Abstract: A quantity of powder material (14) which is less dense than a predetermined density is disposed in a sealed container (12) which is encapsulated in a pressure transmitting medium (16). The pressure transmitting medium (16) is placed within a pot die (26) of a press where it is restrained as ram (24) enters the pot die (26) and applies a force to the pressure transmitting medium (16) and the container (12). The pressure transmitting medium (16) comprises liquid and is capable of transmitting pressure omnidirectionally about the container (12). The container (12) has a porous structure. The container (12) collapses and permanently deforms as the powder (14) compacts. The container does not completely expand to its initial shape after being removed from the pressure transmitting medium (16) and therefore saves the compacted powder (14') from resilient forces of the container (12) tending to rebound the container (12) to its initial shape.

Abstract: A method of forming a fiber reinforced synthetic resin rod-like molding including a rod-like core portion having at least in the outer portion thereof a reinforcing fiber bundle integrally adhered together by a thermosetting resin and a thermoplastic resin layer coating the core portion is disclosed. The outer surface portion of the core portion and the inner surface portion of the thermoplastic resin layer are integrally adhered together due to an anchor effect generated by contacting between the thermosetting resin and the thermoplastic resin in a semifluid state under pressure.

Abstract: When manufacturing an object of powdered material by isostatic pressing of a body (10), preformed from the powdered material, with a gaseous pressure medium, the preformed body is provided with a casing (19) of glass which is made gas-impermeable by heating before carrying out the isostatic pressing. Inside the glass casing there is arranged on the preformed body a barrier layer (11) which counteracts the penetration of melted glass from the enclosure in the preformed body. The barrier layer is built up of at least two layers, of which one layer (12) at least substantially consists of powdered boron nitride and one layer (13) of a mixture of powdered boron nitride and a powdered material with the ability, upon contact with glass from the casing in melted form, to make a layer containing boron nitride tighter.

Abstract: Flashing waste along a rubber or synthetic resin molded article is removed by initially subjecting the article to contact with a cryogenic coolant to embrittle the flashing and then directing the jet of a cryogenic coolant against the article, preferably at the base of the flashing so that the embrittled waste is broken away.

Abstract: The present invention provides for a process for transforming a substantially continuous web of substantially planar, deformable material having an indefinite length, a first surface, and a second surface into a formed material. The material has a transformation temperature range. The process comprises the following steps:(a) The web of material is provided on a forming structure with the first surface of the web of material proximate a forming surface of the forming structure. The forming surface moves in a direction of the length of the web of material and carries the web of material in that direction.(b) A liquid stream is applied to the second surface of the web of material. The liquid stream has sufficient force and mass flux to cause the web of material to be deformed toward the forming surface, such that the material acquires a substantial three-dimensional conformation.

Abstract: A polyacetal copolymer of continuous length is disclosed. The copolymer has an apparent density of 1.20 to 1.46 g/cm.sup.3, and a tensile modulus (X) of 19 GPA or more and a density change percentage (Y) of 85% or more. The relationship between the density change percentage (Y) and the tensile modulus (X) is defined by the following relationship:when 19.ltoreq.X.ltoreq.30, then Y.gtoreq.127.7-1.42X, and when X>30, Y.gtoreq.85.A method for producing this copolymer includes permitting a polymeric material in continuous length to pass through a pressurizing fluid and applying a substantially uniform pressure therearound. A drawing stress is applied to the material while heating it at a temperature not above its softening point, thus subjecting the material to high stretching.

Abstract: Large thermoplastic articles are injection molded, cooled to a self supporting temperature, transferred to a vessel, the articles being maintained under fluid pressure sufficient to prevent the formation of voids on cooling to ambient temperature.

Abstract: A preformed body (12) from powder material of metallic and nonmetallic compositions and combinations thereof, is consolidated to form a densified compact (12") of a predetermined density. An outer container mass (20), capable of fluidity in response to predetermined forces and temperatures and which is porous to gases at lesser temperatures and forces than said predetermined force and temperature, surrounds an internal medium (22). The internal medium encapsulates the preformed body (12) within the container mass (20) and is capable of melting at the lesser temperatures to form a liquid barrier to gas flow therethrough. The internal medium (22) is capable of rapid hermetic sealing during the early stages of preheat. External pressure is applied by a pot die (16) and ram (14) to the entire exterior of the container mass (20) to cause the predetermined densification of the preformed body (12) by hydrostatic pressure.

