Checking the condition of running machines and preparing a thorough inspection plan has become increasingly important. Bearings are the focus of attention because they are the most important rotating parts in all machines. Condition monitoring is an important part of preventive maintenance. Early detection of bearing damage can avoid equipment downtime during unplanned maintenance due to bearing damage. However, not all machines are equipped with such advanced instruments. In this case, the machine operator or maintenance engineer must be highly alert to the "failure signals" of the bearings, such as noise, temperature and vibration. "Listening", "touching" and "observing" are 3 important factors.

Touching

High temperatures often indicate that the bearings are in abnormal conditions. High temperatures are also harmful to the lubricant in the bearings. Sometimes bearing overheating can be attributed to the bearing lubricant. If the bearing is operated at a temperature exceeding 125 degrees Celsius for a long time, the bearing life will be reduced. The causes of high temperature bearings include: insufficient or excessive lubrication, impurities in the lubricant, excessive load, bearing damage, insufficient clearance, and high temperature friction caused by oil seals, etc. Therefore, it is necessary to continuously monitor the bearing temperature, either of the bearing itself or other critical parts. If the operating conditions remain unchanged, any temperature change may indicate that a fault has occurred.

Regular measurement of bearing temperature can be done with the help of a thermometer, which can accurately measure the bearing temperature and display it in degrees Celsius. Important bearings mean that when they fail, they will cause equipment downtime, so such bearings should preferably be equipped with temperature probes. Normally, the bearing will have a natural temperature rise after lubrication or relubrication and last for one or two days.

Observation

If the bearing is well lubricated and properly blocked from debris and moisture, the oil seals should not be worn. However, it is best to visually inspect the bearings when the bearing housing is opened and to check the oil seals regularly. Check the condition of the oil seals close to the bearing to ensure that they are sufficient to prevent hot or corrosive liquids or gases from penetrating the bearing along the axis. Protective rings and labyrinth oil seals should be greased to ensure maximum protection. If the oil seal is worn, it should be replaced as soon as possible. In addition to preventing impurities from entering the bearing, the oil seal also has the function of keeping the lubricant in the bearing housing. If the oil seal leaks, check whether the oil seal is worn or damaged or the oil plug is loose. Oil leakage may also be caused by loose joints in the bearing housing or stirring and oil leakage caused by excessive lubricant addition. Check the automatic lubrication system to ensure the correct amount of lubricant added. At the same time, check whether the lubricant changes color or turns black. If this happens, it usually means that the lubricant contains impurities.

Listening

Using hearing to identify irregular operation is a very common method. For example, using an electronic stethoscope to check for abnormal noise in a part is a method used by experienced operators. If the bearing is in good operating condition, it will make a low humming sound. If it makes a sharp hissing sound, squeaking sound and other irregular sounds, it usually means that the bearing is in poor operating condition. Sharp squeaking noises may be caused by improper lubrication. Improper bearing clearance may also cause metallic sounds. Dents on the outer race of the bearing can cause vibrations and produce a smooth, crisp sound. If there are knock marks caused by installation, there will also be noise, which will vary with the speed of the bearing. If there is intermittent noise, it means that the rolling element may be damaged. This sound occurs when the damaged surface is rolled over, and contaminants in the bearing often cause a hissing sound. Severe bearing damage will produce irregular and loud noises.

Bearing damage can certainly be detected by hearing, but usually at this time, the bearing must be replaced immediately. Therefore, a better method, such as using electronic condition monitoring instruments, can diagnose the operation of the bearing in advance.

Compared with the old method (using a wooden stick or screwdriver against the bearing housing and the other end against the ear), the use of advanced instruments can more accurately estimate the bearing condition.

Grease lubrication

Bearing relubrication is best carried out during planned equipment downtime and replenished regularly. At the same time, clear out the old grease or drain it through the oil drain plug. Wipe the grease nipple clean before adding new oil. If the bearing box does not have a grease nipple, open the bearing box cover or end cover to remove the old grease, and then add the same fresh grease.

Oil lubrication

When checking the oil level of the bearing, make sure that the correct type of oil is used and the vent of the oil level gauge is not blocked.

Take a small amount of oil as a sample and compare it with fresh oil. If the sample looks cloudy, it may be the result of mixing with water and should be replaced. If the sample is darkening in color or thickening, it may mean that the oil is starting to carbonize. The old oil should be replaced completely and, if possible, fresh oil should be used to flush the bearing. When changing the oil, make sure that the oil type replaced must be the same and the oil level must be filled to the required level.

A more reliable way to determine the condition of the oil is to analyze the sample. If the oil is contaminated, the oil seal should be replaced or the filter should be considered.

With an oil bath lubrication system, if the operating temperature does not exceed 50-60 degrees Celsius and the oil is not contaminated, the oil can be replaced once a year. If the operating temperature is 100 degrees Celsius, the oil should be replaced 4 times a year, if the operating temperature is 120 degrees Celsius, the oil should be replaced once a month, and if the operating temperature is 130 degrees Celsius, the oil should be replaced once a week.

Proper installation and maintenance are important factors in achieving the longest service life of the bearing. At the same time, attention must be paid to the cleanliness of the bearing, the correctness of the bearing selection, and the selection of appropriate installation and maintenance tools. The bearing must be protected from contaminants and moisture, and must be properly installed and lubricated. The design of the bearing arrangement, the condition of the oil seal, the type of lubricant and the lubrication cycle, and even specialized maintenance all play an equally important role.