Injection Molding
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Ripples (flow marks) on PP products
Problem Phenomenon
Concentric circular ripples appear around the gate, or wavy patterns appear along the flow direction, obvious on high-gloss surfaces.
Cause Analysis
The melt front advance speed is unstable and the front temperature drops too fast, leaving ripples on the cavity surface; low mold temperature, an unreasonable injection speed curve, and a gate that is too small cause the front to 'stop and go' or cool locally.
Solution
①Optimize the injection speed curve to keep the front smooth; ②appropriately increase the mold temperature and melt temperature; ③enlarge the gate to reduce local throttling; ④check the temperature uniformity of the hot runner; ⑤adjust the gate position when necessary to improve the flow pattern.
Key Takeaway
PP ripples are the externalization of the front's 'disrupted rhythm': smooth the speed curve and preserve the front temperature, and the ripples will disappear; it is essentially a filling stability problem, not a surface treatment problem.
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