For the steel pipe without pre-treatment, the drawing cannot be carried out due to the excessive friction coefficient between the surface of the steel pipe and the mold during cold drawing; only after the pre-treatment process, the steel pipe is derusted first, and then treated by phosphating and saponification. A dense metal soap film is formed on the inner and outer surfaces to reduce the friction between the steel pipe and the mold, thereby ensuring smooth drawing. At the same time, the pre-treatment can also reduce the loss rate of the mold, improve the yield and work efficiency, and make the surface of the finished product smooth and uniform, and the rust prevention effect is good.
The following points should be noted in the pre-treatment of steel pipes:
(1) Pickling and rust removal should be thorough. Once rust that has not been removed is found, it needs to be pickled again.
(2) During production, the component concentration of the phosphating solution and saponification solution should be tested frequently to ensure the production index of the phosphating solution and saponification solution. When it is found that the index is not reached, it should be timely adjusted.
(3) The temperature and operating time of the treatment liquid must be strictly controlled.