Processing Machinery
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PA6 Screw Back Pressure Control
Problem Phenomenon
Air is mixed into the melt and the product has bubbles, or excessive back pressure causes melt overheating and degradation
Cause Analysis
PA6 viscosity is low; excessive back pressure causes obvious shear heating and slows screw recovery, extending the thermal history; too-low back pressure causes uneven plasticizing and air entrapment in the melt, and the nominal back pressure is only about 0.5MPa
Solution
①Keep back pressure at a low value of about 0.5MPa (5bar); ②Screw surface speed not exceeding 0.5m/s, and not exceeding 0.2m/s for flame-retardant grades; ③For plasticizing abnormalities, check back pressure and rotation speed first
Key Takeaway
Low back pressure is the basic principle of PA6 plasticizing; low-viscosity materials cannot withstand shear abuse, and the speed upper limit is executed according to the grade; after confirming effectiveness, solidify the parameters and practices into the work instruction to prevent recurrence
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