Molds & Tooling
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ABS brittle cracking——poor runner design
Problem Phenomenon
Some areas of multi-cavity or multi-gate products are brittle, filling is uneven, accompanied by large internal stress and weak weld lines.
Cause Analysis
The runners are too small, too long, or unevenly configured, causing large pressure loss and fast temperature drop, poor plasticization and filling; uneven filling of each cavity produces internal stress and the product is brittle; this is a mold runner system problem, not something that can be solved by the process alone.
Solution
①Optimize the runner design, appropriately enlarge the cross-sectional area and shorten the length; ②ensure the runners are balanced and reasonable, adjust the runner layout of multi-cavity molds so that the filling speed and pressure of each cavity are consistent; ③check the runner surface roughness and corners; ④change to hot runners to reduce temperature drop and pressure loss when necessary.
Key Takeaway
If ABS brittleness is strongly related to 'certain cavities/certain areas', go back and check the runner system: runner imbalance is a congenital mold problem, machine parameters can only alleviate it, and the cure requires changing the runner design.
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