Precautions for installing and removing bearings

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The items of the work standard are usually as follows: (1) Cleaning the bearings and bearing-related parts; (2) Checking the dimensions and finish of the related components; (3) Installation; (4) Inspection after the bearings are installed; (5) Applying lubricant. It is recommended to open the bearing packaging only just before installation. It is generally lubricated with grease; no cleaning is required, and the grease is simply filled in. Lubricated with lubricating oil, it generally does not need to be cleaned. However, for bearings used in instruments or at high speeds, they must be cleaned with clean oil to remove the rust inhibitors applied to them. Bearings without rust inhibitors are prone to rusting, so they cannot be left unattended. Furthermore, shafts already filled with grease are used directly without cleaning. The method of installing bearings varies depending on factors such as the bearing’s structure and fit. Generally, since rotation around an axis is common, the inner ring requires an interference fit. Cylindrical hole bearings are usually pressed in using a press or installed by thermal methods. In the case of tapered holes, it can be installed directly on a tapered shaft or using a sleeve. When installing it into the housing, a clearance fit is generally used, with an interference fit on the outer ring; it is usually pressed in using a press, or a cold shrinkage fit method after cooling may also be employed. When dry ice is used as a coolant in applications involving cold shrinkage fitting, moisture in the air will condense on the surface of the bearings. Therefore, appropriate rust prevention measures are needed. Installing bearings generally requires the use of specialized tools such as bearing heaters. Installation of cylindrical hole bearings: (1) Press-fitting method – The press-fitting method is widely used for small bearings. Place the shims inside the inner ring, and then use a press to gently apply pressure until the inner ring makes firm contact with the shaft shoulder. Installing the inner ring with a shimming block under the outer ring is the cause of indentations and damage on the raceway, so it must be strictly prohibited. When operating, it is best to apply oil to the mating surfaces in advance. In cases where it is absolutely necessary to use a hammer for installation, a cushion block must be placed on the inner ring during the operation. This practice often becomes the cause of bearing failures; therefore, it is only suitable for cases with a small amount of interference and cannot be used for situations with a large amount of interference, or for medium and large-sized bearings. In the case of non-separable bearings such as deep groove ball bearings, where both the inner ring and the outer ring need to be installed with an interference fit, shims are used, and the inner ring and outer ring are pressed together simultaneously using screws or hydraulic pressure. The outer ring of a self-aligning ball bearing is inclined; even if it is not a tight fit, it is advisable to use shims when installing it. For split-type bearings such as cylindrical roller bearings and tapered roller bearings, the inner ring and the outer ring can be installed on the shaft and the housing respectively. When combining the separately installed inner ring and outer ring, it is crucial to bring them together firmly so as to prevent any deviation in their centers; forcing them together too much can cause damage to the raceway surfaces. (2) Hot fitting method: For large bearings, a great deal of force is required to press them in, making it difficult to do so. Therefore, the hot mounting method, in which the bearing is heated in oil to cause it to expand and then installed on the shaft, is widely used. Using this method, the task can be completed in a short time without applying undue force to the bearings. The heating temperature of the bearing is determined based on the bearing size and the required interference. Precautions regarding hot mounting are as follows: (a) Do not heat the bearing above 120°C ； (b) To prevent the bearing from making direct contact with the bottom of the oil sump, it is advisable to consider placing the bearing on a metal mesh platform or lifting it up ； (c) Heat the bearing to 20°C–30°C higher than the required temperature, so that the inner ring does not cool down during operation, thereby avoiding installation difficulties ； (d) After installation, the bearing cools down and contracts in the width direction; therefore, a shaft nut or some other appropriate method must be used to secure it, in order to prevent a gap from forming between the inner ring and the bearing shoulder. 2. Installation of tapered bore bearings: Tapered bore bearings fix the inner ring to a tapered shaft by means of an interference fit, or they are mounted on cylindrical shafts using set screws or removal sleeves. Large self-aligning bearings are usually installed using hydraulic pressure. 3. Operation check: After the installation is completed, an operation check is necessary to verify that the installation was done correctly. For small machinery, it can be rotated by hand to confirm that it turns smoothly. The inspection items include poor operation caused by foreign objects, scars, or indentations; uneven rotational torque resulting from improper installation or defective manufacturing of the mounting base; high torque due to excessive play, installation errors, or sealing friction. If there are no abnormalities, power can be started at speed N. Since large machinery cannot be rotated manually, the power is turned off immediately after starting without load to allow it to rotate under inertia, during which time vibrations, noises, and any contact between rotating parts are checked. Once no abnormalities are detected, the machinery is brought back online with power applied. The machine is started up at no-load low speed, gradually increasing to the rated operating speed under specified conditions. During the trial run, it is necessary to check for any abnormal noises, changes in bearing temperature, leakage of lubricant, and discoloration, among other things. If any abnormalities are detected during the trial run, operation should be stopped immediately, the machinery inspected, and the bearings removed for inspection if necessary. Bearing temperature can generally be estimated from the exterior of the housing. However, by using oil holes to directly measure the temperature of the outer ring of the bearing, the measurement is more accurate. The bearing temperature begins to rise as operation starts; if there are no abnormalities, it usually stabilizes after 1 to 2 hours. If there are issues with the bearings or their installation, the bearing temperature can rise sharply, resulting in abnormally high temperatures. The reasons include excessive lubricant, too small a bearing clearance, improper installation, and excessive friction in the sealing mechanism. In cases of high-speed rotation, incorrect selection of the bearing