Abstract: A device for producing pellets that has a perforated plate for extruding a melt into a process chamber, and a cutting device for cutting the melt into pellets. The process chamber can have an inlet and an outlet. A conveying device can deliver a process fluid through the inlet, and carry the process fluid and pellets through the outlet. The inlet can have an inlet opening and an inlet channel. A three-way valve can be located between the inlet channel, a process fluid supply line, and a process fluid discharge line, and below the inlet. The outlet can have a discharge opening and an outlet channel. A pneumatic device can provide compressed air to the process chamber for emptying and expelling the process fluid.

Abstract: An apparatus for granulating hot cut, in particular thermoplastic resin material, the material strands melted by an extruder being knocked off into granule pellets in a granulating housing by rotating knives disposed on a shaft driven by way of a motor, the granule pellets being picked up by a cooling medium flowing in the granulating housing, cooled and discharged out of the granulating housing, characterized in that a flow opening establishing a continuous fluid connection between the inside of the granulating housing and the outside environment is designed between the shaft and the region of the granulating housing in which the shaft penetrates the granulating housing.

Abstract: An underwater cutting and pelletizing apparatus includes: a cutting device that cuts, with a cutter in a water chamber, molten resin, extruded from a die, into pellets; a separation device that separates, from carrier water, pellets sent from the water chamber of the cutting device to downstream with carrier water; a tank that is disposed below the separation device and stores carrier water discharged from the separation device; and a circulation path formed so as to circulate carrier water between the tank and the water chamber, wherein a hydroelectric power generator is provided on a return side of the circulation path formed on a downstream side of the water chamber, and generates electricity from the energy of the carrier water flowing downward in this path. According to such a configuration, the underwater cutting and pelletizing apparatus is made so as to achieve energy savings by recovering and reusing potential energy accompanying carrier water pumped up to a higher location.

Abstract: The invention relates to a device for the implementation of a method for the production of pellets of polyamide 6 or copolyamides. The method can include production of a melt of polyamide 6 or copolyamides by means of polymerization, production of pellets from the melt by means of underwater pelletization into a process fluid, removal of the pellets from a site of underwater pelletization in the process fluid, supply of the pellets in the process fluid to an extraction stage, extraction of low-molecular components as extract, and drying of the pellets after extraction, wherein the underwater pelletization stage and the extraction stage take place using the same process fluid.

Abstract: An insulated die plate assembly for use in underwater pelletizing and other granulation processes includes a thin, continuous air chamber formed across the plate assembly generally parallel to the die face such that the heated upstream portion of the die plate assembly is thermally insulated from the downstream portion. The air chamber is atmospherically equilibrated by venting the air chamber to the atmosphere. The plurality of extrusion orifices, either individually or in groups, are formed in extrusion orifice extensions that extend through the insulation chamber so that the process melt to be granulated can pass therethrough. The orifice extensions and the components forming the air chamber around the orifice extensions channel heat along said extensions to maintain the process melt therein at a desired temperature, to help rigidify the die plate assembly and to better seal the air chamber.

Abstract: An apparatus according to various embodiments can be configured to use a cryogen for cooling articles, particularly having applications for chilling extrusions. The apparatus removes thermal energy from an article by conductive and convective heat transfer. The apparatus allows for heat transfer from an outer surface of an article, and from an inner surface of the article.

Abstract: Described herein are extrusion processes to produce hollow pellets. Also disclosed are pelletizer devices that can be used to produce the hollow pellets. The processes and devices make use of an extrusion die having a die orifice and an insert that is placed in the die orifice to produce the hollow pellets.

Abstract: An extrusion and conditioning apparatus, with an extruder in a conveying position, leads into a conveyor housing connected in a sealed manner to a pneumatic supply line and to a pneumatic conveyor line in which extruded material can be removed pneumatically, by means of superheated steam, via the conveyor line. The extruder can be moved from the conveying position into a bypass position, in which the extruder leads to the exterior of the conveyor housing, having a means for sealing the supply and conveyor lines and the conveyor housing from the surroundings when the extruder is in the conveying and bypass positions.

