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      Your current location: Home > Technical center > Q&A > Q&A
      Q&A

      Bearing Maintenance

      2013-08-19
      ?1. Regular Inspection
      Regular maintenance (regular inspection) must be done to achieve the bearing life and performance. Periodic inspection helps to detect early damage and prevent accidents before they occur. It is of vital importance to raise productivity and economic efficiency.?
      1.1 Cleaning
       Before dismounting the bearing for inspection, it suggested to take a photo to record the appearance. In addition, verify the amount of the remaining lubricants and take samples of the lubricants and then perform the bearing cleaning.?
      a. Bearing cleaning is divided into two steps, i.e., rough cleaning and fine cleaning. A metal net rack may be put at the bottom of the used container
      b. While doing rough cleaning, clean away the grease or adhesive material with a brush in the oil. Do not rotate the bearing since the foreign particles may damage the bearing raceway.?
      c. While doing fine cleaning, slowly rotate the bearing in the oil with great care.
      Used detergent is neutral waterfree diesel or kerosene. Sometimes, temperate lye is used as needed. When use a detergent always use filter.
      1.2 Inspection?
      1.2.1 Bearing damage Diagnosis Methods
      Determining or predicting whether the operating bearing is damaged or not without dismounting for inspection is very important to raise productivity and economic efficiency. Main identification methods include:
      a. Sound Identification
      Rich experience is the prerequisite for conducting sound identification. Only sufficiently trained operators can identify the sound of a bearing. Therefore, it needs a specialized operator for this job. The listening gear or listening rod presses against the housing may help to listen to the sound of the bearing.
      b. Identification through Operating Temperature
      This method is called identification through comparison, and is only applicable in the steady state application. Therefore, the temperature must be continuously recorded. Any bearing damage will make temperature rise.
      c. Identification in Reference to the Condition of Lubricant
      Conduct sample analysis on the lubricant. This can determine whether the lubricant is contaminated with foreign particles and metal powers.
      ?This method is very effective for large bearings or bearings which are not easily accessible
      1.2.2 Bearing Inspection
      Inspect the dismounted bearings and related parts during equipment regular maintenance to determine whether the parts can be reused or the service condition of the parts. Carefully examine and record the conditions of the dismounted bearings and their appearances in order to clarify the surplus of the lubricants. After taking samples, the bearing shall be cleaned thoroughly.
      Next, inspect the raceways, the fitting surfaces and the wear of the cages to determine if they have been damaged.
      Whether the bearing can be used again is determined by the bearing condition, machine performance and importance, the operating condition and the inspection cycle etc. If the bearing is found to have been damaged or in abnormal condition, try to find out the reasons and draw up countermeasures. If there are the following damage modes, the bearing can not be used any more. Instead, it should be replaced.
      a. Cracks and fractures appear in any one of them inner ring, outer ring, rolling element and cage.
      b. Spalling occurs in either of them: inner ring, outer ring; rolling element.
      c. Raceway, flange and rolling element have obvious squeeze scars.
      d. Severe wear or rivet loosening of the retainer.
      e. Raceway and rolling element rusts and has scars.
      f. Raceway and rolling elements have obvious denting and stricken marks.?
      g. The bore of the inner ring or the OD of the outer ring have creep deformation.
      h. Severe discoloration caused by overheating.
      i. Severe breakage on the seal and shield of the grease sealed bearing.
      2. Shutdown Inspection
      It is a very important to regularly inspect the bearing to maintain its optimum condition. The optimum inspection time is at the equipment regular shutdown inspection period. Inspection often facilitates planning beforehand and knowing the bearing part number and preparing the spare parts.
      2.1. It is important to keep the bearing and lubrication clean.
      Clean the machine surface before inspection, and then dismount the peripheral parts of the bearing. The oil seal is a very fragile component, great care should be paid dismounting it.. Be sure not to use too much force. Carefully inspect the seal and its peripheral components. If there is any damage, be sure to change it because a non-performing seal will lead to bearing damage and, worse still, machine breakdown..
      2.2 Inspect the Lubricant
      Tap small amount of lubricant and rub it between two fingers. You might feel any foreign particles that are in the lubricant. Alternatively you can put the lubricant on your wrists and then sealed for inspection.
