How to use and maintain rolling bearings
In our daily life, rolling bearings can be used on objects, tools, toys, and household appliances that can be rotated. What do we need to pay attention to when using bearings. This article mainly describes how to properly use and maintain the bearing.
Precautions forbearing use
Rolling bearings are precision parts. When installing and disassembling, they should be carefully operated according to the relevant steps and regulations. Special tools should be used as much as possible.
Strong impact or direct hammering of the bearing is not allowed, and pressure is not allowed to be transmitted through the rolling elements. The installation environment must be clean, and the bearing cannot be wiped with items such as cloth and fibers.
The quality of bearing installation is related to the service life and working characteristics of the bearing. Improper installation may lead to premature bearing damage.
Keep the bearing and its surroundings clean
Even small dust that cannot be seen by the eye can have adverse effects on the bearing. Therefore, it is necessary to keep the surrounding environment clean, so that no dust penetrates into the bearing during use.
A strong impact will cause scars and indentations on the bearing. In severe cases, the bearing will crack and break, which often becomes the cause of the accident. Proper installation tools must be used to avoid damage to the bearing.
Avoid bearing corrosion
It is best to wear work gloves when installing bearings because that sweat on your hands can cause rust.
Bearings are coated with an appropriate amount of anti-rust oil before leaving the factory and packed with anti-rust paper. As long as the packaging is not damaged, its quality will be guaranteed.
However, when stored for a long time, it should be stored on a shelf 30cm above the ground under conditions of humidity lower than 65% and temperature of about 20C.
In addition, the storage place should avoid direct sunlight or contact with cold walls. If the storage environment is suitable and the packaging is intact, it can be stored for several years.
Whether the installation is correct or not directly affects the bearing accuracy, life and performance. The design and assembly department should fully study the bearing installation. It should be installed in accordance with correct and scientific operating standards.
The workflow can refer to the following:
★ Cleaning of bearings and associated parts
★ Check the dimensions of the associated parts and their accuracy
★ Installation work
★ Post-installation checks
★ supply lubricant
Only unpack the bearing when it is necessary to install the bearing. Generally, grease-lubricated bearings do not need cleaning. Lubricating oil does not need to be cleaned on general use occasions.
For instruments or high-speed bearings, it should be washed with clean oil to remove the anti-rust oil applied to the bearings. Bearings with rust inhibitors removed are prone to rust, so they should not be left for too long. For closed bearings, they can be used directly without cleaning.
Different types of bearing installations
The installation method of the bearing varies depending on the bearing structure, fit and conditions. If the shaft rotates, the inner ring should have an interference fit. Cylindrical bore bearings are usually pressed in by a press, or by shrinking.
Tapered bore bearings, mounted directly on a tapered shaft or with a sleeve. When mounted to the housing, a clearance fit is generally used. When there is interference in the outer ring, it is usually pressed in with a press or shrink fit. If ice is used as the coolant, the moisture in the air will condense on the surface of the bearing in the case of shrink fit installation. Therefore, it is necessary to take appropriate anti-rust measures.
Installation of cylindrical bore bearings
☀ Press in
Small bearings can be installed using the press method. As shown in the figure below, place the spacer on the end face of the inner ring, and use a press to slowly press the inner ring until it tightly contacts the shaft shoulder. Pressing the outer ring to install the inner ring will cause indentation and crushing of the raceway, which is absolutely prohibited.
When installing, it is best to apply oil to the mating surface. If installing with a hammer, put a spacer on the inner ring. However, this installation method is easy to cause bearing damage and is only used in the case of small interference, not for large or small and medium-sized bearings.
For non-separable bearings (such as deep groove ball bearings), the inner and outer rings need to be installed with interference as shown in the figure below. After the end faces of the inner and outer rings are placed with spacers at the same time, the inner and outer rings are pressed in at the same time. The outer ring of the self-aligning ball bearing is easy to tilt, even if it is not an interference fit, it should be installed with a spacer.
For separable bearings (such as cylindrical roller bearings, tapered roller bearings), the inner and outer rings can be installed on the shaft and housing holes respectively. When combining the separately installed inner ring and outer ring, pay attention to stably closing the two to prevent the centre from deviating.
☀ Hot pack
Large bearings require a lot of force to be pressed in, so they are difficult to press in. Therefore, the shrink-fit method in which the bearing is heated in an oil tank or an oven to expand and then mounted on the shaft is widely used.
Using this method, the operation can be completed in a short time without adding additional load to the bearing. The heating temperature of the bearing is determined by the bearing size, the required interference and other parameters. Notes are as follows:
Under normal circumstances, the heating temperature of the bearing (80C ~ 9(TC) but the maximum should not exceed 100°C, the temperature is too high will cause seal deformation, secondary tempering of parts, grease leakage and other undesirable situations.
When the bearing is heated, it is best to place the bearing on the metal mesh table or hang the bearing, and heat the bearing to 20°C~30°C higher than the required temperature to prevent the inner ring from cooling and shrinking during operation, which is difficult to install.
