With down-the-hole hammer drilling, the drill principle consists of a combination of percussion and rotation. Unlike the top hammer, here the hammer drill is located directly in the borehole. These devices, known as ‘down-the-hole hammers’, are connected to the rotating drill pipes.
The down-the-hole hammer is driven directly by the flushing medium. Compressed air is usually used for this purpose. Special procedures, though, can also involve flushing with water. The flushing medium is pressed through the drill pipes, down-the-hole hammer and drill bit and is forced back out at the mouth of the borehole, along with the loosened drill cuttings, through the annular gap between the drill pipes and the borehole wall.
Down-the-hole hammers are mainly used for drilling boreholes into hard rock in bedrock. These boreholes serve as anchor holes, blast holes, injection holes and pilot holes.
In the field of anchoring technology, this process can be used to produce both short- and long-term anchors. Typical applications include: