subject: Gear Hardening Techniques For Industrial Machinery [print this page] Falk gearbox gears are most often manufactured from hardened steel. This hardened steel within a gearbox reducer are heat treated to increase gear durability and strength. The structural components within a Falk gearbox are subjected to high operating stress. As a result, these components need the high strength of a hardened structure in order to reduce the likelihood of gearbox repairs, and to resist deformation and wear.
Basic Hardening Procedures for Gears
The elemental process to harden a steel part is to apply heat to the part until the crystal structure changes at the atomic level. A gear may be through-hardened or case hardened, which is a measure of the degree of depth of hardening of the steel parts, whether it is a uniform hardening throughout the gear or mainly a surface hardening.
Following hardening, a process called quenching is used to rapidly cool the part, forming a crystal structure. This crystal structure that is much more resistant to deformation, resulting in greater strength and hardness.
Although quenched steels are stronger, they are also brittle and even slight impacts may cause fracture and require costly gearbox repairs. As a result, quenched parts are tempered, which involves reheating the part to a point below the hardening temperature and allowing the part to slowly cool. Tempering somewhat lowers the hardness and strength of quenched steel, but greatly reduces the brittleness. A heat treatment called stress relieving may also be done to remove internal stresses from gears within a gearbox reducer.
Common Gear Hardening Methods
There are different methods to harden the gears of a Falk gearbox. The through-hardened process involves heating gear parts to the correct temperature in a furnace and using a quenching medium such as oil (or air as for some alloy steels). Following quenching, the parts are then tempered to final working hardness.
For surface hardening, there are several different options, including:
Flame hardening. In flame hardening, a fuel gas flame is subjected to a local section of the gear, followed by quenching as the local section moves out of the heated flame. The typical steels subjected to flame hardening are plain carbon, with an approximate 0.45 carbon content, and low alloy steels. Under this method, the depths of hardening range from 1/8 inch to full depth. Typical steels used are plain carbon, with about 0.45 percent carbon content, and low alloy steels.
Carburizing. During the carburizing process the gear is fully immersed in a hot, carbon-rich medium. This medium can be a carbon-rich molten salt such as sodium cyanide, solid particles of charcoal, or a carbon-rich fuel gas. Following the required time, about a few hours, the gear is transferred to a more conventional heat treatment. Typical materials subjected to this process include low carbon steels, with 0.1-0.3 percent carbon, and the depth of hardening is typically limited to 0.050 inch or less.
Induction. Smaller parts that can be flame hardened may be hardened through induction. The gear or other part is immersed in a quench medium and a coil of wire is wrapped around the part with a high current flow of electricity passing through it. The current flow heats the part to the hardening temperature. After the appropriate amount of time, the wire's current is disabled and the gear is cooled by the surrounding quench medium. Materials used with this method are similar to alloy steels and standard hardening depths range from full depth to 0.01 inch.
Following the hardening process, gears are inspected and shipped to the gearbox reducer manufacturer. A Falk gearbox uses gears formed from the best combination of selected materials and hardening processes, which results in a cost-effective gearbox with a long service life.
