CA1332863C - Process for injection molding and hollow plastic article produced thereby - Google Patents
Process for injection molding and hollow plastic article produced therebyInfo
- Publication number
- CA1332863C CA1332863C CA000616657A CA616657A CA1332863C CA 1332863 C CA1332863 C CA 1332863C CA 000616657 A CA000616657 A CA 000616657A CA 616657 A CA616657 A CA 616657A CA 1332863 C CA1332863 C CA 1332863C
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- mold
- gas
- mold cavity
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- Moulds For Moulding Plastics Or The Like (AREA)
Abstract
A process for injection molding hollow plastic articles includes the steps of sequentially injecting fluent plastic and gas into a mold cavity. A quantity of fluent plastic is initially injected to substantially fill the mold cavity. A charge of pres-surized gas is then injected into the mold cavity to displace a portion of the still fluent plastic into a spill cavity flow coup-led to the mold cavity. The article may be formed with an intern-al wall by introducing first and second gas charges into the mold cavity at separate entry points. In one embodiment, the first and second charges are introduced substantially simultaneously. In a second embodiment, the charges are introduced sequentially. After the hollow plastic article has solidified, the gas is vented.
Description
PROCESS FOR INJECTION MOLDING AND
HOLLOW PLASTIC ARTICLE PRODUCED l~K~Y
TECHNICAL FIELD
The present appllcatlon ls a dlvlslon of appllcatlon Serlal No. 605,037 flled July 7, 1989.
Thls lnventlon relates to plastlc ln~ectlon moldlng and artlcles produced thereby, and more partlcularly, to plastlc ln-~ectlon moldlng and plastlc artlcles havlng hollow lnterlor por-tlons produced thereby.
CROSS ~ CE TO RELATED APPLICATIONS
Thls appllcatlon ls related to U.S. patent appllcatlons entltled ~Apparatus and Method for the In~ectlon Moldlng of Thermoplastlcs", S.N. 071,363 flled July 9, 1987 (now U.S. Patent No. 4,781,554 (James W. Hendry) lssued on November 1, 1988);
"Method and Apparatus for the In~ectlon Moldlng of Plastlc Artlcles", S.N. 098,862 flled September 21, 1987 (now U.S. Patent No. 4,855,094 (James W. Hendry) lssued on August 8, 1989) and "Method and System for Locallzed Fluld-Asslsted In~ectlon Moldlng and Body Formed Thereby", S.N. 133,900, flled December 16, 1987 (now U.S. Patent No. 5,069,859 (Norman Loren) lssued on December 3, 1991), all of whlch have the same Asslgnee as the Asslgnee of the present lnventlon.
-la-BACKGROtT~D ART
In the plastic injection molding art, the usual challenges facing a product designer is to design an article having requisite strength for the product application and uniform surface quality for satisfactory appearance, but to avoid excessive weight, material usage and cycle time. A
design compromise must often be made between strength and plastic thickness. A relatively thicker plastic section in the article, such as a structural rib, will incur greater weight, material usage, cycle time and induce sink marks and other surface defects due to thermal gradients in the area of the thickened section It is known in the plastic molding art to use pressurized fluid in conjunction with the plastic molding of articles The pre~urized fluid is typically nitrogen gas which is introAl~ceA into the mold cavity at or near the completion of the plastic injection The pressurized fluid serve several pu~ First, it allows the article so formed to have hollow interior portion~ which ~GLLe_~O~d to weight and material avings Se~ nA, the pres-~urized fluid within the mold cavity applie~ outward pL~ re to force the pla~tic against the mold surfaces while the article ~olidifies Third, the cycle time is re~l~ceA as the gas migrates through the most fluent inner volume of the plastic and replaces the plastic in these area~ which would otherwise require an extended cooling cycle Fourth, the gas yL~ lre r~ the plastic against the mold surfaces, thereby obta ~ n ~ ~g the maximum coolant effect from the mold Howev-r, as the dimensions of the molded article increasQ, the gas must do more work to ~lgrat- through the volume of the mold cavity to assist in setting up the article within the cavity If the prQs-urQ of the ga~ i~ too great as it enters the mold cavity, there is a risk that it may u~ e or blow out th- pla~tic within th~ mold cavity, i e , th- gas is not containeA within the plastic Thus, there have been practical limitations in the adaptation of gas in~ectlon in the plastic molding field DISCLOSURE OF THE INVENTION
Accordlng to one broad aspect of the present lnventlon, there ls provlded a process for ln~ectlon molding a hollow plastlc artlcle lncludlng the steps of ln~ectlng a quantlty of fluent plastlc lnto a mold cavity of a mold havlng a shape deflnlng at least a portlon of the artlcle, lntroductlon of a charge of pres-surlzed gas lnto the mold cavlty upon substantlal completlon of plastlc ln~ectlon, permlttlng the ln~ected plastlc to solldify by supportlng the ln~ected plastlc ln the mold, ventlng the gas from the mold cavity, and removlng the plastlc artlcle from the mold, whereln the lmprovement comprlses: a portlon of the ln~ected plastlc ls supported wlthln the mold by a movable support means of the mold durlng plastlc solldlflcatlon and whereln the step of ventlng ls accompllshed by movlng the support means to a non-support posltlon to allow the gas to burst through the thereby unsupported plastlc portlon.
