Lined plastic composite steel pipe with PVC-u, PE-RT, pp-R and other plastic tubes for lining materials and adhesives, through the thermal expansion process, cold drawing shrink diameter process, and steel pipe composite, which has the hardness of steel pipe, not easy to deformation, heat, pressure and other characteristics, but also has plastic pipe corrosion resistance, not easy scaling, clean non-toxic, Good insulation, long life and other characteristics. This type of steel pipe quality problems mainly in the "composite", the composite is unsuccessful, it will be easy to appear in the liner shrinkage problem.
The reasons for this analysis are:
1, welding Bar factors High-frequency welded steel pipe In the absence of a place to weld tendons, easy to cause the combination of plastic pipe and steel tube is not tight problem.
If the pores are too large, plastic tube shrinkage will occur.
2, Plastic pipe factors
1) Thermal expansion and contraction
The shrinkage of the plastic pipe is larger than the shrinkage of the steel pipe, so the inner shrinkage of the pipe end of the lining pipe is appeared.
2) Plastic tube Crystallinity
Unlike metals, crystalline resins have a crystallinity of less than 100%.
3) the degree of crosslinking of lined plastic pipe
After the lining-plastic composite steel pipe is placed for a period of time, it is easy to shrink the liner tube with the increase of crosslinking degree.
4) There is no filler or reinforcement material
Besides reducing the cost, the filler of plastic pipe can also improve the rigidity and heat resistance, dimensional stability, shrinkage and creep resistance of the products.
5) Hot Melt Adhesive
Lined plastic pipe for hot melt adhesive requirements, such as the peel of hot melts too low, can not constrain the internal lining of plastic pipe due to temperature changes caused by the stress, resulting in degumming and necking phenomenon.
The residual stress of the plastic pipe when it is drawn into the steel pipe and the temperature influence when the pipe is cut.
To solve the shrinkage problem of lined plastic pipe after lining of steel-plastic composite pipe:
1 in the lining of the crystalline plastic pipe, to reduce the cooling rate, so that the lining of the plastic pipe in the case of maintaining a high degree of crystallinity of the molding. 2 for hot-water lined plastic pipe production, if the use of chemical crosslinking, such as silane crosslinked polyethylene pipe as lined plastic pipe, can be taken before the steel-plastic composite measures.
If the lining plastic pipe in a specific environment for a period of time natural cross-linking or the use of water boiling method to accelerate cross-linking, improve the steel-plastic composite plastic pipe material before the crosslinking, in order to reduce the plastic lining after the crosslinking reaction and contraction.
3 when possible, the lining of plastic tube as far as possible to reduce the outer diameter and pipe diameter difference.
4 the composite after the removal of plastic pipe temperature control around 25 ℃, to prevent too high or too low. 5 The plastic pipe is pulled into the steel tube by traction, releasing the stress caused by traction and then compounding.