Roll classification, performance and fracture analysis
The roll is a rolling tool that plastically deforms the metal. It is one of the important parts of the rolling mill. The pressure generated when the rolls roll can be used to roll the steel. Dynamic and static loads during rolling, wear and temperature changes are the main factors affecting the rolls. Its consumption is determined by three factors, namely:
(1) Rolling mill, rolling stock and rolling conditions, and reasonable selection of rolls.
(2) Roll material and manufacturing quality.
(3) The use and maintenance system of the rolls.
1. Classification of rolls
There are many types of rolls. At present, there are three types of rolls commonly used: cast steel rolls, cast iron rolls and forged rolls. There is also a small amount of cemented carbide rolls on the profile mill.
2. Roll performance
(1) Strength, resistance to thermal cracking
Generally, the rough roll is mainly required for strength and thermal crack resistance. When selecting the rolls, the main material of the safe load is selected according to the basic strength requirements of the rolling mill.
(2) hardness, wear resistance
The finishing roll has a high speed and the final product has a certain surface quality. It is mainly required for hardness and wear resistance, and then considers the wear resistance that should be used when the rolls are used. Due to the complex wear mechanism of the rolls, including mechanical stress, thermal action during rolling, cooling, chemical action of the lubricating medium, and other effects. There is currently no uniform indicator for comprehensive evaluation of roll wear resistance. Since the hardness is easy to measure and can reflect the wear resistance under certain conditions, the radial hardness curve is generally used to approximate the wear resistance index of the roll.
(3) Finish
When rolling thin gauge products, the requirements for the rigidity, uniformity of the structure, processing accuracy and surface finish of the rolls are strict.
(4) Machining performance
When rolling a profiled section of a section, it is also necessary to consider the cutting performance of the working layer of the roll body.
3. Roll breakage
Residual stresses and thermal stresses are generated in the preparation process of the rolls prior to manufacture and use. It is further affected by various cyclic stresses, including bending, torsion, shear, contact stress and thermal stress. The distribution of these stresses along the roll body is uneven and constantly changing, not only because of design factors, but also by the wear, temperature and roll shape of the rolls during use. In addition, abnormal conditions often occur in rolling conditions. Rolls that are improperly cooled after use can also be damaged by thermal stress. Therefore, in addition to wear, the rolls often have various local damages and surface damage such as cracks, breaks, peeling, and indentation. A good roll should have a good match between strength, wear resistance and various other performance indicators. In this way, not only is it durable under normal rolling conditions, but it can also be less damaged in the event of some abnormal rolling. Therefore, in the manufacture of rolls, the metallurgical quality of the rolls should be strictly controlled or external measures should be taken to enhance the load carrying capacity of the rolls. Reasonable roll shape, hole shape, deformation system and rolling conditions can also reduce roll work load, avoid local peak stress and prolong roll life.
During the use of the roll, due to the close contact with the rolled material, the surface temperature of the roll rises rapidly, and the temperature of the roll core rises slowly. At this time, the temperature difference between the roll surface and the core of the roll is at a large value, and the thermal stress of the roll caused by the temperature difference is also at a large value. If the thermal stress of the rolls is superimposed on the residual stress of the rolls and exceeds the strength limit of the core of the rolls, an accident of roll breakage may occur.
Prevention of fracture should be carried out in terms of reducing manufacturing residual stress, mechanical stress, tissue stress and thermal stress. Under normal circumstances, most of the manufacturing residual stress will be eliminated during the heat treatment process, and will be gradually eliminated as the roll storage time is extended. Therefore, the new roll is stored for a period of time and can be used to reduce the risk of breakage. The main method of avoiding large mechanical stress is to avoid overcooled steel. The method of reducing the tissue stress is to control the residual austenite content of the working layer of the roll body to less than 5% by heat treatment. The way to reduce the thermal stress is to cool the rolls well during the rolling process.
(1) Rolling mill, rolling stock and rolling conditions, and reasonable selection of rolls.
(2) Roll material and manufacturing quality.
(3) The use and maintenance system of the rolls.
1. Classification of rolls
There are many types of rolls. At present, there are three types of rolls commonly used: cast steel rolls, cast iron rolls and forged rolls. There is also a small amount of cemented carbide rolls on the profile mill.
2. Roll performance
(1) Strength, resistance to thermal cracking
Generally, the rough roll is mainly required for strength and thermal crack resistance. When selecting the rolls, the main material of the safe load is selected according to the basic strength requirements of the rolling mill.
(2) hardness, wear resistance
The finishing roll has a high speed and the final product has a certain surface quality. It is mainly required for hardness and wear resistance, and then considers the wear resistance that should be used when the rolls are used. Due to the complex wear mechanism of the rolls, including mechanical stress, thermal action during rolling, cooling, chemical action of the lubricating medium, and other effects. There is currently no uniform indicator for comprehensive evaluation of roll wear resistance. Since the hardness is easy to measure and can reflect the wear resistance under certain conditions, the radial hardness curve is generally used to approximate the wear resistance index of the roll.
(3) Finish
When rolling thin gauge products, the requirements for the rigidity, uniformity of the structure, processing accuracy and surface finish of the rolls are strict.
(4) Machining performance
When rolling a profiled section of a section, it is also necessary to consider the cutting performance of the working layer of the roll body.
3. Roll breakage
Residual stresses and thermal stresses are generated in the preparation process of the rolls prior to manufacture and use. It is further affected by various cyclic stresses, including bending, torsion, shear, contact stress and thermal stress. The distribution of these stresses along the roll body is uneven and constantly changing, not only because of design factors, but also by the wear, temperature and roll shape of the rolls during use. In addition, abnormal conditions often occur in rolling conditions. Rolls that are improperly cooled after use can also be damaged by thermal stress. Therefore, in addition to wear, the rolls often have various local damages and surface damage such as cracks, breaks, peeling, and indentation. A good roll should have a good match between strength, wear resistance and various other performance indicators. In this way, not only is it durable under normal rolling conditions, but it can also be less damaged in the event of some abnormal rolling. Therefore, in the manufacture of rolls, the metallurgical quality of the rolls should be strictly controlled or external measures should be taken to enhance the load carrying capacity of the rolls. Reasonable roll shape, hole shape, deformation system and rolling conditions can also reduce roll work load, avoid local peak stress and prolong roll life.
During the use of the roll, due to the close contact with the rolled material, the surface temperature of the roll rises rapidly, and the temperature of the roll core rises slowly. At this time, the temperature difference between the roll surface and the core of the roll is at a large value, and the thermal stress of the roll caused by the temperature difference is also at a large value. If the thermal stress of the rolls is superimposed on the residual stress of the rolls and exceeds the strength limit of the core of the rolls, an accident of roll breakage may occur.
Prevention of fracture should be carried out in terms of reducing manufacturing residual stress, mechanical stress, tissue stress and thermal stress. Under normal circumstances, most of the manufacturing residual stress will be eliminated during the heat treatment process, and will be gradually eliminated as the roll storage time is extended. Therefore, the new roll is stored for a period of time and can be used to reduce the risk of breakage. The main method of avoiding large mechanical stress is to avoid overcooled steel. The method of reducing the tissue stress is to control the residual austenite content of the working layer of the roll body to less than 5% by heat treatment. The way to reduce the thermal stress is to cool the rolls well during the rolling process.
