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The bearing end cap structure is widely used in small and medium-sized motors. The assembly structure, installation accuracy and lubrication system directly affect the system reliability and operation efficiency.
In order to compensate for the Medium-Sized Motors inconsistency of axial expansion length caused by temperature change of moving and stationary parts, the driving end and non driving end are always fixed at one end and floating at the other end.
About motor bearing selection and bearing system
The air gap of the motor is very small and the uniformity requirement is high, so the rolling bearing should be used. Rolling bearings have small Medium-Sized Motors radial clearance, low friction loss, short axial dimension and simple lubrication and maintenance;
Its disadvantages are high noise during operation and poor performance of bearing impact load. For motors of H315 and above specifications, ball bearings are used at the non shaft extension end, which can not only bear radial load, but also bear certain axial load, so as to keep the rotor in the expected axial position and play the role of axial positioning;
Column bearing is generally used at the shaft extension end to bear large radial load; For small size motors and all 2p small and medium-sized Medium-Sized Motors motors, ball bearings are used at both ends, but only one bearing can be used for axial positioning.
Rolling bearings must be equipped with protective devices for storing Medium-Sized Motors lubricating grease and preventing dust infiltration.
Sealed bearings are often used in small-size motors. It is characterized by no inner bearing cover and hot sleeve on the shaft with oil retaining ring, which is convenient for assembly; The bearing outer cover and the end cover are integrated, which can save the outer cover and the screws for installing the outer cover, but the processing cost of the end cover is high.
The outer side of the bearing at the transmission end of the small motor is sometimes equipped with a wave spring plate to press the outer ring of the bearing, so as to reduce the axial working clearance of the bearing and reduce the vibration and noise during motor operation. In order to reduce noise, special low-noise bearings for motors can also be used.
For motors with larger specifications, there are oil retaining grooves on the inner and outer covers of bearings to prevent dust infiltration or grease leakage. If the column bearing Medium-Sized Motors assembly structure is adopted at one end of the motor, the bearing covers at both ends can be close to the outer ring of the bearing.
If the ball bearings are adopted at both ends of the motor, an appropriate gap shall be reserved between the Medium-Sized Motors outer bearing cover and the outer ring of the bearing to compensate for the error of the axial dimension chain of the motor and the hot tight and cold shrink dimension of the shaft.
For large motors, a bearing sleeve is added to the bearing system. When the motor is disassembled, the Medium-Sized Motors bearing can be protected from contamination or damage; However, the manufacturing cost of such a structure is high.
Due to the increasing level of Medium-Sized Motors production automation, the equipped motor is required to operate without maintenance. The bearing is the weak link in the motor. At present, most small motors use closed rolling bearings.
After the bearing is filled with oil, it is no longer necessary to supplement grease. The bearings produced by Medium-Sized Motors regular manufacturers can generally operate continuously for more than two years. The bearing assembly structure of non-stop refueling is adopted for medium-sized motors.
Generally, the new grease is added to the bearing inner cover oil chamber, and the old grease residue is pressed into the outer bearing chamber and then collected in a container that is easy to take out. The effect of this oil filling device is much better than that of the oil filling device from the bearing outer cover.
The lubricating grease used in rolling bearings is composed of lubricant and thickener, and also contains a certain amount of glue solvent and additives. Lubricant is the main body of lubrication, mainly mineral oil, such as spindle oil, cylinder oil, etc.
In addition to thickening, thickeners also have certain lubricating effects, mainly fatty acid salts (soap base), such as calcium soap, sodium soap, etc. Glue solvent is used to improve the dissolution state between soap base and oil body. Additives such as graphite and molybdenum disulfide can improve the properties of grease.
(1) Drop point. That is, the temperature when the grease starts to drip after heating, which indicates the heat resistance of the grease. The high working temperature of various greases shall be 20 ~ 30 ℃ lower than its drip point,
(2) Penetration. At a certain temperature, the penetration of the grease is the depth that a conical hammer of a certain weight falls into the grease for 5 seconds, which indicates the viscosity of the grease.
If the needle penetration is too small, it indicates that the grease is too hard and it is not easy to completely fill the friction surface; If the needle penetration is too large, the lubricating grease is too soft and oil leakage is easy to occur. When selecting lubricating grease, the service conditions,
such as environmental conditions, working temperature, motor speed, etc., shall be considered. When the ambient humidity is high, the grease with strong water resistance shall be selected.
When the bearing speed is very high, the grease with thin consistency shall be selected to avoid large friction loss in the grease at high speed, which will increase the bearing temperature rise and reduce the motor efficiency.
Common grease types
(1) Calcium sodium base grease. The thickener is a mixture of calcium soap and sodium soap. The dropping point is 120 ~ 130 ℃, the penetration is 200 ~ 290mm,
and the water resistance is weaker than that of calcium based grease. It is allowed to work in the environment with steam or humidity. The working temperature is 80 ~ 100 ℃, which is not suitable for too low temperature.
(2) Compound calcium base grease. It is composed of calcium soap, compound agent and lubricating oil. The dropping point is 180 ~ 220 ℃ and the penetration is 210 ~ 350 mm. It has moisture resistance and high temperature resistance. It can be used at 150 ~ 200 ℃.
(3) Molybdenum disulfide compound calcium base grease. It is made of compound calcium base grease and molybdenum disulfide. It can resist high temperature and humidity, and has strong compression resistance. It is suitable for places with high temperature load.
(4) Lithium grease. Using lithium soap as thickener, dropping point 165 ~ 190 ℃, penetration 202 ~ 380 mm; It is characterized by cold resistance, heat resistance, water resistance and good chemical stability. It can be used in low temperature and environment with large temperature variation range.
Bearing installation
When installing the bearing, the bearing must be cleaned first. New bearings are coated with antirust oil and often contain a small amount of iron, ash and other sundries; When it is not cleaned, it is strictly prohibited to rotate by hand to avoid scratching the roller and raceway surface.
Cleaning method: immerse the bearing in No. 2 spindle oil at 90 ~ 120 ℃ for 5 ~ 10 minutes, swing slightly, take out the drip dry antirust oil, immerse it in gasoline for several times, take it out and blow dry with compressed air. Poor cleaning is one of the main reasons for bearing heating and noise.
There are two methods to install the bearing on the shaft: cold pressing and hot sleeve. Cold pressing is only used for small power motors, and the hot sleeve method is generally used. The heating tank is filled with engine oil or transformer oil, and the oil temperature is maintained at 90 ~ 100 ℃.
Put the cleaned bearing into the oil and heat it for about 20 minutes. After taking it out, heat it on the journal. The heating temperature should not be too high and the heating time should not be too long, so as to avoid tempering of the bearing, reducing the hardness and affecting the service life.
When the bearing is hot jacketed, the inner cover of the bearing shall be put on first and the journal and shoulder shall be wiped clean. Burr, paint skin or dust are not allowed. The heated bearing must be pushed close to the shoulder;
If the sleeve is not in place, use the sleeve to counter the inner ring of the bearing and tap it in place with a hammer. It is strictly prohibited to directly tap the bearing. The hot sleeve can be carried out before and after the rotor is sleeved into the stator.
After the bearing is installed, fill the gap between the inner and outer rings of the bearing with grease, and the gap in the bearing cover is only 1 / 3 ~ 2 / 3, which should not be too full. Excessive grease or unclean grease often causes bearing heating and oil leakage.
When the bearing is removed, it must be pulled down smoothly with a bearing pulling tool. The splint shoulder of the tool must be against the inner ring, adjust the pull rod nut to make the force around uniform, and then rotate the ejector screw to pull out the bearing.