The “Down-the-Hole” or DTH hammer is used for drilling holes through a wide range of rock types, the variety of which continues to extend well beyond the original conception of early blast hole drilling.
DTH refers to where the hammer action occurs when compared to drifter hammers, which hammer on top of the drill string. The DTH hammer piston is always makes a direct contact with the drill bit and there is generally no loss of transmitted energy as the hammer drills deeper, as in the case with drifter (top hammer) rigs.
WHY IS DTH APPROACH PREFERRED TODAY?
Although DTH hammers started life in quarries, they are now appreciated throughout the drilling industry where they have become the preferred option due to their significant advantages over other, in particular:
- Capable of drilling in almost all rocks, hard, medium to soft.
- Penetration rates that can outstrip other systems.
- Reduced costs.
- Straighter/cleaner holes.
- Wide range of hole sizes available, without high expenditure.
- Quieter than other percussive systems.
- Check if the chuck and the back head are firmly tightened.
- Lubricate the hammer with rock drill oil. DTH Hammers need 0.2 litre/hour of oil per 3§©/min of air consumed.
- Connect to the hammer to the drill string.
- Open the hammer lubricator valve to continually inject oil into the air stream whilst the hammer is operating
- Start to drill after checking safety
- Rotation Speeds
As a general guide, the harder the rock or the larger bit diameter, the slower the rotation speed required. It may be necessary however to increase the rotation speed where the rock is badly fissured in order to prevent stalling.
CHECKING FOR WEAR AND DAMAGE
Premature wear to internal parts is a result of either:
- Insufficient or incorrect lubrication.
- The ingress of debris in the hammer.
- Incorrect service and storage.