DRIVES & CONTROLS
Circular motion
Motors and drives are the workhorses of capital mining equipment , from large mills and conveyors to electric driven mining trucks . Paul Moore looks at the latest technologies and applications
Render of a 40 ft Metso Outotec SAG mill of 28 MW with Quadrex drive solution
While gearless mill drives ( GMDs ) have become the workhorse of choice for large ball , SAG and AG mills worldwide , supplied by ABB and Siemens , geared drives are still an option . CMD and Ferry Capitain in recent years have developed the Quadrex Mill Drive , which is described as “ the next step in the evolution of mill drive architecture ,” allowing the system to be created with components that are currently available in the market . The platform is already available via some mill OEM offerings – including Metso Outotec , where it is included in designs capable of up to 32 MW of power in horizontal mill comminution .
The system effectively delivers up to twice the power of a traditional twin pinion drive . CMD and Ferry
The Quadrex Mill Drive delivers up to twice the power of a traditional twin pinion drive
Capitain state : “ Moving from a twin pinion to a quad pinion arrangement is a natural development to a sturdy , creative mechanical solution that allows our customers to move forward with large gear driven equipment to meet their comminution goals .” Extensive research was undertaken for the Quadrex Mill Drive system to determine all the parameters influencing the complete kinematic chain . “ Throughout the life of the system , these were assessed for both the drive and the mill itself , ensuring that no single parameter was overlooked .”
Internal torque splitting capability of the Quadrex Mill Drive transmits motor input power to the pinion shaft and evenly divides among two mill pinions . “ Since the early 1960s , this form of torque splitting gear box technology has been in use . To apply high-powered transmission to huge grinding mills in the mining industry , we reconfigured the drive design .” To test the Quadrex Mill Drive torque dividing system under the most severe operating conditions , a full-scale instrumented test bench was designed and built . The test bench , driven by a VFD motor , is composed of two torque splitting sub-assemblies operating in closed loop . Both sides are tested simultaneously . The torque is generated , maintained or adjusted as wanted , to produce the required power of 14 MW .
“ Besides validating our concept at power levels never attained before , our test bench also
helped validate calculation models which were used for developing our solution .”
Standard foundation loading is calculated as derived from mill power , critical speeds , and total mill load . Unlike gearless drive installations , there is no need to perform costly static or dynamic modal analyses . Lubrication for the Quadrex Mill Drive is provided by standard lubrication systems which can be located in a lube room away from the mill operating floor . This type of unit is common in the industry and is easily maintainable . Lubrication for the open gearing is provided by a closed loop oil circulating system , separate from the Quadrex internal gear lube unit . This type of lubrication allow continuous application , oil recycling and filtering for a wide range of lubricants .
The open gearing design is unchanged from that of a dual pinion drive . Gearing components are rated to AGMA or ISO standards . The division of power between four pinions reduces the overall load per pinion which allows ring gear sizing to remain below currently achievable limits . This also keeps the gear material hardness levels at present-day levels .
Motor arrangement for the Quadrex is simple and conventional , similar to the largest dual pinion drive mills in operation . Variable speed motors can be used with power up to 16 MW per drive , extending to 32 MW for dual drives . LSS motors with VSD are coupled to the Quadrex input shaft via a torque limiting coupling . Large brakes and brake foundation piers are not required as seen for GMD installations . Frozen charge upon start-up can also be detected .
The installation procedure of the Quadrex is the same as a standard alignment process used for dual pinon drive mills . A base plate bolted to the foundation and grouted in place is allowing adjustments needed for alignment . Gear to pinion alignment is achieved by shimming and is measured the same way as a standard dual pinion alignment . Unlike a gearless drive , the mechanical portion of the installation can be completed by trained site personnel under supervision .
The Quadrex gear unit can be maintained by
50 International Mining | NOVEMBER / DECEMBER 2022