Common Problems of Roller

Roll is a tool to produce plastic deformation of metal. It is an important consuming part to determine the efficiency and quality of the rolling mill. Roll is an important part of the rolling mill in the rolling mill. The pressure produced by a pair or group of rolls is used to roll steel. It mainly bears the influence of dynamic and static load, wear and temperature change during rolling.

We usually use two kinds of roll, cold roll and hot roll.

There are many kinds of materials for cold rolling rolls, such as 9Cr, 9Cr2, 9crv, 8crmov, etc. There are two requirements for this type of roll：

1. The surface of roller must be hardened.
2. The surface hardness must be in hs45 ~ 105.

The materials produced by hot rolling roll are generally 60CrMnMo, 55mn2, etc. This type of roll is widely used in section steel, bar, rebar, high-speed wire, seamless steel pipe, bloom and other processing. It bears strong rolling force, severe wear and thermal fatigue. Moreover, the hot roll works at high temperature and allows the diameter wear within unit workload. Therefore, it does not require surface hardness, as long as it has a good surface hardness High strength, toughness and heat resistance. The surface hardness of hot rolling roll is hb190 ~ 270.

The common failure forms and causes of rolls are as follows:

1. Cracks

The roller cracks are mainly caused by the excessive local pressure and the rapid cooling and heating of the roller. On the rolling mill, if the emulsion nozzle is blocked, the local cooling condition of the roller is not good, and cracks will be produced. Because of the lower temperature in winter, it is easier to crack than in summer.

2. It’s peeling

If the crack continues to develop, it will form massive or flaky peeling. If the peeling is light, it can be used again after regrinding. If the peeling is serious, it will be scrapped.

3. Draw a hole

Pit marking is mainly due to the strip weld or other debris into the mill, so that the roll surface is marked out of different shapes of pits. Generally, the roll with the pit must be changed. When the weld quality of strip steel is not good, it should be lifted and pressed down when the rolling operation passes through the weld to prevent the scratch.

4. Stick roll

The reason of sticking roll is that in the process of cold rolling, broken pieces, wave folding and broken edge appear, and because of high pressure and instantaneous high temperature, it is easy to form steel strip and roll bonding, resulting in small area damage of roll. After grinding, the roller surface crack can be eliminated and can continue to be used, but its service life is significantly reduced, and it is prone to the spalling accident in future use.

5. Roller

The roller is mainly caused by heavy skin or slight folding of strip steel caused by excessive reduction and heavy skin caused by strip deviation. In case of serious roll sticking, the strip steel will be cracked. When the roller is slightly clamped, the strip steel and roller are clamped.

6. Broken roll

The main causes of roll fracture are overpressure (i.e. excessive rolling pressure), defects in roll (non-metallic inclusions, bubbles, etc.) and stress field caused by uneven roll temperature.