The bearing of stepping motor is the connecting device between the static part and the rotating part of the motor, which not only affects the operation of the motor, but also affects the service life of the motor. Thus affecting the product quality of the motor, so we should pay attention to daily use and maintenance.
1. Analysis of common faults of needle roller bearing
Needle roller bearing has small friction resistance, high mechanical efficiency, convenient lubrication and maintenance, and has been standardized and widely used in stepping motor. Common faults of needle roller bearing are as follows.
1.1 bearing temperature is too high
When touching the small tile cover or bearing cover seat by hand during the operation of the stepping motor, it is normal to feel no hot hand, otherwise it indicates that the bearing temperature is too high. The causes of excessive bearing temperature are:
(1) The quality of lubricating grease does not meet the requirements or deteriorates, the viscosity is too high, and there is too much grease. The motor shall not be added too much or too little, generally accounting for about 1 / 3 ~ 1 / 2 of the bearing seat. Bearings with low speed and light load can be added a little more; Bearings with high speed and load should be added less.
(2) Improper assembly of needle roller bearing, new shaft replacement or reprocessing, no tool return groove between journal and bearing gear, or improper machining size of journal, resulting in improper installation of bearing. If the bearing clearance is too small, the friction loss of scissors due to oil flow in the clearance is too large, which will also cause bearing heating; At the same time, if the clearance is too small, the oil volume will be reduced, and there is no time to take away the heat generated by friction, which will further improve the temperature rise of the bearing. However, excessive clearance will change the dynamic characteristics of the bearing and cause unstable rotor operation. Therefore, it is necessary to select the appropriate bearing clearance for different equipment and service conditions. Adjust the assembly process. If it is unqualified, reassemble it after secondary processing on the upper bed.
(3) Bearing running sleeve. There are two kinds of bearing running sleeves. One is the running sleeve, that is, there is relative displacement between the bearing outer ring and the bearing chamber; The other is running the inner sleeve, that is, there is relative displacement between the bearing inner ring and the journal. When the bearing runs out of the sleeve, it will be heated and accompanied by a "squeak" sound. The treatment method can be relaxed, or disassembled, reprocessed and replaced.
(4) Needle roller bearing is short of oil. The motor makes a continuous and uniform "buzzing" sound during normal operation. If the running motor bearing makes a "grunting" sound and intermittent whistling, it indicates that the bearing is lack of grease. At this time, the oil gun should be used to inject oil into the bearing through the bearing oil filling hole; For the rear bearing, wait until it is shut down and add oil.
(5) The needle roller bearing is damaged in the following 7 cases:
① Metal peeling on raceway surface. The bearing rolling element and the inner and outer race are subjected to periodic fluctuating load, resulting in periodic contact stress. When the number of stress cycles reaches a certain value, fatigue spalling occurs on the working surface of rolling element or inner and outer race raceway. If the bearing load is too large, it will aggravate fatigue. In addition, improper bearing installation, shaft bending, non concentricity of motor shaft and mechanical shaft will also produce raceway peeling. The fatigue spalling of bearing raceway will reduce the running accuracy of shaft and cause vibration and noise of mechanism.
Bearing burns.
Plastic deformation
Bearing race crack
Broken cage
The metal of the holder adheres to the rolling element
Serious wear of race race
1.2 bearing noise
The needle roller bearing is allowed to make slight running noise during operation. If the noise is too loud or there is abnormal noise or impact sound, it indicates that the bearing is faulty. The fault part of needle roller bearing is not used, and the sound is also different; The stepping motor in operation emits a uniform and periodic "click" sound in the continuous "buzz", indicating that there are scars, grooves, corrosion, etc. on the rolling body and inner and outer raceways; When the bearing makes an irregular "click" sound, it indicates that there are impurities such as iron filings or small sand particles in the bearing; When the bearing makes a discontinuous "stem" sound, it may be caused by the fracture of the bearing outer ring and the fracture of the cargo cage; When the bearing makes a periodic "squeaking" sound, it indicates that the bearing runs away from the outer sleeve; When the bearing makes a "grunt" sound and intermittent whistling, it indicates that the bearing is lack of grease.
When the stepping motor makes the above sound, it shall be shut down for maintenance and sent to the manufacturer to check whether the front and rear bearings operate stably and whether there is noise; Then use a flashlight to check whether the cage, groove and inner and outer rings have cracks, scars, corrosion, etc. When there is noise or jamming when the bearing rotates, it should be considered to replace the bearing.
Bearing is not only the key component of stepping motor, but also the vulnerable component. The normal operation of the bearing is related to the smooth operation of the stepping motor. The bearing itself and various external factors often affect the normal operation of the bearing, which makes the fault diagnosis of the bearing complex. Combined with the maintenance practice, this paper analyzes the common faults and treatment methods of stepping motor bearing, uses the simple and practical listening and touching method to detect the running state of bearing, and puts forward the corresponding measures to prevent its damage.