Wlth reference to preferred embodiments, one aspect of the present lnventlon ls a method for ln~ectlon moldlng hollow plastlc artlcles wlth pressurlzed gas whlch provldes for dlsplace-ment by the gas of a portlon of plastlc from the mold cavlty lnto a flow coupled splll cavlty. Thls feature enables plastlc artl-cles of relatlvely greater dlmenslons to be successfully molded wlth the advantages of establlshed gas ln~ection moldlng tech-niques.
More speclflcally, the process lnvolves the lnltlal ln-~ectlon of a quantlty of fluent plastlc lnto a mold cavlty havlng a shape deflnlng at least a portlon of the plastic artlcle to be 3a molded. At or near the completlon of the plastic in~ection, a charge of pressurized gas is introduced into the mold cavity to displace a portlon of the still fluent plastic. The displaced plastic flows through a passage from the mold cavity into a con-nected spill cavity or reservoir. The reservoir may alternatively serve as: (i) an appendage of the complete article; (ii) a separ-ate article; or (iii) a cavity to receive spilled plastic for re-grinding. The plastic which is displaced is generally the hottest and most fluent. In this regard, the introduction of the charge of pressurized gas into the mold cavity can be timed to modulate the amount of plastic displaced, i.e., the longer the delay in introduction, the cooler and less fluent the plastic in the mold cavity.
In another feature of the invention, the hollow plastic article may be formed with an lntegral internal wall by introduc-tion of two or more charges of pressurized gas. Each gas charge tends to form a cell within the article, and the cells are divided by membranes which serve as integral internal walls to enhance the structural properties of the article.
In yet still another feature of the invent-ing, venting of the gas from the mold cavity is accomplished by moving a support mechanism for a portion of the solidified injected plastic to allow the gas to burst through the unsupported plastic portion at the reservoir, the runner or an incon-spicuous part of the article itself.
The present invention admits to molding of relatively large size structural articles for use in diverse product fields, such as a box-sectioned frame member for an automobile or refrigerator door or the hood of a car having a reenforcing beam.
Other advantages and features of the present invention will be made apparent in connection with the following description of the best mode for carrying out the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGURE 1 is a flow chart indicating the basic steps involved in practice of the process of the present invention;
FIGURE 2 is a schematic side view of a plastic injection molding apparatus adapted to carry out the process of the present invention;
FIGURE 3 is a top plan view of the apparatus of FIGURE 2;
FIGURE 4 is another schematic view of a plastic injection molding apparatus illustrating an alternative arrangement for practicing the process of the present invention;
FIGURE 5 is a side schematic view in cross-section showing still another plastic injection molding apparatus adapted to mold a hollow plastic article having an integral internal wall in accordance with the process of the present inven-tion;
FIGURE 6 is a plan view of the apparatus shown schematically in FIGURE 5:
FIGURE 7 is a view similar to FIGURE 5 wherein the internal wall is displaced from the central location of FIGURE 5;
FIGURE 8 is a plan view of the apparatus of FIGURE 7;
FIGURE 9 is a plan view of yet still another plastic injection molding apparatus;
FIGURE 10 is an enlarged side schematic view of the apparatus of FIGURE 9, partially broken away and illustrating one embodiment of a venting step;
FIGURE 11 is a view similar to FIGURE 10 illustrating a second embodiment of the venting step;
FIGURE 12A is a view similar to FIGURE 10 illustrating a third embodiment of the venting step;
FIGURE 12B is a view of the third embodiment after venting;
FIGURE 13A is a view similar to FIGURE 10 illustrating a fourth embodiment of the venting step;
and FIGURE 13B is a view of the fourth embodiment after venting.
