Abstract: The invention comprises a method to quickly heat a mold cavity surface or portions thereof just prior to the injection of a foamable plastic resin. The apparatus comprises one or more thin metal surface sheets or bands of high electrical resistivity in the mold cavity covering those portions of the mold where a smooth surface finish on the product is desired. In an alternative form the surface sheets may be plated or sprayed metal of high resistivity on a layer of thin electrically non-conducting plastic in turn adhered to the mold cavity surface.The thin metal surface sheet is resistance heated approximately 300.degree. F. in a few seconds or less by a low voltage high current source of electric power just prior to the injection of the foamable plastic. The high current passing through the metal of high resistivity causes conversion of electrical energy into sensible heat very quickly to accomplish quick heating of the mold cavity surface sheet.

Abstract: This apparatus is used to improve the heat distribution on the cavity surface in foam molding dies where a smooth finish on the resin filled foam molded plastic product manufactured by an injection molding process is desired. This invention improves the method for heating the mold cavity using a condensing vapor in a molding die by a channel and slit type orifice means in the mold around a portion of the periphery of the part to be molded. Another channel and slit type orifice means around the remaining periphery is included in the die for removing the condensing vapor or condensate from the mold cavity. During the heating process when condensing vapor is introduced into the mold the sprue opening to the extruder is sealed by a valve means to prevent condensate from collecting therein.

Abstract: A method and apparatus is provided for making a composite structural homogeneous resinous article having (a) a smooth, shiny non-cellular or homogeneous relatively thin injection compression molded liner on the outer surface and (b) a cellular relatively thicker injection molded core integral with the molded liner. One extruder is connected by valve controlled passages to a pair of injection devices, each device having an injection chamber. One chamber stores the homogeneous plastic resin and the other chamber stores the foam plastic resin. A first mold assembly having a movable upper mold part and a stationary lower mold part form a cavity, with a gap opening, at a first molding station. The cavity is in communication with the first injection chamber.

Abstract: A form box for manufacturing a form, which form box is adapted to hold a reinforcing preform in position during the period of time that an expanding foam mass is injected into the area between the reinforcing preform and the form box. Pins are secured to the form box and project inwardly into the form cavity in which is located the reinforcing preform. The free ends of the pins engage the reinforcing preform to hold same in a fixed position during the period of time that the expanding foam mass is injected into the cavity between the reinforcing preform and the form box.

Abstract: This invention relates to a process for the production of optionally cellular, elastic, shaped articles having an impervious surface layer of polyurethane-polyurea elastomers by reacting a reaction mixture of organic polyisocyanate, ethylene oxide-tipped polyoxyalkylene polyols, propylene oxide-tipped polyoxyalkylene polyols, catalysts, amine chain extenders and optionally surfactants and blowing agents by the reaction injection molding (RIM) technique.

Abstract: The invention relates to a method of moulding a tire for a wheel rim by means of a mould having mould parts, said mould parts being movable between a closed working position in which they enclose a mould cavity with the shape of the tire and an open position in which said mould parts are spaced apart, wherein in the open position of the mould parts a hollow tire core is positioned in the mould cavity while being receivable with respect to said parts, wherein the mould parts are moved into the working position, in which a residual cavity not occupied by the tire core is left free in the mould cavity, said residual cavity. Preferably the tire core is arranged on the wheel rim before being positioned with respect to the mould parts. The invention also provides a device for moulding a tire and a tire obtained with the aid of the method and device.

Abstract: A method for making closures resembling natural cork for sealing liquid product containers is described. A strand of expandable plastic material is injected into each mold cavity and is permitted to collect in that cavity in randomly oriented groups of coils which expand to fill the cavity and coalesce to create randomly oriented grain lines on the surface of the closure resembling the appearance of natural cork. Also described are methods of molding the closures which preclude the formation of leakage channels on the closure surface and preferred blends of plastic resins and pigment particles used to achieve the cork-like appearance.

Abstract: A padded panel for a vehicle dashboard, console box or the like has an opening for mounting a desired article, such as an instrument, a switch, etc. The panel includes a base plate which is formed with a closed loop groove. A portion of a surface layer, which covers the base plate, is adhered to the surface of the groove to define a completely closed space therebetween. Foamable material is injected into the closed space and caused to foam and harden to form the pad. After completion of hardening of the pad, the base plate and the surface layer are cut along the inner periphery of the groove to form the opening. The bottom surface of the groove affords a seat to accurately position and positively mount the desired article.

