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US 5,344,596 AGranted
Method for fluid compression of injection molded plastic material
AssigneeICP Systems, Inc.
InventorJames W. Hendry
Life of this patent
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AssigneeICP Systems, Inc.
InventorJames W. Hendry
Estimating the term…
A mold apparatus and method is used to form a solid injection molded plastic part having no internal voids, a Class A finish, a sink-free exterior appearance surface, and unevenly distributed structural detail extending from the opposite surface, the detail including free-standing reinforcement ribs, attachment bosses, and the like. In the method the mold portions of the mold apparatus are closed, charges of molten thermoplastic and pressurized gas are sequentially injected into a mold cavity defining the shape of the desired part, and the mold portions are sequentially separated and closed. The pressurized gas forces the hot plastic away from one mold half and against the other mold half, and separation of the mold portions ensures uniform distribution of the pressurized gas behind the hot plastic, which pressure is maintained during cooling. Depending on the application, the plastic completely packs the cavity, fills but does not pack the cavity, and the mating faces can be abutted or maintained partially separated when the mold portions reclosed. A gas seal is formed by the plastic to prevent gas in the mold cavity from reaching the finished exterior surface of the part during shrinkage of the plastic.
In a method of producing a solid injection molded part having no internal voids and a sink-free exterior, the steps of the method comprising attaching a mold apparatus having a part defining cavity formed by a stationary mold portion and a movable portion to a source of hot flowable thermoplastic and to a source of gas under pressure, clamping the mating faces of said mold portions together with a predetermined clamping force, injecting a predetermined quantity of said thermoplastic into said mold cavity, said predetermined quantity of thermoplastic being of a lesser volume than the volume of said mold cavity, introducing said gas into said mold cavity while said thermoplastic is still flowable whereby to pressurize said mold cavity and force said thermoplastic away from one of said mold portions and towards the other of said mold portions, the improvement comprising:
A method of producing a solid injection molded part having no internal voids and a sink-free exterior, the steps of the method comprising:
A method of producing a solid, gas compression, injection molded thermoplastic part, comprising:
In a thermoplastic injection molding process of the type in which hot molten thermoplastic is injected into a mold cavity defined by a pair of relatively movable mold parts, gas is injected into the cavity to displace the thermoplastic in the mold cavity to form a part having no internal voids, means are provided to selectively control the pressure of the gas in the mold cavity, and the resin cools and the mold is opened to remove the molded part, the gas being stored at a storage first pressure as determined by the control means, and the gas at said storage first pressure being reduced to a lower storage second pressure as determined by said control means and the gas introduced into the mold cavity at said lower second pressure to displace the thermoplastic in the mold cavity, the improvement wherein following the injection of gas into the mold at said lower second pressure the mold parts are moved relative to one another to increase the volume of the mold cavity and additional gas at said second pressure is continuously introduced into the mold cavity to completely fill the cavity, and thereafter the gas at said second pressure is increased to a third pressure greater than said second pressure as determined by said control means.
A method for the use of gas in molding a solid plastic article in an injection molding system including combinable mold portions which when combined cooperate to form an article defining cavity, the method comprises the steps of:
A method for the use of gas in molding a solid plastic article in an injection molding system including combinable mold portions which when combined cooperate to form an article defining cavity having opposite cavity walls, the method comprising the steps of:
The method as claimed in claim 39 wherein the step of forcing the mold portions together includes maintaining the mating faces of the mold portions in spaced apart relation.
In an injection molding process for producing a solid injection molded part having no internal voids and a sink free exterior, the process including introducing a predetermined quantity of thermoplastic resin into a mold forming cavity formed by a pair of relatively movable mold portions each having a mold surface and clamping the mold portions together with a predetermined clamping force, the improvement comprising, introducing gas under pressure to pack the resin against one mold surface and away from the other mold surface and to produce a separating force greater than the mold clamping force to force the molds apart, and thereafter increasing the clamping force to drive the molds toward one another.
In an injection molding process for producing a solid injection molded part having no internal voids and a sink free exterior, the process including introducing a predetermined quantity of molten thermoplastic resin into an article defining cavity formed by a pair of relatively movable mold portions each having a mold surface and clamping the mold portions together with a predetermined clamping force, the improvement comprising introducing gas under pressure into the cavity to pack the resin against one mold surface and force the resin away from the other mold surface to form a solid article and to simultaneously force the mold portions away from one another, and then forcing the mold portions towards one another to compress the gas to a second pressure.
In an injection molding process for producing a solid injection molded article having no internal voids and a sink free exterior, the process including introducing a predetermining quantity of thermoplastic resin into a mold forming cavity formed by a pair of relatively movable mold portions and in an amount to pack the mold cavity, the mold portions each having a mold surface, clamping the mold portions together with a predetermined clamping force, and introducing gas into the cavity to pack the resin against one mold surface and away from the other mold surface to form the solid article, the improvement comprising separating the molds following the resin introduction step and prior to the gas introduction step, preforming the gas introduction step and then forcing the molds towards one another to compress the gas.
Dependencies are inferred from the claim text.