This article describes the installation, maintenance and lubrication of rolling mill bearings.
Keywords: rolling mill bearings; installation; maintenance; lubrication
Installation of rolling mill bearings
The service life of rolling mill bearings is not only related to the quality of the bearings, but also closely related to their installation and use. For this reason, attention should be paid to the technical requirements for bearing installation and relevant operating procedures should be followed.
Preparation before installation
(1) Before installation, the mating surfaces of each mating partner, including the roll neck, bearing box, bearing ring and bearing box cover, should be carefully inspected to check whether their size, shape and position accuracy and mating male cover meet the technical requirements of the design. .
(2) The edges and burrs of the surfaces matching the bearings, roll necks, bearing box holes and oil holes must be removed, cleaned and coated with lubricating oil.
Installation of four-row cylindrical roller bearings
(1) Install the labyrinth ring (waterproof cover)
The fit between the labyrinth ring and the roller neck is generally a tight dynamic fit, and a copper rod needs to be tapped gently during installation. The two end faces of the labyrinth ring must be parallel and closely fit with the shaft shoulder and the bearing inner ring.
(2) Install the inner ring
The fit between the inner ring and the roll neck of the four-row cylindrical roller bearing is an interference fit. During installation, the inner ring should be heated to 90-100°C first. Never exceed 120°C to prevent incomplete retraction of the inner ring after cooling. The heating method can be oil tank heating or induction heating. It is absolutely prohibited to use open flame for heating.
The increase in inner diameter when heated by an oil tank is calculated according to the following formula:
△d＝12.5×10-6△t.d
In the formula: △d – the increase in the inner diameter of the inner ring after heating (mm)
△t－The difference between oil temperature and room temperature (℃), the standard room temperature is 20℃.
d－Inner ring inner diameter (mm)
When installing double inner rings such as the FCD type, the end faces of the inner ring and the inner ring, and the inner ring and the labyrinth ring must be brought into contact with each other along the axial direction during the cooling process of the inner ring, and the inspection must be carried out with a feeler gauge.
(3) Install the outer ring
The outer ring of a four-row cylindrical roller bearing and the inner hole of the bearing seat generally have a transition fit. For smaller bearings, the outer ring, rollers and cage can be gently tapped into the bearing seat with a copper rod. For larger bearings, you can use the lifting holes provided on the outer ring or cage to lift the outer ring and outer ring assembly and install them vertically downward into the bearing box.
For FCDP type four-row cylindrical roller bearings with movable ribs, the side retaining rings, outer ring components, and middle retaining rings should not be interchanged with bearings of the same model. The marks I, II, III and IV marked on the end face of the outer ring are the marks of the load area. When first installed and used, the rolling load direction should be aligned with the I mark. When cleaning and reinstalling later, the rolling load can be aligned with the other marks in order to extend the service life of the bearing.
Installation of thrust (positioning) bearings
Thrust bearings include four-point angular ball bearings, double row (single row) angular contact angular ball bearings, two-way thrust tapered and cylindrical roller bearings,
When four-point angular ball bearings and double (single) row angular contact ball bearings are used as thrust bearings, they are not allowed to bear load in the radial direction. Therefore, the inner hole of the bearing seat corresponds to the part where these bearings are assembled, and its diameter must be larger than the outer diameter of the bearing. The diameter is about 0.5 mm larger. Or the roller diameter is about 0.5 mm smaller than the bearing inner diameter.
For four-point contact ball bearings, do not interchange the separation rings of the same model during installation to prevent the factory axial clearance from changing.
The middle ring of a bidirectional thrust tapered roller or bidirectional thrust cylindrical roller bearing must not be interchanged between bearings of the same model to prevent the factory axial clearance from being changed.
The end face of the thrust bearing inner ring must be pressed tightly when installed and locked axially. This is to avoid relative rotation on the roll neck, causing wear and burns on the roll neck mating surface.
When the brake roller axial force bearing is used, it is axially positioned through two pieces of bearing boxes and the axial clearance is adjusted. When installing the bearing box, ensure that the inner and outer rings of the bearing are in close contact with the inner and outer rings of the main bearing. When fixing the bearing boxes on both sides of the frame axially, attention should be paid to eliminating the axial movement of the bearing boxes toward the shaft end that will occur during the introduction of the bearing boxes on both sides of the frame.
Installation of four-row tapered roller bearings
The fit between the inner ring of the four-row tapered roller bearing and the roll neck generally has a gap. During installation, first install the bearing into the bearing box, and then install the bearing box into the journal.
The outer ring of the four-row tapered roller bearing also adopts a dynamic fit with the bearing box hole. First, install the outer ring A into the bearing box. When leaving the factory, character symbols are printed on the outer ring, inner ring, and inner and outer spacer rings. During installation, the bearing housing must be installed in the order of the character symbols. They cannot be interchanged arbitrarily to avoid changes in bearing clearance.
After all parts are installed in the bearing box, axially close the inner ring to the inner spacer ring and the outer ring to the outer spacer ring.
Measure the width of the gap between the outer ring end face and the bearing housing cover to determine the thickness of the corresponding sealing gasket.