Abstract: Provided is a process for making thermoplastic polymer pellets. The process has the following steps: (a) melting a thermoplastic polymer to form a polymer melt; (b) extruding the melt through a die to form a substantially continuous molten polymer extrudate wherein the die has a contact surface bearing a polymer coating having a surface energy of less than 25 mN/m at 20° C.; (c) cooling the extrudate to form a cooled extrudate; and (d) pelletizing the cooled extrudate to form a plurality of polymer pellets. Provided is also a polymer pellet shipping system and a stable thermoplastic polymer pellet.

Abstract: The methods and apparatuses for granulating thermoplastic material emerging from nozzles in a perforated plate are provided. The apparatus can have a motor-driven cutter arrangement having at least one blade located opposite the perforated plate. The at least one blade can pass over the nozzles in the perforated plate and cuts pellets of the emerging thermoplastic material.

Abstract: In the method of manufacturing a strip (8) of rubber for vehicle tires: a strip (8) of rubber is formed; the strip is cooled with water; residual water (40) on the surface of the strip is heated from the exterior of the strip and/or this water is replaced by hotter water; and the water present on the surface of the strip is eliminated.

Abstract: A method and apparatus for underwater pelletizing and subsequent drying of polyethylene terephthalate (PET) polymers and other high temperature crystallizing polymeric materials to crystallize the polymer pellets without subsequent heating. High velocity air or other inert gas is injected into the water and pellet slurry line to the dryer near the pelletizer exit. Air is injected into the slurry line at a velocity of at least about 200 m3/hour. Such high-speed air movement forms a vapor mist with the water and significantly increases the speed of the pellets into and out of the dryer such that the PET polymer pellets leave the dryer at a temperature sufficient to self-initiate crystallization within the pellets.

Abstract: A method and apparatus for underwater pelletizing and subsequent drying of polyethylene terephthalate (PET) polymers and other high temperature crystallizing polymeric materials to crystallize the polymer pellets without subsequent heating. High velocity air or other inert gas is injected into the water and pellet slurry line to the dryer near the pelletizer exit. Air is injected into the slurry line at a velocity of from about 100 to about 175 m3/hour, or more. Such high-speed air movement forms a vapor mist with the water and significantly increases the speed of the pellets into and out of the dryer such that the PET polymer pellets leave the dryer at a temperature sufficient to self-initiate crystallization within the pellets. A valve mechanism in the slurry line after the gas injection further regulates the pellet residence time and a vibrating conveyor after the dryer helps the pellets to achieve the desired level of crystallinity and to avoid agglomeration.

Abstract: A method and apparatus for underwater pelletizing and subsequent drying of crystallizing polymers to crystallize the polymer pellets without subsequent heating is shown in FIG. 5. High velocity air or other inert gas is injected into the water and pellet slurry line (120) toward the dryer near the pelletizer exit (102) at a flow rate of from about 100 to about 175 m3/hour, or more. Such high-speed air movement forms a vapor mist with the water and significantly increases the speed of the pellets into and out of the dryer such that the polymer pellets leave the dryer with sufficient latent heat to cause self-crystallization within the pellets. A valve mechanism in the slurry line (150) after the gas injection further regulates the pellet residence time and a vibrating conveyor after the dryer helps the pellets to achieve the desired level of crystallinity and to avoid agglomeration.

Abstract: An apparatus for manufacturing nonwoven fabric including a spinning nozzle, a fiber extension device, a receiver device and a sprinkler is provided. The spinning nozzle is filled with a spinning solution and has a plurality of spinners, where each of the spinners includes a spinning port and a main gas port surrounding the spinning port. The fiber extension device is disposed under the spinning nozzle and includes at least one secondary gas supply device. The secondary gas supply device has an arc gas distribution portion, such that the direction of gas ejected from the secondary gas supply device is the same as the direction of gas ejected from the main gas port. The receiver device is disposed under the fiber extension device. The sprinkler is disposed above the fiber extension device or the receiver device.

Abstract: A method of crystallizing a plurality of crystallizable polymer pellets includes a step in which the pellets are contacted with a temperature adjusting fluid in a crystallizer. The fluid adjusts the temperature of the pellets by having a temperature sufficient to allow at least partial crystallization of the plurality of polymeric pellets while maintaining the average pellet temperature of the plurality of pellets below the melting temperature of the pellets. A crystallizer implementing the methods of the invention is also provided.

Abstract: A machine for manufacturing a nonwoven fabric includes a conveyer net, a spunbonding apparatus, and a container. In use, the spunbonding apparatus can project at least one fiber onto the conveyer net. The container can contain liquid, wherein the liquid level of the container is higher than at least a part of the conveyer net which the fiber is projected onto.