BEST MODE FOR CARRYING OUT THE INV~N'1'10N
FIGURE 1 is a flow chart of the steps involved in practicing the process of the present invention.
In step 10, a quantity of molten plastic is injected from an injection molding machine into a mold cavity. The plastic is any thermoplastic and works particularly well with glass or mineral filled ther-moplastic polyester, commonly known by the trademark Valox of General Electric Co. The quantity is suffi-cient to provide the mass of the article to be molded, but desirably less than the quantity which would fill the mold cavity.
In step 12, a charge of pressurized gas is introduced into the mold upon substantial completion of the injection of the quantity of molten plastic.
In step 14, the gas flow into the mold is maintained in pressure and duration in amount and time sufficient to displace a controlled quantity of plastic from the mold cavity into a spill cavity which is flow coupled to the mold cavity. The gas tends to displace the hottest, most fluent plastic in the central portion of the mold cavity. Consequently, the molded plastic article has a hollow interior where the least viscous plastic has been displaced. The p~s-ence of the gas affords savings in weight and material usage. Added benefits include enhanced surface quality due to the outward pressure exerted by the gas, and reduced cycle time due to displacement of the relatively hot plastic from the central portion of the article.
In step 16, the article is permitted to solidify within the mold cavity while the internal gas pressure is maint~
In step 18, the pressurized gas is vented from the interior of the molded article preparatory to opening the mold. Numerous ways of venting are possible such as described in the U.S. Patent to Friederich 4,101,617 or as described in co-pending patent application Serial No. 071,363 noted above (now U.S. Patent No.
4,781,554 (James W. Hendry) issued on November 1, 1988).
In step 20, the plastic article is removed from the mold.
In step 22, the purged or displaced plastic is removed from the spill cavity or reservoir. In certain cases, steps 20 and 22 can be the common operation of ejecting the moldings so formed from the article cavity and the spill cavity.
FIGURES 2 and 3 are schematic side and plan views, respectively, of a plastic injection molding apparatus, generally indicated at 24, adapted to carry out the process of the present invention.
A nozzle 26 of a plastic injection molding machine is brought into registering position with a modified sprue bushing 28 associated with a mold. The sprue bushing 28 may be of the type disclosed in the above-noted co-pendin-g application Serial No. 098,862 filed September 21, 1987, (now U.S. Patent No. 4,855,094 (James W. Hendry) issued on August 8, 1989). The sprue bushing 28 has a plastic flow path 30 formed at its center to permit the passage of molten plastic through a sprue 34 into a mold cavity 36.
The modified sprue bushing also includes a gas path 32 to permit the introduction and venting of a charge of pressurized gas.
-7a-The mold cavity 36 is flow coupled through a runner segment 38 to a spill cavity 40. The volume of spill cavity 40 may be varied by any well-known means to control the quantity of displaced plastic such as by a lead screw 42.
A molded article 46 produced by the process described in reference to FIGURE 1 includes an interior void 44 formed by the presence and influence of the pressurized gas. The spill cavity 40 may be formed to mold an integral appendage of the article 46, or a separate article, or simply scrap for regrinding.
FIGURE 4 is another schematic view of a plastic injection molding apparatus, generally indicated at 50, illustrating an alternative arrangement for practicing the process of the present invention. In this case, the apparatus 50 employs first and second spill cavities 54 and 56 which are flow coupled through runners 58 and 60, respectively, to a mold volume 52.
Again, a nozzle 26 from an injection molding machine registers with the sprue bushing 28 to inject a quantity of molten plastic into the mold cavity. A charge of pressurized gas flows along the gas -path 32 in the modified sprue bushing 28 and into the cavity 52 to displace the least viscous plastic from the mold cavity 52 into the first and second spill cavities 54 and 56.
This process, when performed in accordance with the steps of FIGURE 1, will yield a molded article 64 having a central void 62 due to the displacement of plastic by the pressurized gas.
