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Print

Geared motors today, and going forward

Mining & Minerals Product Review

By Matthew Wood – Writer
 
Geared motors may seem like an everyday part of mining life, but the importance continues as innovations, research and development (and a host of other factors) emerge. MMPR investigates by going straight to the source.
 
Jonathan McKey from SEW Eurodrive provided information in terms of essential functions, improvements, innovations and obstacles that may be experiences in the industry.
 
“Geared motors and industrial gearboxes are used in many processes in mining, including agitating, extracting minerals, mixing and conveying material through plants in underground and surface mining,” said McKey.
 
The names of applications include ball mills, strike conveyors, rom belts, overland conveyors, mixers, agitators, magnetic separators, chair lift and vertical winders, to name a few. The geared motors (or ‘gearboxes’ as commonly referred to) are used to drive the applications.
 
Industry advancements
SEW Eurodrive incorporated condition monitoring onto the industrial gearboxes supplied on both surface and underground applications. These include vibration and oil monitoring sensors. 
 
Geared motors have been supplied utilising brake function monitoring sensors on applications such as travel drives on reclaimers.
 
It also assembles powerpacks and other product innovations include motor adaptor and coupling together with guard on a breastplate, ready for installation.
 
Furthermore SEW designs custom application solutions via its engineering department. One of these incluse Bell Housing which is suitable for installation into small spaces underground.
 
Shortcomings and solutions
Many problems occur with geared motor solutions in mining operations as production requirements are ever-increasing by market demand, and sufficient maintenance intervals fall by the wayside.
 
SEW offers sales engineers supported by an in-house engineering division to assist clients with revised, and improved designs suited to the pressures of production mining. SEW South Africa has a team of field service technicians available both nationally and internationally to assist loyal clients for specialised condition checks, urgent field maintenance and repair services when minimum down time is afforded between production shifts, or when removal of the unit for thorough inspection at its operational plant is not an option. 
 
The company employs those who can tailor-make critical application requirements with the right solutions. 
 
Mechatronic engineers, mechanical engineers and many years of site-experienced sales engineers all come together to meet and exceed expectations. 
 
Finally, SEW Eurodrive offers units up to 475kNm through its local stock holding, and have managed to come up with custom designs for many customers enabling them to draw in the campany’s expertise of drive engineering to solve a particular problem.
 
Maintenance and lubrication
“Maintenance on electrical motors gets neglected,” says a Filter Focus wear control specialist. 
 
“Most of the maintenance engineers or the lubrication people that we come across don’t even know that there are bearings on electric motors. The very big electric motors generally do have automatic lubrication systems on them but smaller motors certainly are not looked at and are never greased.”
 
The Specialist explained that an electric motor will arrive on site together with a gearbox which gets lubricated at the manufacturing facility where it is sold, and that is the last time it is normally lubricated. 
 
Generally it is a middle-of-the-range to a low quality lubricant that’s being used, so it’s not going to be sufficient for the life of the motor.
 
These motors are found in confined spaces, hard-to-get places, at heights or under moving conveyor belts – generally not something that can be easily reached. From a safety perspective they are left and not lubricated, and this is when maintenance problems occur.
 
Penny wise, pound foolish
The specialist also emphasises that the choice of lubricants make a big difference.
The image included shows a picture of a model gear box, with high quality lubrication on one side, low quality lubrication on the other. 
 
The section with the low quality produces air bubbles, and air bubbles are a form of contamination. 
 
When gears meet (metal on metal contact) the lubrication cushions the contact, but air bubbles in poorer quality lubrication pop, and thus you have metal to metal contact.
 
This is one factor out of many that affects any type of equipment in a mining operation when the right lubrication is not chosen.
 
Often it is believed that using cheaper lubrications will save the operation lots of money, but the costs associated with the long term maintenance and wear problems are very expensive, a term known as “penny-wise, pound-foolish”.
 
Other maintenance solutions
Removable coatings can be applied to absolutely everything and anything, and in this case can be applied directly onto an electric motor.
 
A lot of motors and gearboxes – or whatever the case may be – rust, corrode or deteriorate when they are put onto site, coupled with the fact that they are often in very aggressive environments as well. With this coating (known to the industry as ‘RustPrufe’), it gets applied over and can be peeled off at at any stage that you want to, and the sub-strata underneath is completely protected.
 
For example, if a gearbox is supplied to Eskom, it often ends up standing outside in the stockyard, and those shafts just start rusting and corroding from day one.
 
Nothing gets done about it, and the day they want to use the gearbox they now need to start sanding it down, rust treating it and trying to protect the surfaces, because they can’t put it into operation with rust on it. 
 
With the coating you can apply it over anything and when you want to take it off you can grab one corner, pull it and the entire thing peels right off. This will last for well over a year in direct sunlight.
 
There are companies in Zambia that will not supply a pump or a motor to customers unless they are coated with this protective coating.
 
So don’t keep replacing machinery because it gets worn down, use the coating; equipment won’t fail and you save lots of money, advised Filter Focus.
 
Gears and motors are very vulnerable to a host of other factors that include dirty environments as well as having low level artisans and cleaners spraying the equipment with water to clean them, often spraying water into the fan, due to lack of training and knowledge.
 
More innovations
“To tackle the marked demand for higher processing plant productivity while dealing with lower ore grades many mining operators opt for larger mills with higher power requirements”, said Erik Pretorius, head of ABB’s mining business in South Africa. “We support our customers in meeting these power and productivity requirements with our innovative gearless mill drive system (GDM) and its service portfolio.”
 
“Our GDM design eliminates all mechanical components of a conventional mill drive system, such as ring-gear, pinion, gearbox coupling, motor shaft and motor bearings and the rotor poles are directly mounted onto the mill, converting the mill itself into the rotor of the gearless motor. This robust system design and the system features reduce unnecessary maintenance downtime, especially since the GMD maintenance can be integrated within regular mill maintenance plans.”
 
“The inherent advantage of the GMD is that it can power much larger mills – we can optimise it to fit different mill sizes – and it ensures delivery of maximum throughput of the mill, thus making it a lot more productive than a conventional drive system. It is the best and most reliable way to increase production. We have one installation here in South Africa; Anglo American Platinum’s Mogalakwena mine decided to go for a 17,5 mW gearless mill drive for its 26ft ball mills.”
 
Pretorius concluded, “Today more than ever, it is key to embrace technology and choose a reliable partner who is not only at the technological forefront as an integrated systems supplier but who also adapts to market changes and has the organisation that can support its technology.” mmpr
 

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