Thermoplastic materials are capable of being molded when heated and hardened when cooled. This process can be repeated because no chemical change takes place during molding and cooling. Only a physical shape takes place to conform to the mold. Since there is no chemical change, molded parts can be reground, mixed in proportions to virgin material, and remolded again if desired.
Thermoplastic materials that are commonly injection molded include:
These thermoplastics would typically use the mold steel materials common for injection molding identified in the Plastic Molding Process selection of this section. Some fillers added to the thermoplastics in injection molding require special consideration, these include:
- Flame retardant plastic: Use stainless steel such as DME # 6 steel.
- Glass filled plastic: Use stainless steel, H- 13, S7, and D-2.
- Vinyl/PVC: Use stainless steel such as DME # 6 steel.
Thermoset materials are set by the application of heat and pressure. A chemical change takes place and the material cannot be returned to its original shape. Fillers of different kinds are used to give the specific properties required. This type of plastic is typically compression molded, with other process methods also used. Plastics found in this category are:
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