Boring head cutter

[00002] This invention relates to tunnel boring equipment and more particular to an improved cutter for cutting tunnel head walls and a process of cutting such head walls.

[00003] Large tunnels for subways, mining and highway are made with tunnel boring equipment. A typical tunnel boring machine includes a large diameter cutter head of a diameter only slightly less than the diameter of a tunnel being bored. The head is rotatively mounted on a machine body which in turn is mounted on wheels for advance as the head is rotated. Conveyors behind the head transport cuttings rearwardly for removal from the tunnel.

[00004] The cutter head carries a plurality of cutters. In the past such cutters have been fixedly and coaxially mounted on hubs for rotation about the hub and cutter axis. Cutter rotation is caused by frictional engagement of each cutter with the head wall as the boring head is advanced and rotated.

[00005] Boring a tunnel is a very slow and time consuming procedure. Accordingly it would be desirable to provide improved cutters which would reduce the time consumed in boring a tunnel.

[00006] The present invention is embodied in improved hub mounted cutters. Each of the improved cutters has a cutting edge disposed within or located symmetrically about an imaginary plane which intersects the axis of the hub on which the cutter is mounted at an acute angle. That angle in the disclosed embodiments is of the order of 75 degrees with its hub's axis at the maximum cutter inclination with respect to the hub axis.

[00007] In one embodiment the cutting edge is a circle such that as the hub rotates when the cutter is in use penetration of the head wall being bored varies due to the skewed mounting of a blade's cutting edge on the hub. Thus, the blade engages the head wall in a scalloped pattern.

[00008] Expressed another way motion a the blade's cutting edge relative to the axis of its hub has reciprocating vectors both parallel and normal to the hub axis. This cutter edge motion relative to the hub axis coupled with the boring head rotation causing the cutters to orbit the head axis produces impacting pressure on the head wall that results in enhanced boring speeds.

[00009] With a second embodiment of the cutter the blade is elliptical with the major dimension being in an imaginary plane which includes the axis of hub rotation and which angularly bisects the blade such that the scalloping action is more pronounced with the eccentric configuration. Expressed another way, the reciprocating vector normal to the hub axis is enhanced.

[00010] Thus, in both embodiments the skewed mounting of the blade results in an impacting of the head wall tending to enhance the fracturing of the wall and accelerate the boring action especially when the material being bored is a relatively hard rock.

[00018] Referring to the drawings a cutter head is shown somewhat schematically at 10 in FIGS. 1 and 2. The cutter head 10 is rotatively mounted on a cutter body 12. The head 10 will be of a diameter only slightly less than the diameter of the tunnel being formed so that cutters mounted on it can cut the head wall to a diameter slightly larger than the cutter head to produce a tunnel of the size desired.

[00019] Referring now to FIGS. 3A and 3B one of the cutters 14 of the embodiment in which a cutter blade 15 is elliptical is shown on an enlarged scale with respect to FIGS. 1 and 2. The cutter 14 is mounted on a cutter hub 16. The hub 16 has a bore 18 for mounting the cutter and hub on the cutter head 10. As is best seen in FIG. 3A the blade 15 defines a cutting edge 20 which lies in an imaginary plane. The angle between the planes of the cutting edge 20 and a center line 22 is 15 degrees. Expressed another way, the imaginary plane of the cutting edge 20 when viewed in the plane of FIG. 3A, intersects the hub axis at approximately 75 degrees. The angle of that intersection is preferably in a range less than 90 degrees with the preferred angle being a variable depending on the type of the material being bored. It should be recognized that in a plane perpendicular to the hub axis and located by the center line of FIG. 3A a radius of the cutter 15 is perpendicular to the hub axis.

[00020] As can be seen from an examination of FIG. 3B, the blade is elliptical with the major axis of the ellipse being in a plane including the hub axis and a plane normal to the hub axis plane and intersecting the blade at its center. The minor axis is normal to the major axis and in a plane paralleling the plane of FIG. 3B and bisecting the cutter.

[00021] By contrast, the blade of FIGS. 4A and 4B is concentric in a plane bisecting the cutter which is the plane of the cutting edge 20′. In the drawings both embodiments are shown at 75 degrees with the hub axis. In the disclosed and illustrative embodiments 75 degrees is the maximum angle of inclination of the cutting edge relative to the hub axis such that the points of contact of the cutting edge as the cutter is rotated produce an arc ranging from 75 degrees to one side of perpendicular to 75 degrees to the other side.

[heading-00022] Operation

[00023] In operation, the head and body 10, 12 are advanced until the cutters 14 are positioned to commence to engage the head wall to be bored. The head 10 is then caused to rotate about its axis while thrust, to the right as viewed in FIG. 1, is applied to force the cutters against a head wall being bored.

[00024] Prior to positioning the boring head 10 adjacent the head wall, cutters made in accordance with the present invention and having optimized skewing and eccentricity or concentricity for the material to be bored will be mounted in the boring head. Thus an operator will determine the type of the material to be bored and use cutters which tests have shown to have optimized amounts of skewing and eccentricity.

[00025] As the boring head is advanced and rotated to apply pressure to the head wall, friction of the cutters against the head wall being bored will cause the cutters to rotate about their respective hub axes. As we have described this rotation will cause the cutting edges 20 to produce cutting vectors which are both parallel to the axis of a cutter's hub and normal to it. The result is a scalloping cutting action illustrated by the solid line 24 of FIG. 5. Forces imparted by the cutters tend to both compress and shear the head wall resulting in fracturing as well as cutting away material from the head wall. The combination of enhanced cutting and fracturing of the head wall results in enhanced boring speed.

[00026] Although the invention has been described in its preferred form with a certain degree of particularity, it is understood that the present disclosure of the preferred form has been made only by way of example and that numerous changes in the details of construction, operation and the combination and arrangement of parts may be resorted to without departing from the spirit and the scope of the invention as hereinafter claimed.