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This post was last edited by TF123 on 2011-1-25 at 11:30. II. Methods for measuring vibration and temperature of bearings — Fag Shenglin imported bearings 1. Vibration of bearings Bearing vibration has a significant impact on the condition of bearings; issues such as flaking, indentation, rusting, cracks, and wear can all be detected through vibration measurements. Therefore, special devices for measuring bearing vibration (such as frequency analyzers) can be used to determine the level of vibration, while frequency analysis can help identify the specific nature of any abnormalities. The measured values vary depending on the operating conditions of the bearings or the installation location of the sensors, etc.; therefore, it is necessary to analyze and compare the measurement values for each machine in advance in order to establish judgment criteria. 2. Methods for measuring bearing temperature: The temperature of a bearing can generally be estimated from the temperature outside its housing; it is more appropriate to directly measure the temperature of the outer ring of the bearing using an oil hole. Typically, the temperature of the bearing gradually rises as it starts to operate, and reaches a stable level after 1-2 hours. The normal temperature of a bearing varies depending on the machine’s heat capacity, heat dissipation rate, speed, and load. If the lubrication and mounting are inadequate, the bearing temperature will rise sharply, resulting in abnormally high temperatures; in such cases, operation must be stopped and necessary preventive measures taken. By using heat sensors, it is possible to monitor the operating temperature of the bearings at any time, and to trigger an automatic alarm or stop the operation when the temperature exceeds the specified limit, thereby preventing bearing burnout accidents. High temperature often indicates that the bearing is in an abnormal condition. High temperatures are also harmful to the lubricant in bearings. Sometimes bearing overheating can be attributed to the bearing’s lubricant. If the bearing operates continuously at temperatures above 125°C, its lifespan will be reduced. The causes of high-temperature bearings include insufficient or excessive lubrication, impurities in the lubricant, excessive load, damaged bearing rings, insufficient clearance, and high friction caused by oil seals, among others. Therefore, it is necessary to continuously monitor the bearing temperature, whether by measuring the bearing itself or other important components. If the operating conditions remain unchanged, any change in temperature indicates that a fault has occurred. Regular measurement of bearing temperature can be carried out using a thermometer, such as an SKF digital thermometer, which allows for accurate determination of the bearing temperature and displays it in degrees Celsius or Fahrenheit. Critical bearings, when damaged, can cause equipment downtime; therefore, it is advisable to install temperature sensors on such bearings. Under normal circumstances, bearings experience a natural temperature rise immediately after lubrication or re-lubrication, and this rise persists for one or two days.

This post was last edited by TF123 on 2011-1-25 at 11:45. III. Fault Analysis of Motor Bearings (I) The \"sizzling\" sound from the retainer: Cause analysis: This sound is generated by the vibration and collision between the retainer and the rolling elements; it can occur regardless of the type of lubricant used. It is more likely to appear when high torque, load, or radial play is present. Solution: 1. Improve the precision of the retainer ； 2. Use bearings with a small clearance or apply preload to the bearings ； 3. Reduce torque load and minimize installation errors ； 4. Choose good oils. (II) Continuous buzzing sound “buzzing…” Cause analysis: The motor produces a buzzing-like sound when operating without load, and axial abnormal vibrations in the motor result in a buzzing sound when it is turned on or off. Specific characteristics: This issue occurs frequently when the lubrication condition is poor, especially in motors used in winter and those equipped with ball bearings at both ends. It is primarily an unstable vibration that results from axial vibrations when the shaft’s self-aligning capability is inadequate. Solution: 1. Use grease with good lubricating properties ； 2. Apply preload to reduce installation errors ； 3. Choose bearings with a small radial clearance ； 4. Improve the rigidity of the motor bearing housing ； 5. Improve the self-aligning capability of the bearings. Note: The fifth point plays a role in achieving fundamental improvement, by using a curvature of 02 for the small grooves and a curvature of 01 for the large grooves. (III) Paint rust – Cause analysis: As the paint on the motor bearing housing dries, the chemical compounds that evaporate from it corrode the end faces, outer grooves, and channels of the bearings; this corrosion leads to abnormal noises. Specific feature: After corrosion, rusting on the bearing surface is more severe than on the first side. Solution: 1. Assemble the rotor and casing after drying them in the air or with a dryer ； 2. Reduce motor temperature ； 3. Select the appropriate paint model ； 4. Improve the ambient temperature in which the motor bearings are located ； 5. Use appropriate oils; fatty oils cause less rust, while silicone oils and mineral oils are the most likely to cause it ； 6. The vacuum impregnation process is used. (IV) Impurity noises: Cause analysis – Caused by the cleanliness of the bearings or grease, resulting in an irregular abnormal noise. Specific