Cores, injection molds

Other recent modifications include lost-core injection molding and gas-assisted injection. The former involves inserting in the mold a low melting metal alloy insert over which the polymer is injected. After solidification and ejection of the part, the insert, which has a melting point lower than that of the polymer, is melted away to yield a hollow part. Gas injection also makes it possible to manufacture hollow parts. After injection of a small volume of polymer, but before its solidification, gas is injected in the mold through a different gate. The gas pushes the molten material... 

FIGURE 1.24 Lost-core injection molding process. ... 

In injection blow mol ding, a parison is injection molded onto a core pin the parison is then rapidly transferred via the core pin to a blow mold, where it is blown by air into an article. This process is appHed to smad and intricate bottles. 

Most PET botties are produced by injection blow mol ding (71) the resin over a steel-core rod. The neck of the bottie is formed with the proper shape to receive closures and resin is provided around the temperature-conditioned rod for the blowing step. The rod with the resin is indexed to the mold, and the resin is blown away from the rod against the mold walls, where it cools to form the transparent bottie. The finished bottie is ejected and the rod is moved again to the injection-molding station. This process is favored for single cylindrical botties, but cannot be used for more complex shapes such as botties with handles. 

Unstable state of plastic as evidenced by changes in physical )roperties not caused by the surroundings. Example is the temporary flexible condition some plastics display after molding. Assembly of all parts making up an injection mold, excluding cavity, cores and pins. 

Mold base Assembly of all parts making up an injection mold, excluding cavity, cores, and pins. 

Figure 5 Optical micrographs of specimens injection molded at 180°C (a-d) and 280°C (e,t). Samples were taken from core (left) and skin region (right). (Sample codes as in Table 1.)...

The composites injection molded at the lower temperature (180°C) did not exhibit any skin/core effect, but rather contained fibers throughout. 

Coring The term coring in IM refers to the addition of steel to the mold for the purpose of eliminating plastic material in that area. Usually, coring is necessary to create a pocket or opening in the product, or simply for the purpose of reducing an overly heavy wall section. For simplicity and economy in injection molds, cores should be parallel to... 

Soluble core molding The soluble core technology (SCT) is called by different names such as soluble fusible metal core technology (FMCT), fusible core, lost-core, and lost-wax techniques (3). In this process, a core [usually molded of a low melting alloy (eutectic mixture) but can also use water soluble TPs, wax formulations, etc.] is inserted into a mold such as an injection molding mold. This core can be of thin wall or solid construction. 

Lost-wax Also called RP molding, fusible-core. A bar (or any shape) of wax is wrapped with RP. After the RP is cured (bag molding, etc.) in a simplified restrictor mold to keep the RP-wax shape, the wax is removed by drilling a hole or removing the end caps by applying a low temperature so that the RP is not effected (review in this chapter INJECTION MOLDING, Modified... 

Water-hydrogen chloride-inorganic compound systems, 13 817-818 Water-immiscible core materials, in microencapsulation, 16 442, 443 Water injection molding, 19 789 Water-in-oil (W/O) emulsions, 11 551, 24 155... 

Figure 5.74 Skin-core morphology of an injection-molded polypropylene structural foam. Reprinted, by permission, from P. R. Hornsby, in Two-Phase Polymer Systems, L. A. Utracki, ed., p. 102. Copyright 1991 by Carl Hanser Verlag.

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