Archive: Apr 2016

Avoiding Bearing Failure with Rapid Speed Changes

Speed Changes Bring Fatigue

Like any industrial part, hardworking bearings are subject to fatigue from a number of different sources. One important factor to keep in mind for bearings is the effect of rapid speed changes on bearing service life.

If companies do not use bearings that are engineered specifically to withstand high speeds and rapid changes, these speed changes can cause slippage in the rolling elements and raceways of bearings, in addition to increased wear and degradation of cage guiding faces.

Detrimental Impacts on Bearings

Rapid speed changes occur across a broad array of industrial applications, from wood milling machines and reversible blooming mills to motor vehicle clutches and beyond. Almost all machinery and various types of motors undergo speed changes at some point during manufacturing processes. Results of such rapid velocity changes may include:

• • Cage Damage — While cage damage can be the result of many different factors, one of the primary causes is a rapid change in speed. When subject to excessive acceleration and retardation, pressure can rise considerably between the contacting surfaces. This often results in stress and fatigue, potentially causing costly bearing failures.

• • Broken Retainers — When used at higher speeds, inertial forces within bearings increase. Frequent stopping and starting combined with inadequate lubrication leads to high forces between the retainer and the rolling elements, resulting in crack in the retainer.

Solutions to Extend Service Life

To avoid the damage caused by rapid speed changes, it is essential for engineers to choose the most appropriate bearings for the given application and provide proper lubrication throughout the life of the bearing.

• • Proper Bearing Selection —  Selecting the ideal bearing suited for your specific project need ensures that your bearing will be prepared to handle the application without premature degradation. For example, bearings with smaller rolling elements and cross-sections can help reduce the mass of rotating bodies. This provides optimal adaptation to harsh conditions like rapid acceleration and retardation.

• • Proper Bearing Lubrication — Lubrication acts as a cushion between a bearing’s rolling elements and cage. The increased stress caused by rapid speed changes increases the need for re-lubrication to diminish the risk of bearing damage over time.

At Emerson Bearing, we maintain a complete array of solutions for virtually any bearing need. To learn how to prevent costly downtime and other results that occur from bearing failure, check out our Emerson Bearing Failure Analysis guide. The guide will help you to choose the best bearings for your applications, maximize efficiency and prevent bearing failure in the future.

Extending Bearing Service Life: Accounting for High Speed

An Important Factor in Bearing Maintenance

While bearings remain some of the most rugged and resilient components, they can still fall prey to the problems of
wear.

Unremedied, worn bearings can result in much larger problems; their failure almost inevitably brings mechanical systems to a halt until they can be repaired. To avoid this expensive downtime, it is essential to learn the various sources of wear in rolling element bearings.

One of these factors is the operating speed of the bearings’ mechanical system. High speed applications play a common role in roller bearings applications; ensuring proper maintenance will help protect against the excessive wear that can lead to system failure.

The Perils of High Speeds

Excessive speed can have a number of impacts on the life of bearings, two of the most important being heat and friction. High speed operation can accelerate wear for bearing systems that are either not designed to handle it or improperly lubricated. The following are a few of the detrimental impacts that can occur under these conditions:

Churning

With high speed operations, bearings can reach very high temperatures by churning in oil or grease. Lubricant is required to mitigate the natural friction that occurs between two bearings operating at high speeds; however, higher levels of bearing action can result in decreased viscosity in lubricants. This loss of viscosity is defined as churning, and continued bearing action during churning causes agitation that can ultimately cause the lubricant to fail and the bearings to overheat.

Breakage

When working at higher speeds, bearings naturally gather greater inertial forces. If lubrication is not adequate, or bearings exhibit sudden stopping and starting, the forces between the retainer and the rolling bearings can become even greater. If not dealt with, these inertial forces can ultimately cause retainers and bearing cages to break, causing overall system breakdowns.

Slippage

Another difficulty that can arise from a lack of lubricant and higher speeds is slippage between the raceways and rolling elements. This most often occurs when the lubricant coating is absent from bearing contact areas. When this contact is made at high speeds and without lubricant, wear can occur at a rapid rate. Tightly loaded bearings have the greatest risk of slippage under these circumstances.

Remedies to Extend Service Life

While the above demonstrates the various difficulties that can arise from high speed operations, the solutions are fairly simple. You can maximize bearing longevity by ensuring proper lubrication and making load adjustments when required.

Lubrication: The Key to Maximum Bearing Service Life

The proper care of bearings will ensure their place as one of the most reliable components in nearly any system. The issues of churning, breakage, and slippage can all be addressed with proper lubrication.

It is essential to get the correct balance when lubricating bearing systems. Too much lubricant runs the risk of churning, while too little does not adequately separate bearing parts. Proper lubrication will reduce bearing wear in the highest speed settings, protecting against costly and potentially dangerous breakdowns.

It is also important to keep in mind that lubrication has a limited service life as well. When subject to mechanical stress and aging, lubrication loses a certain amount of viscosity and lubricity, leading to conditions like churning. Relubrication can be beneficial when this is the case, keeping wear to a minimum during the most difficult industrial conditions.

Adjusting Load and Bearing Sizes

When systems have adequate lubrication, wear from high speed operation can still occur if the bearings have not been properly matched with the load requirements of the application. This can be solved by either changing the system’s overall load, which is not always an option, or employing proper bearings.

For example, in the case of slippage, damage can occur when the load on the bearings is too light. An increased load under these circumstances will lessen the chance of a slip occurring. In lieu of a load increase, this problem can also be lessened by installing smaller bearings. These adjustments are enormously helpful in solving the issues that occur from high-speed applications.

Action Bearing: High Quality Bearings of All Varieties

Action Bearing has more than 50 years of experience in bringing customers the most appropriate roller and ball bearings to fulfill their exact specifications. Quality products from Action provide the industry’s best reliability and longevity — with proper maintenance, they can outlast the equipment in which they are installed.

To learn more about how to prevent failure due to high speeds and other issues, download our Bearing Failure Analysis Guide today.