Abstract: An improved process for the pelletization of polymers is disclosed, using a die in which the die holes incorporate a reverse taper along at least a portion of the length thereof. Conditions for operation of an under melt cutter incorporating this die are also disclosed.

Abstract: A method of crystallizing a plurality of crystallizable polymer pellets includes a step in which the pellets are contacted with a temperature adjusting fluid in a crystallizer. The fluid adjusts the temperature of the pellets by having a temperature sufficient to allow at least partial crystallization of the plurality of polymeric pellets while maintaining the average pellet temperature of the plurality of pellets below the melting temperature of the pellets. A crystallizer implementing the methods of the invention is also provided.

Abstract: A method and apparatus for underwater pelletizing and subsequent drying of polyethylene terephthalate (PET) polymers and other high temperature crystallizing polymeric materials to crystallize the polymer pellets without subsequent heating. High velocity air or other inert gas is injected into the water and pellet slurry line to the dryer near the pelletizer exit. Air is injected into the slurry line at a velocity of from about 100 to about 175 m3/hour, or more. Such high-speed air movement forms a vapor mist with the water and significantly increases the speed of the pellets into and out of the dryer such that the PET polymer pellets leave the dryer at a temperature sufficient to self-initiate crystallization within the pellets. A valve mechanism in the slurry line after the gas injection further regulates the pellet residence time and a vibrating conveyor after the dryer helps the pellets to achieve the desired level of crystallinity and to avoid agglomeration.

Abstract: A thermoforming apparatus having a mold with an internal vacuum chamber and a quench for cooling a thermoplastic sheet while it remains on the mold. Because the quench cools the sheet, conventional cooling lines are eliminated from the mold. One method of using the thermoforming apparatus includes pushing a heated sheet towards the mold with a plug assist, drawing the heated sheet over the mold, creating a partial vacuum in the vacuum chamber of the mold to maintain the sheet on the mold and quenching the sheet on the mold in a quenching tank by moving the quenching tank to the mold.

Abstract: An apparatus for granulating extruded material includes an extruder and an underwater granulator connected to the extruder and having a cutting plate for cutting extruded material, the granulator being hinged so that it can swivel about a swivel axis when disconnected from the extruder. A feed pipe is connected to said granulator for providing process water and a discharge pipe is connected to the granulator for transporting and cooling granulate, the feed pipe and the discharge pipe each having a swivel joint with an axis of rotation which is coaxial to the swivel axis.

Abstract: Infinitely adjustable calibration sleeve for extruded plastic pipes includes an inlet head and two strap layers that intersect like a lattice grate and that are linked with each other at the crossing points. In that manner, the inlet head and the strap layers are adjustable to the pipe diameter, and the inlet head has radially adjustable overlapping segments in a radial plane distributed over the perimeter of the plastic pipe to be calibrated, and the segments mesh and have slots in their overlapping areas. Further, the faces of the segments are configured to lie on the plastic pipe to be calibrated, and the strap layers are linked to the segments flush with the faces. Such a calibration sleeve effectively seals the vacuum tank from the environment and prevents deformations of the entering, extruded plastic pipe.

Abstract: The invention relates to a cooled calibrating device for a plastic extrusion facility, comprising a housing (5) receiving a cooling liquid (2) and calibrating guides (6) through which a plastic profile (1) is passed, in addition to inlet and outlet holes (10, 23) having attached lines for the cooling liquid, wherein an area (21) free of liquid and filled with air remains above the level of the cooling liquid. An outlet hole (10) for the cooling liquid is arranged at the height of the cooling liquid level (20) in the calibrating device so that the cooling liquid can flow out without an additional pump. An outlet line (11) attached to the outlet hole extends vertically and ends in a cooling liquid reservoir (12) that is subjected to an external atmosphere, wherein a compact liquid column (24) is formed in the outlet line (11).

Abstract: A novel apparatus for the preparation of a polymer solution includes a stirring device, an extruder connected to the stirring device, a cooling device connected to the extruder, and a warming device connected to the cooling device. The extruder is a fiber or membrane extruding die. Both the cooling device and warming device are vessels.

