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#057 Stabilizing the Clamping Force of Single Cavity Mold

Category : Molding Defect Countermeasures
September24, 2010

In a single cavity mold, very often the cavity is placed only on one half of the mold plate with respect to the sprue. (See the example in Fig. 1.)
If the size of the mold plate becomes large, since the pressure receiving plate is only on one side, the balance of the mold clamping force becomes disturbed at the time of injection molding, and burrs may appear on the periphery of the molded product.

If the clamping force is set unduly high in order to prevent the generation of burrs in such situations, or if the filling pressure is set lower, it is likely that a different problem occurs in some unexpected part.

[Fig. 1][Fig. 2]

When it is judged that the balance of the mold clamping force is disturbed in a single cavity mold, an appropriate countermeasure is to place a balance block on the symmetrically opposite side with respect to the sprue as is shown in Fig. 2.
Usually, since the parting surface of the cavity and core is projecting by about 5 to 20 micrometers from the parting surface of the mold plate, by placing a balance block, it is possible to put the sealing of the cavity and core parting surface in the desirable condition.

The shape of the balance block can be rectangular or can be circular, and as larger a surface area of receiving the mold clamping force as possible will make the balance more stable.

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