FIGURES 5 and 6 are side and plan schematic views, respectively, of still another plastic injection molding apparatus, generally indicated at 70, adapted to mold a hollow plastic article 78 having an integral internal wall 80. In this case, the injection molding machine nozzle 26 aligns with a sprue 72 which divides into a pair of runners 74 and 76. Each of the runners 74 and 76 connects to a bushing 28', which is modified from the sprue bushing 28 of FIGURE 1 only to the extent required to remove it to the ends of the runners 74 and 76. In this example, the pair of bushings 28' are situated at opposite lateral extremes of the mold cavity 52 to produce a molded article 78 with an integral internal wall 80 at the center. The position-ing of the bushings 28', as defining the gas entrypoints, will determine the resulting position of the integral internal wall 80.
In the apparatus 70 of FIGURES 5 and 6, the gas charges introduced through the paths 32 in the bushings 28' are simultaneous. Each gas charge tends to form a cell, as shown by voids 82 and 84, within the article 78. The cells are divided by a membrane which serves an integral internal wall 80.
In other respects the apparatus 70 of FIGURES
5 and 6 is essentially similar to the apparatus 50 of FIGURE 4. Specifically, the apparatus 70 likewise employs first and second spill cavities 54 and 56 flow coupled to the mold cavity 52 through runners 58 and 60, respectively.
In the apparatus 70 of FIGURES 7 and 8, the gas charges introduced through the paths 32 in the bll-c~inqs 28' are sequential so that the membrane which serves as an integral wall 80' is displaced to one side.
For example, the interval between the gas charges may be between .25 and 1.0 seconds apart.
FIGURES 9 and 10 are plan and side schematic views, respectively, of another plastic injection molding apparatus, generally indicated at 70', adapted to mold a hollow plastic article. The apparatus 70' employs spill cavities 54' and S6' coupled to the mold cavity through runners 58' and 60', respectively.
The plastic in at least one of the spill cavities 54' and 56' is supported during plastic solidification by a movable mold part such as a pin 86 supported within the mold of the apparatus 70'. The gas is vented by moving the pin away from the supported plastic prior to opening the mold to the atmosphere so that the pressurized gas bursts through the now unsupported plastic within the spill cavity. The gas then travels around the pin 86, through the mold and to the atmosphere in a controlled fashion. The pin 86 may be moved relative to the mold in any well-known fashion and is supported in a bore 87 in the mold leaving approximately 0.005 inches clearance around the pin 86 to permit the gas to travel around the pin 86.
FIGURES 11, 12A and 13B show alternate embodi-ments of a pin, generally indicated at 86 ', 86~ and 86'~, respectively, for venting the gas from the article. FIGURES 12B and 13B show the pins 86~ and 86'~ in their venting positions, respectively. Each of the pin~ 86 ', 86~ and 86 ' ~ include an angled end portion 88 ', 88~ and 88 ' ~ , respectively, for receiving and retaining a portion of the solidified injected plastic therein at a plastic reservoir, a runner segment, a sprue portion or an inconspicuous part of the article itself. Movement of the pins 86 ', 86~ and 86 ' ~ away from their Le_~ective supported portions of injected plastic causes their respective end portions 88 ', 88~
and 88~ ' to carry a portion of plastic therewith to facilitate the venting step, as illustrated in FIGURES
12B and 13B.
In the embodiment of FIGURE 11, the pin 86' includes a central ejector 90 which can be operated in any well-known fashion to subseguently eject the solidified plastic from the end portion 88 ' after venting and prior to the next cycle.
The invention has been described in illustra-tive embodiments, but it will be evident to those skilled in the art that variations may be made from the foregoing teachings without departing from the scope of the following claims.
HOLLOW PLASTIC ARTICLE PRODUCED l~K~Y
TECHNICAL FIELD
The present appllcatlon ls a dlvlslon of appllcatlon Serlal No. 605,037 flled July 7, 1989.
Thls lnventlon relates to plastlc ln~ectlon moldlng and artlcles produced thereby, and more partlcularly, to plastlc ln-~ectlon moldlng and plastlc artlcles havlng hollow lnterlor por-tlons produced thereby.
