Knowledge about Rolling Mill Bearing

Knowledge about Rolling Mill Bearing

Definition

Rolling mill bearings refer to the rolling industry bearings used for the rolling of non-ferrous metals, ferrous metals and non-metal products, including the bearings used at the diameter of the rolling roll and on the drum. It usually adopts four-row cylindrical roller bearings to bear radial load, thrust roller or thrust ball bearings and radial angular contact ball or radial roller bearings to bear axial load. At present, oil-air lubrication or oil mist lubrication and grease are mostly used for lubrication and cooling.

Classification

Spherical roller bearings

Rolling mill bearings have different configurations on the rolling mill.

Two sets of spherical roller bearings are mainly installed side by side on the same roll neck.

This configuration basically meets the earlier production conditions, and the rolling speed can reach 600 rpm.

However, as the speed increases, its shortcomings become more prominent: short bearing life, large consumption, low precision of the finished product, serious roll neck wear, large axial movement of the roll, etc.

Four-row cylindrical roller bearings + thrust bearings

The inner diameter of the cylindrical roller bearing and the roll neck are tightly matched to bear radial force.

It has the advantages of large load capacity, high limit speed, high precision, separable inner and outer rings, interchangeable, easy processing, low production cost, convenient installation and disassembly, etc.

The thrust bearing bears the axial force, the specific structure type can be selected according to the characteristics of the rolling mill.

When heavy loads and low speeds are used, thrust roller bearings are equipped to bear the thrust load with a small axial clearance.

When the rolling speed is high, with angular contact ball bearings, not only the limit speed is high, but the axial clearance can be strictly controlled during operation.

The roller can be guided tightly in the axial direction and can withstand general axial load.

This type of bearing configuration not only has the advantages of long bearing life and high reliability, but also has many advantages such as high precision and easy control of rolled products.

Therefore, it is the most widely used.

It is mostly used for wire rod rolling mills, plate rolling mills, foil rolling mills, and dual-backup rolling mills.

Support rolls for cold rolling mills and hot rolling mills.

Four-row tapered roller bearings

Tapered roller bearings can bear both radial force and axial force, without the need to configure thrust bearings, so the host is more compact.

The inner diameter of the tapered roller bearing adopts a loose fit with the roll neck, which is very convenient to install and disassemble, but sometimes it will cause sliding creep due to the loose fit, so the inner diameter is often machined with a spiral oil groove.

The application of this configuration type is still relatively wide, such as the work rolls of four-high hot rolling mills and cold rolling mills, billeting mills, steel beam rolling mills and other occasions.

Features

Bearings used for rolling mills must withstand heavy loads and high speed rotations as well as severe operating environments. 

  • The working load is large, usually the unit pressure of the roll bearing is 2~4 times higher than that of the general purpose bearing.
  • The operating speeds vary greatly, and the operating speeds of different rolling mills vary greatly.
  • The working environment is harsh.

Applications

Rolling necks bearings for rolling mill of steel making equipment.

Precautions for installation of rolling mill bearings

Measurement of assembly quality

  1. The life of the bearing is inseparable from the design of the bearing seat.If the bearing seat is not properly designed and manufactured, it will cause uneven force on the bearing and reduce bearing life. The bearing seat should be self-aligning to prevent the bearing from being eccentrically loaded due to burnt, deflection and deformation of the roll.
  2. Whether the size, geometry, accuracy grade, tolerance range of the spare parts related to the bearing are consistent with the design.
  3. Whether the smoothness and hardness of the contact surface matched with the bearing are within the specified range, whether all clearances and interference fits meet the design requirements, etc.

Installation of inner and outer rings

Installation of inner rings

The inner sleeve and the roll neck of the four-row cylindrical roller bearing should have an interference fit.

The temperature should be heated to 80~90℃ during installation, and the temperature should not exceed 100℃. Otherwise, the bearing ring raceway and rolling element will anneal, which will affect the hardness and resistance, abrasion, leading to reduced bearing life and premature scrapping.

When using the heating method to install the bearing, after the oil temperature reaches the specified temperature for 10 minutes, the bearing should be quickly taken out of the oil and installed on the shaft while it is hot.

When necessary, a slight pressure can be applied to the end face of the inner ring of the bearing with an installation tool to make it easier to install.

