DRILLS"

This invention relates to a method of and means for reconditioning percussion drills and in particular it relates to drill heads of the type which are carried on an actuating string and comprise a stem having a drill head in which are carried a series of drill bits, sometimes known as buttons, the device being actuated by rotating the drill head as the head is axially reciprocated to provide the required percussion effect, the head usually being expanded so that it is approximately of the dimension of the diameter of the hole being drilled but in the base part of the drill head are a series of upwardly projecting drill bits spaced around the periphery of the drill head preferably sloping downwards in an outward direction, the face of the drill head also having a series of bits inserted into it.

With drills of this type the diameter of the hole is fixed by the outwardly projecting drill bits around its periphery and one of the problems experienced with this type of head is that should any of the bits wear or are broken off, the sizing of the hole being formed is not correct with the result that eventually the drill head will tend to jam in the hole because the drill bits around its periphery do not form a hole slightly greater than the drill head itself.

The usual method of fitting the drill bits or buttons is to form apertures in the drill head and to force these into the aperture by shrink-fit methods

so that they are very securely held and therefore when the drill bits are worn or break off the drill head has to be discarded because of its incorrect diameter.

The object of the present invention is to provide a method of and means for reconditioning percussion drill heads of this type and this is achieved according to my invention by forming an ejection duct in the drill head from the periphery of the drill head to the rear part of the socket in which the bit which is to be removed is held and to then use a fluid force behind the drill bit to force the drill bit out of its socket, the force preferably being suffi¬ ciently sharp to have a percussion effect.

The method and means for applying the fluid pressure can be various, but according to a convenient arrangement a hole, which herein is referred to as an ejection duct, is drilled in the drill head to meet the rear of the socket in which the drill bit which is to be removed is held, and this ejection duct is placed into communication with a percussion mechanism such as a high pressure fluid or an explosive cartridge and by generating a high pressure fluid flow in the ejection duct sufficient pressure is generated in the duct leading to the rear of the drill bit to eject it from its socket in spite of the tight interference fit hold.

Various methods and means can be used for providing the necessary fluid pressure and some of these will be described in the detailed description which follows but it is to be understood that the invention need not of necessity be limited to any of these methods

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as any system which builds up a sufficient ^, fluid pressure in the back of the socket in which the drill bit is held will fall within the general scope of the invention.

According to one method a nozzle is held to the outside of the drill head over the ejection duct which leads to the back of the socket to which the explosive force is to be applied so that there is a seal between the nozzle and the drill head, and through this nozzle is fed an explosive force at high pressure which can be obtained for instance from a hydraulic intensifier or an explosive cartridge,

The mechanism which supplies the fluid pressure can be actuated mechanically, or be timer actuated, or electrically controlled but is arranged so that the required shock can be generated at an appropriate time.

The action forces a high pressure fluid into the space behind the rear of the drill bit in the socket and, depending on the volume of the fluid, will entirely eject the drill bit or will dislodge it sufficiently so that it can be extracted by other means.

The drill heads are usually of truncated conical form with a smaller part joining to the stem and the larger part forming the face which extends across the area which is to be drilled and has drill bits in this face projecting downwardly but also has the angularly disposed outwardly sloping drill bits around its periphery and a face is therefore provided on the drill head from which the ejection duct can be

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bored to the socket and sufficient space exists to rigidly engage the nozzle by any convenient means sufficient to withstand the percussion or pressure effect.

As will be understood from the foregoing, the invention resides in the method of and means for reconditioning percussion drill bits by removing worn or damaged drill bits in the drill head and replacing them with new ones, an advantage of the present invention being that because the bits forced out of the original sockets in which they are fitted, no damage to this socket generally results and a new bit can simply be forced in in a manner very similar to the fitting of the original bits although in some cases it may be desirable to reshape the sockets to take the new bits.

It has been proposed to cut an aperture around the damaged bit and to remove it in this way but it is then necessary to build up the space and is a method not generally preferred.

It will be realised that as the drill head itself is formed of a relatively soft material it is possible to drill the ducts to the back of any of the drill bits to allow the application of a fluid force to the sockets to eject the damaged drill preferably by a percussive force.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a drill head and stem held in a machine with one nozzle of a hydraulic actuator pressed against a drilled aperture in

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the drill head which forms the ejection duct in readiness to eject a drill bit when hydraulic pressure is applied to the ejection duct from an intensifier which is hydraulically actuated.

FIG. 2 is a perspective end elevation of a drill head showing the drill which is about to drill the ejection duct in the head.

FIG. 3 shows the nozzle of the hydraulic actuator pressed against the ejection duct in readiness to eject a broken drill bit.

FIG. 4 is a perspective view of a drill head and shaft showing how after drilling the ejection aperture a hand-held gun can be used to blow out the bit, this device using an explosive which generates the necessary ejection pressure, a guard which protects the operator against injury by the bit being ejected being shown in the raised position to allow the operator to correctly position the tapered end of the nozzle of the explosive device to be located in the ejection duct.

