A milling insert and a milling tool

Abstract: A cutting insert(1) for use on a milling tool, comprises an element(1) formed of hard material, such as carbide. The element defines a rear face(2), by means of which it may be mounted in position, and a front face. The front face(8) defines, towards its lower edge, a cutting projection defining a single leading linear cutting edge(9). The front face defines a surface, which may be a curved surface, which extends rearwardly and upwardly from the cutting edge(9). The thickness of the element is between 0.17 and 0.24 cms. The swarf generated by a tool dressed with the inserts has desirable properties.

Description: THE PRESENT INVENTION relates to a milling insert and to a milling tool which utilises the insert. In particular, the invention relates to a milling insert and a milling tool of particular use in down-hole operations in the oil and gas-well industry. Many proposals have been made concerning the provision of different types of "insert" for use on a milling tool. The insert is typically an element made of very hard material, such as tungsten carbide, which is secured to a blade of a milling tool, the insert actually cutting the metal that is to be milled away by the tool. Very particular requirements exist in connection with cutting inserts intended for use on mills for use "down-hole". Whilst, of course, it is desirable that the mill should operate as swiftly as possible, thus cutting away the maximum amount of metal in minimum time, the swarf (or cuttings) produced by the mill must be such that it can readily be carried out of the hole by the mud that flows through the hole. It is undesirable for the swarf (or cuttings) to be too long, since otherwise the swarf may form "bird's nests", which can give rise to significant difficulties. In either event, all of the cutting edges remaining on the insert will subsequently no longer be available to effect cutting. It is also desirable to provide a mill which can operate with the expenditure of a minimum amount of energy. GB-A-2,270,097 discloses a mill in which the leading face of each blade is dressed with individual cutting elements formed of a hard material. Each cutting element has a rear face secured to the blade, an upper face and a lower face and a front face which defines a substantially linear cutting edge. The cutting elements disclosed are relatively small, having a thickness of only 9 millimetres. It has been found to be a relatively time-consuming task to weld or braze the individual cutting elements on to the blade, because of their relatively small size. The present invention seeks to provide an improved cutting insert and a mill incorporating the improved cutting insert. According to this invention there is provided a cutting insert for use on a mill, the cutting insert comprising an element formed of a hard material, the element defining a rear face, by means of which the element may be mounted in position, and a front face, the front face defining, towards its lower edge, a cutting projection, defining a single linear leading cutting edge, the front face defining a surface which extends rearwardly and upwardly from the cutting edge, the element defining upper and lower faces, the thickness of the insert between the upper and lower faces being between 0.17 and 0.24 cms. It is to be appreciated that it has now been found, surprisingly, that it is advantageous to use even smaller inserts than those proposed previously. A technique has been developed for applying the small inserts to the face of the blade. An overall benefit has been found due to the improved nature of the swarf generated by a mill provided with the relatively small cutting inserts, as compared with the prior art. In one embodiment the front face is substantially planar, the arrangement being such that when the cutting insert is located in abutment with adjacent cutting inserts, the upper edge of the planar front face is located immediately adjacent a forwardly extending part of the under-surface of the cutting projection of the next adjacent cutting insert. Conveniently the front face of the projection makes an angle of approximately 19° with the plane defined by the rear face of the insert. Alternatively the upper part of the front face of the insert is of arcuate form. Conveniently the upper part of the front face of the cutting insert is of arcuate form with a radius of curvature which gradually shortens. Advantageously the front face terminates with a upper forwardly projecting protrusion. Preferably the upper face and the lower face of the insert are inclined at an angle of approximately 5° to the perpendicular to the plane defined by the rear face of the cutting insert. Conveniently the thickness of the insert is approximately 0.22 to 0.187 cms. Advantageously the depth of the insert is approximately 0.62 to 0.635 cms. The invention also relates to a mill, the mill comprising a body carrying a plurality of blades, the blades each carrying a plurality of cutting inserts as defined above in a regular array, with the under-face of one insert substantially abutting the upper face of the next adjacent insert. Preferably the front face of the projection of each cutting element makes an angle of approximately 14° with the axis of the mill body. The blades are