The temperature of the motor bearing is too high. What is the maximum temperature that the bearing can withstand?

Motor bearing temperature is too high

1. Too little or too much lubricating oil or grease in the bearing will cause the bearing to heat up.

A proper amount of lubricating oil should always be maintained, and the oil-lubricated sliding bearing is used. The distance between the oil pool surface and the journal is generally 1/2 of the diameter of the journal, or the height of the pool surface is 1/6 of the diameter of the oil ring. ～l/40 Rolling bearings are lubricated with grease. Generally, when the shaft speed is less than 1 500r/min, the amount of grease should be 1/2 of the bearing space; when it is greater than 1 500r/min, the amount of grease should be 1/2 of the bearing space 3 or so.

2. Lubricating oil or grease has been used for too long, the oil is too dirty or has impurities, the viscosity or needle density is too large or too small, etc., which will cause the bearing to heat up.

The oil or grease used according to relevant regulations must meet the requirements, and must be replaced if it is dirty. Generally, the sliding bearing of the water pump uses No. 20 mechanical oil, and the rolling bearing uses calcium-based grease. The rolling bearings of the motor use sodium-based grease, and the two greases cannot be mixed, because if the sodium-based grease is used on the water pump, it will easily emulsify into foam and lose when it encounters water, while the calcium-based grease is used on the motor. High also drains.

3. The oil ring of the sliding bearing does not rotate or the rotation is not flexible, and the oil is not loaded or the amount of oil on the belt is insufficient, which will cause the bearing to heat up.

Note, check the oil ring frequently, and deal with any problems in time.

Sometimes, due to the damage of the water retaining ring on the shaft, the water enters the bearing oil pool along the shaft. Because the water is heavier than the oil, the water sinks into the lower part, so that the oil gradually leaks out and only water is left. The bearing cannot be lubricated by the oil and heats up. Such problems should be discovered in time during the patrol inspection and dealt with immediately.

4. Improper bearing installation, such as poor fit between the shaft and the bearing, excessive clearance, etc., will cause the bearing to heat up. After discovery, it should be repaired or replaced in time.

5. The bending of the pump shaft, the misalignment between the pump shaft and the motor shaft, and the vibration caused by the imbalance of the rotating part will generate additional force on the bearing and cause the bearing to heat up.

6. The balance plate and the balance ring are seriously worn, causing the pump to move axially to the suction side. When a certain value is reached, the bearing begins to bear axial force, causing the bearing to heat up and even be damaged.

Solution: Adjust the gasket at the end of the balance plate or replace the balance plate and balance ring, and replace the bearing.

Attachment 1. Reasons and solutions for excessive motor or bearing temperature

Motor bearing temperature too high:

1. The heat dissipation is not good, strengthen the ventilation, check the fan, and check whether the heat dissipation channel is blocked.

2. Bearing damage or grease content, replace the bearing, the oil content in the bearing chamber is 1/3 of the volume.

3. The room temperature is too high, strengthen the ventilation, and connect an external fan.

4. The current is too large and the load is too heavy. Check the three-phase voltage and current and adjust the load to check whether the load is overloaded or stuck.

5. The motor shaft and the equipment shaft are not concentric, and the height and level should be recalibrated.

6. The coupling is improperly matched and re-aligned.

Attachment 2. Reasons and solutions for higher motor bearing temperature

When the motor is running, the allowable temperature of the outer ring of the bearing should not exceed 95°C. If it exceeds this value, the temperature of the motor bearing is too high, also known as the motor bearing heating.

Bearing heating is one of the most common faults in electric motors.

If it is light, the lubricating grease will be diluted and leaked, and if it is heavy, the bearing will be damaged, causing economic losses to the user. Today, the causes and treatment methods of bearing (NSK bearing) heating are briefly introduced as follows.

1. If the bearing of the running motor is damaged, it may cause the motor bearing to overheat. The balls of the bearings or the bushings of the ball bearings should be inspected for damage and repaired or replaced if damaged.

2. When replacing the grease, if hard particles are mixed in or the bearing is not cleaned cleanly, it will cause the bearing to wear and overheat, and may even damage the bearing. After cleaning the bearing and bearing end cover, replace the grease again, and fill the grease chamber to 2/3.

3. The bearing chamber is short of oil. The motor bearing runs without oil for a long time, and the friction loss is aggravated, which makes the bearing overheat. For regular maintenance, lubricating grease should be added to fill 2/3 of the oil chamber or lubricating oil to the standard oil surface line, so as to avoid the motor bearing running without oil.

4. The grade of grease is wrong. Replace with the correct type of grease as soon as possible. Generally, No. 3 lithium-based grease or No. 3 complex calcium-based grease should be used.

5. There is too much grease blockage in the rolling bearing, and the excessive grease in the rolling bearing should be removed. -- Home of Electrical Technology

6. The grease has impurities, is too dirty, too thick or the oil ring is stuck. The lubricating grease should be replaced, the cause of the jam should be found out and repaired, and the lubricating grease should be replaced when the oil viscosity is too high.

7. The bearing and shaft, bearing and end cover are too loose or too tight. Too tight will cause the bearing to deform, and too loose will easily cause "running". If the fit between the bearing and the shaft is too loose, the journal can be painted with metal paint or the end cover can be inlaid, and if it is too tight, it should be reprocessed.

