Halco Rock Tools Ltd. is a world class manufacturer of down the hole (DTH) drilling equipment. Halco pioneered the development and distribution of DTH hammers in the 1950s, and now their precision-engineered range of performance hammers and drill bits is used globally. Predominantly used for mining, DTH is preferred in other applications such as construction, quarrying, formation sampling, and the drilling of water wells.
Halco Rock Tools, in close cooperation with Stenuick Freres, actually established the development and distribution of the down the hole hammer in the 1950s throughout the UK, Australia, New Zealand, Africa, and India. Produced for more than 60 years, these products continue to be regarded as one of the most reliable and durable available today. This is due to the commitment to customers’ needs, design expertise, and rigorous product testing in extreme drilling conditions.
Halco Rock Tools is located in Halifax, UK.
Hammer OverviewWhat is DTH and How is it Used?
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.
“Down the Hole” refers to where the hammer action occurs when compared to drifter hammers, which hammer on top of the drill string. The DTH hammer piston always makes direct contact with the drill bit, and there is generally no loss of transmitted energy as the hammer drills deeper, as is the case with drifter (top hammer) rigs.What is Reverse Circulation?
Reverse circulation hammers can in most instances carry out continuous sample collection in a fraction of the time necessary with conventional or wireline coring.Why is the 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 systems, 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
Prior to DTH technology, blast hole drilling was normally carried out with drifter equipment. Water well drilling in hard formations was done by cable tool rigs or rotary rigs using roller cone bits.
However, because drifter drilling becomes progressively slower with more depth, unlike DTH hammers, and because the latter can drill in one day what a cable tool rig takes weeks to complete, the quarrying, waterwell, site investigation, civil engineering, and mining industries throughout the world have become more and more aware of the advantages to be gained from using DTH hammers. This is not only as an alternative to drifters, but because of the higher performances when compared to conventional rotary drilling. The DTH hammer concept proved so popular that established manufacturers of drifter steels, bits, and accessories followed our lead and developed their own range of DTH hammers and bits.
How is DTH Better?
Penetration rates with DTH hammers are almost directly proportional to air pressure therefore doubling the air pressure, which results in approximately double the penetration. The first ever hammers were of “valved” design and had an internal liner. This valved technology, together with compressor availability, limited the air pressure capability of the early hammers that were incapable of withstanding air pressures above 170 psi.
The valve itself had operational problems because hammer malfunction occurred when large volumes of water were passed through the hammers or if grit entered the hammer. Modern hammers are generally valveless in design, with fewer internal parts requiring little maintenance.
The removal of the valve has eliminated the operational problems previously experienced. Modern hammers are also of a rigid construction, enabling them to withstand air pressures as high as 435 psi. Further development of DTH hammers will be in terms of their design, which will be related to achieving lower user drilling costs through increased rates of penetration and longer life in the hole. Increases in penetration rates will require the investigation of delivering yet higher air operating pressures to the hammer as in conventional designs, or the use of alternative power sources such as water or oil.
To achieve longer life of the components of the hammer, research of wear- and impact-resistant materials not normally associated with traditional hammer manufacture is essential. Water-powered hammers are being developed for use in underground mines.
Although performance results are encouraging, the design of the hammer is limited to use on sites where large amounts of water are available and can be tolerated and, most importantly, handled and cleaned for return to the hammer. Hydraulic oil-powered hammers have been tested in some quarries, but these need a specially adapted drill rig, drill tubes, and a coupling system.
Spillage with potential contamination of the ground is a major consideration. Furthermore, a separate air supply is needed in order to flush the hole. Because of these limitations, water- and oil-powered hammers are slow to gain ground and air-driven hammers still have the competitive edge. The immediate opportunity for DTH hammers is in developing their use for applications normally drilled using other methods, for example shallow oil and gas field development, shallow wide hole piling, continuous drilling and casing systems, reverse circulation chip sampling, mole drilling, and applications where holes in excess of 36" diameter are required in mining, civil engineering, and construction applications.