Extrusion & Post
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Narrowing of the processing window of calcium-zinc systems in high-speed extrusion
Fenómeno del problema
When the PVC pipe extrusion speed is increased above 25 m/min, using a calcium-zinc stabilizer formulation results in rough pipe surface, uneven inner wall, periodic wave marks, accompanied by aggravated die buildup, and increased shutdown cleaning frequency.
Análisis de la causa
During high-speed extrusion, the residence time of the material in the barrel is shortened, and the thermal stability window of the calcium-zinc stabilizer is compressed; shear heat causes the local material temperature to exceed the set value by 10-15°C; the lubrication system does not match the high-speed working condition, and insufficient external lubrication causes melt adhesion; the dispersion efficiency of metal soap stabilizers decreases under high-speed shear.
Solución
Select calcium-zinc composite stabilizers designed specifically for high-speed extrusion (fine particle size, easy-to-disperse type); increase the external lubricant PE wax/oxidized PE wax dosage by 0.2-0.5 phr; optimize the screw design to reduce the compression ratio from 2.5 to 2.2; appropriately increase the feed zone temperature to shorten the plasticization delay; incorporate special lubricating components into the stabilizer to achieve a self-lubricating effect.
Conclusión clave
High-speed extrusion places higher requirements on the thermal response speed of the stabilizer and lubrication synergy; comprehensive optimization is needed from three aspects: stabilizer selection, lubrication formulation, and process parameters.
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