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Enemies of a Tire – Rocks and Abrasion

Common sense will tell you tire life will be affected by the surface area the operation will be running on. Leaving aside tire pressure maintenance, tire compound, tread type, overloading, and road design etc the surface material will affect the wear rate alone.

Wear Rates and surface material

Tire wear can be high for various reasons and one major factor will be the abrasive qualities of the material constructing the surface and its physical properties. Recommended tire inflation pressures may vary according to rolling resistance, traction properties and the tire footprint contact area created by the surface material.

Material can vary from soft clay to hard rock being in different climates and conditions where the multitudes of combinations bring their own problems. A good haul road base material is critical however most mining environments are limited to the local material. The ideal road base material size is 1 inch diameter, any larger and wear will increase and any smaller over compaction will create dust generation. However a small percentage of fines are required to help bind the material together.

Haul road surface maintenance is often neglected and each haul road will require its own maintenance schedule. The cost verses savings has always been a topic for debate. Caterpillar performed a study at its Arizona testing facility with a fleet of 777 haul trucks using 14G graders subjecting them to various levels of maintained haul roads. The findings are shown in the table below.

# Graders

0

½

1

Rolling Resistance%

11

7

3

Truck Cycle Time

16

11.5

8

Production Rate

  100% eff TPH

  60% eff TPH

 

290

  174

 

405

  243

 

560

  336

Cost ($US/T)

.79

.61

.52

Fuel Consumed (Litres)

3,458,000

2,661,000

1,886,250

Rock Damage and Cutting

Rock damage is the most common form of premature failure on mining operations. The obvious damage is cutting on the tread and side wall of the tire. If the tire does not fail it will usually be continued in service and not be regarded again.

Damage sustained to a tire by rock damage that appears to be superficial may have damaged the construction of the casing where it will eventually fail. When considering the forces being applied to the tire to result in obvious damage it would be advised to remove the tire so preventative repairs can be made. This is more relevant in the larger tires as seen in the contact pressure table below.

4000R57

  240T

2700R49

  95T

1800R33

  40T

Tire Load

Net Contact Pressure

70 Tonnes

8.25Kg/cm2

26 Tonnes

7.7Kg/cm2

9 Tonnes

8.3Kg/cm2

  Rock Surface Area

  Contact Pressure

  Contact Pressure

  Contact Pressure

100 cm2

25 cm2

1 cm2

700Kg/cm2

2,800Kg/cm2

70,000Kg/cm2

260Kg/cm2

1,040Kg/cm2

26,000Kg/cm2

90Kg/cm2

360Kg/cm2

9,000Kg/cm2

The forces applied to concentrated areas in the tire can cause separation between the belt package components and may result in the premature failure of the tire in that area.

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