What are the characteristics of rolling mill work?

• What is a rolling mill？

Equipment for the process of metal rolling. Generally refers to the equipment to complete the whole process of rolling production, including main equipment, auxiliary equipment, lifting transport equipment and auxiliary equipment, etc. But the general mill often refers to only the main equipment. Rolling mills are said to have existed in Europe in the 14th century, but it is recorded that an Italian named Leonardo da Vinci sketched out a #rollingmill in 1480. In 1553, a Frenchman named Brulier rolled sheets of gold and silver to make coins. Since then, rolling mills have appeared in Spain, Belgium and England.

• Job characteristics

(1) The mill load is large, but the roll diameter and bearing size are limited by the roll size, and can not be increased unlimitedly, so the unit pressure of the roll bearing is large, more than 2 ~ 5 times of the general purpose bearing;

(2) High speed is the development trend of modern rolling mills, so the working speed range of roller bearing is changing more and more;

(3) Bad working environment, uneven heating and unstable temperature;

(4) Frequent roll change;

(5) the plate precision requirements are high. According to the working characteristics of the rolling mill, higher requirements are put forward for the roll bearing: high bearing capacity, rotation accuracy, high limit speed, simple structure, easy assembly and disassembly, etc. Therefore, according to the working requirements and actual situation of the rolling mill, the design and selection of rolling mill roll #bearing is very important, which is related to the performance of the rolling mill.

• Types and characteristics of common mill bearings

Radial bearing

It can bear large impact load. There are several kinds of radial bearings used in rolling mills.

①Double row centripetal spherical roller bearings: with the characteristics of automatic self-aligning, can withstand medium load and rolling force, mostly used in small and medium-sized rolling mills supporting roller;

② four row cylindrical bearings: easy to obtain high machining accuracy, thus has the characteristics of high speed rotation and because of its easy installation and disassembly, and can be pressed into the roll neck, circle surface of inner ring raceway surface and roll grinding at the same time, to improve the precision of rolling, multi-purpose at high speed, high precision rolling mill bearing roller, this kind of bearing can withstand the high radial force, unable to bear axial force, must add a separate thrust bearing;

③ Four rows of cone roller bearings: can bear radial load and axial load at the same time, but the assembly needs to be strictly in accordance with the serial number. They are mostly used for supporting roll and work roll of large rolling mills.

Axial thrust bearing

Mainly used to bear axial force, to prevent rolling roll axial channeling and wrong roll. There are several types of roller thrust bearings as follows:

①Double row tapered roller bearings: can withstand bidirectional axial load, suitable for high-speed rolling mills with large load;

② Deep groove ball bearings: can withstand radial and two-way axial load, suitable for high-speed and low load rolling mills;

③ Four point contact ball bearings: can withstand radial and two-way axial loads, suitable for high speed and low load rolling mills.

• The configuration of rolling mill bearings

Self-aligning roller bearings

The configuration pattern of early rolling mill bearings on the rolling mill was different from that of today. At that time, two sets of self-aligning roller bearings were mainly installed on the same roller neck. This configuration basically meets the production conditions at that time, and the rolling speed can reach 600rpm. But with the increase of speed, its shortcomings are more and more prominent: bearing life is short, consumption is large, the finished product accuracy is low, the roller neck wear is serious, the rolling roll axial movement is large, etc..

 Four rows of cylindrical roller bearings + thrust bearings

The inner diameter of the cylindrical roller bearing and the roller neck adopts tight matching, bearing radial force, has the advantages of large load capacity, high limit speed, high precision, inner and outer rings can be separated and interchangeable, easy processing, low production cost, convenient installation and disassembly, etc. Thrust bearing bearing bearing axial force, specific structure can be selected according to the characteristics of the mill. Under heavy load and low speed, with thrust roller bearing, with a small axial clearance to bear thrust load. When the rolling speed of rolling mill bearing is high, with angular contact ball bearing, not only the limit speed is high, but also the axial clearance can be strictly controlled when working. The roller can be closely guided by axial direction, and can withstand general axial load. This type of bearing configuration not only has the advantages of long bearing life, high reliability, but also has the advantages of high rolling accuracy, easy control and so on, so it is the most widely used at present, and is mostly used in wire rolling mill, sheet rolling mill, foil rolling mill, double supporting roll mill cold rolling mill and hot rolling mill.

Four rows of tapered roller bearings

Tapered roller bearings can withstand both radial and axial forces without the need for thrust bearings, making the main engine more compact. The inner diameter of tapered roller bearing and the roller neck adopt loose fit, which is very convenient to install and disassemble, but sometimes it will cause sliding creep due to loose fit, so the inner diameter is often processed with spiral oil groove. This type of configuration is still widely used at present, such as four-high hot and cold rolling mill work roll, billet machine, steel beam rolling mill and other occasions of the roll.

• Lubrication mode of rolling mill bearings

In principle, the lubrication of roller bearings is basically the same as that of other rolling bearings, but the working conditions of roller bearings are relatively bad. Whether the working performance can be effectively played depends to a large extent on the lubrication of bearings.

The main lubrication methods for roller bearings are grease lubrication and oil lubrication.

Grease lubrication grease has both sealing function, sealing structure and lubrication facilities are simple, easy to add grease, so as long as the working conditions allow, roll bearings are generally grease lubrication. The cooling effect of oil lubrication is strong, and it can take dirt and moisture from the bearing. Roller bearings are lubricated by oil lubrication methods including pressure oil supply lubrication, oil injection lubrication, oil mist lubrication and oil and gas lubrication.

Pressure oil supply lubrication is the most effective lubrication method for roller bearing under conventional rotation speed. Oil injection lubrication is to spray the lubricating oil into the bearing at a certain pressure through the nozzle installed on one side of the bearing for lubrication. It is generally used in high-speed roller bearings or occasions where the pressure oil supply lubrication cannot meet the cooling requirements.

Spray lubrication is to spray the dry compressed air containing oil mist into the bearing interior for lubrication. The amount of oil is less. Due to the effect of air, the cooling effect is very strong. Both pressure oil supply lubrication and oil injection lubrication need to be equipped with inlet and outlet tubing, lubrication pump, oil storage device, and sometimes lubricating oil cooler. Therefore, the cost is higher, and generally roller bearings are less used.