The mill roll is a tool for plastically deforming (rolled material) metal and is an important consumable part that determines the efficiency of the rolling mill and the quality of the rolled material. The roll is an important part of the rolling mill in the rolling mill. It uses the pressure generated by a pair or a group of rolls to roll and roll the steel. It is mainly subjected to dynamic and static loads, wear, and temperature changes during rolling.
There are two types of rolls that we usually use, cold-rolled rolls and hot-rolled rolls.
There are many types of materials made of cold rolling rolls, such as 9Cr, 9Cr2, 9Crv, 8CrMoV, etc. This type of roll has two requirements which are
1: The surface of the roll must be quenched
2: The hardness of the surface must be HS45~105.
The materials made of hot rolling rolls generally include 60CrMnMo, 55Mn2, etc. 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-end wire, seamless steel pipe, billet, etc. It has withstood strong rolling force, and severe wear, and tear. Influenced by thermal fatigue, and 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 is only normalized or quenched as a whole, and the surface hardness is required to be HB190~270.
Common failure forms and causes of rolls are as follows:
Roll cracks are mainly caused by excessive local pressure of the roll and rapid cooling and 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.
2. Peel off the skin.
If the cracks continue to develop, they will form massive or flaky peelings. Those with light peelings can be used after regrinding, and rolls with severe peelings will be scrapped.
3. Draw a hole.
The pitting is mainly due to the welding seam of the strip or other sundries entering 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 weld seam of the strip steel is not good, it should be lifted and pressed down when the rolling operation reaches the weld seam to prevent pitting.
4. Sticky roller.
The reason for roll sticking is that during the cold rolling process, broken pieces, wave folds and broken edges appear, and due to high pressure and instantaneous high temperature, it is easy to form a bond between 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.
The rolling is mainly caused by excessive reduction, which causes the strip to produce heavy skin or slight folding and strip deviation to produce heavy skin. When the roll is severely tightened, roll sticking occurs and the strip is cracked. When the roll is slight, there will be stamps on the strip and the roll.
6. Broken roll.
The main reasons for roll breakage are overpressure (that is, excessive rolling pressure), internal defects of the roll (non-metallic inclusions, bubble.