CROSS ~ CE TO RELATED APPLICATIONS
Thls appllcatlon ls related to U.S. patent appllcatlons entltled ~Apparatus and Method for the In~ectlon Moldlng of Thermoplastlcs", S.N. 071,363 flled July 9, 1987 (now U.S. Patent No. 4,781,554 (James W. Hendry) lssued on November 1, 1988);
"Method and Apparatus for the In~ectlon Moldlng of Plastlc Artlcles", S.N. 098,862 flled September 21, 1987 (now U.S. Patent No. 4,855,094 (James W. Hendry) lssued on August 8, 1989) and "Method and System for Locallzed Fluld-Asslsted In~ectlon Moldlng and Body Formed Thereby", S.N. 133,900, flled December 16, 1987 (now U.S. Patent No. 5,069,859 (Norman Loren) lssued on December 3, 1991), all of whlch have the same Asslgnee as the Asslgnee of the present lnventlon.
-la-BACKGROtT~D ART
In the plastic injection molding art, the usual challenges facing a product designer is to design an article having requisite strength for the product application and uniform surface quality for satisfactory appearance, but to avoid excessive weight, material usage and cycle time. A
design compromise must often be made between strength and plastic thickness. A relatively thicker plastic section in the article, such as a structural rib, will incur greater weight, material usage, cycle time and induce sink marks and other surface defects due to thermal gradients in the area of the thickened section It is known in the plastic molding art to use pressurized fluid in conjunction with the plastic molding of articles The pre~urized fluid is typically nitrogen gas which is introAl~ceA into the mold cavity at or near the completion of the plastic injection The pressurized fluid serve several pu~ First, it allows the article so formed to have hollow interior portion~ which ~GLLe_~O~d to weight and material avings Se~ nA, the pres-~urized fluid within the mold cavity applie~ outward pL~ re to force the pla~tic against the mold surfaces while the article ~olidifies Third, the cycle time is re~l~ceA as the gas migrates through the most fluent inner volume of the plastic and replaces the plastic in these area~ which would otherwise require an extended cooling cycle Fourth, the gas yL~ lre r~ the plastic against the mold surfaces, thereby obta ~ n ~ ~g the maximum coolant effect from the mold Howev-r, as the dimensions of the molded article increasQ, the gas must do more work to ~lgrat- through the volume of the mold cavity to assist in setting up the article within the cavity If the prQs-urQ of the ga~ i~ too great as it enters the mold cavity, there is a risk that it may u~ e or blow out th- pla~tic within th~ mold cavity, i e , th- gas is not containeA within the plastic Thus, there have been practical limitations in the adaptation of gas in~ectlon in the plastic molding field DISCLOSURE OF THE INVENTION
Accordlng to one broad aspect of the present lnventlon, there ls provlded a process for ln~ectlon molding a hollow plastlc artlcle lncludlng the steps of ln~ectlng a quantlty of fluent plastlc lnto a mold cavity of a mold havlng a shape deflnlng at least a portlon of the artlcle, lntroductlon of a charge of pres-surlzed gas lnto the mold cavlty upon substantlal completlon of plastlc ln~ectlon, permlttlng the ln~ected plastlc to solldify by supportlng the ln~ected plastlc ln the mold, ventlng the gas from the mold cavity, and removlng the plastlc artlcle from the mold, whereln the lmprovement comprlses: a portlon of the ln~ected plastlc ls supported wlthln the mold by a movable support means of the mold durlng plastlc solldlflcatlon and whereln the step of ventlng ls accompllshed by movlng the support means to a non-support posltlon to allow the gas to burst through the thereby unsupported plastlc portlon.
Wlth reference to preferred embodiments, one aspect of the present lnventlon ls a method for ln~ectlon moldlng hollow plastlc artlcles wlth pressurlzed gas whlch provldes for dlsplace-ment by the gas of a portlon of plastlc from the mold cavlty lnto a flow coupled splll cavlty. Thls feature enables plastlc artl-cles of relatlvely greater dlmenslons to be successfully molded wlth the advantages of establlshed gas ln~ection moldlng tech-niques.