Abstract: A ceramic article of alumina reinforced with silicon carbide whiskers suitable for the fabrication into articles of complex geometry are provided by pressureless sintering and hot isostatic pressing steps. In accordance with the method of the invention a mixture of 5 to 10 vol. % silicon carbide whiskers 0.5 to 5 wt. % of a sintering aid such as yttria and the balance alumina powders is ball-milled and pressureless sintered in the desired configuration in the desired configuration an inert atmosphere at a temperature of about 1800.degree. C. to provide a self-supporting configured composite of a density of at least about 94% theoretical density.

Abstract: In preparing a sintered silicon nitride body by hot isostatic pressing, if a green molded body of silicon nitride and a sintering aid is coated with a compound of high melting point cyrstalline powder (sintering aids of silicon nitride), said crystalline compound works as a pressure media on HIP treatment and is present in the surface of the sintered body. By the presence of this crystal, hot isostatic pressing of this dual density compact mentioned above results surface compression stress, which results not only the strength at room temperature but also the strength at high temperatures is highly improved.

Abstract: Improved electrochemical sensors are provided through isostatic processing techniques. Improved electrochemical sensors, especially those suitable for use in metallurgical melts, having, at once, long-term stability, improved sensitivity, and improved physical properties including thermal shock resistance are provided. In accordance with a preferred embodiment, unitary bodies comprising the sensing electrolyte and a source of reference potential are fabricated through isostatic processing techniques. Methods for the preparation of these improved sensors together with methods for the improvement of sensing, especially of oxygen in metallurgical melts are also disclosed.

Abstract: Sheets of incompletely fixed biological tissue comprising portions for defining valve flaps of a cardiac valve prosthesis are mounted on forming means which can separate in a substantially fluid-tight manner the opposite faces of such portions. These opposite faces are subjected to a fluid pressure difference which produces deformation of the portions towards a conformation substantially identical with the conformation of the valve flaps when mounted in the prosthesis. The biological tissue is finally fixed while the portions defining the valve flaps of the prosthesis are maintained in the said conformation. The sheets of biological tissue are then separated from the forming means to be subsequently mounted in the frame of the prosthesis.

Abstract: A method of producing unitary hollow structures, for example radomes, comprised of fiber reinforced plastic with a large percentage of the fibers being randomly oriented in directions essentially parallel to the wall surfaces of the structures and with at least one surface having grooves to reduce microwave reflection is presented. The structures are produced by packing a layer of fiber filled polymeric material in powder form around a mandrel which may have a pattern of grooves of ridges in its outer surface. The mandrel and packed powder are subjected to isostatic pressing to properly orient the fibers and achieve a density increase and powder cohesion. The pressed structure is sintered and the outer surface subesquently machined to a finished contour.

Abstract: A strong, durable nonwoven fabric comprising polyester and/or polyolefin fibers arranged in a pattern of high density, lightly entangled fiber regions. Distributed throughout the fibers is an adhesive binder material to provide the final fabric with improved strength characteristics.Entangled nonwoven fabrics are dry print bonded to produce nonwoven fabrics having an excellent combination of strength, softness and durability.

Abstract: In a submarine cable optical fibre regenerator housing a copper tail pipe (optionally with a brass end section incorporating an anti-extrusion profile for fitting inside a gland) is provided with a tight fitting length of thermoplastics sleeving by collapsing a thermoplastics preform down onto the tail pipe using heat and air pressure applied to the outside of an elastomeric tube into which the tail pipe and preform have been inserted.

Abstract: In preparing a sintered silicon nitride body by hot isostatic pressing, a composition comprising Si.sub.3 N.sub.4 and a sintering aid is molded to form a green molded body, the surface of the green molded body is coated with a composition comprising Si.sub.3 N.sub.4 and a sintering aid and having a sintering temperature lower than that of the composition of the green molded body, the coated green molded body is preliminarily sintered so that only the coating layer is densified, and the preliminarily sintered molded body is subjected to hot isostatic pressing. The obtained sintered body has a surface compression stress, and by this surface compression stress, not only the strength at room temperature but also the strength at high temperatures is improved.

