What is top hammer drilling?
With top hammer drilling, the drill bit is at the working end of the drill string but all rotation and percussion is provided at the other end. That is, the top hammer unit is located in the drill rig mast. This is why top hammer drilling is never as efficient as DTH drilling since the percussion energy must be transferred through the enter drill string to the bit. And, therefore efficiency decreases with depth.
The top hammer is hydraulic that drives a slide hammer in the mechanism and its rotation. The hammer has a shank adapter in it on which you screw on a flushing head adapter. On the flushing head adapter you can thread a flushing ring, which is used to run water or grouting down through the drill string. For OD drilling, you can also screw a flushing bell onto the flushing head adapter.
Why a top hammer drill?
These are simpler and less expensive, as you essentially need only the equipment in the machine. If the ground conditions are sensitive, this is less intrusive since you don’t need to blow huge amounts of compromised air into the ground. When drilling anchors this is simply the only option.
For foundation drilling in Scandinavia, top hammers are mostly used for drilling SDAs (self-drilling anchors) But this can also be used to drive casings using ring bit or OD systems.
You don’t need a compressor for drilling anchors, rather this uses water or grout as flush medium. To achieve requisite efficiency, it is important to have the right size hammer with the correct anchor dimension. Otherwise, you might damage the hammer, or have low or no capacity