Thermoset plastic staging

Whilst the term thermosetting plastics arose out of the fact that early products of this type were cross-linked by subjecting the intermediate-stage materials to elevated temperature, the term is also widely used where cross-linking takes place at normal ambient temperatures. 

As regards granulation of thermosetting plastics during the production stage, applications for USSR inventor s certificates were first filed in 1966. 

Compression molding is the most common method hy which thermosetting plastics are molded [ 1-3]. In this method the plastic, in the form of powder, pellet, or disc, is dried by heating and then further heated to near the curing temperature this heated charge is loaded directly into the mold cavity. The temperature of the mold cavity is held at 150°C—200°C, depending on the material. The mold is then partially closed, and the plastic, which is liquefied by the heat and the exerted pressure, flows into the recess of the mold. At this stage the mold is fuUy closed, and the flow and cure of the plastic are complete. Finally, the mold is opened, and the completely cured molded part is ejected. 

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. 

When immersed in alcohol or acetone, the plastic will swell but is virtually insoluble and is referred to as B-stage. See A-B-C stages phenolic plastic thermoset plastic. 

Plastics are mosdy solid and stable at ordinary temperatures, and at some stage of their manufacture they are plastic , Le. soft and capable of being shaped. The shaping process is done by the application of heat and pressure, and it is the behaviour of the material when heated that distinguishes between the two classes of plastics thermoplastics and thermosetting plastics. 

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