Vol. 19, 2017
“Visibility doesn't automatically translate into value, don't just be everywhere, be where you are most needed. Visibility without value is vanity.” ― Bernard Kelvin Clive
The Gear Research Institute (GRI) is celebrating its 35-year anniversary in 2017, yet many haven’t heard of the work we are doing or the services we offer to the gear industry. I frequently receive calls from potential sponsors that have stumbled across our website searching for an alternative to in-house gear performance testing. They’re usually delighted to learn of GRI’s testing experience and additional services that can be provided through our relationship with Penn State University; including full access to leading experts in many fields and the latest materials characterization equipment (at discounted rates, I might add). It is with this in mind, that we have initiated a campaign to increase the visibility of GRI.
This brings me to the quote given above. Our objectives are based upon the needs of the gear industry. First, we hope to help more companies implement new technologies into their product lines. Second, our sponsors need access to more qualified gear engineers. This directly relates to GRI’s mission and we have an obligation to improve the status quo. We would like to expand our educational program to include the classroom as well. Unfortunately, there are costs associated with the development of the necessary gear/power transmission curricula. This is where our visibility comes in yet again. We hope to increase the number of corporate members of the Gear Research Institute. Dues paid by Corporate Members are currently used solely to support student activities in the GRI laboratory. Increased membership revenue will be used to support the gear course design. Our current plan is to offer the elective classes to both graduate and undergraduate students. The classes will also be available online through Penn State’s World Campus which expands access to anyone in the world, not only those in State College. Strong support has been received from the college of Engineering Science and Mechanics at Penn State and several industrial partners for this initiative. Potential partnerships with other gear and transmission related education programs are currently being explored.
Our visibility efforts currently include an advertising campaign with Gear Technology (GT) magazine. GRI’s ad appeared in the Jan/Feb issue of the magazine and will continue to run for the rest of 2017. GRI was heavily featured in the issue with a feature article1 on our capabilities and current projects and an interview piece on oil-out/loss of lubrication gear testing2. Early feedback has been very positive. We presented a paper3 at the AGMA 2016 Fall Technical Meeting and it was selected by Gear Solutions magazine for reprint in an upcoming issue.
In the past, GRI’s newsletter was circulated to members only. We have decided to distribute the newsletter to any interested party. The GRI website has been revamped to include a newsletter subscription option as well as an update to our “Member Benefits” section. We will be adding the list of GRI reports that are available to Corporate Members. Reports include 25 years worth of pre-competitive research that is no longer proprietary to the sponsoring group. I also plan to use social media and word of mouth. I plan to post links to relevant articles and news on Linked In and am exploring a Facebook page for GRI.
Managing Director, GRI
Drivetrain Technology Center, ARL Penn State
- Isaacson, Aaron. “Voices: Problem Solving for the Gear Industry,” Gear Technology, Jan/Feb 2017, 12-14.
- Cannella, Alex. “Oil-Out Endurance Under the Lens,” Gear Technology, Jan/Feb 2017, 46-49.
- Isaacson, A.C., Wagner, M.E., Rao, S.B., and Sroka, G. “Impact of Surface Condition and Lubricant on Effective Gear Tooth Friction Coefficient,” AGMA Technical Paper, 2016FTM14, AGMA Fall Technical Meeting, 2016.
Micropitting, as a mode of gear failure, has drawn increased attention in the last few decades. Predominantly occurring in case hardened gears, it is characterized by a large number of miniature pits on the tooth flank that initially lead to profile degradation and can proceed to macropitting. It is an intensely researched topic in many gear research institutions, with a focus on investigating and developing techniques to mitigate this mode of gear failure. The Aerospace Bloc of the Gear Research Institute (GRI) is no exception. It has conducted a phased program in this topic for some time and this article summarizes the status of this research effort.
Phase I of this program consisted of an extensive data mining task, including a literature search and case study analysis of several applicable micropitting occurrences. Attention was focused on literature that was relevant to micropitting of very high accuracy gears, made of very clean steels that are commonly utilized in the aerospace industry. While a significant amount of information on micropitting is available, information on aerospace gears was relatively rare. Operating or test conditions that resulted in micropitting in these cases, were documented and compared. Based on this compiled information, aerospace quality test gears that could be evaluated for micropitting, on the test rigs available at GRI, were designed and manufactured for a phase II of this program This phase is currently ongoing, as described below.
The test rig utilized for this phase was a 6-inch center distance, 8,000 rpm, power re-circulating gear test rig, schematically pictured in Figures 1 and 2. Among all the test rigs available to GRI, this test rig provided the highest pitch line velocity, which was considered desirable for this program. This test rig is also equipped with two test boxes that could help speed up the test program.
