Pinch tube process

Both injection blow molding and pinch tube processes are especially suitable for metallic pigments, because the expansion of the plastic during the blowing process causes further orientation of the metallic pigment parallel to the surface. 

To optimize the metallic effect, the conditions outlined in Section 14.4.4 under Injection Molding should be maintained. The pigments are added as compound, masterbatch, or powder. The use of static mixers or special mixing screws can improve the homogeneity of the blend. For the pinch tube process the high melt viscosity should be considered when preparing the masterbatch. 

Fig. 9-19. Basic pinch-tube blow-molding process. Courtesy Monsanto Co., Hartford, Conn.)...

A variation of the preceding process is used to produce oriented vinyUdene chloride copolymer films. The plastic is extmded into tube form and then is supercooled and subsequently biaxiaHy oriented in a continuous bubble process. The supercooled tube is flattened and passed through two sets of pinch roUs, which are arranged so that the second set of roUs travels faster than the first set. Between the two sets, air is injected into the tube to create a bubble that is entrapped by the pinch roUs. The entrapped air bubble remains stationary while the extmded tube is oriented as it passes around the bubble. Orientation is produced in the transverse and the longitudinal directions, creating excellent tensile strength, elongation, and flexibiUty in the film. The commercial procedure has been described (157). 

Blow molding — The process of forming hollow articles by expanding a hot plastic element against the internal surfaces of a mold. In its simplest form the process comprises extruding a tube (parison) downward between opened halves of a mold, closing the mold, and injecting air to expand the tube, which is pinched on the bottom. 

Process Loosen the Hofmann screw, pour into A water that has been standing in the laboratory for at least twenty-four hours, until the reservoir, E, is two-thirds full then tighten the screw and add more water until the level tube, is three-fourths full clamp A at any convenient height to the iron stand which supports the apparatus. Pinch B to remove any imprisoned air. Fill the eudiometer, F, with some of the same water, invert in the reservoir, and clamp it so that the open end is just below the surface and near the wall of E. 

Among the latest techniques is the Japanese Cuius blow moulding process which produces a preclosed tube from an extrusion process. It is argued that the absence of a base pinch off eliminates the weakest part of a conventionally moulded bottle. The process is suitable for single layer and multi-layer bottles with a wide variety of shapes. 

If you used a buret as the gas measuring tube, measure the volume between the pinch clamp (or stopcock) and the first graduation using the following procedure. Fill the uncalibrated section of your buret with distilled water. Empty the water into your 10-mL graduated cylinder, and note the volume. Repeat this process twice more, and record the average volume of the uncalibrated section of the buret in TABLE 29.IB. 

Blow moulding is a process used for making hollow products, such as bottles, by inflating a precursor tube, called a parison. In the simplest method the tubular parison is produced by extrusion and passes between the two halves of a mould, which are then clamped together, pinching off... 

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