Description: The characteristics and advantages of high-speed steel rolls are introduced. It also introduces the application prospects and benefits of high-speed steel rolls by summarizing the use conditions, accident handling and use effects of the fully continuous bar production line in the third rolling operation area of the steel plant during the use of high-speed steel rolls.
Keyword: High-speed steel rolls; high-nickel-chromium cast iron rolls; bars
Introduction of high speed steel rolls
High-speed steel rolls contain a large amount of alloying elements such as W, Mo, Cr, V, and Co. Higher c and V components can obtain high-hardness MC-type carbides, which can improve the wear resistance of the roll; a higher mass fraction of Cr can make the roll contain a certain amount of Mc-type carbides, which can improve the roughness resistance of the roll surface , reduce the rolling force; Co can improve the pure hardness of high-speed steel rolls, so that high-speed steel rolls can be used in hot rolling mills. The hardness, thermal crack resistance, and thermal shock resistance of high-speed steel rolls are superior to high-nickel-chromium cast iron rolls, and their wear resistance is 4-5 times that of high-nickel-chromium cast iron rolls. Therefore, high-speed steel rolls are used in hot rolling production. The promotion in China is very fast, but how to make good use of high-speed steel rolls is still a major issue in the steel industry.
Use of high speed steel rolls
Cooling of high speed steel rolls
The thermal expansion of high-speed steel rolls is large, and the poor temperature distribution of the rolls is likely to cause uneven thermal expansion and abnormal shedding of the oxide film, which affects the thermal crown and roll gap accuracy of the rolls. The key factor affecting the oxide film and thermal crown of high-speed steel rolls is the roll surface temperature. Therefore, the ideal roll cooling method and shortening the time that the roll surface is in a high temperature state are important means to control the thickness of the oxide film on the roll surface, control the thermal crown, and reduce thermal cracks. The instantaneous contact temperature of the roll during hot rolling is 600-750°C. After the roll surface comes out of the contact arc, the temperature must be lowered from 700°C to below 300°C as soon as possible to prevent further oxidation. After the roll passes through the instantaneous high-temperature contact area, it works quickly in a 100% water-cooled environment, which is conducive to the formation of an oxide film with the best protective performance. By optimizing the cooling water distribution of the roll, such as increasing the cooling water volume at the outlet side, increasing the cooling water volume in the middle of the roll, and reducing the height of the cooling water pipe, the temperature of the roll surface can be significantly reduced. Use flat nozzles instead of conical nozzles, and use 3/4 cooling water to cool the roll outlet side, and control the roll surface temperature below 50~C. The cooling system is a series of nozzles in the form of a ring, which can ensure a continuous and sufficient water jet to the rolling groove. Near the outlet guide should be the main nozzle, the water sprayed from this nozzle is 30% of the total water on the entire rolling groove, and the spray angle is 2°. ~30. , the role of this nozzle is to ensure that the cooling water is quickly sprayed to the part of the rolling groove that has just left the rolled piece. The water pressure is controlled at (4-6)X10Pa, the water volume of each tank is at least 500L/min, the water flow cannot be scattered, the cooling water needs to be precipitated, and the content of solid particles should be reduced as much as possible to avoid damage to the roll.
Maintenance and maintenance of high-speed steel rolls
Due to the high brittleness and poor accident resistance of high-speed steel rolls, management must be strengthened to ensure stable operation of the rolling mill and reduce stacking of steel and burning of bearings. When the high-speed steel rolls used in production appear to jam or stack steel on the rolling groove, the water should be stopped immediately, and the upper roll should be lifted quickly to make the rolling material leave the roll surface and at the same time remove the rolling material accumulated on the lower roll immediately. Allow the heated rolling groove to cool naturally in the air. When reproducing after the accident is handled, the groove must be changed, and the groove must be separated by 2 to 3 grooves. The cooling water is absolutely not allowed to rush or flow to the heated rolling groove. If it is really impossible If it is not possible to change the groove, you must change the roll, and then reinstall the machine after it cools down naturally, otherwise, the cooling water will be poured directly on the overheated rolling groove, and cracks will appear in the rolling groove. The surface of the groove hole of the high-speed steel roll will form an oxide film during the rolling process. The oxide film is orange or light blue at the beginning, and it will become dark blue or purple black when it continues to be used. When the oxide film thickens to a certain extent or there is a When scratched, the oxide film is easy to fall off, and meteor spots are formed on the surface of the groove. In severe cases, the surface of the roller is roughened and even pitted. During the use of the rolling groove, thermal cracks on the surface of the roll due to thermal fatigue are unavoidable, but if the thermal cracks appear and continue to be used, or the cracks are not thoroughly ground during grinding, the cracks will continue to expand during further use. Meat appears. Therefore, the key to the quality of high-speed steel rolls is the use conditions of the rolls and the maintenance of the rolls.
Application effect of high-speed steel rolls
The use of high-speed steel rolls makes up for many defects such as high-nickel-chromium cast iron rolls are not wear-resistant, frequent roll and groove changes, easy to drop meat, rough surface quality of rolled materials, and poor dimensional accuracy, which is conducive to giving full play to the production capacity of the equipment. It is conducive to the smooth flow of production, reduces the labor intensity of rolling line operators, and has remarkable economic benefits.
Improve production stability and technical indicators
When high-nickel-chromium cast iron rolls are used, the rolling groove is replaced once per shift in the K2 pass, and the rolling groove is replaced 3 or 4 times per shift in the K1 pass. The wear of the rolling groove is large, which restricts the increase in production capacity to a certain extent. After using high-steel rolls, the single-groove rolling capacity is 3 to 4 times that of high-nickel-chromium cast iron rolls. The rolling groove is replaced once in 3 or 4 shifts of K2 pass, and the rolling groove is replaced once per shift in K1 pass. The rolling groove is worn The amount is very small, which reduces the time taken for changing slots and rolls, and improves the operating rate of the rolling mill and the stability of production. The biggest advantage of using high-speed steel rolls in the key pass of finishing rolling is that the material shape of the key pass of finishing rolling remains stable for a long time. In the normal production process, the number of adjustments is reduced and the height of the material shape is stable for a long time. The most direct advantage lies in the stable size of the finished product and the small fluctuation of the negative difference. At the same time, due to its good wear resistance and high steel passing capacity, it can effectively guarantee the multi-wire shape size of two-cut and three-cut, which is significantly helpful for stabilizing the size of finished steel products and improving the sizing rate and yield rate indicators. Compared with ordinary rolls, it can increase the finished product rate by 0.1%, and the cut-to-length rate can be increased by 0.1% to 0.4%, and can reduce the number of rolling waste products by about 50%.
Reduced roll consumption
After use, it has been shown that the amount of steel passing through a single groove of the high-speed steel roll is increased, the amount of heavy-duty grinding is reduced, the number of times the roll is used is increased, the finished product size is stable, and the surface quality is improved. Taking on-site rolled rebar as an example, the amount of single-groove passing steel for pre-cutting and finished product sorties is increased by at least 3 times, and the amount of single-groove grinding is reduced by 1/3.
Through a period of use, it has been shown that high-speed steel rolls have better cost performance in the production of bar splitting and rolling, which can greatly shorten the time for changing rolls and grooves, and effectively improve the operating rate. At the same time, its high wear resistance, It is conducive to the stable and high production of production, and the product quality is better guaranteed.