There are thousands of web pages dedicated to inform agrarians what is wrong with their machinery and what to do to fix it. One of the most difficult tasks is to diagnose the issue of the breakage. This article is dedicated to the problem of bearings. In my article I have pointed out some most usual problems so you can diagnose them by yourself instead of relying on a mechanic.
Production of rolling bearings is carried out under stringent quality requirements. This is one of the most accurate devices that are available in engineering. In ideal operating conditions bearings can operate continuously for many years. Due to the fact that working conditions are rarely ideal, bearings never realise their potential in terms of resource use. Service ability of rolling bearings depends on the production, storage, maintenance, installation, working conditions and loading of bearing.
- Surface damage due to fatigue is connected with the problem of lubrication (lubrication discrepancy, its low viscosity and oil film breaks). With further development of the defect raceway surface begins to peel and crack (it should be noted that this detachment is not as serious as ever spalling on the raceway). With the accumulation of fatigue in the material of the raceway surface becomes rough, bearing makes noise and excess heat. Permanent overload, poorly treated and contaminated surfaces inevitably lead to fatigue phenomena. This can be avoided or significantly slow down if the bearing is clean and well lubricated.
- Surface crumbling is similar to surface fatigue, but bearing damage differ and may indicate that the bearing has exhausted its fatigue resource. Cracking and crumbling surfaces is characterised by deep cracks and delamination. This occurs, when internal cracks that occur in locations of non-metallic components in steel of the bearing, reach the surface. Premature cracking is often caused by poor shaft planting, housing curvature and incorrect installation of the bearing, i.e. conditions that cause too high cyclical stress.
- Abrasive wear. Abrasive destroys metal surface of the bearing. Depending on the type of abrasive wear, the surface gets dull grey or metallic colour or mirror polished. Sometimes, bearing due to changes in its geometry breaks down. Small abrasive dust is a common cause of this breakage. This dust can get into the bearing during installation, due to a bad sealing or dirty lubrication. Therefore, when installing the bearing, it is recommended to wipe every element with a clean tissue before lubricating and maintain a clean work surface. Good sealing and lubricants will help to prevent contamination after installing the bearing.
- Atmospheric corrosion. Corrosion caused by moisture, entering the bearing from the atmosphere. Moist air getting inside the bearing, cooling condenses the environment, breaking the oil film at points of contact paths and rolling elements. Atmospheric corrosion can be prevented by using a good oil seals, lubrication and good lubricating bearings. In some cases, special seals may be necessary to avoid grease splattering. Bearing should be filled with the lubrication at every relatively long machine stop.
- Fretting-corrosion. Fretting-corrosion is very similar to ordinary corrosion. It occurs on the surface where the bearing lands on the shaft, as well as on other adjacent surfaces. It is caused by small (microscopic) loads. The particles resulting from wear are black in the absence of air or red in its presence. Fretting-corrosion can cause weakening of landing the inner ring on the shaft; and its wedge at which it can not be removed. Fretting-corrosion leads to breakage of the ring. It may be prevent following the manufacturer’s recommendations and making sure that the items adjusted optimally.
- When brinelling on the surfaces of rings one by one, regularly, appear indentations. This is the result of plastic deformation of metal in the places of indentations, resulting from overexertion metal. Brinelling is the result of high static or shock loads, improper installation technology of the bearing, strong mechanical shock arising from the drop of the machine. Brinelling can be prevented using pressure, during its installation, instead of strokes. If shock strokes are unavoidable during installation or in service, then must be used bearings, designed for larger loads.
- Pseudobrinelling is the same as usual brinelling, characterized by indentation on the rolling raceways. However, unlike ordinary brinelling, identations are characterized not only by metal push in plastic deformation zones, but also its displacement, as a result, damaged places are difficult to see even with careful examination. Pseudobrinelling is the result of strong machine vibration in out-of-work order. Sometimes this occurs during transportation. Also, vibrations of other nearby machines, affect it. This problem can be avoided by ensuring proper mounting of shafts with bearings, when transportating and isolating equipment from adjacent vibrating units, using separate foundations.
- Electrical damage, spot welding occurs as a result of electric welding and often has a regular character on the surface of rolling elements and on the rolling raceway. It occurs in the result of passing of an electric current through the bearing. Electric current can also be caused by random chipping. The most common causes of electric damage is static electricity generated by conveyors belts and current of welding machines. Therefore, transporters should be equipped with earthing straps. Welding equipment also require earthing.
- Rubbing occurs as a result of displacement of metal from one surface to another. Rubbing are caused by slipping of the bearing because of overloading and lack of lubrication. Rubbing on the ends of the cylindrical rollers can occur due to excessive axial load on the bearing. It can also appear as the result of improper assembly or insufficient lubrication of the bearing.
- Scoring on the surface is a result of abrasive wear and appear as deep scratches on the raceways and rolling elements. Some scorings of surface make stress concentration points with possible fatigue disclosure. Surface scoring caused by relatively large particles of material that fall into the bearing and move on raceways at motion of rolling elements. Like other problems connected with pollution, surface scoring can be prevented improving sealing and component cleaning.
- Indentation – a type of damage of bearings, similar to brinelling, because indentions are rather the result of plastic deformation, than wear. However, they occur when surface damage (scratches, abrasion by small foreign particles). Rolling elements when rotating capture foreign particles that fall into the bearing. These particles, once on the rolling raceway, leave random notchings where concentration of stress appears and rupture the oil film, leading to fatigue, chipping metal and the appearance of indentations. Probability of indentations reduces when using good sealings and frequent lubrication of bearings, which washes away foreign particles.
- Damage, while assembling. As an example, damage while assembling is possible when the outer ring is installed improperly and when the bearing was assembled, the rollers left dents on the rolling raceways.
- Overheating is often caused by insufficient lubrication, friction of outer ring and shaft rotation, excessive wringing out of the outer ring, when installing into the car trunk or too high speed of the shaft. In certain cases, overheating of the bearing can be caused by an external source, such as thermal oven.
- Rings misalignment leads to fretting-corrosion and chipping. Misalignment leads to high axial loads, causing destruction and strength surface, spalling because of fatigue.
- The destruction due to imbalance. The imbalance of the rotor provides the main load on the bearing. Sometimes the damage can be detected only in one place on the inner ring. To reduce imbalance it is required to balance individual parts of the rotor as accurately as possible, especially when working at high speeds.
- Flacking, fragmentation of spare parts. The reason is the large bearing overload. Chipping zone due to fatigue inner ring covers the entire width of the ring, and the separator is broken into pieces by transverse cracks in the nest of every ball.
- Damage of the cage, occurs as a result of cracks in it and its destruction. This, in turn, leads to rapid failure of the bearing as a whole, caused because of the cage. The most common cause of failure of the cage is its bending that occurs during movement of balls on intersecting trajectories, because of misalignment. Also, damage of the separator can be caused because of incorrect assembling, pollution or untimely bearing lubrication.