Failure Modes in Gears
Gear Systems or gear trains tend to play a very vital role in all industries and also in our day to day life. Any failure to the gear system leads to the total system failure. Imagine driving a car with a broken gear in its gearbox. Knowing the various modes by which the gears tend to fail helps one to identify the problem at an initial stage and rectify the problem related to the gear. Now let us look into the various modes by which the gears fail:
The various major areas by which the gears tend to fail are
* Shock Loading Failures
* Fatigue Failures
* Failures due to Wear
* Failures due to Scuffing
1. Breakage by sudden shock loads: When the gear system is subjected to a sudden shock load more than it is designed for, it instantly breaks. Though this cannot be identified prematurely, utmost care can be taken to avoid such mishaps.
1. Bending Fatigue: Gears based on their rotational motion and the heavy amount of load they carry are subjected to fatigue. Due to the application of load on the gear teeth, the gear tooth is subjected to bending. When the same is repeated for a very huge number of cycles Bending Fatigue failure of the gear sets in. The fatigue in the gears induces the formation of cracks in the root of the gear tooth which propagates with each rotational cycle of the gear and ultimately leads to the failure of the gear tooth.
2. Pitting: This is a major cause of gear failure accounting for nearly 60% of the gear failures. Pitting is the formation of craters on the gear tooth surface. These craters are formed due to the high amount of compressive contact stresses in the gear surface occurring during transmission of the torque or in simple terms due to compressive fatigue on the gear tooth surface. There are two types of Pitting. They are
a) Micro Pitting: These are basically formed due to
§ Inherent Errors in the gears
§ Presence of water in the lubricant that is lubricating the gears
§ Wrong viscosity selection of the lubricant used.
Visually, micro pitting is not so clearly visible at the first go. One has to study the surface of the gear tooth to identify the micro pitting. They appear as very small dots which one can feel when he runs his finger over the gear tooth.
This sort of pitting normally tends to make the gear useless and damages the whole gear system.