Abstract: A radome combines low dielectric constant and dissipation factor at microwave frequencies with mechanical strength and rigidity as well as resistance to ablation and rain erosion at hypersonic velocities in the range of Mach 4 to 6. Continuous filament glass fabric and/or strand is saturated with PTFE dispersion. Layers are applied to a mandrel and cold isostatically pressed. The pressed layer may be machined between applications and subsequent pressings. After all layers are applied and pressed, optionally including an outer ablation resistant random fiber reinforced PTFE composite, the densified structure is heat cycled above the crystalline melt point of the polymer to maximize mechanical properties.

Abstract: A radome being a unitary structure comprised of a fiber reinforced plastic is produced with a large percentage of the fibers being randomly oriented in a plane parallel to the inner surface of the radome. The radome is produced by packing a layer of fiber filled powder around a mandrel having its outer contour resemble the inner contour of the radome. The mandrel and packed powder are then subjected to isostatic pressing to properly orient the fibers. The radome is finished by sintering the powder and removing the finished form from the mandrel.

Abstract: A continuous, multi-phase process for debossing and perforating a substantially continuous web of substantially planar polymeric film to coincide with the image of one or more forming structures, each having a patterned forming surface with a multiplicity of holes and an opposed surface. Each forming structure is open from the holes in the forming surface to its opposed surface. The web of film has an indefinite length, a first surface, a second surface and a thickness. The thickness comprises the distance between the first surface and the second surface. The process comprises at least two sequential forming phases, one of which involves three-dimensional conformance of the web to the macroscopic profile of the forming structure and another of which involves aperturing of the web to coincide with fine-scale apertures in either the same or a separate forming structure.

Abstract: A process for the production of expandable granules of thermoplastic polymers comprising: (a) the extrusion of the polymer in which an expanding agent is incorporated, through a die-head in order to obtain an expandable polymer; (b) immediate cooling of this polymer in water, kept at a temperature at which the polymer remains in the non-expanded state, but not lower than the Tg of the expandable polymer; (c) cutting of the polymer to granules in water immediately at the outlet of the die-head, and (d) annealing of the thus obtained granules, by slow cooling in a temperature range comprised between at least +5.degree. C. and at least -5.degree. C. the Tg of the expandable polymer, wherein the cooling and the cutting of the polymer to granules and the annealing thereof are carried out under pressure.

Abstract: High strength titanium diboride (TiB.sub.2) articles which are obtained by sintering articles preformed from TiB.sub.2 powder mixed with epoxy resin by means of isostatic molding using sintering temperatures found to be a critical variable for achieving maximum strength. Resistance to aluminum attack is achieved by removing contaminating oxides, nitrides, and carbides of titanium by selecting either annealing the sintered article in a boron nitride (BN) pack or by including a small amount of BN or elemental boron in the original TiB.sub.2 powder, such that the finished article is substantially free of such contaminants.

Abstract: The present invention is directed to a method of manufacturing low thermal expansion modified cordierite compositions which are especially useful in the manufacture of mirrors for high temperature applications, said method comprising the steps of: providing, on a molecular basis, a mixture of about 2 moles magnesium oxide, 2 moles aluminum oxide, and about 5 moles divided between silicon dioxide and germanium oxide; blending said materials; milling the mixture until finely divided and thoroughly mixed; forming said mixture into a desired shape; gradually heating the shape to a temperature at which reactive sintering occurs and a cordierite type structure is formed; gradually cooling the structure; and hot compacting the structure to consolidate the sintered body to very nearly 100 percent of theoretical density.

Abstract: A non-woven fabric having a pattern defined by an array of discrete areas having a reduced fibre density but which are substantially free of perforations is produced by supporting a freshly wet laid web of the non-woven fabric on a porous surface and directing spaced jets of fluid against the unsupported side in order to displace fibres within discrete areas while maintaining in position a proportion of fibres that are within those areas and that are adjacent the porous surface. The fabric web may be supported on a Fourdrinier wire (1) and the jets of fluid (e.g. water) may be directed through the apertures in a perforated cylinder (6), the fluid being supplied under pressure from a water-knife device (11). The apertures in the cylinder (6) preferably have a cross-section that increases in the direction of the water jets.

Abstract: This invention provides a multi-step process for the preparation of ceramic fibers, such as ferrimagnetic spinel fibers which are useful in electromagnetic interaction shielding applications.The process involves subjecting a ceramic powder-filled hollow organic fiber to isostatic pressing, and then pyrolyzing and sintering the compacted fiber to yield a ceramic fiber.

