Crushing

Correct tyre inflation critical to your tyres

While there are factors that affect mining equipment tyre life, including tonne kilometres per hour (tkph), haul road conditions, gradients and operator techniques, ensuring correct tyre inflation pressures are maintained is one of the most critical maintenance activities you can do for your tyres.

Over-inflation is rarely a problem under most operating conditions but under-inflation, due to gradual loss of tyre pressure, is very quick and simple to check ? and prevent.

There are a number of factors that can cause tyre air loss, including casing damage, inner liner fatigue and leaks, through the valve spuds,extensions, housings and the valves themselves.

If you want your operators to improve operating safety and increase tyre life, tell them to check the valve caps and report any that are missing. Valves without caps will leak.

The valve allows the inflation pressure of the assembly to be checked, while the valve cap is the primary inflation pressure seal.

Checking inflation pressure on a tyre is equivalent to checking your blood pressure ? it?s a quick and efficient snapshot of a tyre?s health, just as blood pressure is for humans.

So, why is tyre pressure so important?

The volume and concentration of inflation pressure inside a tyre plays a vital role in supporting the tyre casing. Overloading is one cause of tyre failure (by increasing the casing deflection), but low tyre pressure has exactly the same effect on the structure of a tyre; it overloads the tyre and leads to fatigue and premature tyre failure.

An incorrectly inflated tyre is more vulnerable to damage if excessive speed, overloading and poor haul road conditions and road design come into play.

But even if these factors are addressed, failure to maintain the recommended tyre pressures for the machine, conditions and application will adversely affect tyre life.

And even in the best maintained and run operations, spillage on haul roads can still occur ? and an incorrectly inflated tyre is far more likely to sustain damage.

PITFALLS OF RECOMMENDED TYRE PRESSURES

Less than recommended tyre pressure can result in one or more of the following:
? Distortion of the sidewall, causing casing fatigue or carcass break-up.
? High stress between piles, causing ply separation.
? Excessive tread movement, causing abnormal abrasion and irregular wear.
? Bead slippage, causing rim friction and bead separation.
? Distortion of the bead area, causing rim chafing and erosion of the rubber.
? High stress at the belt edge, causing belt-edge separation.
? Higher levels of heat, causing heat separation.

Results of higher than recommended tyre pressure include:
? High cord tension, increasing the likelihood of casing damage.
? Reduced enveloping power, making the tyre more susceptible to cut impact breaks.
? Belt separation resulting from stress concentration.

For high severity tyre applications, tyre pressures need to be checked daily, and should be on the list of daily checks carried out by operators or maintenance crews.

The latest tyre safety standards ? AS4457:1 (2007) and AS4457:2 (2008) ? specify that if a tyre on a piece of heavy earthmoving equipment has less than 70 per cent of its recommended cold inflation pressure ? and the reason is unknown for this inflation loss ? the tyre must be removed and inspected before it can be put back on the machine.

In the case of dual-mounted tyres, if there is more than a 10 per cent difference in pressure between dual-mounted tyres, it is essential to investigate the reasons for this and take action to correct this.

Ideally, tyre pressures should be taken at ?cold pressure?, when the tyre is at ambient air temperatures. A large earthmoving tyre will take a minimum of eight hours to cool down after a shift.

However, hot tyre pressures are a good indication of the severity of the operation. Tyres that reach an inflation pressure of 25 per cent compared with the cold inflation pressure may start to suffer bonding problems. And at temperatures of just over 100?C, the bonding in a tyre starts to break down and can result in separation.

In conclusion, correct tyre pressure is criticalto ensure optimum tyre operating safety, performance and maximum tyre life.

Constant attention to ensuring all tyres are correctly inflated will contributed to longer tyre life, reduced operating costs, less machine downtime and higher productivity.

And it is such a simple step to take.

CHECKING INFLATION PRESSURE
1. Inflation pressure should be checked daily prior to operation, ideally at the start of each working shift.

2. Check the inflation pressure, and be sure that the pressures are at specified values; when internal air temperature is the same as the ambient temperature, the pressure reading obtained is called ?cold pressure?.

3. Always wear safety glasses, gloves, long sleeve shirts and hearing protection while inspecting tyres.

4.
When a vehicle is used for over 24 hours continuously and the cold inflation pressure cannot be checked daily, monitor the hot pressure. This is how to monitor hot pressure:
? Ensure the tyre is inflated to the recommended cold inflation pressure before the vehicle goes into operation.
? After a full day of vehicle operation, check the inflation pressure to confirm operating inflation pressure.
? Each subsequent inflation pressure check should be within a similar inflation pressure range, taking into consideration changes in the operation of the equipment or changes to ambient conditions.
? If hot tyre pressures are 25 per cent over cold inflation pressure, either slow the trucks down or park them up until pressure drops below 20 per cent over cold inflation pressure.

5. Record the tyre-pressure readings. Reference to these records is an effective method for early detection of tyre problems, eg if one tyre loses pressure more rapidly than the others, the tyre should be dismounted and inspected.

6. Always use an accurate pressure gauge.

7. Check the gauges in use against a master pressure gauge, and have the master gauge calibrated frequently by the manufacturer.

8. After conducting the tyre inflation pressure check, pay careful attention to the appearance of each tyre and wheel; all cuts should be investigated for casing damage. Demount the tyre and wheel, and inspect as required.

Denis Clark is the manager of the Queensland engineering services division for Bridgestone Earthmover Tyres.

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