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Dump-Truck Tire Reliability and the Factors Affecting Their Life

In opencast mines, the shovel-truck system is probably the most flexible system and its reliability and availability are the most important factors in successfully meeting their production target. Tires of dump trucks are an important element of the shovel- truck system and their reliability directly or indirectly affects opencast mines’ overall production performance.

A study concerning dump-truck tires’ reliability revealed that times to failure of the tires followed a normal distribution [6]. It simply means that the failure rate of dump-truck tires is not constant and the reliability of the tires has to be calculated by using the normal distribution representing the tire failure times.

There are many factors that can affect the life of dump-truck tire including over inflation, heat generation, speed and haul length, under-inflation, and tire bleeding

[6,7]. Each of these five factors is described below.

Over inflation. It reduces the amount of tread in contact with the ground and makes tires vulnerable to factors such as snags, impact fractures, and cuts.

• Heat generation. In this case, as rubber is a poor conductor, the heat generated through flexing will lead to heat accumulation. Here, it is to be noted that although the recommended load-speed inflation pressure ensures an equilibrium between heat generated and dissipated, any deviation can result in high pressure.

  • Speed and haul length. In this case, speeds above 30 km per hour and a haul length more than 5 km can considerably affect the tires’ life.
  • Under inflation. It can lead to excessive flexing of the sidewalls and increase in internal tire temperature. In turn, this can cause permanent damage to tires such as casing breakup, radial cracks, and ply separation.
  • Tire bleeding. In this case, lowering tire pressure after a long run is a normal practice. This causes premature failures, increases tire temperature, and makes an under inflated tire withstand high load (i.e., vehicle weight)

Programmable Electronic Mining System Failures

Past experiences over the years indicate that various types of hazards can occur with programmable electronic mining system hardware or software failures [8]. Hardware failures are physical failures and are normally the result of wear and random events. They can involve any physical part/component of the system including power supplied, programmable electronic devices, sensors, and data communication paths. Random hardware failures include items such as mechanical defects, open circuits, short circuits, broken wires, corroded contacts, and dielectric failures.

In contrast, software failures take place due to systematic (functional) errors. Systematic errors include items such as operator errors, software bugs, design errors, requirement errors, management-of-change errors, and timing errors.

A study of data obtained from the US Mine Safety and Health Administration (MSHA), Queensland Mines in Australia, and New South Wales Mines in Australia, concerning programmable electronic-based mining systems, revealed that during the period 1995-2001 there were a total of 100 mishaps. The breakdown of these mishaps is shown in Figure 10.1 [7].

Both systematic failures and random hardware failures shown in Figure 10.1 are described below, separately.

Mishaps, concerning programmable electronic-based mining systems, breakdown

FIGURE 10.1 Mishaps, concerning programmable electronic-based mining systems, breakdown.

Systematic Failures

Periodic systematic failures are also known as functional failures. Sources of these failures include hardware and software design errors, operator errors, errors made during maintenance and repair activities, and errors resulting from software modifications. For the period 1995-2001, analysis of systematic failures of the data for programmable electronic-based mining systems revealed the breakdown of the failures as follows [8]:

  • • Design-error-related failures: 50%
  • • Maintenance-and repair-error-related failures: 40%
  • • Miscellaneous failures: 10%

Random Hardware Failures

The harsh environmental factors in mines, such as water and dirt intrusion, heat, shock, and vibrations, can significantly influence the occurrence of programmable electronic-based mining system hardware failures. These failures involve items such as electrical connectors, power supplies, sensors, solenoids, and wiring. An example of such failures is the degradation of rubber boots/seals used for keeping out dust and moisture.

For the period 1995-2001, analysis of random hardware failures of the data for programmable electronic-based mining systems revealed the following breakdown of the failures [8]:

  • • Sensor-related failures: 33%
  • • Electronic-component-related failures: 26%
  • • Moisture-related failures: 17%
  • • Actuator-related failures: 13%
  • • Miscellaneous failures: 11 %

It is to be noted that in the above breakdown sensor-related failures include switch- related failures as well.

 
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