:: Bateman Roller Supported Mill on De Beers Marine Vessel meets Performance Guarantees

The Bateman Roller Supported Mill (RSM), installed by Bateman Engineering on the MV Ya Toivo, has passed through its 12-month warranty period, successfully meeting its process guarantees. The Ya Toivo is one of De Beers Marine’s sea-going diamond-mining vessels operating off the Namibian coast.

The new RSM, with a 6 m-long shell 2.4 m in diameter and a design throughput capacity of 70 t/h of (dry) feed, was installed to boost the vessel’s ability to mill diamond bearing gravel and shell sucked from the seabed. Experience with similar systems was an important basis for determining the design parameters for the new RSM.

Also crucial to the design was the use of finite-element analysis to ensure that the RSM’s base frame, drive system and its support could accommodate the additional loads on the components of the RSM induced by the motion of the vessel.

At the same time as installing the new RSM, the milling efficiency of the existing RSM, with a similar shell size, was upgraded to the same level as that of the new mill. This was achieved by upgrading the base and roller-support mechanism to handle a heavier ball charge.

The total installed power for each of the two RSMs is 550 kW and both are fitted with variable-speed drives to accommodate the variable nature of the feed. The ball charge in the mill is maintained through manual addition with the feed.

The space constraints for both RSMs were very stringent. The old mill, situated below main deck, had its shell raised and supported while the old base was removed and the new base installed through cut outs in the main and upper tween decks. The shell was then lowered into position. The new RSM was installed above deck within a tightly configured structure.

The order for the new RSM was placed in January 2005 and the unit, pre-assembled and fully tested at the works in Johannesburg, was installed on the ship during a 4-week refit in Cape Town in November 2005.

During the past decade, nearly 20 Bateman RSMs have been installed on land-based or marine diamond-processing plants where they are used as scrubbers and ball mills to process between 25 t/h and 700 t/h of dry material. They consist of horizontally-rotating cylindrical shells mounted on and driven by polyurethane-covered rollers. This feature significantly reduces the capital cost to as low as 50 % of traditional trunion-supported scrubbers. Also, moving parts can be replaced within a few hours, reducing maintenance to regular lubrication checks and occasional liner replacements. The reversible rotation and symmetrical design maximises liner life.