches a preselected position, the actuator 324 is actuated to move the block 322 from a recess engaging position to a recess disengaged position. Further, the cylinder 50 is actuated to move the bar 314 via linkage 326, 326' or 326" so as to extend the opening stroke of the mold station B. During the closing stroke, when the moving platen 16 reaches a preselected position, the cylinder 50 is actuated to retract the bar 314 and the actuator 324 is actuated to cause the block 322 to engage the recess 318. FIGS. 5A -5D shows a fifth embodiment of a linkage mechanism 412 for causing the mold stations A and B of a two level stack mold 410 to open with different or unequal stroke lengths. As in the other embodiments, the basic components of the two level stack mold 410 are identical to those shown in FIGS. 1A - 1C. Further, the moving platen 16 is moved between a mold closed position and a mold open position and vice versa as previously discussed. The linkage mechanism 412 is different from the linkage mechanisms shown in the previous embodiments. The linkage mechanism 412 is formed by channel 414 mounted on a center pivot 416 attached to the central mold section or carrier 20. As can be seen in FIG. 5D, the channel 414 has a central passageway 415. The linkage mechanism 412 further includes a center arm 418 mounted inside the channel 414. The center arm 418 is connected to first and second link arms 422 and 424 which are in turn respectively connected to the stationary platen 14 and the moving platen 16. The center arm 418 has a plurality of through slots 417 and can be adjustably slid through the passageway 415 such that the distance between its ends and the center, L1 and L2, can be altered such that they are unequal. Once adjusted, the center arm 418 can be locked in position with respect to the channel 414 by using suitable through pins 420 which pass through two slots 417 in arm 418. This configuration of a linkage mechanism provides the means to cause the mold sections A and B to travel different opening strokes S1 and S2 such that the mold station A has a different opening stroke from mold station B. FIGS. 6A and 6B show a four level stack mold 510 using the linkage mechanism 12 shown in FIGS. 1A - 1C. The mold 510 includes a stationary platen 14, two central section carriers 20 and two moving platens 16. The mold 510 also includes columns 30 attached to the moving platens 16 for moving the mold stations A, B, C, and D between mold closed (FIG. 6A) and mold open (FIG. 6B) positions. Any suitable mechanism known in the art for moving the platens 16 can be connected to the columns 30. Four mold stations A, B, C, and D are formed by mold core plates and mold cavity plates mounted to the platens 14 and 16 and the central section carriers 20. The four mold stations can be opened simultaneously using the linkage mechanism 12 with stations A and D being opened differing amounts from mold stations B and C and from each other since cylinders 50 and 50' can be programmed to operate with different strokes. FIGS. 7A and 7B illustrate yet another linkage mechanism 612 for opening the mold stations of a four level stack mold 610 by different or unequal stroke lengths. The basic components of the four level stack mold 610 are identical to the components described in connection with the embodiment of FIGS. 6A and 6B. Similarly, the method for causing the moving platens 16 to move from a mold closed position (FIG. 7A) to a mold open position (FIG. 7B) and vice versa is the same as that previously discussed. The linkage mechanism 612 includes racks 614, 616, 618 and 619 mounted to the platens 16, 14 and 16' respectively. The linkage mechanism 612 also includes gears 620 and 622 mounted to central section carriers 20 and 20' respectively, a central link member 32 pivotally mounted to the stationary platen 14, and link arms 34 and 34'. The link arms 34 and 34' are each connected at one end to the central link member 32 and at a second end to one of the gears 620 and 622. The link arm 34 preferably has a longer length than the link arm 34'. The gears 620 and 622 preferably have different diameters such that when they engage their respective racks, they cause the