Molds & Tooling
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ABS brittle cracking——too small gate shear overheating
Fenómeno do problema
The product is brittle near the gate; the gate often has burnt marks or gas marks; the brittleness is concentrated in the area around the gate.
Análise das causas
A too small gate causes the shear rate to increase sharply when the melt passes through, generating shear heat, local overheating and degradation, and high internal stress; at the same time, insufficient filling makes the local density low and the toughness poor; the two superimpose to cause brittleness near the gate.
Solução
①Appropriately enlarge the gate according to the product size; ②when the structure is limited, add auxiliary gates to disperse the filling pressure and reduce stress concentration; ③reduce the injection speed through the gate to reduce shear heat; ④check the temperature control of the hot runner gate to avoid local overheating; ⑤change to a fan/lap gate when necessary.
Conclusão principal
A small gate saves material but may exchange for brittle parts: the shear heat and internal stress at the gate are hidden killers; if appearance allows, making the gate a little bigger often solves local brittleness better than adjusting a bunch of parameters.
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