Rapid Injection Molding

When this work began, an important application for TPU elastomers was in automobile exterior body components associated with impact absorbing bumper systems. Cold impact strength, resilience, resistance to heat distortion at paint oven temperatures and rapid injection molding cycles were all required. 

Injection molding is used to fabricate ceramic components with complex shapes because cycle times can be rapid, injection molding can be a high-volume process. The major limitation is that the initial tooling costs of the mold can be quite high. The mold to fabricate an individual turbine blade can be > 10,000 and a mold for a turbine rotor may be > 100,000, but such molds are reusable since they are never subjected to high temperatures. 

Casttool, Rapid injection molds for prototypes, Metalcast Engineering... 

By the 1950s P/M parts were used in postage meters and home appHances. In the 1970s P/M superaHoys for aerospace appHcations were used, followed by steel P/M forgings. The 1980s opened the way for rapid soHdification processing, P/M tool steels, and metal injection molded parts. 

Liquid-Injection Molding. In Hquid-injection mol ding (LIM), monomers and oligomers are injected into a mold cavity where a rapid polymerization takes place to produce a thermoset article. Advantages of these processes are low cost, low pressure requirement, and flexibiHty in mold configuration. Conventional systems, such as isocyanate with polyol, release Htfle or no volatiles. The generation of substantial volatiles in the mold is obviously undesirable and has represented a significant obstacle to the development of a phenoHc-based LIM system. A phenoHc LIM system based on an... 

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. 

The catalysts are primarily DCPD-soluble derivatives of tungsten and molybdenum and the activators are aluminum alkyls (63—64). Polymerization is accompHshed by mixing equal amounts of Hquid DCPD (at >32° C), one part of which contains the catalyst and the other of which contains the activator. The mixture is rapidly injected into a mold, where the polymerization takes place. Polymerization times are from under 30 seconds to several minutes, depending on the size of the part, mold temperature, and modifiers added to the polymerizate. 

Reaction injection molding (RIM) describes [27-29] the process whereby two liquid reactants are rapidly mixed... 

The rapid cooling of certain plastic products can result in frozen in stresses and strains (particularly with injection molding). The stresses may decay with time in a viscoelastic manner. However, they will act like any other sustained stress to aggravate cracking or crazing in the presence of aggressive media and hostile environments like UV radiation. 

Polycarbonate can be readily injection molded. Polycarbonates typically require only a short injection molding cycle time, because the polymer flows into the mold easily and solidifies rapidly. We injection mold polycarbonate to produce a wide variety of commercial goods, including compact disks, jewel cases, aircraft windows, kitchen utensils, and clear refrigerators drawers. Polycarbonates are also found in a wide range of disposable medical devices, such as the flow locks on intravenous tubes and the hard, disposable components of dialysis machines. Impact resistant polycarbonate is used to manufacture sports and other safety helmets. Glass fiber reinforced polycarbonate is used in the housings for power tools. 

Crystallization of PCT is relatively rapid, but because of its higher Tg (90 °C) the maximum rate of crystallization occurs at a higher temperature than is typical of other crystalline polymers such as PET (Tg at about 70 °C) or PBT (Tg at about 35 °C). Figure 7.2 compares the crystallization half-times of PET and PCT from both the glass and the melt (data were obtained via DSC measurements). The effect of the higher Tg on the temperature of maximum crystallization rate (i.e. minimum half-time) is most clearly seen in the data from the melt. The basic rapid crystallization rate of PCT allows it to be used as a high-performance injection molding material. 

PCT forms the basis of a family of reinforced, crystalline plastics for injection molding. As mentioned above, the high melting point of the polymer is a key property, as this results in high heat deflection temperatures (HDTs) in glass-fiber-reinforced formulations. Good toughness, flow into the mold, and rapid crystallization are also important in these applications. 

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