Equipment engineers are responsible for the selection and verification calculations of bearings in equipment. However, the installation of the equipment bearings also plays a crucial role in their normal operation. Inappropriate installation methods often cause initial damage to the bearings.
This damage can sometimes be detected during the factory testing of the equipment, but at other times it is discovered after the equipment is put into use due to its impact on bearing operation.
The damage caused by improper bearing installation ranges from minor to severe. If the installation process causes relatively severe bearing damage, the bearing will show abnormal noise, vibration, or even overheating during factory testing.
At this point, for the equipment manufacturer, corrections can be made in time and the bearing replaced. Though this does not cause trouble for the equipment user, it does result in direct losses for the equipment manufacturer.
If the damage caused by improper bearing installation is relatively minor, it may not be easily detected during the equipment’s factory testing. Once the equipment is put into operation, the damage caused by improper installation often becomes the cause of subsequent secondary failures, leading to other serious problems.
Such bearing failures are typically discovered during the equipment failure diagnosis process. The losses caused at this time are not only for the equipment manufacturer but also for the equipment user.
This article introduces some factors of bearing installation damage and the diagnosis and analysis of the damage.
Firstly, cleanliness is crucial.
Bearings themselves are precision mechanical components. When a bearing is in operation, only a very thin lubricant film separates the rolling elements and the raceway. The thickness of this lubricant film is only about one to two hundredths of the thickness of a piece of paper. This lubricant film is a vital factor for the normal operation of the bearing.
If the lubricant film is damaged, it will result in direct metal-to-metal contact within the bearing. Generally, the diameter of dust particles is far greater than the thickness of the lubricant film.
Therefore, when contamination is present inside the bearing, it can lead to pollutants piercing the lubricant film, affecting the lubrication performance of the bearing. This is a major cause of premature bearing failure.
The image below illustrates the damage caused by internal contamination within a deep groove ball bearing.
Additionally, if liquid contaminants infiltrate the bearings, it can lead to issues such as corrosion of the bearings and degradation of the lubricating grease, both of which can result in lubrication failure.
Hence, one of the critical factors during the bearing installation process is cleanliness. This cleanliness pertains to the environment where the bearing is installed, the cleanliness of the installation tools, the shaft, and the bearing housing. All of these need to be thoroughly cleaned before installing the bearing.
Moreover, care must be taken to avoid contaminating the bearing and lubricant during the installation process.
Installation force through rolling elements
For non-separable bearings, the outer and inner rings are often integrated. Typically, at least one component among the bearing, shaft, or bearing housing would be a tight fit. For example, in horizontally mounted rotating machines, the inner ring is often a tight fit. Therefore, during the installation, a certain amount of installation force is sometimes applied. For bearings with a diameter less than 100mm, a cold installation method is utilized, applying an external installation force.
Bearings possess a certain load-bearing capacity. The installation force applied during a cold installation is typically axial. However, the axial load-bearing capacity of the bearing during operation is dynamic, whereas the installation force during a cold installation is a static (non-rotating) impact load.
Such an impact load can cause certain effects on the rolling elements’ surface. When this impact load results in initial damage on the surface of the rolling elements, it begins with tiny indentations. Bearings with these indentations may sometimes produce noise during operation.
If these minor indentations are not detected during the factory inspection, stress concentration at the edges of the indentations may occur during bearing operation, leading to secondary damage. The image below shows a minor installation indentation on a deep groove ball bearing.
The previously mentioned two factors are the main types of bearing installation damage. In addition to these, improper bearing installation also includes: incorrect amount of bearing grease filling; inadequate bearing grease filling; and other impacts causing bearing damage and deformation, among other issues.
An incorrect amount of bearing grease filling and inadequate lubrication can result in bearing noise and abnormal heating of the bearing. Damage and deformation caused by external impact on the bearing are sometimes visible to the naked eye. Such damage may lead to problems like bearing fractures due to stress concentration.