Abstract: An apparatus for removing NMMO-water mixture which collects in the interior of a tubular film which is produced by the NMMO process comprises a spinning vat and a wash vat. Between the two vats is situated a conveyor belt which circulates endlessly over two rollers. The conveyor belt is directed upward at an incline from the spinning vat to the wash vat. The tubular film, in the interior of the spinning vat, is passed vertically downward, then reversed and conducted vertically out of the spinning vat and passes over the inclined conveyor belt into the wash vat. Above the conveyor belt is situated a spray device having spraying nozzles from which wash liquid at a temperature between 60 and 80° C. is sprayed onto the tubular film which is transported via the conveyor belt.

Abstract: The present invention relates to a method and an apparatus for extruding continuously molded bodies, wherein an extrusion solution, in particular an extrusion solution containing water, cellulose and a tertiary amine oxide, is extruded through an extrusion orifice into a continuously molded body and is then deflected by means of a deflector (7). To improve the quality of the continuously molded bodies produced by the method or apparatus of the invention, the extrusion orifices are arranged in a row such that the individual, continuously molded bodies exit in the form of a curtain (3) form the extrusion head. This curtain is then deflected by the deflector.

Abstract: An apparatus for producing and cooling polymer pellets. Hot pellets cut from a die plate extruder are impelled through air and quickly enveloped in a stream of cooling liquid. The stream is then directed to flow in a first horizontal and vertically descending path, and deflected and inverted into one or more succeeding horizontal and vertically descending paths forming a cascade array, until the pellets are cooled to a predetermined temperature.

Abstract: An apparatus and a continuous process for manufacturing a ring-dyed polymeric filament. A filament, formed by melt extrusion is directly fed into a tank containing a dye solution for a predetermined period of time. The resulting ring-dyed filament includes an outer cross-sectional region colored with the dye and an inner cross-sectional region not colored with the dye. The outer cross-sectional region may be of uniform thickness over the length of the filament. A quenching step can be performed either before or during the ring-dyeing step.

Abstract: An apparatus for manufacturing a liner for installation in an existing conduit in reduced form. The apparatus includes an extruder for extruding heated thermoplastic pipe material through a die to form a tubular shape, a shaping station for shaping the extruded tubular plastic material to the reduced form, a cooling station to cool the liner so that the liner maintains the reduced form and a reheating station to render the liner pliable to be put in suitable form for storage. The liner may be spooled on itself in a layered condition or on a solid spool.

Abstract: The invention relates to a continuous process for the formation of monofilaments having a diameter of from 60 .mu.m to 500 .mu.m from filament-forming polymers by melt-spinning the polymer, optionally quenching the formed polymer filaments below the melt-spinning head with a cooling medium, cooling the filaments in a liquid bath having a temperature of from -10.degree. C. to 150.degree. C., removing the entrained water and post-treating the filaments by spin finishing, drawing and fixing at a filament delivery speed which is greater than 600 to 4000 m/min after the fixing step.

Abstract: The present invention relates to an improved method for regenerating cellulosic sausage casings which includes the steps of extruding viscose through an annular extrusion die submerged in an aquarium to form a tubular product and partially gelling and coagulating the gel tubing in the aquarium, supporting the partially gelled and coagulated tubing on at least two upwardly moving inclined belt such that different sides of the casing are disposed in an upward facing orientation on the different belts and applying an intermediate regenerating solution to the tubing supported by the belts until it is partially cured, and conveying the partially cured tubing into at least one coagulation/regeneration bath which completes regeneration of the tubing.

Abstract: The invention relates to an extrusion installation for elongate products, more particularly plastics tubes, having an extruder 1, followed by a water-cooled calibration sleeve 8 which can be acted upon by negative pressure and a wall thickness measuring device having an ultrasonic sensor 13. The characterizing feature of the invention is that the calibration sleeve 8 is preceded by a retaining device 10 by which the at least single ultrasonic sensor 13 is borne fixed or rotatable concentrically in relation to the elongate product with a predeterminable distance between its measuring head and the external surface of the elongate product 23, and the retaining device 10 has a releasable attachment sleeve 12 whose diameter so corresponds to the inlet side internal diameter of the calibration sleeve 8 that the attachment sleeve 12 performs a precalibration.

Abstract: A wet-spinning process for producing filament utilizes a pair of rollers in the spinning machine which have axes which are skewed to one another, i.e. include angles in projections both in vertical and horizontal planes and so inclined that the interturn spacing of the filament decreases from the upstream wet zone to the downstream drying zone.

