Bearing Failure Analysis
When bearings fail to meet their expected life or performance levels, they can create a long list of unanticipated consequences including loss of revenue and increased expenses. To help mitigate failures and provide remedial action, AST can expertly examine, test, and analyze a wide range of bearing performance parameters in our laboratories. We can perform failure analysis on your bearings regardless of brand, and even if they were sourced elsewhere.
Simply stated, AST has the tools and experience to guide it’s customer into understanding what may or did cause the early failure and guide customers towards preventive action. Through the use of video microscope, dimensional inspection including roundness, raceway radius, and surface roughness (Ra), hardness, torque, and digital noise/vibration, AST has the means to isolate and identify the root cause of an early failure.
AST may find one or more of the following while identifying an early bearing failure:
- Brinelling – Bearing raceway damage that is usually caused by the mounting or dismounting of the bearings (typically from a thrust force). It is identified by minute dents corresponding with the ball locations high on the shoulder of the race. However, brinelling can also be caused by hammer blows to the bearing or a shock load exerted on a static shaft.
- Cage Damage – There are a number of causes for cage damage, some of these are: vibration, excessive speed, wear, & blockage.
- Contamination – Contamination failure is caused by the entrance of foreign objects into the bearing which leave marks such as, scratches, pits, and lapping of the raceways.
- Electric Arcing – Electric Arc Erosion occurs when an electric current, passing through a bearing, is broken at the contact surface between races and rolling elements. This can produce high temperatures at localized points. This produces pits on the raceways and rolling elements. Some causes are static electricity from belts along with faulty wiring and short circuits.
- False Brinelling – Bearing ring damage which is caused by vibration in a static bearing. This may occur during transport of equipment or by vibration from running equipment. The tell-tale indications are axial and circumferential indentations on the raceways. Although its appearance is similar to that of Brinelling, False Brinelling is characterized by attrition of the steel and is the result of a combination of mechanical and chemical action.
- Fatigue Failure – Is commonly characterized by flaking or spalling of the raceway. Fatigue failure is a result of a granular weakening of the bearing steel which begins at the sub-surface and propagates to the raceway. While this may occur at the end of the normal life expectancy of the bearing, it frequently occurs before then due to an excessive loads.
- Lubrication Failure – If the grease is stiff or caked and changed in color, it indicates lubrication failure. The original color will usually turn to a dark shade or jet black. The grease will have an odor of burnt petroleum oil. Lubricity will be lost as a result of lack of oil. In cases of Lithium base greases, the residue appears like a glossy, brittle varnish which will shatter when probed with a sharp instrument.
- Misalignment – Ball or Roller Path; When one side of a bearing is misaligned in relation to the other, the ball or roller path will run from one side of the race to the other around one-half of the circumference on the non-rotating ring. The rotating ring will have a wide roller path. This can result in high temperature and destroy the lubricant
- Path Patterns – By examining the wear path pattern in a dismantled bearing that has been in service, it is possible to gain a good idea of the conditions under which the bearing has operated. By understanding a normal and abnormal wear path, it is most likely possible to assess correctly if the bearing has run under the proper conditions.
Valuable information is obtained if bearings are disassembled and examined not only after failure but after a certain time of operation. If you dismount bearings for our analyses, please mark the bearing rings so you can reproduce the original position.
Contact us if you would like AST to assist in determining why any of your bearings failed to meet your expectations in performance or life expectancy. We will provide you “Value Beyond the Part.”