Roll design refers to the process of designing the shape of the roll. Reasonable roll shape design and optimization is not only beneficial to the shape control but also has the effect of extending the service life of the roll in the wear area of the roll.
In order to maintain the straightness and uniform thickness of the steel plate during rolling, it is necessary to keep the shape of the roll gap uniform and symmetrical during the rolling process, as parallel as possible. Therefore, it is necessary to design the rolls in a certain shape in advance according to the elastic deformation of the rolls and other related conditions to ensure that the shape of the roll gap is uniform, symmetrical, and as parallel as possible during the rolling process. This roll shape is called roll shape, and the process of designing the roll shape is called roll shape design.
The rational determination or design of the original roll shape is based on the relatively stable rolling load, roll body temperature and roll body wear characteristics under normal production conditions. In essence, it plays the role of offsetting and compensating the mutual influence of various factors to ensure the minimum transverse thickness difference (section crown) of the steel plate.
The design basis of the original roll shape is:
In the formula, △D0——the original roll shape;
△Dh——thermal convexity, the convex roll type is positive, and the concave roll type is negative;
f——The sum of elastic deformation (deflection) of the upper and lower work rolls, f=f1s+f1x
Because the wear of the rolls is difficult to determine in advance, the original roll shape of the work rolls is only determined by the elastic deformation and thermal crown of the rolls, and the wear is compensated by means of roll changing and rolling specification adjustment.
The main steps of roll design are divided into four steps:
The first step is to find the roll shape value (camber or concavity) required to compensate for the uneven thickness of the steel plate caused by the roll deformation;
The second step is to select a reasonable roll form and assign the total crown value;
The third step is to design the roll profile reasonably;
The fourth step is to formulate a reasonable roll change system according to the wear condition of the rolls.
Principle of consideration
Generally, the following factors should be considered when designing the roll shape.
1. Steel straightening quality
The roll designer should not only try to make the steel meet the requirements of the national standard after the straightening machine, but also consider the elimination of defects. For example, during the continuous straightening process of steel, for some reason, the roll surface produces lumps or other defects, which affects the surface quality of the steel. When considering the roll design, it should create convenient conditions for eliminating roll surface defects.
2. Section of the finished product after rolling
The hot-rolled finished hole shape of some special-shaped steels is sometimes different from the standard shape, so it must be adapted to the straightening roll shape design. For example, channel steel has a straight rolling method and a steep-slope bending rolling method. When the former method is used for rolling, the fluctuation degree of the steel waist width tolerance should be considered in the roll design; when the latter rolling method is used, not only the waist width fluctuation but also the steel should be considered in the roll design. of shaping.
3. The opening of the straightener
The design of the straightening roll ring diameter and roll working diameter should be determined according to the pitch and opening of the straightening machine. In general, half of the sum of the diameters of the upper and lower work rolls plus the thickness of the steel to be leveled should be less than the pitch of the leveler and the opening of the leveler.
4. Axial movement of the leveler
For the straightening machine that has been used for a long time, the body and various parts are seriously worn, the straightening roller is not firmly fixed on the shaft, and the axial string momentum is large, the roller design must adapt to the above characteristics to make up for the adverse effects of equipment defects. , In particular, the design of the slope of the side walls of the channel steel and channel steel should be paid more attention.
5. Easy and safe operation
In order to ensure that the steel is in a stable state in the straightening roll, the roll shape designer should maximize the contact area between the roll shape and the steel. In addition, when determining the placement position of the roll shape, the shape of the steel, the deformation direction after cooling, and the safety and convenience of operation should also be considered.
6. Straightening output
For the leveler driven by the lower roller, when the diameters of the upper and lower rollers are inconsistent, the working diameter of the lower roller should be increased as much as possible to increase the speed of the straightening line. Increasing the diameter of the lower roller is one of the main measures to tap the potential of the leveler and increase the leveling output.
7. Roll fillet
The arc radius of the rolled fillet is generally the same as the arc radius of the steel section. Under the premise of not affecting the straightening quality, try to avoid the sharp corners of the roll shape, so as to avoid stress concentration when the roll is quenched, which will burn out or quench cracks.