The importance of bearing inspection to ensure accurate life calculations
When considering basic bearing life, there are certain assumptions that one might make. One could surmise, for instance, that the bearing is adequately lubricated and has been properly mounted and aligned. You might also presume that the bearing contains no debris, possesses “conventional” loading, rotational speed, operating temperature and design of internal (rolling contact) geometry, and has encountered proper manufacturing processes.
These might be among the assumptions when performing a load rating or life calculation using the ISO 281 standard, And, to a degree, that’s okay. The rating life associated with this standard is reliable for a bearing manufactured with commonly-used, high-quality, hardened steel and which retains sound manufacturing quality and function under conventional operating conditions. “This can be very valuable from a high-level bearing selection perspective,” Andrew Hvizdzak, senior bearing engineer at Napoleon Engineering Services (NES) said. “If you’re in the early stages of selecting bearings for your application and you need to compare different general bearing sizes against your applied load and speed conditions, then ISO 281 is a quick and easy way to down select based on bearing size.”
BUT WHAT IF your bearing deviates from any of these assumptions?
Under those circumstances, it’s important to note: the accuracy of that life calculation could well be compromised.
Or suppose that one or more of the following is true: You possess detailed knowledge about a bearing’s specific geometry; you’re comparing a seemingly identical bearing from two different suppliers; or, you have an extensive understanding of your application conditions. In any of those instances, it would be appropriate for an individual to incorporate the following ISO standards to improve the accuracy of their bearing performance estimations: ISO/TR 1281-1 (for load rating) and ISO/TS 16281 (for life).
ISO/TS 16281 is a more advanced and sophisticated method for estimating fatigue life for a specific application. With ISO/TS 16281, many of the limitations associated with the assumptions related to ISO 281 are either removed altogether or improved upon, producing a more accurate bearing life calculation.
And this is important. But why?
A typical design engineer might not understand the presumptions that are being made when using the ISO 281 standard, or that those assumptions might not apply to their particular bearing or application, resulting in a life calculation with considerable inaccuracy.
“With ISO/TS 16281, we can accommodate for misalignment, material properties, internal bearing geometry and load distribution for each rolling element, among other things,” Chris Napoleon, NES president and chief engineer, said. “One critical element for accurate life calculation is inspecting the bearing to define the design and manufacturing characteristics of the bearing itself.”
In most cases, one would be better suited to take this next step. To do so, you need all available inspection data, bearing software and, oftentimes, a bearing engineer who’s specifically experienced in this area.
And that’s where Napoleon Engineering Services comes in.
“We have those three things,” Napoleon said. “You can’t get from ISO 281 to ISO/ TS 16821 without NES. Because you need the inspection data, you need the software capability, and oftentimes, the knowledge of a bearing engineer to bring those two things together – the understanding the 16281 standard and the inspection data – to determine your most accurate life.
“That’s what we’re here to help you with.”
NES UTILIZES bearing expertise and equipment to develop valuable technical information so that customers can make informed decisions about bearing and supplier performance.
The most reliable way to meet this standard is through testing. But testing generally comes with a significant cost. To offset this, NES has long boasted a first step that customers can take toward the implementation of ISO/TS 16281 for a more accurate estimate of bearing life: its renowned Source Qualification Inspection (SQI).
A unique industrial reverse engineering program, its objective is three-fold: to define design intentions, determine manufacturing capability and evaluate quality of workmanship. Among its many advantages is that it allows original equipment manufacturers (OEMs) to eliminate costly physical test programs using known deficient product, openly communicate design issues with a bearing manufacturer and determine why suppliers might perform differently. As noted, the ISO/TS 16281 standard requires more sophisticated calculation methods. And there are commercially available software programs that can assist one in incorporating those techniques. NES, however, can also take that practice a notch further through its bearing modeling service, which allows it to translate those inspection characteristics into potential operational performance.
BOTH STANDARDS – ISO 281 and ISO/ TS 16281 – are readily accessible. Anyone can open a bearing catalog, consult a reference sheet or download available software. The question is, how does a potential customer go about navigating those standards, understanding the difference, and forging further ahead by implementing the more advanced standard?
That’s the important thing. And that’s where NES sets itself apart.
“We’re going to help you summit this mountain,” Napoleon said. “We are experts at bearing inspection, know how to interpret the standards, possess the necessary bearing modeling software, and our bearing engineers know what to inspect so that an accurate stress distribution can be calculated.”
Additionally, as part of the company’s services, NES also houses a 15,000-squarefoot area dedicated specifically to bearing dynamic testing, which includes 100 available test rigs for a variety of bearings.
“We’re the guides,” Napoleon went on.
“We know how to utilize the ISO/TS 16281 standard to determine the most accurate (bearing) life.”
And it starts with NES’ Source Qualification Inspection program.
“If you’re a design engineer for an OEM who’s using a large volume of bearings, your exposure is significant. You’re at risk,” Napoleon said. “You need to be more accurate with your life calculation. You must put your best foot forward; you’ve got to have a game plan.
“NES is your game plan.”
(Courtesy of J.P. Butler, Marketing Coordinator, Napoleon Engineering Services)