Abstract: Process of hot isostatic pressing of MnZn ferrite material for producing ferrite close to theoretical density without a significant increase in grain size. Permeability is increased with the increase in theoretical density. The process includes the steps of pressurizing an entire ferrite sample which is surrounded by pieces of similar composition while in alumina crucibles with fused alumina grain there between and an optional oxygen getter on top of the grain, introducing an inert atmosphere, elevating pressure and temperature, the temperature elevated to a value below that previously used for sintering or hot pressing, and maintaining temperature to optimize density without excess grain growth. Density is thereby optimized without excess grain growth, while maintaining or improving the magnetic properties.

Abstract: A quantity of material (10), which is at less than a predetermined density, is disposed within a sealed container (12) which is, in turn, encapsulated in a pressure-transmitting (18) medium which is, in turn, placed within a pot die (20) of a press where it is restrained as a ram (24) enters the pot die (20) and applies a force to the pressure-transmitting medium (18) to densify the material within the container into a compact (10') of predetermined density. The pressure-transmitting medium (18) is characterized by a rigid interconnected ceramic skeleton structure (26) which is collapsible in response to a predetermined force and fluidizing glass (28) capable of fluidity and supported by and retained within the skeleton structure (26). The glass (28) becomes fluidic and capable of plastic flow at temperatures utilized for compaction whereas the ceramic skeleton (26) retains its configuration and acts as a carrier for the fluidic glass (28).

Abstract: A method for producing a high strength sintered silicon carbide, the method comprising: molding a mixture of silicon carbide powder and a sintering aid into a green compact of a predetermined shape: preliminarily sintering the green compact to obtain a preliminarily sintered compact having a relative density higher than 80%; charging the preliminarily sintered compact in a HIP equipment without using a capsule; and subject the preliminarily sintered compact to a HIP treatment in a high-temperature and high-pressure N.sub.2 gas atmosphere maintaining a pressure higher than 500 atms and a temperature in the range of 1400.degree.-2300.degree. C.

Abstract: The invention relates to a process for producing plates of a metallic or semimetallic material.The latter is in the form of a liquid mass entirely separated from the walls of a crucible by a liquid film of a second material. A group of plates is lowered into the crucible, in order that the liquid mass can solidify, while being separated from the plates by the protective liquid film.Application is to the production of photovoltaic silicon plates.

Abstract: A sintered ceramic body for cutting tools having a residual porosity of not exceeding 0.2% by volume and mean crystal grain size of not exceeding 2.mu. is obtained by sintering a mixture substantially consisting of 70-95% by volume alumina and the balance of titanium nitride and Zr-containing component(s) such as Zr, ZrC and/or ZrN wherein the volumetric ratio of TiN/Zr-containing component(s) ranges 95/5-50/50 under the pressure application of 50-3000 Kg/cm.sup.2. The sintering may be carried out by hot pressing or HIP process.

Abstract: A portion of a plastic tube (16) heated to a temperature at which stretching induces a molecular orientation, is clamped in a sleeve (14), a fluid under pressure is introduced into the portion of tube and the sleeve is moved along the portion of tube to cause its progressive radial expansion until it makes contact with a mould (1).

Abstract: A method of hot isostatic pressing in which a shaped work immersed in molten glass is subjected to a hot isostatic pressing treatment, the method basically including embedding a shaped item to be worked on in glass powder filled in a crucible; loading the crucible into a movable heating furnace having a heater and a heat insulating structure; charging the furnace into an atmospheric chamber; adjusting the atmosphere in the chamber into a predetermined condition and heating the crucible by the heater to soften and melt the glass in the crucible; transferring the furnace from the atmospheric chamber into a high pressure container while maintaining a high temperature in the furnace; admitting a pressing gas medium into the high pressure container while raising the temperature of the furnace to let the work in the crucible undergo a hot isostatic pressing treatment; and upon completion of the hot isostatic pressing treatment, taking out the furnace from the high pressure container with the work still in loaded st

Abstract: A hydrostatic extrusion apparatus whereby semicrystalline thermopolastic polymers can be hydrostatically extruded in a solid state is described. The apparatus includes an outer tooling support means; a container assembly aligned within one end of the outer support means and having pressure means contiguous therewith whereby pressure is applied to the apparatus to both rigidly align the tooling and provide sufficient pressure for extrusion of a polymer billet within the container assembly and a receiver assembly coaxially aligned with the container assembly in the other end of the tooling means. The container assembly includes a container means, sealing means to prevent leakage of hydrostatic fluid in the container means and a die portion on the inner forward surface of the container means. The receiver assembly includes a concentrically aligned mandrel which supports and aligns a mandrel-head in spaced relationship with the die portion of the container means.

