Injection moulding shot size

Foamed plastic articles may be produced with good results using normal screw-type injection moulding machines (see Fig. 4.43(a)). However, the limitations on shot size, injection speed and platen area imposed by conventional... 

The two main parameters for machine size are, the maximum shot size that can be injected in a single forward movement of the screw, and the maximum mould clamping force / damp- The shot size is usually quoted in terms of the mass of polystyrene that can be injected. The clamping force, typically in the range from 100 kN to 100 MN, restricts the maximum projected area A of a moulding onto the mould parting plane (Fig. 5.24). A typical average melt pressure p in the mould is 20 MPa, and the condition... 

Ln-line screw system. The in-line screw system, or screw ram system as it is sometimes called, is the most important development in injection moulding. In this system the plastics is softened by passing it through a heated cylinder by the use of an extruder type screw, the softened plastics building-up in front of the screw. The build up of plastics in front of the screw causes the screw to move axially backwards. The shot size can therefore be easily controlled by stopping the screw rotation at a predetermined position. When the preplasticising operation is complete, the screw is moved forward under pressure pushing the plastics into the mould (Fig. 2). 

The shot capacity is the full amount as a weight or volume of material injected during moulding from the screw. This is usually given as a shot capacity for polystyrene, and will vary with material. The shot size is the amount of material required to fully fill a moulding tool. 

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