More speclflcally, the process lnvolves the lnltlal ln-~ectlon of a quantlty of fluent plastlc lnto a mold cavlty havlng a shape deflnlng at least a portlon of the plastic artlcle to be 3a molded. At or near the completlon of the plastic in~ection, a charge of pressurized gas is introduced into the mold cavity to displace a portlon of the still fluent plastic. The displaced plastic flows through a passage from the mold cavity into a con-nected spill cavity or reservoir. The reservoir may alternatively serve as: (i) an appendage of the complete article; (ii) a separ-ate article; or (iii) a cavity to receive spilled plastic for re-grinding. The plastic which is displaced is generally the hottest and most fluent. In this regard, the introduction of the charge of pressurized gas into the mold cavity can be timed to modulate the amount of plastic displaced, i.e., the longer the delay in introduction, the cooler and less fluent the plastic in the mold cavity.
In another feature of the invention, the hollow plastic article may be formed with an lntegral internal wall by introduc-tion of two or more charges of pressurized gas. Each gas charge tends to form a cell within the article, and the cells are divided by membranes which serve as integral internal walls to enhance the structural properties of the article.
In yet still another feature of the invent-ing, venting of the gas from the mold cavity is accomplished by moving a support mechanism for a portion of the solidified injected plastic to allow the gas to burst through the unsupported plastic portion at the reservoir, the runner or an incon-spicuous part of the article itself.
The present invention admits to molding of relatively large size structural articles for use in diverse product fields, such as a box-sectioned frame member for an automobile or refrigerator door or the hood of a car having a reenforcing beam.
Other advantages and features of the present invention will be made apparent in connection with the following description of the best mode for carrying out the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGURE 1 is a flow chart indicating the basic steps involved in practice of the process of the present invention;
FIGURE 2 is a schematic side view of a plastic injection molding apparatus adapted to carry out the process of the present invention;
FIGURE 3 is a top plan view of the apparatus of FIGURE 2;
FIGURE 4 is another schematic view of a plastic injection molding apparatus illustrating an alternative arrangement for practicing the process of the present invention;
FIGURE 5 is a side schematic view in cross-section showing still another plastic injection molding apparatus adapted to mold a hollow plastic article having an integral internal wall in accordance with the process of the present inven-tion;
FIGURE 6 is a plan view of the apparatus shown schematically in FIGURE 5:
FIGURE 7 is a view similar to FIGURE 5 wherein the internal wall is displaced from the central location of FIGURE 5;
FIGURE 8 is a plan view of the apparatus of FIGURE 7;
FIGURE 9 is a plan view of yet still another plastic injection molding apparatus;
FIGURE 10 is an enlarged side schematic view of the apparatus of FIGURE 9, partially broken away and illustrating one embodiment of a venting step;
FIGURE 11 is a view similar to FIGURE 10 illustrating a second embodiment of the venting step;
FIGURE 12A is a view similar to FIGURE 10 illustrating a third embodiment of the venting step;
FIGURE 12B is a view of the third embodiment after venting;
FIGURE 13A is a view similar to FIGURE 10 illustrating a fourth embodiment of the venting step;
and FIGURE 13B is a view of the fourth embodiment after venting.
BEST MODE FOR CARRYING OUT THE INV~N'1'10N
FIGURE 1 is a flow chart of the steps involved in practicing the process of the present invention.
In step 10, a quantity of molten plastic is injected from an injection molding machine into a mold cavity. The plastic is any thermoplastic and works particularly well with glass or mineral filled ther-moplastic polyester, commonly known by the trademark Valox of General Electric Co. The quantity is suffi-cient to provide the mass of the article to be molded, but desirably less than the quantity which would fill the mold cavity.
In step 12, a charge of pressurized gas is introduced into the mold upon substantial completion of the injection of the quantity of molten plastic.
In step 14, the gas flow into the mold is maintained in pressure and duration in amount and time sufficient to displace a controlled quantity of plastic from the mold cavity into a spill cavity which is flow coupled to the mold cavity. The gas tends to displace the hottest, most fluent plastic in the central portion of the mold cavity. Consequently, the molded plastic article has a hollow interior where the least viscous plastic has been displaced. The p~s-ence of the gas affords savings in weight and material usage. Added benefits include enhanced surface quality due to the outward pressure exerted by the gas, and reduced cycle time due to displacement of the relatively hot plastic from the central portion of the article.
In step 16, the article is permitted to solidify within the mold cavity while the internal gas pressure is maint~
In step 18, the pressurized gas is vented from the interior of the molded article preparatory to opening the mold. Numerous ways of venting are possible such as described in the U.S. Patent to Friederich 4,101,617 or as described in co-pending patent application Serial No. 071,363 noted above (now U.S. Patent No.
