(3) FIELD OF THE INVENTION This invention relates to drilling equipment for use in high temperature and abrasive environments. Although not so limited the invention finds useful application when used for refractory furnace taphole drilling.

(4) PRIOR ART DESCRIPTION Presently drill bits generally similar to conventional drills and drill bits having knobs at their leading ends, thus abrasively piercing a lining, are used for piercing refractory linings. The problem experienced with such drills is that they tend to wear very rapidly. Also as regards the coupling of the drill bits to their drive shafts, the method of in situ welding easily fractures during use owing to the extreme forces involved.

(5) BRIEF DESCRIPTION OF THE DRAWING The invention is now described, by way of example, with reference to the accompanying drawings. In the drawings Figure 1 shows drilling equipment, according the invention, in the form of furnace taphole drill bit, in side elevation, Figure 2 shows the drill bit of figure 1 in front end view, Figure 3 shows the drill bit of figure 1 in trailing end view,

Figure 4 shows the drilling equipment, as also including a mounting shaft, to the leading end of which the drill bit is mounted, thus being in the form of a drill bit and mounting shaft combination, with both the drill bit and the combination forming part of the invention, in partly cut away three dimensional view, Figure 5 shows the combination of figure 4 in the direction of arrow A in figure 4, Figure 6 shows in side elevation a particular method of mounting of the drill bit to the mounting shaft that enables its release from the shaft, Figure 7 shows in detail the semi-helically formed drill bit engaging end of the mounting shaft of figure 6 that thus enables the release of the drill bit from the shaft, Figure 8 shows in side elevation the coupling part of the mounting shaft that is in the form of two inter-releasable sections, secured to one another by way of a coupler, as a variation to a unitary shaft, and Figure 9 shows the coupling part of the mounting shaft of figure 8 in exploded side elevation. ii (6) DETAILED DESCRIPTION OF THE DRAWINGS Referring to figures 1 to 3 of the drawings drilling equipment, according the invention, in the form of furnace taphole drill bit, is generally indicated by reference numeral 10.

The drill bit 10 is formed with a thrusting core 12 that is integrally fitted with four symmetrically arranged cutting formations 14 while the trailing end of the drill bit 10 extends in the form of a stub 16 by means of which the drill bit 10 is securable to a mounting shaft.

The drill bit 10 is designed for use under very high temperature and abrasive conditions. To address the problem of abrasive wear the drill bit 10 is formed with the planes 18 of the cutting faces 20 of the various formations 14 passing through the central axis 22 of the drill bit 10. The cutting faces 20 thus radially sweep about the central 22 axis of the drill bit 10 once in use. The bodies of the formations 14 consequently extent behind the cutting faces 20 as regards the direction of operative rotation of the drill bit 10, shown by arrow 24. Each cutting face 20 is laterally and forwardly bordered by a cutting edge 26 formed along the leading side, as regards the direction of rotation 24 of the drill bit 10, along a cutting action involved outer edge 28. The outer edge 28, and consequently also the cutting edge 26, of each formation 14 extends rearward from the apex 30 of the drill bit 10 along a broadening leading formation section 14.1 into a fixed formation width trailing section 14.2. The cutting edges 26 and outer edges 28 thus extend through a discontinuity at positions 29. To

counteract quick wear of the formations 14 they are suitably fusion coated abrasion resistant hardfaced. The drill bit 10 is conveniently in the form of an appropriate low carbon steel casting.

The condition of high temperature is addressed by rendering the formations 14 of adequate thickness to withstand deformation. In addition to being of adequate thickness the drill bit 10 is arranged to enable a flow of cooling fluid into the working area and to enhance the ejection of dust and debris accumulating between the formations 14 once in operative use.

