Question

What materials can be used in a gearbox where gears are expected to live at least 5 years, while operating 8 hours a day, and shafts are expected to live an infinite life?

Answer 1

A gearbox is defined as a machine for the majority of drives requiring a reliable life and factor of safety, and with the pitch line velocity of the gears limited to below 25 m/s, as opposed to mass produced gearboxes designed for a specific duty and stressed to the limit, or used for very high speeds., e.g. automobile, aerospace, marine gearboxes.

It should also be noted that some motors can run at varying powers and speeds. The maximum torque is used for rating the gears for power based on an equivalent life to suit the duty cycles, while the maximum speed is used to ascertain the pitch line velocities

It is usual to equate a running time of 10 hrs/day to a total life of 22,000 hrs, and 24 hrs/day to 50,000 hrs.

If we talk about the life and heat treatment, through hardened pinions should be made approximately 40 BHN harder than their mating wheel to even out the life of the two parts with respect to fatigue and wear. Most gear manufacturers dislike machining steel over 350 BHN, as not only does it reduce tool life, it must also have an effect on machine life as well

The most common steels (to PN-EN 10083-1+A1:1999) in this group is being C40, C45, C50, C55 and C60. Complete set of gear box will work for the more than 5 years if it is nade with these materials.