Feature Clutches, brakes & couplings
Modular braking takes hold at a Canadian copper and gold mine
A modular braking system has been supplied by Twiflex for use on a SAG mill at a mine which is expected to produce 81 million pounds of copper and 194,000 ounces of gold each year
expected to have a life of 22 years. The mine will provide mill feed at a nominal rate of 60,000 tons per day (21.9 million tons per year) from which copper and gold will be extracted using a combination of crushers, ball mills and SAG mills.
A six-brake mill
The braking system is a vital
consideration for the SAG mill
t the beginning of this year, copper prices rose to a record $9,781 a ton, and analysts are now predicting that demand will outstrip supply by between 435,000 and 635,000 tons. Prices are expected to top $11,000 per ton next year. Added to this, recent gains in gold supply have also failed to keep up with market demand, increasing costs. Thompson Creek Metals Company is therefore making significant investment in Mount Milligan Mine. Located within the Omenica Mining Division in North Central British Columbia, the mine will begin production in 2013 and is expected to produce 81 million pounds of copper and 194,000 ounces of gold annually. This open pit mine is
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Metso Minerals was commissioned to supply the primary crusher, two ball mills and a SAG mill, as well as other associated plant equipment, for the mill. With such equipment, however, braking is a vital consideration, so Metso contacted Twiflex for the braking solution for the 22MW SAG mill, which measures 12.2m in diameter and is 7.31m long.
The scope of supply for the six-brake SAG mill project includes two stations with Twiflex VMS-DP brakes, plus an electro-hydraulic power pack. VMS-DP units are spring applied, hydraulically released safety brakes designed for the most arduous condi- tions. The brakes offer a compact, modular, mine-ready design that does not need guarding.
In static operation, the brakes will be used to hold the mill during liner replacement and general mill mainte- nance. For dynamic operation the system can operate in two modes: stop- ping the mill from full speed in an emergency, or giving inching/creeping
Simulating and analysing braking systems G
units to broaden its software use from Hypermesh and HyperView to also include RADIOSS, OptiStruct and other tools. RADIOSS as an explicit solver for finite element (FE) calculations, a benefit when handling large models that include many contacts. OptiStruct is being used for topology optimisation during the development process. “What we like about HyperWorks is that we have a tool at hand to solve most, if not all, of our development tasks with only one licence agreement and one software family,” said Dr. Frank Günther, manager of technical analysis/ simulation at Knorr-Bremse Systems for Rail Vehicles. Altair Engineering
www.altairhyperworks.com Design Solutions 1971-2011 OCTOBER 2011
operations in the event of bearing lubrication problems or power fail- ure. For the first a controlled applica- tion of the brakes is required and for the second the brakes are operated quickly to give the accurate stops needed by the mill operator. The VMS-DP is a floating brake (±10mm) with an adjustable clamping force from 735 to 920kN. It can be used on installations with a disc (or extended mill flange) diameter of at least 4.5m and thickness of 117mm to 130mm, but the braking path needs to be 300mm minimum on the radius. The maximum disc diameter is 20m. The hydraulic power pack offers versatile brake control as it allows both local and remote operation for inching and creep- ing duties through a control panel.
Brake technology
The braking system at Mount Milligan will generate up to 30MNm braking torque acting on a 13.48m mill flange diameter. The VMS-DP calipers weigh 1.85 tonnes each and are able to deliver 940kN clamping force. With a full process charge of 1043 tonnes, the braking system is able to stop a mill in less than two seconds. To achieve this, the friction material has been chosen specifically for grind- ing mill installations and provides high performance with excellent wear properties. The material is a blend of carefully selected non-asbestos friction modifying elements held together with a binder to give a friction coefficient of 0.4 at 300˚C.
erman braking system manufacturer Knorr-Bremse is using Altair’s HyperWorks suite of computer-aided engineering (CAE) tools in its CAE centres in Germany, Hungary and India to simulate and analyse braking systems and components. The company manufactures its braking systems for both rail and commercial vehicles. Its products include brake control systems such as those for high speed trains, truck ESP (electronic stability program) and ABS (antilock brakes), disc brakes, and systems for compressed air production. Recognising the benefits of HyperWorks for such an application, the company has recently acquired additional license
The brakes are mounted across the mill flange symmetrically and held in place by two half brackets bolted either side of the pedestal vertical member, ensuring the braking force is equally distributed. Each brake has a spring module with two spring-applied, hydraulically retracted pistons. The module is bolted to a reactive backplate featuring two cast bosses, one either side of the brake assembly. Of addi- tional benefit, the brakes have a special ‘parked-off’ feature due to the long piston stroke, meaning they can be installed with zero hydraulic pressure, and the friction pads can be changed safely without special tools.
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Twiflex T: 01234 350311
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