Abstract: A flexible insulation blanket having a smoothly surfaced, secondarily bonded, ceramic matrix composite (CMC) outer layer, and a method of producing a flexible insulation blanket having a secondarily bonded CMC layer by forming a CMC prepreg layer comprising a woven ceramic fabric layer impregnated with a pre-ceramic slurry and layering the prepreg layer with a flexible insulation blanket. The blanket and prepreg layer are then compressed such that the prepreg layer abuts a rigid smoothly surfaced plate and the ceramic material is cured by heating while under compression. Pressure is then released and the insulation is fired to sinter the ceramic material of the CMC layer.

Abstract: A concrete pipe making machine having a packerhead consisting of a rollerhead and a longbottom in which the rollerhead and longbottom are quickly assembleable and disassembleable as a unit from the packerhead drive means with one connector and brought into final adjustment off the machine, said drive means providing no obstruction to the flow of wet concrete toward the compaction area, the speed ratios between the rollerhead and longbottom being infinitely variable, and easily replaceable protective wear rings for precluding erosive deformation of the permanent parts of the machine due to undesired penetration of wet concrete into the longbottom.

Abstract: A method and method to ensure the uniform collapse and diminished loading forces of a prosthesis, the prosthesis having at least one layer of biocompatible material. The device includes a way to stabilize the prosthesis, wherein the prosthesis can be incrementally axially rotated, and a way to manipulate the layer of biocompatible material simultaneously at several distinct points along an axis of the prosthesis so that a set of alterations is formed in the biocompatible layer.

Abstract: A rotomolded plastic wall and ladder structure (10, 50, or 58)), which may be an article such as a window well (10) or a manhole (50 or 58), includes a thermoplastic wall (12), a ladder (16) whose rungs (18) each include an elongated metallic core (20) and a thermoplastic sleeve (22). Mold apparatus (70) includes a thermoplastic rotomold (72), an elongated hollow metallic core (20) having a heating passage (74) therein, and means for flowing hot air through the heating passage (74). The method includes disposing the hollow metallic core in a mold, placing a quantity of a thermoplastic inside a mold, heating the mold, rotating the heated mold, flowing heated air through the hollow metallic core, and bonding a layer of the thermoplastic onto the hollow metallic core.

Abstract: A process for rotomolding using novel melt-extruded melt-fabricable TFE copolymer minicubes, wherein at least 80% of the minicubes are in the size range of 200 to 1200 &mgr;m.

Abstract: The invention concerns a procedure for the production of tubes from concrete mix, whereby the concrete mix is filled into a shaping device, for the purpose of shaping, where it is condensed with a tool. The invention should enable an effective and fast production of concrete tubes with high quality regarding the uniformity of the material characteristics. In such a procedure the concrete mix is condensed in an interspace between two parts of a tool that rotate relative to each other.

Abstract: To make a seamless tube of polyimide, an amount of polyamic acid precursor to constitute the final tube is applied eveny as a solution to a cylindrical mandrel. The mandrel is rotated while a canted doctor blade smoothes the solution. The solvent is then expelled and the remaining precursor cured by heat.

Abstract: A process for the production of polyolefin hollow articles comprises charging the polyolefin with a stabilizer combination comprising (a) at least one compound from the group of the organic phosphites or phosphonites, (b) one or more compounds selected from the group consisting of i.) hydroxylamine derivatives and ii.) amine oxide derivatives and (c) at least one compound from the group of the hindered amine stabilizers, filling this mixture into a mold, heating this mold in an oven to above 280° C., such that the stabilized polyolefin fuses, rotating the mold around at least 2 axes, the plastic spreading to the walls, and cooling the mold while still rotating, opening it and taking the resultant hollow article out.

Abstract: It is an object of the present invention to reduce variations in dimensional accuracy such as the outer-diameter accuracy and roundness of a flare shape and the concentricity between the bulb portion and the flare portion. According to the present invention, a lower mold (1) formed of a metallic material and forming a recess flare shape (1a) that is subjected to surface treatment forms a flare shape (21b) almost identical to the flare shape (1a) by means of the rotational motion of a rotating head portion (2). An upper mold (10) is fitted in the lower mold (1) to form a flare-shaped gap portion (13), into which glass is forced to form a flare shape (22).

