On the understanding of out of roundness and out of roundness rate of abrasives

Release time:2021-02-04     Views

  The out of roundness and out of roundness rate of the grinding body do exist in the use of the grinding body (steel ball and steel section). The out of roundness of the grinding body reduces the grinding effect and reduces the output of the grinding machine. However, due to the lack of specific statistical data, the national standard GB / t17445-2009 and building materials industry JC / t533-2004 do not make specific provisions for the time being.


  The so-called out of roundness is that the grinding body changes from round to polyhedron in the process of use. According to the normal law, the large ball should be ground into small ball (or large section into small section), and the shape still remains spherical (or cylindrical). The reason of out of roundness is that the ball (segment) surface peels off or sinks one by one to form polyhedron, apple shape or irregular shape

  (1) In general, the production process of abrasives is the combination of gate and riser, and the gate is also the final solidification place, where the crystallization time is long, the grains are coarse, and the impurities gather, which is the weakest part of the structure or toughness of abrasives. Especially, the medium and low chromium balls without austenitizing heat treatment (transformation from pearlite to martensite or bainite) are more likely to sag and become brittle Apple shaped ball.

  (2) The reasons for the uneven surface hardness of the abrasives are the segregation of the chemical composition of the abrasives and the uneven heating or cooling of the heat treatment. The abrasives with high hardness wear slowly, while the abrasives with low hardness wear fast. Especially for the abrasives with poor hardenability, the hardness difference from the surface to the center is large (the hardness is uneven inside and outside). Due to the non-uniformity of wear, the force of the abrasive body itself in the process of work is bound to be uneven, so the abrasive body gradually forms polyhedron or irregular shape in the grinding process.

  (3) After heat treatment of high chromium steel ball and steel segment, there is still a lot of retained austenite in the matrix. Under repeated impact and temperature influence in the mill, the surface of the grinding body will work hardening with retained austenite, resulting in volume expansion and increase of internal stress. When the stress exceeds the yield strength of the matrix, massive spalling will occur. This phenomenon is more common in wind swept mill and coal mill It can also be out of round or deformed.

  (4) It is easy to cause out of roundness or deformation due to unreasonable use scheme of grinding body. For example, unreasonable grading specifications, too much or too little ball loading, too large or poor grindability of material particles, uneven material supply and other factors need to be used, so the manufacturer should strictly formulate reasonable grinding body use scheme and supplement scheme according to the use condition and grinding index.

  (5) According to the foreign regulations on grinding ball out of roundness, the ball out of roundness is more than 7% after 2000 hours of use. Out of roundness = (maximum diameter - minimum diameter) / average diameter × 100%. The percentage between the total amount of out of roundness and the total amount of grinding ball used is out of roundness rate.

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