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Roll FAQ

2020-02-20

Roller is a tool that plastically deforms (rolled material) metal. It is an important consumable part that determines the efficiency of rolling mill and the quality of rolled material. Rolls are important parts on rolling mills in rolling mills. They use the pressure generated by a pair or set of rollers to roll steel. It mainly withstands the effects of dynamic and static loads, wear and temperature changes during rolling.


There are two kinds of rolls we usually use, cold rolls and hot rolls.


There are many types of materials for cold rolling rolls such as 9Cr, 9Cr2, 9Crv, 8CrMoV and so on. Two requirements for this type of roll are


1: The surface of the roll must be quenched


2: The hardness of the surface must be HS45 ~ 105.


Materials produced by hot rolling rolls are generally 60CrMnMo, 55Mn2, and the like. This type of roll is used in a wide range of fields. It can be used in some processing such as section steel, bar, rebar, high wire, seamless steel pipe, and blanking. It has withstanding strong rolling force, severe wear and The effect of thermal fatigue, and hot rolls work at high temperatures, and allow diameter wear within unit workload, so surface hardness is not required, only higher 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 forms and causes of rolls are as follows:


1. Cracks.


The occurrence of roll cracks is mainly caused by excessive local pressure of rolls and rapid cooling and heating of rolls. On the rolling mill, if the emulsion nozzle is blocked, which causes the local cooling conditions of the roll to be poor, cracks will occur. Because of the lower temperature in winter, cracks are more likely to occur than in summer.


2. Peel off.


If the crack continues to develop, it will form block or sheet peeling. Those who peel lightly can re-grind and continue to use it. Rollers with severe peeling are scrapped.


3. Pit.


The pitting is mainly because the weld seam of the strip or other debris enters the rolling mill, so that the roller surface of the roll is marked with pits of different shapes. Generally pitted rolls must be changed. When the quality of the strip welding seam is not good, the rolling operation should be lifted down to prevent pitting.


4. Sticky roller.


The reason for sticking rolls is that in the cold rolling process, broken fragments, wave folds and broken edges appear, and due to the instantaneous high temperature when high pressure occurs, it is easy to form a steel strip and roll bonding, resulting in small area damage to the roll. After grinding, the surface crack of the roll can be used continuously, but its service life is obviously reduced, and it is prone to peeling accidents in future use.


5. Le roller.


Le rollers are mainly caused by the excessive reduction of the strip, which causes heavy stripping or slight folding of the strip, and heavy stripping due to strip deviation. When the roll is severe, sticky rolls are generated and the strip is cracked. When the pinch roller is light, there are pinch marks on the strip and roll.


6. Broken roller.


The causes of roll breakage are mainly over-pressure (that is, too high rolling pressure), internal defects in the roll (non-metallic inclusions, bubbles, etc.), and uneven stress fields caused by the roll temperature.