The Calyx Drill

The Illawarra coal industry has from its early days seen much in the way of technological development, a feature which has continued to the present day.  This has occurred on both small and large scales, the latter exemplified by the development of computer-controlled longwall mining. One development over this time has interest both for its novelty, and also for its connection with the longer term development of the mining industry in Australia.  This was the use of specialised equipment to ‘drill’ shafts of large diameter for mine ventilation, using the so-called “Calyx” drill, a form of core drill.Core drills are those drills of annular shape which by their hollow nature produce coherent ‘cores’  of the material through which the drill has been driven. This may be for the purpose of mineral prospecting (for which purpose relatively small diameter cores may well be adequate), for investigation of geological structures for construction or mining (requiring a larger core to be produced), or ultimately for personnel or equipment access purposes, requiring a core removal of some considerable size.  The application here relates to the latter, with the equipment being used to drill or excavate air shafts of up to two metres in diameter.

The first core drills to be used (largely for the first purpose) were diamond drills, so named as the annular ‘bits’ of the drills had embedded in them diamonds to abrade and cut the hard rock which they would encounter.  While effective, the operation of such drills was, not surprisingly, expensive given the loss of diamond material in the cutting process. There was also a natural limit on the size of drill bit which could be economically manufactured and used.  Among those seeking a better way was Francis Harley Davis – an Australian engineer. He would appear to have been an early member of the sponsoring institution of this website, the Australasian Institute of Mining and Metallurgy (AusIMM): in an interview in New Zealand in 1896 (three years after the founding of the institution), he was described as “…Mr Francis Harley Davis, M.A.I.M.M. (sic) of the well-known firm of Davis and Knapp, engineers etc. of Melbourne.”

Davis is widely credited with the development of the so-called ‘Calyx Drill’.  His first drill patent however was not for that, but rather for a device “..to provide means for rotating and feeding the drill and for automatically connecting and disconnecting the drillrod sections…”.  This patent (US 642,587 lodged in 1898) showed a metal toothed drill, of a type unlikely to have been particularly successful in rock cutting. That did not preclude him however from proclaiming its virtues in the interview noted above, as he prepared to leave for the US.  It was from the US that his later patents were lodged.

Davis’ principal contribution to drill technology was to conceive of a drill which could replace the function of the diamond drill.  The method he developed was to replace the embedded diamond cutting material in the drill head with a freely-flowing stream of hardened steel shot, this shot functioning to abrade the rock being drilled as it passed under and around with the cutting end of the drill cylinder.  He also made another important conceptual contribution to the improvement of the drill designs of the time. He recognised that the process of using water to flush out the material cut by the drill was power-intensive for the water pump, as the material was being returned to the surface, with consequent increase in pressure requirements as the drill descended.  His alternative was to design a mechanism whereby the flushing water returned only a short distance to the top of the core section then being cut – being taken to the surface when that core section was removed. A later patent included also a means whereby the feed of shot could be managed on the drill head proper, with the inclusion of a shot feed hopper in the drill head.

The following figure depicts Davis’ concept of shot-assisted drilling.  The actual equipment used to implement that principle was considerably more complex, as may be seen in later equipment drawings below.

“..said hollow bit adapted upon rotation to coöperate with a free or loose grinding material, such as a plurality of chilled iron spheres and known in the art to which this invention appertains as “shot,” and thereby to mill and grind an annular channel in the rock or other material..”  (extract)

Later patents around the Calyx Drill were taken out by the Ingersoll-Rand Company, which largely commercialised the product.  As is often the case, the equipment became more complex as experience grew in its use. The Ingersoll-Rand patent drawings of 1934 and 1944 show the mechanical drive details, and the shot-feed mechanism detail respectively.

The AIS Calyx Drill 

The particular unit used in the Illawarra was originally purchased by the Victorian State Electricity Commission (SECV) in Peru, where it had been used for drilling large diameter openings for the penstocks of a hydro-electric scheme.  Following the completion of that work, this Calyx Drill was offered for sale and purchased by the SECV for use in the construction of an underground power station as part of the Kiewa hydroelectric power scheme in the Australian Alps in north-eastern Victoria.  Changes in the design of that power station led to its being located on the surface rather than underground, and as a result  the Drill was put up for sale by the SECV. A senior member of BHP management advised Mr. G. M. Hindmarsh, then Superintendent AIS Collieries in the Illawarra, that this plant was being offered for sale.  After further investigation by AIS Collieries staff the Drill was purchased by the Collieries.

The major components of the Calyx drilling rig are shown below:

The supporting headframe was 22 metres high, and enclosed an area 8 metres by 12 metres at ground level, where a combined drill and man handling rope hoist powered by a 150 kW electric motor, was installed.  The figure shows the assembly of plant involved in sinking the shaft in one view (left) and the plant involved in extracting the drilled core from the shaft in the second view (right). 

Operation

The core lifting cylinder was 1600 mm in length and consisted of an inner and an outer shell.  The outer shell was tapered on its inside, while the inner shell had slots cut into it from the bottom to about half- way up the shell, to create a series of flexible ‘fingers’ that surrounded the core when it was about to be extracted from the shaft.  While the inner shell was able to slide inside the outer shell, the two shells remain attached to each other when they were being lowered into the shaft by the hoist to surround the drilled core. When the inner shell had come to rest around the core near the bottom of the shaft, it was detached by the drill operator, so that it was the outer circular shell which remained supported by the hoist.  The outer shell was then raised to the surface by the operator, using the hoist. As it was raised, a wedge-shaped ring located at the lower end of the outer shell would make contact with the flexible tapered fingers on the inner shell, resulting in the fingers tightly gripping around the drilled core, supporting it in being hoisted to the surface.

Prior to the core being hoisted to the surface, it was broken free from the core remaining in the shaft, either by firing a small charge of explosive attached to the bottom of the core, or by manually driving wedges into the slot created  between the core being hoisted and the partially drilled core remaining in the shaft.

Drill Use in Illawarra Mines

The equipment was first used by AIS in the 1950s at the Nebo Colliery to sink two mine ventilation shafts.  The image above shows one of the core segments extracted during that operation, the cores being around two metres in diameter.  The image is a good demonstration of the unique capability of the Calyx Drill. The core segment shown would be expected to weigh in excess of six tonnes. 

Following the successful sinking of those shafts, the Calyx as it became known was moved to the Kemira Colliery to drill two mine ventilation shafts for that colliery.  The shafts were typically some two metres in diameter. On completion of the shaft sinking at the Kemira Colliery the Drill was placed in storage. During the 1970’s the Calyx Shaft Hoisting plant was used to install the shaft winding ropes on the Corrimal No3 Shaft Bulk Skip Hoist and later the Cordeaux and Tower Collieries Shaft Winder installations. 

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