Abstract: The present invention proposes a process for manufacturing an object intended to be held in the hand and which comprises a body made from a plastic material reinforced inside by means of a frame and comprising at least one grasping zone having a hardness less than that of its other parts. This process consists in placing the frame in a mould comprising an injection aperture in the part of its cavity corresponding to the grasping zone of the object, closing the mould, injecting into the cavity a definite amount of a compact plastic material, this amount being insufficient to completely fill the mould, then injecting an amount of expanded plastic material to completely fill the cavity, the expanded plastic material, which while penetrating inside the volume of the non-solidified compact material, forces this latter to come into contact with the whole internal surface of the cavity of the mould and to cover the frame, and removing the object from the mould after cooling of the two plastic materials.

Abstract: A hand grip for a hand-held implement, e.g., a golf club, that consists of a rigid cap and a one-piece flexible foam tubular sleeve. The cap is structured to cooperate with the implement's handle shaft for locating and retaining the grip on that shaft, and for protecting the end of the shaft and the outer end of the foam sleeve. The one-piece flexible foam sleeve, preferably with an outer skin thereon to resist abrasion, provides a cushioned grip to the user. A novel method is also provided by which the rigid cap and foam sleeve grip are fabricated.

Abstract: A tire is cast and cured in a stationary mold having an annular mold cavity, an inlet opening and an outlet vent. The mold is tilted for optimum foam flow and minimum air or bubble entrapment. A liquid reactive mixture is injected into the mold through the inlet opening and moves through the mold cavity in different directions providing two leading surfaces which meet to form an interface adjacent the outlet vent. The air, foam gases and interface portion are extruded from the mold cavity through a slot in the vent into a reservoir. After curing of the elastomeric material formed by the liquid reactive mixture in the mold, the material in the slot and reservoir may be severed from the tire.

Abstract: A foam composition comprising an ethylene-chlorotrifluoroethylene copolymer, a blowing agent and a nucleating agent. The nucleating agent is the carbonate or oxide of a metal cation from the group of metals consisting of magnesium, calcium, barium, zinc and lead. The invention also is a method of making the above foam copolymer composition.

Abstract: A cross-linked, cellular elastomeric composition is made from a formulation which includes one or more natural and/or synthetic rubbers, a cross-linking agent, a monomeric metallic salt of an ethylenically-unsaturated carboxylic acid and a blowing agent. The metallic salt is preferably basic zinc methacrylate. The composition may be used to provide a core for a tennis-ball or a sponge for a table-tennis bat. The former use enables advantage to be taken of the properties hitherto only found in pressurized playballs, while the latter use leads to a marked increase in the speed of the ball when struck by the bat.

Abstract: A molding apparatus in which a slider is slidable in an inclined channel into which a passage opens at one side for communication with a mold cavity while a pair of passages open at the opposite side for communication with a plasticating (worm) cylinder and a further cylinder provided with a plunger or piston. The slider has a U-shaped passage, the arms of which are positioned to interconnect both of the passages on the other side of the channel in a position of the slider in which the passage to the mold is blocked but which connects only the accumulating cylinder passage through the bight of the U-shaped passage to the mold in another position of the slider. A check valve is provided in the passage of the worm cylinder.

Abstract: The present invention relates to a method and a device for producing shaped articles from a multi-component reaction mixture which forms, for example, polyurethane, epoxy resin, polyester resin or polyamide, by mixing at least two of the individual components in at least two premixing chambers to form multi-component reaction mixture and these mixtures are subsequently mixed in a single-stage mixing chamber to form a mixture which is introduced into a shaping zone in which it is cured to form the shaped article.

Abstract: The invention relates to a method of filling cavities and, in particular, mold cavities, with a reactive solid-forming or foam-forming mixture, wherein at least two reactants are introduced into a spatially limited mixing zone, mixed therein as they pass through, and the mixture produced is introduced into a mold cavity where it reacts and wherein the mold cavity is initially enlarged in-part for storing a portion of the mixture, which portion is subsequently transferred to the final mold cavity volume. The object of the invention is to produce plastic articles which are shaped in molds, but also to fill out other cavities, for example, for the purposes of reinforcement.

