Roll forming in a tube electric welding mill

This process has many similarities with furnace welding. However, the following significant differences can be pointed out. 1) If the pipe is subjected to bending in a cold state, its elastic properties under load are clearly expressed. 2) The blanks exposed to forming have a higher thinness (d/s = 4 + 35 at furnace welding machines; 10 + 75 and more at TECA), which ultimately reduces their longitudinal resistance to bending action from the stands and increases the possibility of corrugation on the edges, especially with d/s values > 50.

Forming conditions

The number of stands, the distance between stands, and the angle of folding of the strip in each stand - in such mills should be determined on the basis of two conditions: 1) ensuring unobstructed progress of the strip through the mill. 2) elimination of corrugation. The first condition implies compliance with the established process of capturing the metal rolls. In fact, mills of various sizes use from 6 to 11 drive stands with horizontal rolls. Roll guides or other stands with vertical, non-driven rolls (EDG stands) are used between stands.

Forming Stages

The horizontal stands take all or most of the plastic and elastic deformation during forming. It is produced in the previous, out-of-contact zone. The elastic recoil of the profile (upsetting after deformation in the horizontal stand) must be carried out in the main area by means of vertical rolls. It is also necessary that a new out-of-contact area of elastic-plastic deformation (new local center of forming) is created in the next stand, because after the passage of the vertical rolls the springing occurs. The deformation of the bending and, in particular, of the edges occurs non-monotonically, namely with a periodic increase and periodic decrease of the folding angle, which is an indicator of the division of the entire molding center into local ones. In addition, as a result of this deformation, edge stretching increases and the probability of corrugation increases. When forming thin-walled billets with d/s> 50 it is very important to have a monotonic hearth, to create which between the horizontal stands specially tuned guides with short cylindrical rollers are installed. The realization of part of the bending deformation is possible in roller guides. Installation of stands in which the lower (central) formation of the tubular billet contributes to the reduction of the corrugation process. In this case the level of the bottom caliber of the lower horizontal rolls smoothly decreases during the forming process.

The calibration of the rollers ensures:

• versatility. The same rolls in the first stands can be used for forming pipe billets with different diameters. This, in turn, lowers the number of rolls;
• Stability of the strip and billet, which prevents them from slipping along the roll axis;
• implementation of the forming process for thin-walled billets;
• Intensive mode of forming (this mode reduces the number of working stands);
• lower wear of the rolls.

The above-mentioned conditions for the most part cannot be realized in the process of a single calibration. Therefore, different types of calibration have been developed.

Single radius calibration.

In this type of calibration, the tube billet makes one radius g* in each gauge, which is reduced in stages during the forming process to the value gn. This value is approximately equal to the radius of an already welded stainless tube. Single-tile calibrations are the most common due to the combination of requirements, which ensures versatility, despite other comparatively high values

Double-radius calibrations

With this calibration profile is described by two different radii (the central part - Rts; edges - radius r, one of the radii is constant along the process of molding and equal to gp, the second - the variable, which gradually decreases) and other ... Moulding mills have different drive stands: a group and the individual.

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