Frequently asked questions.

Frequently asked questions.

Why does the hot roll shaft wear?

The working conditions of the rolls in the rolling mill components are relatively complicated, and they are mainly affected by dynamic and static loads, wear and temperature changes during rolling. Residual stress and thermal stress are generated in the preparation process of hot rolls before manufacturing and use. In use, it is further subjected to various periodic stresses, including bending, torsion, shear, contact stress and thermal stress. The distribution of these stresses along the roll body is uneven and constantly changing. The reasons are not only design factors, but also the continuous changes of roll wear, temperature and roll shape during use. In addition, the rolling conditions are often abnormal. Improper cooling of the roll after use will also be damaged by thermal stress. Therefore, in addition to abrasion of the roll, various local damages and surface damages such as cracks, fractures, peeling, and indentations often occur.

Therefore, how to solve the wear problem, we must first understand the reason. During hot rolling, the temperature of the hot roll contacting the material itself can reach 1200°C. At the same time, the plastic deformation heat of the rolling piece and the contact surface of the roll and the rolling piece make the temperature of the roll rise, and the bearing The lubrication performance decreases linearly at high temperatures, and it can also cause defects in the size, shape, material and mechanical properties of the roll. Although a large amount of coolant is sprayed on the rolls to cool during the rolling process, the rolling process is in the cycle of periodic heating and cooling curve changes. The roll surface, roll bearing position and various configurations of the rolling mill are all due to periodic heating. The impact of contact stress, performance yields, and therefore wear.

Secondly, the rolling piece and the roll are in instantaneous contact, and the relative speed formed by the sliding speed inertia is large, and the bearing position of the roll is completely different from the bearing capacity when the bearing is working at the three positions of the roll entrance, neutral point and exit. At the same time, the friction force during the traveling process of the rolling piece has obvious negative damping characteristics, which leads to the generation of self-excited vibration of the roll. It is the shaft and the bearing that produce fretting wear under such small amplitude relative vibration, which will increase with the number of rolling. And time delays and intensifies.

In addition, rolling mills now generally use emulsion as a process lubricant. Under the chemical action of the emulsion, the wear process of the metal material of the roll is intensified, especially the permeable corrosion of the metal under the action of high temperature.

How to choose a process to deal with the wear of the roll shaft:

Many hot-rolling roll shaft wear repair processes still use power transfer technology, which may be repaired, but the steps are complicated and not conducive to the subsequent use of the equipment itself, and damage will still occur during production.

Therefore, Sole Carbon Nano polymer materials just make up for this shortcoming, such as the commonly used machining repair technology:

  • Surface baking oil: Use oxygen acetylene to bake the oil on the bearing surface until there are no sparks and the surface is dry;
  • Place the shaft on the machine tool and fix it. While keeping the speed low, roughen the surface of the bearing position. The rougher the surface, the better. If necessary, thread the surface of the bearing position;
  • Calculate the amount of material according to the amount of unilateral wear of the bearing position, and adjust the Sole carbon nano-polymer repair material according to the proportion, and the harmony is uniform, without color difference, and the adjusted material is first applied to the surface of the bearing position thinly;
  • Material solidification: Adjust the machine speed to the lowest to ensure that the shaft solidifies in the rotating state. When curing the material, it is recommended to use an iodine tungsten lamp to heat, the heating temperature should be about 50℃, and the curing time should be 3 hours;
  • After the material is cured for 3 hours under heating, it meets the machining conditions and is finished to the required size;
  • After the machining and repairing is completed, hot-install the bearing.

Steel ingots or billets are difficult to deform and process at room temperature. They are generally heated to 1100 to 1250°C for rolling. This rolling process is called hot rolling. The termination temperature of hot rolling is generally 800 to 900°C, and then it is generally cooled in air, so the hot rolling state is equivalent to normalizing treatment. Most steels are rolled by hot rolling.

The steel delivered in the hot-rolled state has a certain degree of corrosion resistance due to the high temperature, so it can be stored in the open air. However, this layer of oxide scale also makes the hot-rolled steel surface rough and the size fluctuates greatly. Therefore, it is required to use hot-rolled semi-finished products or finished products as raw materials and then cold-rolled production of steels with smooth surface, accurate size and good mechanical properties.