Abstract: The invention relates to a method of producing molded bodies of expanded plastic having a predetermined density, based on a starting material in granulate form to which a blowing agent and optionally a cross-linking agent have been added, said starting material being introduced into an injection molding machine/press in which it is heated and injected/pressed into a mold. In order to obtain an efficient production process without loss of raw material and a product whose density can be determined in advance, the material in the injection molding machine/press is heated to a temperature which is below the temperature required to initiate the reaction of the blowing agent/cross-linking agent, and the blank thus formed is subsequently transferred to an expansion mold having the shape of the desired final product, but larger, than the blank. The blank is caused to expand in the expansion mold and final expansion takes place outside the expansion mold.

Abstract: A novel apparatus and method are provided for monitoring gas entrainment in liquid precursors for reaction injection molding (RIM). In accordance with the invention, a nucleated RIM precursor is sampled and the sample subjected to a controlled volumetric change. The measured pressure of the expanded or compressed sample is compared to that corresponding to the ideal degree of gas entrainment. The comparison is used to control the addition or withdrawal of entrained gas.

Abstract: The instant invention is directed to a process for filling a cavity with a flowable reaction mixture through an inlet opening located at the bottom of the cavity. The process broadly comprises injecting a relatively small amount of reaction mixture into the cavity to cover the inlet opening with reaction mixture. The injection process is then briefly interrupted. Thereafter, the remaining amount of reaction mixture is injected into the cavity. The invention also relates to apparatus useful in performing the above-described process.

Abstract: A method is disclosed for incorporating particulate material in reactive resin mixes produced by the RIM method in the molding of foamed or unfoamed plastic articles, wherein the particulate material is introduced into the resin mix in a manner which substantially eliminates the severe abrasive effect such particulate material produces under conditions existing in prior methods due to flow through the various passges of the mixing head. The particulate material may constitute reinforcement for a plastic article, in which case short lengths of glass, carbon, graphite or other mineral or metal fibers and the like may be used. Alternatively, granular particulates such as carbon black, metal or mineral oxides, pigments, etc. may be incorporated for coloring the product, or increasing its resistance to actinic rays, or for imparting increased rigidity to the molded product, etc.

Abstract: A method and apparatus for incorporating particulate material in reactive resin mixes produced by the RIM method in the molding of foamed or unfoamed plastic articles, wherein the particulate material is introduced into the resin mix in a manner which substantially eliminates the severe abrasive effect such particulate material produces under conditions existing in prior methods due to flow through the various passages of the mixing head. The particulate material may constitute reinforcement for a plastic article, in which case short lengths of glass, carbon, graphite or other mineral or metal fibers and the like may be used. Alternatively, granular particulates such as carbon black, metal or mineral oxides, pigments, etc. may be incorporated for coloring the product, or increasing its resistance to actinic rays, or for imparting increased rigidity to the molded product, etc.

Abstract: Low density, lightweight foam articles may be provided with certain portions or regions thereof, that are reinforced, having higher density and strength, obtained by compression of the foam in these locations, during or after formation of the foam. Such locations may be made sufficiently strong and dense to allow the article to be attached in place by fastening means, imbedded therein. The increase in density can be as much as from 5 pcf to 10 pcf or higher, depending upon the particular application.Many foam materials, capable of being molded, extruded, or otherwise shaped to a predetermined configuration, may be made with this combination of high and low density, including foams of styrenic polymer or copolymer compositions, urethanes, vinyls, and even non-thermoplastic based materials, such as phenolic foams.

Abstract: Instrument panels or other such panels are made by injection and distribution of foam precursors into a cavity between rigid and flexible sheets tightly clamped at their borders. FIG. 3 shows relative portion of rigid sheet (A), flexible sheet (B) and mold members (M1) and (M2). Injection preferably occurs through an injection port at a parting line between (M1) and (M2) defined also by sheets (A) and (B).

Abstract: Injection moldings have excellent surface gloss and freedom from sink marks are obtained using a pressurized mold and molding composition containing a volatile fluid foaming agent, a thermally decomposable foaming agent and a finely divided nucleating agent.

