10 Villains who are attacking your bearings and how to fight them.

Bearings are precision parts and as such we must treat them, they are the dynamic supports of the rotating machinery.

In general, all the large bearing manufacturers secure in their production processes that the bearings comply with the highest quality standards, thereby ensuring a reliable bearing. 

Even so, some bearings will fail prematurely causing damage to the machinery and production processes, below we present ten villains that are attacking your bearings, what are their failure tactics and modes and what to do to fight them. 

1. LUBRICATION: It is no secret to anyone that about three quarters of bearing failures is due to an inadequate lubrication, this is because the most important part is the lubricant film created through the viscosity of the base oil, the causes that provoke this deficiency include: inadequate lubricants, excessive amounts, degradation, starvation, and lack of it. 

FAILURE MODE: The most appropriate way to discover this type of failure is through the ISO 15243 standard where it is characterized by abrasive and adhesive wear, raceways fatigue, overheating, it is common to find scratches and discoloration. 

WHAT TO DO TO PREVENT FAILURE: Use the correct lubricant, with the appropriate frequency, in the precise quantity, applying in the correct place, using the appropriate method and with the appropriate condition.

Right now, we have the technology and knowledge to migrate to a condition-based lubrication, which is the best way to avoid this kind of failure. 

2. CONTAMINATION: Caused by the ingress of foreign particles typically contained in the lubricant due an incorrect application or by the process itself with the ingress of water or solid particles. 

FAILURE MODE: Indentations on raceways and rolling elements, micro crater formation, and V-shape marks.

 WHAT TO DO TO PREVENT FAILURE: Implement procedures focused on the correct storage of lubricants, filter new lubricants, identification and labeling to avoid miscibility, clean work areas, grease fittings and greasers, use clean gloves to reduce the risk of contamination , improve sealing systems on equipment. 

3. FALSE BRINELLING: Caused by vibration between rolling elements and raceways, lack of rotation, inappropriate transport, improper storage, also occurs in backup, emergency or idle equipment due to vibration transmissibility.

FAILURE MODE: Reddish-colored discolorations at the same distance from the rolling elements, marks of the rolling elements on the raceways, shearing on raceways.

WHAT TO DO TO PREVENT FAILURE: Implement procedure to secure during transport for repaired equipment by fixing the shaft, properly store the bearings isolated from vibrations, dust and high ambient temperatures, periodically rotate field spares in/out of service, implement maintenance tasks for backup equipment. 

4. FETTING CORROSION (LOSS OF INTERFERENCE AT SHAFT LEVEL OR HOUSING): Caused by improper machining of the contact surfaces shaft or housing, typically the rotating ring is the one with the strongest adjustment, It can also occur by locating both bearings and not allowing axial displacement, or excessive vibration. 

FAILURE MODE: Since there are surfaces that are not fully in contact a chemical reaction takes place that leads to the oxidation of the surfaces, together with micro movements of the adjacent components cause loss of material, in extreme cases fracture of some of the rings.

 WHAT TO DO TO PREVENT FAILURE: Carry out a procedure to measure the shaft and the housing with a micrometer in each bearing replacement, compare it with the recommended shaft and housing fits, if it is out of dimension and / or shape proceed to machine properly, avoid use chisels, chemical composites or shaft knurling. 

5. COLD MOUNTING OVERLOAD (TRUE BRINELLING): Occurs when the bearing is cold mounted with unsuitable methods, for example: chisels, scratch awl, direct hammering, wood, steel or bronze bars. 

FAILURE MODE: The rolling elements being of a harder steel than the rings receives the impacts axially causing depressions on raceways, on early failure stages they cause scratches or small craters, in advanced stages there is loss of slack in the cage alveoli causing abrasive wear.

WHAT TO DO TO PREVENT FAILURE: Apply mounting force on the ring that rotates all over the circumference, if not possible at least 180° of it, follow the recommended assembly instructions and train your staff. 

