Saws

Abstract: A saw comprises a blade (10) having a working portion bonded to the periphery thereof and presenting a working surface (22), the working portion comprising a plurality of segments (12) bonded to the periphery of the blade and presenting a working surface (22), the working portion comprising a bonding matrix and having one or more elongate cutting elements (14) so located therein as to present cutting points or edges in the working surface (22).

Description: BACKGROUND OF THE INVENTION This invention relates to saws. Diamond impregnated saws are used for cutting stone, concrete and other hard and abrasive materials. Such saws consist of a circular metal blade having a working portion bonded to the periphery thereof. The working portion may consist of a continuous rim or a plurality of spaced segments. The working portion, whether it is in the form of a rim or segments, will generally consist of a metal matrix having a mass of diamond particles uniformly distributed therethrough. Examples of bonding matrices are cobalt, cobalt-bronze or molybdenum, optionally reinforced with carbide. Abrasive compacts are abrasive bodies which consist of a mass of ultra-hard abrasive particles such as diamond and cubic boron nitride bonded into a hard conglomerate form. Abrasive compacts are polycrystalline masses containing a high content of the ultra-hard abrasive particle, e.g. at least 70 percent by volume. Abrasive compacts come in a variety of forms and shapes. One such form is as an elongate pin. DE-C-0 878 477 discloses a stone working tool such as a stone saw having a plurality of spaced cutting elements in the working portion. The spaced cutting elements consist of metal inserts embedded in carbide tips, the metal inserts comprising diamond grains in a metal matrix. US-A-4 190 126 discloses a rotary abrasive drilling bit of a construction wherein teeth are equipped on the fore part of a bit body attached to a rotary drill pipe. Each of said teeth is composed of a plurality of chips which are made of cemented tungsten carbide and the matrix thereof is soft and inferior in abrasion resistance relative to said cutting elements or chips. Each chip is shaped like a thin stick and extends along the cutting direction of said bit body. The matrix surrounds said chips. In the matrix of each tooth, the chips are orderly arranged to leave a desired interspace along the direction of radius as well as the direction of circumference of the bit body. European Patent Publication No. 0 391 683 describes a rotatable crown for a rotary drill which comprises a working end and an opposite end for engagement in a drill rod, stringer or adaptor coupling. The working end has a cutting face and a plurality of discrete, spaced abrasive compact pins located in the cutting face such that each pin presents a cutting point which is defined by a corner of the pin. The pins are made of thermally stable diamond compact. Such compacts will not degrade to any significant extent when exposed to a temperature of the order of 1200°C in a vacuum or inert or reducing atmosphere. European Patent Publication No. 0 487 355 describes a rotatable crown for a rotary drill bit comprising a working end which presents a working face for the crown and an opposite end for engagement with a drill rod, stringer or adaptor coupling. The working end comprises a mass of discrete abrasive particles uniformly distributed through a bonding matrix, and a plurality of abrasive compact pins so arranged in the matrix that the ends thereof are located in the working face. The working face has a serrated profile with alternating peaks and troughs. The ends of the pins are located in the peaks. SUMMARY OF THE INVENTION According to the present invention, a saw comprises a blade having a working portion comprising a plurality of segments bonded to the periphery thereof and presenting a working surface, the segments comprising a mass of discrete abrasive particles uniformly distributed in a bonding matrix and one or more elongate cutting elements made of thermally stable diamond compact or CVD diamond so located therein as to present cutting points or edges in the working surface. The elongate cutting elements or pins will preferably be so located in the working portion as to reduce undercutting, or reinforce the segments to maintain optimum profile during life of the saw, or to maintain both an optimum profile and reduce undercutting. BRIEF DESCRIPTION OF THE DRAWINGS Figures 1 to 6 are plan views of sections of embodiments of saws of the invention, Figure 7 is a perspective view of a portion of a saw of Figure 1, Figure 8 is a plan view of a section of another embodiment of a saw, Figure 9 is a plan view of the segment 1 of Figure 8, Figure 10 is a view in the direction of arrow "A" of Figure 9, Figure 11 is a plan view of segment 2 of Figure 8, Figure 12 is a view in the direction of arrow "A" of Figure 11, Figure 13 is a plan view of a section of another embodiment of a saw, Figure 14 is a plan view of the segment 1 of Figure 13, Figure 15 is a view in the direction of arrow "A" of Figure 14, Figure 16 is a plan view of the segment 2 of Figure 13, and Figure 17 is a view in the direction of arrow "A" of Figure 16. DESCRIPTION OF EMBODIMENTS The blade may be circular or straight-edged and will provide a peripheral edge, generally fairly thin, to which the working portion is bonded. The blade will generally be made of a metal such as steel. The invention has particular application to diamond impregnated saws. The working portion of the saw is characterised by containing one or elongate cutting elements so located therein as to present cutting points or edges in the working surface. These elongate cutting elements will each have a longitudinal axis. The longitudinal axis may lie at any angle to the working surface of the working portion. When the blade is circular, the longitudinal axes of the cutting elements will generally lie axially or tangentially to the working surface. When the working surface is