Extrusion & Post
11 조회수
Melt fracture (sharkskin) in PP extrusion
문제 현상
Periodic fine roughness, sharkskin-like or orange-peel-like texture appears on the surface of PP extruded sheets, profiles, or pipes, becoming more obvious after the line speed increases.
원인 분석
The shear stress of the melt at the die exit exceeds the critical value, and the surface layer flow becomes unstable, forming periodic fracture; the viscosity characteristics of PP make it easier to trigger during high-speed extrusion; low die temperature, excessive line speed, and rough die lips all aggravate it.
해결 방법
①Increase the die temperature by 3~5℃ to reduce the melt viscosity at the exit; ②appropriately reduce the screw speed/line speed; ③clean and polish the die lips to reduce exit resistance; ④add a fluoropolymer processing aid (PPA) to form a lubricating layer on the die wall; ⑤for stubborn cases, evaluate switching to a low-viscosity or easy-to-process grade.
핵심 요약
The main line for PP extrusion surface roughness is 'reduce exit shear': use the four-piece set of raising temperature, reducing speed, polishing, and adding PPA in order; when pursuing output, especially find the critical balance point between speed and surface quality.
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