To this effect the body of each formation 14 thickens from its outer edge 28 by way of a trailing side face 32 that runs into the root 34 of the following formation 14. The trailing side faces 32 each extends from bevelled sections 36 and 38 that, in turn, extend from the trailing sides of the outer edges 28 of the respective formations 14. While the planes of the trailing side faces 32 are parallel to the central axis 22 they each slope inward into the direction of its root 34 at a slope that causes a marginal thickening of the relevant formation 14. The thickness of each of the formations 14 is mainly attributable to the slopes of the bevelled sections 36 and 38 respectively.

While the various cutting edges 26 are naturally defined along specific lines the outer edges 28 of the formations 14 are strip fashion formed. As the planes along the outer edges 28 of each formation 14 extend transverse to its cutting face 20 the original cross sectional area of the various cutting faces 20 are retained for some distance (being the widths of the outer edges 28) into the bodies of the various formations 14. While the effect of the planes 18 of the cutting faces 20 passing through the central axis 22 already ensures an improved effective drill bit life, the strip fashion formed outer edges 28 enhance this effect.

Referring also to figures 4 and 5 the drill bit 10 is operatively secured to a mounting shaft 40, as conventionally drivable by a drive source, in response to its stub 16 being spigot and socket fashion receivable into a matching socket 42 formed into the leading end of this shaft 40. This results in the drill bit 10 co-axially fitting the shaft 40. In the case where cooling fluid is used to cool the formations 14 during operative use of the shaft 40 as fitted with the drill bit 10, the shaft 40 is naturally hollow (as more clearly shown in figure 4) and connectable to an upstream cooling fluid supply. The stub 16 is consequently formed with drill bit central axis axially directed hollowed out sides 41, as shown in figure 3, that cause the formation of cooling fluid flow channels 43 between the inner wall of the shaft 40 and the stub 16 despite engaging by way of a firm and snug fit with the shaft 40 once so connected. As a further development the shaft can be fitted with a non-return valve 45 situated along its flow

passage 47 to limit the possibility of the flow of molten metal along the passage 47 when the shaft 40, as fitted with the drill bit 10, is used for refractory lining piercing in extracting molten metal from a furnace.

Although the stub 16 forms a snug fit into the socket 42 the force exerted on the drill bit 10 during operative use requires its further locking against relative swivelling with respect to its shaft 40, at least once operatively rotated. To achieve this the drill bit 10 can be permanently secured to the shaft 40 by, for example, welding it thereto. The drill bit 10 can, in fact, be without a stub and still be permanently secured to the leading end of the shaft 40. This invention also extends to an assembled drill bit and shaft combination 44 in whichever way permanently secured to one another.

Despite the drill bit 10 of the invention having an enhanced effective life span as compared to conventionally used drill bits, abrasion will eventually cause the drill bit 10 to lose its cutting ability while also causing a reduction of effective drilling diameter. At this stage the drill bit 10 will have to be replaced. When it is permanently secured to its shaft 40 both the drill bit 10 and the shaft 40, as permanently combined in the combination 44, will have to be replaced.

To address this problem the combination 44 can be arranged to enable the release of the drill bit 10 from the shaft 40 when replacement is required. As the equipment of the invention is used under extreme conditions of temperature and abrasiveness the conventional methods of achieving releasable engagement cannot be effectively used as the drill bit 10 and the shaft 40 tend to deform with respect to one another if not corroding or partly fusing into one another during use.

The force that is exerted on the drill bit 10 during use of the combination 44 that causes it to become stuck in the material into which a hole is drilled is naturally exerted during the drilling process. When the drill bit 10 becomes so stuck while the shaft 40 is still turning the shaft 40 and the drill bit 10 effectively commences swivelling relative to one another. The primary requirement for achieving a firm and non-inter-swivellable coupling between the drill bit 10 and the shaft 40 is thus to limit the possibility of their relative swivelling once the drilling equipment is operatively used as the firm engagement resulting from the spigot and socket fashion coupling is otherwise adequate.

