The present invention relates to rock boring ma¬ chines, and in particular to a new rotary cutterhead con¬ struction for use on such a machine.

Rotary cutterheads have for some time been used in conjunction with various types of earth tunneling machines. Two examples of somewhat different tunneling machines are disclosed by U.S. Patent No. 3,86l,7-*+8, granted January 21, 1975 and by chapter 21 of the* 1976 BETC Proceedings authored by Carlo Goraridori and published on or about June 14, 19 6. The tunneling machines which are disclosed by these two pub¬ lications include in basic form a frame structure which is composed of a cutterhead support and rearwardly projecting beam. A cutterhead carrying forwardly directed cutters is mounted on the cutterhead support for rotation about an axis corresponding to the longitudinal center of the tun¬ nel being bored. The cutterhead support and usually at least the forward portion of the beam are encircled by a tubular shiled having a diameter moderately less than the diameter of the tunnel being bored. A rear gripper assembly, which includes a set of gripper shoes for pressing laterally outwardly to bear against the side walls of the tunnel, is supported for sliding movement along the length of the beam. If the boring machine is to be used in relatively soft ground material, a rear shield may also be provided to encircle the rearwardly portion of the beam. The rear shield is pro¬ vided with openings through which the rear gripper shoes may extend and retract.

Longitudinally disposed thrust rams interconnect the cutterhead support and the rear gripper assembly for

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lengthwise relative movement of the rear gripper assembly along the beam. Typical types of thrust rams are dis¬ closed by U.S. Patent No. 3,203,737 granted August 31, 1975 and by the aforesaid U.S. Patent No. 3,861,7*^*8.

In operations, when the rear gripper assembly is positioned forwardly on the beam, the gripper shoes are hy- draulically moved outwardly to gripping contact with the side walls of the tunnel. Then, the rotary cutterhead is rotated by drive motors while the thrust rams are simultan¬ eously extended to thereby push the cutterhead and main frame, including the beam, longitudinally ahead. When the thrust rams reach their forward limits of travel, the rear gripper shoes are withdrawn from the tunnel wall and then thrust cylinders are retracted to thereby draw the gripper assembly forwardly along the length of the beam into a new position. Thereafter, the rear gripper shoes are again moved outwardly into contact with the tunnel wall and the above procedure is repeated.

If the tunneling machine is to operate in relative¬ ly soft ground material, a forward gripper assembly, which is mounted on the main frame forwardly of the thrust rams, may be required to maintain the cutterhead and main frame in position while the rear gripper assembly is being reposi- tioned. Similarly to the operation of the rear gripper as¬ sembly, the shoes of the front gripper assembly are hydrauli- cally moved outwardly into gripping contact with the side wall of the tunnel. Thereafter, the thrust cylinders are retracted to pull the gripper assembly forwardly into a new position. Then the front gripper shoes are withdrawn while the rear gripper shoes are extended outwardly into contact with the tunnel wall to begin new boring sequence.

Various types of cutterheads have been commonly used in conjunction with the earth boring machine described above. The particular type of cutterhead with which this in¬ vention is concerned is termed an "open face" cutterhead and is characterized by openings in the face of the cutterhead

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to permit mined material to pass directly rearwardly through the cutterhead itself so that such material can then be car¬ ried out through the rear of the tunnel being bored.

An open face type of cutterhead having a typical arrangement of -eutters is disclosed in U.S. Patent No. 3,375 _* 332, granted September 4, 1973. This particular cut¬ terhead includes a plurality of disc cutter assemblies po¬ sitioned on the cutterhead for cutting concentric kerfs in the ground material. The disc cutters include circumferen¬ tial cutting edges which are flanked by sloping breaker sur¬ faces that serve to fracture and dislodge the rock material located between the kerfs which are cut by the cutting edges. A majority of the cutter assemblies are mounted on the front walls of radial spoke beams, which beams form part of the structure of the cutterhead. Other cutter assemblies are mounted on the front side of an auxilary frame structure which is angularly offset from the radial spoke beams.

