Rollers are tools for the plastic deformation of metals (rolling materials), and are also important consumable parts that determine the efficiency of the rolling mill and the quality of the rolled material. Rollers are an important part of rolling mills, using the pressure generated by a pair or a group of rollers to roll and grind steel. They mainly withstand the effects of dynamic and static loads, wear, and temperature changes during rolling.
We commonly use two types of rollers: cold rolling rollers and hot rolling rollers.
Cold rolling rollers are made of many different materials, such as 9Cr, 9Cr2, 9Crv, 8CrMoV, etc. This type of roller has two requirements
1. The roller surface should be quenched.
2. The surface hardness should be HS45~105.
The material of hot rolling rollers is generally 60CrMnMo, 55Mn2, etc. This type of roller can be used in a wide range of fields. It can be used in the processing of shaped steel, bars, rebar, high-speed wire rod, seamless steel pipes, blooms, etc. It withstands strong rolling forces, severe wear, and thermal fatigue. In addition, hot rollers work at high temperatures, allowing for diameter wear within the unit workload, so surface hardness is not required, only high strength, toughness, and heat resistance are needed. Hot rolling only uses overall normalizing or quenching, and the surface hardness requirement is HB190~270 hardness.
Common failure modes and causes of rollers are as follows:
High-speed steel roller ring manufacturer: Cracks.
Cracks in rollers are mainly caused by excessive local pressure on the rollers and too rapid heating and cooling of the rollers. On the rolling mill, if the emulsion nozzle is blocked, resulting in poor local cooling conditions for the rollers, cracks will occur. Due to the lower winter temperatures, cracks are more likely to occur than in summer.
High-speed steel roller ring manufacturer: Scaling.
If the cracks continue to develop, they will form blocky or flaky spalling. Mild scaling can be re-ground and reused, while severe scaling should be scrapped.
High-speed steel roller ring manufacturer: Pitting.
Pitting marks are mainly caused by the entry of steel strip welds or other impurities into the rolling mill, marking the roller surface with pits of different shapes. Rollers with general scratches should be replaced. When the quality of the steel strip weld is poor, it should be lifted and pressed down when the weld passes through the rolling operation to prevent pitting.
High-speed steel roller ring manufacturer: Roll sticking.
The cause of roll sticking is the occurrence of broken pieces, broken waves, and broken edges during cold rolling, and due to the high pressure and instantaneous high temperature, it is easy to form adhesion between the steel strip and the roller, resulting in relatively small area damage to the roller. After grinding and eliminating surface cracks, the roller can continue to be used, but the service life is significantly reduced, and spalling accidents are prone to occur in later use.
High-speed steel roller ring manufacturer: Roll pinching.
Roll pinching is mainly caused by excessive reduction, resulting in uneven thickness or slight folding of the steel strip, and the steel strip running off center causing uneven thickness. When the roller is severely squeezed, it will stick to the roller, and the steel strip will crack. When the roller is slightly pinched, there will be marks on the steel strip and the roller.
High-speed steel roller ring manufacturer: Roller breakage.
The main causes of roller breakage are overpressure (i.e., excessive rolling pressure), internal defects in the roller (non-metallic inclusions, bubbles, etc.), and uneven roller temperature causing stress fields.