Every bearing will sooner or later become unserviceable over its intended life. Even when it is installed and serviced according to manufacturers recommendations. Raceway surfaces and rolling contact surfaces are subjected to compressive loads, and the surfaces eventually become subject to flaking.
However other failure modes which are a more common cause of failure include seizing, breakage, wear, false brinelling, and corrosion. In many cases, these failures are due to improper handling, poor selection, bad bearing design and poor maintenance. This article is intended to provide an overview discussion on key points to follow as a standard maintenance guideline.
Inspection of Bearings
Inspecting the bearings after initial installation while the machine is in operation will help in preventing future bearing failures. The following is a list of procedures you should follow.
Inspection when machine is running
Check the bearing temperatures and bearing vibration/noise and determine if the bearing is lubricated properly or needs more lubrication.
Inspection of bearings after operation
Bearings should be carefully examined in periodic maintenance inspections for you to note any damage. If damaged the bearing can be analyzed and the cause of failure determined. Remedies can then be provided to prevent further problems.
It is important to determine inspection procedures and establish regular inspection intervals.
Bearing Temperature
Bearing temperature generally will increase at start-up and stabilize at a temperature slightly lower than at start-up (normally 10 to 40 ̊C higher than room temperature) over a set period of time. The time for the operating temperature to stabilize depends on the size, type, speed, and lubrication. The heat dissipation depends on the operating environment of the surrounding components. The stabilization can range from as little as 20 minutes to several hours.
The thing to watch is if the bearing temperature does not stabilize but continues to rise. If the temperature continues to rise it may be the result of one of the following reasons:
- Extremely insufficient or excessive lubricant
- Poor installation of the bearings
- Extremely small bearing clearance or extremely heavy load
- Extremely high friction between lip and seal groove
- Improper lubricant type
- Creep between the fitting surfaces
If any of these conditions are present then operation should be stopped and an appropriate corrective action should be taken. A desirable bearing operating temperature is generally below 100 ̊C.
Mounting and Dismounting of Bearings
For bearing handling use gloves. When moving larger bearings use special lift and carrying tools designed specifically for mounting and dismounting bearings. Both SKF and Schaeffler offer these special types of tools and can be purchased from PIB by going to www.pibsales.com. The use of heat and oil-resistant gloves is recommended when handling hot or oily bearings. These gloves should have a durable outside and a soft non-allergenic inside. We recommend SKF TMBA gloves.
If large, heavy bearings are to be moved or held in position using a lifting tackle they should not be suspended at a single point utilizing a steel band or fabric belt. A spring between the hook of the lifting tackle and the belt facilitates proper positioning for the bearing when it is to be pushed onto a shaft.
Alignment tools
Misalignment of shafts, belt drives, and chain drives will contribute to machinery breakdowns.
Accurate alignment will prevent a large number of machinery breakdowns and reduce the number of shutdowns. Accurate alignment will help to extend the life of the bearings and machines.
In today’s challenging environment for cost reduction, the necessity of accurate alignment is needed more than ever.
Preparing for Mounting of bearings
Prior to the mounting process, one must ensure that the bearing, the shaft, and the housing are clean and free of any foreign particulates. It’s important to remember that even microscopic debris, when lodged between rolling elements, will cause excessive wear. Bearings should be kept in their original packaging until the moment of installation to prevent contamination.
Maintenance Tools
1. Bearing Pullers
A bearing puller is a mechanical tool specifically designed for the dismounting of bearings from a shaft. It typically consists of a central mandrel and two or more adjustable arms that grip the bearing securely. By turning the mandrel, a constant axial force is applied, enabling the removal of the bearing without damaging adjacent components. Different configurations, such as three-arm or two-arm pullers, cater to various bearing sizes and applications.
2. Bearing Induction Heaters
These devices utilize electromagnetic induction to generate controlled heat, facilitating the thermal expansion of bearings. Comprising a coil encased within a metallic core, bearing induction heaters pass an alternating current through the coil, inducing a magnetic field. The bearing, when placed within this field, heats uniformly. This controlled heating ensures that the bearing can be mounted onto the shaft with reduced force, minimizing the risk of installation damage.
3. Shaft Alignment Tools
Shaft misalignment can lead to uneven load distribution in bearings, reducing their operational life. Laser shaft alignment tools are designed to achieve precise alignment between two connected shafts. Utilizing laser diodes and detectors, these tools measure angular and radial deviations, providing real-time feedback to technicians. With such data, necessary adjustments can be made, ensuring optimal bearing function.
4. Lubrication Dispensers
Correct lubrication is vital for bearing longevity. Lubrication dispensers, which include manual grease guns and automatic lubricators, deliver a specified amount of lubricant to the bearing. Precision in lubrication application reduces frictional wear, prevents contamination ingress, and ensures efficient heat dissipation.
5. Stethoscopes and Vibration Analyzers
For diagnostic purposes, mechanical stethoscopes and vibration analyzers are employed. Mechanical stethoscopes, equipped with a probe, allow technicians to listen to the operational sounds of a bearing, identifying irregularities like pitting or misalignment. Vibration analyzers, on the other hand, measure the amplitude and frequency of vibrations from the bearing. By analyzing this data, one can ascertain issues like imbalance, misalignment, or early signs of wear.
Conclusion
Bearings play a pivotal role in machinery operation. Adopting a good maintenance strategy, as detailed in this discussion, can optimize equipment efficiency, minimize operational interruptions, and yield considerable economic benefits.
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Selecting appropriate shaft and housing tightness fits are critical in optimizing a single row radial ball bearing’s performance and life. A bearing can only perform to its full capacity when it is correctly fitted on the shaft and in the housing. Improper fits can lead to undesirable operating conditions and early failure.
Below are some of the common considerations bearing users should consider:
Direction, type, and magnitude of loads
Based on the actual applied axial and radial loads an equivalent radial load is calculated. Generally, tighter fits are required as the load increases. Further, rings subjected to circumferential loading should have tight fits. For rings subjected to only point loading, a loose fit may be used.
Inner or outer ring rotation
Typically, the ring that is rotating requires an interference fit, and the non-rotating ring would have a slightly loose fit.
The size and type of bearing specified
Thin type and miniature bearings are very sensitive to interference fits due to loss of radial play. Bearings with heavier cross sections generally require tighter fits.
Material and manufacturing tolerances of mating components.
Fit tolerances are based on cast iron or steel housings and shafts. For alloys such as aluminum (with a different modulus of elasticity), a tighter fit is required to achieve rigid seating.
Operating temperature
With tight fits and a temperature differential between the inner and outer ring, the radial internal clearance in the bearing is reduced. This must be taken into consideration when selecting the internal clearance. Additionally, if the materials used for the housing or shaft are dissimilar, they will have different coefficients of thermal expansion than the bearing rings. This must be taken into consideration to achieve rigid seating.
Running accuracy required
In order to achieve high running accuracy, the same high standard of accuracy and surface quality expected in the bearing must be applied to the shaft and housing as well. In addition, with miniature and thin type bearings irregularities on the shaft or in the housing are transferred to the relatively thin walled bearing rings.
Want to learn more about radial ball bearings and the factors that can extend or shorten their operating lives? Try AST’s new calculator.
If you need assistance with understanding radial ball bearings fits, our team of bearing experts are standing by to provide engineering consulting and design.
The global bearings market size is expected to reach USD 186.1 billion by 2025, according to a new report by Grand View Research, Inc.
Bearings are essential in almost every application that involves motion and they help minimize friction between different mechanical components in several industrial machinery and equipment, resulting in reduced energy consumption.
Hence, this machine element finds application in all industries, ranging from automobiles, household appliances, and aerospace to industrial machinery, using machinery or related motor-driven linkages.The bearings market is estimated to witness a considerable growth in the forthcoming years, ascribed to the aim to achieve energy efficiency.
Energy saving and bearings go hand-in-hand.
The main objective of this element is saving energy by reducing friction, be it during the rotation of shafts of a transmission or the wheel of a vehicle.
Additionally, rising demand for commercial vehicles is expected to catapult the demand from automotive sector across the world.Technological advancements including smart bearings, development of advanced materials and lubricants, and integrating sensor units, are anticipated to provide high growth potential to the market.
