The primary goal of almost every mine in the world is ore extraction at the lowest possible cost. To achieve this, the safe delivery of production tons is always the number one priority. Efficiency of equipment and processes are crucial components for achieving this objective. Equipment downtime of any sort pushes production costs up sharply. It is, therefore, a key business imperative to manage and control these costs. Considering the fact that tyres rank in the top five cost drivers in most mining operations, mine management needs to have a clear understanding and focus on best utilization practices with their tyres.
We attempt with this article to de-mystify this subject and provide perspective to the realities faced with underground mining tyres.
The universal problem faced in underground mining operations is that the production equipment used has no suspension whatsoever. These machines must rely entirely on tyre deflection to protect their axles, drive trains, chassis and the operator from the transmission of shock forces generated in the movement over underground mine operating conditions. In most cases, these conditions are extremely severe. The contact patches of these tyres are very small considering the giant tasks they must perform. These contact patches move the ore from the mine face to a tip area providing four essentials functions: Suspension, Traction, Steering and Stability. High expectations, indeed, are placed on these tyres and the mine transportation equipment!
In the search for the lowest tyre cost per ton, let’s review some of the available options:
Pneumatic Tyres: They have excellent deflection rates—and in ideal operating circumstances, they are well suited for the job. However, pneumatic tyres still have a few downsides.
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They are prone to penetrations and will deflate quickly, resulting in costly downtime.
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Incorrect inflation is the killer. Uncontrolled inflation leads to premature failure and these costs have a huge impact on overall extraction cost.
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Inflation management has a high maintenance cost tag. Managing tyre pressures requires the need for semi-skilled labour, lots of time to check and inflate, as well as compressors and the appropriate tools and equipment that go with this critical process.
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Pneumatic tyre and rim assemblies have an inherent high-risk element. This combination is deadly when rim componentry is not correctly matched or is worn.
All is not lost. The major manufacturers of OTR tyres are continuously evaluating and improving their products to meet the demands imposed by extreme underground mining environments – extra cut and wear resistance with increased casing durability. Millions have been spent and are still being spent on R&D to give the mining industry rugged products that can cope with the increasing production demands in most modern-day operations, i.e. bigger equipment, more load and higher speeds.
Polyurethane-filled Tyres: Polyurethane-filled tyres have been used effectively in underground mining production for nearly 50 years now, and their place on the cost management curve is well understood. However, polyurethane filled tyres do have a downside with extra weight added to a wheel and tyre unit. They therefore require extra care with handling.
On the plus side, polyurethane tyre filling offers significant benefits over pneumatic tyres, especially in very severe mining operations.
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The tyre is totally flat-proofed. This technology enables operators to easily glide over typical work site debris without tyre puncture or damage.
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The deflection rate is around 10% less than a pneumatic tyre, thus offering better protection for the machine drive train and operator comfort.
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They require no pressure maintenance.
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Polyurethane-fill can be recycled and re-used reducing the carbon footprint significantly.
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The rim and tyre assembly has no explosive force and is therefore very much safer.
These benefits translate into cost-efficient machine “uptime” in the production chase. Polyurethane-fill compounds are being continuously developed and improved, matching the improvements in mining tyres. Most of the major Original Equipment Manufacturers and their axle suppliers have endorsed the use of reputable brand polyurethane-filling products.
There is an ongoing debate into the efficacy of PU-filled tyres in an underground mining environment. It is pertinent to note that in the event of a fire, the tyre would need to burn out before any noxious materials from the inert cured polyurethane tyre core could become hazardous to mine personnel.
Solid Rubber Tyres: The testing of solid tyres in underground mining operations is nothing new. They have been tried in many forms over the last 30 years. Solid tyres most certainly fulfill the flat-proofing need in mining tyres and could conceivably extend the usage lifespan under the most severe operating conditions.
The main problem with solid tyres as has been shown in many tests in the past is that they are extremely rigid and have very little flex to absorb surface shock transfer.
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Standard all-rubber tyres do not flex sufficiently and can cause collateral damage to machine drive trains and chassis. Operators complain of physical stress and have been known to refuse to work with them.
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Other tests have been conducted with softer centre section solid rubber tyres. Most of these tyres sheared circumferentially after a few hours in service.
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Solid tyres with apertures drilled or molded through their center sections to add flexibility are being used in some less aggressive operations. Earlier versions of these aperture “solids” failed after a short service life due to pressure cracking between the apertures.
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Newer generation aperture solids are being tested in underground mines around the world with some apparent success. The cost/performance ratio needs to be calculated before they can be considered.
Solid tyres work very effectively on static equipment such as lighting plants where suspension shock resistance is not important. There is a place in the market for a solid tyre that would overcome the effects of extreme shock transfer on production machines. OEMs must still endorse solid tyres as original fitment in underground mining operations. The new solid tyres that have a lower core durometer and those with oval apertures molded into them must still prove themselves in service before they can be considered as cost-effective alternatives. Time will tell.
Steel and rubber tracks have also been tested on underground mining equipment. However, the cost vs. benefit vs. performance ratio has so far, not made business sense.
Pneumatic tyres remain a good choice in a highly controlled environment. However, it is likely that polyurethane filled tyres will remain the most cost-efficient answer in severe underground operations. For solid tyres to overcome their current limitations and become a viable option for underground mining transportation, manufacturers will need to develop something unique.
Ultimately, the goal remains to deliver the lowest tyre cost per ton.
Peter Klein is the Business Manager for Africa for Accella Tyre Fill Systems, the leading global supplier of polyurethane-filled tyre technology and other integrated road care solutions. He has worked in the mining tyre and rim space for over 30 years and is based in Johannesburg Area, South Africa