Bearing is an important part of contemporary machinery. Its main function is to support the mechanical rotating body, reduce the friction coefficient during its movement, and ensure its accuracy.

The inspection items in operation include the rolling sound, vibration, temperature, and lubrication status of the bearing. The details are as follows:

Bearing rolling sound

The sounder is used to check the size and sound quality of the rolling sound of the running bearing. Even if the bearing is slightly peeled off, abnormal sounds and irregular sounds are emitted, which can be distinguished by the sounder.

Bearing vibration

Bearing vibration is very sensitive to bearing damage. For example, peeling, indentation, rust, crack, wear, etc. are reflected in the bearing vibration measurement. Therefore, vibration can be measured by using a special bearing vibration measuring device (frequency analyzer, etc.). The size of the frequency can not be inferred from the specific circumstances of the abnormality. The measured values vary depending on the conditions of use of the bearing or the mounting position of the sensor. Therefore, it is necessary to analyze and compare the measured values of each machine in advance to determine the judgment standard.

Bearing temperature

The temperature of the bearing is generally estimated by the temperature outside the bearing. If the oil hole can directly measure the temperature of the bearing outer ring, it is more suitable. Usually, the temperature of the bearing rises slowly as the operation starts, and reaches a steady state after 1-2 hours. The normal temperature of the bearing varies with the heat capacity, heat dissipation, speed and load of the machine. If the lubrication and installation are not suitable, the bearing temperature will rise sharply and abnormal temperature will occur. At this time, it is necessary to stop the operation and take necessary precautions. Based on a large amount of test data, Table 4-1 lists the average value of the outer ring temperature when the bearings are working in various machines for reference. Since the temperature is affected by lubrication, speed, load, and environment, the values in the table only indicate the approximate temperature range. The thermal sensor can be used to monitor the working temperature of the bearing at any time, and automatically alarm the household when the temperature exceeds the specified value or stop the occurrence of the burning shaft accident.

lubricating

First, the role of bearing lubrication

Lubrication has an important influence on the fatigue life of rolling bearings and friction, wear, temperature rise, vibration, etc. Without normal lubrication, the bearings cannot work. Analysis of the cause of bearing damage indicates that about 40% of bearing damage is associated with poor lubrication. Therefore, good lubrication of the bearings is an effective measure to reduce bearing friction and wear. In addition, the lubrication of the bearing also has various functions such as heat dissipation, rust prevention, sealing, and mitigation of impact. The role of bearing lubrication can be briefly explained as follows

a. forming an oil film between the two rolling surfaces or sliding surfaces that are in contact with each other to separate the two surfaces, reducing friction and wear of the contact surface.

b. When using oil lubrication, especially when using circulating oil lubrication, oil mist lubrication and fuel injection lubrication, the lubricating oil can take away most of the friction heat inside the bearing and play an effective heat dissipation effect.

c. When grease lubrication is used, it is possible to prevent foreign matter such as dust from entering the bearing and sealing.

d. Lubricants have the effect of preventing metal corrosion.

e. Extend the fatigue life of the bearing.

Second, the comparison of grease lubrication and oil lubrication

The lubrication method of the bearing is roughly divided into two types: grease lubrication and oil lubrication. In order to fully utilize the function of the bearing, it is important to use a lubrication method depending on the purpose of use reduction and use. Table 4-2 shows the advantages and disadvantages of grease lubrication and oil lubrication.

Third, grease lubrication

Grease is a lubricant consisting of a base oil, a thickener and an additive. When selecting, you should choose a grease that is very suitable for the conditions of use of the bearing. Due to the different trademarks, there will be great differences in performance, so you must pay attention when choosing. Commonly used greases for bearings include calcium-based greases, sodium-based greases, calcium-sodium-based greases, lithium-based greases, aluminum-based greases, and molybdenum disulfide greases. The amount of grease filled in the bearing is preferably 1/2-1/3 of the internal space of the bearing. It should be reduced to 1/3 at high speed. Excessive grease causes the temperature to rise.

Fourth, the choice of grease

When selecting the grease according to the working temperature, the main indicators should be the dropping point, oxidation stability and low temperature performance. The dropping point can generally be used to evaluate the high temperature performance. The actual working temperature of the bearing should be lower than the dropping point of 10-20 °C. Synthetic grease should be used at a temperature below the drop point of 20-30 °C. When selecting the grease according to the bearing load, the grease with a small penetration should be selected for the heavy load. When working under high pressure, in addition to the small penetration, it also has higher oil film strength and extreme pressure performance. When selecting grease according to environmental conditions, calcium-based grease is not easily soluble in water and is suitable for drying and low moisture environments.

