Systems of molding
Many processing systems are in use today owing to the variety of materials available and because manufacturers were reluctant to scrap old equipment and techniques as new methods were developed. Compression an transfer molding are used extensively for materials which harden or set under heat and pressure. Such materials are called thermosetting or hot set plastics. The thermosetting materials may also be injection molded in injection machines.
The hardening of thermosetting materials is effected through chemical change in the resin which takes placeunder heat and pressure. The press and mold hold the compound under great pressure while this action is in process. After the chemical change is effected, the cured or set resin will continue to hold the filler particles of the compound in compression when the mold pressure is released. The piece has then been formed to the shape of the mold.
Injection molding is used primarily for materials which are plastic when heated and solid after cooling. These materials are called thermoplastic or cold-set plastics. In molding thermoplastic products, the material is melted or made plastic by heat, mechanical work, and pressure. The plastic mass of hot material is injected in to a relatively cold mold, which causes the material to harden and retain the shape of the mold.
When thermosets are injection molded, the hot screw-plasticized compound is injected into a hotter mold, which advances the hardening of the product while the material is held under pressure in the mold.
By: Mold-Sources.com
