Rolling Mill Category, Development, Selection And Maintenance
Apr 11, 2023
Variety classification of rolling mill:
Rolling mills can be classified according to the arrangement and number of rolls, as well as the arrangement of stands.
Two hi rolling mill.
Simple structure and wide range of applications. It is divided into reversible and irreversible forms. The former includes blooming mills, rail and beam mills, medium and heavy plate mills, etc. Irreversible types include billet continuous rolling mills, stacked thin plate rolling mills, thin plate or strip cold rolling mills, temper mills, etc. In the early 1980s, the largest two high rolling mill had a roll diameter of 1500 millimeters, a roll body length of 3500 millimeters, and a rolling speed of 3-7 meters per second.
Three high rolling mill.
The rolled piece is alternately rolled from the top and bottom roll gaps to the left or right, and is generally used as a section steel rolling mill and a rail beam rolling mill. This type of rolling mill has been replaced by an efficient two high rolling mill.
Lauter type three roller.
The upper and lower rollers drive, the middle roller floats, and the rolled piece passes alternately from above or below the middle roller. Due to the small diameter of the middle roller, the rolling force can be reduced. Commonly used for rolling rail beams, section steels, medium and thick plates, and also for opening small steel ingots. This type of rolling mill is gradually being replaced by a four high rolling mill.
Four-hi rolling mill.
The diameter of the work roll is small, transmitting rolling torque, and the rolling pressure is borne by the larger diameter support roll. The advantages of this type of rolling mill are high relative stiffness, large reduction, low rolling force, and the ability to roll thinner plates. There are two types: reversible and continuous rolling, widely used in medium and heavy plate rolling mills, hot or cold rolling mills for plates and strips, and temper mills.
Five-hi rolling mill.
There are two types: one is the C-B-S (contact bending straightening) rolling mill, which is a four high rolling mill with a small diameter (1/20 of the working roll) idle roll that bends the rolled piece, and its reduction is many times larger than a typical four high rolling mill. The rolled piece undergoes plastic bending deformation around a small idle roller, which can roll metal and alloy strips that are difficult to deform. Another type is that the position of the middle small roller can be adjusted along the inlet or outlet direction of the rolling mill to maintain the correct thickness of the rolled piece, used for rolling stainless steel, carbon steel, and non-ferrous metal strips with very small thickness tolerances.
HC
High performance, controllable roll crown rolling mill. It is equivalent to adding a pair of axially movable intermediate rolls between the work roll and the support roll of a four high rolling mill, and adjusting the corresponding ends of the two intermediate roll bodies to the positions corresponding to the two edges of the strip steel, in order to improve the uniformity of pressure distribution and elastic flattening of the work roll, ensure the dimensional accuracy of the strip steel, and reduce defects such as ultra-thin and cracking at its edges. HC rolling mill is suitable for cold rolled wide strip steel.
Offset eight hi rolling mill.
It is a variant of a four high rolling mill. The diameter of the work roll is 1/6 of the support roll, and it is offset relatively to prevent horizontal bending of the work roll. The rolling force is half smaller than that of a four high rolling mill. The work roll has good stability and high horizontal stiffness, and can be used to roll some products that need to be rolled using a twenty high rolling mill. Its structure and adjustment are much simpler than those of a twenty high rolling mill. This type of rolling mill can be modified into several types, including two, four, eight, and sixteen rolls, suitable for the needs of multiple varieties, hence it is also known as a multi-purpose rolling mill. It has two types: reversible and continuous rolling, used for cold rolling difficult to deform steel, silicon steel, and non-ferrous metal strip.
Six hi rolling mill.
Consisting of a pair of work rolls and two pairs of support rolls, it has a relatively stable roll system. But its rigidity is similar to that of a four roll rolling mill, and its operation is inconvenient, so it is not widely used. It is generally used for rolling high-precision copper strips for submarine cables.
Multi hi rolling mill.
There are three types: twelve roll, twenty roll, and thirty-six roll. The pair of rolls with the smallest diameter in the middle of the rolling mill is the work roll, while the rest are the support rolls. It has advantages such as high relative stiffness, large reduction, low rolling force, and the ability to roll extremely thin strips. The initial multi roll rolling mill was driven by work rolls, and later by intermediate support rolls. Can roll foil with a width of 200-1000 millimeters and a thickness of 0.02-0.0015 millimeters.
Two large diameter support rollers drive two sets of planetary roller systems, and the slab or flat ingot can be hot rolled into thin strips in one pass, with a reduction rate of 90-95%. If a continuous casting machine is used in the previous process and a leveling machine is used in the subsequent process, the production process of hot rolled strip steel can be simplified. The length of the roll body of a large planetary rolling mill can reach 1450 millimeters.
Universal rolling mill.
It consists of a pair of horizontal and vertical rollers, all of which are powered. Used for rolling slabs or flat steel.
Universal steel beam rolling mill.
The structure is similar to a universal rolling mill, except that the axis of the vertical roller and the horizontal roller are placed in the same vertical plane, and the vertical roller is driven. Suitable for rolling wide edge steel beams with a height of 300-1200 millimeters.