flat, as for example in reciprocating saws, the longitudinal axes of the elongate cutting elements will generally be normal, or substantially normal, to the working surface. It is also possible for the longitudinal axes of the elements to lie in, or below, the working surface and substantially parallel thereto. The elongate cutting elements may be made of thermally stable diamond compact such as that described in any of United States Patent Specifications Nos. 4,534,773, 4,793,828 and 4,224,380. The elongate cutting elements may also be made of CVD diamond. CVD diamond is diamond produced by chemical vapour deposition, a method now well established and known. CVD diamond has excellent thermal stability properties making it a particularly useful material when hot pressing is used to produce the working portion of the saw. The bonding matrix for the working portion of the saw will generally be metallic. Any suitable metallic bonding matrix known in the art may be used, e.g. cobalt, cobalt with tungsten or tungsten carbide particles, infiltrated with bronze. The working portion may be produced using infiltration or hot pressing. Hot pressing is preferred because a denser, more abrasion resistant bonding matrix is produced. The working portion of the saw contains a mass of discrete abrasive particles uniformly distributed therein. The abrasive particles will generally be fine. The abrasive particles are preferably diamond abrasive particles and more particularly such particles of the saw or SDA type. The working portion may consist of a continuous rim bonded to the periphery of the blade. According to the invention, the working portion comprises a plurality of segments bonded to the periphery of the blade. Every segment may contain one or more of the elongate cutting elements. Alternatively, some of the segments may contain no elongate cutting element and only discrete abrasive particles. Generally, there will be no more than five elongate cutting elements in any one segment. Embodiments of the invention are illustrated diagramatically by the attached drawings. Referring first to Figures 1 to 6 each is a plan view of a section of a saw comprising a circular blade 10 having a plurality of segments bonded to the periphery thereof. The arrow in each of Figures 1 to 6 illustrates the direction of rotation of the saw. Referring to Figure 1, each segment 12 comprises a mass of abrasive particles uniformly dispersed through a bonding matrix and a single elongate abrasive compact (elongate pin) 14 located on a side edge thereof. Adjacent segments have the pins 14 located on opposite side edges 16, 18 and in each instance the pin 14 is located close to the leading edge 20 of the segment 12. Figure 7 illustrates a perspective view of a portion of the saw of Figure 1. The pins 14, as shown in this figure, are square in cross-section. It will be appreciated that the pins may have other cross-sections such as circular or triangular. The pins 14 are located axially in the segments, i.e. each pin 14 has a longitudinal axis which is normal to the working surface 22 of the segments 12. The pins may be so located in the segments that they are located just inside the side edges 16, 18 of the segments. The pins could also be so located in the segments that elongate edges 24 lie in the side edges 16, 18, i.e. they are coincident therewith. The embodiments of Figures 2 to 6 are similar to those of Figure 1 and 2. In particular, the perspective view of the Figure 1 embodiment, as illustrated by Figure 7, applies equally to these embodiments, save that the elongate pin location will vary, as illustrated. Referring to the Figure 2 embodiment, segments 30 contain elongate pins 32 and these segments alternate with segments 34 which contain no such pins. Both the segments 30 and the segments 34 will comprise a mass of abrasive particles such as diamond particles uniformly dispersed through a bonding matrix. Two pins 32 are located in each of the segments 30, one on each of opposite side edges 36, 38. The location of the pins 14, 32 in the embodiments of Figures 1 and 2 have the effect of reinforcing the segments thereby maintaining an optimum profile (normally flat or slightly concave) throughout the life of the saw. In the Figure 3 embodiment, the saw has a plurality of segments 40 bonded to the periphery of a circular blade 10. The segments each have a single elongate pin 42 located in the centre of each segment and at the leading edge 44 thereof. In this embodiment, the location of the pins has the effect of reducing undercutting at the leading edge of the individual segments. Undercutting is a particular problem in soft, highly abrasive material such as asphalt and green concrete. In the Figure 4 embodiment, alternating segments 50, 52 are provided. Segments 50 have two elongate pins 54, 56, the pin 54 being located in the centre of the segment and at the leading edge 58, while the pin 56 is located on a side edge 60. Segments 52 also contain two elongate pins 62, 64. The elongate pin 62 is located in the centre of the segment at the leading edge 66, whilst the other pin 64 is located on a side edge 68, this being an edge opposite to that on which the pin 56 is located in the adjacent segment 50. This arrangement of pins has the effect both of maintaining an optimum profile and of reducing undercutting of the leading edge of individual segments. In the Figure 5 embodiment, alternating segments 70, 72 are provided. The segments 70 each have two elongate pins 74, located in the leading corners 76 of the segment. The third elongate pin 78 is located in the centre of the trailing edge 80 of the segment. The segments 72 each have two elongate pins 82 spaced from each other and located at the leading edge 84. In the Figure 6 embodiment, alternating segments 90, 92 are provided. The segments 90 each have three elongate pins 94 extending in spaced relationship from a side edge 96 to the opposite side edge 98. The segments 92 each have two elongate pins 100 located in spaced relationship