Analysis of the Causes of Surface Pitting During the Production of PVC Pipes and PE Pipes

Ningbo Fangli Technology Co., Ltd. is a mechanical equipment manufacturer with nearly 30 years’ experiences of plastic pipe extrusion equipment, new environmental protection and new materials equipment. Since its establishment Fangli has been developed based on user’s demands. Through continuous improvement, independent R&D on the core technology and digestion & absorption of advanced technology and other means, we have developed PVC pipe extrusion line, PP-R pipe extrusion line, PE water supply / gas pipe extrusion line, which was recommended by the Chinese Ministry of Construction to replace imported products. We have gained the title of “First-class Brand in Zhejiang Province”.

PVC pipe, PE pipe production process of surface pitting may be due to impurities in the molten material, the caliber of water flow is not appropriate or the water contains impurities and other reasons.

1. Due to the head or barrel of the raw materials in the heating time is too long, the head and barrel is not clean or processing temperature is too high or screw damage is prone to aging material, extrusion to form a large pitting into a hole, especially when adding recycle material, this situation should be stopped in about 1.5 hours and stop adding crushed material. Minimizing the degree of decomposition of raw materials. And also should pay attention to check whether the processing temperature adapts to the extrusion requirements.

2. When the raw material is wet PE pipe and PVC pipe surface produce small bubbles after shaping the formation of pitting, observe such pits in the opposite direction of extrusion with the formation of a small tail of stretching. Then the need for the raw material drying process.

3. Raw materials have difficulty to plasticize impurities, and will also produce pitting, this type of pit larger when you can see the impurity components in the middle of the pitting.

4. Raw materials have more difficult to plasticize the crystal ingredients can also produce pits. Then need to improve the processing temperature or replace the raw materials.

5. The uneven cooling water of the caliber causes pitting on the surface of the pipe. The reason is that with the increase in diameter, the cooling water distribution in the caliber is affected by gravity, the more cooling water is needed, the more difficult it is to form a complete water film, the water flow of each inlet pipe should be adjusted, and the water flow in the upper part should be increased or the water flow in the part with poor cooling effect should be increased.

6. Due to the caliber of cooling water channel blockage resulting in uneven water volume will cause a regular distribution of pits, sometimes a straight line arranged locally on the surface of the pipe, in this case, should be cleared to adjusting the flow channel pores to ensure that the uniform cooling water into the film, so as to avoid the appearance of pits.

7. Too much water caused by PVC pipe fittings surface pitting, this situation mainly occurs in the hole type shaped set, due to the shaped set of the internal flow channel is not partitioned, water by gravity under the action of part of the water pressure, more water, while the upper part of the water is smaller, the pipe surface is softer, resulting in the appearance of pitting where the water pressure is large.

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