Lubrication reduces energy consumption of mill motors

3rd October 2014

By: David Oliveira

Creamer Media Staff Writer


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Interim studies by South Africa-based wear control, lubrication and filtration company Filter Focus have indicated reduced energy consumption of up to 12% on the milling motors at mining major Impala Platinum’s UG2 mine, in Rustenburg, following the introduction of Filter Focus’s Pyroshield lubrication to the mills’ shrouded open gears, in May.

Filter Focus COO Craig FitzGerald tells Mining Weekly that Pyroshield reduced power on the dual-drive milling motors by 600 kW/h.

Pyroshield is an oil-based product that contains almasol – an aluminium/magnesium/silicate active ingredient that reduces the friction coefficient on open gears, enabling mills to operate at the same capacity while using less energy.

“With Pyroshield, one of two things is going to happen. Clients will either achieve greater throughput from the mill or they will see a reduction in electricity consumption. Either way, this equates to a reduction in the amount of kilowatts used for every ton of ore milled,” he explains.

FitzGerald says that, for the past 60 years, the lubrication of choice for large, shrouded open gears, which are located on the sides of mills, has been asphaltic grease. He adds that asphaltic grease is used as a cushioning compound against the extreme rotational forces between two gears, with some mills having to move rock loads of up to 5 t.

“Unfortunately, no matter how perfectly a milling service runs or how perfect a milling system is, one will always find microscopic peaks and troughs, known as asperities, on the surface of the gears. When the gear surfaces come into contact with each other and come in and out of mesh, there are extreme forces across the driveline of the gears, causing the asperities to break through the lubrication, resulting in micro- welding and pitting on the gear surfaces,” he explains.

Pyroshield’s active ingredient, however, covers the asperities and troughs, preventing asperities from breaking through the lubrication. “Under extreme force, there is almasol-to-almasol contact and, instead of microwelding, the almasol coating bends the peak back into the trough. This phenomenon is known as plastic deformation, which results in a burnishing effect across the gear. This effect, in turn, is known as the gear-healing phenomenon,” notes FitzGerald.

He adds that the presence of grease also causes increased vibration on mills because it builds up on the roots of the gears, which could become so severe that the foundation of the mills could crack.

“Because Pyroshield is an oil, which has cohesive and adhesive properties, there is no grease build-up at the gears’ roots and, therefore, vibration is not increased.”

FitzGerald adds that Pyroshield can also improve the yield of precious metals and explains that asphaltic grease is sprayed onto the surface of open gears while they are rotating, resulting in a significant amount of the grease being flung off the gears and into the process fluid used to extract precious metals. Asphaltic grease is a hydrocarbon, which reduces the yield of precious metals when placed in process fluid.

He tells Mining Weekly that, by changing from asphaltic grease to Pyroshield, platinum-group metals (PGMs) producer Lonmin increased its PGMs yield by 0.75% to 1%, owing to a decrease in hydrocarbons in the process fluid.

FF116 Filtration System
FitzGerald further highlights that Filter Focus has successfully extended the life of socket liners and the inner eccentrics of crushers ten-fold by introducing the company’s FF116 high- capacity, microfine offline filtration system at several of platinum mining major Anglo American Platinum’s and iron-ore major Kumba Iron Ore’s mines.

He notes that, before the introduction of the FF116, the original equipment socket liners on crushers lasted three months. Since the introduction of the FF116, the oil in operation is dramatically cleaner and socket liners are replaced every three years.

“We have installed the FF116 on 25 crushers at Kumba’s Sishen operation, in the Northern Cape, which has helped the mine save more than R1.5-billion a year on lubrication and machine downtime.”

FitzGerald adds that, during some months, oil consumption at the Sishen operation was as high as 3 000 ℓ for a crusher, but since the filtration systems were installed, consumption has been reduced to between 0 ℓ and 200 ℓ, with Kumba no longer needing to top up with new oil in its crushers, as the oil in operation remains clean and free of contamination or wear particles.

Edited by Samantha Herbst
Creamer Media Deputy Editor


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