Search Stories by: 
&/or
 

Maintenance, Load & Haul

Articles from CONSTRUCTION PLANT & EQUIPMENT (464 Articles), LOADERS (447 Articles), HAUL TRUCKS (399 Articles)











Whole-life costs of off-highway earthmoving tyres can be reduced significantly through longevity, fuel savings, improved performance and reduced downtime.
Whole-life costs of off-highway earthmoving tyres can be reduced significantly through longevity, fuel savings, improved performance and reduced downtime.

Don’t lose your grip: Getting the most from your earthmover tyres

With tyres still a precious commodity in the earthmoving market, whole-life costs can be managed effectively with a sensible approach to correct usage, maintenance and the right conditions, according to specialists at tyre manufacturer Michelin.

Tyres are often seen as a distress purchase by the earthmoving industry, and this is perhaps unsurprising given the investment required to replace them.

But if the right quality of tyre is chosen for the right job, and those tyres are maintained properly, whole-life costs can be reduced significantly through longevity, fuel savings, improved performance and reduced downtime. Additional benefits of getting to know your tyres include added comfort, lower emissions and enhanced safety.

CHOOSING THE RIGHT TYRE

The industry has five machine category codes:
C   Compactor.
G   Grader.
E   Earthmoving (transport).
L   Loader and dozer.
H   Highway.

The compactor category is used mainly in the road surface laying industry. Highway is almost exclusively for mobile cranes, and specialised grader tyres, in Europe, tend to be passed over for a loader/dozer tyre.

Figure 1. Presenting the dump truck at a 45o angle to the material to be loaded is more tyre-friendly.
Figure 1. Presenting the dump truck at a 45o angle to the material to be loaded is more tyre-friendly.

The industry has seven main tyre category codes:
S   Smooth (no pattern, for mines and hard ground).
1   Ribbed (circumferential ribs, for smooth surfaces).
2   Traction (regular).
3   Rock (regular).
4   Rock (deep tread).
5   Rock (extra deep tread).
7   Flotation (for soft ground).

Smooth tyres tend to be used in underground applications, ribbed are mainly for ports and flotation are for mobility over soft, yielding surfaces.

These codes are combined to highlight different applications, so an E3, for example, is a general purpose transport tyre with a rock pattern, used where the risk of accidental damage is relatively low. An E4 is a deep tread transport tyre where a higher level of damage resistance and/or longer tread life is required.

Deeper tread tyres have greater tread mass but lower speed capability, to offset the effects of the internal heat generated.

Some tyre manufacturers have developed products that do not fit exactly into the code system, so new codes such as Super E3 or E3+ have been adopted to indicate a tyre that falls between the E3 and E4 groups.

TREAD DEPTHS
Figure 2. The X Super Terrain+ E4 (left) and XADN+ E3 tyres are suitable for articulated dump trucks.
Figure 2. The X Super Terrain+ E4 (left) and XADN+ E3 tyres are suitable for articulated dump trucks.

If we say categories 2 and 3 have a standard level of tread depth of 100 per cent, then category 4 will have about 150 per cent compared with categories 2 and 3, and category 5 will have about 250 per cent.

The deeper the tread, the lower the tyre’s ability to dissipate heat. We know an L5 tyre has about 2.5 times the original tread depth of an L3 tyre but does not cost 2.5 times as much, so on the face of it the better deal would be to go for L5 tyres when buying loader tyres.

However, a Michelin XHA2 L3 can be used for a maximum of 16km in an hour, while a Michelin X Mine D2 L5 tyre can be used for a maximum of 6km in an hour. If those maximums are exceeded, the tyres could overheat and fail.

TREAD PATTERNS

In general, the more rubber mass in the contact area with the ground, the slower the tyre will wear. The less rubber in contact with the ground, the greater tractive effort from the tyre.

LOADER TYRES

There are two main types of operation that a loader shovel will undertake, working at the face in relatively arduous conditions and during load and carry applications. Quarry managers need to take into account the exact conditions in which machines will be working, and manage tyres according to the relative importance of tread life, damage resistance and traction.

Face machines, where damage resistance and tread life are priorities, would favour deeper treaded tyres, whereas more open treaded tyres would be better where traction is the key.

