The roll is a tool that causes the metal to produce plastic deformation. It is an important consuming part that determines the efficiency of the rolling mill and the quality of rolled products. The 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 the steel. It mainly bears the dynamic and static loads, wear and temperature changes during rolling.
We usually use two kinds of rolls, cold roll and hot roll.
There are many types 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 the roll must be quenched
2: The surface hardness must be hs45~105.
The materials produced by hot rolling rolls generally include 60CrMnMo, 55mn2, etc. This type of roll is used in a wide range of fields. It can be used in some processing such as section steel, bar steel, deformed steel, high-speed wire, seamless steel pipe, billet, etc. it bears strong rolling force, severe wear and thermal fatigue. Moreover, the hot roll works at high temperature and allows the diameter wear within the unit workload. Therefore, it does not require surface hardness, but only high strength, toughness and heat resistance. The hot rolling roll is only normalized or quenched as a whole, and the surface hardness shall be hb190~270.
Common failure forms and causes of rolls are as follows:
1. Cracks.
The roller cracks are mainly caused by excessive local pressure and rapid cooling and heating of the roller. On the rolling mill, if the emulsion nozzle is blocked, resulting in poor local cooling conditions of the roll, cracks will occur. Because of the low temperature in winter, cracks are more likely to occur than in summer.
2. Peeling.
If the crack continues to develop, it will form block or sheet peeling. Those with light peeling can continue to use after regrinding, and the rolls with serious peeling will be scrapped.
3. Draw a pit.
Pit marking is mainly because the weld joint of the strip steel or other sundries enter the rolling mill, so that the roll surface is marked with pits of different shapes. Generally, the rolls with pits must be replaced. In case of poor weld quality of strip steel, when the rolling operation passes the weld, it shall be lifted and pressed down to prevent pit scratching.
4. Stick the roll.
The reason for sticking the roll is that during the cold rolling process, broken fragments, wave folding and broken edges appear, and when the high pressure and instantaneous high temperature occur, it is very easy to form the bonding between the steel strip and the roll, resulting in small-area damage to the roll. Through grinding, the roller can be used again after the surface crack is eliminated, but its service life is obviously reduced, and it is easy to peel off in future use.
5. Roller.
The sliver roll is mainly caused by excessive reduction, resulting in double skin or slight folding of the strip steel and deviation of the strip steel. When roll stranding is serious, roll sticking occurs and the strip steel is cracked. When the roller is slightly bent, there are traces on the strip steel and the roller.
6. Roll break.
The main causes of roll fracture are overpressure (i.e. excessive rolling pressure), defects in the roll (non-metallic inclusions, bubbles, etc.) and the stress field caused by uneven roll temperature.
Post time: Jun-08-2022