Rolls are tools for plastically deforming (rolled) metals, and are important consumable parts that determine the efficiency of rolling mills and the quality of rolling materials. Roller is an important part on the rolling mill of the rolling mill, which uses the pressure generated when a pair or group of rolls roll to roll the steel. It mainly bears the effects of dynamic and static loads, wear and temperature changes during rolling.
There are two types of rolls that we use at ordinary times, cold rolls and hot rolls.
There are many types of materials made of cold-rolled 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 hardness of its surface must be HS45~105.
The materials made by hot rolling rolls are generally 60CrMnMo, 55Mn2 and so on. This type of roll is used in a wide range of fields, and can be used in some processing such as section steel, bar, rebar, high wire, seamless steel pipe, billet, etc. It withstands strong rolling force, severe wear and tear. Thermal fatigue is affected, and the hot rolls work at high temperatures and allow diameter wear within a unit workload, so surface hardness is not required, only high strength, toughness and heat resistance are required. The hot roll only adopts overall normalizing or quenching, and the surface hardness requires HB190~270 hardness.
The common failure modes and causes of rolls are as follows:
The occurrence of roll cracks is mainly caused by the excessive local pressure of the roll and the rapid cooling and rapid heating of the roll. On the rolling mill, if the emulsion nozzle is blocked, resulting in poor local cooling conditions of the roll, cracks will occur. Due to the lower temperature in winter, cracks are more likely to occur than in summer.
If the crack continues to develop, it will form block or flake peeling. Those with light peeling can be reground and continue to be used. Rollers with serious peeling will be scrapped.
3, draw a pit.
The pitting is mainly due to the fact that the welding seam of the strip or other debris enters the rolling mill, so that the roll surface is marked with pits of different shapes. Generally, rolls with scratches must be replaced. When the quality of the strip weld is not good, it should be lifted and pressed down when the rolling operation reaches the weld to prevent scratches.
4. Sticky roller.
The reason for the sticking of the roll is that in the process of cold rolling, broken pieces, wave folds and broken edges appear, and due to the instantaneous high temperature due to high pressure, it is easy to form the bonding of the steel strip and the roll, resulting in small area damage to the roll. Through grinding, the roll can continue to be used after the surface cracks are eliminated, but its service life is significantly reduced, and peeling accidents are prone to occur in future use.
5, Le roller.
The roller is mainly caused by the excessive reduction of the strip, which causes the heavy skin or the slight folding and the deviation of the strip to produce the heavy skin. When the roller is seriously injured, sticky rollers will occur, and the strip will be cracked. When the roll is light, there are stamps on the strip and the roll.
6. Broken roll.
The reasons for the breakage of the rolls are mainly due to overpressure (that is, excessive rolling pressure), defects in the rolls (non-metallic inclusions, air bubbles, etc.) and uneven temperature of the rolls to generate stress fields.