New diamond drilling system improves mine productivity, lowers costs

14th September 2012 By: Sashnee Moodley - Deputy Editor Polity and Multimedia

Mines and contractors can now use electricity and compressed air, depending on their availability, to power a new diamond drilling offering by drilling company Lesedi Drilling & Mining Contracting.

The manufacturing of the drill began in March but the concept design was completed more than a year ago. After repeated attempts at first reducing the accident rates of conventional air-powered drills, a decision was made, however, to produce the first three drills for evaluation purposes. The testing of the drill will take place in October.

“We needed to be sure that the drill effi- ciently uses the energy supplied by compressed air. The test confirmed this, the drill’s maximum speed of penetration and the speed it achieves when it withdraws and pushes drill rods into a hole. We also needed to be abso- lutely sure that the operating system was indeed safer than others on the market, which is perhaps the major reason for its construction,” Lesedi CEO Gordon Hogan states.

The new drill was also developed to tackle the challenge of immediately converting an entire mine from using compressed air to using electricity.

Hogan explains that converting a diamond drilling system from compressed air to electricity is a major logistical and skills set challenge for a mine.

“This system allows mines to manage their conversion at a sustainable rate, making the change from compressed air to electricity more cost efficient, as the mine does not need to buy new drilling equipment. Diamond drilling contractors are also given the luxury of not requiring two different sets of tech- nologies, as only the primary motor needs to be changed from compressed air to electricity or vice versa,” he enthuses.

Hogan says South African mines currently have a medium-term goal to change from compressed air to electricity to power under- ground equipment.

“Using compressed air as an energy source to operate equipment is extremely inefficient, as a result of energy losses in its production and transmission. Given the rising costs and limited availability of electricity in South Africa, the mines need to determine how to run their operations by consuming electricity in the most efficient manner possible,” he states.

Lesedi’s new diamond drill uses a compressed-air motor to run a hydraulic pump in a dual-purpose power pack. The drill is then hydraulically powered. The air motor can also be removed from the power pack and replaced with a 22 kW electric motor.

This enables mines to use one drilling solution in different areas of the mine if either electricity or compressed air is not available.

Further, the hydraulic technology allows engineers to design more intricate operations, such as operations required to enable the machine to handle diamond drill rods, than those using compressed air allow for, which enables the drill to operate with limited human intervention, Hogan says.

Therefore, the level of safety is increased as the drill operators are removed from rotating machinery, and the risk of drill rods accidentally dislodging from a hole, which Hogan says is a common problem, is also eliminated.

Traditionally, pneumatic diamond drilling entails the attachment of a face clamp to the rock at the opening of the hole. This clamp is manually operated and a set of jaws is opened when drilling begins, allowing the rods to spin freely.

When another rod needs to be added to the rod string, the face clamp jaws are manually closed to hold the rods in place in the hole to prevent them from dislodging.

“The machine has a chuck to hold the rods in place while drilling takes place and this requires coordination between the machine operator and his assistant. If this coordination breaks down, many things can go wrong. One of the main problems is that the drill rods can fall out of the hole owing to operator error and gravity, killing or injuring the assistant operator,” explains Hogan.

Therefore, a hydraulically operated machine is a major advantage, as the operator can handle the entire operation from his remote control panel and the assistant operator is not needed to open and close the face clamp.

The electric version of Lesedi’s drill also has fewer moving parts and will have lower running costs than the air-powered version of the drill.

A compressed-air drill has many gears and counter-rotating shafts, as well as an expensive feed screw and feed nut, which are replaced every 700 m. The new air over hydraulic drill has all the parts of the air motor, but has only two gears in the gearbox and two hydraulic cylinders, which are expected to last more than 700 m.

Hogan says the lower running costs should offset the higher capital costs of the equipment.

The drill will also turn the rods at more than 2 000 rpm and this results in higher drilling productivity. The machine can also pull 100 m of rods from a hole in under 15 minutes, another aspect of its increased safety and improved production.