BACKGROUND TO THE INVENTION Both manually operated and automated machinery exist which are adapted for use in the removal of surface layers of hard materials by means of conventional hammering or milling techniques. For example, devices such as jack hammers are commonly used for breaking and chipping hard material. Such devices generally include a hammer head that is repeatedly oscillated back and forth along a single axis to provide a concentrated force at a particular location, thereby causing extreme stress and cracking to occur at that location. However such devices do not provide the operator with sufficient control over the finish of the surface and also do not provide sufficient control over the size of pieces that are removed from the surface. Also, such devices are prone to damaging the underlying substrate material. Furthermore such machinery is unsuitable for use in the removal of highly abrasive materials such as refractory materials owing to factors such as high tool wear, the high stresses involved, and the extremely high temperatures that exist in the areas where materials such as refractory materials are commonly used.

At least some of the shortcomings of such conventional machinery have been partly addressed by Arbortech Industries Pty Ltd with the Allsaw KS270 apparatus. This apparatus has a pair of closely spaced blades which oscillate in parallel planes at 180 degrees out of phase with respect to each other. During each cycle of oscillation, the cutting edge on each blade moves through a closed elliptical path. The oscillatory motion is achieved by two opposed cams with a fixed lift of around 2 mm. This device produces vibrations which are translated to a cutting ellipse for each cutting comer of the blades.

The apparatus is normally operated as a hand tool and guided manually, and is typically used to make grooves, remove mortar and cut bricks, concrete blocks and timber to a depth of about 300mm. Different versions of the apparatus exist for different materials.

However this apparatus is not suitable for use in a high temperature environment such as may be experienced during the removal of refractory materials or slag. The apparatus is also unsuitable for the rapid removal of large volumes of material in continuous surface cutting. Furthermore the apparatus has no provision for adjusting the amplitude and phase of the oscillatory motion of the cutting blades in order to optimise material removal rates and create the required surface geometries.

It is an object of the present invention to overcome or ameliorate at least one of the disadvantages of the prior art, or to provide a useful alternative.

DISCLOSURE OF THE INVENTION Accordingly, one aspect of the present invention provides an apparatus for removing a hard material from a substrate, said apparatus including a cutting head

having a barrel with a plurality of teeth extending outwardly therefrom for engaging an exposed surface of said hard material, the apparatus further including drive means adapted to effect rotation of the barrel about an axis and to effect oscillation of the barrel thereby to induce rotary percussion between the teeth and said exposed surface such that said hard material is progressively removed as the cutting head advances across the surface.

Preferably the cutting head includes a plurality of barrels which, in use, undergo both rotational and percussive motion with respect to the exposed surface ensuring that at all times the teeth of at least one barrel are in contact with the exposed surface. For example, in a preferred embodiment the cutting head may include two barrels having a 180° offset high frequency percussive action. This percussive action will allow the teeth of the two barrels to alternatively contact the material surface.

Preferably, each barrel is driven at the same low rotational speed of around 20 rev/min. and is powered from the same source.

The teeth are preferably aligned in rows equally spaced apart along the barrel and positioned in identical but deliberately offset sequences characterised by a varying systematic circumferential spacing along each row, extending outwardly from, the barrel periphery, thereby producing a repeatable trajectory across the material surface. This ensures the value of half of the amplitude will always be higher than the feed rate per tooth, thereby promoting and ensuring effective material removal.

Preferably the teeth are fabricated from special steels and ceramics exhibiting excellent high temperature strength and toughness using plasma microwave welding.

Advantageously, this joining method can result in joints between the steel and ceramic

components that can withstand the high temperatures experienced by the teeth face during operation.

Alternatively, the teeth may include a tip or contact surface coated with a suitably hard material. For example, the coating may be a layer of ceramic material. Before applying the hard surface layer, a suitable layer of material may be applied to improve adhesion of the joint and protect the underlying material from experiencing the most extreme temperatures. Current coating technologies available offer the possibility of coating a variety of different shaped cutting edges, including that used in the present apparatus.

It has been found by the applicant that air jet cooling of the teeth is highly effective as a means of reducing the temperature experienced by the teeth. Preferably the cooling is applied through the barrel or via the teeth holders. The effectiveness of the air cooling which resulted in the tooth face temperature remaining below 300°C during hot cutting trials, provides a high level of confidence that teeth of the type used in the trials could be expected to successfully remove material heated to 1200°C in industrial applications.