8. The belt is too tight, too loose, the coupling is poorly assembled, or the center of the motor and the driven mechanical shaft are not on the same straight line, which increases the bearing load and generates heat. The tightness of the belt should be adjusted; the coupling should be corrected.

9. Due to improper assembly, the tightness of the fixed end cover screws is inconsistent, resulting in the centers of the two shafts not being in a straight line or the outer ring of the bearing being unbalanced, making the bearing rotation inflexible, and the friction is aggravated after being loaded to generate heat, so it should be reassembled. Motor bearing temperature

10. The end caps or bearing caps of the motor are not assembled properly, usually not parallel, causing the bearings to not be in the correct position. Fit the end caps or bearing caps flat, and tighten the bolts.

11. If the wrong type of bearing is replaced during maintenance, the bearing of the correct type should be replaced as soon as possible. -- electrician

12. The quality of the bearing is poor, such as some steel balls are not round, the inner and outer rings of the bearing are corroded, etc., the bearing should be adjusted or replaced (NSK bearing).

13. When the motor vibrates too much, it will cause the motor bearings to wear more and cause the bearings to overheat.

Reasons for excessive vibration of the motor: low strength of the casing or foundation; uneven foundation or loose fixing screws; excessive bearing clearance;

The rotor is unbalanced or the shaft is bent; the iron core is deformed or loose; the stator core is not pressed tightly; the fan is unbalanced; the transmission device is bad; the mechanical load vibrates, etc.

Approach:

Reinforcement; use a level to measure whether the foundation is level, visually inspect whether the installation angle of the motor is suitable for the dragged machinery, and check whether the base or other fixing screws are loose;

Overhaul the bearing and replace it if necessary; correct the dynamic balance of the rotor and straighten the shaft; correct the overlapping iron core; check the iron core and re-tighten it;

Overhaul the fan, correct balance, correct its geometry; overhaul the transmission; find out the cause of mechanical load vibration and eliminate it.

14. When the rotating part of the motor rubs against the stationary part, the bearing will be eccentrically worn, and the load will also increase at the same time, causing the bearing to overheat.

The main reasons for the collision between the stator and rotor of the motor are: the bearing is seriously damaged; the shaft and iron core are bent; the end cover of the motor is worn, etc. There is still an upward trend, and the high temperature resistant grease is added, and the temperature rises to 102 degrees and then drops to normal temperature.

The highest temperature the bearing can withstand

The standard stipulates that the working temperature of the rolling bearings of small and medium-sized motors should not be higher than 95°C. What is the highest temperature the bearing can actually withstand? This is mainly limited by the heat resistance temperature of the bearing steel, cage, sealing material, and lubricant.

Dimensional stability temperature of heat treatment of bearing steel

For ordinary bearing steel, there is a stable temperature for heat treatment. Below this temperature, the bearing maintains dimensional stability, and the hardness of the bearing steel material also meets the requirements for use. The heat treatment stabilization temperature of general bearings is 150°C. The heat treatment stability temperature of the specific bearings of each manufacturer will be different.

FAG:

150°C for bearings with an outer diameter <240mm;

200°C for bearings with an outer diameter ≥ 240mm;

Other bearings are identified with a suffix.

SKF:

120°C for deep groove ball bearings;

150°C for cylindrical roller bearings;

200°C for spherical roller bearings.

Bearing cage temperature range

Usually steel or brass cages can withstand a relatively large temperature range. The heat-resistant temperature of steel cages can reach 300 ° C, and brass cages can reach 250 ° C. However, for nylon cages, they can generally withstand -40 ~ +120 °C temperature range.

Seal temperature range

For enclosed bearings, shields made of metallic materials, no special consideration of the temperature range is required. For rubber material seals, it needs to be considered.

The working temperature range of nitrile rubber (NBR) is -40～+120℃, it can work stably within 100℃, and work at 120℃ for a short time;

For fluorine rubber (FKM), it can work stably at -30~+200°C, and work at 230°C for a short time.

Permissible temperature range of bearing grease

Temperature is one of the most important factors affecting lubrication life.

Grease base oil viscosity decreases as temperature increases. Based on the grease life calculated at 70°C, the grease life will be reduced by half for every 15°C increase in operating temperature.

The allowable working temperature of the motor bearings should be the intersection of the allowable temperature ranges of the various components of the bearing (the narrowest range). Only in this range can the safe operation of the bearing be guaranteed. Therefore, whether a bearing can operate in a high temperature environment mainly depends on the choice of lubricant, followed by the bearing sealing material (only for closed bearings) and cage, and finally the bearing steel.

In actual application, the temperature generally measured is the temperature near the outer ring of the bearing, and the difference between different measurement methods and locations can be up to 15°C. Generally, the heat dissipation condition of the bearing seat is better than that of the shaft, so the temperature of the inner ring and rolling elements is 5~10°C higher than that of the outer ring.

Therefore, when the test location is outside the bearing chamber, if the measured temperature is 95°C, the hottest point temperature of the inner ring may reach 120°C. It has reached the stable heat-resistant temperature of nylon cage, imported deep groove ball bearing steel and grease.