Abstract: Annularly or helically ribbed or corrugated semi-rigid thermoplastic pipe is modified to have a smooth outer wall. The ribbed or corrugated pipe is passed through a heated sleeve to squash and smooth the outer profile of corrugated pipe or bend over ribs of ribbed pipe and mold a smooth outer skin of the pipe. Apparatus for forming the modified pipe includes a travelling mold tunnel for the production of ribbed or corrugated pipe and a smoothing sleeve downstream thereof. The smoothing sleeve has a heater to heat it sufficiently to mold the smoother outer skin.

Abstract: The invention concerns apparatus for molding tube (20) utilizing a travelling mold tunnel. The tunnel is made up of mold blocks (16) each comprising parts (13, 15) which are hinged together to be closeable to form the tunnel and openable to release tube from the tunnel. The opened mold blocks (16) from the downstream end of the tunnel are opened and returned to the upstream end without change in their orientation to reform the tunnel about an extrusion nozzle (18) for thermoplastic extrudate.

Abstract: Annularly or helically ribbed or corrugated semi-rigid thermoplastic pipe is modified to have a smooth outer wall. The ribbed or corrugated pipe is passed through a heated sleeve to squash and smooth the outer profile of corrugated pipe or bend over ribs of ribbed pipe and mold a smooth outer skin of the pipe. Apparatus for forming the modified pipe includes a travelling mold tunnel for the production of ribbed or corrugated pipe and a smoothing sleeve downstream thereof. The smoothing sleeve has a heater to heat it sufficiently to mold the smoother outer skin.

Abstract: Annularly ribbed tube comprises one or more coaxial co-extruded inner layers and a coaxial outer layer of thermoplastic material. The tube has sharply upstanding annular or helical ribs having a width which is small in comparison to distance between annular ribs or between turns of the helix. At least one of the inner layers of extrudate fills a hollow outer shell of each rib which is formed by the outer layer. An innermost layer may be a smooth inner skin or may have a smooth inner wall and another wall which bulges into the rib cavity.

Abstract: The invention concerns a cooling plug for sizing the interior surface of thermoplastic extruded pipe. Vacuum and/or pneumatic pressure is applied at the surface of the plug. The pneumatic pressure may cause the inner wall to balloon outwardly to form bells within a mold or within an outer wall, to fit into corrugations of an outer corrugated tube, etc. The vacuum may be used to pull the inner wall back to the surface of the plug after application of pneumatic pressure.

Abstract: The invention concerns an apparatus and process particularly for molding profile thermoplastic tubing and process. The apparatus includes the travelling mold type for molding profile tubing, e.g. corrugated or ribbed, including double walled tubing of various types. A sizing plug for the internal diameter of the pipe is provided with suction applying device which applies suction of diminishing strength in the upstream direction of the plug to the inside diameter of the pipe to provide a smooth inside wall of the pipe and allowing faster pipe formation. Suitably, the plug is a cooling plug and provision may be made for communicating the suction to cooling liquid to draw it to the surface of the plug to provide lubrication for a faster pipe forming process.

Abstract: The invention concerns extrusion dies for apparatus for producing seamless thermoplastic tubing. An elongate hollow core is provided extending through a bore in the extrusion head. The hollow core may carry service lines to downstream parts of the apparatus and may act as or may carry an inner mandrel extending coaxially in an extrusion nozzle. The invention provides hollow core, the diameter of which is not greater than the diameter of the bore of the extrusion head. Thus, it may be possible to withdraw the core in a downsteam direction for tool changes and the like without the necessity of dismantling the extrusion head.

Abstract: The invention concerns apparatus for molding thermoplastic tubing having solid annular ribs. The apparatus is of the type where a tubular mold is defined by cooperatively interengaged mold block of a pair of mold assemblies. An annular extrusion orifice for the tube extends into the mold tunnel and tubing is extruded about a mandrel. The invention provides an accumulator chamber in the region of the extrusion nozzle to provide for pressure differences which build up at that point. Thus, the effective volume of the accumulator chamber can compensate for the varying requirement for the thermoplastic material resulting from the varying radial wall thickness.

Abstract: The invention concerns apparatus for making corrugated tubing. Mold blocks for formation of a travelling mold tunnel are provided with suction to the mold face by means of communication between suction passages in the mold block and a suction chamber. Each mold block has a channel which slidingly engages a track of the suction chamber to receive suction as the mold blocks travel over the track. Tongue and groove connectors are provided between the channel of each block and the track of the suction chamber and communication surfaces of the tongue and groove connectors to provide suction from the suction chamber to the mold face.

Abstract: The invention concerns an extrusion die assembly, especially for use where accurate centering of a mandrel is important. The assembly includes the first member having a mandrel projecting therefrom and an extrusion passage generally in line with the mandrel, which extrusion passsage is, at one end, of cross-section to conform with a passage carrying extrudate for the extrusion head and which merges, over its length, into an extrusion passage at the other end, at least partially surrounding the root of the mandrel. This member is adjustably located in an outer member, which together with the mandrel defines an extrusion nozzle. Since the extrusion passage passes through the first member, it is possible to provide positioning means for the first member and the mandrel without interfering with extrudate's flow.

