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To ensure the long life of a gearbox, regular servicing and maintenance must be done.

By: Chinnappan Selvaraj

Machines over a period of time go through a lot of wear and tear. The gearbox is the heart and soul for any machine to keep running. To ensure its longevity, regular maintenance and servicing is a must.

One of the main problems that gearboxes suffer from is friction and heat due to lack of timely maintenance and care, and this can prove to be very costly, not to mention disastrous. To prevent this from happening, here are some of the key areas that one must take into consideration during a service.

Gearbox condition monitoring

When gearboxes are in operation, one needs to monitor the conditions periodically by measuring several parameters like temperature, noise, and vibration to name a few.

The previous table indicates the parameters and frequency with which they must be checked regularly.

Based on the observations made during the monitoring, corrective action needs to be taken for the gearbox to be in operation.

For instance, in case of oil leakages, one must change the oil seals, apply the adequate amount of sealants in the bearing caps and casing joining faces and so on. Vibration and noise bearing conditions to be checked. Axial and radial plays to be adjusted. Noise observed in gear meshing, contact pattern for mating gear and pinion to be checked and adjusted accordingly. Oil grades used and oil levels to be corrected by adding oils to maintain the correct oil levels.

Critical issues that need to be looked at during servicing

Generally gearboxes are designed for 40,000 hours for bearing
life. However, these days, designers are looking at infinite life
also. During regular monitoring maintenance, the following
issues are likely to crop up. These are:
• Bearing noise
• Gear and pinion noise
• Gear tooth worn out /damages
• Gearbox housing bore worn out

Major activities to be carried out during
servicing of gearboxes
1. Selection of appropriate raw materials for gears
2. Selection of correct heat treatment of process
3. Possibility of improving the rating of the gearbox by using right material, face width and tooth parameters of gears.
4. Incorporating temperature, vibration sensors, Inspection windows to make maintenance easy

Selection of raw materials/heat treatment/process
Forty years ago, gearbox manufacturers didn’t have many options before them. They would select raw materials based on what would be available at the time.

However, nowadays, while replacing a gear set during servicing, designers check the possibility of using the latest alloy steels to improve the rating of gearboxes.

In addition to this, they choose the gear tooth parameters to enhance the rating by selecting appropriate heat treatment processes such as carburising & case hardening, gas nitriding, induction hardening and profile grinding operation to name a few. Previously, a supplier may have used herringbone type gears without gear profile grinding, but to make the manufacturing easy now, designers may opt for double helical gear design with case hardened and profile ground designs. Therefore, in this manner, a good improvement on gearbox rating is attained.

Steps to be followed during repairing of gearbox housing
a) Housing bores to be enlarged. Top and bottom housing face to be machined
b) Housing to be dismantled as top and bottom housing
c) Depending on the bore worn out , housing bore to be welded with appropriate welding electrode in consultation with welding experts
d) Top and bottom housing to be rejoined
e) Re-boring of housing to be done using CNC Horizontal machining centre/CNC Horizontal boring machine
f) Bores to be inspected by CMM to ensure the correct center distance

Advantages of servicing gearboxes
The gearbox after servicing can run for an additional 5-10 years
The rating of the gearboxes can be improved by going in for service
They can incorporate the latest technology in old gearboxes also
Customers can avoid to going for capex for buying new gearboxes