Extrusion of Tubing

Tubes and blown Aims can be produced as multilayer structures by employing multiple extruders and coextrusion manifolds and dies. Figure 12.44 is a schematic representative of a conventional and new spiral coextrusion die. The designs can be used for both blown-film and blown-molding parison dies. In the extrusion of tubes, such as rigid PVC or PE pipe, the extrudate passes over a water-cooled mandrel and enters a cold-water bath whose length depends on the tube thickness the tube leaves the bath well below its Tm (if it is crystalline) or Tg (if it is amorphous) and is sectioned to the desired lengths. 

Extrusion of tubes, hose, and profiles is done on standard extruders for rubber. The usual temperature pattern is a gradual increase of temperature from the feed zone to the die. The die temperature is typically 100°C (212°F) and the screw temperature is approximately the same as the temperature of the feed zone.37 Processing aids are almost always required to improve the surface appearance and to increase the extrusion rate. Extrusion represents only a small proportion (about 10%) of the total consumption of fluorocarbon elastomers.37... 

Extrusion with subsequent calendaring. Extrusion of tubes for subsequent calendaring is a particular method adopted for the production of extra wide fine ceramic wall and floor tiles. This process involves initial ex-... 

Internal mandrel cooling n. In extrusion of tubing and pipe, the mandrel, which is an extension of the die core, is usually cooled internally so that the hot extrudate, cooled from both surfaces, cools faster than if cooled only on the outside, and with better control of dimensions. 

As an example, we will consider the extrusion of tubing with an inside diameter of 10.0 mm with a wall thickness of 1.0 mm. The cross-sectional area of this product is ... 

A dummy-block is placed against the face of the extrusion ram. For the extrusion of rods the dummy-block is centered on a bolt being inserted in the solid ram and for the extrusion of tubes by means of a hollow ram, on the mandrel. The transition from the cylindrical part of the ram to its flange takes a tapered form. The bearing surface of the flange is dimensioned for a permissible specific unit pressure of about 4,000 kg/cm-. The area of the thrust ring which transmits the ram power to the cross-head, is dimensioned for a surface loading of about 1,500 to 2,000 kg/cm. On account of its stress-concentration index the surface and the central... 

Teflon TFE-Fluorocarbon Resins Extrusion of Thin-Walled Tubing, buUetia, E.I. du Poat de Nemours Co., lac., Wilmington, Del., 1957. 

Fig. 6. Extrusion of blown film A, blown-film die B, die inlet C, air hole and valve D, plastic tube (bubble) E, air ring for cooling E, guide roUs G,...

Extrusion. Extmsion techniques are used in the preparation of tubing, hose, O-ring cord, preforms and shaped gaskets. Typical extmsion conditions are 70 to 85°C for the barrel temperature and 95 to 110°C for the head temperature. The extmded forms are normally cured in a steam autoclave at 150 to 165°C. Some special grades of peroxide curable fluorocarbon elastomers can be hot air vulcanized. 

Integrally formed tubes, in which the extended surface is produced by cold-forming fins onto the surface of the tube by extrusion of the parent tube. 

In extrusion of solid rubber sections, the shaped metal plate fitted in the head of the extruder to produce the desired contour in extrusion of hollow tubing the outer circular part which fits over the pin, pencil or nozzle to give the hollow section. 

In the extrusion of rubber tubing, a central core determines the inside diameter. This core is supported by the spider or core-bridge which is itself fitted in the head of the extruder and may be adjusted laterally and vertically to produce a concentric tube. 

A laminar-flow reactor (LFR) is rarely used for kinetic studies, since it involves a flow pattern that is relatively difficult to attain experimentally. However, the model based on laminar flow, a type of tubular flow, may be useful in certain situations, both in the laboratory and on a large scale, in which flow approaches this extreme (at low Re). Such a situation would involve low fluid flow rate, small tube size, and high fluid viscosity, either separately or in combination, as, for example, in the extrusion of high-molecular-weight polymers. Nevertheless, we consider the general features of an LFR at this stage for comparison with features of the other models introduced above. We defer more detailed discussion, including applications of the material balance, to Chapter 16. 

Intact lake cores are retrieved from the lake bottom in a polycarbonate tube. Bottom-up extrusion of the sediment... 

Hot Extrusion of Shells. A modification of the Ugine-Sejournet hot extrusion process (using glass as lubricant) is used by Scaife Company of Oakmont, Pennsylvania. In this process a complete shell (such as 4.2 inch) can be produced in one piece from a simple billet. Important features of the development are in the substitution of readily available billet stock for seamless steel tubing, a critical material in times of war. Another feature of this process is that it requires about 25% less steel Refs Ordnance, 38, 753 (1954) 2) Iron Age... 

An interesting study of the extrusion of lubricated polytetrafluoro-ethylene powders has been published by Lewis and Winchester (LI), who have concluded that much of the shearing takes place in the taper of the die before the fluid enters the tube, or hole, of the die itself— i.e., that the end affects are of primary importance. Furthermore the data were interpreted to indicate an outstanding importance of the flow of the polymer in the material chamber well ahead of the die itself, an importance which is difficult to accept. Much further work is needed to... 

The viscous dissipation term is normally not important. Its significance has been considered in connection with lubrication theory (VI), flow through tubes (B20), extrusion of plastics melts (BIO), and viscometry in rotating-cylinder systems (W6). There is also an additional contribution to the energy flux vector describing energy transport by radiation. See discussion in connection with Eq. (29). 

In some countries (e.g. in the U.S.S.R. and in the U.S.A.) thick strips (for cannon powders) may be cut immediately after the extrusion of the tubes. This is possible only when pyrocollodion cotton is used for the manufacture of the powder since it is easily soluble and requires only a small amount of solvent (about 80% by weight of nitrocellulose). After cutting the powder is subjected to predrying. When... 

A few patents have been issued covering the use of screw presses [39], but they do not include details of the design of the presses. However these do not differ from the screw presses widely used for extrusion of plastic rods, tubes and other shapes. A detailed description of the screw presses used in plastics technology can be found in monographs [40, 41]. A diagrammatic representation of a screw press is given in Fig. 266. 

Screw extruders usually are built with a single screw as shown, but may have as many as four screws and the die may have multiple holes of various cross sections. An 8 in. dia screw can have a capacity of 2000 Ib/hr of molten plastics. Tubing can be extruded at 150-300 ft/min. To make pellets, the extrudate goes to cutting machines in which parts as small as washers can be made at rates as high as 8000/min. The extrusion of plastics is described at length by Schwartz and Goodman (Plastics Materials and Processes, Van... 

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