Abstract: A core is made of a biodegradable material, reinforcing fibers and non-hardened resin are laminated on the core so as to form a fiber-reinforced composite material. Then, the fiber-reinforced composite material is hardened, and then biochemically active substances, such as microorganisms and enzymes, are brought into contact with the core so that the core is biochemically degraded and removed.

Abstract: A composite with a thermoplastic matrix and fiber reinforcement is made by rotation of an exit die about a roving of continuous fiber in the presence of a thermoplastic melt. The rotation causes opposing inner and outer helical flow conditions which reduce the melt viscosity of the polymer by shear thinning while dragging and directing the polymer into the fiber roving thereby wetting and dispersing the fiber. A composite structure is formed with a polymer rich skin and a core region of unidirectionally aligned polymer and fiber. The polymeric skin is composed of helically aligned polymer chains which are coiled by the rotation around the core to compress the core region and enhance fiber wet out.

Abstract: This invention relates in general to the formation of thick films having a biaxial molecular orientation. Such films are prepared in accordance with the present invention from rod-like extended chain aromatic-heterocyclic ordered polymers. Such films have high tensile strength, modulus, and environmental resistance characteristics. A preferred ordered polymer for use in the present invention is poly (para-phenylenebenzo bisthiazole), (PBT), a compound having the structure: ##STR1## The present invention is also directed to methods and apparatus suitable for producing biaxially oriented films, coatings, and like materials from ordered polymers, preferably PBT.

Abstract: An improved method is provided for extruding ePTFE tube (12) for use in medical applications. A tube (12) of PTFE is extruded, preferably in an extrusion process, using counter-rotated die components (22, 26). The die component (16) is maintained at a constant temperature during processing. The resulting green tube (12) has enhanced fibrous state formation in a direction perpendicular to the direction of extrusion. The PTFE green tube (12) is then subjected to secondary operations such as stretching and expansion to yield medical product. The ePTFE tube (12) structure is defined by nodes interconnected by elongate fibrils. Both the nodes and fibrils are substantially randomly tilted with respect to the longitudinal axis of the tube (12). This particular structure yields a tube (12) which exhibits a high degree of radial tear strength useful in medical applications.

Abstract: Process for moulding a thermoplastic material by injection onto a rotating core, in which the relative rotation of the various parts of the mould takes place during at least a part of the dwell stage and ends before the end of this stage. This process, which yields good results with polyolefins, makes it possible to manufacture articles such as receptacles and cylinders, exhibiting good mechanical properties.

Abstract: Flow lines are eliminated from workpieces injection-molded from liquid crystal polymers, fiber-filled or mineral-filled thermoplastics by selecting a liquified polymer having a linear coefficient of thermal expansion less than (2-6).times.10.sup.-6 /.degree.K, providing a flow path in a mold for the polymer in two directions around a core in the mold, and subjecting the polymer to a shearing energy only simultaneously with mold filling over at least part of the flow path, whereby molecules of the polymer are disoriented and fail to produce a rigid alignment.

Abstract: Process for injection moulding on a rotating core of a thermoplastic material exhibiting a modulus of relaxation in shear G.sub.n (7.5) higher than 0.15. This process, which gives good results with polyolefins, makes it possible to manufacture articles such as receptacles and cylinders exhibiting good mechanical properties.

Abstract: A molding process includes flowing a polymer melt into the cavity of a mold which includes a core pin. After the mold is filled and skin layers of solidified polymer have formed adjacent the mold wall and core pin wall, the core pin is spun transversely to the direction of polymer melt flow. The invention includes hollow articles of improved mechanical properties made by the process.

Abstract: The method for manufacturing a tube-like extrusion profile includes the steps of: simultaneously conveying a number of, in the circumferential direction of the profile, divided streams of material of at least two different compositions to a molding-nozzle; and, making the streams flow together in the molding-nozzle. At least one of the streams is supplied rotating in a circumferential direction. Preferably at least two streams of material are supplied rotating in opposite directions, so that at least two helically shaped bands of material extend in opposite directions in the extrusion profile. The method also includes the step of: allowing the combined streams of material to cool off into the extrusion profile so that the streams of material supplied in a rotating manner extend helically in the extrusion profile formed by the method.

Abstract: A compaction head of a production machine for reinforced concrete pipes has a smoothing cylinder, non-rotatably mounted on its drive shaft, for smoothing the inside of the concrete mixture that has been filled into a vertical mold. On a covering wall of the smoothing cylinder, the rolls, for the radial compaction of a concrete mixture, are mounted axis-parallel and orbiting on a circular path around and driven by the drive shaft at a specified orbiting speed about the axis of the drive shaft and about their own axis, such that the direction of rotation of each of the rolls about its own axis is opposite to that of the covering wall also driven by the drive shaft.

