Gears Drive Industry
September 11, 2012
As it happens, much of this month’s coverage focuses on gears or the processes used to harden them. This month’s article topics include nitriding, hardening atmospheres, heating elements, furnace inspection, and gear materials and their heat treatment. The Heat Treat Doctor begins a multi-part column discussing atmosphere gas carburizing, which is also used for gears.
The objective of effective gear heat treatment is to produce optimal case depth with high residual compressive stress on the surface. Gears can be conventionally hardened, quenched and tempered to form a case. They are also case hardened using flame or induction processes. Some gear designs utilize surface treatments such as carburizing and nitriding. Based on these processing options, several of this month’s topics apply well to gears.
Gears come in all sizes, and the size affects the type of thermal processing required. Larger gears typically experience more distortion during thermal processing. Gears and other industrial parts seem to be trending to larger and larger sizes. As size grows, material development will be key. For batch processing, the goal will be to increase size and section thickness while maintaining gas quenching to minimize distortion. These gear steels will need to have higher hardenability to obtain the necessary properties with gas quenching.
The geometry of a gear tooth had historically challenged induction hardening, which hardened the tooth too much where it was not needed and not enough where it was. But advances in technology, materials and processing have increased the flexibility of induction hardening for gears. Induction power supplies now allow control of not just output power but also its frequency. Dual-frequency methods are being applied in two ways. The first uses one frequency to preheat and another to harden. Another option applies the dual frequency simultaneously. This allows the root section of the gear tooth to be hardened with lower frequency and the tooth tips with higher frequency.
Improving the flexibility of induction has allowed for the hardening of gears such as spiral-bevel automotive pinions. Previously, gears of this type were carburized. Induction’s benefits include fast heating cycles, accurate heating patterns and cores that remain relatively heat-free and stable. Induction can also be incorporated well into cellular manufacturing or production lines.
Several of these topics were discussed in an Everyday Metallurgy column called “Take a Load Off.” You can read it at www.industrialheating.com/Gears or link directly on your smart phone using the previous Mobile Tag. You will learn more about the history of gears and what purpose they serve and read a brief discussion about the various types of gears from spur to worm.
FNA on the HorizonSeptember’s column would hardly be complete without mentioning the key industry event of the year. FNA 2012 is now less than a month away. There’s still time to make your arrangements to join us in Nashville on Oct. 2. Technical sessions include presentations in the following five tracks: Atmospheres: Vacuum & More; Energy Savings – Process Controls; Surface Treating; Heat Treating Tools and Process Design; and Planning & Modeling.
Adding to the technical benefits of FNA is the exhibition hall full of colleagues and the latest technologies from the industry’s key suppliers. Networking with these industry experts is a great perk of FNA. If you’re still not quite sure why you should attend, check out MTI’s short video by using this Mobile Tag. The video can also be found at www.furnacesnorthamerica.com. See you there! IH