Dec 08 2012

Sprue gate

Category: feed system,plastic mouldAlice @ 6:12 am

To obtain the optimum filling conditions the type of gate must be carefully chosen.On most occations,however,the choice will be obvious as only one type of gate will meet the particular requirements for the moulding on hand.

The types of gate commonly used are:sprue gate,edge gate,overlap gate,fan gate,disphragm gate,ring gate,pin gate,subsurface gate and winkle gate.

When the moulding is directly fed from a sprue or secondary spru,the feed section is termed a sprue gate.The main disadvantage with this type of gate is that it leaves a large gate mark on the moulding.The size of this mark depends on:(1)the diameter at the samll end of the sprue,(2)the sprue angle,and (3)the sprue length.Thus the gate mark can be minimized by keeping the dimensions of the above factors to a minimum.Note that as the sprue entry is controlled by the nozzle exit diameter,and,as it is undesirable to reduce the sprue angle below two degree inclusive for withdrawing pruposed,the sprue lengthe is the logical dimension for the designer to attempt to reduce.An extension nozzle  can used to advantage,because it enters a recess in the plastic mold and cuts down the overall sprue lengthe.One basic two-plate molds the sprue gate is used only for single-impression molds.In this case the impression is positioned in the centre of the plastic mold and the sprue is a direct feed into it.An example of the sprue gate is shown in Figure 4.13.

A modifed form of sprue gate is also used on underfeed molds and runnerless molds.In both of these,any number of impressoins can be accommodated and the sprue gate(Figure 1.14),now termed secondary sprue,are fed from runner systems situated below the parting furface.

ALICE CHEN
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