Regular inspection of the hottest bearing

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Regular inspection of bearings

inspect the bearings removed during the regular maintenance of equipment, operation inspection and replacement of peripheral parts, so as to judge whether they can be reused or whether the use condition is good or bad. Carefully investigate and record the removed bearings and appearance. In order to clarify and investigate the residual amount of lubricant, clean the bearings well after sampling. Secondly, check the condition of the raceway surface, rolling surface and mating surface, as well as the wear state of the cage for damage and abnormalities

to judge whether the bearing can be used again, we should decide after considering the degree of bearing damage, machine performance, importance, operating conditions, inspection cycle, etc. According to the inspection results, if the bearing is damaged or abnormal, find out the cause and formulate countermeasures. In addition, according to the inspection results, if there are the following defects, the bearing can no longer be used and needs to be replaced with a new bearing

a. any one of the inner and outer rings, rolling elements and cages has cracks and debris

b. any one of the inner and outer rings and rolling elements has peeling

c. the raceway surface, retaining edge and rolling element are significantly jammed

d. the cage is seriously worn or the rivets are seriously loosened

e. the raceway surface and rolling element are rusty and scarred

f. there are significant indentations and scratches on the rolling surface and rolling body

g. there is creep on the inner diameter surface of the inner ring or the outer diameter of the outer ring

h. overheating and severe discoloration

i. the sealing ring and dust cover of the grease sealed bearing are seriously damaged

(1) inspection and troubleshooting during operation

the inspection items during operation include the rolling sound, vibration, temperature, lubrication state, etc. of the bearing, and the specific conditions are as follows:

I. rolling sound of the bearing

use a sound detector to check the size and sound quality of the rolling sound of the running bearing. Even if the bearing has slight peeling and other damage, it will also produce abnormal sound and irregular sound, which can be distinguished by a sound detector

II. Bearing vibration

bearing vibration is very sensitive to bearing damage, such as spalling, indentation, rust, cracks, wear, etc., which will be reflected in bearing vibration measurement. Therefore, the magnitude of vibration can be measured by using a special bearing vibration meter (frequency analyzer, etc.), and the specific abnormal situation can not be inferred by frequency division. The measured values vary according to the service conditions of the bearing or the installation position of the sensor, so it is necessary to analyze and compare the measured values of each machine in advance to determine the judgment standard

III. bearing temperature

the temperature of the bearing can generally be inferred from the temperature outside the bearing chamber. It is more suitable if the temperature of the outer ring of the bearing can be directly measured by using the oil hole. Usually, the temperature of the bearing starts to rise slowly with the operation and reaches a stable state after 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 parts are appropriate, the bearing temperature will rise sharply, and abnormal high temperature will occur. At this time, the operation must be stopped and necessary preventive measures must be taken

IV. lubrication

1. The role of bearing lubrication

lubrication has an important impact on the fatigue life, friction, wear, temperature rise, vibration, etc. of rolling bearings. Without normal lubrication, bearings cannot work. Analysis of the causes of bearing damage shows that about 40% of bearing damage is related to poor lubrication. Therefore, good lubrication of bearings is an effective measure to reduce the friction and wear of bearings

in addition, bearing lubrication has many functions, such as heat dissipation, rust prevention, sealing, mitigation of impact and so on. The function of bearing lubrication can be briefly described as follows:

a. an oil film is formed between the two rolling surfaces or sliding surfaces in contact with each other to separate the two surfaces and reduce the friction and wear of the contact surface

b. when using oil lubrication, especially when using circulating 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. when grease lubrication is used, it can prevent foreign matters such as external dust from entering the bearing and play a sealing role

d. lubricants can prevent metal corrosion

e. prolong the fatigue life of bearings

2. Comparison between grease lubrication and oil lubrication

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

3. Grease lubrication

grease is a lubricant composed of base oil, thickener and additives. When selecting, the lubricating grease that is very suitable for the service conditions of bearings should be selected. Due to different trademarks, there will be great differences in performance, so we must pay attention to it when selecting. The commonly used greases for bearings include calcium base grease, sodium base grease, calcium sodium base grease, lithium base grease, aluminum base grease and molybdenum disulfide grease. The amount of grease filled in the bearing should be 1//3 full of the internal space of the bearing. It should be reduced to 1/3 at high speed. Too much grease raises the temperature

