1 upper roll and 2 side rolls
The three-roll squeezing method –”1 upper and 2 side” is equivalent to a short-circuit or current bypass device across the squeezing welds. The current short circuit or current bypass may have different upper roll diameters for different design and welded pipe diameters.
The diameter of the upper roll is different, and the position of the short-circuit point is also different. The larger the diameter of the upper roll, the more the position of the short-circuit point is farther away from the pressing point, that is, the more the closing point of the steel strip is advanced, the more the current is bypassed. Early, the most typical phenomenon is that the upper roll is heated intensely, and the service life is very short. The horizontal stripes of the roll are cracked, and a large amount of water is needed for cooling.
The smaller the upper roll is, the closer the short-circuit bypass point is to the welding extrusion point and overlaps with the earlier healing point at the edge of the steel strip. The smaller the bypass effect on the current is. However, the size of the upper roll is limited by the structure and heating. In fact, the diameter of the upper roll is the same as that of the side rolls. The effect of the upper roll on the welding efficiency is usually not less than 10%, and the loss can be up to 25% at high temperature. The measured average value is 15%-18%. And the smaller the diameter and the thicker the wall thickness, the greater the efficiency loss of the structure.
Another potential hazard of the “1 upper roll and 2 side rolls” three-roll squeezing method is the stricter requirement of processing accuracy, which has been neglected or neglected in the past.
1. If the center line of the upper roll is moved backward by d1, the upper roll of the microscopic top is pressed twice after the welding side is squeezed, and the flow line is bent or formed into a shoulder on the metallographic phase, or the metallographic asymmetry of the left and right sides is asymmetrical. This kind of defect can not be found in the usual flaw detection, longitudinal flattening, impact, hydraulic or other experimental methods. The only thing is that the weld crack will occur when flattening is occurred.
2. If the upper roll is moved forward by d2, as described above, it will cause earlier weld seam closure, then side squeezing, it will cause high energy usage and low welding efficiency.
2 upper rolls and 1 lower roll
The three-roll squeeze method of “2 upper rolls and 1 lower roll” can be said to be the best squeeze method for small diameter welding (steel pipe diamerter under 114 mm). Three rolls adjust independently, three rolls coordinate and rotate as a whole to make the adjustment consistent. Each of the three squeeze rolls contains nearly 120 degrees. The diameter and load of each roll are reduced effectively. Vee length = pipe diameter is the most efficient. The two upper rolls effectively fit the edge of the strip in the form of angle, forming good squeeze force and strip edge control. It avoids many disadvantages of two rolls and three upper rolls, so it is an ideal welding squeeze device.
The disadvantages are technical requirements, processing accuracy requirements and relatively high cost, and adjustments are difficult, thus limiting the promotion. Usually used on higher demand steel pipe lines.
1 upper roll and 2 lower rolls
Although the “1 upper roll and 2 lower rolls” three-roll squeeze method has the characteristics of independent adjustment, three-roll unification, integral rotation, simple adjustment, and also has the characteristics of three squeeze rolls each containing 120 degrees, each roll diameter and load effectively reduced, which avoids many disadvantages of the two-roll and the top three-roll squeeze method, but the upper roll form is still absent. The method avoids the shortcomings of three-roll extrusion mode of independent upper roll. However, due to the small diameter of the roll, the bypass current is much less than that of the upper roll extrusion device. But there are also some problems in equipment manufacturing, such as technical requirements, processing accuracy requirements, relatively high cost and relatively difficult adjustment. At present, only a few manufacturers use it.
Post time: Apr-02-2019