mold sections on which the racks are mounted to move different distances D1 and D2 as shown in FIG. 7B. FIGS. 8A and 8B illustrate yet another linkage assembly 712 for opening the mold stations of a stack mold such as that shown in FIGS. 1A and 1B by different or unequal stroke lengths. The linkage assembly 712 could be used in lieu of link 34 and/or the combination of link 36, rotatable link element 38, member 41 and cylinder 50. As shown in FIGS. 8A and 8B, the linkage assembly 712 includes a first link 736 formed by spaced apart arms 738 and 740. The link 736 is connected to the central link member 32 by pin connection 742. Pin connection 742 may comprise any suitable connection known in the art which allows relative rotational movement between central link member 32 and linkage assembly 712. As before, central link member 32 may be pivotally connected to a central section carrier such as carrier 20. Each of the arms 738 and 740 is provided with two rows of offset bores 744. The linkage assembly 712 further includes an adjustable link arm 746 which is joined to at least one of the platens such as moving platen 16. The arm 746 may be joined to the platen by any suitable means known in the art which allows rotational movement between the arm 746 and the platen. In a preferred embodiment, the arm 746 has an aperture 748 into which a bushing 750 and a surrounding self lubricating bearing 752 are inserted. Thrust washers 754 are then placed adjacent the sides of the arm 746. The arm 746 may be pivotably joined to the platen by press fitting the bushing 750 into the platen and securing the arm 746 to the bushing by pin member 756. The end 758 of the arm 746 opposed to the end containing aperture 748 is positioned between arms 738 and 740. A plurality of pins or bolts 760 are placed into the bores 744 and tightened so as to cause a frictional engagement between the arm 746 and the arms 738 and 740. By providing this type of frictional engagement, there are an infinite number of positions of the arm 746 relative to the arms 738 and 740. Further, the adjustments can be easily made by loosening the pins or bolts 760 and retightening them. The connection between the pins or bolts 760 and the bores 744 may be a threaded connection or any other suitable connection known in the art. The principal advantage of this linkage assembly is that the stroke length may be easily adjusted manually as required to mold a certain part. By positioning arm 746 in a desired location relative to the arms 738 and 740, the length L between the center of pin connection 742 and the center of bushing 750 can be increased or decreased as needed. FIGS. 9A and 9B illustrate an alternative embodiment of the linkage assembly 712. In this embodiment, the arms 738 and 740 are each provided with only one row of bores 744. The type of linkage assembly may be used with small, lightweight molds, while the linkage assembly of FIGS. 8A and 8B may be used on heavier molds or where a higher degree of frictional engagement is required. Besides ease of assembly and adjustment, the linkage assembly 712 has the virtue of being easy to manufacture. Further, existing stack mold machines can be retrofitted with it. While the present invention has been described with reference to a number of linkage mechanism examples mounted directly to the mold sections, it should be apparent that the linkage mechanisms can equally be mounted on carriers that remain part of the molding machine after the mold sections have been removed or changed. Further, it should be recognized that the linkage mechanisms disclosed herein are designed to be adjustable in that the various different strokes they cause can be altered for different mold section installations by either simple control changes or by changing out a few components in the mechanism, such as the different gear diameters of the embodiment of FIGS. 7A and 7B. Thus, the linkage mechanisms taught herein are universal in their application to stack molds having two or mold sections. While the invention has been described in the context of a single article being molded at each mold station, it should be apparent that multiple articles could be molded at each station.

