Developing standards for mill rollers

A challenge in the procurement and the effective ownership of a fleet of mill rollers is the number of variations that exist to cover the installed plant. Although there are physical variations due to mill shell lengths that are centred on three generic populations of mills, i.e. 6 foot (1829 mm), 7 foot (2134 mm) and 8 foot (2439 mm) mills, there are also variations within requirements for a mill roller to suit a particular manufacturer's mill design and additional variations that have developed over time due to local preferences. Wilmar Sugar Australia has forty-nine mills, each with five rollers (not including underfeed rollers), giving a total of 245 rollers in service. Additional to this number are about eighty rollers that are either spares at the mill or being re-shelled, making a total fleet of around 325 mill rollers. The mill roller sizes used at Wilmar Sugar vary from the minimum size of 1829 mm (6 ft) shell length and 965 mm shell diameter to a maximum size of 2550 mm shell length and 1375 mm shell diameter. With continued complexity in procurement and maintenance of mill rollers throughout the group and continued failures of mill rollers in service, it became apparent that opportunities existed within the current standards and designs for improvement. This paper presents the rationalisation and improvement process for mill roller shafts and shells to improve life and reduce the number of variations within the fleet to enable more effective utilisation of funds employed. It was identified that there were 154 different shaft drawings for the 6 foot, 7 foot and 8 foot shaft populations. This work has reduced the number of shaft drawings for the roller fleet to 22 and will significantly alleviate the complexity in procurement and maintenance of mill rollers throughout the group as well as reducing the funds employed to cover in-service roller failures.