Gear life depends on many factors and steel cleanness is a critical one. TimkenSteel has a century of experience producing clean steel for the gear industry. We continually develop and test our materials, building in-depth knowledge about product and material characteristics that affect gear life. This is an example of how we work with customers to tackle their challenges and improve gear performance.
A customer needed to supply power transmission systems that fit in a space the size of your fist. They needed power capabilities of 400+ horsepower, which is equivalent to the horsepower of a Porsche 911, Mustang or Camaro.
TimkenSteel is one of a few suppliers of forging bar for this application. We send our special bar quality (SBQ) steel to a forging shop, which in turn produces gear blanks for a manufacturing firm, which finishes the gears and manufactures and builds mechanical power generation and transmission systems. We sat down with the teams from both companies in order to target improved gear performance.
Gears can fail for a variety of reasons, and any number of processing steps during the gears’ manufacture could contribute to these failures. We started by assessing the current manufacturing processes – from bar making, forging, machining, heat treatment and finish machining. Strong engineering optimization efforts had been completed in the forging, machining, heat treatment and finishing of the gears, resulting in significant improvement in gear performance. The TimkenSteel team reviewed their efforts to produce premium quality air-melted and vacuumed refined steels with improved fatigue life.
Through engineering analysis provided by the TimkenSteel team, it was proposed that inclusions greater than 10 micrometers (about 1/5th the diameter of a human hair!) would represent a significant fatigue risk and reduce gear performance. The TimkenSteel Virtual Component Fatigue Model (VCFM) was used to illustrate the impact of steel cleanness on the performance of the gears using a range of steel cleanness levels.
All parties agreed that optimizing the steel cleanness was probably the best way to move forward toward improved gear performance. Steel samples from each of the suppliers, including TimkenSteel, were collected by the forge shop and supplied to TimkenSteel for in-depth scanning electronic microscope (SEM) steel cleanness evaluation. Each steel sample was produced by domestic SBQ steel makers to meet stringent bearing industry specifications. TimkenSteel was shown to be much cleaner when evaluated by our proprietary automated SEM image analysis and inclusion population characterization techniques.
The graphs below compare the cleanness results. The first graph plots the reduced variate – a measure of the accumulated area inspected via SEM – against the largest inclusion found on each of 32 samples. Of the 32 TimkenSteel samples evaluated, two exhibited inclusions greater than 10 micrometers, while virtually all of the samples from our domestic SBQ competitor’s samples exhibited maximum inclusion sizes greater than the critical inclusion size. The second graph shows a frequency histogram of inclusion counts by their size. This figure illustrates that it’s not just size of the largest inclusion, but also the overall number of larger inclusions in our domestic competitors’ steel that put the gear performance at significant risk.
Armed with this information the team decided to go forward with producing some gears from TimkenSteel Ultrapremium™ certified air-melt technology, and testing gear sets on the customers’ test system which simulates the harshest of service environment conditions. The customer tested 10 gear sets to 100 hours under these accelerated test conditions, with intermittent disassembly and inspection. Based on historical test results, the customer anticipated multiple failures under these harsh conditions.
All 10 gear sets passed with no failures or signs of fatigue.
As a result, they will be specifying TimkenSteel Ultrapremium technology for these high power dense applications, allowing them to meet their customers' demanding requirements with a cost competitive product.
Buddy Damm is an advanced steel solutions scientist at TimkenSteel. He is responsible for developing new products for customers and improved processes for TimkenSteel’s manufacturing operations. With more than 20 years’ experience, he has expertise in Integrated Computational Materials Engineering (ICME), thermodynamics and kinetics of microstructure evolution, thermo-mechanical processing, fatigue and fracture mechanics and failure analysis. Buddy holds a bachelor's degree in metallurgical engineering from Michigan Technological University and a master's degree and doctorate in material science and engineering from the Colorado School of Mines.