Processing Machinery
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ABS brittle cracking——improper screw plasticizing parameters
Problem Phenomenon
The product is brittle, accompanied by local overheating of the melt or uneven plasticization, directly related to the screw speed and back pressure settings.
Cause Analysis
When the back pressure and speed during screw pre-plasticizing are too high, the melt is strongly sheared, producing local temperature rise and thermal degradation, and the molecular chains are damaged and brittle; when the back pressure is too low and the speed too slow, the plasticizing is insufficient, which also affects the toughness——both excessive and insufficient shear cause brittleness.
Solution
①Appropriately reduce the back pressure and speed of screw pre-plasticizing to make the melt slightly loose and reduce shear overheating degradation; ②at the same time ensure sufficient plasticizing, adjust by observing the melt state (uniform, no lumps, no yellowing); ③avoid blindly increasing the speed to catch up with the cycle; ④regularly check the screw wear.
Key Takeaway
ABS screw parameters should be 'moderate': the speed and back pressure are not the higher the better, shear heat is an invisible degradation source; using the actual melt state as the criterion is more reliable than memorizing the parameter table.
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