Injection molding, of thermoplastics

T. Whelan and J. Goff, Injection Molding of Thermoplastics, Vols. 1 and 2, Society of Plastics Engineers, Brookfield Center, Conn., 1990. 

The molds in a RIM-process plant are located in a separate assembly, which has devices for opening and clamping a mold and, in some cases, for changing it. The pressure in the RIM-process is considerably lower than in traditional injection molding of thermoplastics thus, the requirements for the mold material are less rigid. Molds may be made from aluminum or reinforced plastics, since high-strength steel is not necessary. 

One of the key parameters in reactive processing is the distribution of residence times and temperatures for all particles in the liquid, because their reactivity depends on temperature, and the degree of conversion is determined by the dwell time inside the mold. Since the fountain effect changes residence time distribution from that in the hypothetical case of steady unidimensional flow, this factor becomes especially important in chemical (reactive) processing, more so than in standard injection molding of thermoplastic materials.284... 

Additional Considerations. Compared to injection molding of thermoplastics, compression molding is less capital intensive, more labor-intensive, and takes a longer... 

Lord, H.A. Williams, G. Mold filling studies for the injection molding of thermoplastic materials transient flow of plastic materials in the cavities of injection molding dies. Can. Controls Instrum. 1975, 318-328. 

Liu, S.-J. Chen, Y.-S. Water-assisted injection molding of thermoplastic materials effects of processing parameters. Polym. Eng. Sci. 2003, 43, 1806-1817. 

Rubin II. Injection molding of thermoplastics. In Berins ML, editor. SPIPlastics Engineering Handbook. 5th ed. Boston Kluwer Academic Publishers 1991. p 133. 

Molds used for injection molding of thermoplastic resins are usually flash molds, because in injection molding, as in transfer molding, no extra loading space is needed. However, there are many variations of this basic type of mold design. 

In-mold decoration can be done with either injection molding of thermoplastics or compression molding of thermosets. Thermosetting plastics are decorated with a two-stage process. For melamine products, for example, the mold is loaded with the molding powder in the usual manner and closed. It is opened after a partial cure, and the decorative "foil or overlay is placed in position. 

The viscosity of the curable molding compounds (before curing is completed) is usually very low (at 70-120 °C) - around 1-50 Pa s. Thermoplastic melts are between 200 Pa s and 800 Pa s (see Table 10, Sect. Processing of thermoplastic elastomers ). In contrast to injection molding of thermoplastics, duroplastics form flashes and skins the subsequent removal of which is expensive. 

Many of the relationships described in detail below, in most cases for injection molding of thermoplastics, between the process parameters and the structural component properties are applicable to other processes when modified accordingly. 

Molecular orientations resulting from shearing forces applied during processing vary widely depending on the process. In injection molding of thermoplastics and TPEs, molecular and fiber orientations have a dominant influence on the structural component properties. 

As in injection molding of thermoplastics, the location of the sprue also influences the surface quality of injection-molded structural components made from phenolic resin molding compounds. 

Tools can be produced by electroforming for plastic injection molding. Electroformed molds have been used successfully for injection molding of thermoplastics, for the die casting of zinc, for the pressing of ceramic materials, and for the pressing of glass. 

In the 1970s, attention turned to simulation of injection molding of thermoplastics, with the first papers concerned with either isothermal mold filling [R8, W8] or nonisothermal filling very simple molds [Kl]. From the late 1970s, commercial computer software for simulating nonisothermal injection... 

Injection molding of thermoplastics materials, I/by Tony Whelan and John Goff, p. cm. 

Fisa, B. (1990) Injection molding of thermoplastic composites. Composite Materials Technology (eds P.K. Mallick and... 

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