5. Oil lubrication Under the conditions of high speed and high temperature, oil lubrication can be used when grease lubrication is not suitable.

A large amount of heat can be taken away by the circulation of the lubricating oil. Viscosity is an important characteristic of lubricating oil. The viscosity directly affects the fluidity of the lubricating oil and the thickness of the oil film formed between the friction surfaces. The viscosity of the lubricating oil at the working temperature of the bearing is generally 12-15 cst. The higher the speed, the lower the viscosity, and the heavier the load, the higher the viscosity. Commonly used lubricating oils include mechanical oil, high-speed mechanical oil, turbine oil, compressor oil, transformer oil, cylinder oil, and the like. Oil lubrication methods include:

a. Oil bath Lubricating oil bath lubrication is the most common lubrication method. It is suitable for the lubrication of low and medium speed bearings. Part of the bearing is immersed in the groove. The lubricating oil is taken up by the rotating bearing parts and then flows back to the oil groove. Should be slightly below the center of the lowest rolling element.

b. Drip oil lubrication Drip lubrication is suitable for bearing parts that need to supply lubricating oil quantitatively. The amount of oil dripping is generally one drop every 3-8 seconds. Excessive oil quantity will cause the bearing temperature to increase.

c. Circulating oil lubrication The oil pump delivers the filtered oil to the bearing components, and the oil after passing through the bearings is filtered and cooled for use. Since the circulating oil can take a certain amount of heat to cool the bearing, this method is suitable for bearing parts with higher rotational speed.

d. Spray lubrication The dry compressed air is mixed with the lubricating oil by a sprayer to form an oil mist. In the injection bearing, the air flow can effectively cool the bearing and prevent the intrusion of impurities. This method is suitable for the lubrication of high speed, high temperature bearing components.

e. Injection lubrication The oil pump shoots the high pressure oil through the nozzle into the bearing, and the oil injected into the bearing flows into the oil groove through the other end of the bearing. When the bearing rotates at high speed, the rolling elements and the cage also form a gas flow at the relatively high rotation speed of the surrounding air. It is difficult to send the lubricating oil to the bearing by the general lubrication method. At this time, the lubricating oil must be sprayed by the high-pressure injection method. In the bearing, the position of the nozzle should be placed between the inner ring and the center of the cage.

Sixth, solid lubrication

Under some special conditions, a small amount of solid lubricant is added to the grease. For example, adding 3~5% of molybdenum disulfide No. 1 can reduce wear and improve pressure and heat resistance. For high temperature, elegance, high vacuum and corrosion resistance. Special conditions such as anti-radiation and extremely low temperature, the solid lubricant can be added into engineering plastics or powder metallurgy materials to make bearing parts with self-lubricating properties, such as bonding the solid lubricant to the raceway with an adhesive. A lubricating film is formed on the cage and the rolling elements, which has a certain effect on reducing friction and wear.

7. Replenishment and replacement of lubricants

a. Grease replenishment interval due to mechanical action, aging and contamination increase, the lubrication base filled in the bearing configuration will gradually lose its lubricity. Therefore, the lubrication rank needs to be continuously supplemented and updated. The interval between lubricant replenishment varies depending on the formation, size, and rotational speed of the bearing, and the approximate interval between replenishment of the grease is required depending on the operation time. In addition, when the bearing temperature exceeds 70 ° C, for every 15 ° C rise in the bearing temperature, the supplemental interval of the grease is reduced by half. Double-sided closed bearings have been filled with grease at the time of manufacture. “HRB” uses standard greases in these products. The total operating temperature range and other properties are suitable for the specified conditions, and the amount of grease is also corresponding to the bearing size. The service life of the grease can generally exceed the bearing life. Except for special occasions, no grease needs to be replenished.

b. Lubricating oil replacement cycle The replacement period of the lubricating oil varies depending on the conditions of use and the amount of oil. Under normal circumstances, when the operating temperature is below 50 ° C and the dust is used in a good environment, it is replaced once a year. When it reaches 100 °C, it should be replaced in 3 months or less.

Installation and maintenance

Points to note

From the point of view of use, to ensure that the bearing can work reliably, pay attention to the following points:

1. Improve the lubrication quality, control the pressure, temperature and flow of the oil, and strengthen the oil filtration.

2. Use fuel and lubricating oil that meet the requirements.

3. Controlling the temperature state of the diesel generator set is unfavorable in the case of overcooling and overheating. In cold weather, the diesel engine should be preheated before starting, and the crankshaft should be turned by hand to make the oil enter the friction surface.

4, bearing and journal surface quality and geometry should be strictly guaranteed.

