Why is nitriding gears and other parts so critical?
As we’re looking at manufacturing things, we need to make them so they last. Heat treating is a very important aspect of that, and nitriding is one heat-treat process many manufacturers find important because it provides a very hard surface layer, which can significantly increase resistance to wear and abrasion, enhance fatigue strength, and provide corrosion resistance. It also is a very low distortion process.
What applications are best suited for nitriding?
Large gears like those found in wind turbines are the kinds of components that can particularly lend themselves to this process because it needs those kinds of properties. This includes any gears or shafts or anything that needs a hard, wear-resistance surface.
What types of industries would be using a nitriding process?
In addition to wind-turbine gears, large shipbuilders have very large gears as well where this process would be very useful. We also do a lot with light vehicle, heavy vehicle, agriculture, construction, and the mining industries.
What equipment does Nitrex offer that advances this process?
We specialize in nitriding, and we have a division that actually makes equipment that performs nitriding. Our heat-treating services division has a significant amount of equipment that does nitriding. We also do some conventional carburizing, carbonitriding, and vacuum. But the largest heat-treat service we provide is nitriding. One advantage we have is that we have equipment that can be used on very large components. We currently have equipment that can process components up to 50,000 to 55,000 pounds. We’re now installing what we believe is the largest nitrider in North America. It’s four-and-a-half meters in diameter and three-and-a-half meters in depth and can process components up to 80,000 pounds. That puts us very much in the bullseye for wind and other large industrial gears and marine gears.
What processes are involved in nitriding large gears?
Nitriding can be gas or plasma. Our large equipment is a gas nitrider. It involves first heating the furnace. We then introduce a nitrogen-bearing gas once the part components get up to heat. What I think differentiates Nitrex from other companies is in the precise control of pressure and what we call KN or the nitrogen potential. We have a very sophisticated control system that maintains the pressure and the gas flows with the use of mass flow meters. This allows us to precisely develop the case depth the customer is looking for in the nitride layer and white layer. By precisely controlling the nitride potential, we can control that nitride layer and white layer very exactly and hold it at that temperature and KN for the amount of time required to get the depth of case we’re looking for, and then cooling it back down to room temperature. This is a low-temperature process, so there is very minimal distortion, and a relatively low amount of energy is required.
How does nitriding make parts more wear-resistant and enhance their fatigue strength?
Essentially, we’re diffusing nitrogen into the surface of the material, and that diffused nitrogen creates stresses at the surface, and those stresses that are induced harden and provide that wear-resistant surface. It essentially creates metallic nitride that provides a very wear-resistant surface. Additionally, that nitrogen diffusing into the surface also creates compressive stresses, and compressive stresses at the surface of components increase fatigue property, meaning that you can operate that component with cyclic loading and unloading, which is what happens when you’re running a gear — when you’re having that load impact upon that tooth. Through rotation, it’s applied and removed. That cyclical loading and increased fatigue strength is very important in those kinds of applications.
Why is having minimal distortion in a gear important, and how does nitriding prevent that?
The geometry of a gear is very important, so maintaining that geometry through the heat-treating process is critical to the performance of that gear — not only just to the life of that gear, but also the amount of noise that would also be created by that gear. Having gears that run smoothly and quietly is very important now as well. By having a process that can increase the wear and abrasion resistance as well as the fatigue life and create minimal distortion helps maintain the dimensional integrity of that gear and improves the performance, and we do that by diffusing that nitride in with a low temperature process.
What are some of the environmental benefits to nitriding gears and other parts?
Nitriding takes place in the neighborhood of 550 to 600 degrees Celsius. Conventional hardening takes place anywhere from about 850 to 950 degrees Celsius. Because we’re heating it to a lower temperature, we have less energy that’s being used. Energy always comes with an environmental impact, so nitriding uses less energy to create less of an environmental impact. Additionally, there’s no quenching involved in nitriding, so there’s no oil, salt, or polymer quench. Petroleum-based, polymer-based, or salt-based quenches have an environmental impact. Since there’s no quench, we’re don’t need to heat that quench, so we’re using even less energy. All those things help minimize the environmental impact over traditional heat-treat processes.
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