Ball Mill Repairs Gears without Downtime
A zinc concentrator near Montreal, Quebec, began to experience significant vibrations in a ball mill after welding a large crack in the shell. The repair left the mill shell distorted, which caused the axial and radial runouts to fall outside of the recommended values. The company had a spare mill on hand, but due to operational demands and a foundation crack, they were unable to install the new gearset until 10 to 12 months later. Meanwhile, the vibrations were so extreme, they decided to continue running by reversing the direction of the single pinion drive, but that did not stop the vibrations.
A gear inspection revealed that vibration levels were approaching levels exceeding the ISO 10816-1 standard on mechanical vibrations. Furthermore, tooth flank temperatures were running high. The edge-to-edge temperature differential was over 15°C, indicating the contact pattern was less than 50 percent. The condition of the tooth flank could not be determined due to the over application of an asphaltic-based, open-gear lubricant that prevented visual inspection of the tooth flanks.
A repair procedure was recommended using Klüberfluid B-F 2 Ultra and Klüberfluid D-F 1 Ultra running-in and repair lubricants. A member of the Klüber Lubrication Global Competence Center was able to perform the repair over a 24-hour period. After the repair, the operational open-gear lubricant was changed to Klüberfluid C-F 3 Ultra. This lubricant is transparent on the gear surface, which allows the tooth flank condition to be monitored visually. Klüberfluid C-F 3 Ultra also offers improved wear protection while reducing the amount of lubricant needed.
The repair lubricants reduced overall tooth flank temperature by 12°C. The edge-to-edge differential temperature fell from 15.1°C to 1.9°C, indicating a contact ratio greater than 90 percent. The vibration levels were reduced up to 48 percent — bringing the ball mill back to acceptable limits according to ISO 10816-1.