Abstract: The object of the present invention is to recondition cardboard or similar tubes with deformed parts, notably at the ends, whilst avoiding the usual milling techniques and without removing any material. The deformed parts of each tube (1) are recalibrated to their initial thickness by being rolled between pairs of rollers (15, 20), of which at least one is driven in rotation. The tube (1) is then supported only by the rollers. Each internal roller (20) can be mounted on a movable support (18) which brings it into its working position in the tube. Application for the reconditioning of tubes serving as supports for textile yarn reels.

Abstract: An improved extrusion method is employed in a process which is used to form tubing for medical applications. The method includes providing an extrusion apparatus having a die which includes a die cavity and a mandrel within the die cavity. The die is rotated in a first rotational direction while the mandrel is rotated in a second rotational direction opposite the first direction. While the die and the mandrel are rotating, a PTFE paste is passed through the annular passage defined between the die and the mandrel. The die cavity is cooled to maintain the PTFE paste passing therethrough at a substantially non-elevated temperature.

Abstract: A counter-rotating compaction head for manufacturing a concrete pipe is vertically positioned in a vertical mold within the longitudinal axis of the mold so as to be rotatable about and axially slidable along the longitudinal axis of the mold. The counter-rotating compaction head has a distributing head with distributing devices for distributing concrete and a cylindrical mantle. A first drive shaft rotates the distributing head. A smoothing piston with a smoothing mantle is rotatably driven by a second drive shaft counter to the distributing head. At least one vibrator for compacting and smoothing an inner wall surface of the concrete pipe to be manufactured is operatively connected to at least one of the cylindrical mantle of the distributing head and the smoothing mantle of the first smoothing piston so as to vibrate the respective mantle.

Abstract: A method for manufacturing concrete panels by continuously pressing and an apparatus for carrying out the method. The concrete panels are successively manufactured by continuously feeding pallets onto a conveyor, feeding a concrete material onto the pallets, continuously pressure frames against the concrete material from the upper side and both lateral sides of the concrete material while imparting vibrations to the pressure frames, forming hollows in the concrete material by thrusting a rotary screw-type core rod therethrough to provide a panel shape hollow molding, and cutting the molded concrete material into a length corresponding to the length of each pallet. In the manufacture process, an organic or inorganic fiber material may be incorporated into the concrete material for the purpose of reinforcement of the finished products.

Abstract: An improved combination counter rotating packerhead and vibrator assembly is provided. A counter rotating packerhead including counter rotating roller assemblies, longbottom assemblies or a combination thereof is disposed directly over an annular pneumatic vibrator. The coaxial drive shaft for the counter rotating packerhead passes through the vibrator thereby permitting the power transmission means to be located below, and isolated from, the vibrator. The vibrator is disposed below, but adjacent to, the counter rotating packerhead for faster pipe production.

Abstract: A method of producing a spliceless annular tread cap (2), whereby a portion (23) of an extruded tube (21) of green elastomeric material is fed inside an annular body (8), the inner annular surface (17) of which presents a diameter approximately equal to but no smaller than the outside diameter of the tubular portion (23), and negatively reproduces the pattern of the finished tread cap (2). The tubular portion (23) is expanded and calendered against the inner surface (17) of the annular body (8) by means of a roller (34) moved into a position coplanar with and eccentric in relation to the annular body (8).

Abstract: Coextrusion apparatus for forming tubular elastomeric ply made up of first, second and third concentric streams of elastomeric material and a pair of coaxial helical patterns of individual reinforcing elements wound in opposite direction with respect to each other contained within the first and third streams of elastomeric material and separated by the second stream of elastomeric material. A pair of reinforcing element guides are rotatably mounted within the apparatus between stationary flow channels for the three streams of elastomeric material, and are rotated in opposite directions with respect to each other. The two helical patterns of reinforcing elements and three streams of elastomeric material merge together substantially simultaneously in concentric circles which lie in a plane generally perpendicular to a central axis of the coextrusion apparatus to form the tubular ply. A method for producing such a reinforced tubular elastomeric ply also is presented.