characteristics: The sound appears intermittently, with no regular pattern regarding intensity, and it occurs more frequently on high-speed motors. Solution: 1. Choose high-quality oil ； 2. Improve cleanliness before fat injection ； 3. Improve the sealing performance of the bearings ； 4. Improve the cleanliness of the installation environment. (V) High-frequency, vibrating “tap-tap...” sound. Specific characteristics: The sound frequency varies with the bearing’s rotational speed; the surface waviness of the components is the main cause of this noise. Solution: 1. Improve the surface machining quality of the bearing raceway to reduce the waviness amplitude ； 2. Reduce bruises ； 3. Correct the preload and fit of the clearance; check the operation of the free-end bearing; improve the precise installation method for the shaft and bearing housing. (VI) Temperature rise: Specific feature – After the bearing starts operating, its temperature exceeds the specified range. Cause analysis: 1. Excessive grease leads to increased resistance from the lubricant ； 2. Excessive internal load caused by too small a clearance ； 3. Installation errors ； 4. Friction of sealed equipment ； 5. Crawl of bearings. Solution: 1. Choose the right type of grease and use an appropriate amount ； 2. Adjust the clearance preload and fit, and check the operation of the bearing at the free end ； 3. Improve the accuracy of the bearing housing and the installation method ； 4. Improve the sealing design. (7) Poor feel when handling the bearing: Specifically, when holding the bearing and rotating the rotor, a sense of impurities or obstruction inside the bearing can be felt. Cause analysis: 1. Excessive clearance ； 2. Improper fit between the inner diameter and the shaft ； 3. Channel damage. Solution: 1. The clearance should be as small as possible ； 2. Selection of tolerance zones ； 3. Improve precision and reduce channel damage ； 4. Selection of oils and fats.

IV. Various types of rolling bearings Rolling bearings can withstand radial loads as well as bidirectional axial loads. Suitable for high-speed rotation applications as well as those that require low noise and low vibration. These are sealed bearings equipped with steel plate dust covers or rubber seals, and pre-filled with an appropriate amount of lubricant. The outer ring features a stop ring or flange, which facilitates both axial positioning and installation within the housing. The dimensions of the maximum load type bearing are the same as those of a standard bearing, but it has loading grooves on the inner and outer rings, which increases the number of balls and thus raises the rated load. 1. Self-aligning ball bearings are bearings in which drum-shaped rollers are installed between an inner ring with two raceways and an outer ring whose raceway is spherical in shape. The center of curvature of the outer raceway surface coincides with the bearing center, thus it possesses the self-aligning capability of auto-aligning ball bearings. When the shaft and housing bend, it can automatically adjust the load as well as the axial loads in two directions. It has high radial load capacity, making it suitable for applications with heavy loads and impact loads. Bearings with a conical bore for the inner diameter of the inner ring can be installed directly. Or it can be installed on the cylindrical shaft using a retaining sleeve or a removal tube. The retainers use stamped steel retainers, molded polyamide retainers, and machined copper alloy retainers. 2. Needle bearings (solid needle bearings) have the same basic structure as inner-ring bearings of the NU type cylindrical roller bearings; however, due to the use of needles, their size can be reduced, and they are capable of withstanding large radial loads. Unlike inner-ring bearings, these types do not require the installation surface of the shaft, which must have the appropriate precision and hardness, to be used as the raceway surface. 3. Thrust needle bearings: These separate-type bearings consist of a race ring along with needle and cage assemblies, and can be combined arbitrarily with either stamped thin race rings (W) or machined thick race rings (WS). A non-separable bearing is an integrated bearing consisting of a raceway ring that has been precision-stamped, along with needle rollers and a retainer assembly. These bearings can withstand unidirectional axial loads. It occupies little space, which facilitates a compact design of the machinery; it usually uses only needle and retainer assemblies, with the mounting surfaces of the shaft and housing serving as the raceway surfaces. 4. Tapered roller bearings: These bearings are equipped with tapered rollers, which are guided by the large flange on the inner ring. The design ensures that the vertices of the conical surfaces of the inner ring raceway, the outer ring raceway, and the roller rolling surface all intersect at a point on the bearing’s center line. Single-row bearings can withstand radial loads and unidirectional axial loads, while double-row bearings can withstand radial loads as well as bidirectional axial loads; they are suitable for withstanding heavy loads and impact loads. 