Abstract: A ceramic insulator body for receiving and electrically isolating two parallel terminal rods is manufactured by radial isostatic compaction of a ceramic powder about a core member having an hourglass cross section. The core member produces a bore comprising two parallel terminal-receiving channels connected by a constricted passage that is sized and shaped to space apart two terminal rods in the channels.

Abstract: A pipe of oriented thermoplastic polymeric material having an integral socket is manufactured by expanding a tubular blank having a portion of greater wall thickness which is positioned in a portion of a female mould defining the socket. The tubular blank is heated by circulation of hot water to a temperature at which deformation will induce oriention of the polymer molecules, and is then expanded radially outwards against the mould by application of internal pressure. In this manner the wall thickness and rigidity of the socket are increased.

Abstract: An apparatus and method for forming components having one or more inner cavities wherein material forming the component is laid up about a number of eutectic salt mandrels corresponding to the inner cavities. The mandrels are melted and the laid up material compressed during the formation of the component by hydraulic pressure transmitted through the molten mandrels.

Abstract: A hydrostatic extrusion apparatus whereby thermoplastic polymers can be hydrostatically extruded in a solid state is described. The apparatus includes:(a) an outer casing or tooling support means,(b) a container assembly concentrically contained within the outer casing and having pressure means attached thereto to provide extrusion pressure to a fluid in the assembly, sealing means to prevent leakage of the fluid, means for holding a polymer billet and including a die portion, and(c) a receiver assembly axially aligned with the container assembly concentrically within the outer casing having pressure means to clamp the container and receiver assemblies together, a mandrel for holding and aligning a mandrel-head in spaced relationship with the die, and means for receiving, lubricating and cooling the extrudate.Optionally, means for preheating and loading the polymers into the container assembly are provided whereby the press may be operated on a semi-continuous or continuous basis.

Abstract: A solid crystalline organic polymer is made into a filament, rod, or film by ultra-drawing it at a temperature within 70.degree. C. of but below its melting point at the operating pressure while subjecting the polymer during and immediately after drawing to a hydrostatic pressure of at least about 500 atmospheres applied by a fluid medium inert to the polymer. High-density polyethylene and isotactic propylene are preferred polymers. A draw ratio of at least 20:1, and as high as 60:1, may be used. Pressure may be up to 2500 atmospheres or more. The rate of drawing for polyethylene is above 500 percent per minute. The ultra-drawn products are transparent, essentially free of internal voids, and exhibit very high tensile moduli of elasticity, up to 65 to 70 Giga-Pascals in the case of polyethylene.

Abstract: The invention is directed to biaxially oriented thermoplastic polymer flexible film having a substantially uniform thickness between about 0.005 and 0.030 of an inch (0.13 mm and 0.76 mm) and characterized by a structure comprised of discrete, platelet-like spherulitic crystalline aggregates compressed transversely to the plane of the film and biaxially oriented in the plane of the film and having a combination of improved properties and also to a rigid conduit or extrudate having a plurality of thermoplastic crystalline polymer layers each of which has a unique microstructure and improved properties.

Abstract: A mould for use in the manufacture of thermoplastics eg PVC pipe by radial expansion of a pipe blank, the mould comprising a cylindrical central portion 10 and two removable mould end portions 11, 12. The pipe blank 14 is located centrally within the mould by mandrels 13 within each mould end portion 11, 12. Water inlet/outlet ports 15, 16 are provided in each mould end portion 11, 12 to admit water to and remove it from the region between the blank 14 and the mould walls, and the mandrels 13 are hollow to permit inlet/outlet of water through the interior of the blank 14.

Abstract: A method of manufacturing thermoplastics pipe by the radial expansion of a pipe blank within a mould. The blank 28 is inserted horizontally into a raised central mould portion 12, with the ends of the blank 28 extending outwardly of the ends of the central mould portion 12. Portion 12 is then lowered to a first position where mandrels 19, 20 enter the blank 28 from each end, and then a second position where mould end caps 15, 17 are closed onto the central mould portion 12, and heating and expansion of the blank 28 is then effected.