A second type of open face cutterhead is disclosed by the aforementioned publication of Carlo Gorandori. This second type of open face rotary cutterhead includes a plur¬ ality of forwardly open, radially extending troughs. Roller cutters are mounted within the troughs to cut concentric kerfs upon rotation of the cutterhead. Segments which form breasting rings occupy the regions of the cutterhead be¬ tween the radial troughs. The Gorandori publication states that the rings support loose material against the tunnel face so that such material can be broken up into small enough pieces to thereby prevent damage to the tunneling machine. Accordingly, the ring segments are raised above the bottom of the trough to an elevation which permits the cutting edges of each cutter to project slightly forwardly of the ring seg¬ ments. With reference to the direction of rotation of the cutterhead, the trailing end portion of each ring segment is fixedly attached to a shovel which forms the front wall of each radially extending trough. Fractured ground material theoretically passes rearwardly through the cutterhead through

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annular openings located between adjacent ring segments.

A disadvantage of this particular type of cutter¬ head stems from the fact that the "rings" are composed of segments and thus are not continuous. Pieces of rock which are too large to pass through the annular openings between the rings segments slide along the length of said openings until they abut against the shovel wall located at the ter¬ minal end portions of each ring segment. Thereupon, the large chunks of rock either damage the cutterhead as it con¬ tinues to rotate or wedge so tightly between the front of the cutterhead and the face of the tunnel that the cutterhead is prevented from rotating, thus requiring the tunneling ma¬ chine to be retracted so that such chunks of rock material can be manually broken up.

Furthermore, some of the individual ring segments in this second type of cutterhead are not of uniform width, but are wider near the terminal end portion of the ring seg¬ mentj correspondingly, the annular openings are narrower in these areas. Thus, pieces of fractured rock which slide a- long the annular openings become wedged between the ring segments and are thereby prevented from freely passing rear¬ wardly through the cutterhead.

The present invention relates to a rotary cutter¬ head for an earth boring machine, including a main frame by which the cutterhead is mounted onto an earth boring machine for rotation about an axis of rotation, a plurality of rol¬ ler cutters and cutter mounting means for mounting said rol¬ ler cutters within said cutterhead from the rear side of said main frame, each of said roller cutters having peri¬ pheral cutting edge portions projecting forwardly of said main frame to cut concentric kerfs upon rotation of the cut¬ terhead, a plurality of cut-ground-material passageways dis¬ posed between said roller cutters and extending through said main frame, and a plurality of radially spaced apart face- support-ring members located on the cutterhead, and disposed forwardly of said main frame and slightly rearwardly of said

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roller cutter peripheral edges, said face-support-ring mem¬ bers being circumferentially continuous except where such continuation of a face-support-ring member would interfere with the proper placement of a roller cutter, said face-sup¬ port-ring member-,at any such roller cutter interference lo¬ cation being cut ^" away a minimum amount needed to accommodate such roller cutter.

In accordance with the invention, the ring members are radially spaced apart a distance sufficient to permit rocks of a desired maximum size to pass there between and then into the cu -ground-material passageways. Furthermore, the construction of the face-support-ring members not only prevents loose material at the tunnel face from collapsing at a rate faster than the rate at which such material can pass through the cutterhead, but also permits chunks of rock which are too large to pass directly between the ring members to slide circumferentially over the front face of the ring member or between adjacent ring members until they reach a cutter whereupon the chunks are broken up into small enough pieces to pass through the adjacent ring members. Because the ring members are continuous and also because each annular opening between adjacent ring members is of constant width, pieces of rock are free to slide along between adjacent ring members while only making line contact with the edges of such ring members.

According to a further preferred feature of the invention, the front of the cutterhead is closed off in all regions except within the roller cutter ounts or within the cut-ground-material passageways.

According to another preferred feature of the in¬ vention, radially disposed scraper cutters are positioned between adjacent face-support-ring members at the trailing edge of each cut-ground-material passageways front openings. Each of the scraper cutters has a leading blade or tip por¬ tion which projects forwardly of the face-support-ring mem-

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bers, but rearwardly of roller cutter peripheral cutting edge portions. Locating the scraper cutters at the trail¬ ing edge of the passageway openings does not block off or hinder fractured material which travels between the ring members from entering into the passageways.

Another preferred aspect of the invention, involves wear beads which are deposited in a grid pattern over the front face of each of the face-support-ring members. The wear beads are formed from material which is substantially harder than the material from which the corresponding face- support-ring members are constructed to thereby protect the face-support-ring members from abrasion by the rocks being excavated during operation of the cutterhead.