5, the bearing clearance should be appropriate, the generator set is too large to produce impact, too small, the lubrication is poor, may burn the tile.

How to ensure reliable bearing work

Generally speaking, pay attention to the following points from the perspective of use:

1. The bearing clearance should be appropriate, too large to produce impact, too small, the lubrication is poor, and may burn the tile;

2. Bearing and journal surface quality and geometry should be strictly guaranteed;

3. Improve lubrication quality, control oil pressure, temperature and flow, and strengthen oil filtration;

4. Use qualified fuel and lubricants.

In order to fully utilize the bearings and maintain their proper performance for a long time, regular maintenance (regular inspection) must be performed. Through proper periodic inspections, early detection of failures and prevention of accidents are important to improve productivity and economy.

installation

Whether the bearing is installed correctly affects accuracy, life and performance. Therefore, the design and assembly department should fully study the installation of the bearing. I hope to install according to the operating standards. The items of the job standard are usually as follows:

(1) Cleaning bearings and bearing related parts

(2) Check the size and finishing of the connected parts

(3) Installation

(4) Inspection after mounting the bearing

(5) Supply lubricant

I hope that the bearing package will be opened before the installation. Generally grease is lubricated, not cleaned, and directly filled with grease. Lubricating oil is not necessary for cleaning. However, for instruments or high-speed bearings, it should be cleaned with clean oil to remove the rust inhibitor applied to the bearing. The bearing with the rust preventive removed is easy to rust, so it cannot be placed. Furthermore, bearings that have been sealed with grease are used without cleaning.

The mounting method of the bearing varies depending on the bearing structure, fit, and conditions. Generally, since the shaft is mostly rotated, the inner ring needs an interference fit. Cylindrical bore bearings, press with multiple presses, or use hot charging methods. For taper holes, mount directly on the taper shaft or with a sleeve.

When installed in the outer casing, the general clearance fits a lot, and the outer ring has an interference amount, which is usually pressed by a press or a cold shrink fit method after cooling. When dry ice is used as the coolant and the shrinkage is installed, the moisture in the air will condense on the surface of the bearing. Therefore, appropriate rust prevention measures are required.

maintenance

Disassembly

The disassembly of the bearing is carried out on a regular basis and the bearing is replaced. After disassembly, if you continue to use it, or if you need to check the condition of the bearing, the disassembly should be carried out as carefully as the installation. Attention should not damage the bearing parts, especially the disassembly of the interference fit bearing, which is difficult to operate.

It is also important to design and manufacture disassembly tools as needed. When disassembling, study the disassembly method, sequence, and investigation of the fitting conditions of the bearing according to the drawings, so as to obtain the foolproof operation.

To remove the interference fit outer ring of the outer ring, install a few outer ring extrusion screw screws on the circumference of the outer casing, and tighten the screw evenly while disassembling. These screw holes are usually covered with a blind plug, a tapered roller bearing, etc., and a plurality of slits are provided on the shoulder of the outer casing, and the spacer is used, disassembled by a press, or gently tapped and disassembled.

The removal of the inner ring is the easiest to pull out with a press. At this time, pay attention to let the inner ring withstand its pulling force. Moreover, the pull-out fasteners shown are also mostly used, and regardless of the type of fixture, they must be firmly stuck on the side of the inner ring. To do this, consider the size of the shaft shoulder or study the groove at the shoulder to use the pull fixture.

The inner ring of large bearings is dismantled by hydraulic method. The oil pressure is applied to the oil hole of the bearing to make it easy to pull. The bearing with a large width is used in combination with the hydraulic chucking method and the drawing device.

The inner ring of the cylindrical roller bearing can be removed by induction heating. A method of heating a part in a short time to expand the inner ring and then pull it. In the case where a large number of such bearing inner rings are required to be installed, induction heating is also used.

Cleaning

When the bearing is removed and inspected, the appearance record is first recorded by photography. Also, verify the amount of lubricant remaining and sample the lubricant before cleaning the bearings.

a. The cleaning of the bearing is carried out by rough washing and fine washing, and a metal mesh frame can be placed on the bottom of the used container.

b. When rough washing, remove the grease or adhesive with a brush or the like in the oil. At this time, if the bearing is rotated in the oil, be careful that the rolling surface will be damaged by foreign matter or the like.

c. When washing finely, slowly rotate the bearing in the oil and carry out it carefully.

The cleaning agent generally used is a neutral non-aqueous diesel oil or kerosene, and a warm alkali liquid or the like is sometimes used as needed. Regardless of which cleaning agent is used, it is often filtered and kept clean.

Immediately after cleaning, apply anti-rust oil or anti-rust grease to the bearing.