lubrication method is also a cause. The disassembly of rolling bearings is one of the important tasks in mechanical maintenance. Disassembly must follow the basic rules for removing and installing bearings, and different disassembly tools and methods should be used depending on the type of bearing. When the bearing has a tight fit with the shaft and a looser fit with the housing bore, the bearing and shaft can be removed together from the housing, after which the bearing can be detached from the shaft using a press or other removal tools. Next, I will introduce several common bearing removal methods: 1. Removal of the inner/outer rings – To remove an outer ring that is in an interference fit, several screw bolts for squeezing the outer ring are installed around the circumference of the housing. The bolts are tightened evenly while the ring is removed. These screw holes are usually covered with plug plugs. For split bearings such as tapered roller bearings, several cuts are made on the housing shoulder; shims are used, and they can be removed using a press or by gently tapping them. 2. Removing cylindrical hole bearings is simplest by using a press. At this point, care must be taken to ensure that the inner ring bears its pulling force. The inner ring of large bearings is removed using a hydraulic method. Oil pressure is applied through oil holes provided on the shaft to facilitate drawing. For bearings with a large width, both the hydraulic method and pulling fixtures must be used in order to remove them. The inner ring of NU and NJ type cylindrical roller bearings can be removed using induction heating. A method that involves heating a specific area for a short period to cause the inner ring to expand, followed by drawing. 3. Disassembly of tapered bore bearings: For disassembling smaller bearings with set screws, use a stop block fixed to the shaft to support the inner ring; turn the nut a few times, then use shims and a hammer to carry out the disassembly. A method for large bearings, where removal is made easier using hydraulic pressure; oil is pressurized and sent into the oil holes on the tapered-shaft to expand the inner ring and thus remove the bearing. During operation, there is a risk of bearings suddenly coming loose; it is best to use nuts as stoppers. 4. Breaking off method: Breaking off is the simplest and most common method of disassembly. It is a disassembly method that uses the force of hammering to cause the mating parts to shift and separate from each other, thereby achieving disassembly. The common tools used for demolition are a hand hammer, namely a regular blacksmith’s hand hammer, a punch, and a cushion block. The punch is made of steel, and the top part that comes into contact with the hammer is shaped into a ball. The end that touches the workpiece is usually fitted with a soft metal such as copper or aluminum, and is made flat or shaped to fit the workpiece, in order to protect the surface of the workpiece from damage. When removing components, different methods and steps should be adopted depending on the structure of the various parts. Both the sliding bearing bushings and the rolling bearing housings have an interference fit in the holes; to remove them from there, impact removal is also commonly used. When striking to remove, a cushion block should be placed under the end face of the bushing that is being hit by the hammer. When removing small-diameter bushings, it is best to use a stepped punch, whose small diameter matches that of the bushing’s inner hole, while its large diameter is about 0.5 mm smaller than the bushing’s outer diameter. For the removal of large-diameter bushings and rolling bearings, sleeves are commonly used. To remove a standard small bearing cover, it is common to use inclined shims inserted symmetrically in order to open the cover. Precautions for using bearings: Rolling bearings are precision components, and their use must therefore be carried out with due care. No matter how high-performance the adhesive is, if it is not used properly, the expected high performance will not be achieved. The precautions for using bearings are as follows: 1. Keep the bearings and their surrounding area clean. Even tiny amounts of dust that are invisible to the naked eye can increase bearing wear, as well as vibration and noise. Bearings and their surrounding components should be kept clean, especially free from dust and dirt; tools as well as the working environment must also be kept tidy. 2. Careful attention must be paid during installation; forced pressing is not allowed, hitting the bearing with a hammer is not permitted, and pressure transmission through the rolling elements is not allowed. 3. Use appropriate and accurate installation tools. Try to use specialized tools, and avoid using materials such as cloth and short fibers at all costs. 4. Preventing bearing rust: When handling bearings with your hands, make sure to wash off any sweat from your hands thoroughly and apply high-quality mineral oil before proceeding. Special attention should be paid to preventing rust during the rainy season and in summer. However, under certain specific operating conditions, bearings can achieve a longer lifespan than traditionally calculated, especially under light loads. These special operating conditions consist of the rolling surfaces (tracks and rolling elements) being effectively separated by a lubricating film, which prevents surface damage that could be caused by contaminants. In fact, under ideal conditions, the so-called permanent bearing life is possible. Common problems with bearings and corresponding solutions:
Harsh metallic noise: 1. Abnormal loads: Select appropriate assembly clearance and preload. 2. Poor assembly: Improve the precision of shaft machining and optimize installation methods. 3. Insufficient lubricant: Top up or use a suitable lubricant.
Regular noise: 1. Foreign objects causing rust, dents, or scratches in the grooves: Clean the relevant parts and use clean grease. 2. Groove degradation: Due to fatigue wear, replace the bearing.
Irregular noises: 1. Presence of foreign objects: Clean the relevant parts and use clean grease. 2. Excessive clearance: Pay attention to fit and select an appropriate clearance. 3. Damage to steel balls: Caused by fatigue or foreign object entanglement; replace the bearing.
Abnormal temperature rise: 1. Excessive lubricant: Reduce the amount of lubricant used. 2. Insufficient or inappropriate lubricant: Increase the amount of lubricant or use a suitable one. 3. Creep of mating surfaces or oversized sealing elements: Adjust the outer or inner diameter mating surfaces of the bearing or change the type of seal.
Excessive rotational vibration of the shaft: 1. Groove degradation: Due to fatigue wear, replace the bearing. 2. Poor assembly: Improve the precision of shaft machining and optimize installation methods. 3. Presence of foreign objects: Clean the relevant parts and use clean grease.
Excessive lubricant leakage and discoloration: 1. Excessive lubricant: Reduce the amount of lubricant used. 2. Presence of foreign objects: Clean the relevant parts