초록 ▼

A method of molding articles of plastic having an expanded plastic cellular core using a closable and sealable mold having a sealed mold cavity and including at least one mold core extending into the cavity, comprises, directing the plastic melt material containing a foaming agent into the mold cavi

A method of molding articles of plastic having an expanded plastic cellular core using a closable and sealable mold having a sealed mold cavity and including at least one mold core extending into the cavity, comprises, directing the plastic melt material containing a foaming agent into the mold cavity under pressure so as to form a flow front of the melt which progresses through the cavity and which spreads out in all directions and flows around the mold core and tends to form a pocket of gas in the vicinity of the mold core, and venting the cavity adjacent the core so as to remove gas from any gas pocket which may be formed in the vicinity of the core. The apparatus for carrying out the invention includes a vent line which extends from the cavity in the vicinity of the mold core out of the cavity and which has a control valve for opening the vent line to vent any gas which forms in the cavity and which might tend to form a pocket after the buildup of a pressure in the mold cavity. The vent passage includes at least one capillary-action, gas-pervious passage portion. The vented area advantageously comprises an intermediate space formed between the two mold cores which are connected with a vent line through a very small diameter intermediate space between the core and the hole in the mold cavity containing the vent core. The construction may also advantageously include an ejector plate having pins which penetrate to sealed areas of one of the mold parts and extends into the cavity through an enlarged chamber portion which communicates with the cavity through small diameter capillary-size holes.

대표청구항 ▼

A method of injection molding articles of foamable plastic material having a smooth surface and an expanded cellular core, using a closable mold having a sealable mold cavity with a gas therein and at least one fixed mold core extending into the mold cavity, with at least one intermediate shadow spa

A method of injection molding articles of foamable plastic material having a smooth surface and an expanded cellular core, using a closable mold having a sealable mold cavity with a gas therein and at least one fixed mold core extending into the mold cavity, with at least one intermediate shadow space of the mold cavity adjacent the mold core, comprising: injecting a melt of the plastic material containing a foaming agent into the cavity against the counter-pressure of the gas which is provided to prevent expansion of the melt during the mold filling operation, the flow front of the melt spreading out in all directions within the cavity and thereby the gas being progressively displaced while the melt flows around the mold core and tends to form inclusions of pressurized gas in the intermediate shadow space; venting the gas which is progressively displaced from the cavity as the melt flows around the core and forms the inclusion of pressurized gas in the intermediate shadow space adjacent the core; and separately venting each inclusion of pressurized gas adjacent each core immediately after it has been enclosed by the melt. In an apparatus for molding foamed plastic articles having a smooth surface and a porous core, comprising a mold having a sealable mold cavity, a sprue connected into the mold cavity for injecting a plastic melt containing a foaming agent into the cavity, means for supplying a gas under pressure for the cavity with the plastic melt being injected against the counter-pressure of the gas to prevent expansion of the melt during the mold filling operation, means for discharging the gas progressively displaced by the melt as the mold cavity is filled, and at least one fixed mold core projecting into the cavity around which the melt flows and tends to form an inclusion of pressurized gas in a flow shadow space adjacent the core; an improvement comprising: venting means separate from the means for discharging the gas including a vent line extending from the shadow space of each core and out of the cavity; and valve control means connected to said vent line to open said vent line at a selected time during the mold filling operation when the gas inclusion is being formed to additionally relieve the gas inclusion in the flow shadow behind the core.