IMPROVEMENTS RELATING TO TUNNEL-BORING MACHINES

Abstract: A cutter head assembly for a tunnel-boring machine includes a generally flat rotary cutter head (10) and one or more cutter discs (17) mounted via rotary bearings (15) upon respective cantilevered shafts (12). Each bearing (15) has an inner race (14) supported upon the shaft (12) and an outer raceway (18) formed integral with the cutter disc (17).

Description: Improvements Relating to Tunnel-Boring Machines The present invention is concerned with machines by means of which tunnels are excavated by boring through rock or other ground by means of rotary cutter heads. The invention relates in particular to the cutter discs mounted within such cutter heads. The cutter discs in tunnel-boring machines of the foregoing type are mounted so as to be free to rotate about an axis generally transverse to the direction of movement of the machine. The discs are pressed hard into the excavation face and function initially by crushing the material of that face and then shearing away the resulting chips or flakes of material, or in a generally similar manner in the case of a "soft" or composite excavation face. To enable the cutter discs to rotate freely, they are conventionally mounted by means of bearings upon a fixed shaft. However, as the desired diameter of the required tunnel becomes less, for example if it is desired to excavate a sewerage tunnel of, say, less than 800 mm diameter, so the cutter discs themselves must necessarily be smaller and the bearings then become a more significant feature of the overall cost of the discs. A further associated problem is that, when the size of each cutter disc is reduced, it is undesirable to reduce the size of the bearings too far as they would then be unable adequately to survive the very heavy loads which are applied to the discs. On the other hand, if bearings of proportionately larger dimensions are retained when designing smaller cutter discs, then the walls of the discs must be made correspondingly more thin in order to accommodate the bearings. As a result, the discs themselves are less able to survive the required working loads. It is an object of the present invention to provide an improved cutter head assembly, which makes possible the design of cutter heads of smaller working diameter while retaining at least to some extent the integrity of a cutter head of larger design. In a conventional cutter head of this general type, the bearing for each cutter disc comprises an inner race mounted upon the shaft or spigot upon which the disc is supported, and an outer race or cup secured within the cutter disc. The cutter head assembly according to the present invention comprises a generally flat rotary cutter head and one or more cutter discs mounted via rotary bearings upon respective cantilevered shafts, each said bearing comprising an inner race supported upon said shaft and an outer raceway formed integral with the cutter disc. Because the bearing is formed integral with the cutter disc rather than as a separate entity installed in the disc, the body of the disc may be formed with a greater thickness than would be the case with a conventional cutter disc bearing and the inherent strength of the disc is thereby improved. Thus, as contrasted with conventional cutter discs, the cutter disc assembly according to the present invention makes possible cutter discs of greater strength and thus longer life, for a given external disc diameter. The outer raceway may be formed by grinding, on the metal of the inner surface of the cutter disc body . In one particularly preferred form of the present invention, the cantilevered shafts upon which the cutter discs are supported are mounted at an angle to the plane of the face of the cutter head. A suitable such angle lies within the range from 5 to 25 degrees, more preferably within the range from 8 to 15 degrees, for example at 10 degrees. The cutter disc in this form of the invention is rotationally symmetrical but it is preferred that the axis of the cutting edge of the disc be inclined forwardly by the same angle as the inclination of the shaft, in order to present the tip of the disc squarely to the excavation face when the machine is in operation. By inclining both the shaft and the cutting edge in this way, it becomes possible to transfer the load to the shaft more effectively, via the bearings. The invention will now be further described with reference to the accompanying drawings, which illustrate, by way of example only, two alternative preferred embodiments of the cutter head assembly according to the present invention, shown in cross- section. The illustrated cutter head assemblies each comprise a generally flat cutter head plate 10 having a flat face 11 which, in operation of the tunnel boring machine, is directed towards the rock or other face being excavated. Mounted within the cutter head plate 10 are a number of cantilevered shafts 12 (only one of which is illustrated in each case), each inclined relative to the cutter head face 11 by an angle 13, which in the illustrated embodiments is 10 degrees. The inner race 14 of bearings 15 is located upon the shaft 12 and retained in place by a cap 16. The cutter disc itself 17 is ground on its inner face to form a raceway 18 upon which the bearings 15 engage. The cutter disc is thus able to rotate freely upon the bearings 15 about the cantilevered shaft 12 as its axis. The radially outer edge 19 of the cutter disc 17 is inclined to the right as illustrated by 10 degrees, to compensate for the inclination of the shaft 12 and thereby enable the cutting edge 19 to approach the excavation face squarely. The bearings are sealed by seals 20 and by an outer cap 21, to prevent debris from the cutting operation entering the bearings. As will be apparent, the illustrated forms of cutter head assembly allow the construction of cutter discs of a robust design, even in the case of discs of relatively small diameter.

Claims: CLAIMS 1. A cutter head assembly for a tunnel-boring machine, characterised in that it comprises a generally flat rotary cutter head (10) and one or more cutter discs (17) mounted via rotary bearings (15) upon respective cantilevered shafts (12), each said bearing comprising an inner race (14) supported upon said shaft and an outer raceway (18) formed integral with the cutter disc. 2. A cutter head assembly according to Claim 1, characterised in that the outer raceway (18) is formed by grinding, on the metal of the inner surface of the cutter body (17). 3. A cutter disc assembly according to either of the preceding claims, characterised in that said cantilevered shafts (12) are mounted at an angle (13) to the plane of the face (11) of the cutter head (10). 4. A cutter disc assembly according to Claim 3, characterised in that said angle (13) lies within the range from 5 to 25 degrees. 5. A cutter disc assembly according to Claim 4, characterised in that said angle (13) lies within the range from 8 to 15 degrees. 6. A cutter disc assembly according to any of Claims 3 to 5, characterised in that the axis of the cutting edge (19) of the disc(s) (17) is inclined forwardly by the same angle (13) as the inclination of the shaft (12).

Inventors: EGERTON CHARLES WILLIAM, ROOKE ALAN, EGERTON, CHARLES, WILLIAM, ROOKE, ALAN
Applicants: ANDARAY ENG LTD, EGERTON CHARLES WILLIAM, EURO ISEKI LTD, ROOKE ALAN, ANDARAY ENGINEERING LIMITED, EGERTON, CHARLES, WILLIAM, EURO ISEKI LIMITED, ROOKE, ALAN
Application year: 1997
Main classification: E21B10
IPC codes: E21B10, E21D9