Claims: An injection molding machine comprising: a stationary platen (14), a movable center section carrier (20) movable relative to the stationary platen (14) and a moving platen (16) also movable relative to the stationary platen (14), the movable center section carrier (20) having: a first face facing a first complementary face of the stationary platen (14); and a second face facing a second complementary face of the moving platen (16); the injection molding machines further comprising: a linkage mechanism (12) for moving said movable center section carrier (20) and said moving platen (16) between respective first positions and second positions, the first positions being where a separation between the stationary platen and a respective one of the movable center section carrier (20) and said moving platen corresponds, in use, to a mold open position and the second position being where a separation between the stationary platen and the respective one of the movable center section carrier (20) and said moving platen corresponds, in use, to a mold closed position; the injection molding machine characterized in that : the linkage mechanism (12) includes means for separating the movable center section carrier (20) and the moving platen (16) from the stationary platen (14) by unequal stroke distances such that separations attained, in use, at the mold open positions between the first face and the first complementary face and between the second face and the second complementary face are different from each other. The injection molding machine according to claim 1, further comprising first and second mold assembles each formed from a pair of mold halves, (22, 24; 26, 28) each mold half of the first mold assembly being held in one of the first face and the first complementary face and each mold half of the second mold assembly being held in one of the second face and the second complementary face and wherein mold shut heights of the first and second mold assemblies are different from each other. The injection molding machine according to claim 1 or 2, wherein the separating means comprises first means (34) for separating the movable center section carrier (20) from the stationary platen (14) by a first stroke distance and second means (36, 38) for separating the movable center section carrier (20) from the moving platen (16) by a second stroke distance which is greater than the first stroke distance. The injection molding machine of claim 3, further comprising means (50) for actuating said second means (36, 38) when one of said movable platen (16) or said movable center section carrier (20) reaches a preselected position. Machine according to claim 3 or 4, wherein: said first means comprising a linkage assembly pivotally connected to said central section carrier (20); and said second means comprising a rotatable link arm (38) mounted to said movable platen (16) and connected to said linkage assembly. Machine according to claim 5, further comprising means for causing said rotatable link arm (38) to rotate when said movable platen has reached a preselected position, said means for causing said rotatable link arm (38) to rotate comprising an actuation cylinder(50) mounted to said movable platen. Machine according to claim 5 or 6, wherein: said linkage assembly comprises a central link member (32) pivotably connected to said central section carrier (20) and a first link arm (34) connected to a first end of said central link member (32) and to said stationary platen (14); and said second means further comprises a second link arm (36) connected to a second end of said central link member and to said rotatable link arm (38), said second link arm (36) being pivotally connected to said rotatable link arm (38) so that said second link arm (36) and the rotatable link arm (38) can change their angular relationship to each other. Machine according to claim 7, wherein: said rotatable link arm (38) has a plurality of spaced slots (42-48) for changing the distance said movable platen can travel; and said second link arm (36) is connected to said rotatable link arm (38) by a pin which passes through one of said slots. Machine according to claim 3, further comprising: a plurality of tiebars (18); said first means comprising a linkage assembly (112) connected to said central section carrier (20); and said second means comprising a bracket (116) connected to said linkage assembly (112) and means (118) for releasably clamping said bracket member to said movable platen. Machine according to claim 9, wherein: said releasable clamping means (118) is operable to release said bracket when said movable platen reaches a preselected position; said linkage assembly including a central link (32) connected to said central section carrier (20) and a first link arm (34) connected to a first end of said central link and to said stationary platen; said second means further comprising a second link arm (36) connected to a second end of said central link and to said bracket, and a movable frame (114) attached to said second link arm (36) for carrying an end thereof. Machine according to claim 3, wherein: said first means comprises a linkage assembly (212) connected to said central section carrier (20); and said second means comprises a bar (214) attached to said linkage assembly, said bar (214) being slidably mounted to said movable platen (16). Machine according to claim 11, wherein said second means further comprises an actuation unit and first (216) and second (218) links each connected to said actuation unit and to said bar and wherein said actuation means causes relative movement between said bar and said movable platen when said movable platen reaches a preselected position and wherein said linkage assembly comprises a central link member (32) connected to said central section carrier (20) and a first link arm (34) connected to said stationary platen and to a first end of said central link member (32), and said second means further comprises a second link arm (36) connected to a second end of said central link member and to an end of said