Pitting – Risk factor for gearbox failure
Causes & avoidance strategies
How does pitting occur on metal surfaces?
Pitting formation on roller bearings and gears caused by tribological stress
- due to the material: the surface hardness and quality, as well as the depth of the hardness penetration
- due to the form: fault in the flank form of gears and in the peripheral speed
- due to the environment: lack of oil viscosity, unsuitable additives in oil, wrong temperature, high humidity
By the way, the dimples caused by pitting can be seen very easily on railroad tracks with the naked eye. These must be reground regularly to maintain their operational reliability.
How does pitting damage manifest?
In roller bearings, pitting damage causes a change in the performance of the bearing. If the damaged bearings are to be examined more accurately, you need to check not only the bearing itself, but also the components of the adjacent parts, the seals and lubrication. Another cause may also be environmental and operating conditions, for example too high temperatures or too much humidity. If gearboxes, bearings or gear constructions are not checked and maintained regularly, there will be long-term irreparable damage, making a complete replacement necessary and bringing with it very high costs. Similar damage may occur in the case of unusually long running times and permanently high loads.
How can pitting be prevented?
Basically, a clean design, the right material for a particular purpose, and exact dimensions of the individual components are the prerequisite against pitting damage. In mechanical engineering there are recognised and permitted values for the maximum possible surface pressure. Forms and profiles of the components must be calculated accurately to ensure that these values can actually be adhered to. Otherwise, damage can occur very quickly.
Other significant measures to prevent pitting are regular inspection, proper servicing and maintenance of roller bearings, gears and gearboxes to the manufacturer's instructions. Optimising the sealing system, more frequent filtering of the lubricant to remove any foreign bodies or basically using a suitable lubricant all help too.