The finishing process of steel pipes is an indispensable and important process to eliminate defects in steel pipes, further improve the quality of steel pipes, and meet the needs of special uses of products.Steel pipe finishing mainly includes: steel pipe straightening, end cutting (chamfering, sizing), inspection and inspection (including surface quality inspection, geometric dimension inspection, non-destructive inspection and hydraulic test, etc.), grinding, length measurement, weighing , painting, printing and packaging processes. Some special-purpose steel pipes also need surface shot blasting, mechanical processing, anti-corrosion treatment, etc.
(I) Steel pipe straightening defects and their prevention
⒈ The purpose of steel pipe straightening:
① Eliminate the bending (non-straightness) produced by the steel pipe during the rolling, transportation, heat treatment and cooling processes
② Reduce the ovality of steel pipes
⒉ Quality defects caused by the steel pipe during the straightening process: related to the straightening machine model, hole shape, hole adjustment and the characteristics of the steel pipe.
⒊ Quality defects in steel pipe straightening: steel pipes are not straightened (pipe end bends), dented, squared, cracked, surface scratches and indentations, etc.
(ii) Steel pipe grinding and cutting defects and their prevention
⒈ The purpose of grinding surface defects of steel pipes: to eliminate surface defects that are allowed to exist by steel pipe standards but must be ground clean to improve the surface quality of steel pipes.
2. Defects caused by surface grinding of steel pipes: The main reason is that the depth and shape of the grinding points after grinding exceed the requirements specified in the standard, causing the outer diameter and wall thickness of the steel pipe to exceed the negative deviation or have an irregular shape.
⒊ Steel pipe surface grinding should generally meet the following requirements:
① After the surface defects of the steel pipe are repaired, the wall thickness of the repaired area cannot be less than the negative deviation of the nominal wall thickness of the steel pipe, and the outer diameter of the repaired area should meet the requirements of the outer diameter of the steel pipe.
②After the surface of the steel pipe is ground, it is necessary to keep the ground surface of the steel pipe as a smooth curved surface (excessive arc). Grinding depth: width: length = 1:6:8
③ When grinding the steel pipe as a whole, there should be no overburning or obvious polygonal marks on the surface of the steel pipe.
④The surface grinding points of the steel pipe shall not exceed the number specified in the standard.
⒋ The main defects caused by steel pipe cutting include: the end face of the steel pipe is not vertical, there are burrs and loops, and the bevel angle is incorrect, etc.
⒌ Improving the straightness of the steel pipe and reducing the ovality of the steel pipe are prerequisites for ensuring the cutting quality of the steel pipe. For steel pipes with high alloy content, flame cutting should be avoided as much as possible to reduce the occurrence of pipe end cracks.
(iii) Steel pipe surface processing defects and their prevention
⒈ Steel pipe surface processing mainly includes: surface shot peening, overall surface grinding and mechanical processing.
⒉ Purpose: To further improve the surface quality and dimensional accuracy of steel pipes.
⒊ The tools for overall grinding of the outer surface of steel pipes mainly include: abrasive belts, grinding wheels and grinding machine tools. After the overall grinding of the steel pipe surface, the oxide scale on the surface of the steel pipe can be completely eliminated, the surface finish of the steel pipe can be improved, and the surface of the steel pipe can also be removed. Some minor defects such as small cracks, hair lines, pits, scratches, etc.
① Use an abrasive belt or grinding wheel to completely grind the surface of the steel pipe. The main quality defects that may result include: black skin on the surface of the steel pipe, excessive wall thickness, flat surfaces (polygons), pits, burns and wear marks, etc.
② The black skin on the surface of the steel pipe is caused by the grinding amount being too small or the pits on the surface of the steel pipe. Increasing the grinding amount can eliminate the black skin on the steel pipe surface.
③ The steel pipe wall thickness is out of tolerance because the negative deviation of the wall thickness of the steel pipe itself is too large or the amount of grinding is too large.
④ Burns on the surface of the steel pipe are mainly caused by the excessive contact stress between the grinding wheel and the surface of the steel pipe, the grinding amount of the steel pipe in one grinding, and the grinding wheel used is too rough.
⑤ Reduce the amount of steel pipe grinding at one time. Use a coarse grinding wheel for rough grinding of the steel pipe and a fine grinding wheel for fine grinding. This can not only prevent surface burns on the steel pipe, but also reduce the wear marks produced on the surface of the steel pipe.
⒋ Shot peening on steel pipe surface
① Steel pipe surface shot peening is to spray iron shot or quartz sand shot of a certain size on the surface of the steel pipe at a high speed to knock off the oxide scale on the surface to improve the smoothness of the steel pipe surface.
②The size and hardness of the sand shot and the injection speed are important factors affecting the quality of shot peening on the surface of the steel pipe.
⒌ Steel pipe surface machining
①Some steel pipes with higher internal and external surface quality requirements require mechanical processing.
②The dimensional accuracy, surface quality and curvature of machined pipes are unmatched by hot-rolled pipes.
In short, the finishing process is an indispensable and very important process to ensure the quality of steel pipes. Strengthening the role of the finishing process will undoubtedly help to further improve the quality of steel pipes.
Post time: Apr-01-2024