Cold-drawn pipe inner surface defects
High-precision cold-drawn pipe inner surface roughness Ra ≤ 0.8μm, inner diameter size accuracy can reach H9 ~ H10, only in this way to ensure that after honing to H7 ~ H8 inner hole size and Ra ≤ 0.2μm inner surface roughness requirements. The main factors that affect the surface roughness of the honing tube In addition to the precision of the honing machine, the quality of the inner surface of the cold drawn tube is another key point. The internal surface defects of the cold drawn tube are classified by the measured data of the domestic A factory, there are mainly three kinds.
1. Point
After the cold-drawn tube is roughed, it can be found that its surface is composed of many pit-shaped defects. If such defects are not worn out, it will seriously affect the finish of the inner bore of the cylinder barrel, which is a waste product for the cylinder barrel.
2. Scratch
Scratch defects are generated during cold drawing. Generally, a scratch along the axial direction of the steel pipe must have a honing allowance exceeding the depth of the scratch, so that it is possible to wear off such defects and process a qualified cylinder.
3. Not round
When the cold drawn tube is in production, the inner mold fixed on the core rod can float up and down. Therefore, the inner diameter of the cold drawn tube is not as straight as the machine tube. In addition, some hot-rolled pipes and the wall thickness of the same pipe are relatively large, and there is a non-uniform deformation of the pipe during cold-drawing deformation, and the out-of-round spots of the cold-drawn pipe are easily generated. After the tube is polished, it will be found that the inner hole has a sheet surface with different reflectance in other places. If the grinding amount is small, the phosphate layer in the cold drawing is not worn out. Seriously affect the cylinder surface quality.
