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Improvement of centrifugal roll

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Improvement of centrifugal roll

  • Time of issue:2022-10-08 13:46

Improvement of centrifugal roll

  • Time of issue:2022-10-08 13:46
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      In view of the performance of high-speed centrifugal rolls , some powerful roll companies have begun to develop high-speed steel materials suitable for rough rolling mills and finishing mills. These two centrifugal rolls are different from the high-speed steel in the finishing part, and their performance design directions are as follows:

  (1) The rolling pressure of the roughing mill is high, and the rolling temperature is the greater the bite angle of the rolls, the greater the extrusion force and friction on the surface of the centrifugal roll . Therefore, in consideration of wear resistance, the roll is required to have not only high strength and toughness but also high resistance to thermal cracking and crack growth. Combined with the characteristics of rough rolling stand tool steel and high chromium steel, the rough rolling stand high speed steel has the characteristics of low carbon, high chromium, high molybdenum, high vanadium and low nickel, forming intermittent network carbides.  

  (2) Compared with finish rolling and rough rolling, the slab temperature of the stand after finish rolling is lower, the steel passing speed is faster, and the impact of the steel plate on the roll surface is greater. Abrasive wear is the main form of wear. Rolls with poor wear resistance will affect the shape control of the strip section and have higher requirements for the flatness of the roll surface. Therefore, centrifugal rolls are required to have high wear resistance and smoothness. For a long time, high-nickel-chromium infinitely chilled cast iron has been used for rolls in the later stages of finishing rolling. This cast iron contains fine graphite, which has a certain self-lubricating effect during the rolling process and has a good roll surface finish. However, with the development of the iron and steel industry, the steel is developing in the direction of ultra-thin, and the use conditions of the rolls are getting worse and worse. Defects such as high brittleness and fast crack growth of high-nickel-chromium infinitely quenched materials gradually emerged, and the wear resistance gradually failed to keep up with the development requirements.

  The composition design of the finished high-speed steel roll in the later period is characterized by high carbon, high molybdenum, high chromium, high vanadium, and low tungsten, and a certain amount of niobium alloy is added to refine the structure, thereby forming high carbide content, eutectic structure dispersion and fine particles And other microstructure characteristics, so as to realize the excellent performance of the roll, such as high wear resistance, high surface finish and good accident resistance. 

  (1) Material composite process: The centrifugal roll adopts vertical centrifugal casting, which is divided into two layers of materials (high-speed steel outer layer and core ductile iron) for multiple castings.

  (2) Pouring process: After the outer layer is poured, the inner surface is evenly covered with molten glass slag (liquid) to protect the surface from being oxidized at high temperatures. After the middle layer is solidified layer by layer through the external cooling mold, the appropriate pouring time and pouring temperature are selected according to the cavity temperature parameters. The warmer middle layer remelts part of the outer layer to fuse the inner and outer layers together. After the intermediate layer is poured for about 5 minutes, the molten iron core is poured to complete the entire pouring process.  

  (3) After pouring is completed, the entire cold mold is hoisted into the heat preservation pit, and the box is opened after more than 7 days of heat preservation, and then subsequent rough grinding, heat treatment, and processing of the green body are carried out.

 

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