In also referring to figures 6 and 7 a firm engagement between the drill bit 10 and its shaft 40 during use while permitting their release is achieved by forming the leading end 40.1 of the

shaft 40 to spiral along an arc that extends for about a quarter of the length of the circumference of the shaft 40, as shown by arrow 46 in figure 7. This has the effect of forming a shoulder 48 against which a trailing situated drill bit stop 50, formed by one of the formations 14.3 extending trailing as regards its direction of forward motion beyond the other formations 14, shoulders, as shown more clearly in broken lines in figure 6. It is obvious that the direction of spiralling and the consequent formation of the shoulder 48 is in and faces the direction of operative rotation of the shaft 40, as shown by arrow 52, to cause the drill bit 10 to lock against the shaft 40 once its stop 50 urges against the shoulder 48.

While the object of the spiralling arc 46 is to define a shoulder 48 and to obtain a smooth path along the leading end 40.1 of the shaft 40 running from the shoulder 48, the advantage of letting the arc 46 spiral for only a quarter turn lies therein that, except for the formation 14.3, the lengths of the trailing ends of the other formations 14 need not differ from one another. This is naturally not essential. The leading end 40.1 can thus spiral along a full turn, which will be accommodated by appropriately forming the formations 14.

The stop 50, as shouldering against the shoulder 48, consequently forms an effective lock between the drill bit 10 and the shaft 40 against inter-swivelling during operative use of the equipment. The way of engagement against relative swivelling during operative use still enables the release of the drill bit 10 from the shaft 40 by simply forcing their inter-swivel relative to one another in the direction opposite to that in which they lock to one another. As said above, the circumstances of use of the equipment has the effect of very firmly tying the drill bit 10 to the shaft 40. This can still be overcome by the exertion of large opposite mechanical forces that is conventionally easily applied by way of methods such as the use of vices and/or appropriate spanners. The spiralling effect of the arc 46 results in the automatic linear disengagement of the drill bit 10 from the shaft 40 in the direction of arrow 54 owing to the cam effect between the stop 50 and the leading end 40.1 once the drill bit 10 and the shaft 40 are forced into swivellable disengagement. Once the tie between the drill bit 10 and the shaft 40 is broken its subsequent release follows easily.

In also referring to figures 8 and 9 and in a further development of the invention, the shaft 40 is constituted from two shaft sections 40.2 and 40.3 of which the facing ends 40.4 are both suitably spirally formed, similar to the discussed under figures 6 and 7. Each thus defines a shoulder 54,54. 1 and 54,54. 2. The shaft assembly incorporates a coupler 56 presenting opposite hollow stubs 58 that firmly though releasably engage with spigoted facing ends 40.5 of the sections 40.2 and 40.3. Owing to a firm fit the fluid flow passage along the shaft 40, as

passing through the coupler 56, is retained. To obtain a non-swivelling fit between the shaft sections 40.2 and 40.3 in the direction of operative swivelling the coupler 56 is fitted with stops 60 that each engages in a similar way with the shoulders 54.1, 54.2 respectively as is the case of the drill bit 10 with the leading end of the shaft 40 as discussed with reference to figures 6 and 7. The spiralling effect of the facing ends 40.4 naturally spiral in one direction when couplably facing one another to ensure a drive connection between the sections 40.2 and 40.3.

When the conditions of use of the assembly 44 is so severe that, despite the drill bit 10 being in essence releasably coupled to the shaft 40 by way of the technique discussed with reference to figures 6 and 7, they cannot be released from one another, at least part of the equipment can still be retained for re-use by disengaging the part holding the drill bit 10 from the re-useable trailing part that is under conditions of use coupled to a shaft drive. The method of disengagement will naturally be the same as discussed in the case of the drill bit and shaft combination 44 under figures 6 and 7 while the cam and follower effect is found between the stops 60 and the facing ends 40.5 of the respective shaft sections 40.2 and 40.3. The invention also extends to equipment in which the shaft 40 is formed with releasable sections while the drill bit 10 is permanently secured to the shaft 40.