5. Cylindrical roller bearings can be classified into single-row, double-row, and multi-row cylindrical roller bearings, depending on the number of rows of rolling elements in the bearing. Among them, the single-row cylindrical roller bearings with retainers are those that are used most frequently. In addition, there are also cylindrical roller bearings with other designs, such as single-row or double-row full complement rollers. Single-row cylindrical roller bearings are classified into types such as N, NU, NJ, NF, and NUP, depending on the flange design of the rings. Cylindrical roller bearings have a high capacity to bear radial loads, and depending on the design of their ring flanges, they can also withstand certain amounts of axial load in either direction. NN and NNU type double-row cylindrical roller bearings have a compact structure, high stiffness, large load-carrying capacity, and minimal deformation under load; they are primarily used for supporting machine tool spindles. FC, FCD, and FCDP types of four-row cylindrical roller bearings can withstand large radial loads and are commonly used in heavy machinery such as rolling mills. 6. Self-aligning roller bearings: These bearings have spherical rollers between the spherical raceway of the outer ring and the double-raceway inner ring; depending on their internal structure, they are classified into four types: R, RH, RHA, and SR. Since the center of the arc of the outer raceway coincides with the center of the bearing, it possesses self-aligning capabilities, allowing it to automatically adjust any misalignment caused by the bending or out-of-centerness of the shaft or housing. It can withstand radial loads and bidirectional axial loads. In particular, it has a high radial load capacity, making it suitable for withstanding heavy loads and impact loads. Tapered bore bearings can be installed on or removed from the shaft by using fasteners or release sleeves. Spherical roller bearings can withstand large radial loads, as well as a certain amount of axial load. The outer ring race of this type of bearing is spherical in shape, which gives it self-aligning capabilities; the bearing can still function when the shaft is bent or tilted, causing the center line of the inner ring to tilt relative to the center line of the outer ring by no more than 1° to 2.5°. 7. Thrust roller bearings Thrust roller bearings include thrust self-aligning roller bearings, thrust cylindrical roller bearings, and thrust tapered roller bearings. Thrust self-aligning roller bearings can withstand both axial and radial loads, but the radial load shall not exceed 55% of the axial load. Another important feature of this type of bearing is its self-aligning capability, which makes it less sensitive to misalignment and shaft deflection. As long as the loads are P and P. Not exceeding 0.05C, and as the ring rotates, the bearing permits a certain range of self-aligning angle. Small values are suitable for large bearings, and the allowable self-aligning angle decreases as the load increases. 8. Spherical bearings are preferably used in applications where simplicity in equipment and components is required, such as in agricultural machinery, transportation systems, or construction equipment. It is primarily used to withstand combined radial and axial loads, with radial loads being the dominant type; it is generally not suitable for withstanding axial loads alone. Such bearings allow the inner ring (with the complete set of rollers and retainers) and the outer ring to be installed separately. This type of bearing does not allow the shaft to tilt relative to the housing, and an additional axial force is generated under radial loads. The magnitude of the axial play in such bearings has a significant impact on their proper operation; when the axial play is too small, the temperature rise is high ； When the axial clearance is large, the bearing is prone to damage. Therefore, special attention must be paid to adjusting the axial play of the bearings during installation and operation; if necessary, pre-interference installation can be used to increase the stiffness of the bearings. 9. Joint bearings: Joint bearings are available in lubricated and self-lubricating types. A joint bearing is a type of sliding bearing with a special structure. Its structure is simpler than that of rolling bearings; it mainly consists of an outer ring with an inner spherical surface, and it is capable of withstanding large loads. Depending on the inner ring with an outer spherical surface and its various types and structures, it can handle radial loads, axial loads, or combined radial and axial loads. It is generally used for swinging motions at relatively low speeds (i.e., angular motion); it can also perform tilting motions within a certain angle range (i.e., self-aligning motion), as the sliding surfaces are spherical. It can still function properly even when there is a significant misalignment between the support shaft and the shaft housing hole. 10. Linear bearings: Linear ball bearings are primarily used in mechanical devices where linear reciprocating motion is required; they offer advantages such as low friction, smooth operation, and ease of maintenance and replacement. It is widely used in fields such as textile machinery, printing machinery, pharmaceutical machinery, precision machine tools, electrical cutting machines, and automatic recorders. 11. Angular contact bearings, also known as contact ball bearings, can withstand both radial and axial loads; they can also handle pure axial loads, and have a relatively high maximum speed. The ability of this type of bearing to withstand axial loads is determined by the contact angle; a larger contact angle implies a higher capacity to bear axial loads. 12. Pressure bearings: Pressure bearings are separate-type bearings, and based on their structural design, they are divided into single-direction pressure ball bearings and double-direction pressure ball bearings. A unidirectional pressure bearing can withstand axial loads in one direction, while a bidirectional pressure bearing can withstand axial loads in two directions. None of them can withstand radial loads.