substantially within the outer edges 102, 104. It will be noted that the pins of similar segments are in register with each other, when viewed in the direction of rotation, and are out of register with the pins of the other neighbouring segments, when viewed in the same direction. With the embodiments of Figures 5 and 6 (which do not form part of the invention), it has been found that the pins can be used as the only abrasive cutting elements with the result that there is no need to include a mass of abrasive particles in the segments in addition to the pins. A further embodiment of the invention is illustrated by Figures 8 to 12. Figure 8 is a plan view of a section of a saw comprising a saw blade 120 having alternating segments, indicated as segment 1 and segment 2, bonded to the periphery thereof. The direction of rotation is shown by the arrow. Segment 1 is illustrated by Figure 9 (a plan view) and Figure 10 (a view in the direction of arrow "A"). This segment has two pins 122 located axially one on top of the other. The pins 122 are both located tangentially to the working surface 124 of the segment. Segment 2 is illustrated by Figure 11 (a plan view) and Figure 12 (a view in the direction of arrow "A"). This segment has a single pin 126 located in the centre of the segment and tangentially to the working surface 128. In this embodiment, the pins 122 and 126 are all located such that an end thereof is at the leading edge of the segment. Yet a further embodiment of the invention is illustrated by Figures 13 to 17. Figure 13 illustrates a plan view of a section of a saw comprising a saw blade 130 having a plurality of alternating segments 1 and 2 bonded to the periphery thereof. The direction of rotation is shown by the arrow. Segment 1 is illustrated by Figure 14 (a plan view) and Figure 15 (a view in the direction of arrow "A"). This segment has two pins 132 an end of which is located at the leading edge 134 of the segment. The one pin is located axially above the other. The pins 132 are located in the segment tangentially to the working surface 136. In addition, a third pin 138 is provided. The pin 138 is located axially in the segment and normal to the working surface and presents a cutting corner 140. It will be noted that all three pins are located to one side of the segment. Segment 2 is illustrated by Figure 16 (a plan view) and Figure 17 (a view in the direction of arrow "A"). This segment also has three pins which are located as the mirror image of the arrangement of segment 1 and like parts carry like numerals. In an example of the invention, a segmented saw, essentially as illustrated by Figure 1, was produced. Each saw segment had a cobalt/bronze bonding matrix in which were dispersed diamond particles. The elongate cutting elements or pins were made of a thermally stable diamond compact material sold under the trade name Syndax®. The segments were produced by infiltration. Concrete was sawn with the saw in a green condition approximately 15 hours after laying. The concrete was medium coarse limestone aggregate containing a high sand content making the material of medium abrasiveness. The concrete was reinforced with high tensile steel rope. The concrete was provided in beam form. The concrete beams were cut in one pass using a 200mm depth of cut. The feed rate was then modified to maintain a constant machine cutting power. The blade was flooded with water during cutting. The saw achieved a satisfactory life and was found to cut between 15 and 30 percent faster than a conventional saw in which the segments contained no elongate cutting elements. Further, it was noted in the saw of the invention that a pattern of segment wear resulted which gave rise to a "sandwich" configuration, i.e. more wear in the centre than at the periphery. This is considered a positive mode of wear as it restricts lateral deviation of the blade in cutting.

Claims: A saw comprising a blade (10) having a working portion comprising a plurality of segments (12) bonded to the periphery thereof and presenting a working surface (22), the segments (12) comprising a mass of discrete abrasive particles uniformly distributed in a bonding matrix and one or more elongate cutting elements (14) made of thermally stable diamond compact or CVD diamond so located therein as to present cutting points or edges in the working surface (22). A saw according to claim 1 wherein the blade (10) is circular and the elongate cutting element or elements (14) are so located in the working portion that longitudinal axes thereof lie axially or tangentially to the working surface (22). A saw according to claim 1 wherein the working surface is a flat working surface and the elongate cutting elements (14) are so located in the segments (12) that longitudinal axes thereof are normal, or substantially normal, thereto. A saw according to any one of Claims 1 to 3 wherein each segment (12) has an elongate shape with side edges (16) and a leading edge (20) and one or more of the segments (12) have at least one elongate cutting element (14) located at, or close to, a side edge (16) of the segment. A saw according to claim 4 wherein adjacent segments (12) have at least one elongate cutting element (14) located at, or close to, a side edge (16) opposite to that (18) of its neighbour. A saw according to any one of claims 1 to 5 wherein each segment (12) has an elongate shape with side edges (16) and a leading edge (20), and one or more of the segments (12) have at least one elongate cutting element (14) located at, or close to, the leading edge (20). A saw according to any one of the preceding claims wherein the discrete abrasive particles are diamond abrasive particles.

Inventors: CLARK IAN ERIC, MACKENZIE KENNETH ALEXANDER, SHAFTO GEORGE RICHARD, TOMLINSON PETER NOEL, WILSON STUART MARTIN, CLARK, IAN ERIC, MACKENZIE, KENNETH ALEXANDER, SHAFTO, GEORGE RICHARD, TOMLINSON, PETER NOEL, WILSON, STUART MARTIN
Applicants: BEERS DE, DE BEERS
Application year: 1995
Main classification: B28D1
IPC codes: B28D1