Molds & Tooling
4 조회수
Insufficient weld line strength of PP
문제 현상
Obvious line marks appear on the product at hole positions, behind inserts, or at the confluence of multiple gates; under stress or drop the product often cracks along the weld line, becoming a structurally weak band.
원인 분석
PP crystallizes quickly; if the temperature is insufficient when two melt fronts converge, the molecular chains freeze and set before they can fully entangle, resulting in weak interfacial bonding; when venting is poor, the fronts entrain gas and cold material, further weakening the weld line strength and making it more conspicuous.
해결 방법
①Appropriately increase the melt temperature and injection speed so that the fronts converge at a higher temperature; ②open vent grooves at the confluence position, and set overflow wells when necessary to lead the cold front out; ③adjust the gate position and number to move the weld line to non-appearance, low-stress areas; ④appropriately increase the mold temperature to delay front crystallization; ⑤when strength requirements are high, select a high-flow grade.
핵심 요약
PP weld lines are difficult to eliminate completely; the correct approach is the three-pronged 'relocate the position + increase the convergence temperature + improve venting', and to avoid it in advance as a structural design issue rather than forcing adjustments on the machine afterward.
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