4. Selection of lubricating grease

when selecting lubricating grease according to the working temperature, the main indicators should be the drop point, oxidation stability and low temperature performance. The drop point can generally be used to evaluate the high temperature performance, and the actual working temperature of the bearing should be lower than the drop point ℃. The service temperature of synthetic grease should be lower than the drop point ℃. When selecting grease according to bearing load, select grease with small penetration for heavy load. In addition to small penetration, it also has high oil film strength and extreme pressure performance when working under high pressure. When selecting grease according to environmental conditions, calcium based grease is not easily soluble in water and is suitable for dry and less moisture environments

v. oil lubrication

under the conditions of high speed and high temperature, oil lubrication can be used when grease lubrication is no longer suitable. Through the circulation of lubricating oil, a lot of heat can be taken away. Viscosity is an important characteristic of lubricating oil. The viscosity directly affects the fluidity of lubricating oil and the thickness of oil film formed between friction surfaces. The viscosity of lubricating oil at bearing working temperature is generally CST. The higher the speed, the lower the viscosity should be selected, and the heavier the load, the higher the viscosity should be selected. Commonly used lubricating oils include machine oil, high-speed machine 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, which is suitable for the lubrication of low and medium speed bearings. A part of the bearing is immersed in the groove, and the lubricating oil is carried by the rotating bearing parts, and then flows back to the oil groove. The oil surface should be slightly lower than the center of the lowest rolling element

b. oil dripping lubrication

oil dripping lubrication is suitable for bearing components that need a quantitative supply of lubricating oil. The amount of oil dripping is generally one drop per second. Excessive amount of oil will cause the bearing temperature to increase

c. circulating oil lubrication

use the oil pump to transfer the filtered oil to the bearing parts, and then use it after filtering and cooling the lubricating oil after passing through the bearing. Since the circulating oil can take away some heat and cool the bearing, this method is applicable to bearing components with high speed

d. spray lubrication

use dry compressed air to mix with lubricating oil through a spray to form an oil mist. In the spray bearing, the air flow can effectively cool the bearing and prevent the invasion of impurities. This method is suitable for the lubrication of high-speed and high-temperature bearing parts

e. spray lubrication

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

VI. solid lubrication

under some special conditions of use, a small amount of solid lubricant is added to the grease. For example, adding 3~5% molybdenum disulfide 1 can reduce wear and improve the compression and heat resistance. For special conditions such as high temperature, high pressure, high vacuum, corrosion resistance, radiation resistance, and extremely low temperature, adding solid lubricant to engineering plastics or powder metallurgy materials can make bearing parts with self-lubricating performance, If the solid lubricant is bonded to the raceway, cage and rolling element with adhesive to form a lubricating film, it has a certain effect on reducing friction and wear

VII. Supplement and replacement of lubricants

a. replenishment interval of lubricating grease

due to mechanical effects, aging and increased pollution, the lubricating base filled in the bearing configuration will gradually lose its lubricating performance. Therefore, the lubricating grease needs to be constantly supplemented and updated. The interval of lubricant replenishment varies with the formation, size and speed of the bearing, and the approximate interval of grease replenishment is required according to the operation time. In addition, when the bearing temperature exceeds 70 ℃, the replenishment interval of lubricating grease should be reduced by half for every 15 ℃ increase in the bearing temperature. The double-sided closed bearing has been filled with grease during manufacturing. HRB uses standard grease in these products. The common operating temperature range and other properties are suitable for the specified occasions, and the grease filling amount is also corresponding to the size of the bearing. The service life of the grease can generally exceed the service life of the bearing. Except for special occasions, there is no need to supplement grease

b. replacement cycle of lubricating oil

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

(2) shutdown inspection

it is very important to check the bearing seal regularly to maintain the bearing in the best condition. The most advantageous inspection time is to arrange regular downtime inspection period

importance of cleaning the shaft:

a. it is very important to keep the bearings and lubrication clean

b. clean the machine surface before inspection, and then disassemble the parts around the bearing

the oil seal is a very fragile part, so it needs to be carefully disassembled. Do not apply excessive force, and then carefully check the oil seal and its surrounding parts. If there are bad symptoms, be sure to replace it. The bad oil seal will lead to bearing damage and equipment shutdown in serious cases

c. check lubricant

rub a little lubricant between your fingers. If there are pollutants, you can feel them, or apply a thin layer of lubricant on the back of your hand, and then check

d. change the lubricant

after draining the old engine oil, fill in fresh engine oil and let the machine rotate at low speed for a few minutes if possible. Make the engine oil collect residual pollutants as much as possible, and then drain the engine oil. It is best to filter the engine oil before use. For grease lubricated bearings, the arbor used when replacing grease should avoid connecting the angle of cotton to any part of the bearing, because these residual fibers may wedge between the rolling parts and cause damage, especially for the application of small bearings

f. cover the exposed bearings

when checking the bearings, do not expose the bearings to pollutants or moisture. If the work is interrupted, cover the machine with oil paper, plastic sheet or similar materials

if it is possible to clean the naked bearing without disassembly, it should be stained with a brush for coating

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