4,781,554 (James W. Hendry) issued on November 1, 1988).
In step 20, the plastic article is removed from the mold.
In step 22, the purged or displaced plastic is removed from the spill cavity or reservoir. In certain cases, steps 20 and 22 can be the common operation of ejecting the moldings so formed from the article cavity and the spill cavity.
FIGURES 2 and 3 are schematic side and plan views, respectively, of a plastic injection molding apparatus, generally indicated at 24, adapted to carry out the process of the present invention.
A nozzle 26 of a plastic injection molding machine is brought into registering position with a modified sprue bushing 28 associated with a mold. The sprue bushing 28 may be of the type disclosed in the above-noted co-pendin-g application Serial No. 098,862 filed September 21, 1987, (now U.S. Patent No. 4,855,094 (James W. Hendry) issued on August 8, 1989). The sprue bushing 28 has a plastic flow path 30 formed at its center to permit the passage of molten plastic through a sprue 34 into a mold cavity 36.
The modified sprue bushing also includes a gas path 32 to permit the introduction and venting of a charge of pressurized gas.
-7a-The mold cavity 36 is flow coupled through a runner segment 38 to a spill cavity 40. The volume of spill cavity 40 may be varied by any well-known means to control the quantity of displaced plastic such as by a lead screw 42.
A molded article 46 produced by the process described in reference to FIGURE 1 includes an interior void 44 formed by the presence and influence of the pressurized gas. The spill cavity 40 may be formed to mold an integral appendage of the article 46, or a separate article, or simply scrap for regrinding.
FIGURE 4 is another schematic view of a plastic injection molding apparatus, generally indicated at 50, illustrating an alternative arrangement for practicing the process of the present invention. In this case, the apparatus 50 employs first and second spill cavities 54 and 56 which are flow coupled through runners 58 and 60, respectively, to a mold volume 52.
Again, a nozzle 26 from an injection molding machine registers with the sprue bushing 28 to inject a quantity of molten plastic into the mold cavity. A charge of pressurized gas flows along the gas -path 32 in the modified sprue bushing 28 and into the cavity 52 to displace the least viscous plastic from the mold cavity 52 into the first and second spill cavities 54 and 56.
This process, when performed in accordance with the steps of FIGURE 1, will yield a molded article 64 having a central void 62 due to the displacement of plastic by the pressurized gas.
FIGURES 5 and 6 are side and plan schematic views, respectively, of still another plastic injection molding apparatus, generally indicated at 70, adapted to mold a hollow plastic article 78 having an integral internal wall 80. In this case, the injection molding machine nozzle 26 aligns with a sprue 72 which divides into a pair of runners 74 and 76. Each of the runners 74 and 76 connects to a bushing 28', which is modified from the sprue bushing 28 of FIGURE 1 only to the extent required to remove it to the ends of the runners 74 and 76. In this example, the pair of bushings 28' are situated at opposite lateral extremes of the mold cavity 52 to produce a molded article 78 with an integral internal wall 80 at the center. The position-ing of the bushings 28', as defining the gas entrypoints, will determine the resulting position of the integral internal wall 80.
In the apparatus 70 of FIGURES 5 and 6, the gas charges introduced through the paths 32 in the bushings 28' are simultaneous. Each gas charge tends to form a cell, as shown by voids 82 and 84, within the article 78. The cells are divided by a membrane which serves an integral internal wall 80.
In other respects the apparatus 70 of FIGURES
5 and 6 is essentially similar to the apparatus 50 of FIGURE 4. Specifically, the apparatus 70 likewise employs first and second spill cavities 54 and 56 flow coupled to the mold cavity 52 through runners 58 and 60, respectively.
In the apparatus 70 of FIGURES 7 and 8, the gas charges introduced through the paths 32 in the bll-c~inqs 28' are sequential so that the membrane which serves as an integral wall 80' is displaced to one side.
For example, the interval between the gas charges may be between .25 and 1.0 seconds apart.
FIGURES 9 and 10 are plan and side schematic views, respectively, of another plastic injection molding apparatus, generally indicated at 70', adapted to mold a hollow plastic article. The apparatus 70' employs spill cavities 54' and S6' coupled to the mold cavity through runners 58' and 60', respectively.
