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Check and deal with the fault in bearing operation

Check and deal with the fault in bearing operation

2020-07-06

The rolling sound of the bearing

The sound detector is used to check the rolling sound and sound quality of the bearing in operation. Even if the bearing is slightly damaged such as peeling, abnormal sound and irregular sound will be emitted, which can be distinguished by the sound detector.

Vibration of bearing

Bearing vibration is very sensitive to bearing damage, such as spalling, indentation, corrosion, crack, wear and so on will be reflected in the bearing vibration measurement, so, through the use of a special bearing vibration measuring device (frequency analyzer, etc.) can be measured the size of the vibration, through the frequency can not be inferred from the specific circumstances of abnormal.The measured value varies with the use condition of the bearing or the installation position of the sensor, so it is necessary to analyze and compare the measured value of each machine before determining the judgment standard.

Three, bearing temperature

The temperature of the bearing, generally there is the temperature of the bearing outside can be inferred, if the use of oil hole can directly measure the temperature of the bearing outer ring, it is more appropriate.Usually, the temperature of the bearing starts to rise slowly with the operation and reaches a stable state 1-2 hours later.The normal temperature of the bearing varies with the heat capacity, heat dissipation, speed and load of the machine.If the lubrication and installation part are appropriate, the bearing temperature will rise sharply and abnormal high temperature will occur. At this time, the operation must stop and necessary preventive measures must be taken.Based on a large number of test data, table 4-1 lists the average temperature of the outer ring of bearings in various machines for reference.Since the temperature is affected by lubrication, rotation speed, load and environment, the median value in the table only indicates the approximate temperature range.The use of heat sensor can monitor the working temperature of the bearing at any time, and realize the automatic alarm or stop when the temperature exceeds the specified value to prevent shaft accidents.

Four, lubrication

(1) The role of bearing lubrication

Lubrication has an important influence on the fatigue life, friction, wear, temperature rise, vibration and so on of the rolling bearing. Without normal lubrication, the bearing cannot work.Analysis of the cause of bearing damage shows that about 40% of bearing damage is related to poor lubrication.Therefore, good lubrication is an effective measure to reduce bearing friction and wear.In addition, bearing lubrication and heat, rust, sealing, impact relief and other functions, bearing lubrication can be briefly described as follows:

A. Form an oil film between the two rolling or sliding surfaces in contact to separate the two surfaces and reduce friction and wear on the contact surfaces.

B. In the case of oil lubrication, especially in the case of circulation oil lubrication, oil mist lubrication and oil injection lubrication, the lubricating oil can take away most of the friction heat inside the bearing and play an effective role in heat dissipation.

C. Grease lubrication can prevent external dust and other foreign matters from entering the bearing and play a sealing role.

[D] Lubricants have the effect of preventing metal corrosion.

E. Extend the fatigue life of bearings.

Comparison between grease lubrication and oil lubrication

The lubrication methods of bearings can be divided into grease lubrication and oil lubrication.In order to give full play to the function of the bearing, it is important to adopt lubrication method according to the adjustment and use purpose.

Grease lubrication

Grease is a lubricant consisting of base oils, thickeners and additives.When the choice, should be very suitable for bearing lubrication conditions, due to the different trademarks, there will be a great difference in performance, so in the choice, we must pay attention to.Commonly used grease in bearings are calcium base grease, sodium base grease, calcium sodium base grease, lithium base grease, aluminum base grease and molybdenum disulfide grease.The amount of grease to be filled in the bearing shall be adequate to fill 1/2-1/3 of the bearing interior space.It should be reduced to 1/3 at high speed.Too much grease raises the temperature.

(iv) selection of grease

When selecting grease according to working temperature, the main indexes should be drop point, oxidation stability and low temperature performance. Drop point can be used to evaluate high temperature performance generally. The actual working temperature of bearing should be lower than 10-20℃.Synthetic grease should be used at a temperature lower than the drop point of 20-30℃.When selecting grease according to bearing load, select grease with low needle insertion for heavy load.In addition to low penetration, it also has higher oil film strength and extreme pressure performance.When selecting grease according to environmental conditions, calcium base grease is not easily soluble in water and is suitable for dry and less moisture environment.

