Bearing Myths No. 4 Misapplication
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Join in and watch the series as we Reveal Mounting Bearings Myths - busted. This sereis covers Misalignment Myths
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Bearing Myths No. 4 Misapplication
- 1. Mounting Bearing Myths and Misconceptions Brought to you by Power Transmission Solutions
- 2. Reasons Bearings Fail Source: Combined published industry data and Emerson – Power Transmission Solutions compiled records. For more details visit www.emerson-ept.com.
Editor's Notes
- Punch line – if you can service and lube a bearing properly, you’ve addresses 2/3 of the reasons for failure
- Sealed For Life / Lubed For Life Means It Should Last Forever. Sealed for life bearings only last as long as the grease does. Once the bearing breaks down and can no longer provide adequate lubrication to the bearing, the bearing will fail. Grease life is dependent on the severity of the application. Bearing speed, load, temperature, contamination level, etc. can all have an effect on the life of a grease. Enhanced sealing, proper installation, and a good preventative maintenance program can increase bearing life. L10 is the number or hours that 90% of a batch of bearings are expected to survive in laboratory conditions. (Laboratory conditions consist of a clean, temperature controlled environment with sufficient lubrication.) More on next page …
- Sealed For Life / Lubed For Life Means It Should Last Forever. (cont’d) The Theoretical Life of a Ball Bearing can be calculated by using the equation on this slide. Tapered Roller and Spherical Roller Bearings utilize a different version of this equation. Please refer to the manufacturer’s catalog for more information on Theoretical Bearing Life. It is important to note that the L10 equation is only based on the properties of the steel and the geometries of the raceways and rolling elements. The effects of lubrication are not included in the L10 equation ... it assumes adequate lubrication, stable operating temperature, no contamination, etc.
- Bearing Failures are Always the Manufacturer’s Fault. Bearings are typically subjected to a number of rigorous inspections to ensure proper operation. On rare occasions a manufacturing anomaly can occur, however most failures are due to misuse and/or application related problems. Modes of failure could include loss of shaft lock, inadequate lubrication, overloading, impact loading, external vibration, contamination, excessive heat exposure, static misalignment, dynamic misalignment, thrust loading …
- Bigger Bearings Are Better. Larger bearings may carry more load and show an increased theoretical life (L10), but they can’t run as fast. Skidding can occur when light loads & high speeds are present. In the case of Skidding, the rolling elements slide along the raceways instead of rolling. This sliding motion causes friction, which produces heat and can lead to a reduction in bearing performance.
- Bearings Can Only Rotate in One Direction. Bearings can rotate in both directions, however Eccentric Locking bearings can only maintain shaft lock by rotating in one direction. During installation, the Eccentric Lock Collar must be locked in the direction of shaft rotation. If the direction of rotation is reversed, the Eccentric Lock Collar could come loose and the bearing may lose lock to the shaft. If reversing shaft rotation is present in the application, a set screw or concentric collar locking bearing has a better chance at maintaining shaft lock.
- Locking Mechanisms Are All the Same. Set Screws bite into the shaft and can lead to shaft marring. Eccentric Lock Collars hold the shaft between the collar and the inner ring. Concentric Lock Collars provide a 360° friction grip between the shaft and the inner ring. Tapered Adaptor Sleeves provide a near 360° friction grip between the shaft and the inner ring. Bearing can also be Press Fit onto the shaft. The more concentrically the shaft can be held, the lower the vibration (Concentric Lock Collar, Tapered Adaptor Sleeve). The roundness charts on the far right of this slide show the roundness of the inner raceway when the locking mechanism is attached to the shaft. These charts are on a 200 micro-inch scale, so the roundness is significantly amplified. The actual deformation would be difficult to see without the aid of measurement equipment.
- The Bearing Shouldn’t Burn My Hand When I Tough It. Under normal bearing operation, the bearings should not exceed 120°F, however extreme operating conditions could result in bearing temperatures above 180°F. As operating temperatures exceed 120°F, the grease will break down more readily and an increased relubrication frequency may be needed. Operating temperatures above 200°F may warrant the need for a high temperature grease. Just as a point of reference, the dishes and silverwear in restaurants are washed with 180°F water because it kills all the bacteria at that temperature. It will burn you. The graph in the bottom right corner of this slide shows an example of what happens to the operating temperature of a bearing at start-up. There is an initial temperature rise, which should eventually drop and stabilize. The same situation may occur during relubrication. The temperature will drop back down to normal operating temperatures once the grease volume inside the bearing stabilizes. The stabilized operating temperature of a bearing is the result of many factors. The key influences on operational temperature are bearing style, lubrication type, operational factors, environmental conditions and the level of maintenance. The particular bearing style (ball, roller, sleeve, etc.), the shaft mounting style (slip fit, adapter mounted, press fit, etc.) and auxiliary items (housings, seals, shields, flingers, etc.) all contribute to a final operating temperature. For a given set of application conditions, a particular bearing type will generate friction given off as heat. A typical bearing temperature rise range would be 40°F to 80°F (4°C to 27°C) for most industrial applications. However, a bearing temperature rise over ambient of up to a 120°F (49°C) can be observed at extreme conditions.
- Notice the fractured SAF style housings.