Process and apparatus for molding plastic articles

Abstract: Molded plastic articles are prepared in accordance with the process and apparatus of the present invention. A first mold cavity is filled via a feeding unit in engagement with a first mold cavity with plastic containing a volume expanding agent, the filled first mold cavity and feeding unit are moved away from each other and a second mold cavity and the feeding unit are moved into engagement with each other, the second mold cavity is filled with plastic containing a volume expanding agent via the feeding unit, the plastic is expanded in the first mold cavity via the volume expanding agent while the second mold cavity is in engagement with the feeding unit, and the expanded article is ejected from the first mold cavity.

Description: CROSS-REFERENCE TO RELATED APPLICATION This application claims the benefit of Provisional Application Serial No. 60/069,640 for PROCESS AND-APPARATUS FOR MOLDING PLASTIC ARTICLES, filed December 15, 1997. BACKGROUND OF THE INVENTION The present invention relates to a method and apparatus for making plastic articles, especially wine corks, from plastic resin in a continuous and efficient operation. Articles such as wine corks as well as others are made using a plastic resin which contains a blowing agent such that after injection of the resin into a mold cavity gas bubbles are formed in the plastic resin. The plastic resin expands in volume as the mold cavity volume is allowed to expand. Plastic wine corks are particularly useful as they represent an alternative to cork for sealing wine bottles. These and other articles may be prepared by the process described above which is termed "foam molding". This process and apparatus requires that the mold cavity can expand to allow Gas bubbles to form in the resin as it cools. This is shown in US-A-4 413 744. Unfortunately, however, this procedure takes a substantial amount of time as cooling a relative this part, particularly a relatively thick part that contains gas bubbles therein, is inherently slow especially due to the very poor thermal transmission properties of the gas filled plastic. SUMMARY OF THE INVENTION The main object of the present invention is to provide an efficient and expeditious process and apparatus for preparing relatively thick plastic parts containing gas therein. Another object of the present invention is to provide a process and apparatus as aforesaid for efficiently and expeditiously preparing such relatively thick plastic parts, as plastic wine corks. A further object of the present invention is to provide a process and apparatus as aforesaid that separates the cooling phase of the molding cycle from the remainder of the cycle allowing the operation to be more effectively performed. The present invention performs the molding operation in a first state of the cycle. Subsequent stages permit mold cavity expansion, article cooling and article expansion while at the same time permitting the molding of further articles. The final stage of the cycle is the ejection of the cooled and expanded article. Thus, the present invetnion efficiently permits the continuous formation of additional articles while the initially formed article or articles continue their processing steps, as by cooling expansion and ejection. Thus, the present invention comprises a process for preparing a molded article, as for example wine corks, which comprises: injecting plastic containing a volume expanding agent into a first mold cavity via a feeding unit in engagement with said first mold cavity; moving the first mold cavity with injected plastic therein and feeding unit away from each other, moving a second mold cavity and said feeding unit into engagement with each other and injecting plastic containing a volume expanding agent into said second mold cavity via said feeding unit; expanding to volume of said plastic in said first mold cavity via said volume expanding agent while said second mold cavity is in engagement with said feeding unit including the step of expanding the first mold cavity to provide space therein for expansion of the volume of said plastic; and ejecting the expanded article from the first mold cavity; whereby said first and second mould cavities are carried and moved on a holding means. The present invention also comprises an apparatus for forming a molded article, which comprises: first and second mold cavities spaced from each other for forming molded articles; a feeding unit for separately feeding plastic containing a volume expanding agent into said first and second mold cavities; means for separately moving said first and second mold cavities and said feeding unit into and out of engagement with each other; wherein said plastic is expanded in said first mold cavity via said volume expanding agent and via means of expanding the first mold cavity to provide space therein for expansion of the volume of said plastic while said second mold cavity is in engagement with said feeding unit; and means for ejecting the expanded article from the first mold cavity; and a holding means for carrying said first and second mould cavities operative to move said first and second mould cavities. Further features of the present invention will appear hereinbelow. BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be more readily understood from a consideration of the accompanying drawings, wherein: Figure 1 is a partly schematic, sectional view of the present invention in a mold closed position and during injection; Figur 2 is a partly schematic sectional view of a further stage of the present invention in a mold open position with the mold closing slides in the closed position; Figure 3 is a partly schematic, sectional view of a further stage of the present invention after a frist 90 degree rotation of the mold; Figure 4 is a partly schematic, sectional view of a still further stage of the present invention after a second 90 degree rotation of the mold; Figure 5 is a partly schematic, sectional view of a still further stage of the present invention after a third 90 degree rotation of the mold and with ejection of the final part; and Figure 6 is a partly schematic, sectional view of the present invention showing a multi-cavity block with each face having four cavities. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS The process and apparatus of the present invention preferably uses a machine and process where the mold indexes to different positions, such as shown in copending U.S. Patent Application Serial No. 08/611,362, Referring to Figure 1 herein, mold block 10 contains a mold cavity 12 therein. Piston 14 slides in mold cavity 12. Mold block 10 is mounted via spacers 16 to machine turret block 18 which in turn is mounted on a slidable carriage (not shown) which moves towards and away from stationary platen 20 of the injection molding machine. Mounted to the stationary platen 20 is hot runner block 22 which in turn contains hot runner manifold 24 and conventional valve gated hot runner nozzle 26 for conveying the heated plastic resin to the mold cavity 12. Mold closing slides 28, 30 are attached to the front of mold cavity 12 and are moved aside to permit access to mold cavity 12 by the closing movement of turret block 18 towards hot runner block 22. The angled faces 32 on slides 28, 30 contact the conical nozzle tip body 34 and move transversely to the closing motion thereby permitting nozzle access to the mold cavity 12. Cylinders (not shown) may be mounted to mold block 10 to act against slides 28, 30 and to urge the slides in a closing motion to maintain a seal against nozzle 26. A clamp force which is generated by known means (not shown) keeps the mold block 10 pressed against hot runner block 22 during injection of the plastic resin into the mold cavity 12. The plastic resin is then injected into mold cavity 12 to fill the cavity. As indicated hereinabove, the plastic resin contains a blowing agent in accordance with known practice. As shown in Figure 2, after the mold cavity 12 is filled with plastic resin, the turret block 18 moves away from stationary platen 20 by cylinders (not shown) in the direction of arrow A, thereby causing slides 28, 30 to close across mold cavity 12 in the direction of arrows B, urged by the slide cylinders (not shown). Simultaneously, piston 14 begins to retract in mold cavity 12 causing the volume of mold cavity 12 to increase. Piston 14 is moved via rod 36 which is connected to plate 38 which in turn is moved by cylinder 40 mounted within turret block 18. Naturally, other means may be used to move piston 14 or to expand the volume of mold cavity 12. As the mold cavity volume increases the pressure acting on the plastic resin in the mold cavity is reduced which allows gas bubbles to form in the plastic resin. After turret block 18 has moved away from stationary platen 20 to provide clearance for rotation of the turret block, the block rotates 90 degrees in the direction of arrow C on rod 41 as shown in Figure 3 to present a new face of mold cavities to be filled in a known fashion (not shown). Naturally, the 90 degree rotation is exemplificative only and other degrees of rotation may be used. In the new position shown in Figure 3, the filled mold cavity 12 continues to expand as piston 14 is retracted all the way to the end of the mold cavity in the direction of arrow D. Retraction to the end of the mold cavity may of course take place in a different stage of the operation. The molded part 42 continues to cool and more gas bubbles form therein. A second rotation of a further 90 degrees as shown in Figure 4 allows the operation to continue as a third set of mold cavities are filled (not shown). In the Figure 3 and Figure 4 position, slides 28, 30 continue to be in the closed position. After a third rotation of a further 90 degrees as shown in Figure 5, mold cavity 12 with cooled part 42 therein is facing downwards and slides 28, 30 are moved aside by their cylinders (not shown) in the direction of arrows E. A further set of articles may then be molded as before. The piston 14 is now advanced its full stroke in the direction of arrow F to push part 42 out of mold cavity 12 as shown in Figure 5. Thereafter, the slides 28, 30 are repositioned to the position shown in Figures 1-4 and turret block 18 rotates a final 90 degrees in the direction of arrow C to begin the cycle again. Figure 6 shows a representative process and apparatus of the present invention with a multi-cavity block with each face showing four mold cavities and with four faces. In fact, if desired, each face could have a plurality of rows of mold cavities, as for example, a 4 X 4 array with therefore 16 mold cavities on each face. Thus, referring to Figure 6, turret block 118 includes four faces 150, 152, 154 and 156. Each face includes four mold cavities 112 with each mold cavity including a piston 114 and with slides 128, 130 associated with each mold cavity. Conventional valve gated hot runner nozzles 126 feed plastic resin into the mold cavities on mold face 150 as shown in Figure 6 while the previously injected molded parts 142 in the mold cavities on mold faces 152 and 154 continue to cool and more bubbles form therein as shown in Figures 3 and 4, and with mold block 118 rotating in the direction of arrow C'. Molded parts 142 in the mold cavities on mold face 156 are then ejected as in Figure 5. Otherwise the operation is similar to that shown in Figures 1-5. Naturally, a different number of mold faces and a different number of cavities may be used, if desired. It is apparent that the present invention represents an efficient and expeditious operation. The time consuming cooling and gas bubble forming part of the cycle is performed outside of the mold filling station, permitting a much more efficient use of equipment and energy and at the same time additional articles are formed permitting a high volume operation. Naturally, other articles in addition to wine corks may be molded in accordance with the present invention.

