Wear of gears: A case study at Shiraz Cement Plant

Abstract

A case study has been conducted on the wear problem of a set of large helical gears of a ball mill used for cement production at the Shiraz Cement Plant. The ball mill has a nominal capacity of 80 t h −1. The overall diameter and length are respectively 4000 mm and 12990 mm. The total weight of the ball mill when fully charged is about 280 t. The ball mill is driven through a girth gear at a speed of 16 rev min −1 and is mounted on the head wall of the ball mill. The girth gear, 6360.6 mm in diameter, is driven by two pinions, each being connected via a gear box and coupling to a 1560 kW electric motor. The speed ratio between the pinion and the girth gear is 7:1. Severe wear problems have occurred on the pinions reducing their actual service life to less than a fifth of the designed life. This obviously is a serious matter. The procedure adopted in the investigation of the problem includes the following: examination of the type of wear that had occurred, study of the properties of the pinion and the girth gear materials; strength calculation for static loads and surface fatigues, lubrication method; vibration measurements and deflection studies of the ball mill, installation and maintenance methods, etc. A cause and effect (CE) diagram and a Pareto diagram have been used to identify the major influencing factors. Based on the findings, recommendations have been made to remedy the wear problems.