Dust. While it is a natural by-product of rock processing, dust can also be the bane of quarrying operations, covering and infiltrating plant and equipment, permeating the air and impacting on neighbouring properties, prompting angry outbursts from residents. In turn, it is, at the very least, an irritant for quarry workers, both in terms of exposure to the eyes and skin and breathing clean, unadulterated air.
Overall, though, it is just inconvenient for most quarrying operations, resulting in breakdown of equipment, downtime and reduced profits.
Dust is the natural enemy of electric motor drives in bulk handling and process operations in general. Environmental debris and particles can quickly destroy bearings, windings and brushes on expensive electric motors and add considerable expense to service, maintenance and repair bills.
?Dust impedes the flow of air over an electric motor, and the cooling fan on the electric motor,? explains Neil Kinder, the managing director of bulk materials handling solutions provider Kinder & Co.
?The motor fails because the bearing heats up. The whole mechanism runs at the specified temperature that the motor is designed to. That?s why there are cooling fans there.?
Maintenance of a pristine operating environment seems the most obvious answer to optimising motor performance and longevity in your plant and equipment. Neil agrees that this is common sense and that in a quarry environment in particular, there should be procedures to minimise dust exposure. However, he also concedes that it is not always possible to keep electric motor drives free of dust, as the nature of many bulk materials tasks means spillage and debris is virtually inevitable, as is collateral damage from motor and drive positioning.
?Most motors under crushers and pumps can be very large and weigh between 150 and 200 kilograms,? Neil explains. ?How then do you get that out, aside from resorting to winches? It becomes a big issue to get the dust out. The problem is not just confined to crushing and screening, it also affects conveyors but it?s more prone to the crushing industry. On a conveyor high in the air, the wind may blow some of the dust off the motor, but dust underneath the crusher gets into very confined and hard to reach places.
?Dust is a big thing in what it does to machinery, particularly an electric motor. It leads to more maintenance, it involves pulling motors out, and it?s not just the cost of replacing the motor,? Neil continues. ?Motors are not that expensive. The expense is in the labour. You need a fitter and an operator. One fitter can?t work by himself, there also has to be someone who can manage the paperwork to do all the tag outs. You also need an electrician on-site to assist the fitter. So, the bottom line is if you maintain your machinery properly and protect it from dust exposure, you won?t have the motor problem.?
PROTECTIVE COVERS
Over the years, some bulk handling and process operations, including quarry operations, have sought to protect electric motors from dust infiltration with DIY covers like old cut-offs from a conveyor belt or loose sheets of steel. Neil Kinder says that while this may have worked to varying degrees in the past, such temporary covers were akin to ?someone having a car and choosing to cover their radiator while driving through a bit of dust to avoid clogging. The whole radiator is covered up without any thought given to the consequences of it not being able to function! Putting a piece of conveyor belt over an electric motor is very, very short sighted, as it ignores the function of the fins and the fan at the back.?
There is now no need for quarry operators to have to resort to such DIY measures to protect their motors from dust. What has replaced them, though, is still a relatively keep it simple solution (or ?KISS?). Kinder & Co is now the Australian distributor of the K-MotorShield motor covers. These lightweight, durable fibreglass covers were first developed in the US by Worthington Products under the name of OrangeShield and have been instrumental in minimising motor maintenance and service costs in quarries, mines and mineral processing plants worldwide. The motor covers are certified by the US National Electrical Manufacturers Association (NEMA) and are available in standard NEMA frame sizes to cover different size electric motor housings, eg from 143/145 to 447/449, peaking at 8010.
?The covers were designed in the US and have been patented in Australia. The biggest users of the covers in the US are probably the mining and coal industries,? Neil explains. ?Mining materials and coal are very wet and very, very dusty. The pulp and paper industry is also a very big user of motor covers in the US. At Kinder, we?ve spoken to a few people in the quarry industry who think it is a fabulous idea.?
Neil Kinder says the K-MotorShield motor cover is designed for all motors, particularly in screen houses and closed-in areas around the crusher that are prone to dust. It is a form-fitting cover that does not require clamps or fittings to be affixed to a motor housing ? it is merely ?clipped on? or ?snap fitted? ? and can be easily removed ? or ?ripped off? ? if there is a need to inspect the motor.
?The fabricated motor drives or covers in the past would generally have been made out of a piece of fabricated sheet steel or conveyor belt cut-off,? elaborates Neil. ?If the cover was a piece of sheet iron, it would not have snapped fit, you would have had to fit it. Therefore, to inspect the motor, you would have had to undo it. That?s a lot of tools and it becomes a fitter?s job. With the K-MotorShield, it?s no tools and you can lift it off to have a look at the motor. It?s simply an operator?s job, rather than a fitter?s job.
?The beauty of the K-MotorShield is that it?s basically fibreglass, it is lightweight, it?s not fixed by clamps, it?s actually just the action on the fibre glass with a spring in it, to actually clip over it, so you can rip it off.?
ENCOURAGING RESULTS
In overseas studies, the motor covers have been quite effective in simplifying cleaning and maintenance from the outset by keeping debris away from motors and improving heat transfer efficiency from the motor?s cooling fins.
?The K-MotorShield increases the air flow over the motor and because the bearing is sealed, it does not overheat,? Neil explains. ?Studies and test reports by the Institute of Electrical and Electronics Engineers (IEEE) and the Technical Association of the Pulp and Paper Industry have indicated that by keeping the motor at an operating temperature, you should get about 60 per cent better performance out of the life of the motor.?
According to the IEEE report, which considered the performance of covered and uncovered motors in a US pulp operation, a motor with a protective cover and a clean air intake area enjoyed a 130.4 per cent higher average air flow than a motor without the cover. The average temperature rise in the winding end turns of a motor with a cover was 1.8 degrees (Celsius) lower (about 69.5?C) than the average temperature rise without a cover.
The study revealed similar results for the stator slots, the frame and the DE bearing (1.9?C, 3.1?C and 0.4?C respectively), leading to the conclusion that the use of a cover improved motor cooling by a small percentage and that the extrapolation of the differences to rated conditions increased the expected reduction in the temperature rise in the winding to 2.7?C.
Kinder & Co has made initial sales with the K-MotorShield covers in the mining industry, primarily in Queensland. Neil expects the quarrying industry will also utilise the covers because they are inexpensive, light and compact, and have a proven record.
He is also confident that, in addition to dust, the K-MotorShield covers will guard against fine powder, slurry and spillage particles, also the natural enemies of electric motors in bulk handling and process operations.
?In a sand plant where you have people dealing with a lot of water falling over the motor, slurry is going to be a big problem,? Neil concludes. ?The slurry will get caught in the motor. The K-MotorShield cover will guard against slurry build-up in a washing plant?s motor in a sand operation.?
FURTHER READING
Valenzuela MA, Tapia JA, Rooks JA. Effect of protecting covers for TEFC induction motors covered by pulp. Worthington Products LLC, Ohio, USA. www.orangeshield.com (home page, click on ?Resources?).