Transfer Molding And Extrusion Plastic Molding Process Of Making Plastics

Transfer molding, also called extrusion or gate molding , is the process of forming articles in a closed mold, where the fluid plastic material is conveyed into the mold cavity under pressure from outside of the mold.

The material, often a preheated preform, is placed in a heated transfer pot. As soon as the material is sufficiently softened, the plunger forces the almost fluid plastic through the orifice (sprue) into the closed mold where final cure takes place. Pressures used are 50 to 100% higher than those used for compression molding ; thus better details and higher strengths are possible .

Extrusion Molding :

Extrusion means the continuous flow of material through a die. Extrusion molding is used mostly for production of sheet, tube bar and typical applications in thermoplastic materials. Granulated powder made of such materials as vinyl resins, cellulose derivatives, nylon, polyethylene and polypropylene make up the materials used in the process.

Plastic extrusion machine consists of hopper into which the powder or pellets are fed into a heated cylinder, the screw feeding mechanisms, a nozzle and the die assembly. The rotating screw carries the heated plastic forward and forces it through heated die orifice of the required shape. As it leaves the die, it is gradually cooled by carrying it through cooling media while resting on a conveyor, It is then wound into coils or cut to desired lengths.

There are advantages to the extrusion process. The tooling is low- cost compared to Injection molding. Material thickness can be accurately controlled. In addition, production rates are high and intricate profiles can be produced.

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