Abstract: The invention is directed to an apparatus for the preparation of a reaction mixture, from fluid components, comprising storage tanks, feed pipes leading from said storage tanks to a mixing head via metering pumps and opening into a mixing chamber via injection apertures, said mixing chamber formed by the bore of a housing, a control piston displaceable within said bore and being capable of blocking flow through said apertures, return lines branching off upstream of said apertures and leading up to said storage tanks, and a shut-off means for stopping the flow of said material through at least one of said return lines, the activation of said shut-off means being dependent upon the position of said control piston within said bore.

Abstract: The instant invention is directed to a process for the production of microcellular elastomeric moldings comprising:(A) introducing a reaction mixture into a closed mold, said reaction mixture comprising:(i) an organic polyisocyanate,(ii) a hydroxyl group containing compound having a molecular weight of from 1800 to 12,000,(iii) a catalyst for the reaction between hydroxyl groups and isocyanate groups,(iv) an active aromatic diamine having at least one alkyl substituent in the orthoposition to a first amino group and two alkyl substituents in ortho-position to a second group, and(v) air and/or nitrogen dissolved under pressure in any one or more of Components (i), (ii), (iii) or (iv),(B) allowing said reaction mixture to react in said mold and(C) removing the resultant product from said mold, the improvement wherein in any of Components (i), (ii), (iii) or (iv) which does contain said air and/or nitrogen dissolved therein there is included an inorganic, finely divided, nitrogen adsorbing agent in an amount suf

Abstract: A method of manufacturing a panel, provided with a frame of a synthetic material at least at one side edge face thereof, a laminate composed of a particled board core coated on either side with a coating, with reservation of a molding cavity along the entire or partial panel circumference for the frame to be formed, being applied in the bottom portion of a mold likewise containing a cover portion, after which the mold is closed, while the cover portion is sealingly clamped onto the bottom portion, after which a curing bi-component synthetic material foaming through exothermic reaction is admitted substantially pressure-less into the mold cavity and the panel is removed from the mold after curing, whereby the exothermic reaction of the bi-component synthetic material is utilized for increasing the pressure and the temperature in the molding cavity during the foaming and curing.

Abstract: A reaction injection molding process for producing a coated polyurethane part in which a liquid mixture of polyurethane reactants is injected into a mold where it is reacted and molded into a shaped part at elevated temperatures. The surface of the mold is coated, prior to molding, with a coating composition containing a polyurethane catalyst. The catalyst acts to bond the coating composition to the molded part so that the shaped part upon removal from the mold contains a firmly adherent coating of the coating composition.

Abstract: An article of manufacture, such shelves, tables, stools and chairs. The article has a cold molded edge formed by combining a panel with support frame fitted thereagainst into a mold and then adding plastic to cast the panel and frame together to a desired shape with a cold molded edge.

Abstract: Auto parts prepared from polyurethane are manufactured by a process comprising:(a) preparing a polyol component by blending a stabilizer combination of (A) nickel dibutyldithio carbamate with (B) N-mono- or dimethylphenyl-N'-mono- or dimethylphenylphenylenediamine and/or (C) N,N'-diphenyl-p-phenylenediamine with a polyol and carbon black;(b) reacting said polyol component with a polyisocyanate: and(c) molding said reacted mass.

Abstract: An injection molding arrangement and process for producing regularly shaped pieces of gasified candy which effect a pleasant sizzling sensation in the mouth. A confectionary solution, which may be a sugar melt, is subjected to a superatmospheric carbonating pressure in a carbonating vessel to cause absorption therein of carbon dioxide. An injection mold for forming the solution into suitably shaped pieces of candy is prepressurized at a superatmospheric carbonation pressure prior to the injection therein of the confectionary solution. The solution is then injected into the mold at a pressure substantially above the superatmospheric pressure in the carbonation vessel. The solution is then allowed to cool and solidify in the pressurized mold, producing regularly shaped pieces of carbonated candy.

