Why do seamless steel pipes fold outward?

Why do seamless steel pipes fold outward?

External folding is a common external surface defect of seamless steel pipes, which is characterized by spiral layered folds on the outer surface of the steel pipe. The outward folding of seamless steel pipes is mostly caused by defects in the steel billet. During the rolling process of steel pipes, because the steel billet is often subjected to alternating tensile stress, the stress state is relatively bad, and it is easy to expand the defects of the steel billet. The corresponding inner surface defect is the inward folding of the seamless steel pipe, which is characterized by linear or spiral or semi-helical jagged defects on the inner surface of the steel pipe.

Seamless steel pipe external folding is divided into steel external folding and operating external folding

1.Steel folding

There are two main types of external wrinkles in steel: the first is irregular sheet-like wrinkles on the outer surface of the steel pipe. The outer edges of the wrinkles are jagged, or due to the influence of certain factors during the processing, the outer wrinkles on the steel pipe are jagged. When ladling and baking alloy materials, a large number of bubbles may appear. However, after the steel pipe was opened, bubbles leaked out and cracks gradually formed. Another reason is that the cold skin produced by the billet during the casting process has not been cleaned up.

Second, there are regular large spiral wrinkles on the outer surface of the steel pipe. The main reason for such defects is generally that the surface of the billet is scratched by the edge of the limiting roller during the continuous casting process, forming straight rails or lugs. Or there are cracks on the surface of the continuous casting billet, the straight track is not cleaned during the finishing of the billet, or the edge transition of the straight track is not smooth, causing wrinkles on the outer surface during perforation.

2. Folding operation

There are mainly two types of outward folding: straight short line and spiral outward folding. Short linear outward folding is mainly caused by the deep and steep grooves in the bite part of the piercer roll; spiral outward folding is mainly caused by the use of rollers with surface damage or improper adjustment of the rolling profile during rolling.

3. Methods and solutions to control external wrinkles.

1) Ensure billet quality. and strengthen the cleaning work during enforcement

2) Appropriately improve the performance of the mold slag to improve the rolling quality of seamless pipes, and ensure that a sufficient amount of liquid slag flows into the air gap wall between the solidification shell and the crystallizer by reasonably controlling the thickness of the liquid slag layer.

3) Reasonably adjust the pass pattern of the piercing machine and rolling mill. If the roller surface is seriously worn, it should be replaced in time. Set cooling water baffles at the roll positions of the continuous rolling mill to avoid affecting the quality of steel billet production due to non-diversion of cooling water.

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