      2.3 Lubricant Renewal
      After excreting the used oil out of the bearing, if possible, pour in new oil and run the machine at a low speed. Make the oil collect the contamination as much as possible and then drain the oil. The oil should be filtered before it is used again.
      The eliminator used to replace the grease for the grease lubricated bearing should be prevented from touching any part of the bearing because these residue fibers may wedge into between the rolling elements and cause damage. More attention should be made to the small bearings.
      2.4. Cover the exposed bearing
      While inspecting the bearing, be sure not to expose the bearing to contaminants or an environment with moisture. If the operation is suspended, cover the machine with oil paper plastic film or similar materials.
      If inspection is performed to clean an exposed bearing without dismounting it, brush the bearing with white spirit and dry it with lint-free cloth or compressed air. (Attention: do not rotate the bearing)
      Use a small mirror or a probe similar to the dental probe to inspect the raceways, cage and rolling elements. If the bearing is not damaged, further lubrication should be made in accordance with the lubrication instructions given by the manufacturer
      Do not clean sealed bearings or shielded bearings. Cleaning its external surface is enough. Replace the bearing if the bearing seems damaged. Compared with replacing the bearings during the machine shutdown for regular maintenance period, it is more economical than the machine accidental breakdown caused by bearing failure.
      3. Inspection and damage analysis in Operation
      Check on bearings’ sound, vibration, temperature and lubrication condition during inspection. Use these factors in your analysis when considering introducing lubrication.?
      3.1. Function of Bearing Lubrication
      Lubrication plays an important part in the bearing fatigue life span, without the appropriate lubrication the bearing could experience friction, wear, temperature rise, and vibration and will not work. Analysis of the reason for the bearing damage indicates that about 40 percent of bearing damage is related to poor lubrication. Therefore, good lubrication is a good measure to reduce bearing friction and wear. Apart from this, bearing lubrication also functions to dissipate heat, protect against corrosion, and seal the bearing against contaminants.
      A layer of oil film is formed between two rolling or gliding surfaces. The oil film layer separates the two surfaces and reduces friction and wear at the interface.
      b. Oil lubrication, including circulating oil, oil mist and splash oil systems can take away most friction heat within the bearing.
      c. While using grease lubrication, foreign particles like dust may enter the bearing, working as a seal.
      d. All lubricants help to prevent corrosion.
      e. Improve the bearing fatigue life.
      3.2. Grease Lubrication
      Greases consist of base oil, a thickening agent and additives. Bearing application conditions should be considered when choosing type grease. Grease performances may vary for different brands. Special attention should be paid choosing one. Frequently used greases include calcium soap grease, sodium soap grease, calcium-sodium soap grease, lithium base grease, aluminum base grease, .molybdenum disulfide grease, etc. The quantity of the grease filling in the bearing is about ? ~ 1/3 of the bearing volume. The amount of grease should be reduced by 1/3 for the high speed application. Excessive grease will cause high temperature.
      3.3. Grease selection
      Grease should be selected with regard to its dropping point, oxidation stability and cryogenic property at operating temperature. Dropping point is often used to assess grease high-temperature property and the actual operating temperature of the bearing should be 10-20℃ lower than the dropping point. Operating temperature of synthetic grease should be 20-30℃lower than the dropping point. Bearing load should be considered when selecting the grease. For heavy load applications, you should apply low penetration grease. For high pressure applications, in addition to the low penetration property the grease should also have thicker oil film and extreme pressure property. Calcium -based greases have excellent water resistance and are used in industrial applications where water ingress is an issue.
      3.4 Replenish and Replacement
      ?Due to mechanical action, aging and contamination, bearing lubricants will gradually lose their properties. Therefore, lubricants must be continuously replenished and renewed. The interval of lubricant replenishment will differ with the type, size and the speed of the bearing. Therefore, the interval is according to the operating speed. A rule of thumb, the replenishment interval should be reduced by half for every 15° C increase in temperature when bearing operating temperature is over 70° C. Double sided sealed bearings have been filled with greased during manufacturing. “HRB” uses standard grease in these products. The operating temperature range and other properties are applicable to the general application, and the filling grease amount corresponds to the size of the bearing. Generally, grease operational life is longer than the bearing life.. Except for special occasions, there is no need to replenish lubricating grease.
      3.5 Bearing Damage analysis and solutions?
      Although bearings can not be observed while in operation, bearing damage can be detected though noise, vibration, temperature, lubrication, etc.
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