Precautions for running bearing inspection

It is increasingly important to check the condition of the running transfer and to have a thorough inspection plan in advance. Among them, the bearing is the focus of attention, because it is the most important rotating part of all the turning, condition monitoring is an important part of preventive maintenance. Bearing damage was detected early to avoid unplanned equipment downtime due to bearing damage.

Especially in important machines or in harsh environments, bearings should be inspected frequently. There are quite a few systems and instruments on the market to monitor bearings. Most of these instruments are based on vibration measurements.

However, not all instruments are equipped with these advanced instruments. In this case, the operator or maintenance engineer of the transfer must be highly alert to the "fault signal" of the bearing, such as noise, temperature and vibration. “Listening,” “touching,” and “observing” are three important methods. The following comments can be used as a reference.

1. Listening

Using auditory to identify irregular movements is a very common approach. For example, the use of an electronic stethoscope or a mechanical listening needle to detect abnormal noise of a part is often a method used by experienced workers. If the bearing is in good operating condition, it will make a low hum. If it is a sharp hum, arpeggio and other irregular sounds, it usually indicates that the bearing is in poor working condition.

Sharp humming noise can be caused by improper lubrication, and improper bearing clearance can cause metallic sound. The indentations on the outer ring of the bearing cause vibration and result in a smooth and crisp sound. If the knocking flaw caused by the installation also produces noise, the noise will vary with the speed of the bearing. If there is intermittent noise, it means that the rolling parts may be damaged. This sound occurs when the damaged surface is crushed. If there are pollutants in the bearing, it will often cause a noise. Severe bearing damage can result in irregular and large noise.

Bearing damage can be detected by hearing, but usually it has reached the stage where the bearing must be replaced immediately. Therefore, a better method is to use an electronic condition monitoring instrument to pre-diagnose the operation of the bearing.

Compared to the old method (using a wooden stick or screwdriver to the bearing housing and the other end to the ear), advanced equipment can be used to accurately predict the bearing condition.

2, touch

High temperatures often indicate that the bearing is in an abnormal state. High temperatures are also detrimental to the lubricant in the bearing. Sometimes the bearing overheating can be attributed to the lubricant of the bearing. If the bearing runs for a long time at a temperature exceeding 125 °C (260 °F), the bearing life will be reduced, and the high temperature of the bearing may be caused by insufficient lubrication or excessive lubrication, and the lubricant contains Impurities, excessive load, bearing damage, insufficient clearance and high friction caused by oil seals.

Therefore, it is necessary to continuously monitor the bearing temperature, whether it is measuring the bearing itself or other important parts. If the operating conditions are the same, any temperature change may indicate that a fault has occurred.

The periodic measurement of the bearing temperature allows precise measurement of the bearing temperature by means of a thermometer.

The importance of the bearing means that when it is damaged, it will cause the equipment to stop. Therefore, it is better to install a temperature detector for this type of bearing.

Under normal conditions, the bearing will naturally rise in temperature after lubrication or relubrication for one or two days.

3. Observe

If the bearing is well lubricated and can ensure proper blocking of debris and moisture, the oil seal should be free of wear. However, it is best to visually inspect the bearings and periodically check the oil seals when the bearing housing is opened again. Check the condition of the oil seal near the bearing to ensure they are sufficient to prevent hot liquid or corrosive liquid or gas from penetrating the bearing along the shaft. The protective ring and the labyrinth oil seal should be greased to ensure a large amount of protection. If the oil seal has worn out, it should be replaced as soon as possible.

In addition to preventing impurities from entering the bearing, the function of the oil seal is to keep the lubricant in the bearing housing. If there is oil leakage in the oil seal, immediately check whether the oil seal has worn out or the oil plug is loose. Oil leakage may also result from loosening of the joint surface of the bearing housing or agitation and oil leakage due to excessive lubricant addition. Check the automatic lubrication system to ensure that the oil or grease enters the bearing correctly and ensure the correct amount of addition. At the same time, the lubricant is discolored or blackened. If this is the case, it usually indicates that the lubricant has deteriorated or contains impurities. Replace it.

