- Reasons for scratches on the surface of welded pipes:
The use of roll-formed welded pipes requires the strip to be bent transversely into a circle. This is achieved by deforming the strip through a series of rolls with different groove shapes. Each pair of rolls rotates at a certain speed, but the linear speed of the roll surface is different due to the rotation radius. However, the difference in linear speed causes sliding friction between the strip and the forming roller, which is the fundamental cause of scratches on the surface of the welded pipe.
Most welded pipe units adopt the horizontal forming method. For this unit, the bottom diameter of the driving rolls of the roughing roll, guide ring roll and sizing roll is considered to be the driving diameter. The linear speed of these roll bottom diameters is basically equal to the conveying speed of the strip. , due to the different rotation radii, the roll edge of each roll causes large relative sliding friction between the strip and the roll surface, resulting in surface scratches.
Friction affects the surface quality, and the friction will cause scratches. When the friction increases, the positive pressure on the strip increases, and the deformation of the strip increases, causing the roller to strain the strip and produce surface scratches.
- Proper roll design and processing
1. Use traveling flange rollers
In order to reduce the relative sliding between the strip and the roll surface, the driving roller uses a traveling flange roller, a typical moving flange roller structure. Its design is that the traveling flange is supported by bearings, and its rotation speed depends on the conveyance of the strip. Speed, different from the speed of the roll, using this kind of roll can reduce the relative sliding between the strip and the surface of the roll, thereby reducing or even removing scratches on the surface of the welded pipe.
2. Four-roller forming
In addition to using traveling flange rollers for forming, some welded pipe units use four-roller forming. Four-roller forming is used for guide ring rollers and sizing rollers. At this time, the horizontal rollers use active rollers and the vertical rollers use passive rollers. The speed of the vertical rollers depends on The delivery speed of the strip is beneficial to reducing the relative sliding and sliding friction between the strip and the surface of the vertical roller.
3. Escape angle and clearance
In addition to changing the roll design, roll modification can also reduce surface scratches on the welded pipe. A common method is to process an appropriate escape angle or clearance on the roll edge. This gap can reduce the surface pressure of the strip at that location, thereby reducing the surface pressure of the strip. To reduce surface scratches, the processing gap not only depends on the welded pipe material, pipe diameter and unit characteristics, but also depends on the roll shape of each roller during the forming process. The escape angle or gap requires that the strip can escape from the roller surface. For different purposes The surface quality of welded pipes, such as high-strength low-alloy steel structural pipes, is not as high as that of welded pipes that need to be renovated. In order to reduce production costs, there is no need to spend too much effort to eliminate surface scratches (if the roll scratches are within the standard requirements).
The surface treatment process can form a hard wear-resistant layer on the surface of the roll. The wear-resistant layer includes physical coating, chemical coating and thermal diffusion layer. The coating material generally contains titanium nitride and titanium carbide. The coating can increase the durability of the roll. Wear resistance and reduced friction coefficient, but the application of rolls in this field is limited by roll deformation and difficulty in repair. When the surface roughness of the steel pipe is serious, surface treatment of the rolls can be considered.
Scratches on the surface of the welded pipe may be caused by simple reasons such as high surface friction or difference in linear speed on the roll surface. However, it is troublesome to analyze and eliminate surface scratches. The entire forming process includes the design of the roll, the installation and adjustment of the roll, and the lubrication system. Reasonable use must be analyzed in order to produce high-quality products.