bar (214). Machine according to claim 3, wherein: said first means comprises a linkage assembly (312) connected to said central section carrier (20); and said second means comprising a bar (314) connected to said linkage assembly, said bar and said movable platen being movable relative to each other. Machine according to claim 13, further comprising: said bar having a recess (318) ; and said movable platen having a locking unit (320) for securing said bar in a fixed position relative to said movable platen by engagement with said recess, wherein said locking unit disengaging from said recess when said movable platen reaches a preselected position, thereby allowing relative movement between said movable platen and said bar. Machine according to claim 13, further comprising: means for causing relative movement between said bar and said movable platen when said movable platen reaches a preselected position, said relative movement causing means comprising an actuator (324) connected to said movable platen and first (328) and second (330) link arms, each of said link arms being connected to said actuation unit at one end and to said bar at a second end. Machine according to claim 13, wherein said linkage assembly (312) comprises a central link member (32) pivotally connected to said central section carrier (20) and a first link arm (34) connected to said stationary platen and to a first end of said central link member and said second means further comprises a second link arm (36) connected to a second end of said central link member and to an end of said bar. Machine according to claim 1 or 2, wherein: said separating means comprises a channel (414) pivotally connected to said central section carrier at a center pivot (416), a center arm (418) positioned within said channel and being movable relative to said channel so that the distance between its ends and said pivot point can be changed, a first link arm (422) attached to one end of said center arm and said stationary platen and a second link arm (424) attached to a second end of said center arm and said movable platen. Machine according to claim 17, further comprising: said center arm (418) having a plurality of slots (417) for allowing the position of said center arm relative to said channel member to be changed; and pins (420) for securing said center arm in a desired position relative to said channel member, said pins passing through at least two of said slots. Machine according to claim 1 or 3, in which: said machine has four movable members including two central section carriers (20) and two movable platens (16); said first means comprising a linkage assembly (12) pivotally connected to each of said central section carriers; and said second means comprising a rotatable link arm (38) mounted to each of said movable platens (16) and connected to a respective one of said linkage assemblies (12). Machine according to claim 19, further comprising actuation means for causing each said rotatable link arm to rotate when said movable platen to which it is connected has reached a preselected position, said actuation means for causing each said rotatable link arm to rotate comprises an actuation cylinder (50, 50') mounted to each said movable platen (16). Machine according to claim 19, wherein: each said linkage assembly (12) comprises a central link (32) pivotably connected to a respective one of said central section carriers (20) and a first link arm (34) connected to a first end of said central link member and to said stationary platen (14); and said second means further comprises a second link ann (36) connected to a second end of said central link member and to said rotatable link arm (38), each said second link arm (36) being connected to a respective one of said rotatable link arms (38) so that said second link arm and the rotatable link arm (38) change their angular relationship relative to each other. Machine according to claim 1 or 3, further comprising: four movable members including two central section carriers (20) and two movable platens (16); four mold assemblies formed by mold halves attached to said stationary platen, said central section carriers (20) and said movable platens; said separating means comprising a plurality of racks (614, 616, 618, 619) attached to said stationary platen and said movable platens, gear means (620, 622) mounted to said central section carriers for engaging said plurality of racks, and a linkage assembly (612) pivotably mounted to said stationary platen; said linkage assembly (612) being rotatably mounted to said stationary platen and having a first link arm (34') connected to a first one of said gears and a second link arm (34) connected to a second one of said gears, said second link arm being longer than said first link arm, whereby rotation of said linkage assembly causes two of said mold assemblies to be separated by a first stroke distance and causes the remaining two of said mold assemblies to be separated by a second stroke distance greater than said first stroke distance. Machine according to claim 22, wherein said gear means (620, 622) comprises two gears, and one of said gears having a larger diameter than the other of said gears and wherein said linkage assembly includes a central link member (32) rotatably mounted to said stationary platen and each of said first and second link arms (34, 34') being connected to a respective end of said central link member. Machine according to claim 3, wherein at least one of said first and second means is formed by a manually adjustable linkage assembly (712). Machine according to claim 24, wherein said manually adjustable linkage assembly (712) comprises two spaced apart arms (738, 740) each connected to an actuator connected to a first one of said movable members and a third arm connected to at least one of said stationary platen and a second one of said movable members and each of said two spaced apart arms has a plurality of bores (744) and said third arm is positioned between said two spaced apart arms and said linkage assembly further comprises at least one pin