In all but the simplest injection moulding configurations, there will occur in the mould filling process a situation in which two, or more, distinct melt streams will interact with each other. This may occur because of flow splitting by an insert within the mould and the subsequent recombination of the separated flows, or because of the collision of flow fronts originating from two, or more, individual gates. (This may be considered as flow splitting of melt before entering the mould.) At any event, two separate flow streams moving in different directions will merge with each other, setting up an interface, which will be retained in the final component to a greater of lesser degree, dependent on melt properties and processing conditions. This interface, which is frozen into the moulding, has become known as a weld, or knit, line and its effect on the overall strength of a plastic component is becoming the source of much interest, particularly as there is relatively little information in the published literature.
KeywordsFatigue Life Injection Rate Injection Mould Weld Line Mould Temperature
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