Bearing Damage Analysis for Tapered Roller Bearings
During operation, Timken Tapered Roller Bearings undergo enormous amounts of stress. This stress can cause extensive damage to the bearing if it has inadequate or contaminated lubricant, was damaged or dropped during installation, or was adjusted or installed improperly. Today, we’ll look at ways to tell what went wrong with a bearing by looking at the type of damage it received.
First, we look at the effects of debris contamination on the bearing. Debris contamination causes small bruises or indentations along the raceway, reducing the lifespan of the bearing. This debris can come from any number of sources, including a leaky seal, contaminated lubricant, other fatigued parts, or the use of a brass tool during installation. This is why cleanliness during bearing installation is so vital to ensuring safe operation.
Water or moisture contamination is also a common cause of bearing damage. This moisture could enter the bearing during the installation or could be the result of fluctuating temperatures forcing the steel to sweat or extract moisture from the air. This moisture rusts or etches away at the raceway material creating dark lines along the race roller contact points. If a bearing with etching damage is used, the resulting stress along the damaged sections will cause it to look something like this. As you can see, the etched areas of the raceway have suffered deep, extreme line spalling, due to the elevated stress in temperature the bearing undergoes during operation. Chunks of the raceway material have been torn off by the rollers as they pass causing damage to the bearing.
We don’t like to see it happen but we know that no matter how careful you are, sometimes a bearing is going to get dropped. If this happens, it is important to immediately examine the bearing for damage or deformation to the cage component. The damage shown in this picture is an extreme example and a lot of the time, the damage is not so obvious. For a closer examination, you can place the coned assembly into the cup, giving you an accurate reference point for spotting potential damage. Any time you damage the cage, we recommend discarding the bearing in favor of a new one.
This picture shows another possible result of cage damage. This damage, however, isn’t the result of a dropped bearing. What happened here, is that during the installation process, the operator made contact and pressed down on the front face of the cage causing it to spread or expand. This forced the cage into contact with the cup during operation, causing drag that skewed and deformed the cage ruining the bearing.
Using the proper tool during installation is vitally important. If the tool is made of a harder steel than the bearing components, it can cause deformations in the raceway that will result in spalling under the stress of operation. This is why we recommend the use of a mild steel bar (1020 to 1040) drift while handling our bearings.
Inadequate lubrication, either from a lack or shortage of lubrication, the use of improper lubrication, or worn out lubrication, can cause heat or welding damage similar to what you see in this picture. The damage will typically show up first along the large rib of the cone and the larger ends of the roller components. This is because the two areas are the only sections of our bearings that undergo sliding contact, which produces high levels of friction and heat when inadequately lubricated. Peeling or micro-spalling is also caused by inadequate lubrication, especially during high loads. This happens when an inadequate lubrication or overloading forces metal-to-metal contact between the raceway and the rollers generating excess heat and wearing away the raceway material. A more extreme case is shown here. Excessive preload during adjustment and/or overloading the vehicle can sometimes cause rapid and deep spalling, as seen in this picture. The enormous stress on the bearing caused by this excessive load heats the bearing to extreme temperatures, softening the material and allowing large chunks of material to be torn from both the raceway and the individual rollers.
At the opposite end of the spectrum, leaving excessive end-play during adjustment, or any improperly seated cup, can cause the sort of misalignment damage seen in this picture. Excessive end-play beyond our recommended .005 inches a mile, can allow the hub to rock back and forth during operation, disrupting the even distribution force along the rollers that our bearings depend on. This will result in one-sided deep spalling along the raceway or cone.
This ends our examination and discussion of the various causes of bearing damage. The common factor among all the examples given has been human error during the adjustment, handling, or lubrication stages of installation. This is because human error is the single most common cause of bearing failure.