Roller is the core component of rolling mill. The use of rolls involves the selection of the rolling mill, the preparation of the rolls, the maintenance and the regular trimming during the rolling process, which are all factors that affect the productivity, product quality and production economy of the rolling mill. Since the rolling process is a continuous process, the operator needs to constantly check the roll condition so that the product can meet the user's requirements for stricter tolerances and surface quality. In order to maintain the competitiveness of products, it is necessary to continuously require mill operators to reduce production costs, that is, to increase the rolling speed, increase the production flexibility of the mill, and reduce the consumption of rolls. So what should be paid attention to when surfacing roll?
(1) Before surfacing, it is necessary to remove the fatigue layer or defects on the surface of the roller body, especially cracks;
(2) During surfacing, in order to prevent cracks, the roller body needs to be preheated first, and the preheating temperature depends on the roller and surfacing material;
(3) In order to obtain an ideal surfacing layer, it is necessary to comprehensively consider some variable factors, such as welding voltage, welding speed, roll speed, roll insulation, welding current, welding materials, etc. For some high carbon and alloy elements of the roll core, in order to prevent the brittle zone cracks, in addition to certain preheating measures, but also often use low carbon and low alloy transition layer for pre-surfacing.
(4) Slow cooling turning after roller surfacing. In order to reduce the cracks caused by the volume stress caused by different cooling rates on the surface and inside, the cooling rate should be controlled. The overlay roll is then rotated to restore the original dimensions and smoothness.
And the performance of the roll after surfacing:
(1) The service life of the roll after surfacing is generally more than doubled;
(2) greatly reduce the cost per ton of steel and improve the production effect;
(3) The surfacing roller has good crack resistance, wear resistance and thermal fatigue resistance. The main links in the manufacturing process of cold roll are smelting, forging, heat treatment, processing and inspection.
Roller in the working process to bear a lot of rolling stress, rolling welding, inclusions, edge cracks and other problems easily lead to instantaneous high temperature, so that the work roll by a strong thermal shock, resulting in cracks, sticky roll, peeling and even scrap. Therefore, the roll should have the ability to resist cracking and spalling caused by bending stress, torsion stress and shear stress, and should also have high wear resistance, high contact fatigue strength, high fracture toughness and thermal shock strength. Therefore, how to improve the service life of the roll has been a major problem facing the roll manufacturing industry.
The nondestructive testing of rolls is usually carried out by ultrasonic flaw detector. In the cold roll flaw detection standard, the roll identity is usually classified as the surface area, the central area and the middle area according to the force situation, and then the critical size of the allowable defects in each area is specified according to the principle of fracture mechanics. Flaw detection workers should have the knowledge of roll manufacturing, in order to determine the nature of defects, should also have the knowledge of the use of rolls, in order to estimate whether these defects in the specific conditions of use will cause the use of damage.