Optimization of shearing process of channel steel
The 400mm unit in the steel plant is a profile unit mainly producing medium-sized angle steel and channel steel, with an annual output of 650000 tons, of which the product specification of channel steel is 638 ~ 1208, accounting for about 25% of the total output. The sectional operation of finished channel steel is carried out by one 400t cold shear. The shear quality of channel steel has a great impact on the subsequent process, especially the welding quality. If there are shoulder collapse, burr, tear, skew and other defects at the shear fracture, there will be a large gap in the butt joint of channel steel, which will affect the welding quality, especially the strength index, resulting in a large potential safety hazard.
With the improvement of production rhythm and output, the above shear defects are becoming more and more prominent, and the standard rate of internal control of shear quality is only 94.2%. Moreover, the service life of the cutting edge is getting shorter and shorter, and it is replaced once per shift, resulting in an increase in production cost and labor intensity of employees. In view of these problems, the process, technology and operation are carefully analyzed, and the corresponding improvement measures are put forward, which has achieved good results.
1. Process reasons
The design capacity of the unit is 200000 t / A, but the output has reached 600000 T / A. the problem of insufficient production capacity in the cooling bed area is very prominent. Compared with the production of angle steel, the cooling speed of channel steel is slow, resulting in higher channel steel temperature during shearing, prone to shoulder collapse, burr, tear and other defects, and has a great impact on the service life of the shear blade.
2. Reasons for shear blade design
The basic basis for the design of channel steel cutting edge is the finished pass shape of channel steel, as shown in Figure 1 (taking 100# channel steel as an example). This design is prone to the following problems in the shear process: first, compared with other parts, the two shoulders of the channel steel are relatively thick, the required shear force is also large, and the wear of the shear blade is fast. After the shear blade is used for a period of time. The relative wear of this part is large, resulting in large shoulder clearance and easy shoulder collapse; Second, compared with the waist, due to the influence of the shear angle, when the shear blade is worn, when cutting the two legs, the shear amount becomes smaller, the shear of the legs changes from normal cutting to tearing, and the end face of the channel leg is very prone to burrs; Third, the inclination of the legs of the upper and lower shear edges is basically the same as that of the finished channel steel. In this way, the legs are basically stressed at the same time during shear, the shear force is large, and the shear edge is worn quickly. On the one hand, the shear indentation at the leg end is serious, on the other hand, after the shear edge is aged, it is very easy to tear and Burr the shear part of the channel steel. The latter two points are the main reasons affecting the shear quality of channel steel.
In view of the above three problems, corresponding measures are taken respectively.
1. In view of the slow cooling speed of the cooling bed, a water mist fan is added in the cooling bed area to improve the cooling speed of the cooling bed area, and a group of water mist nozzles are added at one ruler in front of the shear to reduce the temperature of the shear part of the channel steel, so as to avoid the shear defects caused by the high steel temperature.
2. In view of the problems existing in the design of channel steel cutting edge, combined with the actual production situation, the cutting edge is designed as the shape shown in Figure 2 (taking 100# channel steel as an example). The width of the upper shear edge is changed from 100mm to 99mm to reduce the gap between the upper shear edge in the left and right directions and improve the shear quality of the two corners of the channel steel; The circular arc size of the two corners of the lower shear edge is changed from r8mm to r7mm to improve the shear overlap of the two corners and the shear quality of the shoulder of the channel steel; The upper width of the lower shear edge is changed from 79mm to 80mm, and the lower width is changed from 97mm to 94mm, so that the slope of the leg end of the lower shear edge is less than the slope of the finished channel steel pass. In this way, when the leg is cut, the upper and lower directions of the leg will not be stressed at the same time, so as to reduce the shear force and improve the shear quality.
3. Through the data regression analysis of the actual shear quality and shear clearance of each specification of channel steel, the shear clearance specification of each specification is formulated, specifically: 63# channel steel is 0.20 ~ 0.30mm, 80# channel steel is 0.20 ~ 0.35mm, 100# channel steel is 0.25 ~ 0.35mm, 120# channel steel is 0.25 ~ 0.40mm, and different gaskets with thickness of 0.20 ~ 1.00mm are made. When replacing the cutting edge each time, measure the clearance first, and then select the corresponding gasket to ensure that the shear clearance is controlled within the range of process requirements.