The rolling process is the main process to determine the wall thickness of seamless steel pipes, and its function is to reduce the wall of perforated rough pipes. The main defects are: uneven wall thickness of rough pipes, surface cracks, pits, abrasions, rolling folds, punctures (breaks), etc.
1. Quality defects of automatic rolling: When the automatic rolling mill rolls rough pipes, the rough pipe quality defects produced include: uneven wall thickness of rough pipes, rough pipe “ears” and rolling folds, rough pipe inner surface straight lines and pits, rough pipe surface cracks and abrasions, etc.
The uneven wall thickness of rough pipes: The main quality defects produced when the automatic rolling mill rolls pipes are related to the uneven wall thickness of the rough pipes and the uneven temperature of the rough pipes, as well as the structural type of the rolling mill itself, the shape of the roller hole, the deformation, the shape of the head, and the operating technology.
“Ears” and rolling folds of rough pipes: mainly caused by the unreasonable distribution of deformation, incorrect hole shape, tool wear, etc. Any condition that is not conducive to the axial extension of the rough tube and promotes the lateral expansion of the metal is likely to cause the rough tube to produce “ears” and rolling folds.
Straight and pitting on the inner surface of the rough tube: The inner straight is a quality defect of the inner surface of the rough tube that is easy to appears in the automatic tube rolling machine, and it is also a difficult problem to solve. In most cases, the inner straight of the rough tube is slight and will not make the steel pipe become scrap. The inner straight is a linear scratch along the axial direction on the inner surface of the rough tube, mainly produced in the wall reduction area of the rough tube. The surface state of the plug, the iron oxide scale on the inner wall of the rough tube, the distribution of deformation, and the lubrication conditions are all related to the inner straight of the rough tube. Spraying lubricant into the inner hole of the rough tube to improve the lubrication effect of the plug can reduce the rolling pressure, reduce the wear of the plug, and prevent the plug from sticking to the steel, thereby reducing the occurrence of inner straight of the rough tube. The inner pit is manifested as uneven pits in a certain area on the inner surface of the rough tube. This is mainly because the numerous iron oxide scales on the inner surface of the rough pipe are not blown clean, or it may be caused by the accumulation of antioxidants or lubricants in a certain area on the inner surface of the rough pipe after being damp and agglomerated. To reduce the internal pits of the rough pipe, the angle of the air nozzle used in the iron oxide removal device should be properly adjusted and sufficient wind pressure should be ensured to completely remove the iron oxide scale.
Surface cracks and scratches on rough pipes: There are two types of cracks on the surface of rough pipes, one is caused by the rough pipe itself, and the other is caused by the automatic pipe rolling process. When the deformation is too large, the deformation distribution is unreasonable, or the hole type is improperly adjusted, and the surface wear of the rolling tool is relatively serious, surface cracks will occur. Any measures to reduce the uneven wall thickness of the rough pipe and reduce the uneven deformation of the metal are conducive to reducing the surface cracks of the rough pipe. The surface scratches of the rough pipe are caused by the rough surface of the deformation tool, or by the relative movement between the rough pipe and the workpiece in contact with the rough pipe surface. To reduce the surface scratch defects of the rough pipe, the inspection and adjustment of the pipe rolling tools and workpieces should be strengthened.
2. Quality defects of periodic tube rolling
The defects of rough tubes rolled by periodic tube rolling mills are caused by the rough tubes themselves, and the other is caused by the self-pipe tying process. The defects include: uneven wall thickness (uneven transverse wall thickness, uneven longitudinal wall thickness and wall thickness runaway, etc.), surface defects (surface scratches, internal and external scars, internal straight lines, cracks, internal pits, etc.), rolling folds (rolling folds, punctures, “baby mouths”, etc.)
The uneven wall thickness of rough tubes: It is the main quality defect caused by periodic tube rolling mills, including uneven transverse wall thickness, uneven longitudinal wall thickness, convex wall thickness, and “bamboo” wall thickness. Factors affecting uneven wall thickness of rough pipe: A. Roller hole shape; B. Process parameters; C. Pipe rolling tools; D. Operating technology;
Surface defects of rough pipe: mainly surface scratches, inner straights, inner pits, inner and outer scars, rough pipe rolling (transverse rolling, longitudinal rolling), etc.; Surface scratches of rough pipe are mainly caused by surface defects of mandrel and roller, and scratches on the surface of rough pipe by the rear guide groove of the pipe rolling machine. The inner straight is a straight groove of rough pipe formed by scratching the inner surface of rough pipe during rolling due to steel sticking, severe wear, “meat loss” on the surface of mandrel, or hard iron oxide scale and iron filings remaining on the inner surface of rough pipe. To reduce surface scratches and inner straight defects of rough pipe, the surface of the mandrel and roller should be smooth, and the cooling of the roller and lubrication of the mandrel should be strengthened. The rolling and folding of the rough pipe are mainly divided into transverse rolling and folding caused by the deformation of the metal being accumulated on the surface of the rough pipe due to the obstruction of axial flow, and longitudinal rolling and folding caused by the wide metal forming “ears” at the roll gap of the roller. For the quality defects caused by periodic tube rolling, the quality of the rough pipe should be guaranteed first, and the control of the tool quality should be strengthened, the hole design of the roller and the adjustment of the process parameters should be emphasized, and the adjustment and operation level of the tube rolling machine should be improved.
3. Quality defects of continuous rolling tubes
The remarkable characteristics of the continuous rolling tube machine are its large production capacity and high production efficiency. The rough pipes rolled are long in length, good in product quality, and wide in specification range. However, the investment is large, the relevant technical requirements are many, and the degree of automation is high. The quality defects of the continuous rolling rough pipe mainly include: uneven wall thickness of the rough pipe, surface defects, and rolling and folding (including concave). The cause of concave: the uneven heating temperature of the rough pipe will increase the uneven deformation of the rough pipe, which is easy to cause concave and crushing of the rough pipe. The larger the diameter-to-wall ratio D/S of the rough pipe, the smaller the tensile force required for the rough pipe wall to be stretched and deformed, and the greater the possibility of denting and rolling. The prevention of denting mainly involves measures such as strengthening the adjustment of rolling process parameters and hole type of the continuous rolling mill.
4. Quality defects of oblique rolled pipes
One type of defect of rough pipe oblique rolling is caused by the rough pipe itself, and the other type is caused by the self-rolling process. The defects are related to the hole shape and adjustment of the oblique rolling mill, the deformation process parameters and adjustment, the quality of the tool, the lubrication conditions of the mandrel, etc. The defects are: surface defects, uneven wall thickness, torsion, and irregular head and tail shapes. To prevent the quality defects of rough pipes generated during the oblique rolling process, it is necessary not only to improve the steel quality of the tube blank, improve the heating quality and perforation quality of the tube blank, ensure the quality of the perforated rough pipe, and eliminate the defects such as rolling folds, cracks, pits, and scars on the surface of the rough pipe, but also to reasonably design the hole type, optimize the deformation process parameters, carefully adjust the hole type according to the process parameters, ensure the quality of the rolling tool, and improve the lubrication conditions of the tool.
Post time: Dec-17-2024