6. HOT MOUNTING FAILURE (OVERHEATING): Caused by heating the bearing at temperatures greater than 257°F (125°C) affecting dimensional stability of the bearing, it is also occurred by heating the bearing with torches, oil bath without temperature control. 

FAILURE MODE: When heated above permitted temperature, the bearing undergoes an elastic deformation, the material may change metallurgically and produce alterations in diameter or hardness, in combination with load and speed this failure can provoke “clean” fractures.

WHAT TO DO TO PREVENT FAILURE: Mount the bearing with an induction heater at a temperature of 230°F (110°C9, train your personnel in the correct use of tools, wear clean protective gloves, push the bearing along the shaft as far as the abutment and hold the bearing in position, pressing until a tight fit is obtained. 

7. ELECTRICAL EROSION: Caused by the passage of current to the bearing or by excessive voltage, it is mainly due to the operation of equipment with frequency inverters (VFD), loss of insulation in connections, by electric arc when performing welding work and grounding on equipment plate or fixation bolts. 

FAILURE MODE: In the case of excessive voltage, sparks occur when current pass through the rolling elements causing loss of material which melts on the raceways causing t localized pitting both on the rolling elements and on the raceways. In case of current leakage there is a low intensity of current that is circulating between the components of the bearing which causes indentations and development of fluting in the raceway as well as gray and dark discolorations in the rolling elements, this happen due to the mechanical resonance vibration caused by the mechanical stress as the Hertzian contact zone passes over the small craters.

WHAT TO DO TO PREVENT FAILURE: Use insulated bearings to cut off the current flow, properly insulate your equipment, develop procedures for welding work where physical earth locations are indicated, use shaft grounding rings. 

8. MOISTURE CORROSION: Caused by long-term storage of equipment with lubricated bearings, also due to sealing failures and water ingress in backup equipment, mainly pumping equipment. 

FAILURE MODE: When condensation occurs or water ingress a chemical reaction occurs that causes oxidation leaving traces of engraving, the same happens in stored lubricated equipment the oil separates from its thickener causing damage.

WHAT TO DO TO PREVENT FAILURE: Implement a maintenance task for stored equipment where the shaft is rotated with certain frequency, use a lubricant with suitable properties, improve sealing systems on idle equipment.

9. MISALIGNMENT: Occur by not maintaining collinearity between equipment, the stress forces provoke overload in the bearing leading to a decrease in life and premature failure, can be caused in the same way by a shaft outside of tolerance, shoulders and housings, also occurs by mechanically fixing both bearings and not allowing shaft axial displacement by thermal growth. 

FAILURE MODE: Bearing overload, premature wear in the ring that rotates throughout its circumference, in the static ring wear appears on the loading area starting at one side going towards the center and ending in the opposite side.

WHAT TO DO TO PREVENT FAILURE: Improve your machining processes, implement proper mounting procedures, train your staff and align your shafts and pulleys using laser alignment systems. 

10. INCORRECT STORAGE AND HANDLING: Occurs when the bearing is not stored correctly, when the bearing is in its original packaging the damage is caused by external vibrations, also occurs for long periods of storage with high humid and temperature conditions, in case of being out of its packaging the damage is caused by the entry of contaminants. 

FAILURE MODE: The bearing receives external vibrations by machinery or heavy truck passing, also by storing several bearings horizontally, the rolling elements cause damage by impressions on raceways.

WHAT TO DO TO PREVENT FAILURE: Train your warehouse personnel, keep the shelves free of vibrations and dusts, control the temperature and humidity of the warehouse, do not remove the bearing from its original packaging until the moment of use, in case of losing the packaging cover the bearing with waxed paper and spray it with anticorrosive. 

Undoubtedly there is a large area of opportunity to establish procedures, tasks and standardization in their processes throughout the life cycle of the bearing and thereby avoid premature failures that affect your maintenance and reliability management system.

Thanks for reading, if you have any questions you can send me an email aperez@mtfrodamientos.com

-Alejandro Pérez