preferably fixed blades which extend radially outwardly from the body, but the blades may be pivotally mounted blades. The blades may be aligned with the axis of the body or may exhibit a negative rake, typically of approximately 5°, but possibly up to 10° relative to the axis of the mill. The cutting inserts may be brazed to the blades by applying a foil of brazing metal or alloy to the blade, applying the inserts to the blade and heating the blade to melt the foil, and permitting the molten brazing metal to solidify to secure the inserts to the blade. The foil may be a foil of silver brazing alloy. In order that the invention may be more readily understood, and so that further features thereof may be appreciated, the invention will now be described, by way of example, with reference to the accompanying drawings in which: FIGURE 1 is a perspective view of one cutting insert in accordance with the invention, FIGURE 2 is a side view of a plurality of cutting inserts of Figure 1 when located adjacent each other, FIGURE 3 is a perspective view of an alternative form of cutting insert in accordance with the invention, FIGURE 4 is a side view showing a plurality of cutting inserts of the type shown in Figure 3 located adjacent one another, FIGURE 5 is a side view, with parts cut away, of a mill provided with cutting inserts of the type shown in Figures 1 and 2. Referring initially to Figures 1 and 2 of the drawings, one embodiment is a cutting insert in accordance with the invention comprises an element 1 made of a very hard material such as, for example, tungsten carbide. The insert may be made in a conventional way, but the insert is made to have a novel shape and configuration as will now be described. The insert comprises a substantially cuboidal block of hard material. The rear face 2 of the block, which is a vertical face in the orientation illustrated, is substantially planar and is used, as will be described hereinafter, for mounting the block in position. The top face 3 and the under-face 4 of the block are parallel with each other but are not perpendicular to the plane defined by the rear face 2 of the block. The top face 3 and the under-face 4 are downwardly inclined from a perpendicular to the rear face at an angle 5 (see Figure 2) which is approximately 5°. In an alternative preferred embodiment, the angle 5 may be up to 10°. The side faces 6 and 7 of the block are parallel and extend perpendicularly to the plane defined by the rear face 2. The front face 8 of the insert is a substantially planar face inclined at an angle to the plane defined by the rear face 2 by an angle α which is approximately 19°. The lower part of the front face 8 thus forms a cutting projection, defining a leading single linear cutting edge 9 which extends substantially horizontally. The front face 8 forms a surface which extends rearwardly and upwardly from the linear cutting edge. As can be seen from Figure 2, a plurality of cutting inserts 1 of the type illustrated in Figure 1 may be located adjacent each other, with the rear faces 2 of the inserts being aligned to be co-planar, the upper face 3 of one insert being located substantially at abutment with the lower face 4 of the next adjacent insert. The upper edge of the planar front face 8 of the lower insert is located immediately adjacent a forwardly extending part of the under-surface of the cutting projection of the next adjacent cutting insert. The inserts may be located in orthogonal rows and columns, or alternatively, the inserts in alternate rows may be off-set to provide an effect like bricks in a brick wall. The overall thickness (T) of the block shown in Figure 1 (i.e. the distance between the upper face 3 and the lower face 4) may be 0.187 cms (0.074 inches), and the total depth (D) of the block shown in Figure 1 (i.e. the distance between the cutting edge 9 and the rear face 2) may be 0.635 cms (0.250 inches). Figure 3 illustrates an alternative form of cutting insert for use in accordance with the invention. The cutting insert 10 shown in Figure 3 is again in the form of an element made of very hard material, such as tungsten carbide. The insert may again be made in a conventional way, but is made to have a novel shape and configuration. Again the insert comprises a substantially cuboidal block of the hard material having a rear face 11 which is substantially vertical in the orientation illustrated. The insert 10 has a top face 12 and an under-face 13 which are parallel with each other, but which are not perpendicular to the plane defined by the rear face 11 of the block. The top face and the under-face are inclined downwardly, relative to a perpendicular from the rear face, at an angle 13 (see Figure 4) which is approximately 5°. In an alternative embodiment, the angle 13 may be up to 10°. The insert has side faces 14,15 which are parallel and which extend perpendicularly to the plane defined by the rear face. The front face 16 of the block is of an arcuately recessed form. The block thus defines a lower cutting projecting portion 17 which defines a single leading linear cutting edge which extends substantially horizontally. The projecting portion 17 has an upper surface which is initially of substantially planar form but subsequently, at an upper position, curves 18 with a radius of