Abstract: A process and mold for producing padded motor vehicle seat backs containing a metal framework surrounded by polyurethane foam in a plastic coating. The framework is inserted through a slit in the coating which is then sealed. Then the polyurethane foam is injected through a flexible filler neck into the coating and allowed to polymerize. After polymerization the filler neck is cut off. The framework may be contained in a plastic bag together with a relatively resilient foamed plastic body. The coating may be pressurized inwardly and pressure in the mold may be reduced during injection of the polyurethane foam. The mold comprises a pair of lateral mold parts and a central mold part together defining the mold cavity. The lateral mold parts are movable toward and away from the central mold part by hydraulic or pneumatic rams.

Abstract: The invention relates to a method, and an apparatus, for the production of articles which consist of filler-containing synthetic material, in particular a foam, wherein flowable reactants, at least one of which has previously been charged with filler, are injected into a mixing zone under predetermined injection pressures, wherein the reaction mixture is subsequently introduced into a mold.Cellular materials such as flexible, semi-rigid, rigid or structured foam based, for example, on polyurethane or isocyanurate, and also non-cellular materials such as elastomers, may be produced by methods of this type.

Abstract: The instant invention broadly relates to a process and apparatus for filling a cavity with a reactive mixture. More particularly, the invention relates to a process for filling cavities, particularly mold cavities, with a reactive, flowable mixture which preferably forms foam, wherein at least two reaction components are brought into a mixing zone, where they are mixed and then brought into the cavity, the improvement wherein at the beginning of the filling process, during a limited time interval, the reaction mixture is fed into the cavity under low flow velocity until the mixture has reached a certain level in the cavity, and subsequently the remaining mixture to be injected, is fed in under increased flow velocity.

Abstract: A method for injection molding an article wherein additives are selectively introduced into the polymer melt downstream of an accumulation device and upstream of a static mixer just prior to its introduction into the mold cavity. The additives include U.V. stabilizers, flame retardant materials, colorants and blowing agents. The method produces injection molded articles with selective amounts of additives in either the skin or core portions of the articles.

Abstract: A process is disclosed for molding a foamed thermoplastic article characterized by a foamed core, a non-foamed exterior shell and a surface that reproducibly and faithfully replicates a predetermined portion of the inner surface of the mold in which the article is made, wherein a foamable mixture comprising molten thermoplastic material and blowing agent is introduced through a nozzle into a mold cavity defined by said inner surface of said mold and expands and is rigidified while in said mold cavity.

Abstract: The invention is a method for making reaction injection molded polyurethane of improved properties. The product comprises the cured reaction product of a high molecular weight polyhydric polyether, a low molecular weight active hydrogen containing compound of at least two functionality and a polyisocyanate. The reaction product is cured by subjecting it to an ambient temperature of from about 290.degree.-425.degree. F. for a time sufficient to achieve an improvement in properties. The invention is also the resulting polyurethane.

Abstract: A mixing head for mixtures of reactive components, e.g. two-component synthetic-resin systems to be discharged into a mold, in which the orifices for the two components open into a mixing chamber and can be selectively blocked or unblocked by a plunger or piston which serves to drive the mixture out of the chamber. According to the invention a blocking body (baffle barrier) is provided on a connecting rod which extends through the plunger and, in a retracted position of the latter, is located in the path of the jets of the reactive components emanating from the orifices.

Abstract: Manufacture of ornamental vehicle wheels wherein a mold surface of desired decorative contour is sprayed with one or more layers of a polyurethane reaction mixture and partially cured in situ. A steel wheel is then placed over the mold surface and a polyurethane reaction mixture which includes a foaming agent is poured into the mold cavity formed therebetween. The poured mixture is then cured and the layers are finish-cured in situ to form an integral ornamental elastomeric structure adhered to the wheel.

Abstract: A process for producing cork lines which comprises holding a leader or leaders with a pair of metal molds having at the junctional surfaces thereof one or more cavities for forming a float or floats and one or more furrows formed so as to pass through said cavity or cavities for holding said leader or leaders, injecting a molten synthetic resin mixed with a foaming agent into said cavity or cavities to effect molding and foaming of said resin, cooling said metal molds and taking out a float or floats integrally fixed to said leader or leaders from said metal molds.

