This paper compares and contrasts heat treat processes and equipment typically used to harden gears. It discusses the basic design and operation of vacuum, controlled atmosphere, and hybrid furnaces and process techniques such as carburizing, carbonitriding, nitriding, nitrocarburizing, and neutral hardening. It also includes information on operating and maintenance costs, using batch integral quench furnaces as the base case for comparison. A discussion on when to consider continuous furnace types is included as well.

A review of vacuum processing in a multiple-chamber vs. single-chamber vacuum furnace and the advantages and disadvantages of both design concepts will be presented. Cycle calculations will be shown to illustrate the differences in the floor-to-floor time, heating energy required to process and cooling power to quench a normalized load. Additionally, the presentation will discuss the differences in residual atmosphere for a given vacuum level for the two furnace concepts. Differences in operation and maintenance between the two concepts and appropriate processes to run in each will also be discussed.

There are many inherent advantages with utilizing two-chamber, or multiple chamber vacuum furnaces. These include energy efficiency, reduced processing time, and a plethora of processes. Design of multiple chamber vacuum furnaces will be discussed including heating, cooling, and maintenance.

Ferritic Nitrocarburizing and nitriding processes are available in various atmosphere blends and a myriad of equipment designs. Atmosphere choices can dictate process capabilities. Equipment design should be reviewed to select the proper choice for the part application. Atmosphere control, nitriding potential calculations, as well as selecting atmospheres and proper heat treat equipment are included.