What are ‘Down-the-Hole’ (DTH) Drill Bits and how are they used?
Down-the-hole drill bits are used with down-the-hole hammers for drilling holes through a wide range of rock types.
In conjunction with our DTH hammers, our drill bits are designed with a splined drive for rotating the bit in the ground. Drill bits are available in a range of different sizes and configurations so they can drill a wide range of holes sizes, in different ground conditions.
How have DTH Drill Bits developed?
Rapid advances in drill bit technology have occurred throughout the last 40 years. The first type of drill bits used with down-the- hole hammers were ‘cross bit’ design. Four chisel shaped lengths of tungsten carbide were brazed creating stresses within the drill bit thereby limiting its life. A further disadvantage of the cross bit design was that the majority of the carbide was situated around the centre of the bit face and not towards the outer edge of the drill bit where there is the most rock to cut.
In the late 1960s however, the button bit was introduced; this was a landmark in the progress of DTH equipment, which led to bit lives previously unheard of.
Cylindrical button inserts were precision ground to extremely close tolerances and pressed into the bit as an interference fit. This resulted in improved carbide insert retention by eliminating brazing stresses and other defects associated with brazing and braze materials.
Buttons inserts are distributed more efficiently than cross bit inserts by providing more cutting power where it is needed at the outer edge of the drill bit face.
In many cases, the need to sharpen the drill bit was eliminated
with the arrival of the button bit and the improved cutting action provided While the cross bit design is still used in some rotary and drifted applications where the rock is very soft, the button bit is now used in virtually every DTH application.
Applications for Overburden Systems
Soft soil is normally drilled with augers or by the rotary method but DTH hammers have been adapted to handle soft conditions by being able to drill and case a hole simultaneously by using a concentric bit, which can be withdrawn on completion of the bore hole; leaving the casing in situ, thus preventing hole collapse.
As with all Halco hammers it is crucial that you choose the right drill bit otherwise it will cost you both in time and money. We pride ourselves on having a comprehensive range of drill bits on offer so you can be sure that you will definitely find a suitable bit for any project you are undertaking.
Our carburised drill bit are among the best in the world providing outstanding performance and durability.
We produce all our drill bits at our
specialised plant where they are made out of high quality nickel chrome alloy steel, carburised and heat-treated to offer extra protection against wear and fatigue. Every hole in the bit head is machined to within microns and fitted with carbide inserts which provide the cutting action of the rock.
We have three different bit heads on offer, Flat Face, Concave and Convex, which are available with three different inserts. We guarantee that we have a drill bit that can tackle any challenge and rock face formation. The two most important factors
in choosing the right drill bit are productivity and reliability.
For soft to medium rock formations where penetration rates are high, the ballistic and semi-ballistic inserts coupled with flat face or concave bit heads are more suitable.