LOADING PRACTICE
Figure 3. The X Quarry S and XDT are suitable for rigid dump trucks and have the option of “rock” or “traction” patterns.
Figure 3. The X Quarry S and XDT are suitable for rigid dump trucks and have the option of “rock” or “traction” patterns.

Operator behaviour also affects tyre longevity and effectiveness. For example, tight turns and high speed will wear tyres more quickly. Presenting the dumper/truck at a 45o angle to the material to be loaded is much more tyre-friendly. See Figure 1.

DUMPER TYRES

Articulated dump trucks (ADTs) are mainly fitted with traction tyres, where you can trace the tread groove from one shoulder of the tyre to the other. This leaves the choice between E3 (standard) or E4 (about 1.5 times the tread depth of E3), but usually only with a “traction” tread pattern to cope with the demands of poor haul roads. See Figure 2.

Rigid dump trucks (RDTs) have a wider choice on offer, as they have the option of “rock” or “traction” patterns. See Figure 3 on page 36.

A rock type pattern has high damage resistance and relatively long tread life, but it will give less traction and will have a relatively small maximum distance per hour capability. The traction tyre will be good for traction and maximum distance per hour, but damage resistance and longevity will be reduced.

FACTORS on DUMPER TYRE LIFE

Tyre pressure
Pneumatic tyres are designed to be filled with a gas. To get the maximum tread contact area, the internal pressure is matched to the load imposed: the higher the load, the higher the pressure, and vice versa. See Figure 4.

A low pressure in relation to the load imposed results in reduction in traction, uneven tread wear on the shoulder, wear from the flange on the tyre and increased fuel consumption. At extremes, the casing is in danger of fatigue and failure.

A high pressure in relation to the load imposed also leads to reduced traction and uneven tread wear – this time in the centre. There is less resistance to damage and the risk of wear from the bead seat.

No matter whether the tyre is over or underinflated, there will still be the same amount of torque, steering, braking and load carrying to be undertaken. With less than the full tread footprint in contact, there is less rubber to transmit these forces and therefore wear is accelerated.

Running a tyre 20 per cent underinflated reduces tread life by about 25 per cent, while 20 per cent overinflation reduces tread life by about 30 per cent. Running for just a couple of weeks at +/- 30 per cent will have a major impact on tread wear.

Figure 4. Recommended pressure vs tyre performance and potential risks.
Figure 4. Recommended pressure vs tyre performance and potential risks.

THE IMPORTANCE OF HAUL ROADS

Gradients
Increasing gradients above eight per cent will result in substantially reduced tyre life. A 10 per cent slope can lead to tyre life reduction of 20 per cent while that figure jumps to more than 50 per cent when haul trucks operate “downhill laden”, compared with running uphill laden on an 85o slope.

Terrain and road conditions
If rock-free soil is taken as the ideal terrain for tyre life, that longevity is reduced by 10 per cent when scattered rocks are present – and a similar reduction is seen on a maintained road with smooth gravel. A poorly maintained road with ungraded gravel brings down tyre life by at least 30 per cent, and scattered blast rock reduces life by at least 40 per cent.

Speed in curves
Having tight turns on a haul road can also have an adverse effect on tyre tread life. The tighter the turn, the lower the speed should be. Tight turns result in dynamic load transfer and can cause rapid tyre wear.

LOCAL FACTORS

The factors outlined above have one thing in common – the site can control them locally.

Getting the most out of your earthmover tyres should be a three-way operation: the tyre manufacturer should give recommendations for pressure and maintenance; the tyre service provider/dealer should examine the tyres on a regular basis and give advice on when they need to be changed and pressure maintenance; the site itself should have a routine of tyre visual inspection and haul road maintenance.

If all three are in place, and quarry managers learn how terrain and usage affect tyre life and performance, the savings and productivity benefits are significant.

Operator behaviour, eg tight turns and high speed, will affect tyre longevity and effectiveness.
Operator behaviour, eg tight turns and high speed, will affect tyre longevity and effectiveness.


Source: Michelin
This article first appeared in the November 2014 issue of Quarry Management UK and reappears in Quarry with kind permission.











enewsletter banner 2
advertisement








Monday, 26 August, 2019 12:57pm
login to my account
Username: Password:
Skyscraper 2
advertisement
Free Sign Up

Receive FREE newsletter and alerts


CONNECT WITH US
Display 2
advertisement
Skyscraper 1
advertisement