After installation, the bearing cools down and shrinks in the width direction, so use a shaft nut or other suitable method to tighten it to prevent a gap between the inner ring and the shaft shoulder.
In addition to the oil heating method, electromagnetic induction heating or oven heating methods are also widely used.
Induction heating device, a built-in excitation coil, after electrification, due to the effect of electromagnetic induction, the bearing heated by the current drive generates heat due to the resistance of the bearing itself. Therefore, it can be heated uniformly in a short time. Shrink-fit operation of bearings is efficient and pollution-free.
In the occasions where installation and disassembly are frequent, such as cylindrical roller bearings for spoke necks of rolling mills and axles of railway vehicles, special induction heating devices can be used to install and remove the inner ring.
Installation of tapered bore bearings
The tapered bore bearing is to directly fix the inner ring to the tapered shaft or install it on the cylindrical shaft with an adapter sleeve and a dismounting cylinder, as shown in the figure below.
Large self-aligning bearings are installed with hydraulic pressure. Install the self-aligning bearing while checking the reduction in radial clearance.
As the size of the bearing increases, due to the elliptical deformation of the outer ring due to its own weight when the bearing is installed on the shaft, if the clearance is measured at the lowest part of the deformed bearing, the measured value will be larger than the actual clearance. The backlash will cause too much interference or too little actual remaining clearance.
When installing the self-aligning ball bearing sleeve on the shaft, make sure that the outer ring can be freely aligned, and the clearance after installation should not be too small.
After the bearing is installed, the small machine can be rotated by hand to check whether it rotates flexibly, and check whether there is any poor operation caused by foreign objects, scratches, indentations, and excessive rotational torque caused by poor installation and poor machining of the mounting seat. If there is no abnormality, the loading operation can be started.
Large machinery cannot be rotated manually. Turn off the power immediately after starting with no load, perform inertial rotation, and check whether there is abnormal vibration before determining whether to enter the power operation.
Power operation, starting at low speed with no load and slowly increasing to-rated condition operation. Temperature rise during a test run, lubricant leakage and discolouration, etc. If any abnormality is found during the test run, the operation should be stopped immediately, the machinery should be checked, and if necessary, the bearing should be removed for inspection.
The bearing temperature is generally inferred from the appearance of the housing. Using the oil hole, it is more accurate to directly measure the temperature of the bearing outer ring. The bearing temperature gradually rises from the start of the operation, and usually stabilizes after 1 to 2 hours.
Due to poor bearing or installation, the bearing temperature will rise sharply, resulting in abnormally high temperature. The reasons are such as too much lubricant, too small bearing clearance, poor installation, improper selection of bearing structure and lubrication method, etc.
The rotating sound of the bearing can be detected by a sound detector. If there is a loud metal sound, abnormal sound, irregular sound, etc., it means that the operation is abnormal. Causes include poor lubrication, poor shaft housing accuracy, damage to bearings, and intrusion of foreign matter. The following list gives specific countermeasures for the reasons for the abnormal running state of the bearing. In case of special circumstances, please contact us.
|Running state||Detection reason||Countermeasures|
|Abnormal sound||Abnormal load||Correct fit, bearing clearance, adjust preload, correct housing shoulder position|
|Bad installation||The machining accuracy of shaft and housing, improving installation accuracy and method|
|Inappropriate lubricant||Supplementary lubricant, choose the appropriate lubricant|
|Rotating parts are in contact||Modify the contact part of the seal|
|Indentation, rust, scratches due to foreign matter on the rolling surface||Replace bearings, clean parts, improve seals, use clean lubricants|
|(after carburizing of steel) surface deformation||Replace bearings|
|Raceway surface fracture||Replace bearings|
|Excessive clearance||Study fit and bearing clearance, modify preload|
|Foreign body intrusion||Replace bearings, clean parts, improve seals, use clean lubricants|
|Steel ball injury||Replace bearings|
|Abnormal temperature rise||Too much grease||Drain the excess grease before running|
|Insufficient grease, unsuitable||Supplementary grease, select appropriate grease|
|Abnormal load||Modify fits, study bearing clearance, adjust preload, modify shoulder position|
|Bad installation||Improve shaft, housing, machining accuracy, installation accuracy, and installation method|
|Creep of the mating surface, excessive friction of the sealing device||Replace bearings, study fits, modify shafts, housings, change seal forms|
|Vibration (shaft runout)||(after carburizing of steel) surface deformation||Replace the bearing, pay attention to the operation|
|Bad installation||Improve the accuracy of bearing housing and amend the installation method|
|Foreign body intrusion||Replace bearings, clean related parts, improve seals|
|Lubricant leakage and discolouration||Excessive lubricant, foreign matter intrusion, generation of friction powder, etc.||Appropriate use of lubricants, research and replacement of lubricants, research on replacement of bearings, and cleaning of housings|
|Occurs during sudden acceleration and deceleration (starting or stopping)||Mechanical resonance||Increase the rigidity of the shaft|