The exceptional performance of a gear reducer at a coal mine in Mpumalanga, South Africa, has led to the purchase of a second unit to be installed on another key conveyor.
Kwena coal mine initially purchased an ABB Dodge torque arm reducer from Bearings International (BI) in 2013, at a time when the mine was looking for ways to increase operational efficiencies and lower production downtime. A gear reducer allows for the modification of the torque and speed between a motor and a load. The Torque Arm II (TA II) gear reducer is used in the drive mechanism of a 200-m-long, 600-mm-wide coal conveyor carrying 700 t/h of coal. This main conveyor is a critical application, feeding coal into the wash plant.
The shaft-mounted TA II gear reducer mounts directly onto the driven shaft and is seen as particularly suitable for tough applications where a long operating life is essential. The reducer can be used in a range of environments due to the availability of a number of accessories.
The reducers are manufactured according to American Gear Manufacturers’ Association standards at ABB’s Greenville plant in South Carolina in the US, utilising heavy-duty tapered roller bearings throughout the unit for an average bearing life of 25 000 hours at a 1.0 service factor.
The company states that regular quality checks are performed throughout the process, ensuring materials and finished components meet stringent requirements. The gear reducers are subject to final test runs upon assembly, to ensure all parameters are within technical specifications.
The TA II gear reducer’s dual-seal system features inner seals made from hydrogenated butadiene nitrile rubber (HBNR ) on the input and output shafts. The primary function of the heavy-contact seals is to retain oil inside the reducer.
The light-contact seals are fitted outward from the heavy-contact seals, aimed at keeping dust and debris away from the inner seal and prolonging the life of the seals. The HBNR material has an operating temperature range of -40 °C to 150 °C and is said to show less wear on the shafts than other types of seals with similar high points.
The TA II gear reducer uses a twin-tapered bushing that aims to eliminate fretting corrosion and to simplify fitment with the use of hand tools, allowing the gearbox to be removed quickly if a conveyor pulley or bearings between the gear reducer and the pulley, need to be changed.
Various shaft sizes can be accommodated by a single gear reducer, which helps to simplify stock-holding and eliminates the need for a different gear reducer for each shaft size on the plant.
The externally accessible backstop means that direction changes can be achieved in the field without needing to disassemble the gear reducer. These backstops are compatible with oils containing extreme pressure additives. The complete lift-off design aims to ensure zero drag or shaft wear once up to operational speed.
Pry slots along the mating surface also help to facilitate reducer repairs, without damaging the case. Service parts are offered in different levels of kits, to assist in the selection of appropriate replacement parts.