Bearing Failure Causes and Prevention
Bearings are in use throughout aircraft, automobiles, and marine craft. As such, they are subject to extreme conditions that, over time, can wear them down and eventually lead to failure. Factors such as fatigue, contamination, brinelling, misalignment, lubrication failure, and more can all be causes of bearing of failure. This blog will explore the two main causes of bearing failure - fatigue and contamination - how to identify them, and what causes them.
The first and most common cause of bearing failure is fatigue. Like any machine component, bearings are susceptible to wear and tear over time. Identifying fatigue is relatively simple - there are two hints that indicate your bearings are nearing failure: flaking of the raceway and noisy running of the bearing. Flaking of the normally smooth raceway is caused by weakening of the bearing steel on a granular level. This weakening begins as a small, internal fracture that progresses to the bearing surface and causes particles of metal to flake. This degradation will make the surface rough, increasing vibration and noise.
There are three causes of fatigue failure: normal wear and tear, bearing overload, and low-quality bearing steel. The lifespan of a bearing depends upon the load and speed imposed on the bearing. Fatigue failure occurs when a bearing is in use for longer than its intended lifespan. Unfortunately, this wear and tear can not be avoided. Even in a great machine with proper lubrication and use, the load and speed a bearing experiences will inevitably break it down over time. Bearing overload occurs when a bearing is radially or axially loaded beyond its intended capacity. Improper or misaligned installation can also make a bearing more susceptible to bearing overload. The final cause of fatigue failure stems from the use of non-bearing quality steel. This is common in roller bearings
, which often operate on raceways supplied by the customer. If the raceway is not made of proper steel, it will degrade far quicker than a raceway of higher quality steel.
The second most common cause of bearing failure is contamination. Contamination can occur due to debris, rust, or moisture. Debris can be identified by scratching around the outside of the raceway, indicating that particles of dirt or dust have entered the inner part of the bearing. When rust forms on the outer ring of a bearing, it will not typically interfere with the bearings performance, but could be indicative of rust within the bore, which is far more serious. If rust is found in the raceway or rolling elements, the bearing should be replaced immediately. The third identifier, moisture, can damage a bearing in multiple ways, namely corrosion and staining. Either of these will diminish bearing performance, increase noise, and make the bearing fail prematurely.
The causes of contamination are debris, abrasive waste materials, and moisture. Debris found in dirty work conditions are one of bearing’s most problematic issues. Taking measures to prevent outside materials from entering the bearings can save thousands of dollars each year. Abrasive waste material is a by-product of many bearing applications such as paper making, metal working, and food processing. The waste created by these actions will infringe on the bearings and eventually cause failure. The final cause of failure, moisture, results from water entering a bearing and reacting with the lubricant to form an acidic or corrosive chemical compound that attacks the bearing surface. Unlike other types of damage, moisture damage occurs when the bearing is stationary. This is because the lack of lubricant in the roller elements contact zones leads to degradation at points of contact.
Posted on May 14, 2020