Abstract: An apparatus for the production of encapsulated bodies employing a dropping tank for a fluid to form the cores of the encapsulated bodies and a reaction tank containing a solution capable of forming gel skins upon contact with the core material in communication therewith. Double-walled cylindrical nozzles are arranged in a lower part of the drop tank, the inner and outer walls of the double-walled cylindrical nozzles being coaxial. A pressurized air feed pipe is in communication with an upper part of the dropping tank. The peripheral walls of the reaction tank are in the form of a double-walled cylinder whose upper peripheral portion of its inner wall contains a screen. A liquid feed pipe and a capsule discharge port are provided in communication with the interior of the reaction tank through lower parts of the double-walled cylinder. A liquid discharge port also is provided in communication with an annular spacing of the double-walled cylinder through its outer wall.

Abstract: For the continuous automated production of powders that are well suited for hot pressing, i.e. those consisting essentially of spherical or cubic particles, of high-temperature resistant polymers without damage to the polymer structure in the course of the production process, a concentrated solution of the polymer in an aprotic polar solvent is continuously expressed into a twisting cone of hot aqueous precipitant. In doing so, short irregular wormy formations form, which are united to a fleece-like web, washed with aqueous solvents and finally with water, dried and comminuted. The plant provided for carrying out the process requires comparatively little space, since it does not include treatment tanks for extraction and drying.

Abstract: Reduced-size granulation chamber for extruders of materials such as plastics, constituted by a rotating drum wherein the cooling water remains adherent to the walls due to the centrifugal force and which has openings for the exit of the water and of the granules and is inserted in a basket which is in turn inserted in a container, both being fixed and separating the water from the granules, the granules being thrust by inclined fins arranged outside the drum in the chamber defined between the drum and the basket while the water falls by gravity into the second chamber defined between the basket and the fixed chamber.

Abstract: An apparatus for the production of a collagen tube to be used as a vascular prostheses or nerve suture, including a cylindrical tubular spinneret having a feed end for an aqueous solution of collagen gel and a discharge end and a coagulant tube concentrically disposed in the spinneret with all around circumferential clearance and terminating upstream of the discharge wherein a tube of aqueous acid collagen gel is extruded through the clearance around the coagulant tube. The coagulant tube has its inner wall contacted with a coagulating solution emerging therefrom before the tube of aqueous collagen gel reaches the discharge end of the cylindrical tubular spinneret. The discharge end of the tubular spinneret terminates in a bath of coagulating solution and a bed is disposed in the bath to receive the extruded collagen tube from the end of the tubular spinneret. The tubular spinneret is capable of being displaced with respect to the bath.

Abstract: A method for the production of thermoplastic tubes comprising: (1) extruding the thermoplastic tube of which the interior surface in a molten state by a heating unit disposed within the area of a mandrel near the nozzle of an extrusion mold, and (2) sliding the interior surface of the tube on an additional mandrel supported to the front end of the mandrel through a heat-insulating material in axial alignment with the hollow mandrel in a manner to bring the interior surface of the tube into contact with the smooth surface of the additional mandrel and simultaneously cooling the interior surface of the tube with a cooling medium.

Abstract: Apparatus including an extruder, a die member and a vacuum device connected in series. The vacuum device includes a chamber and a device at at least the outlet thereof to air-tightly seal the chamber around the extruded mass of foamed thermoplastic resin. The air-shielding or sealing device is an annular tube which is inflatable radially inwardly having a flexible inner face which seals around the extruded mass. A durable, abrasion-resistant, flexible protective sheet can be interposed between the mass and the tube.

Abstract: A process and apparatus for the vulcanization of the insulation of an electric cable in which the cable core with the insulation thereon are passed through a tube filled with a liquid having a specific weight substantially equal to the specific weight of the insulation. The section of the tube nearer the entrance end is supplied with degassed liquid at vulcanizing temperature and the following section is supplied with degassed liquid at a temperature for cooling the insulation, and because the liquid has different viscosities at the two temperatures, a liquid interface is produced between the two portions which interface is maintained during the vulcanizing of the insulation. During the vulcanizing of the insulation, a portion of the liquid in at least one section is removed and treated to remove vulcanization products.

