NORD and Jacmor solution for complex alumina application
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filed under:
Print Edition
by
The Australian Journal of Mining
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created
Jun 10, 2011 04:19 PM
NORD Drivesystems AU and Jacmor Engineering combined forces to provide an intelligent drive solution to solve an expansive performance specification for large screw conveyors moving alumina hydrate.
The screw conveyors’ fabrication and final assembly near completion at Jacmor Engineerings’ Thomastown factory.
When faced with a complex performance specification for two very large 750 mm diameter screw conveyors, the team at Jacmor approached NORD for assistance.
The initial performance specification supplied from the customer, an alumina refinery, in collaboration with its design consultants, called for helical geared motors to drive the screw conveyors between 0.25 rpm and 25 rpm, a 100:1 turndown, and to provide full load torque capacity across the entire operating range.
The screw conveyors are required to move between 3 and 300 tonnes per hour of alumina hydrate. The specification also required the helical geared motors to run 24 hours a day and seven days per week, and to start fully loaded up to six times per hour.
Other requirements involved a minimum service factor of 1.5, and both screw convey-ors would be controlled by a frequency inverter and control programme as supplied by the customer.
This initial performance requirement was expected from one single electric motor source, resulting in a proposed operating frequency range between 0.5 Hz and 50 Hz. Utilising only one electric motor for this performance specification would have resulted in a very specialized and costly supply.
Solution and selection
Jacmor Engineering and NORD Drive systems worked together to determine and select a solution from the NORD Industrial Gear Unit ( IGU ) range. The NORD products selected and supplied were the SK12407 ASHCS-IEC315 bevel helical gearbox, complete with an auxiliary mounted SK9072.1VF-IEC160helical bevel gearbox.
According to Tony Sculpher, regional sales manager, Victoria, South Australia & Tasmania, NORD Drivesystems, the dual gearbox combination allowed the screw conveyors to be started and operated up to the full load torque requirements across the screw conveyors’ complete speed range.
The larger NORD bevel helical gearbox provides up to a maximum 60kNm torque, for product processing up to 300 tonnes per hour, while the smaller helical bevel gearbox provides up to 40kNm torque for smaller volumes in the production process. The larger bevel helical gearbox features a 2.1 service factor, and the auxiliary gearbox has a service factor of 1.59. Both service factors are based on fully installed power.
The selection process involved an initial size and speed selection from NORD’s IGU range. The selection was supported with both bearing life and gearbox thermal capacity calculations completed at NORD Drive systems’ Derrimut factory.
To meet the required thermal capacity, NORD included an external oil/air cooling unit on each assembly. These external cooling units provided 7 kW of cooling power and were mounted beside each assembly. A full load test for each assembly was also completed after their assembly in Germany.
Design details
The smaller auxiliary helical bevel gearboxSK9072.1VF-IEC160 is attached to the larger bevel helical gearbox SK12497ASHCS-IEC315 via a compact cast flange housing.
The internal shaft connection features a one way sprag clutch, and speed sensors were provided to supply rotational feedback to the customer’s frequency inverters.
Attachment to the screw conveyor shafts for the bevel helical gearboxes required a hollow shaft design together with an elastic style torque arm support. The 190 mm hollow bore utilized a shrink disc for more efficient surface contact and for easy assembly/disassembly on each screw conveyor shaft.
Both gearboxes feature an IEC electric motor adaptor to accept the alternative brand of heavy duty mining electric motors as specified by the alumina refinery. The larger gearbox was driven by a 132 kW electric motor, and the auxiliary gearbox was driven by a 15 kW electric motor.
The two screw conveyors are mounted side by side, and called for a mirror image installation of the helical geared motor assemblies, with an M4 vertical mounting position for each assembly. The total weight for each assembly including oil, the mining motors and external oil/air coolers, was approximately 4,800 kg.
Conclusion
“The other drive alternative considered was a hydraulic motor and gearbox combination,” said Sculpher. “This option was subsequently eliminated in the selection process due to cost. The NORD helical gear solution complete with AC electric motors offered an approximate 50% cost saving on the purchase of the screw conveyor drives.
“NORD Industrial Gear Units have been developed according to the tried and tested Unicase housing principle. The Unicase is a one-piece housing, into which all the bearings are integrated. This allows the shafts’ axis to be staggered, resulting in a more compact design which allows the use of larger roller bearings to guarantee a long operating life.”
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