Micro Pitting and Related Phenomena in Case Carburised Helical Gear

Abstract

Helical gears play a crucial role in the torque transmission in parallel shaft arrangement in newlineany industry. With the improvement of metallurgical process and tools it became possible newlineto modify the material property of the steel to a desired possible level where its torque newlinetransmission capability can be enhanced. Case hardening and surface grinding is one such newlinemethod which is used to leverage the surface durability and core strength of gears. With newlinethe enhancement in the torque transmission capability the load per unit area of face width newlinealso increased causing huge surface pressure. This attracted a surface failure due to fatigue newlineloading. The initiation of such failure at starting is known as micropitting and is the subject newlinematter of this research work for which helical gear is considered as a sample. newlineApplication to which the subject helical gear is applied is fluid mixing application. These newlineapplications either run in batch or are continuous processing cycles. For each batch and newlinecontinuous process there is timeline defined and after that there is a certain gap allotted for newlinemaintenance activity. The time cycle for batch processing may end in few weeks to months newlinewhereas the continuous processing it goes in 6 months to year. Batch processing newlineapplication is the concerned zone of this subject gear where the gears was subjected to newlinefatigue failure on the surface in the form of micropitting, spalling and sometimes tooth newlinebreakage. The cycle time considered in this research work is exact from the practical site newlinemeasurement and is 774 hours of operation which ended in 84 days. It includes two equal newlinecycles of testing spread over nine month such that the first testing cycle was done to get newlinethe surface failure recognised which consists of 387 hours, and the other testing cycle newlinewhere the improvement was done. These tests were conducted in a very safe condition on newlineweekdays only. newline