The test procedure for generating micropitting on this test rig is based on FZG’s (Munich) micropitting test.4 Utilizing this procedure, GRI researchers were successful in developing various stages of micropitting, as illustrated in Figures 3 and 4. Figure 3 depicts micropitting shortly after initiation. Figure 4 shows the progression to severe micropitting, resulting in profile loss sufficient to exceed the established failure criterion. The phase II objective was the successful and reproducible generation of micropitting failures. With further phases to evaluate techniques for mitigation. However, there has been a delay of the transition to the next phase.
Figure 1: Schematic of the 6 Inch, PC Test Rig
Figure 2: 6 Inch PC Test Rig
Figure 3 and 4: Examples of Initial and Severe Micropitting
The aerospace quality of the test gears have a high quality surface finish. When combined with the operating temperature of the lubricant in this test rig, it results in operating λ ratios that are not very amenable to the phenomenon of micropitting. Consequently, the test results obtained were only possible at higher than ideal loads for these test gears. If mitigation techniques are to be successfully evaluated in the next phases, it is very likely that these test gears would then have to be loaded in excess of their designed operating loads to generate micropitting. This was considered undesirable as testing at loads in excess of design loads could activate other modes of gear failures.
Several options to address this issue were considered and the most cost effective option was to add a heater to the lubricant system of this test rig so that the operating temperature of the lubricant could be increased. Increased lubricant temperature, i.e. lower lubricant viscosity, will result in obtaining a more severe condition (lower λ ratio) and should initiate micropitting at lower load levels. Mitigation techniques will then be explored in the further phases of this program without overloading the test gears. This modification to the test rig is in progress and updates of this program will constitute the contents of future newsletters.
- FZG Munich, “FVA Information Sheet – Test Procedure for the investigation of the micropitting load capacity of gear lubricants”. Research Projects Nr. 54/I-IV Micro-pitting. July 1993.
Education and Training
In order to assist with replenishment of the gear industry’s aging work force, the Gear Research Institute has developed a hands on education for students at both the undergraduate and graduate levels. The results of the program are entry level engineers that have been trained in the basics of gearing. This involves incorporating engineering undergraduate students, at the junior/senior level and graduate students in the Institute’s research laboratory while being paid by a grant from the sponsoring industrial entity. Summer internships have also been arranged at the sponsor’s facility, so that the student and the sponsor have an opportunity to assess each other with future employment in mind.
Typically, students get hands on experience by setting up and monitoring gear test equipment with additional training topics such as gear metrology, failure analysis, metallurgical characterization, vibration monitoring for failure detection, statistical analysis of test data and more.
Tyler Snyder, currently a sophomore in the College of Engineering, started working in the lab in May 2016. Initially, Tyler was setting up and running four square gear test rigs. He has since taken on a project to redesign the control system of a rolling contact fatigue (RCF) test machine. The redesign will result in the RCF rig being controlled by a National Instruments system, which will dramatically improve our data reliability and record keeping practices.
On April 26, 2017 at the age of 103, the gear community lost a brilliant theoretician, a teacher, an author, a great colleague and a good friend, Dr. Faydor L. Litvin. It is impossible to list the many inventions and patents developed by Dr. Litvin used to advance the understanding of gearing during his distinguished career. More notable, however, is how many people he has touched both at the University of Illinois, Chicago as Professor of Mechanical Engineering and Director of the Gear Research Center and in the gear industry. I had the honor and privilege of working with Dr. Litvin several times during my gearing career and he would always take to time talk to you and never would try to overwhelm you, he always had a way to talk to one’s level. One of my greatest gifts from Dr. Litvin is an autographed copy of his “Theory of Gearing” (1997, NASA RP-1406) which I will cherish forever. Dr. Litvin, you will be missed.
The Gear Research Institute is a non profit corporation. It has contracted with the Applied Research Laboratory of The Pennsylvania State University to conduct its activities, as a sponsor within the Drivetrain Technology Center. The Gear Research Institute is equipped with extensive research capabilities. These include rolling contact fatigue (RCF) testers for low- and high-temperature roller testing, power circulating (PC) gear testers for parallel axis gears with a 4-inch center distance (testers can be modified to accommodate other center distances), single tooth fatigue (STF) testers for spur, helical and spiral bevel gears, and gear tooth impact tester. Extensive metallurgical characterization facilities are also available at Penn State in support of the Gear Research Institute. For further details on our testing capabilities please go to www.gearresearch.org or call Aaron Isaacson, Managing Director, at (814) 865-5832..