After the bearing is installed on the shaft, the inner ring must be pressed immediately until it cools down.

It is usually heated by induction heater or engine oil, and it is forbidden to use cutting torch to bake.

When the inner sleeve is installed on the roll neck, it is in close contact with the water retaining ring to prevent the water retaining ring from moving.

Installation of outer rings

The outer shell of the four-row cylindrical roller bearing is a transitional fit with the inner hole of the bearing seat.

When assembling, use a copper rod to lightly drive the whole body composed of the outer shell, roller, and cage into the bearing seat, and fix the end cover tightly against the inner side.

When installing the outer ring, pay attention to the markings on the end face and the cage end face.

They cannot be reversed.

They should be installed in the order of the initial state when the bearing is unpacked to prevent the bearing from burning due to uneven force on the rollers.

When installing the bearing, the bearing should be placed horizontally.

After the bearing is installed, the stress area should be marked to prepare for the key inspection when changing the roller.

Reasonable assembly of bearing seals

The bearing seals can be considered to use ordinary fluororubber skeleton seals, which are not only low in price, but also can achieve good results with reasonable use.

When the rolling mill is in a horizontal state, the lip of the shaft seal ring in the static labyrinth on both sides must be installed outside the bearing, which can effectively prevent the splashing of cooling water and oxide scale.

When the rolling mill is in a vertical state, the drive side labyrinth The sealing ring lip is installed toward the inside of the bearing, which can effectively prevent the overflow of lubricating oil due to the downward gravity.

The sealing ring lip of the non-transmission side labyrinth is also installed outside the bearing, which can effectively prevent the splashing of cooling water.

Reasonable selection of bearing grease

Since the grease commonly used in bearings is ordinary 3#MoS2 lithium-based grease, it has the disadvantages of high viscosity, low penetration, inability to withstand high temperatures and high speeds.

Maintenance

Periodical maintained and monitored is essential

Keep the lubricating oil road unobstructed, select the type of lubricant according to the regulations, and refill the lubricant regularly and in sufficient quantities.
Ensure that the rolling surface of the roller and the sliding surface of the roller and the rib are kept well lubricated with wax.

Regularly check the sealing condition of the seals, and replace the damaged seals in time. Ensure the sealing performance of the bearing to prevent water and iron oxide from entering the bearing and prevent the leakage of bearing lubricant.

According to the actual situation of the company, actively carry out the monitoring of the bearing operation status.

Noise monitoring: There should be a steady buzzing sound during normal operation.

Regularly monitor and compare with the normal sound to find abnormalities in time.

Lubricant monitoring: Normal lubricants should be clear and clean. If the lubricant has become dirty, there will be worn particles or contaminants.

Temperature monitoring:When the temperature rises, the operation will be abnormal. The company has started temperature monitoring and is willing to serve customers more widely.

Establish a record card to record the number of days the bearing is used online, the amount of steel passing and the maintenance and monitoring status, etc., to strengthen the management of the bearing’s operating status.

After the rolling mill is turned on, the bearing grease dry plate and heating jam are serious.

Moreover, it is prone to accidents such as abnormal wear and burning of the bearing due to the hardening of the grease and the inability to normally lubricate the bearing.

In view of these disadvantages that are not conducive to the use of bearings, it is recommended to select extreme pressure lithium complex grease based on comprehensive consideration of the above factors.

Storage and custody of rolling neck bearings

Bearing is a kind of precision mechanical component, which has strict requirements for its storage and custody.

Warehouse temperature: The bearings are coated with anti-rust oil before leaving the factory. Too low or too high temperature will cause deterioration of the anti-rust oil. The room temperature should be controlled at 0-25 ℃.

Warehouse humidity: Too high humidity will corrode the bearings, and the relative humidity of the warehouse should be maintained at 45%-60%.

Warehouse environment: The bearings are best stored separately. When they must be stored together with other items, the other items stored together must not be chemicals such as acids, alkalis, and salts.The bearing should be placed away from the ground and away from heating pipes.

Regular inspection: According to the anti-rust regulations of bearing products, regular inspections are carried out every 10-12 months.If the oil seal packaging is found to be rusty, the oil seal packaging should be re-packed.

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