(5) Oil lubrication

Under the condition of high speed and high temperature, grease lubrication can be used when it is no longer suitable.Through the circulation of the lubricating oil, a lot of heat can be carried away.

Viscosity is an important characteristic of lubricating oil. The viscosity directly affects the fluidity of lubricating oil and the oil film thickness formed between the friction surfaces. The viscosity of lubricating oil at bearing operating temperature is generally 12-15CST.The higher the rotating speed, the lower the viscosity, and the heavier the load, the higher the viscosity.Common lubricants are machinery oil, high speed machinery oil, turbine oil, compressor oil, transformer oil, cylinder oil, etc.

Oil lubrication methods include:

A. Oil bath lubrication

Oil bath lubrication is the most common lubrication method, suitable for low and medium speed bearing lubrication, bearing part soaked by the groove, lubricating oil from the rotating bearing parts, and then flow back to the oil groove oil level should be slightly lower than the center of the lowest rolling body.

B. Drop lubrication

Drop lubrication is suitable for bearing parts that require a fixed supply of lubricating oil. Drop of oil is generally recommended every 3-8 seconds. Excessive amount of oil will cause the bearing temperature to increase.

C. Circulation oil lubrication

Use oil pump to transfer the filtered oil to the bearing parts, and then use after filtering and cooling through the lubricating oil after bearing.Because the circulating oil can take away some heat and cool the inlet bearing, the method is suitable for bearing parts with high speed.

D. Spray lubrication

The dry compressed air is mixed with lubricating oil by the sprayer to form oil mist. The air flow can effectively cool the bearing and prevent the invasion of impurities.This method is suitable for lubrication of high speed and high temperature bearing components.

E. Jet lubrication

The high-pressure oil is injected into the bearing through the nozzle with an oil pump, and the oil injected into the inlet bearing flows into the oil groove through the other end of the bearing.When the bearing rotates at a high speed, the rolling body and the cage also make the surrounding air flow at a fairly high rotation speed. 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 into the bearing by high-pressure injection.

Solid lubrication

Used in some special conditions, adding a small amount of solid lubricant grease, such as adding 1 of 3-5% molybdenum disulphide can reduce wear and improve the compressive strength heat-resistant ability, for high temperature, high, high vacuum, corrosion resistance, resistance to radiation, and the special conditions such as extremely low temperatures, the solid lubricant in engineering plastics and powder metallurgy material, lubricating bearing parts can be made with, such as the solid lubricant with adhesive bonding on the raceway, cage and rolling body, lubrication film formation, has certain effects on reducing the friction and wear.

(VII) Supplement and replacement of lubricants

A. Time interval between grease replenishment

Due to mechanical action, aging and increased pollution, the lubricating base filled in the bearing configuration will gradually lose its lubricating properties.Therefore, the rank of lubrication should be constantly supplemented and updated.The interval between lubricants replenishment will vary with bearing formation, size, and speed, etc., and the approximate interval between lubricants replenishment will vary according to the running time.In addition, when the bearing temperature exceeds 70 ° C, every 15 ° C increase in the bearing temperature will reduce the interval between the use of grease by half.Double-sided sealing bearing has been loaded with grease when manufacturing, "HRB" is used in these products is the standard grease, the total operating temperature range and other properties suitable for the specified occasions, and the amount of grease and bearing size corresponding, grease service life can generally exceed the bearing life, except for special occasions, do not need to add grease.

B. Replacement cycle of lubricating oil

The replacement cycle of lubricating oil is different due to different service conditions and oil amount. Generally, it should be replaced once a year in a good environment with operating temperature below 50℃ and less dust. When the oil temperature reaches 100℃, it should be replaced once in 3 months or less.


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