As a technical supplier, you’ve probably experienced this often: A customer complains about a broken bearing and is convinced that the fault lies with the manufacturer’s production. In fact, this is only rarely the case; damaged bearings are almost always the result of improper use. This article will help you identify possible causes of damage to rolling bearings and includes images that you can use to compare with the damaged bearings. Detailed fault and failure analyses can also be obtained from the respective manufacturer upon request.

As with all mechanical components, technically correct mounting and careful maintenance/care of rolling bearings are essential for a long service life. If not, damage can occur that may cause loss of performance, downtime and increased maintenance costs. The reasons for premature bearing failure are manifold and can have several causes, some of which are interrelated and the result of previous failures.

First, let’s take a closer look: Damaged rolling bearings can fail either prematurely or after their calculated service life. Since they are subject to wear, material fatigue is unavoidable after a certain period of time and occurs naturally. With higher loads, this happens after a shorter period of use than with moderate loads. In addition to time, stress also plays a decisive role here. If the standard service life has been exceeded, it is time to replace the bearing or machine/application.

With premature bearing failures, however, the situation is different: As mentioned before, failures here are due to improper handling and can usually be avoided. Statistically, as many as 99% of all premature rolling bearing failures are caused by mounting or maintenance errors. (Source: Schaeffler)

Possible reasons are:

1. Handling and mounting errors

Improper mounting of the rolling bearings can have far-reaching consequences for the application. Therefore, it is essential to carefully follow the manufacturer’s instructions and use appropriate tools and techniques for mounting the bearings. If the bearing is not properly aligned or mounted with the correct tightening torque, this will sometimes result in increased load, vibration and premature failure. Improper installation may also cause physical deformations such as indentations, cracks or fractures to the bearing. External warning signals include the application developing a high temperature and/or unusual noise when operating.

2. Contamination

If contaminants such as dust, dirt, metal chips, liquid or other particles enter the rolling bearing, they can break through the lubricant film, damage the surfaces, lead to corrosion and accelerate abrasive wear. Abrasive wear occurs when hard particles rub across a surface. As a result, the raceway material gradually wears away, so that the bearing can no longer operate properly and eventually fails. You can detect contamination, for example, by foreign bodies in the bearing and/or by (irregular) indentations, deformations or corrosion on the raceway. A clean environment and the use of seals or covers help minimise contamination and reduce the risk of damage.

3. (Excessive) load

Each bearing type has a maximum load limit, which is specified by the respective manufacturer in the product catalogue. If the limit is exceeded, wear, cracks, material chipping, fatigue or deformation often occur. Excessive load can also be caused by misalignment or insufficient/incorrect lubrication – it is sometimes a combination of both that causes premature failure of the bearing. Regular checks of the load limits and compliance with the manufacturer’s specifications are essential to prevent consequential damage.

4. Vibrations

Vibration and shock loads are caused, for example, by incorrect machine alignment, improper installation or imbalance of the application and can also promote increased wear on the rolling bearing or damage to surrounding components. Regular checks of machine alignment, the use of vibration damping elements and the reduction of shock loads help to minimise the risk of rolling bearing damage due to vibration.

5. Lubrication

Lubrication significantly influences the service life of rolling bearings. Insufficient, excessive or irregular lubrication as well as the use of incorrect lubricants lead to increased friction and overheating and, as a consequence, ultimately to premature bearing failure. It also promotes adhesive wear, which means that material is transferred from one surface to another. This can happen if the lubricant film is so thin that it disappears during operation (for example at high speed) and the metallic surfaces ‘rub’ against each other. This in turn promotes the formation of cracks or fractures within the bearing.

In addition, different lubricants must not be mixed, as they may consist of different chemical compositions that react with each other. This can reduce the performance of the bearing and, in the worst case, cause damage to the components. That is why most manufacturers recommend the use of certain lubricants that are specifically designed for their products. Failure to follow these recommendations and mixing lubricants or using them in non-recommended temperature ranges may void the warranty. Therefore, it is particularly important to observe specified lubrication intervals, use the recommended lubricants and ensure that the lubrication system is functioning properly.

6. Corrosion

Corrosion damage can have several triggers, but moisture is always involved. Corrosion involves a chemical reaction between a metallic surface and the oxygen in the air or an oxidizing substance such as water, steam, or acid. This causes rust to form on the steel. Rust consists mainly of iron oxide, which forms when iron reacts with oxygen and water. It is often triggered by incorrect storage or use in excessively humid locations, inadequate sealing or packaging of the bearing, or due to insufficient use of corrosion protection agent.

Handling without appropriate hand protection can also lead to corrosion of the bearing, as the protective oil film can be broken through unprotected contact. This can be recognised by fingerprints on the outer ring, for example. It is therefore strongly recommended to wear work gloves when handling rolling bearings.

Fretting corrosion is due to a combination of moisture, corrosion and friction. It only occurs on the mating surfaces of the rolling bearings. Rolling bearings are designed to minimise possible friction through their movements.

However, interfering factors such as moisture and corrosion often lead to increased friction, which in turn generates heat, thus further accelerating the potential corrosion.

‘Standstill marks’ or ‘ripple formations’ occur in the rolling contacts of bearings. In this case, micro-movements are caused by vibrations, which cause indentations on the running surfaces and displace the lubricant film from the contact area. The lack of lubrication makes the area vulnerable to vibratory corrosion.

7. Electrical current

In addition to ‘classic’ corrosion, there is also electrocorrosion. Also referred to as ‘electroerosion,’ it is caused by damaging electrical currents in applications such as electric motors and power generators. When current flows through the bearing, a concentrated electrical discharge occurs. Due to the heat generated, small craters form on the bearing and the material is eroded. Such electroerosion can be prevented by appropriate insulation, for example by ceramic coatings on the outer or inner ring or by rolling elements made of ceramic. These interrupt the conductivity of the metal and thus render the current flow harmless to the bearing.

Conclusion: Bearing damage can be avoided in many cases through proper installation, regular inspections, adequate lubrication, and minimising contamination, vibration, and shock loads.

If damage does occur, the component will display characteristics that point to the root cause. Sometimes a chain of several causes is responsible for the failure. In any case, technical experts are able to identify the damage and find out the causes. If you use the above points as a guide, you will be well prepared for an initial damage assessment in the event of a customer complaint.