Mold parts Restricted gate

The location of holes through the walls of a molded part is important relative to the gate location and the flow path of the material. The holes represent dams across the flow path of the material that it must flow around and then rejoin on the opposite side. This restriction in flow can lead to poor flow and weld lines in the material where the material rejoins. These weld areas tend to be weak spots in the... 

SBCs and TPVs are shear-thinning materials. Therefore, as such they are benefited from the flow restrictions at the entry of molds and this allows the provision for small diameter, short landed gates. For TPVs and SBCs, it is suggested that gates should be 20%-30% of the wall thickness of the part to be filled. 

The gate usually produces a mark on the finished molding. Naturally, this mark should not occur in an especially visible part of the article. At the same time, however, there is a limit to the allowable complexity of the numer system s design. This is also a function of the maximum permissible flow-path length for the plastics material chosen, or the additional loss of material caused by a larger runner system. For these reasons, the position of the cavity within the mold is also subject to restrictions in some cases. Other limitations with the position of mold cavities arise from the ease, with which the molded article can be removed fi om the mold, without suffering damage. 

Splay Mark Also called silver streak. Fan-like or streaking on the surface of fabricated plastic parts. Causes include moisture in the plastic material, thermal degradation of plastic material, relatively cold plastic on mold or die surface due to fast an operation (called jetting), injection mold gate restriction, foam molding, etc. 

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