Reasonable use of roll neck bearings can reduce bearing loss

Aug 07, 2023

At present, roll neck bearings mainly include rolling bearings and sliding bearings. These two bearings have their own advantages and disadvantages, among which rolling bearings are the most used.

Most of the rolling bearings use spherical roller bearings, double-row tapered roller bearings, four-row tapered roller bearings, and multi-row cylindrical roller bearings. Rolling bearings have high rigidity and low coefficient of friction, but poor impact resistance and large dimensions. Sliding bearings are divided into semi-dry friction and liquid friction according to the friction method. Semi-dry friction sliding bearings are mainly open phenolic cloth resin bearings (ie bakelite tiles) or copper tiles and nylon tiles. They are lubricated by water, have a large friction coefficient, low precision, and severe wear. They are mainly used in blooming mills and have been gradually eliminated by various rolling mills. Fluid friction bearings are usually called oil film bearings, and there are three types: dynamic pressure, static pressure, and static dynamic pressure. The lubricant is high-pressure oil, which establishes an oil film between the roll neck and the bearing, avoiding their direct contact friction, small friction coefficient, wide speed range, good rigidity, high precision and long service life. Because of these advantages, oil film bearings are increasingly accepted and recognized by customers.

The following is an analysis of the advantages of oil film bearings.

1. The friction coefficient is small because of the isolation effect of the oil film. In stable operation, the friction coefficient is 0.001~0.005, which is roughly the same as that of rolling bearings, with low friction loss and energy saving.

2. High bearing capacity means that under the same roll diameter, the roll neck of the oil film bearing is conical, and the roll neck of the rolling bearing is cylindrical. The root size of the roll neck of the oil film bearing is much larger than that of the rolling bearing, and the strength is about 40% higher.

3. The speed range is wide, which means that whether it is used in high-speed wire rod rolling mill (120m/s) or strip rolling mill (10~40m/s), it can ensure high rolling accuracy (<0.02mm), especially for medium plate single-stand reversible rolling mill, after forward rolling, the rolls stop and then reverse start. And "strip pressing" often occurs, that is, it stops before the tail of the rolled piece is thrown out, and it is loaded (pressed) at zero speed and then reversed to start. Oil film bearings are suitable for rolling speed from positive to zero, from zero to negative reversible (forward, reverse) work.

4. Long service life means that the oil film bearing is liquid friction, the wear of the bearing working surface is close to zero, and there are no wearing elements (rollers, cages). Under normal use conditions, its service life can reach 10 to 20 years. The rolling bearing life is about 1 year.

5. Small size and compact structure, which means that when the bearing capacity is the same, its volume is smaller than that of rolling bearings. Because oil film bearings have no rollers and cages, the axial space of the bearing housing is greatly reduced. When the size of the roll and the window of the archway are similar. At the same time, the extra space on the bearing seat can be equipped with roll balance cylinder, roll bending device and arch prestressing device to realize automatic control of plate shape and thickness.

6. Strong impact resistance, which means that the load of the bearing is the rolling force, that is, the deformation resistance of the rolled piece. Usually, the rolled piece is rolled when it is bitten in. The load is suddenly established, and the roll bearing suffers is the impact load, the rolling bearing is a rigid contact, it can not bear the impact load, so the life is short, and the oil film bearing is the oil film pad between the roll neck and the bearing to play a buffer role, when the roll is impacted, it will be squeezed between the roll and the bearing oil, but the gap is small, the oil is sticky, and the oil is pressed to produce a huge resistance, which balances the sudden impact load and protects the bearing from damage.

7. Strong anti-pollution ability refers to the poor environment of the medium plate mill, dust, cooling water, iron oxide scale, and high temperature. Rolling bearings have poor sealing conditions and are easily polluted, while oil film bearings are well-sealed, have fixed seals and rotary seals, and can work normally in extremely poor environments for a long time. Because oil film bearings have many of the above advantages, they have been widely used in the roll bearings of medium and heavy plate rolling mills and hot and cold continuous rolling mills. However, the lubricating system of oil film bearings is complicated and requires a large investment. Oil film bearings require high oil filtration accuracy to ensure oil film thickness, large lubricating oil flow to ensure circulating lubrication and cooling, and high sensitive self-adjustment ability to meet speed changes, so the lubrication system is huge. The establishment of the underground lubrication station makes a very large one-time investment.

It is urgent to reduce the consumption of rolling bearings. Rolling bearings have poor anti-pollution and impact resistance, short service life, high accident rate, and high consumption, which affects production. In view of the above-mentioned limitations of the use of rolling bearings, in order to maximize the service life of the bearings and avoid accidents, in recent years, steel rolling enterprises have continuously made the following improvements to the use, manufacture and installation of backup roller bearings.

First is to add oil lines to the four-row cylindrical rollers and four-row tapered rollers, so that the bearings can be fully lubricated during operation. The second is to improve the grease. The third is to improve the sealing effect. The sealing effect is not good, resulting in a large amount of immersion of cooling water and iron oxide scale, loss of grease, and pressing of the iron scale, resulting in pressure pits, pitting, peeling, and even jamming. Therefore, every time the bearing is assembled, carefully check the sealing condition and confirm whether the steel skeleton is slightly deformed, whether the rubber is aging, and whether the elasticity has disappeared. Record the use of sealing rings and replace them in time. The fourth is to formulate a reasonable use and replacement cycle. After a period of use, rolling bearings will generate fatigue stress inside, shorten the use time, eliminate stress in time, and replace them regularly to avoid accidental damage. These improvements have greatly reduced bearing consumption, saved costs, and maintained smooth rolling production.