Claims: A process for preparing a molded article (42, 142), which comprises: injecting plastic containing a volume expanding agent into a first mold cavity (12, 112) via a feeding unit in engagement with said first mold cavity (12, 112); moving the first mold cavity (12, 112) with injected plastic therein and feeding unit away from each other, moving a second mold cavity and said feeding unit into engagement with each other and injecting plastic containing a volume expanding agent into said second mold cavity via said feeding unit; expanding the volume of said plastic in said first mold cavity (12, 112) via said volume expanding agent while said second mold cavity is in engagement with said feeding unit including the step of expanding the first mold cavity to provide space therein for expansion of the volume of said plastic; and ejecting the expanded article (42, 142) from the first mold cavity (12, 112); whereby said first and second mold cavities are carried and moved on a holding means (18, 118). A process according to claim 1, including a plurality of said mold cavities (112) spaced from each other, and separately injecting plastic into each mold cavity (112) while the other mold cavities (112) are spaced from the mold cavity (112) having plastic injected therein. A process according to claim 1, including at least in part moving said mold cavities (12, 112) in a rotary manner. A process according to claim 2, including the step of expanding said plastic in said second mold cavity (12, 112) via said volume expanding agent while a separate mold cavity is in engagement with said feeding unit, and ejecting the expanded article from said second mold cavity. A process according to claim 1, including carrying said mold cavities (12, 112) on a mold block (18, 118). A process according to claim 1, including filling the first and second mold cavities with injected plastic and expanding the mold cavities to provide space therein for expansion of said plastic. A process according to claim 1, including mold cavity orifices for engagement with said feeding unit, and including the step of closing said mold orifices after injecting plastic into said mold cavities ( 12, 112) have been filled. A process according to claim 7, including mold closing slides (28, 30; 128, 130) for closing said mold orifices, including the step of opening said mold closing slides (28, 30; 128, 130) to permit ejection of expanded articles (42, 142) from mold cavities (12, 112). A process according to claim 6, wherein said mold cavities (12, 112) are expanded by expanding elements (14, 114) which are also operative to eject the expanded parts. A process according to claim 1, including greater than two mold cavities (112), wherein one of which is in engagement with said feeding unit while plastic is expanded in at least some of the other of said mold cavities. A process according to claim 1, wherein said mold cavities are expanded by expanding elements within the mold cavities. A process according to claim 7, including the step of providing mold closing slides for opening and closing said mold orifices. A process according to claim 12, wherein engaging the feeding unit with the first mold cavity causes the slides to open said mold orifieces. A process according to claim 13, wherein the slides close said mold orifices upon disengagement of said feeding unit from the first modl cavity. Apparatus for forming a molded article (42, 142), which comprises: first and second mold cavities (12, 112) spaced from each other for forming molded articles (42, 142); a feeding unit for separately feeding plastic containing a volume expanding agent into said first and second mold cavities (12, 112); means for separately moving said first and second mold cavities and said feeding unit into and out of engagement with each other; wherein said plastic is able to be expanded in said first mold cavity (12, 112) via said volume expanding agent and via means (14, 114) of expanding the first mold cavity to provide space therein for expansion of the volume of said plastic while said second mold cavity is in engagement with said feeding unit; means (14, 114) for ejecting the expanded article from the first mold cavity (12, 112); and a holding means (18, 118) for carrying said first and second mold cavities (12, 112) operative to move said first and second mold cavities. Apparatus according to claim 15, including a plurality of said mold cavities (122) spaced from each other, wherein said feeding unit separately feeds said plastic into each mold cavity (112) while the plastic is expanded in at least some of the other mold cavities. Apparatus according to claim 15, wherein said means (18, 118) for moving at least in part moves said mold cavities (12, 112) in a rotary manner. Apparatus according to claim 16, wherein said plastic is expanded in said second mold cavity via said volume expanding agent while a separate one of said mold cavities is in engagement with said feeding unit, and means (14, 114) for ejecting the expanded article from said second mold cavity. Apparatus according to claim 15, including a mold block (18, 118) for carrying said mold cavities (12, 112). Apparatus according to claim 15, including mold orifices for engagement with said feeding unit, and means (28, 30; 128, 130) to close said mold orifices after said mold cavities (12, 112) have been filled. Apparatus according to claim 20, including mold closing slides (28, 30; 128, 130) for closing the mold orifices, wherein said mold closing slides are operative to open to permit ejection of expanded articles (42, 142) from the mold cavities (12, 112). Apparatus according to claim 15, wherein said means (14, 114) for expanding said mold cavities (12, 112) are expanding elements which are also operative to eject the molded parts (42, 142).

Inventors: KOCH MICHAEL, KOCH, MICHAEL
Applicants: HUSKY INJECTION MOLDING, HUSKY INJECTION MOLDING SYSTEMS LTD.
Application year: 1998
Main classification: B29C33
IPC codes: B29C45, B29C44, B29L31, B29K105