curvature which gradually shortens to form an upper forwardly projecting protrusion 19. It can be seen that when the cutting inserts, as described, are super-imposed, as shown in Figure 4, with the under-face 13 of one cutting insert located in abutment with the upper face 12 of the next adjacent insert, the upper protrusion 19 of one insert is substantially aligned with the lower projection 17 of the next adjacent insert. The inserts maybe located in orthogonal rows and columns, or alternatively, the inserts in alternate rows maybe off-set, to provide an effect like bricks in a brick wall. A cutting insert as shown in Figures 3 and 4 may have a thickness (T) of approximately 0.22 cms (0.087 inches) and may have a depth (D) of approximately 0.62 cms (0.247 inches). A plurality of inserts as described with reference to Figures 1 and 2, in the orientation shown in Figure 2, may be mounted on a mill 20 as shown in Figure 5. It is to be understood that alternatively a plurality of the inserts 10 as described with reference to Figures 3 and 4, in the orientation shown in Figure 4, may be mounted on a mill in a directly corresponding manner. The mill 20 comprises a generally cylindrical body 21 provided, at its upper end, with the threaded connection pin 22 (or a connection box) to enable the body to be connected to another part of a drilling string, as is conventional. As is also conventional, the body is provided with a central flow passage 23 for mud or other drilling fluid. The body is provided, adjacent its lower end, with a plurality of stabiliser blades 24 of a conventional design. The body is provided, towards its upper end, with a plurality of substantially radially outwardly directed cutter blades 25, each blade having a 5° negative rake. The front face 8 of the insert of Figure 1 thus makes an angle of 14° with the vertical axis of the mill. Each cutter blade has a substantially radially outwardly extending lower surface 26 comprising a cutter surface. Mounted on the front face of each blade 25 is a regular array 27 of cutting inserts 1 as shown in Figure 1, with the inserts being located adjacent each other, in orthogonal rows and columns, in the manner illustrated in Figure 2. Alternatively, the inserts may be located in the manner of bricks in a brick wall. The rear face 2 of each cutting insert is welded or brazed to the blade 25. In performing the brazing process, initially steps are taken to ensure that the blade 25 and the cutting inserts 1 are clean and free from grease or oil. The front face of the blade 25 is coated with flux paste, as is the rear face of each of the carbide inserts. After applying flux to the blade, a clean sheet of an appropriate foil of brazing metal, such as a silver alloy, may be applied to the fluxed blade and then the fluxed cutting inserts are applied to the blade. The silver alloy may contain copper and other metals. If this procedure is adopted, when the blade is heated to an appropriate temperature, the foil will melt. If this procedure is utilised, it is appropriate for steps to be taken to ensure that the inserts do not move when the flux melts and the silver brazing material flows. After the brazing process has been completed, the cutting inserts are to be cleaned so that no flux or other material is present on the cutting face. It is found that when a mill of this type is used, the swarf or cuttings that are generated are relatively cool, as compared with the temperature of cuttings produced by a significant proportion of the prior art mills. It is also found that less power has to be provided to the mill to provide a predetermined cutting effect. It is found that the cuttings or swarf generated by the mill, when cutting a typical pipe as found down-hole in an oil or gas-well, are relatively short, typically being of the order of 1 millimetre long. It is believed that this is caused by the relative spacing between the various protrusions or cutting edges present on the front of the abutted cutting inserts. In the arrangement as shown in Figure 2, the spacing between the various cutting edges is equivalent of the thickness (T) of the insert (and a similar comment applies to the spacing between the cutting edges of the insert 10 as shown in Figures 3 and 4). It is believed that with the inserts of Figures 1 and 2 the swarf cut travels substantially upwardly from the cutting edge being spaced from the face 8 of the insert effecting the cutting, and is deflected when reaching the under-face 4 of the next adjacent cutting insert. The bent swarf curls over and breaks when a sufficient bending moment is imparted to the swarf. The swarf may effectively coil over until the swarf re-contacts the pipe being cut. The swarf then snaps off. With the insert 10 as shown in Figures 3 and 4, the swarf travels initially upwardly from the lower protrusion 17 across the recess defined by the curved portion 18, and is then deflected when reaching the upper part of the curved portion 18 which leads to the upper projection 19. The swarf thus curls over and breaks when a sufficient bending moment has been imparted. Again, the swarf may coil over until the swarf re-contacts the pipe being cut. Since the swarf contacts the portion 18 of the element effecting the cutting, the swarf does not contact the next higher