Abstract: A method of manufacture of an ultra-high molecular weight polyethylene thin-wall pipe which is uniform in thickness and free from a folded mark. The ultra-high molecular weight polyethylene thin-wall pipe is manufactured by supplying ultra-high molecular weight polyethylene into and melting and kneading, continuously extruding the molten substance of the ultra-high molecular weight polyethylene from a die connected to a screw of the screw extruder to form a cylindrical roughly shaped article, and diametrically expanding the cylindrical roughly extruded article by means of a tapered core and taking up.

Abstract: An improved method for lining a section of pipe with a cement mortar. After a wet cement mortar has been applied to a cleaned interior surface of a pipe, carbon dioxide is introduced into the freshly lined section of the pipe in such quantity that a crust of calcium carbonate will be formed on the surface of the wet cement mortar lining as the carbon dioxide reacts with calcium compounds of the wet cement mortar in a relatively short period of time. This crust is provided to tolerate a low-velocity flow of water to protect the underlying mortar from scouring until the normal hardening of the underlying mortar through hydration can take place so as to substantially reduce the out-of-service time of the section of pipe which is being lined.

Abstract: To rehabilitate an internally corroded underground pipeline, excavations are made at its opposite ends to which launching and receiving pipe structures are then secured. Various pig member sets, with appropriate treatment fluids carried thereby, are air-driven through the entire length of the pipeline to successively acid clean, etch, and neutralize its interior surface. The interior pipeline surface is then thoroughly dried by flowing dehydrated air through the pipeline. Specially designed leading and trailing extruder pigs, with 100% solid, high viscosity, solvent-free epoxy coating material therebetween, are then air-driven through the pipeline to extrude a first protective coating layer onto its interior surface. The first layer is then dried with dehydrated air.

Abstract: Extruded catheters and other flexible plastic tubing may be manufactured with improved rotational and/or longitudinal stiffness, compared with catheters made of more conventional plastics. A tubing of liquid crystal polymer plastic-containing material may be extruded through a tube extrusion die while rotating the inner and outer die walls to provide circumferential shear to the extruded tube. Thus the liquid crystal polymer is oriented in a helical manner to provide improved properties, including greater rotational stiffness.

Abstract: A method of forming a bio-compatible vascular prosthesis comprising making a polymer material by coagulation in which the polymer, dissolved in an organic solvent, is formed into the material in a coagulant, the method being carried out at such low temperature as not substantially to degrade the polymer.

Abstract: A packerhead assembly for use in making concrete pipes. The packerhead assembly includes a rollerplate with rollers mounted thereto, and a long segmented longbottom assembly comprised of two substantially identical troweling members, one of which is inverted with respect to the other. The two troweling members combine to form an elongated troweling surface which allows the use of concrete mixes having high fluidity. The longbottom assembly also utilizes removable wear bands which limit the ingress of concrete material to the interior of the longbottom assembly. The wear bands are of particular value when utilizing highly fluid concrete mixes.

Abstract: A method for forming cementitious material, such as gunite or the like, to a desired cross-sectional profile for an interior structure such as a swimming pool, skateboard bowl or the like. A forming assembly includes a cutting edge, which is formed so as to correspond to the final desired profile of the structure. The forming assembly is mounted so as to be pivotable about a pivot axis substantially coincident with the center of the structure being formed. In this manner, when the cementitious material is applied to the side walls and bottom of the excavation to a depth slightly greater than that as finally desired, and the forming assembly pivoted 360.degree. about its pivot axis, the final desired cross-sectional profile of the structure is attained due to the action of the forming assembly striking off the excess material applied to the excavation.

Abstract: Apparatus for producing flexible kink resistant tubing having one or more non-reinforced section(s) and one or more spirally-reinforced section(s). The apparatus includes a rotatable member having an extrusion passgeway for extruding a second thermoplastic material in a filament within a first thermoplastic material to form a reinforcing filament in tubing formed by the first thermoplastic material. The rotatable member is rotated at a predetermined velocity to form the reinforcing filament in a spiral or helical pattern in the wall of the tubing. A diverter valve is provided for selectively providing the second thermoplastic material so that filament reinforced and non-reinforced longitudinal sections of tubing may be formed without interruption. A method of producing such kink resistant tubing is also disclosed.