Disc piercing machine.
The axis of the rolled piece is lower than the axis of the disc. When the disc rotates, it causes the rolled piece to spiral forward against the core rod, rolling the solid round steel into a hollow blank pipe, suitable for rolling seamless steel pipes of 60 to 150. There is another type of cross rolling piercing machine, which has drum shaped rollers that intersect and rotate diagonally. Its working principle is similar to that of a disc piercing machine, and it is suitable for rolling seamless steel pipes of 60 to 650 meters. The cross rolling piercing machine, along with the automatic pipe rolling machine, leveling mill, sizing (reducing) machine, and diagonal roll straightening machine shown in Figure 7, is a seamless steel pipe hot rolling unit.
Wheel rims rolling mill.
The inner and outer circles of the tire are rolled by a pair of opposing rollers, and the two end faces of the tire are rolled by a pair of slanted conical rollers. Used for rolling inner and outer rings of wheels or rolling bearings.
Round ball rolling mill.
A rolling mill with a spiral semi circular groove on the roll, where the bar material spirals forward between the rotating rolls and is rolled into a ball, capable of rolling a ball with a diameter of 60-650 millimeters.
Selection of rolling mill:
Select the type and size of finished or semi-finished rolling mills according to the requirements of product variety, specifications, quality, and output, and equip them with necessary auxiliary, lifting, transportation, and auxiliary equipment. Finally, balance and select according to the requirements of various factors.
Development of rolling mill:
The trend of modern rolling mill development is continuous, automated, and specialized, with high product quality and low consumption. Since the 1960s, significant progress has been made in the design, research, and manufacturing of rolling mills, which have improved the performance of strip cold and hot rolling mills, thick plate rolling mills, high-speed wire rolling mills, H-shaped rolling mills, and continuous tube rolling mills. A series of advanced equipment has emerged, including wire rolling mills with rolling speeds of up to 115 meters per second, fully continuous cold rolling mills for strip, 5500mm wide and thick plate rolling mills, and continuous H-shaped steel rolling mills. The unit weight of raw materials used in rolling mills has increased, and hydraulic AGC, flatness control, electronic computer program control, and testing methods are becoming more and more perfect, resulting in a continuous expansion of rolling varieties. Some new rolling methods such as continuous casting and controlled rolling, as well as various special structures of rolling mills that meet new product quality requirements and improve economic benefits, are being developed.
Troubleshooting:
Due to the harsh working environment of the rolling mill, during the working process, the rolling cooling water quickly atomizes when encountering the red hot billet, and sprays around with the iron oxide powder falling off from the billet surface. The roll has a greater impact on the frame memorial archway through the bearing pedestal, causing varying degrees of corrosion and wear on the window surface inside the mill frame memorial archway, the bottom surface of the frame memorial archway, etc., making it difficult to effectively control and manage the gap between the mill frame and the roll bearing pedestal, There is often a phenomenon where the gap between the rolling mill frame and the roller bearing seat exceeds the management limit value. The increase of the mill memorial archway clearance worsens the working conditions of the main drive system of the mill, which makes the main drive vibrate and impact heavily. When the ingot bites, it is easy to slip, affecting the control of plate shape and product quality.
Most of the rolling mill memorial archway are made of ordinary steel castings, and the window surface is vulnerable to corrosion and wear during long-term service, resulting in deterioration of working conditions. The online machining method is usually used to repair the memorial archway, that is, to remove materials through machining, remove the damaged layer on the surface of the memorial archway, and level the contact surface. The expanded size is compensated by increasing the thickness of the lining plate. This repair method is simple and convenient to operate, but it does not change the nature of the memorial archway surface. After a period of use, the surface of the memorial archway will be corroded and worn out, and the strength and stiffness of the memorial archway will be adversely affected by repeated machining. Considering the sensitivity of the rolling mill to stiffness and the limited margin available for processing, this repair method can only be a temporary solution. Manual arc welding can restore the enlarged size of materials removed after machining, but large area arc surfacing on such rigid structure may cause deformation of memorial archway structure. If the structure undergoes distortion, instability, and deformation, it will be fatal and cannot be corrected. This is something that is never allowed to happen in factory production. Therefore, this repair method will bring significant risks and is generally not adopted.
Up to now, polymer composites can be used to solve the wear of mill memorial archway. Polymer composite repair materials have superior adhesion and can firmly adhere to the surface of metal substrates, ensuring long-term operation without detachment; The product itself has extremely high compressive strength, and even under the rolling force of up to 1900 tons, the material will not be damaged; The unique polymer structure endows the material with good impact resistance, which can absorb the impact of the bearing block on the memorial archway and avoid wear; At the same time, the product has good corrosion resistance, which can prevent the surface of memorial archway from being eroded by cooling water. Special materials are used to repair the wear of rolling mill memorial archway, without removing materials, without affecting the overall strength and stiffness of memorial archway, and without deformation caused by repair welding thermal stress, which has solved the problems that the enterprise has been unable to solve for many years.
