I was invited by Tom Astrene of TLT to write a response to the July 2010 TLT article (Ref. 1). My rebuttal — “In Search of a Fatigue Limit: A Critique of ISO Standard 281:2007” — was published in Tribology and Lubrication Engineering, TLT, August 2010 edition (Ref. 10). While this article is also available online, I will attempt to summarize the essence of my response.

Until now the estimation of rolling bearing life has been based on engineering models that consider an equivalent stress, originated beneath the contact surface, that is applied to the stressed volume of the rolling contact. Through the years, fatigue surface–originated failures, resulting from reduced lubrication or contamination, have been incorporated into the estimation of the bearing life by applying a penalty to the overall equivalent stress of the rolling contact. Due to this simplification, the accounting of some specific failure modes originated directly at the surface of the rolling contact can be challenging. In the present article, this issue is addressed by developing a general approach for rolling contact life in which the surfaceoriginated damage is explicitly formulated into the basic fatigue equations of the rolling contact. This is achieved by introducing a function to describe surface-originated failures and coupling it with the traditional, subsurface-originated fatigue risk of the rolling contact. The article presents the fundamental theory of the new model and its general behavior. The ability of the present general method to provide an account for the surface–subsurface competing fatigue mechanisms taking place in rolling bearings is discussed with reference to endurance testing data.

For the lubrication of open gear drives used in different industrial applications such as cement and coal mills, rotary furnaces, or where the sealing conditions are difficult, semi-fluid greases are often used in preference to fluid oils. For girth gear applications the greases are used with a splash or spray lubrication system. The selection of such greases influences pitting lifetime and the load-carrying capacity of the gears, as well as wear behavior

Slow speed operation of fan systems within the air handling industry is generally performed due to two reasons: a coast down operation is required for hot (induced draft) fans to cool down before shutdown (often by using a turning gear), and operational efficiency improvements can be achieved during non-peak periods by slow speed operation using a VFD. In either case, when these fans are supported by hydrodynamic bearings, it is the oil film thickness developed from the bearing-shaft interaction that limits the minimum speed that can be maintained without causing premature wear and bearing failure. This paper will present a brief overview of lubrication theory and critical design parameters to achieve slow speed operation.

Matthew Jaster, Senior Editor Because the general metalworking industry can’t have all the fun in Chicago this September, here’s a quick guide t...

In order to analyze the different gear oils suitable for the lubrication of wind turbine gearboxes, five fully formulated ISO VG 320 gear oils were selected. In between the selected gear oils, four PAO base oils can be found: PAOR, PAOM, PAOC and PAOX. A mineral-based oil (MINR) was also included as reference.

End users and OEMs frequently specify "lubed-for-life" mounted bearings, thinking the lubed-for-life bearings will deliver the same life — without lubrication — as bearings that currently require periodic lubrication. The truth is it depends on many factors, and only a detailed review of the application and testing will provide a more accurate answer.

In this century’s complex, ever- changing world of manufacturing, such capabilities as hardware and software expertise, effective location and distribution, business savvy and yes, even luck, are some of the cardinal requirements for running a successful business.

in the performance and life of a rolling element bearing. Less than 10 percent of bearings reach their theoretical L10 life, and poor lubrication can be attributed to 80 percent of those that fall short. Ideally, a lubricant forms a film layer between moving components in a bearing, separating moving parts, minimizing friction and preventing wear between balls or rollers, raceways and retainers. Lubricants also protect metal surfaces from corrosion and moisture, dissipate heat and can even prevent the ingress of contaminants.