Abstract: A concrete pipe is produced by introducing a wet concrete mass into a pipe form to produce a cylindrical mass having an inner wall, compacting the cylindrical concrete mass by applying pressing rollers to the inner wall, smoothing the inner wall of the compacted cylindrical concrete mass, and applying a liquid impregnation medium to the inner wall under pressure after the concrete mass has been compacted, the inner wall has been partially smoothed and the concrete mass is still damp. The pressure is sufficient to cause the impregnation medium to permeate the damp concrete mass to a depth of at least 10 mm.

Abstract: A method of producing a thread-reinforced, extruded rubber body by a shear head wherein the threads are continuously supplied, embedded in a rubber mixture which is in a continuous forward motion and fixed in the rubber body by vulcanizing the rubber mixture. The method is such that the reinforcing threads are helically twisted in the finished rubber body. The rubber body is thus reinforced not only in longitudinal direction but also additionally in circumferential direction.

Abstract: A device for manufacturing concrete parts, particularly concrete pipes, and based on the principle of sinking mold whereby a molding bottom ring together with a jacket are continuously lowered relative to a stationary mold core while concrete mixture is poured from above and distributed into the emerging molding space by a radial pressing device mounted on the top end of the mold core. Simultaneously with the lowering of the mold jacket and the molding bottom ring a supply device for delivering the concrete material is also lowered such as to keep a constant distance from the open top end of the mold jacekt. The radial pressing device is designed to compact the incoming concrete material in radial direction without imparting any torque thereto. In this manner any stress in the finished part, particularly between the concrete and reinforcing wire mesh is effectively avoided.

Abstract: A hollow forming machine capable of rotating moulds in both horizontal and vertical directions wherein a motor is used to drive sleeves to rotate in both vertical and horizontal directions, and through the engagement of outer gears of the sleeves and the drive gear shaft, a horizontal mandrel is driven to rotate in the same direction as the sleeves, and through the engagement of two bevel gears, the rotation of the horizontal rotation of a vertical mandrel to drive a mould seat to rotate in both horizontal and vertical directions. An air pipe is disposed in hollow pipes of the horizontal and vertical mandrels to communicate an air extractor and the mould for performing air extracting and air blowing so that the molded product has fine quality and uniform wall thickness without bubbles on the surface.

Abstract: This invention relates in general to the formation of thick films having a biaxial molecular orientation. Such films are prepared in accordance with the present invention from rod-like extended chain aromatic-heterocyclic ordered polymers. Such films have high tensile strength, modulus, and environmental resistance characteristics. A preferred ordered polymer for use in the present invention is poly (para--phenylenebenzo bisthiazole), (PBT), a compound having the structure: ##STR1## The present invention is also directed to methods and apparatus suitable for producing biaxially oriented films, coatings, and like materials from ordered polymers, preferably PBT.

Abstract: The production of tension-proof, liquid impermeable, flexible bands which are preferably utilized for presses to dewater fiber material webs and are subjected therein to substantial tensile stresses between a press-shoe and a press-roll as the same glide across the press-shoe which is effected by means of penetration of a flowable mixture of a prepolymer with a cross linking agent onto the reinforcing band, preferably formed of fabric and receiving the tension forces in a direction longitudinally of the press band. Penetration most effectively occurs through covering the fabric band by pouring thereover of the flowable mixture as the band is in stretched condition and is moved.

Abstract: In the production of a thread-reinforced hose from polymeric material, the still formable material, a mold core, and the reinforcing thread or threads are fed continuously into a shear head and united. This takes place while utilizing the rotary movement of the shear mandrel contained in the shear head such that each thread used is passed axially through the shear mandrel and is wound around the mold core after emerging from an opening at the end. The embedding of the thread into the material and its winding about the mold core take place simultaneously. After the finished hose emerges from the nozzle of the shear head the material solidifies and the mold core is removed.

Abstract: A screw extruder and a method of operation thereof. The screw extruder comprises a barrel including a section that is supported for rotation about the longitudinal axis of the barrel. A screw extends and is supported for rotation in the barrel; and, in use, rotation of the screw rotates and advances plastic material through the barrel. Rotation of the screw also causes the rotatable barrel section to rotate, and a brake is connected to that rotatable section to maintain the rotational speed of the rotatable section less than the rotational speed of the extruder screw. The rotational speed of the screw relative to the rotatable barrel section controls the relative rates at which plastic is mixed, heated, and pressurized in the barrel.