Abstract: Apparatus for forming pellets from extruded strands of thermoplastic material which includes a liquid-filled tank, an extrusion die face disposed beneath the liquid in the tank, at least one knife blade movable in a direction of movement over the die face to cut pellets from at least one strand of material extruded through an orifice communicating with the die face, a wing extending from the knife blade in a direction opposite the direction of movement of the knife blade and defining a space between the wing and the die face, and means for injecting a purge gas into the space to purge the liquid therefrom. Also disclosed is a method of forming pellets from a strand of thermoplastic material extruded below the surface of a quantity of liquid.

Abstract: Apparatus for continuously vulcanizing a covered material on a conductor comprises a feed device for feeding the conductor in one direction at a constant speed and an extruder for applying the covered material to the conductor fed from the feed means. A vulcanizing tube extends from the extruder, the cable passing through the vulcanizing tube. The vulcanizing tube has a curing section extending from its inlet to a location intermediate its inlet and outlet. A take-off device is disposed forwardly of the vulcanizing tube for hauling the cable. A load applying device is disposed between the extruder and the take-off device for applying a load to the traveling cable at a location forwardly of the curing section of the vulcanizing tube, so that a tension exerted on the cable in a direction opposite to the direction of travel of the cable is applied to the traveling cable.

Abstract: A production line for the manufacture of (unreinforced, reinforced or prestressed) concrete comprising concrete casting means, a circuit for hardening it and means for removing the hardened elements. It includes a chain of floats adapted to be moved in a moat of liquid and means for placing the concrete elements which have just been cast, on said floats, which by moving in the moat, transport the concrete elements through the hardening circuit, means being provided to bring back the floats to the concrete casting means. The installation is applied in the manufacture of piles, posts for electric cables, slabs, beams, panels and curbs.

Abstract: A device for the continuous spinning of viscose rayon includes a main or cessing roller and a plurality of secondary or advancing rollers set askew with respect to the processing roller. The processing and advancing rollers are carried bracket-like by a support arm in which they are rotatively supported. The actuating structures are located in the vicinity of the supports of the respective rollers. The support arm is hollow and contains the roller supports and the actuating structures, and is located at the end of the unit at which the yarns leave the same after being processed. A plurality of spinning units are arranged in rows and the rows are born by a frame carrying all the necessary accessory devices. Means are provided for preventing the escape of fumes from the treatment liquors into the surrounding room.

Abstract: A method and an apparatus for effecting in a continuous manner the three operations of extruding, biaxially stretching and surface coating a seamless tubing of thermoplastic resin such as polyethylene, polypropylene, polyethylene terephthalate, etc. The coating material in a molten state is applied to the tubing while a formative state and prior stretching. A coated film is obtained which is dimensionally stable and is useful for food packaging.

Abstract: A horizontal type vulcanizer for continuous production of an elongated member made of a natural or synthetic polymer. The elongated member passes through a pressurized liquid heat medium to achieve vulcanization. Leakage from the liquid bath seal is prevented by having an intermediate separation portion and balancing the pressure in the bath with that in the intermediate portion. Thermal deterioration of the seal is prevented by cooling the liquid bath in the region adjacent the seals to increase the viscosity of the bath in that region. A water jacket positioned in contact with the front face of the extruder head prevents scorching of the elongated member prior to vulcanization.

Abstract: An apparatus for spinning artificial filaments relates to continuous spinning frames. It comprises a reservoir with spinning solution containin a spinneret and a portion of one cylinder of a pair where complete recovery of the filament takes place. A partition dividing the reservoir into a complete recovery zone and a filament spinning zone is located in the reservoir between the spinneret and that portion of cylinder which is dipped into the spinning solution, said partition filtering the spinning solution flowing from the complete recovery zone to the spinning zone. A collector for feeding the spinning solution is mounted in the complete recovery zone, whereas a collector for discharging the spinning solution is mounted in the spinning zone. This makes it possible to reduce substantially amount of the spinning solution circulating within the apparatus and to separate from the solution elementary sulphur.

Abstract: Polystyrene foam is extruded upwardly as a tube into a cooling media of boiling water, both the interior and exterior surfaces of the cylindrically shaped extrudate passing through a bath of boiling water of variable depth. The polystyrene foam extrudate produced by such a method has a high density at the interior and exterior surfaces, with the density progressively decreasing from these surfaces toward the center core of the extrudate.