H.D.Plastics provide a wide variety of Extruded PVC pipe and PE pipe s to customers, in standard diameters, lengths, and colors to meet the requirements of your application. Often, we have noticed some surface impurities or defects for pipe extrusion parts, today we will present some cause analysis of surface pitting in the production process of PVC pipe and PE pipe.

red PE tubing pipeWhite ASA Pipe extrusion

Extruded PVC pipe or PE pipe production

1. Impurities in the melting barrel in the extrusion process of Extruded PVC pipe or PE pipe production.

Due to the overheating of raw material with the unclean barrel as well as high processing temperatures, it is easy to result in the aging materials. So Large pits and cavities are formed during PVC or PE pipe extrusion especially when adding recycled materials. In this case, actually, the pulverized material should be stopped after the shutdown for about 1.5 hours. If the machine is not turned on for 4 hours after the shutdown, the temperature should be quickly lowered to 150-200℃ to minimize the degree of decomposition of the PVC resin. We should check whether the processing temperature is suitable for extrusion requirements to avoid aging material.

When the raw material is wet, small bubbles are generated on the surface of the PE pipe and PVC pipe to form pits. Observe that these pits have small tails stretched in the opposite direction of extrusion. At this time, the raw materials need to be dried.

When there are impurities that are difficult to plasticize in the PVC materials, pits will also occur. When such pits are large, the impurities on the PVC pipe can be seen clearly.
4. Pockmarks can also occur when there are more crystal points that are difficult to plasticize in raw materials. At this time, it is necessary to increase the processing temperature or replace the raw materials.

2. Improper water flow in the shaping jacket

The uneven cooling water flow of the shaping sleeve causes pitting on the surface of those Big round PVC pipe. This phenomenon occurs more or less in various big PVC round pipes above Φ300. The reason is that with the increase of the diameter, the distribution of the shaping sleeve is much more affected by gravity.  The larger the amount of cooling water required, the more difficult it is to form a complete water film. The water flow of each inlet PE pipe should be adjusted, and the upper water flow should be appropriately increased or the water flow of the parts with poor cooling effect should be increased.

Due to the blockage of the cooling water channel of the shaping jacket, the uneven water volume will cause the pitting to be distributed regularly, sometimes linearly arranged on the surface of the pipe. In this case, the pores of the flow channel should be cleared to ensure the uniform film formation of the cooling water. So as to avoid pitting.

3. Impurities in the water flow

Too much water causes pitting on the surface of PVC pipe fittings. This situation mainly occurs on the hole-shaped sizing sleeve. Because the internal flow channels of the sleeve are not partitioned, the water is under the action of gravity and the water pressure is large, and the water volume is large. The upper part of the water volume is small, and the pipe surface is soft, causing pitting in places with high water pressure

The manufacturability of Extruded Pipe Extrusion with OEM customization

Materials1), Flexible Tubing: Polyurethane, PVC, LDPE,2), Semi-Rigid Tubing: PP and HDPE

3), Rigid Tubing: Polycarbonate, UPVC, ABS, high impact polystyrene HIPS and Acrylic

ColorsTransparent, Semi-translucent, Opaque, or Custom Color
ShapesRound, Oval, Square, Rectangular, Triangular
SizesCustom
Other1), Cut to length2), Logo Printing

3), Hole punching

4), Surface painting