Analysis of the cause of the surface roughness of PE pipe
1. First, eliminate the roughness caused by moisture. Only for PE new materials.
、 PE管材粗糙只发生在表面很薄的一层，也是熔体破裂的一种，但与通常所说的熔体破裂不同，通常的熔体破裂是整个熔体都发生了不稳定流动，而表面粗糙只是发生在管材表面很薄的一层。 2. Roughness of PE pipe only occurs in a thin layer on the surface, and it is also a kind of melt fracture. However, unlike the so-called melt fracture, the usual melt fracture is the unstable flow of the entire melt. Rough surface occurs only on a thin layer of the surface of the pipe. PE pipe roughness is formed in the die section. 是 熔体表面的分子在出口模前必须达到一定的松弛程度。 The condition of smooth PE pipe surface is that the molecules on the surface of the melt must reach a certain degree of relaxation before exiting the die.
3. Physical explanation of rough surface of PE pipe :
A, PE pipe roughness is caused by the friction between the melt and the surface of the mold, and has nothing to do with the surface roughness of the mold (not considering scratches). This friction is caused by adhesion between the melt and the metal surface of the mold.
B. Lubrication is needed for PE pipe surface light.
Low-viscosity high-density polyethylene forms a lubricant on the surface of the mold as the extrusion progresses. Due to the relatively few molecular chain entanglement points of low-viscosity polyethylene, with the progress of extrusion, a part of the molecular chains will be detached from the melt under the action of the mold surface, and "hang" on the mold surface to form a lubricant This lubrication is dynamically balanced. For polyethylene with high viscosity, due to the strong entanglement force between the molecular chains, the molecular chains are not easily detached from the melt, so it cannot form effective lubrication, and the surface of PE pipes will be rough.
高粘度聚乙烯表面粗糙。 C. Rough surface of high viscosity polyethylene.
熔体与口模的摩擦也是口模积料产生的原因。 D. The friction between the melt and the die is also the cause of the die accumulation.