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The best conditions for repairing and repairing rolling bearings

Rolling bearings are mass-produced mechanical parts, and the manufacturing precision is very strict, and the degree of specialization in technology is very high. Therefore, for most of the easy-to-buy bearing types, it should be more cost-effective to buy than in the following cases. Only consider the bearing repair problem, namely:
(1) A large number of bearings of the same type used in large factories are mainly in the form of wear on the rolling surface, fatigue or fretting abrasion, especially the damaged parts are mostly cages or rolling elements, and the ferrules or gaskets are still repaired. value;
(2) Large and extra large bearings, which have no major damage to the parts due to failure or failure, or valuable bearings must be managed to extend their useful life;
(3) Some types of bearings that are really difficult to purchase, have no spare parts after failure and have to be repaired, especially imported bearings;
(4) The bearing has slight damage, such as slight rust generated during the inventory period, and slight fretting abrasion caused by transportation. It is a pity that such repair is easy and abandon.
In addition to economics, the repair of the bearing is also technical, which requires the repairer to fully understand the corresponding technical requirements of the bearing, and the structural, technical and material characteristics of the bearing and its parts, otherwise it is difficult to ensure that the bearing repair has The desired effect.
First, the economic benefits of bearing repair
In general, the number of bearings is small, the number is large, the price of a single bearing is high, or the structure of the bearing is simple. If the size is large, the cost of repair is relatively low, and the economic benefit is higher.
In addition, monitoring the operation of the bearing, and planning to repair the bearing before failure, can get twice the result with half the effort. Following a reasonable process, using efficient repair equipment and tools, and getting help from a professional bearing plant can help increase economic efficiency.
Second, the benefits of cooperation with professional bearing companies
In the business of repairing bearings, if the cooperation of professional bearing companies can be obtained, the following benefits may be obtained:
(1) The technical requirements of each process of repair can be clarified, and how to ensure the overall quality of the repaired bearings,
(2) It is possible to utilize many of the specialized experience of specialized bearing plants, which can reliably, efficiently and economically meet process requirements;
(3) It is possible to order a tool for a professional bearing company, which can be economical and saves a lot of trouble;
(4) Orders such as cages, rolling elements, rivets, etc. can be ordered from professional bearing companies, which may make the repair work simple, convenient and economical.

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Cause Analysis and Repair of 5M1083A Centerless Grinder Wheel Bearing Spindle Bearing

Among the gold cutting equipment used in a factory, there is a M1083A centerless cylindrical grinding machine produced by Haining Machine Tool Plant. The equipment is characterized by good rigidity, high production efficiency, good equipment performance, and can meet the needs of mass production. The grinding wheel and the front and rear bearings of the guide wheel main shaft adopt the membrane feedback static pressure bearing, and the bearing has a symmetrical structure of four oil chambers. The equipment recently appeared in the grinding wheel spindle hydrostatic bearing vice research and death, we have successfully repaired it. The following is a summary of the repair process of the hydrostatic bearing by combining the repair process with the cause of equipment failure. Fault reason analysis The grinding wheel spindle (grinding wheel spindle) bearing grinding causes mainly in two aspects: the first is the blockage of the oil pumping oil passage: the second is the blockage of the main oil passage entering the bearing oil chamber. These two reasons will directly lead to insufficient lubricant oil or insufficient oil pressure to enter the bearing oil chamber, which will cause the bearing pair to break out when the grinding wheel spindle is started.

The blockage of the oil supply circuit is mainly at the oil filter. M1083A has a triple oil filter on the oil supply road, especially the fine filter is easy to be blocked or the filter paper melts, causing the oil supply pressure to drop, the oil quantity is insufficient, the oil pressure is too low, and the spindle starter electrical interlock system fails, resulting in static The pressure bearing vice researched and died.

The oil passage blockage into the bearing oil chamber is mainly at the gap of the membrane feedback throttle valve. When the gap is severely blocked, the amount of oil entering the oil chamber is small, the oil pressure is very low, the spindle does not float well in the bearing, and if the grinding wheel is turned, it will not move or be heavy. The main shaft also causes the hydrostatic bearing to die.

