Open Cut » Maintenance & Equipment
Current above ground mining practices in open cut / strip mining requires the topsoil or 'over-burden to be removed so as to provide easy access to the target material ie coal and ore. Over-burden can be removed by numerous methods, but is predominantly performed by the walking draglines and face loading shovels.
The sheer size and capabilities of these machines make them ideal for the job at hand, and they are by far the most efficient means of over-burden removal. Although these machines perform their tasks differently, both use a large bucket in order to dig. Over-burden comes in many different forms such as soil, rock, limestone and coal, these materials by their very nature are abrasive and therefore cause considerable wear to the bucket and associated equipment.
In order to prolong the life of the buckets, which are very costly, a system of replaceable componentry is used all over the buckets. Such items are referred to as the wear components, and they are generally held on via mechanical means. The objectives of this project were to investigate and develop an alternative method of securing the wear components to the buckets, in particular the bucket teeth.
As mentioned earlier, the draglines and shovels are very large pieces of equipment that are very expensive to have idle, when you consider the lost productivity as these primary machines often have numerous other machines which are dependant on them eg dump trucks. In addition to the costs involved with the equipment, the sheer size brings about the possibility of safety issues that may effect the personnel who are required to work on and around the buckets.
The size and weight of the bucket teeth require large forces to be applied in order to have them fitted to the bucket correctly. Ideally, the most structurally sound way of holding the teeth on would be to weld them, the problem with this through is that it would be very hard to replace the worn teeth in this manner. Since lost time is lost money, the quick change system was developed to speed up the replacement process. Existing methods used a spool and wedge system, were the wedge is driven in using 25lb hammers. This method of operation exposes mine personnel to several possible areas/causes of injuries, both direct and indirect.
Direct injuries may be sustained by the swinging of the sledge hammers, injuries such as serious jarring, hernia and lower back muscular straining. Indirect injuries are commonly caused as a result of steel fragments flying off after the steel on steel impact between hammer and wedge. Both direct and indirect injuries can result in serious lost time or even worse permanent disability of personnel.
Therefore, it was our goal to develop a retaining system and procedure of use that would minimise the replacement time of a set of bucket teeth and at the same time minimise the exposure of danger to maintenance and nearby personnel.