1. Uneven wall thickness
1)Features: The wall thickness of the steel pipe is uneven on the same section, and the difference between the maximum wall thickness and the minimum wall thickness is large.
2)Reason: The uneven wall thickness of the pipe material is too large, and the drawing line is inconsistent with the axis of the steel pipe during drawing. The plug is worn or the back hole of the plug is eccentric. Correction of the centering hole of the tube blank. The curvature and cut slope of the tube blank are too large.
3)Prevention: In order to reduce the uneven wall thickness of the steel pipe, the uneven wall thickness of the pipe material should be as small as possible, and at the same time, the mold should be carefully checked and the pipe pulling machine should be adjusted.
2. The wall thickness is too large or too small
1)Features: Those with super positive deviation are called super thick wall thickness; those with super negative deviation are called super thin wall thickness.
2)Reason: The main reason is improper mold matching, or ignoring the change in mold size due to wear; uneven heating of the tube blank will also lead to uneven wall thickness
3)Prevention: In order to prevent this situation, the mold should be properly matched and the position of the mandrel should be adjusted correctly. And the wall thickness change of the empty-drawing pass steel pipe should be estimated accurately.
3.The outer diameter exceeds the standard
1)Features: The outer diameter of the seamless steel pipe exceeds the standard, and those with excess positive difference are called large outer diameters, and those with excess negative differences are called small outer diameters.
2)Cause: The hole pattern of the sizing machine is too worn, or the new hole pattern design is unreasonable. The final rolling temperature is unstable.
1)Features: The steel pipe is not straight along the length direction or the end of the steel pipe is bent like a goose head
2)Reason: The following reasons may cause the steel pipe to bend: local water cooling during manual thermal inspection, improper adjustment during straightening, serious wear of the straightening roller, improper machining, assembly and adjustment of sizing machine, and bending during hoisting and transportation.
5. The length exceeds the standard
1)Features: The length of the seamless pipe exceeds the requirements, the excess positive difference is called a long ruler, and the excess negative difference is called a short ruler.
2)Causes: The length of the billet exceeds the standard, the rolling is unstable, and the slitting is not well controlled.