How to prevent quality defects in rolled tubes

The tube rolling process is the main process to determine the wall thickness of the seamless steel pipe, and its function is to reduce the wall of the perforated capillary. The main defects are: uneven wall thickness of the waste pipe, surface cracks, pits, abrasions, rolling, puncturing (pulling) and so on.

Quality defect of automatic rolling tube

When the automatic pipe rolling machine rolls the capillary, the quality defects of the waste pipe include: uneven wall thickness of the waste tube, “ears” and folds of the waste tube, straight lines and pits on the inner surface of the waste tube, cracks and scratches on the surface of the waste tube and other defects.

Uneven wall thickness of barren pipe: The main quality defect produced by automatic pipe rolling mill is not only related to the non-uniformity of capillary wall thickness and the non-uniformity of capillary temperature, but also to the structure of the rolling mill itself. , Roll pass shape, deformation, plug shape and operating technology and other factors.

“Ears” and folds of waste pipes: mainly caused by unreasonable distribution of deformation, incorrect hole shape, tool wear and other reasons. Any conditions that are not conducive to the axial extension of the capillary tube and promote the lateral expansion of the metal are likely to cause “ears” and folds in the waste tube.

Straight track and pit on the inner surface of the barren pipe: The inner straight track is a quality defect on the inner surface of the barren tube that often occurs in automatic pipe rolling mills, and it is also a difficult problem to solve. In most cases, the straights in the waste pipe are slight enough not to make the seamless carbon steel pipe waste. The inner straight channel is a linear scratch on the inner surface of the waste pipe along the axial direction, which is mainly generated in the wall-reduced area of the capillary. The surface state of the plug, the scale of iron oxide on the inner wall of the capillary, the distribution of deformation, and the lubrication conditions are all related to the straight path in the barren pipe. Spraying lubricant into the inner hole of the capillary 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 straight paths in the waste pipe. The inner pit is manifested as uneven pits in a certain area of the inner surface of the waste pipe. The main reason is that the numerous iron oxide scales on the inner surface of the capillary tube have not been blown clean, or it may be caused by the accumulation of antioxidants or lubricants in a certain area of the inner surface of the capillary tube after being wet and agglomerated. In order to reduce the inner pit of the waste pipe, the angle of the tuyere used in the iron oxide scale removal device should be properly adjusted and sufficient wind pressure should be ensured to completely remove the iron oxide scale.
Cracks and scratches on the surface of the barren tube: There are two types of cracks on the surface of the barren tube, one is caused by the capillary itself, and the other is generated in the automatic tube rolling process. When the amount of deformation is too large, or the distribution of the amount of deformation is unreasonable, or when the pass pattern is adjusted improperly and the surface of the rolling tool is severely worn, surface cracks will occur. All measures to reduce the uneven wall thickness of the waste pipe and reduce the uneven deformation of the metal are conducive to reducing the surface cracks of the waste pipe. The surface scratches of the waste pipe are caused by the unsmooth surface of the deformation tool, or the relative movement between the waste pipe and the workpiece in contact with the surface of the waste pipe. In order to reduce the surface scratch defects of the waste pipe, the inspection and adjustment of the pipe rolling tools and workpieces should be strengthened.

Periodic rolling tube quality defects

One of the defects of the waste pipe rolled by the periodic pipe rolling mill is caused by the capillary itself, and the other is produced in the self-tying process. The resulting defects include: uneven wall thickness (uneven lateral wall thickness, uneven longitudinal wall thickness and running wall thickness, etc.), surface defects (surface scratches, internal and external scarring, internal straights, cracks, internal pits, etc.), Roll fold (roll fold, puncture, “doll mouth”, etc.)

Uneven wall thickness of the barren pipe: it is the main quality defect caused by the rolling of the periodic pipe rolling mill. all. Factors affecting the uneven wall thickness of the waste pipe: A. Roll pass shape; B. Process parameters; C. Pipe rolling tools; D. Operation technology;

Surface defects of barren pipes: mainly the surface scratches, inner straights, inner pits, inner and outer scars, and rolling (horizontal rolling, vertical rolling) of the barren pipes; the surface scratches of the barren pipes are mainly mandrel Scratches on the inner and outer surfaces of the barren pipe caused by surface defects of the rolls, as well as the scratches on the surface of the barren pipe caused by the guide groove behind the pipe mill. The inner straight channel is a straight groove formed by scratching the inner surface of the capillary during the rolling process due to the sticking of steel on the surface of the mandrel, severe wear, “dropping meat” or hard iron oxide scale and iron filings remaining on the inner surface of the capillary tube. mark. In order to reduce the scratches on the surface of the waste pipe and the defects of the inner straight, the surface of the mandrel and the roll should be smooth, and the cooling of the roll and the lubrication of the mandrel should be strengthened. The barren pipe rolling is mainly divided into the transverse rolling caused by the deformed metal being deposited on the surface of the barren pipe due to the obstruction of axial flow, and the longitudinal rolling caused by the “ear” formed by the widened metal at the roll gap. For the quality defects caused by periodic rolling, the quality of the capillary should be guaranteed first, and the control of tool quality should be strengthened.

Continuous rolling tube quality defect

The distinguishing feature of continuous tube rolling mill is its large production capacity and high production efficiency. The rolled waste pipe has long length, good product quality and wide range of specifications. However, the investment is large, the related technical requirements are many and the degree of automation is high. The quality defects of continuously rolled barren pipes mainly include: uneven wall thickness of barren pipes, surface defects and rolling (including concave) and so on. The reason for the denting: the uneven heating temperature of the capillary will increase the uneven deformation of the barren tube, which is easy to cause the barren tube to be dented and rolled. The larger the diameter-to-wall ratio D/S value of the barren tube, the smaller the tensile force required for the tube wall of the barren tube to be stretched and deformed, and the greater the possibility of denting and rolling. To prevent the occurrence of dents, the main measures are to strengthen the adjustment of rolling process parameters and pass types of continuous tube mills.

Quality defects of skew-rolled pipes

One of the defects of capillary skew rolling is caused by the capillary itself, and the other is produced in the self-rolling process. The resulting defects are related to the pass shape and adjustment of the skew rolling mill, deformation process parameters and adjustment, tool quality, and mandrel lubrication conditions. The resulting defects are: surface defects, uneven wall thickness, torsion and irregular head and tail shapes. In order to prevent the quality defects of the barren pipe produced during the skew rolling process, it is necessary not only to improve the steel quality of the pipe blank, but also to improve the heating quality and perforation quality of the pipe blank, to ensure the quality of the perforated capillary, and to eliminate the rolling folds, cracks and pits existing on the surface of the capillary. In addition, it is necessary to reasonably design the pass shape, optimize the deformation process parameters, carefully adjust the pass shape according to the process parameters, ensure the quality of the rolling tools and improve the lubrication conditions of the tools, etc.