Common Problems with Rolling Mill Rolls

Rolling mill rolls are the tool that plastically deforms the (rolled material) metal and are the important consumable part that determines the efficiency of the rolling mill and the quality of the rolled material. The roller is an important part of the steel rolling mill. It uses the pressure generated by a pair or a group of rollers to roll the steel. It mainly bears the influence of dynamic and static loads, wears and temperature changes during rolling.

There are two types of rolls that we usually use, one is cold rolling mill rolls and the other is hot rolling mill rolls.

There are many types of materials produced by cold rolling mill 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 within HS45 ~ 105.

The materials produced by hot rolling mill rolls are generally 60CrMnMo, 55Mn2, etc. This type of roll is used in a wide range of fields, and can be used in some processes such as section steel, bar, rebar, high-speed wire, seamless steel pipe, billet, etc. It withstands strong rolling forces, severe wear and thermal fatigue, and the hot roller works at a high temperature, and allows the diameter wear per unit of workload, so no surface hardness is required, only high strength, toughness and heat resistance are required. The hot rolling mill roll only adopts the whole normalizing or quenching, and the surface hardness requires to be HB190 ~ 270.

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

1. Cracks

The occurrence of roll cracks is mainly caused by the excessive local pressure of the rolling mill rolls and the rapid cooling and heat of the roll. On the rolling mill, if the emulsion nozzle is clogged, resulting in poor local cooling conditions of the roll, cracks will occur. Because the temperature is lower in winter, it is more prone to appear cracks than in summer.

2. Peel

When the crack continues to develop, it will form a lump or flake peeling. Those with light peeling can be regrinded and continue to use it. Rolls with serious peeling will be scrapped.

3. Scratching

The pitting is mainly due to the welding seam of the steel strip or other debris entering the rolling mill, so that the roll surface is marked with pits of different shapes. Generally, the pitted rolling mill rolls must be changed. When the quality of the steel strip weld is not good, the rolling operation should be lifted and pressed when the weld is over to prevent pitting.

4. Sticky roller

The reason for sticky rolls is that during the cold rolling process, broken fragments, wave folds and broken edges appear, and due to the instantaneous high temperature for high pressure, it is easy to form a bond between the steel strip and the roll, resulting in a small area of damage to the rolling mill rolls. Through the grinding, the roller surface cracks can be continued to use, but its service life is significantly reduced, and it is prone to peeling accidents in the future.

        5. Broken roller

The main reasons for the roll breakage are overpressure (excessive rolling pressure), defects inside the roll (non-metallic inclusions, bubbles, etc.) and stress fields due to uneven roll temperature.