Precautions for inspecting bearings during operation

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It has become increasingly important to check the condition of operating transfer machines and prepare a thorough inspection plan. Among these, bearings are of particular focus, as they are the most important rotating components in all machinery, and condition monitoring is a crucial part of preventive maintenance. Early detection of bearing failure helps to avoid unplanned equipment downtime caused by such failures. Bears in critical machinery or harsh environments should be inspected more frequently. The market now offers a considerable number of systems and instruments for monitoring bearings, most of which are based on vibration measurement. However, not all instruments are equipped with these advanced devices. In such cases, the operators or maintenance engineers in charge of the transfer station must be highly vigilant to the \"failure signals\" of the bearings, such as noise, temperature, and vibration. “\"Listening,\" \"touching,\" and \"observing\" are three important methods. The views provided below can serve as a reference for you. 1. Listening: Using hearing to detect irregular operation is a very common method. For example, using electronic stethoscopes or mechanical listening probes to detect abnormal noises from a certain component is a method commonly employed by experienced technicians. When bearings are in good working condition, they emit a low humming sound; if they produce a sharp hissing, squealing noise, or other irregular sounds, it usually indicates that the bearings are not functioning properly. A sharp screeching noise may be caused by inadequate lubrication, while an improper bearing clearance can result in a metallic sound. Grooves on the outer ring race of the bearing can cause vibration and result in a smooth, crisp sound. Noise can also be generated by impact marks caused during installation, and this noise varies depending on the speed of rotation of the bearing. If there is intermittent noise, it indicates that the rolling elements may be damaged; this sound occurs when the damaged surface is pressed. Contaminants inside the bearing often cause a hissing sound. Severe bearing damage can produce irregular and loud noises. Although bearing damage can be detected by listening, by that point it is usually already time to replace the bearing immediately; therefore, a better approach is to use electronic condition monitoring devices to diagnose the bearing’s operating condition in advance. Compared to the old methods (using a stick or screwdriver pressed against the bearing housing with the other end against the ear), advanced instruments allow for a more accurate assessment of the bearing’s condition. 2. Touch: High temperature often indicates that the bearing is in an abnormal condition. High temperatures are also harmful to the lubricant inside the bearings. Sometimes, bearing overheating can be attributed to the bearing’s lubricant. If a bearing operates at temperatures above 125°C (260°F) for an extended period, its lifespan is reduced. Causes of high bearing temperatures include insufficient or excessive lubrication, impurities in the lubricant, excessive load, damaged bearings, inadequate clearance, and high friction caused by oil seals. 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 may indicate a fault has occurred. Regular measurement of bearing temperature can be carried out using a thermometer, which allows for an accurate determination of the bearing temperature. Bearings of critical importance mean that their failure can cause the equipment to stop operating; therefore, it is advisable to install temperature sensors on such bearings. Under normal circumstances, bearings experience a natural temperature rise shortly after being lubricated or relubricated, and this rise persists for one or two days. 3. Observation: If the bearing is properly lubricated and can effectively prevent the entry of debris and moisture, it indicates that the oil seal is not worn out. However, it is best to visually inspect the bearings and regularly check the oil seals whenever the bearing housing is opened again. Check the condition of the oil seals near the bearings to ensure that they are sufficient to prevent hot liquids, corrosive liquids, or gases from seeping into the bearings along the axis. The protective ring and labyrinth oil seal should be coated with grease to ensure their maximum level of protection. If the oil seal is worn, it should be replaced as soon as possible. In addition to preventing contaminants from entering the bearing, another function of the oil seal is to retain the lubricant within the bearing housing. If oil leakage occurs from the oil seal, it is necessary to immediately check whether the seal is worn or damaged, or whether the oil plug is loose. Oil leakage can also be caused by loose joints in the bearing housing, or by agitation and leakage resulting from an excessive amount of lubricant being used. Check the automatic lubrication system to ensure that oil or grease reaches the bearings properly and in the correct amount. Also, inspect the lubricant for any discoloration or darkening; such conditions usually indicate that the lubricant has deteriorated or contains impurities, and it should be replaced immediately.