Replacement tooth for girth gear 

Another fast-track repair was needed when an operator experienced fatigue cracking at the root of a girth gear on one of its two ball mills in October 2020.  

Girth gears are the large gears that run around the exterior circumference of the ball mill. They provide mechanical leverage so that a motor can power the mill’s rotation. A cracked tooth is a major issue. Left unchecked, the crack would eventually propagate and cause the tooth to fail, preventing rotation of the mill and stopping production.  

Ordering a new gear would require several months of lead time and logistics to forge and machine a component of this size and arrange for its delivery to the site. Replacing the gear in situ was the fastest and most effective option as the gear is integral to the body of the ball mill, therefore it was not possible to remove it and carry out repairs in the workshop.  

With this in mind, the project scope was to remove the tooth, weld a replacement into place and shape it to the correct geometry.