1.2-105mm and bearing fit clearance 0.055 ~ 0.060mm2.2-? 105mm ovality, taper tolerance 0.002mmM1083A wheel frame spindle sketch M1083A wheel frame spindle parts as shown on the right. 2Remediation process After we removed the grinding wheel spindle, we found that the fault was mainly in the front bearing of the main shaft, and the rear bearing had no obvious grinding marks. First, we use the micrometer to accurately measure the front journal of the spindle. The actual size is 105-0.008-0.007mm. The inner diameter of the bearing is measured by the inner diameter dial gauge to be 105+0.048+0.051mm. The clearance requirement of the static pressure bearing pair is 0.006D (D is the nominal size of the spindle journal), the M1083A spindle journal D=105mm, and the technical requirements of the fit clearance should be 0.063mm. The matching clearance required by the design is 0.055~0.060mm. After the actual measurement size, it can basically meet the requirements of the matching clearance between the main shaft and the bearing. The roundness error of the spindle journal is 0.001mm, which meets the tolerance of 0.002mm roundness required by the drawings, thus ensuring the rotation precision and rigidity of the spindle parts of the equipment. It can be seen from the removed spindle that there is no obvious scar on the surface of the spindle journal. We polished the surface of the spindle journal on the C630-1 lathe to make the surface reach Ra0.8μm. The journal is re-measured and measures 105-0.010-0.008 mm. In addition, if there is obvious scratch on the surface of the spindle journal, the spindle journal must be finely ground to ensure the surface roughness: if the journal becomes smaller after grinding, the clearance between the spindle and the bearing cannot be met, then it must be The spindle journal is reliably plated to ensure that the matching clearance of the spindle-bearing pair meets the technical requirements, otherwise the rigidity and normal operation of the equipment will be seriously affected.

Check the inner hole of the bearing, and find that there are obvious friction marks on the front bearing hole, and the precision of the main shaft journal and the like are basically within the tolerance range, and the excessive tolerance of the main shaft is excluded. At the same time, check the lubricating oil road and find that the oil circuit is seriously blocked. After the spindle journal polishing reaches the required surface roughness, the repair of the bearing bore is more complicated, difficult to operate, and the accuracy is not guaranteed. We first design a diameter of 105+0.038+0.040mm test mandrel according to the spindle journal?105-0.010-0.008mm size and the required clearance between the main shaft and the bearing 0.063mm, the taper and roundness tolerance It is 0.002mm, as the final inspection tool, at the same time, the design and production of the 105+0.038+0.040mm mandrel can be smoothly inserted into the bearing inner hole and the contact between the inner hole of the bearing and the inner hole of the bearing is checked with the powder. carry out. Finally, use an internal diameter dial gauge to accurately verify the bore size of the bearing.

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Type of damage in plain bearings

1. Scratch (two-body abrasive wear)

The hard particles moving together with the shaft diameter are in contact with the friction surface, which is the lower contact stress between the particles and the metal surface, and they are drawn on the surface of the bearing pad; the hard particles semi-inlaid on the surface of the bearing pad are also on the surface of the shaft diameter. Lines are scarred and are called scratches. Scratch is a two-body abrasive wear, and the direction of the linear flaw is consistent with the direction of the shaft diameter.

The lubricating oil film is broken, and the hub peak on the shaft diameter surface will also scratch the bearing bush, and many linear scratches appear, which is also the two-body abrasive wear.

The hard particles are embedded in the surface of the bearing shell and fall off, causing scratches of the point-like scar.

Most of the above particles are iron and sand.

The scratching causes the surface of the friction pair to be roughened, thereby reducing the load bearing capacity of the lubricating oil film, and forming new hard particles and hub peaks that can scratch the friction surface, causing a vicious cycle.

2. (three-body) abrasive wear

The smaller hard particles entering the bearing gap migrate between the two friction surfaces, creating extremely high contact stress on the friction surface, forming a three-body abrasive wear, similar to the grinding action, causing the bearing pad and the shaft diameter surface to wear. The high contact stress between the hard particles and the friction surface causes plastic deformation or fatigue damage to the friction surface of the ductile metal, causing brittle fracture or peeling of the friction surface of the brittle metal.

The scratches of the abrasive wear are also linear, and the direction is also consistent with the direction of the shaft diameter.

When there is edge contact, lack of lubricating oil or cracking of the oil film, severe abrasive wear will occur. Abrasive wear will result in shaft diameter and/or bearing geometry and shape changes, loss of precision, and increased bearing clearance, causing the sliding bearing performance to deteriorate dramatically before the expected life.

3. Bite (gluing)

In the state where the lubricating oil film is broken or lacks oil, a large friction factor causes a large amount of frictional heat to be generated, and the bearing temperature rises. At high temperatures, the low melting point metal of one friction surface adheres to the other friction surface due to softening, and the adhered metal is detached from the original surface and transferred to the other friction surface due to the shearing action caused by the rotational movement of the shaft diameter. Causes obvious pits and raised scratches on the friction surface. This damage is adhesive wear.

When bite sticking occurs, the friction sharply increases and the bearing temperature further rises, forming a vicious circle. When the adhesion is serious, the power of the shaft diameter rotation can no longer cut the bonding point, the shaft diameter movement will be terminated, commonly known as the "holding shaft", and the bearing is completely damaged.

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