June 14, 2022
Big equipment often requires special processing equipment. Those 300-ton locomotives used unique heat treatment on the gears which required the design and construction of an integrated thermal processing line that stretched to over 200 feet in length. I had never heard of “brine quenching” before I hired on at a railroad gears manufacturer and was amazed that somebody invested the time and effort to automate a process for a single customer. Previous assignments had not required a detailed knowledge of heat treating. You ran your gear design software, copied the required specifications on the drawing, and counted on your vendor to provide a part that met the requirements. When I was an apprentice, heat treat duty was a disciplinary assignment and I was careful to avoid getting sent into that fiery hell hole. Such trips became a daily adventure at the locomotive gear shop. The most important thing I learned was “know enough to detect when you are being mislead.” The second lesson was just as important—identify “the expert” in the heat treat shop who truly knows what is going on behind the smoke screen. In the years since, I have learned a great many more “rules” of the dark art, some because of painful personal experience. There is a lot going on “back there” beyond heating things up and dunking them in oil. With the advent of ground tooth gearing, expectations of hardness and case depth control are strict. Specifications for microstructure require extensive lab work and cut up samples. Our understanding of hardness vs. depth for various alloys now informs material selection. It makes perfect sense then that the AGMA Fall Technical meeting now includes sessions on heat treating and metallurgy. The co-location of Heat Treat 2019 with the Motion + Power Technology Expo makes it convenient for gear people to acquire knowledge they need. You will come home with questions, so remember those keywords and use them in our online archives.