insert. Thus, this next higher insert will not be damaged before it, in its turn, effects the cutting. It is to be noted that if a cutting edge which is operative is subjected to a severe shock due, for example, to an irregularity in the item being cut, only the cutting insert 1 carrying that cutting edge will be dislodged from the tool. The remaining inserts will stay in position. The next adjacent cutting edge will thus relatively swiftly be brought into operation. Whilst not wishing to be bound by any theory the applicant believes that some of the brazing material, in this example, a silver alloy, is located between the individual cutting inserts, and forms a shock absorbing material. The silver alloy is not as hard and unyielding as the tungsten carbide, and if the cutting insert is subjected to a shock it is better able to withstand the shock, due to the relatively small size of the cutting insert, and the shock absorbing brazing material. Whilst the invention has been described with reference to an embodiment where the blades on the tool are substantially vertical, it is to be appreciated that the invention may equally be applied to an embodiment in which the blades on the tool have a negative rake. Typically, such a negative rake may be 5°, but may be as much as 10°. In such an embodiment of the invention, the cutting inserts may be substantially as described above, save that the angle 5 (see Figure 2) or the angle 13 (see Figure 4) will be increased by an amount equivalent to the angle of negative rake. Thus, the angle 5 may be 15° or 20°, and the angle 13 may be 15° or 20°. Consequently, when the cutting inserts are in position on the blade, and the tool is in use, the front face of the blade will make the same angle with a pipe to be cut, as the front face of the embodiments described and illustrated. For inserts having a front face 8 of the type shown in Figure 1, the face 8 should make an angle of approximately 14° with the axis of the tool. Whilst the invention has been described with reference to a tool having "fixed" blades, it is to be appreciated that the invention is equally applicable to tools having movable blades. Many tools are used downhole, where the blades are initially in a retracted position, and are then extended to an operative position once the tool is at an appropriate depth within a well.

Claims: A cutting insert (1) for use on a mill, the cutting insert comprising an element formed of a hard material, the element defining a rear face (2), by means of which the element may be mounted in position, and a front face (8), the front face defining, towards its lower edge, a cutting projection (9, 17), defining a single linear leading cutting edge, the front face defining a surface which extends rearwardly and upwardly from the cutting edge, the element defining upper (3) and lower (4) faces, characterised in that the thickness (T) of the insert between the upper and lower faces being between 0.17 and 0.24 cms. A cutting insert according to Claim 1 wherein the front face (8) is substantially planar, the arrangement being such that when the cutting insert (1) is located in abutment with adjacent cutting inserts (1), the upper edge of the planar front face (8) is located immediately adjacent a forwardly extending part (9) of the under-surface (4) of the cutting projection of the next adjacent cutting insert. A cutting insert according to Claim 2 wherein the front face (8) of the projection makes an angle (α) of approximately 19° with the plane defined by the rear face (2) of the insert. A cutting insert according to Claim 1 wherein the upper part (18) of the front face of the insert is of arcuate form. A cutting insert according to Claim 4 wherein the front face terminates with a upper forwardly projecting protrusion (19). A cutting insert according to any one of the preceding Claims wherein the upper face (3, 12) and the lower face (4, 13) of the insert are inclined at an angle (5, 13) of approximately 5° to the perpendicular to the plane defined by the rear face (2, 11) of the cutting insert. A cutting insert according to any one of the preceding Claims wherein the thickness of the insert is approximately 0.22 to 0.187 cms. A cutting insert according to any one of the preceding Claims wherein the depth (D) of the insert is approximately 0.62 to 0.635 cms. A mill (20), the mill comprising a body (21) carrying a plurality of blades (25), the blades each carrying a plurality of cutting inserts (1) according to any one of the preceding Claims in a regular array, with the under-face of one insert substantially abutting the upper face of the next adjacent insert. A mill according to Claim 9 wherein the front face (8) of the projection of each cutting element makes an angle of approximately 14° with the axis of the mill body (4). A mill according to Claim 9 and 10 wherein the inserts (1) are brazed to the blades (15) by applying a foil of brazing metal or alloy to the blade, applying the inserts to the blade, and heating the blade to melt the foil, and permitting the molten brazing metal to solidify to secure the inserts to the blade.

Inventors: MCGARIAN BRUCE, MCGARIAN, BRUCE
Applicants: SMITH INTERNAT NORTH SEA LTD, SMITH INTERNATIONAL (NORTH SEA) LIMITED
Application year: 1995
Main classification: E21B29
IPC codes: E21B29