Abstract: An extrusion die for externally annularly ribbed seamless plastic tubing has an elongated nozzle within which a hollow mandrel is placed. The nozzle and mandrel define an annular extrusion orifice for extrusion of a parison. The orifice has a coaxial conical portion with its generatrix forming an angle of more than 45.degree. with the longitudinal axis of the nozzle for efficient filling of mold cavities corresponding to annular ribs of the formed tube. The diameter of the inner conical portion at its delivery end may be at least that of the outer portion.

Abstract: An extrusion die for two-ply seamless plastic tubing, includes an extrusion head with a first nozzle provided with a first centering means; a first hollow mandrel placed within said nozzle; an elongate carrier bearing a second mandrel, a second nozzle and a spider in turn supporting a distributor splitting an extrudate. The first nozzle and the distributor define a first annular extrusion orifice for an outer parison of the tubing while the second nozzle and the second mandrel define a second annular extrusion orifice for the inner parison of the tubing. A threaded member longitudinally adjusts said carrier to vary the size of the first extrusion orifice. A coupling means interconnects the carrier and the first mandrel and allows only the axial, without rotation, movement of the carrier. A second centering means mounts the distributor uniformly spaced around the spider.

Abstract: An apparatus for producing helically wound double-walled fused thermoplastic pipes, corrugated outside and smooth inside. The apparatus includes extruder means forming two bands of a thermoplastic material, a former shaping the corrugated configuration of and helically winding the first extruded band, a cooled element pressing the second band to the inside of the corrugations and having passages communicating with the second band and with a vacuum means.

Abstract: An extrusion die for externally ribbed seamless plastic tubing, including an extrusion head with an elongate nozzle within which a hollow mandrel is placed. The nozzle and mandrel define an annular extrusion orifice forming a parison of the tubing and having a coaxial conical portion with its generatrix forming an angle of substantially more than 45" with the longitudinal axis of the head, the diameter of the mandrel at its delivery end being not less than that of the nozzle. The die can be supplied also with an electrical heater incorporated inside the mandrel after said orifice, with a centering means mounting said nozzle uniformly spaced around the mandrel, with a threaded member for adjusting longitudinally said mandrel to vary the size of the extrusion orifice, and with a coupling means interconnecting said mandrel and the head and allowing only the axial, without rotation, movement of the mandrel.

Abstract: A system is disclosed for the production of double-walled helically wound thermoplastic pipe. The apparatus includes an endless former (10) of the axially advancing and rotating type for forming a band of thermoplastic material (24) into a corrugated outer wall (26). An internal extruding device (28) extends along the core of the former and extrudes a second band (34) of thermoplastic material onto the interior of the outer wall. A cold shoe (36) presses the inner wall against the outer wall to form a smooth inner wall (42) of the double-walled pipe. It is also possible to provide for the insertion of a reinforcing profile in the corrugations of the outer wall.

Abstract: An apparatus for molding externally ribbed and corrugated thermoplastic pipes, including a pipe die for extruding a parison of a thermoplastic material; moldblock halves circulating in endless paths and cooperating with each other to form a travelling mold; and a means withstanding the hydraulic pressure of molding. The means is represented by yokes having shanks for engagement with complimentary recesses made in the halves. The yokes are provided with rollers guided in parallel paths ensuring that the shanks are driven toward and away from the recesses in a progressive motion without changing their orientation.

Abstract: A pipe perforating apparatus has a spindle carrying a cutting tool and a drive for rotating the spindle about its own axis while revolving the spindle about the pipe. The cutter periodically engages and perforates the pipe. To provide for small, uniform sized holes in the pipe, the cutting tool is an end cutting punch and the spindle is rotated and revolved around the pipe to roll the punch into and out of the pipe without exerting a tangential force on the pipe.

Abstract: In an apparatus such as a corrugator for manufacturing thermoplastic pipe with a corrugated outer wall and a smooth inner wall, a calibrator is employed to provide a smoother inner wall and a more rapid inner wall cooling. The calibrator includes a tube wound into a helical coil and an adjustment mechanism for adjusting the coil diameter. A cooling fluid may be passed through the tube.

Abstract: An article is molded from a thermoplastic material matrix having a particulate filler distributed throughout the matrix. The article is then expanded to develop fissures between the thermoplastic matrix material and particles of the filler material and particles of the filler material, so as to render the article porous. Apparatus for expanding a pipe from the inside or expanding the sides of corrugations in a pipe are also disclosed.

Abstract: Method and apparatus for molding of plastic tubing, including an elongate nozzle receiving an extrudate of an expandible plastic material under pressure from an extrusion head and a coaxial mandrel with air supply and evacuating passages communicating with a vortex generation tube for cooling air before its introduction to the interior of the formed tubing for its blowing and conforming to the walls of a tubular mold cavity formed by a series of forwardly moving molds.