FIG. 5 is a similar view but showing the guard lowered with the explosive about to be actuated.

FIG. 6 is a longitudinal section of a drill head and part of the stem showing a broken drill bit in position and showing the ejection duct drilled to the rear part of the socket in which the bit is held.

FIG. 7 is a central sectional view showing a preferred form of the explosive device used in FIGS. 4 and 5.

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Referring first to the embodiment described in FIGS. 1, 2 and 3, the drill head 1 is held in a machine comprising a frame 2 having two longitudinal shafts 3 and 4 with hand-wheels 5 and 6 respectively thereon, the shafts 3 and 4 being threaded and engaging bearings 7 supported by the frame 2 so that they can be positioned to hold the drill head and shaft between them as illustrated.

The hand-wheel 8 operates a shaft 9, again threaded, which applies thrust to the side of the drill head 1 while on the opposite side the frame 2 carries a hydraulic pressure generator 10 comprising a main pressure cylinder 11 and an intensifier cylinder 12 the pistons of which are interconnected and dimensioned to generate the required hydraulic pressure at the nozzle 13 to eject the bit when the pressure is generated.

The hydraulic pressure generator can take any usual approved form as it is well known to provide hydraulic pressure intensifiers where very high pressures are required and it is found in practice that by holding the nozzle 13 in the outer part of the ejection duct 14 a sufficient seal is possible because the drill head is of relatively soft material and the nozzle 13 has a hardened end, to transfer the hydraulic energy from the hydraulic pressure generator 10 to the ejection duct 14 and thus to the socket 15 in which the bit 16 is held, the bit as shown in FIG. 4 being held in the socket 15 by initially being driven into it or shrunk fitted or otherwise secured with sufficient grip to ensure that during the operation it remains in position, but as is known the bits 16 wear or tend to fracture and particularly with the sizing bits, which of

those shown extending beyond the outer diameter of the drill head 1 and then produce a smaller bore hole with consequent eventual jamming of the drill head 1 in the hole. It is therefore highly important that when bits 16 are damaged or worn they be replaced. In the past this has been extremely difficult because the bits are too hard to be conveniently bored out and extraction is difficult because at that stage there may be no projection of the bit 16 beyond the surface of the drill head itself.

By noting the state of the worn bit 16A on the drill head 1 in FIG. 6 this feature will be readily appreciated. The sockets are designated 15. The drill for forming the ejection duct 14 is designated 18 and is shown in FIG. 2.

The ejection duct 14 is formed as near to the rear of the socket 15 as possible and experience has shown that if a sufficient force is applied, particularly if this is a percussion force, the bit can be ejected even if- seized in the aperture. Generally it is advantageous to have a very sharp forced application which can be effected by rapid supply of hydraulic fluid to the actuating cylinder of an intensifier, or it can be produced by means of an explosion by using for instance a device of the form shown in FIGS. 4, 5, and 7.

That device again utilises an ejection duct 14 formed by drilling or in any convenient manner which leads to the inner part of the socket 15 in which the bit 16 which is to be ejected is positioned, but in this case the ejection is by gas pressure sharply applied from a cartridge 20 which is held in a barrel 21 having a tapered hardened end to form a nozzle 22 and a

communicating aperture 23, the barrel being secured to a body 24 which carries in it a striker 25 rearwardly loaded by a spring 26 disposed between a shoulder 27 on the striker 25 and a blast isolating spacer 28 which is apertured to allow the firing pin 29 to strike the cartridge 20 when firing is to take place.

As shown in FIG. 4, a movable guard 30 encircles the assembly just described and when in the position shown in FIG. 4 allows the nozzle 22 to be directly located in the ejection duct 14 after which the guard 30 is moved down to the position shown in FIG. 5 where it safeguards the operator against injury by the ejecting bit 16.

In operation the nozzle 22 is.unscrewed from the barrel 21 to allow the cartridge 20 to be placed into position within it and the nozzle 22 is then replaced but the spring 26 keeps the firing pin 29 clear of the cartridge 20 until the device is positioned whereupon a guard 30 is moved to its protecting position as shown in FIG. 5 and the striker 25 is struck inwards to cause the firing pin 29 to engage the cartridge 20 and produce the explosion, the gasses of which then pass through the communicating aperture 23 into the ejection duct 14 to effect the necessary ejection of the bit 16.

The hand-held explosive device could be mounted on the frame described with reference to FIGS. 1, 2 and 3.

From the foregoing it will be realised that the invention consists in the recovery of damaged drill heads by ejecting by means of suitable fluid pressure the damaged bit and as the action does not damage the socket in which the bit was held,

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a new bit can readily be inserted by forcing it into the socket and either holding it by an inter¬ ference fit between the bit and the socket, or the junction between the drill head and the bit at the surface of the drill head can have a weld applied but generally this is not necessary.

Modifications of the foregoing can be effected within the spirit of the invention.

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