Abstract: Polymer blends comprising a continuous matrix phase of thermoplastic polymer with a discontinuous phase of thermoplastic polymer distributed through it are produced by extruding a blend of immiscible thermoplastic polymers through an annular extrusion die which subjects the polymer blend to transverse shear forces prior to passing through the die lips. The application of the shear forces to the polymer blends produces improved uniformity of distribution of the continuous phase within the matrix, producing better properties in the finished article which may be a blown film or a blow molded product. The continuous matrix phase is suitably a polyolefin such as polyethylene and the discontinuous phase may be selected to provide the desired properties in the extruded article, for example, vapor barrier properties, strength, stiffness, and tear resistance. Typical polymers for the discontinuous phase are polyamides, EVA copolymers, polyacrylonitrile, polystyrene and various copolymers.

Abstract: Disclosed is an improved packerhead or drycast concrete product forming apparatus and method for making a concrete product therewith. The apparatus typically includes a mold having a lower curing pallet, a platform for supporting said mold at the pallet, and a vibrator table having a vibrator ring for association with said curing pallet. The improved apparatus of the present invention preferably comprises a vibrator ring having selectively engageable (and disengageable) means to rigidly connect the vibrator ring to the curing pallet when said vibration means is activated. The preferred vibrator ring selectively engageable means comprises electromagnet means and the preferred product of the process comprises concrete pipe.

Abstract: Method and slide-casting machine for the casting of hollow precast units of concrete by means of slide-casting. Concrete mix is extruded onto a base by using one or several shaping members that form a cavity and the mix is compacted by moving the shaping members. The outer face of the shaping members is provided with a projection or projections, or a projection or projections are formed at the outer face of the shaping members from time to time. The locations of the projections are changed to the longitudinal axis of the shaping members. Thereby the shaping members produce forces compressing the mix in the surrounding mix, i.e. forces that compact the concrete. It is possible to use shaping members in which the shape of the mantle portion can be changed so that the distances of the different points at the outer face of the shaping member from the longitudinal axis of the shaping member vary.

Abstract: A method of lining pipes comprises the steps of laying along the pipe (56) hoses (63) filled with constituent components of a settable resinous lining composition, axially slitting the hoses, conveying the constituent components to a mixing chamber (65), and centrifugally impelling the mixed lining composition against the wall of the pipe (56). A lining apparatus (50) for carrying out the method is advanced along the pipe (56) and comprises delivery tubes (62) with slitting blades (70) at their leading ends which are pushed through the holes (63) and which communicate with a mixing chamber (65) which, in turn, is open to a centrifugal impeller (57) of a lining machine. The slit and emptied hoses (63) may be left in situ in the pipe (56) or removed therefrom in advance of the lining apparatus (50). A trowelling arrangement using a thin-walled, flexible tube (112) of, for example, a cellulose polymer and a conical trowel (112) is employed to smooth the pipe lining.

Abstract: A method of manufacturing extruded pipes where plasticized material, for example plastic material, is advanced to an extrusion nozzle comprising a circular gap (2). The method is especially characterized in that the material is transported axially in said gap (2) while material is moved, for example rotated, in the circumferential direction of the gap (2) so that the material at least partially is caused to assume an orientation deviating from the axial direction, whereby a non-axial orientation will prevail in the extruded pipe (3) and increase the strength. The invention also relates to an apparatus for carrying out the method.

Abstract: Grittiness in soap-containing formulations, one source of which is the reworking of previously processed soap, is reduced in an efficient manner by passing the formulation through a cavity transfer mixer.

Abstract: Molten oxide of grinding material, refractory material, etc., being poured into a circular casting space formed between coaxially arranged inner and outer cylinders and cooled by the water contained in the inner cylinder. Thus, the molten oxide is cooled radially from the center of the inner cylinder and solidified. The outer cylinder includes two segments which separate from each other for facilitating putting the molten oxide into the casting space and taking the resulting solidified product out of the casting space.

Abstract: The present invention relates to a method of forming the primary core of a concrete pipe. A steel cylinder is disposed vertically on the base of the pipe forming machine. A conventional rotary packerhead having a diameter less than the inner diameter of the steel cylinder is lowered concentrically to the bottom thereof. Concrete is then introduced within the steel cylinder through the upper end thereof. The packerhead is rotated to force the concrete into the annular gap between the packerhead and the steel cylinder. As the primary core is formed, the packerhead is raised and rotated while concrete is introduced within the steel cylinder, thereby forming a primary core consisting of a steel cylinder having an inner lining of concrete. In an alternative embodiment, the steel cylinder is completely embedded within the concrete.