The Function of Sprue Puller

Sprue puller is very common design in cold runner plastic injection moulds, but different companies have different desing. But there are two basic designs of sprue puller, in one the undercut is produced within the cold slug well region, and is situated below the parting surface. In the other design, the undercut portion of the sprue pulling device is situated above the parting surface. To differentiate between these two basic types, we designate them type A and type B respectivity.

                                                                                

It is very important that sprue is pulled absolutely from the sprue bush when the mould opens. For single-cavity moulds, the sprue feeds directly into the base of the component. The sprue is pulled at the same time as the moulding is pulled from the cavity.

For multi-cavity moulds which using a basic feed system the sprue would probably be left in the sprue bush each time the mould was opened. This would be waste time since it needs worker to remove the unwanted sprue, then continue production. To avoid this disgusting problem and save labor cost, an arrangement for pulling the sprue should always be adopted in the design.

About common sprue pulling methods, it adopts an undercut pin or an undercut recess situated directly opposite the sprue entry. The plastics material which flows into the undercut, upon solidifying, it will provide sufficient adhesion to pull the sprue as the mould is opened. This is the most common design among mould industry.

In a word, in order to help customer save labor cost, material usage and improve the production efficiency, the best sprue design should be as short as possible. What’s more, the bushing should have a smooth, tapered internal finish that has been polished in the direction of the draw in order to ensure clean separation of the sprue and the bushing.

Post by Miss Mandy

Email: auto@sinomould.com

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