V. Maintenance of the thrust bearings in centrifugal compressors The main technical requirements for maintaining thrust bearings are as follows: (1) Thrust clearance The thrust clearance of the thrust bearings must meet the design specifications. (II) Thrust bearing shells: 1. The babbitt layer of the thrust bearing shells shall be free from defects such as delamination, wear, cracks, burning, crushing, roughening, erosion, and electroerosion. The bricks were inspected by coloring or dipping in kerosene, and the babbitt bonded well with the base metal. 2. The surface of the thrust washer must not have any radial grooves or scratches; the depth of circumferential grooves or scratches shall not exceed 0.01 mm. 3. The wear patterns of tiles in the same group should be roughly equal; if the wear patterns are uneven, it indicates that the tiles are not bearing loads evenly, and the cause should be identified. 4. Use red lead to check the contact between the babbitt surface of each individual tile and the surface of the thrust plate; the contact area should be no less than 80%, and the thickness variation among tiles in the same group should not exceed 0.01 mm. 5. The load-bearing surface on the back of the tile is smooth, with no signs of heavy loading such as burning, bonding, or indentations. 6. All limit pins are securely fixed, and neither the pins nor the pin holes show any wear. After assembly, the tiles can swing freely. 7. For thrust bearings equipped with thermistors, it is necessary to check the stability of the fixation of these thermistors within the bearings; the temperature sensing wires should not interfere with the free movement of the bearings. The thermosensitive element and leads, together with the tile, are inspected by the instrument; the insulation and measurement accuracy meet the instrument specifications. (III) Base ring and level block: 1. The load-bearing surface of the level block is smooth, with no signs of heavy wear such as abrasion, scorching, or indentations; it can swing freely within the base ring without any sticking. The stop pin has an appropriate length and is firmly fixed; it maintains sufficient clearance from the pin holes of the level blocks, does not press against the equalizing blocks, and does not cause uneven wear on the pin holes. 2. There are no indentations on the contact lines between the working surfaces of the level blocks, their surfaces are smooth, and the level blocks can swing freely after assembly. 3. The base ring shows no warping; the joint surface between the two halves of the base ring is flat with no cracks, and there are no indentations at the point where it contacts the level block. The back surface of the base ring exerts even pressure on the end face of the thrust bearing housing. The anti-rotation key on the base ring is securely fixed, and there is no wear in the corresponding keyway on the housing. (IV) Thrust disc: 1. The surface of the thrust disc must be smooth and even, with a surface roughness Ra value of less than 0.8 μm. Radial grooves are not allowed, and the depth of circumferential grooves should not exceed 0.05 mm. 2. The thrust disc is connected by keys; there are no signs of compression between the keys and the keyways, and the keyways have been inspected for cracks and show none. The thrust disc makes even contact with the shaft shoulder and the end face of the back nut; the key is properly fitted in the keyway of the thrust disc, and the side clearance, top clearance, and the fit between the thrust disc and the shaft meet the design requirements. The total runout of the end face of the assembled thrust disc is less than 0.015 mm. 3. When a hydraulic mounting/dismounting thrust plate structure is used, it is necessary to check the contact condition between the inner hole of the thrust plate and the shaft surface, as well as the contact condition between the end face of the thrust plate and the shaft shoulder; in both cases, the contact ratio must be at least 80%. All surfaces are free of burrs, scratches, and damage; the fit dimensions between the inner hole of the thrust washer and the shaft are within tolerance. 4. The circumferential deviation of the thrust disc thickness shall not exceed 0.01 mm. 5. The thrust bearing shimming washer is a single piece; it must be smooth and flat, with a thickness variation across its entire circumference of less than 0.01 mm. 6. The inner and outer diameters of the oil slinger are properly matched and do not become loose. 7. Clean the bearing housing; all oil supply holes must align with and be unobstructed from the oil holes on the bearing block.