Abstract: A station for running foam-plastics material into shut molds has a mixing head with first and second driving systems, the one for moving the mixing head sideways to an inlet opening of each mold, and the other for moving the mixing head downwards into and upwards out of the inlet opening. The mixing head and the first driving system together with the second driving system are supported by a slide or carriage, which is guided along a section of the transport way of the smoothly moving molds. By way of a driving connection, the slide may be joined up with the mold which is to take up the plastics material and cleared from it again when the mold is full.

Abstract: Process is disclosed wherein plastic material is passed into a mold cavity; pressurizing fluid is injected into the plastic material under controlled pressure and at a controlled rate to cause the plastic material to flow out and assume the contour of the cavity, the gas pressure being maintained until the plastic material is self-supporting. The resulting article has an outer skin and a generally hollow center containing skin-connecting structural "webs".

Abstract: Covers a polyurethane elastomer of improved moldability, particularly useful in RIM applications which comprises the reaction product of an aromatic polyisocyanate, a high molecular weight polyether triol containing an internal mixed propylene oxide-ethylene oxide segment comprising 2-35% ethylene oxide by weight and 65-98% by weight of propylene oxide and an ethylene oxide cap such that said polyol has a primary hydroxyl content greater than 50% and preferably greater than 90%, and a chain-extending agent. Also covers the method of making said elastomer.

Abstract: A method for introducing reactants into molds and articles produced. The method involves placing a body member into a receptacle located on a turntable; aligning the body member within the receptacle; positioning a foaming spacer on the body member around an aperture in the body member; lowering a liner on a plug fixture into the body member so that the foaming spacer abuts both the body and the spaced apart liner; inserting a foam machine head into the aperture in the body; injecting suitable reactants through the head, through the spacer, into the chamber formed between the liner and the body; maintaining the contact between the head and the body for a few seconds to allow the reactants to activate and set; removing the head from the aperture of the body; and further rotating the turntable to allow the reactants time to cure. The apparatus for facilitating the introduction of reactants is the foaming spacer of the above method.

Abstract: A method is disclosed comprising in-mold coating a structural foam part made from a thermoplastic aromatic polycarbonate resin or a thermoplastic ABS polymer resin with a thermosetting in-mold coating composition at a pressure of from about 25 to 50 p.s.i. and at a temperature not in excess of about 200.degree. F. for from about 1 to 10 minutes, preferably for from about 1 to 3 minutes, to provide hard, smooth and adherent coatings, said thermosetting in-mold coating composition comprising an ethylenically unsaturated polyester resin and an ethylenically unsaturated monomer(s) catalyzed with an organic perioxide initiator including an accelerator for the initiator.

Abstract: Low temperature curable organic resin compositions, for example, epoxy resins are provided, which can be either exothermically cured or cured in several minutes or less at relatively low temperatures. Certain diaryliodonium salts have been found to spontaneously release strong protonic acids when used in combination with a copper salt and a reducing agent.

Abstract: Molten synthetic resin material containing foaming agent in an amount of 0.05 to 5 percent by weight is injected into a pre-pressurized mold cavity in a mold which is closed by a relatively low clamping force having a coefficient in the range of 10 to 40, said coefficient being represented as a ratio of clamping force to maximum injection shot volume. The above injection step is carried out for at least 3 seconds. After the injection step has been initiated, the pre-pressurized mold is released to atmosphere during the injection step at the soonest. At least two molds may be used to be alternately charged with said material.

Abstract: The instant invention relates to a one-step process for the production of elastomeric moldings which have a compact surface by the technique of reaction injection molding, using highly reactive systems of specific polyisocyanates, polyhydroxyl compounds and specific active aromatic polyamines. The instant invention further relates to active hydrogen containing blends useful in preparing elastomeric moldings, said blends comprising polyhydroxyl compounds, and specific active aromatic diamines. The blends herein may also contain catalyst for the reaction between hydroxyl groups and isocyanate groups.

Abstract: A method for injection molding a product having a non-cellular skin layer and a cellular core portion. The method involves successive or simultaneous injection of a non-foamable resin material and a foamable resin material through a sprue bushing having an injection channel connected to the mold cavity and a pair of fixed feed channels intersecting with the injection channel. The injection mold has a bore with a sprue bushing therein. The sprue bushing having an injection channel therein and intersecting with a pair of fixed feed channels. Injection units deliver the materials to the pair of fixed feed channels.

Abstract: 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.