Cradle to grave
The proper maintenance of tyres is essential in any mining operation.
Leon Louw
Getting the most from tyres
A
potential safety risk in opencast mines comes in the form of the ultra-large tyres on off-the-road( OTR) vehicles. Over the past couple of decades, there have been recorded instances of these tyres catching fire and, in some cases, actually exploding— with potentially serious consequences. However, nitrogen tyre inflation has proven to be very effective at preventing tyre fires and explosions.
NitraLife, established in 1996, was the first international company to use a membrane separation process to generate high-purity nitrogen for commercial tyre inflation and subsequently also in large OTR mine vehicle tyres.
“ When a tyre is under load on the road, it is continuously flexing. Over time, flexing and the resulting heat lead to the accumulation of tiny rubber( carbon) particles and other flammable compounds inside the casing. When a tyre is inflated with compressed air, oxygen is added to this mix. Now, if heat is added by a bad repair or some kind of mechanical failure, the stage is set for a potentially lethal explosion,” explains Tom Sowry, marketing director of NitraLife.
In an extension of this overheating scenario, on certain mines, nitrogen tyre inflation has been used to protect tyres against lightning strikes. The power of lightning is such that it will earth through the tyre to the ground, and has in the past been the cause of tyre fires. There are instances of mines parking their vehicles with air-inflated tyres in safe areas during lightning storms— an expensive exercise when one considers the cost of downtime.
“ To date, we are not aware of an instance of tyre combustion at any mine using our nitrogen tyre inflation systems,” says Sowry.
Cost is also another good reason why the mining sector has increasingly adopted nitrogen tyre inflation. Nitrogen permeates through tyre walls about four times more slowly than oxygen, and 117 times more slowly than water vapour. Under the sometimes very harsh conditions under which OTR tyres operate, nitrogen inflation ensures that tyre pressures remain optimal for longer.
“ Tyres at the correct pressure flex less, and are less likely to overheat— a factor that is a major cause of premature tyre failures. Based on many years’ experience and customer feedback, we conservatively estimate that nitrogen tyre inflation extends OTR tyre life by at least 10 %,” says Sowry.
“ Oxygen and water vapour degrade rubber, gradually weakening tyre casings. By removing those elements, tyres last longer, particularly if they are being used in harsh climatic regions where heat and moisture are prevalent,” Sowry adds. Oxygen and water vapour also rust the steel rims of OTR vehicles, as tyre beads do not seat well on rust-pitted rims, which leads to consistent pressure loss and the risk of tyres running under-inflated.
Furthermore, for most of their operational time, haul trucks drive on the steep gradients of unsurfaced pit ramps, which places tyres under even greater stress. In these testing conditions, correct tyre inflation is more important than ever.
On remote mines, NitraLife nitrogen generators offer a troublefree solution to removing oxygen and water vapour from inside tyres.
“ The generator is completely pneumatic— requiring no electricity— has no moving parts, and is fed air by a conventional compressor, requiring minimal maintenance.
“ We also customise our membrane generators to suit a mine’ s specific requirements, and can supply both large and small mining companies, through either a rental or purchase option. Additionally, the portable nitrogen trailer— another innovation we have developed— is perfect for mines in remote sites requiring a mobile nitrogen solution,” Sowry enthuses.
As an option with a generator, NitraLife offers digital automatic tyre inflation. Manual analogue gauges tend to drift out of calibration as the moving parts inside them age. With automatic digital tyre inflation, the correct tyre pressure is entered into the control panel. The digital inflator monitors the pressure during inflation, automatically shutting the generator off when the pressure is correct.
[ 40 ] MINING MIRROR FEBRUARY 2018