A further aspect of the present invention provides an apparatus for removing a hard material from a substrate, said apparatus including a drive means is adapted to allow adjustable control over the surface finish and shape of the exposed surface, said drive means including : a first hydraulic motor which through a first coupling rotates a shaft, which in turn controls a first and second disk and their respective first and second blocks, these blocks translate through a set of parallel links and arms to create a percussive amplitude upon a first and second barrel, independently, a second hydraulic motor turns adjoining first and

second gearsets which correspondingly create a rotational motion with the first and second barrels.

The present invention, at least in a preferred embodiment, provides an apparatus which provides effective continuous surface cutting through the use of a plurality of cutting heads. These cutting heads preferably use air jet cooling, allowing the apparatus to operate at temperatures of approximately 1200°C. The invention also provides an apparatus wherein tooth wear is minimised or negated and accuracy of the surface finish and shape of the surface can be controlled.

The preferred embodiment further provides an apparatus capable of removing hard material, which further includes an articulated support arm adapted for connection to a movable support platform or base. In a preferred embodiment the base forms part of a prime mover. These preferments permit the present invention to rotate in all directions allowing the teeth of a cutting head access to all areas of the workpiece.

Advantageously, the present invention may be configured so as to provide an apparatus, capable of removing hard, abrasive and/or hot material, which can be mounted as a head on mining and construction equipment, on a heavy movable robotic arm or on a handtool and traversed along a defined path.

BRIEF DESCRIPTION OF DRAWINGS A preferred embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings in which : Fig. 1 is a schematic plan view depicting a preferred embodiment of the arrangement of the cutting heads of the present invention ;

Fig. 2 illustrates the effect of the progressive change in spacing of the cutting tools on a disk on the trajectory of the tools and removal of material ; Fig. 3 is a schematic side view of a preferred embodiment of the invention illustrating the motion of the cutting heads ; and Fig. 4 is a schematic perspective view illustrating a preferred gearing system for driving the cutting heads.

PREFERRED EMBODIMENT OF THE INVENTION Referring to Fig. 1, the apparatus of the present invention includes cutting heads 10,11 which include a pair of barrels 12a, 12b mounted for rotation about their respective longitudinal axes 13a, 13b. The barrels 12a, 12b each include a plurality of teeth, or cutters, 14 which extend radially outwardly from the barrels for engaging on an exposed surface of a hard material. The cutters 14 are mounted on radially extending disks 15 attached in evenly spaced rows along the two barrels. The cutters are mounted around the circumference of their respective barrel.

Preferably the cutters in each row are grouped in sets of three. The cutters are positioned in a common repeatable sequence, wherein the position of a cutter on the circumference of the barrel is defined with reference to the position the cutter would occupy were the cutters equally spaced around the circumference, (ie. their nominal positions having an angular spacing equal to 2yT l t, where t = the number of teeth in a row). The first cutter in each set of three is positioned at the nominal position, with the second cutter in each set of three being offset from the nominal position by a negative angular displacement according to the following formula :

where: f = feed rate N = frequency of oscillation D = diameter of cutting tips path n = rotational speed of barrels The third cutter in each set of three is offset from its nominal position by a negative angular displacement equal to : The sequence recommences with the fourth cutter (ie. the first cutter in the subsequent set of three cutters) being positioned at its nominal position.

Therefore there is a progressive increase in the spacing between the cutters as their location gets further away from the leading cutter in a sequence. This enables the cutting paths of sequential cutting tools to overlap in a repeatable fashion. The effect of the progressive change in spacing of the tools on one disk on the trajectory of the tools and removal of material is illustrated in Fig. 2, where A represents the amplitude of the motion of each cutting head.

Additionally, there is a uniform progressive increase in offset in the position of tools as one moves from disk to disk across the barrel.

It is further preferable that the position of the leading cutter (ie. the starting point of the sets) varies from row to row as the row is located further away from the outside

edge of the barrel with the angle (a) between the line of leading cutters and the barrel axis being defined as follows : <BR> <BR> <BR> <BR> <BR> P<BR> α=tan-1 km km where: m = number of rows k = spacing between rows P = circular spacing between the positions the teeth would occupy at their nominal positions The arrangement provides for two cutting tools on the barrel to be in contact with the work material at any one time when the depth of cut is as follows : where : t = number of cutters in a row Preferably the same sequence of cutting tools and spacing arrangement is used on all disks.

