The crack of Sendzimir roll occurs at the transition from Sendzimir work roll body to upper roll neck, within 40 ~ 100mm from the upper end of Sendzimir work roll body. Most of the roll neck cracks are transverse cracks, including ring cracks and local cracks. If the crack is light, it can be found during processing. If the crack depth is less than the machining allowance, it can be removed during processing. If there are still cracks after processing, it shall be scrapped; If the crack is serious, a circle of ring cracks can be seen as cast, which will cause the roll neck to break in serious cases.
(1) Chemical composition. When producing rolls in a chemical furnace, the melting sequence is arranged from low to high according to the roll name (SI): cold hardening roll, ball core roll, ball compound roll, infinite cold hardening roll and nodular iron roll. In order to ensure that the outlet temperature of the first ladle of molten iron of 10t cupola is greater than 1400 ℃, the height of bottom coke is specified as 2.8m. Due to the high coke at the bottom of the cupola, the increment of W (c) and w (s) of the molten iron in the front several packages are relatively serious, resulting in the w (c) of the alloy chilled cast iron roll as high as 3.75% ~ 3.80%, w (s) as high as 0.115% ~ 0.120%, and sometimes even as high as 0.132%.
(2) Pouring temperature. When using cupola to produce rolls, the outlet temperature of the first and second ladle of molten iron in front is generally low. In addition, the temperature of the front furnace and molten iron ladle is low and the heat absorption is large, resulting in low pouring temperature of molten iron, poor fluidity of molten iron, early solidification of riser, crusting, damage to directional solidification and increase the tendency of cracks.
(3) The deeper the white layer of the roll, the greater the scrapping amount of Sendzimir roll crack. This is because the contraction of white mouth is larger than that of hemp mouth and gray mouth.
(4) The inner wall of the riser sand mold is uneven, which hinders the free downward contraction of the roll neck.
(5) The greater the ratio of the length of Sendzimir work roll body (L) to the diameter of Sendzimir work roll body (d), the higher the scrap rate of Sendzimir roll crack. as φ 355mm × L020mm roll, L / D = 2.87, the scrapping rate of Sendzimir roll crack is as high as 50%. The greater the ratio of L / D, that is, the longer the length of the Sendzimir work roll body, the greater the shrinkage in the length direction of the Sendzimir work roll body, and the higher the probability of tensile crack of the upper roll neck.
(6) The length of Sendzimir work roll body is more than 700mm, and the diameter of Sendzimir work roll body is less than φ For the 350mm slender roll with roll neck sand core, the sizing block is not removed after pouring, or the outer circle of the sand core is too large and fits too tightly with the cold mold, thus losing the function of reducing the shrinkage resistance of the roll neck sand core (which can move down after pouring).
(7) The crack of Sendzimir roller is related to the characteristics of pig iron. In the production process, it is often found that when a pig iron is replaced, the roll is prone to cracks (including longitudinal crack of Sendzimir work roll body, edge crack of upper and lower roll, neck crack, etc.), while after another pig iron is replaced, all kinds of cracks are reduced or disappeared. It may be due to the influence of heredity of cast iron structure, which increases the shrinkage of roll and is easy to cause cracks.
(8) When the tellurium content is too high, the crack tendency of Sendzimir roll increases. Adding tellurium to the cold hardening roll can increase the pure white mouth depth and shorten the length of the hemp mouth, which is conducive to improving the wear resistance of the roll and the surface quality of the steel. In order to obtain a relatively pure white layer, our factory adds 8 ~ 12g tellurium per ton of molten iron, which is higher than that of domestic peers, so the scrap rate of roll neck crack is also higher than that of domestic peers. Tellurium is a strong anti graphitization element. Due to the high amount of tellurium in molten iron, the amount of graphite precipitated during solidification is reduced and the tendency of crack generation is increased.
If you are interested in the Sendzimir Roll, please mail at marketing2@hanrm.com, or kerrirollingmill@gmail.com.
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