Plant Equipment and Hire March 2020 | Page 28

MAINTENANCE mines. This usually entails regular grading and spraying or wetting of the haul road surface. Dust suppression chemicals consist of surfactants and binding agents that are diluted into water to overcome the natural hydrophobic characteristics of dust particles, resulting in full wetting. Truck tip and crusher areas are considered for short term application of dust suppressant and is surfactant bases. Stockpile feeding and multiple transfer areas are considered medium term application areas and a binding agent is added, which under normal circumstances will remain effective for up to two weeks. Encrusting agents are added to the mixture for areas of long-term single application and can under normal conditions have a life of up to three months before re-application is needed. Vista Training, a US-based company, has identified the main causes of mine trackless vehicle tyre damage. They found that most commonly sidewall damage resulted in tyre failure and it happens when trucks and earthmoving equipment move too close to berms and high bank faces. This is more common on narrow haul roads where trucks operators steer to the outside edge of the haul road to pass trucks each other and corners the second most often. The other identified incident areas are associated with loading at a shovel or tipping point, where backing up over spilled material or backing up too far until the truck's rear duals are resting upon the edge of the pit face. Trackless mine vehicles that run on a rutted road is noted as another hazard as it can cut the sidewall and put stress on the carcass when entering and leaving the rut. A rut will cause the tyre to wear unevenly due to surface variations, reducing the life of the tyre. As a remedial measure, trackless fleet operators should be encouraged to use different areas within the haul lane to avoid creating or enlarging ruts as far as possible. Tyre pressure Tyres need to be inflated to the correct pressure for the terrain in which it is operating. Underinflated tyres experience significant sidewall deflection, especially when the truck is travelling with a load. The result is higher tread wear, stress in tread and plies, weakened bonding and increased heat build-up. Proper inflation ensures maximum ground contact area, optimum sidewall flexibility and reduced heat levels of the tyre. Overinflated tyres on the other hand can loosen traction as the shape of the tyre becomes deformed, decreasing the contact footprint area. The overinflated tyres are also more prone to damage, as stiffer tyres do not react to road features. Washboard profiles (corrugated road surfaces) on sections of a haul road create a bouncing motion if the vehicle operator is driving over it at high speed. These conditions affect the sidewalls of the truck's tyres. Too much bouncing may cause tyres to momentarily leave the Travelling downhill laden with a full load increases the load on the front axle, generally by the value of the gradient. 26 MARCH 2020 road surface, amplifying sidewall flexing. Damage from excessive flexing is not immediately noticeable but is cumulative and can be hard to spot in the early stages. Excessive speed during cornering has a similar effect. The best remedial action is to grade the haul road to retain a smooth operating surface. Maintaining the road Haul vehicle operators should avoid running over any material that has spilled onto the haul road. The best short-term course of action is to safely manoeuvre around the material until it can be safely removed. The road maintenance crew should be informed of the spillage either by the operator responsible for the spillage or the first operator to encounter it. The edge of a concrete bumper block at the mine's dump pit or load-out area can be a severe tyre hazard and haul vehicle operators should try to avoid making direct contact with it. When backing up to a bumper block or crusher, the operators need to take care that no spillage occurs in the pocket. Backing over spilled material or sitting on top of it while dumping a load will place excessive stress on the tyres. Windrows, the long line of material heaped created by normal grader road www.equipmentandhire.co.za