Preferably, in order to promote effective material removal the value of half of the amplitude (A) is higher than the feed rate of a cutter.

Advantageously, by placing the cutting tools in a pattern across the disks characterised by a repeatable helical curve, a smooth loading on the barrels and a good balance during machining is achieved.

Referring to Figs. 1 and 4, the apparatus of the present invention further includes drive means 20 which is adapted to effect rotation of the barrels 12a and 12b about their respective axes 13a, 13b and is further adapted to also effect oscillation of the barrels 12a, 12b so as to induce rotary percussion between the teeth 14 and the exposed surface

such that the hard material is progressively chipped away as the cutter heads 10,11 advance across the surface being machined.

In use, the barrels 12a, 12b rotate in a common direction and the axes of the barrels oscillate in the same plane, but at 180 degrees out of phase with respect to each other so as to provide a very high frequency percussive action. This percussive action is such that as one barrel cutter is entering the work material, the second barrel cutter is exiting from the work material.

A preferred drive arrangement for the creation of the rotary and percussive motion of the cutter heads 10,11 is shown in Fig. 4. The drive arrangement 20 includes a hydraulic motor 21 which, via coupling 22, rotates disks 23 and 24 mounted on shaft 25.

Disks 23 and 24 include radially extending slots 26,27 in which blocks 28 and 29 are slidably mounted. Preferably the blocks are movable in their respective slots and may be fixed in position at any point along their slots. This provides a degree of adjustment to the mechanism to alter the amplitude of the oscillating motion of the cutter heads 10,11.

Preferably the two blocks are offset at equal radial distances from the axis of rotation of the disks, but in opposing directions. Two identical systems of mechanical linkages join the blocks to the barrels 12a, 12b and transform the offsets into the percussive amplitude (A) of barrels. Preferably each linkage system includes a link 30 from a roller bearing (not shown) mounted on the block (28 or 29) at one end to a sliding bearing (not shown) at the other end. Thus, the value of the offsets translate, with the aid of links 30 and arms 31, to create a percussive amplitude, A, for the barrels 10 and 11. Sleeve bearings 37 permit the arms 31 to swing on shaft 32 which is connected to the main body, or frame, of the machine. The values of the amplitude A and frequency n (ie. revolutions of

motor 21) are fully adjustable to accommodate the toughness of the material to be machined. Generally the amplitude, A, is from 4 to 10 mm and the frequency, n, is from 750 to 1500 rev/min. Preferably the arrangement further includes a two stage gear train.

The first stage, 35, of this gear train translates the rotation from hydraulic motor 33 to the rotating shaft 32. The second stage, 36, through separate gear trains located at each end of the rotating shaft 32, imparts rotational movement to each barrel.

To effect rotation of barrels 10 and 11 independently of each other, a hydraulic motor 33 rotates shaft 34 through gearsets 35 and 36. For a barrel of 350 mm nominal diameter, the speed of rotation of the cutting barrel for machining refractory materials is normally around 20 rev/min.

In use, the performance of the apparatus is dependent on the speed of barrel rotation and the amplitude and phase of the percussive motion relative to the machined material. Preferably the feed rate of the cutter heads is maintained at a sufficiently high rate so as to provide for efficient machining whilst at the same time enabling adequate control over the operation of the apparatus.

The present invention can advantageously be used for continuous surface cutting of hard materials in both low and high temperature environments. The use of air jet cooling, plasma microwave welding of the teeth, and the ability to provide rotation of a barrel about a central axis whilst also being able to produce independent oscillation thereby inducing rotary percussion not only can produce superior material removal but also minimise or negate tooth wear and ensure accuracy of the surface finish is controlled and minimise damage to the substrate.

The advances of the present invention open up other potential industrial applications for automated hot material removal within foundries and steel works including the repair and maintenance of refractory items such as main refractory troughs, runners, spouts, and torpedo ladles.

Although the invention has been described with reference to specific examples, it will be appreciated by those skilled in the art that the invention may be embodied in many other forms.