The main reason is that the rolls with different characteristics can be selected reasonably from the difference of the hole type of each unit, the deformation characteristics of the rolling parts, and the accuracy requirements of the products.
The main properties of the rolls are marked with core strength and work layer wear resistance.
When selecting the roll, in addition to considering the economy and the change of the groove change cycle and the downtime, it is more important to select the different performance characteristics from the difference of the hole type of each unit, the deformation characteristics of the rolling stock, the product precision requirements, etc. Roller. The main task of the bar rolling mill roughing frame is to reduce the section at high temperature, which has large rolling force and low rolling speed. Roll performance is generally considered in terms of both the strength and thermal crack resistance of the rolls.
For general steel grades and normal rolling temperatures, centrifugally cast plain iron cast iron rolls can be used. The medium-rolling mill of the bar mill generally adopts an elliptical-round hole type system, which mainly undertakes the task of extending the rolling stock and providing accurate material type for the finishing mill. The rolling force is moderate and the hole type wears evenly. Therefore, the general centrifugal casting is generally used. Ductile iron roll or medium nickel-chromium spheroidal cast iron roll. In order to ensure the dimensional stability of the outlets of the unit, high-nickel-chromium alloy ductile iron rolls or high-speed steel composite rolls can also be used for the outlet frame. The bar finishing mill has many varieties of rolling, the shape of the hole is complex, the deformation distribution is uneven, the rolling speed is high, and the rolling force varies greatly. Therefore, the performance of the roll is mainly based on wear resistance and toughness, taking into account the resistance to hot cracking. Sex and intensity. For the extended hole type of the simple cross-section, a high-nickel-chromium alloy ball cast iron roll is generally used, and a high-speed steel composite roll can also be used.
For the production of round steel or ribbed steel bars, it is recommended to use high-speed steel composite rolls or tungsten carbide composite rolls with higher wear resistance. Since the round hole of the round steel is very small, the best wear-resistant tungsten carbide composite roll should be used, and the high-speed steel combination roll with high surface hardness can also be used. The finished hole of the ribbed steel bar is affected by the transverse ribs, and it is easy to generate hot cracks or micro cracks during use. When heavy trucks are used, all the transverse ribs must be removed, and the heavy trucks are large. Therefore, expensive tungsten carbide is selected. The economics of the combined rolls are greatly affected, and high-speed steel composite rolls are preferred. For the pre-cutting holes of the cut varieties, due to the serious uneven deformation in the use, the high-speed steel composite roll with good toughness and wear resistance of the working layer and moderate hardness should be selected. . Cutting the hole Because of the existence of the split wedge, it is required not only that the roll has good wear resistance and toughness, but also that it has reliable thermal crack resistance. The test proves that the current high-speed steel composite roll and tungsten carbide composite roll do not have such characteristics, and the use of the middle pole is prone to the phenomenon of split-wedge peeling, so only high-nickel-chromium alloy ball cast iron roll can be used.