Abstract: Apparatus for use in the manufacture of socketed thermoplastics pipe by the radial expansion of a pipe blank. The apparatus includes an open-ended central mould portion 12 which can be raised or lowered on stanchions 10, 11 to three predetermined positions; a pair of mould end portions 15, 17 each having a supporting mandrel 19, 20 engageable with the pipe blank 28, end portions 15, 17 being advanceable to and retractable from the central mould portion 12. One of the mould end portions 15 is internally contoured to provide part of the socket-forming portion of the mould. The mould end portions 15, 17 can be held in an intermediate position, partially advanced towards the central portion 12 to locate the blank 28 on mandrels 19, 20 before closing of the mould.

Abstract: A thick-walled, seamless, rigid conduit having a substantially uniform wall thickness which is not less than about 0.5 percent of the outside diameter consisting essentially of an oriented crystalline thermoplastic polymer characterized by a structure comprised of radially compressed discrete, platelet-like spherulitic crystalline aggregates and having a combination of good ultimate tensile strength and low temperature tensile impact strength is described.The conduit is fabricated by solid state hydrostatic extrusion of a substantially non-oriented semi-crystalline thermoplastic polymer preform which may contain up to about 60 weight percent filler. The polymer is substantially simultaneously elongated in both circumferential and axial directions by compressive forces with the circumferential elongation being at least 100 percent.

Abstract: A method for molding a bulge comprises a step of jetting a pressure fluid from a nozzle into a shaped blank fitted thereto thereby causing air trapped in the shaped blank to be agitated into air bubbles to allow the fluid pressure to be applied onto the inner surface of the shaped blank during discharging the liquid from within the blank.

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: A nonwoven fabric having alternating stripes of high fiber density and low fiber density is made in such a manner that the high fiber density stripes run across the fabric and maximize the cross direction strength to a point that the cross direction/machine direction strength ratio approaches unity. This advantageous and desirable characteristic can be achieved by hydroforming card web; first disposing the carded web on a relatively fine mesh screen and placing a finger-like striping bars over the web with the axis of the bars at 90.degree. to the card web's general fiber orientation. Water was then sprayed over the assembly with sufficient force to rearrange the fibers in the web thereby producing the nonwoven fabric of this invention.

Abstract: A method of curing a polymeric hose are provided wherein a hose to be cured is confined within a tubular preformed spiral confining wall of a mold structure to thereby provide optimum support for the exterior surface of such hose during curing which assures provision of a precision outside surface yet enables curing of a substantial length of hose in a comparatively compact volume.

Abstract: Fine-grained halide bodies are formed which have comparable optical properties to a single crystal halide body. The halide bodies are formed by press forging while an essentially constant fluid pressure is applied to the halide body.

Abstract: A method of applying a vermicular expanded graphite composite material to the interior surface of a conduit by a two-step in situ compression process is disclosed.

Abstract: An improved method and apparatus for shaping sheets of thermoplastic material is disclosed in which sheets are pressure molded against a mold member by the direct application of a liquid coolant under pressure thereto. The coolant contacts the surface of the sheet and upon pressure reduction vaporizes and accordingly, due to the heat of vaporization effect, rapidly absorbs a large amount of heat from the sheet so as to form a solidified skin on the outer surface of the sheet after or simultaneously with the shaping of said sheet. The sheet thus remains in the mold for a shorter dwell time inasmuch as the sheet becomes more quickly shape retentive because of the rapid cooling. This accordingly permits smaller and less bulky equipment to be utilized in sheet shaping processes. The attendant reduction in equipment size can result in substantial cost savings for such equipment.

Abstract: An extrusion pelletizing process is disclosed wherein coolant is injected into the stream of thermoplastic material being extruded in such a fashion to interrupt the flow thereof and form discrete material lengths thereof as the material moves through the extrusion die and exits at the other end thereof in the form of pellets. The coolant is permitted to at least partially vaporize upon contact with the material stream and accordingly forms a solidified shell therearound including end portions of adjacent pellets so as to effectively separate such as they pass through the die. Such system enables the formation of discrete material lengths or pellets without the need of conventional cutting apparatus such as knives and the attendant support equipment necessary in their use.