Maintenance and monitoring of rolling mill bearings
Bearings should be maintained and monitored during use to extend their service life.
1. Keep the lubricating oil path unobstructed, select the type of lubricant according to regulations, and add sufficient lubricant regularly. Ensure that the rolling surface of the roller and the sliding surface of the roller and the rib are well lubricated by oil and wax.
2. Regularly check the sealing condition of the seals and replace damaged seals in time. Ensure the sealing performance of the bearing to prevent water and iron oxide scale from entering the bearing and prevent the leakage of bearing lubricant.
3. Based on the actual situation of the enterprise, actively carry out monitoring of bearing operating conditions.
Noise monitoring: There should be a steady hum during normal operation. Regularly monitor and compare with the normal sound to detect abnormalities in time.
Lubricant monitoring: Normal lubricant should be clear and clean. If the lubricant becomes dirty, there will be wear particles or contaminants.
Temperature monitoring: When the temperature rises, abnormal operation will occur.
Establish a record card to record the number of days the bearing has been used online, the amount of steel passed, and the maintenance and monitoring status, etc., to strengthen the management of the operating status of the bearing.
Lubrication of rolling mill bearings
The importance of lubrication
The lubrication of bearings uses oil films to separate relatively moving rolling surfaces from each other to prevent excessive wear and failure due to rough point contact. If users can attach great importance to bearing lubrication technology, they can ensure that stable performance and rotation accuracy can be maintained during the predetermined working life.
Types and properties of grease
The lubrication of rolling mill bearings is divided into grease lubrication and oil lubrication. The advantages of grease lubrication are that the lubrication facility is simple, the grease is not easy to leak, and it has a certain ability to prevent water, air and other impurities from entering the bearing. Therefore, grease lubrication is widely used under normal circumstances. Use oil for lubrication under heavy load, high speed, high temperature and other working conditions.
Grease is composed of base oil, thickener and additives. The viscosity of the base oil plays an important role in the lubrication performance of the grease. The composition of the thickener has an important impact on the performance of the grease, especially temperature characteristics, water resistance, oil separation, etc. Additives are mainly used to enhance the vaporization resistance of the grease. , anti-rust, extreme pressure and other properties.
Greases are classified according to different types of thickeners, including lithium-based, nano-based, and other types. Lithium-based grease is commonly used in rolling mill bearings. Lithium-based grease is characterized by good water resistance and high dropping point, and can be used in mechanical parts that are wet and in contact with water. Grease is divided into several grades according to its fluidity, that is, penetration. The higher the penetration value, the softer the grease.The domestically produced roll bearing grease is a multi-complex lithium-based grease composed of high-grade fatty acids and synergists. It is also suitable for the lubrication of rolling mill bearings.
The properties of commonly used lithium-based greases are shown in the table below
| grease | Penetration1/10mm | Dropping point C≥ | composition | 特性 | |
| Name | Brand | ||||
| General purpose lithium grease | ZL-1ZL-2ZL-3 | 310-340265- 295265-295 | 170175180 | Natural fatty acid lithium soap thickened medium viscosity lubricant plus antioxidant | Good water resistance, mechanical stability, water resistance and oxidation stability. Applicable to -20–120℃ temperature range. |
| Extreme pressure lithium grease | 012 | 315-385310- 340275-295 | 170 | Good mechanical stability, water resistance, rust resistance, extreme pressure and wear resistance and pumpability. Applicable to -20–120℃ temperature range. | |
Grease filling amount
The filling amount of grease is appropriate to fill one-third and one-half of the space of the bearing and bearing shell. If too much grease is added, the grease will deteriorate or soften due to the heat swept away by stirring. On high speed it should only be filled to a third or less. When the rotational speed is very low, in order to prevent external foreign matter from entering the bearing, the housing space can be filled up.
Grease replacement
The service life of grease is limited, its lubrication performance gradually decreases during use, and wear gradually increases, so it must be replenished and replaced at certain intervals.
The grease replenishment cycle is related to the bearing structure, rotation speed, temperature and environment, and should be determined according to the specific working conditions of the enterprise. When replacing grease, please note that greases of different brands cannot be mixed. Mixing greases containing different types of thickeners will destroy the structure and consistency of the lubrication. If it is necessary to replace greases with different brands, the original ones in the bearing should be removed. After the grease is completely removed, add new grease.
Storage and preservation of rolling mill bearings
Bearings are precision mechanical components that have strict requirements for their storage and preservation.
(1) Warehouse temperature: Bearings are coated with anti-rust oil before leaving the factory. If the temperature is too low or too high, the anti-rust oil will deteriorate. The room temperature should be controlled at 0-25°C.
(2) Warehouse humidity: Excessive humidity will cause bearings to rust. The relative humidity of the warehouse should be maintained at 45%-60%.
(3) Warehouse environment: 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. Bearings should be placed off the ground and away from heating pipes.
(4) Regular inspection: According to the regulations on anti-rust of bearing products, regular inspection should be carried out every 10-12 months. If the oil seal packaging is found to be rusty, the oil seal packaging should be repackaged.
