Internal mandrel

Calibration is a technique for maintaining the shape and dimensions of the product from the time the melt exits from the die until it can be cooled enough to solidify and stabilize it. Depending on the size and shape of the product, calibrators can use water-cooled plates, internal mandrel, internal air pressure, external vacuum, or a post-extrusion die to change the shape of the molten extrudate before it solidifies. 

The French patented Ugine Kuhlman process uses a die with an internal mandrel, as shown in Figure 10. The outer skin is quickly frozen via a water-cooled sizing die while the mandrel forms an internal void in the extrudate that is filled by the inward foaming action. The process creates a thick-skinned part with a foamed core. The process is very important for structural members such as window frames using PVC as a wood replacement. 

The fixturing and tooling requirements differ for both the fixed-pin and adjustable selfreacting (ASR) pin tools (Fig. 13.4). The fixed-pin configurations require an internal mandrel... 

FIs. 1 3.36 Prototype pipe welding system showing external friction stir welded head and internal mandrel (inset). Courtesy of MegaStir, Inc. 

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. 

Pinhole perforations were discovered in the walls of chiller condenser tubes of an air-conditioning system. Close laboratory examination of the internal surfaces of affected tubes revealed distinct patches of small pits (Fig. 12.18) and pit sites aligned along longitudinal mandrel marks and fine scratches (Fig. 12.19). In some locations, transversely oriented pit sites that were aligned with the locations of the fins on the external surface branched off the primary longitudinal pit alignment (Fig. 12.20). 

Figure 12.19 Attack sites aligned along mandrel marks or scratches on the internal surface. (Magnification 7.5x.)...

Bundle Preparation. Packages of multifileiment yarns are backwound to prepare bundles necessary for the manufacture of a reverse osmosis module. A proprietary winder for this operation has been designed and constructed at Albany International Research Co. This device is capable of helically winding multifilament yarns into bundles around a mandrel. This is done in a manner such that the resulting bundle has uniform cylindrical dimensions and uniform fiber density. This minimizes channeling and optimizes exposure of membrane surface area. 

A unique and considerably more elaborate multiaxial test employs a thick-walled hollow sphere test specimen which may be pressurized internally or externally with a nearly incompressible liquid. Figure 20 illustrates the essential features of the test device as described by Bennet and Anderson (5). The specimen is prepared by casting propellant in a mold fitted with a sand-poly (vinyl alcohol) mandrel inside the sphere which may be removed easily after curing. A constant displacement rate instrument drives the piston to pressurize the chamber and apply large deformations. The piston s total displacement volume is transferred to... 

Injection The injection blow moulding machine is based on an extruder barrel and screw assembly which melts the polymer. The molten polymer is fed into a manifold where it is injected through nozzles into a hollow, heated preform mould. The preform mould forms the external shape and is clamped around a mandrel (the core rod) which forms the internal shape of the preform. The preform consists of a fully formed bottle/jar neck with a thick tube of polymer attached, which will form the body. 

Foamed polystyrene sheet and fUm are manufactured by a tubular fUm-extrusion process using conventional methods with specially treated expandable-polystyrene pellets, or by injecting a propellant directly into a section of the extruder barrel with standard polystyrene resins and additives. In both techniques the extrudate passes through an annular tubing die and is expanded, either by blowing air inside the tube, or by drawing the tube over an internal sizing mandrel (6). 

Fig. 3 Schematic of spiral mandrel blown film die operation (1) ring-shaped melt distribution (2) die body (3) spiral flow mandrel (4) sizing ring (5) spreader (6) film bubble (7) frost line (8) solidified film (9) bubble collapsing rollers (10) nip rollers (11) external bubble cooling air (12) internal bubble cooling air inlet (13) internal bubble cooling pipe and (14) heated internal bubble air return.

The extended mandrel technique, illustrated in Fig. 6.22b, is highly desirable for fluoropol5miers because it provides internal cooling and support to the tube. The shrinkage of the plastic as a result of cooling causes a tight contact between the tube and the metal mandrel that can extend up to 30 cm beyond the die. Longer mandrels have been difficult to use due to mechanical difficulties. Surfaces will eventually cor-... 

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