The plastic in at least one of the spill cavities 54' and 56' is supported during plastic solidification by a movable mold part such as a pin 86 supported within the mold of the apparatus 70'. The gas is vented by moving the pin away from the supported plastic prior to opening the mold to the atmosphere so that the pressurized gas bursts through the now unsupported plastic within the spill cavity. The gas then travels around the pin 86, through the mold and to the atmosphere in a controlled fashion. The pin 86 may be moved relative to the mold in any well-known fashion and is supported in a bore 87 in the mold leaving approximately 0.005 inches clearance around the pin 86 to permit the gas to travel around the pin 86.
FIGURES 11, 12A and 13B show alternate embodi-ments of a pin, generally indicated at 86 ', 86~ and 86'~, respectively, for venting the gas from the article. FIGURES 12B and 13B show the pins 86~ and 86'~ in their venting positions, respectively. Each of the pin~ 86 ', 86~ and 86 ' ~ include an angled end portion 88 ', 88~ and 88 ' ~ , respectively, for receiving and retaining a portion of the solidified injected plastic therein at a plastic reservoir, a runner segment, a sprue portion or an inconspicuous part of the article itself. Movement of the pins 86 ', 86~ and 86 ' ~ away from their Le_~ective supported portions of injected plastic causes their respective end portions 88 ', 88~
and 88~ ' to carry a portion of plastic therewith to facilitate the venting step, as illustrated in FIGURES
12B and 13B.
In the embodiment of FIGURE 11, the pin 86' includes a central ejector 90 which can be operated in any well-known fashion to subseguently eject the solidified plastic from the end portion 88 ' after venting and prior to the next cycle.
The invention has been described in illustra-tive embodiments, but it will be evident to those skilled in the art that variations may be made from the foregoing teachings without departing from the scope of the following claims.
Claims (6)
1. A process for injection molding a hollow plastic article including the steps of injecting a quantity of fluent plastic into a mold cavity of a mold having a shape defining at least a portion of the article, introduction of a charge of pressurized gas into the mold cavity upon substantial completion of plastic injection, permitting the injected plastic to solidify by supporting the in-jected plastic in the mold, venting the gas from the mold cavity, and removing the plastic article from the mold, wherein the improvement comprises: a portion of the injected plastic is supported within the mold by a movable support means of the mold during plastic solidification and wherein the step of venting is accomplished by moving the support means to a non-support position to allow the gas to burst through the thereby unsupported plastic portion.
2. An injection molded hollow plastic article produced by the process of claim 1.
3. The process as claimed in claim 1 wherein the support means includes an angled end portion for receiving and retaining the portion of the injected plastic therein and wherein movement of the support towards the non-support position removes the por-tion of the injected plastic from the rest of the injected plas-tic.
4. The process as claimed in claim 1 wherein the mold has a spill cavity coupled to the mold cavity and wherein the portion of the injected plastic is located in the spill cavity.
5. The process as claimed in claim 3 wherein the mold has a runner segment coupled to the mold cavity and wherein the portion of the injected plastic is located in the runner segment.
6. The process as claimed in claim 3 wherein the support means includes a movable pin having extended and retracted posi-tions for removing the portion of the injected plastic from the angled end portion in the extended position of the pin.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000616657A CA1332863C (en) | 1988-07-11 | 1993-05-31 | Process for injection molding and hollow plastic article produced thereby |
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US217,175 | 1988-07-11 | ||
| US07/217,175 US5098637A (en) | 1988-07-11 | 1988-07-11 | Process for injection molding and hollow plastic article produced thereby |
| CA000605037A CA1327874C (en) | 1988-07-11 | 1989-07-07 | Process for injection molding and hollow plastic article produced thereby |
| CA000616657A CA1332863C (en) | 1988-07-11 | 1993-05-31 | Process for injection molding and hollow plastic article produced thereby |
Related Parent Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000605037A Division CA1327874C (en) | 1988-07-11 | 1989-07-07 | Process for injection molding and hollow plastic article produced thereby |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1332863C true CA1332863C (en) | 1994-11-08 |
Family
ID=25672865
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000616657A Expired - Fee Related CA1332863C (en) | 1988-07-11 | 1993-05-31 | Process for injection molding and hollow plastic article produced thereby |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1332863C (en) |
-
1993
- 1993-05-31 CA CA000616657A patent/CA1332863C/en not_active Expired - Fee Related
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