connection (742) for creating frictional engagement between said third arm and said two spaced apart arms. Machine according to claim 25, wherein said spaced apart arms and said third arm define a stroke length which may be changed by positioning said third arm in a number of different positions relative to said spaced apart arms. A method of fabricating molded articles using a stack mold machine having a stationary platen (14) and at least two movable members (16, 20) movable relative to said stationary platen (14), the stack mold machine further having at least two mold assemblies formed by mold halves (22, 24, 26, 28) attached to said stationary platen and said at least two movable members (16, 20), the method comprising: while said at least two mold assemblies are in a mold closed position, forming said molded articles by injecting melt into at least one cavity formed within each of said mold assemblies; separating the mold halves (22, 24, 26, 28) of said at least two mold assemblies by moving the least two movable members relative to the stationary platen, the at least two movable members moved to a mold open position where said molded articles are to be ejected; the method characterized in that : separating the mold halves to respective mold open positions results in the mold halves of the first mold assembly being separated by a first stroke distance and the mold halves of the second mold assembly being separated by a second stroke distance larger than the first stroke distance. The method according to claim 27, wherein the step of separating comprises separating said mold halves forming the first mold assembly at a first rate of speed different from a second rate of speed used to separate the mold halves forming the second mold assembly. The method according to claim 27, wherein said step of separating said mold halves forming the second mold assembly includes actuating a rotatable link to increase the stroke distance when one of said at least two movable members reaches a preselected position, the rotatable link mounted to said one movable member. A linkage assembly (12) for mounting, in use, to a center-section carrier (20) of a stack mold, the center section carrier (20) arranged to be positionable and movable between a stationary platen (14) and a moving platen (16) of an injection molding machine, the linkage assembly (12) comprising: a central link member (32) centrally rotatably mountable to the center section carrier (20), the central link member (32) having a first end and a second end; a first link arm (34) pivotally coupled to the first end of the central link member, the first link arm (34) arranged to be connectable, in use, to the stationary platen to effect relative displacement of the central section carrier (20) with respect to stationary platen (14) by a first distance; and a second link arm (36) having a first end and a second end, the first end of the second link arm (36) pivotally coupled to the second end of the central link member (32); the linkage assembly characterized by : a linkage sub-assembly (38, 50. 116, 214, 218, 424) coupled to the second end of the second link arm (36), the linkage sub-assembly configured to be connectable, in use, to the moving platen, the linkage sub-assembly providing means for allowing the moving platen (16) to be displaced from the center-section carrier (20) by a second distance greater than the first distance, thereby permitting an injection molding machine fitted with the linkage assembly (12) to operate with differing opening stroke distances. A stack mold assembly for mounting, in use, between a stationary platen (14) and a moving platen (16) of an injection molding machine, the stack mold assembly comprising: a center-section carrier (20) having a first face and a second face each arranged to receive, in use, a mold half; a central link member (32) rotatably mountable to the center section carrier (20), the central link member (32) having a first end and a second end; a first link arm (34) pivotally coupled to the first end of the central link member, the first link arm (34) arranged to be connectable, in use, to the stationary platen to effect relative displacement of the first face central section carrier (20) with respect to stationary platen (14) by a first distance; and a second link arm (36) having a first end and a second end, the first end of the second link arm (36) pivotally coupled to the second end of the central link member (32); the stack mold characterized by : a linkage sub-assembly (38, 50. 116, 214, 218, 424) coupled to the second end of the second link arm (36), the linkage sub-assembly configured to be connectable, in use, to the moving platen, the linkage sub-assembly providing means for allowing the moving platen (16) to be displaced from the second face of the center-section carrier (20) by a second distance greater than the first distance, thereby permitting an injection molding machine fitted with the stack mold to operate with differing opening stroke distances between the first face and the stationary platen (16) and the second face and the moving platen. The linkage assembly according to claim 30 or the stack mold assembly of claim 31, wherein the linkage sub-assembly includes one of: a third arm (38) and a cylinder (50) combination, the third arm (38) coupled to the second end of the second link arm (36) and connectable, in use, to the moving platen (16), the cylinder (50) arranged to be connected to the moving platen (16), the cylinder further including an arm pivotally connected to the third arm; and a bracket (116) and a frame (114) combination, the bracket coupled to the second end of the second link arm (38), the bracket further having a clampable end portion, the frame (114) also coupled to the second link arm (36), the frame arranged to carry the bracket (116) and the second link arm (36).

Inventors: SCHAD ROBERT D, TENG ALEX, SCHAD, ROBERT D., TENG, ALEX
Applicants: HUSKY INJECTION MOLDING, HUSKY INJECTION MOLDING SYSTEMS LTD.
Application year: 1999
Main classification: B29C45
IPC codes: B29C45