Mandrel wrapping

Terpolymers of chlorotrifluoroethylene and ethylene were developed ] that were stress crack-resistant. The inventors in this case incorporated minor amounts (0.1-10 mole percent) of 3,3,3-trifluoro-2-trifluo-romethyl propene [(CF3)2C=CH2] into copolymers of 40 to 60 mole percent of ethylene with 40-60 mole percent of chlorotrifluoroethylene. The resulting terpolymers had improved stress crack-resistance relative to the copolymers of CTFE and Et. Stress crack-resistance was measured by ASTM D2951 (mandrel wrap test) at 180 or 200°C. Another method is called the bent strip test in which a 6.25 cm x 6.25 cm x 1.5 mm strip of the copolymer film is bent over a 6.25 mm diameter bar while the free ends are clamped together. A load of 1,150 g is attached to the clamp (hung from the strip ends) and the entire assembly is placed in an oven at 180 or 200°C. The time required for the film strip to break is a measure of resistance to stress cracking. 

Tube winding is either spiral (a continuous winding where adhesive is applied to outer plies as they are wrapped on a cylindrical mandrel), or convolute (where the sheet is as wide as the mandrel is long, and the mandrel wraps the sheet over itself). The tube is removed from the mandrel by a pusher arm. Convolute adhesives are usually used cold, while spiral adhesives may be used at 131°F (55°C). Many starch products may be used, but 50% solids borated dextrins are common, as seen in Table 4. 

One ASTM test procedure has suggested (24) that foamed plastics be classified as either rigid or flexible, a flexible foam being one that does not mpture when a 20 x 2.5 x 2.5 cm piece is wrapped around a 2.5 cm mandrel at a uniform rate of 1 lap/5 s at 15—25°C. Rigid foams are those that do mpture under this test. This classification is used in this article. 

Chemical Properties. LLDPE is chemically stable. Very few analyses and tests related to its chemical properties are carried out routinely. Resistance to thermal stress-cracking is determined by exposing film wrapped on a metal mandrel to hot (100°C) air for 48, 96, and 168 hours (ASTM D2951-71). 

The uncured wool from the forming conveyor is separated into pelts , which are converted into pipe sections by being wrapped around a heated mandrel, and the wall thickness set by counter rollers. The sections are then passed through a curing oven before being trimmed, slit, covered and packaged. 

It is often easier to wind a spiral on a mandrel or former of carbon, metal tubing or glass tubing wrapped with asbestos paper. A right-angle bend is made in the tube to give a short portion at the end which... 

Hose constmcted by wrapping the reinforcing fabric and the calendered cover on to the inner tube which has been fitted over a mandrel of the desired diameter. The application of the fabric, the cover and of the wrapper may be done either by hand or by machine. 

An advantage of the autoclave for smaller components, is that a large volume of the same or different products can be vulcanised at the same time, provided that the curative systems in use do not interact between the different compounds. It is usual to support extrusions and low hardness products in talc. Products formed on mandrels and sheeting, for example, are cloth wrapped to prevent distortion. 

Hose may be hand built using a three roll wrapping machine. The centres of the three rolls form an equilateral triangle. The hose during construction sits on the junction between the two lower rollers and pressure is exerted to consolidate the composite by the upper movable roller. An extruded inner liner, after fitting to a solid inner mandrel, is placed into the machine between the rollers and then the various layers of rubber coated or resorcinol-formaldehyde-latex treated, fabric are applied in a spiral form, with overlap. Once the reinforcement layers have been added the cover rubber is applied and a cloth, usually nylon, is spirally wrapped around the constructed hose using the roller system. The hose is now ready for vulcanisation. 

Flo-turning differs from spinning in diat metal is displaced rather than bent into shape. The wall thickness of a spun part is basically maintained but the outside diam of the blank is reduced as it is wrapped over a mandrel. Flo-tuming maintains its outside diam thruout the process and has a. resultant wall thickness equal to the sine of the angle of the finished piece multiplied by die blank thickness... 

Thick walled tubes are built-up to the required thickness of say 25 to 50mm from calendered sheets of about 1 mm thickness and the same is wrapped with wet cloth which gives additional pressure when shrunk, thus giving better consolidation. The tubes are built up on mandrels. The preferred method of curing is by using hot water. 

It is often more convenient with extrusions to wrap them around a mandrel, although the resulting strain is generally less well defined than it is with strips. ASTM D117131 is complementary to D1149 and specifically... 

To overcome weld line problems, the cross-head tubing die is often used. Here, the die design is similar to that of the coat-hanger die, but wrapped around a cylinder. This die is depicted in Fig. 3.17. Since the polymer melt must flow around the mandrel, the extruded... 

The spiral die, commonly used to extrude tubular blown films, eliminates weld line effects and produces a thermally and geometrically homogeneous extrudate. The polymer melt in a spiral die flows through several feed ports into independent spiral channels wrapped around the circumference of the mandrel. This type of die is schematically depicted in Fig. 3.18. 

One of the easiest ways to get a long piece of material in a small (convenient) area is to wrap or wind the material around a mandrel. The typical mandrel used on SPRTs is made of either mica or alumina. The sheaths covering the wrapped thermometer may be borosilicate, silica glass, or a ceramic (see Fig. 2.33). Note that both examples in Fig. 2.33 show four leads where, logically, there should be only two. This is done to reduce any unwanted resistance from the region beyond the thermometer. 

Figure 11.6 A tandem extrusion process for the manufacture of polystyrene foam sheet. (1) Primary extruder (2) blowing agent addition system (3) screen changer (4) secondary extruder (5) annular die (6) cooling mandrel (7) S-wrap (8) winders...

MIL-HDBK-304 - Chapter 6 has a simple xocedure in which strips of cellular cushioning materials are wrapped around a cylinder or mandrel under standard conditions through a total angle of 180°. The specimens are then examined for failure, such as cracking, delamination, surface spalling, etc. 

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