According to further preferred aspect of the in¬ vention, a plurality of scoop walls are located within the interior space of the cutterhead and orientated such that- the plane of each scoop wall is disposed both perpendicularly to the circumference of the annular beam and radially about the axis of rotation of the cutterhead. One each of the scoop walls extend between the forwardly directed surfaces of the annular beam and the corresponding rearwardly and radially inwardly directed portions of each of the radial spoke beams.

A preferred embodiment of the present invention will now be described with reference to the accompanying drawings, wherein like element designations refer to like part throughout, and wherein:

FIG. 1 is an enlarged fragmentary side elevational view illustrating a typical cutterhead constructed according to the present invention and portions of the cutterhead sup¬ port ^" of a tunnel boring machine, with some parts in axial section

FIG. 2 is a front elevational view of the typical cutterhead

FIG. 3 is an isometric view taken from the front and looking downwardly toward the upper and side portions of a typical cutterhead frame, with a foreground portion of such frame cut away;

FIG. ^{' '} is a view similar to FIG. 3, but directed towards the rear side of the typical basic cutterhead frame, with an upper foreground portion of such frame cut away

FIG. 5 is a rear elevational view of the typical basic cutterhead frame shown in FIG. 4 with portions broken away;

FIG. 6 is a fragmentary cross-sectional view of the cutterhead shown in FIG. 1 taken substantially along lines 6-6 thereof;

FIG. 7 is an enlarged fragmentary cross-sectional view of the cutterhead shown in FIG. 6 taken substantially along lines 7-7 thereof;

FIG. 8 is an enlarged, fragmentary cross-sectional view of the cutterhead shown in FIG. 6 taken substantially along lines 8-8 thereof;

FIG. 9 is an enlarged fragmentary view, partially in section and partially in elevation, of typical Inter¬ mediate roller cutter exemplifying one method of mounting the cutter;

FIG. 10 is a split cross-sectional view, wherein the outer portion is taken along line lOa-lOa of FIG. 9 wherein the lower portion is taken along line lOb-lOb- of FIG. 9 and

FIG. 11 is an exploded isometric view of the typ¬ ical intermediate cutter and its corresponding mounting struc¬ ture.

Referring initially to FIG. 1, shown in side elevational view is a typical rotary cutterhead 20 constructed according to the present invention and which is also the best mode of the invention currently known to applicant. Cutter¬ head 20 is mounted on the front portion of a tunneling ma¬ chine 22 for rotation about an axis generally corresponding

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to the longitudinal center line of the tunnel T being bored. The advance direction of tunneling machine 22 is coincident to the rotary axis of the cutterhead 20 and the tunneling machine 22 follows the cutterhead 20 into the opening for¬ med by said cutterhead.

In the ^" preferred form illustrated, cutterhead 20 comprises a main frame 24 which, as best illustrated in FIGs. 3-5, includes a central hub structure 26 from which six in¬ dividual radial spoke beams 28 extend radially outwardly and then rearwardly to intersect with an annular member in the form of annular box beam 30 by which box beam the cut¬ terhead 20 is mounted on tunneling machine 22. A center cutter assembly 32 is mounted within central hub 26, and a plurality of individual intermediate cutters 34 and gauge cutters 3 and their associated cutter mounts 38 and 40, respectively, are receivable between corresponding side plate members 42 and 44 of each of said spoke beams 28. Cutter¬ head 20 also includes a plurality of generally radially elon¬ gate cut-ground-material passageways 46 and a plurality of concentric, radially spaced apart face-support-ring members 48 which are disposed forwardly of and overlie cutterhead main frame 24. As shown in FIGS. 2, 6 and 7, a radially dis¬ posed scraper cutter 50 is positioned between adjacent face- support-ring members 48 at the trailing edge of each cut- ground-material passageway. Except in the areas within t h cut-ground-material passageways 46 and within each cutter mount 38 and 40, the front face of main frame 24, as shown in FIGS. 1 and 2, is covered by plating 52.

Now referring specifically to FIGS. 3-5, main frame 24 includes a plurality of radial spoke beams 28 which are interconnected between a box-like central hub structure 26 and an annular box beam 30. Hub structure 26 is general¬ ly hexagonal in shape and includes six peripheral walls 54 orientated such that a one spoke beam 28 radiates outwardly from each of said walls 54. The shape of hub structure 26 and the corresponding number of spoke beams 28 are dependent

on the relative radial placement and the total number of cutters 34 and 36 which are required for a cutterhead of a particular size and for the particular ground material being excavated. A rectangularly shaped opening 5 extends through the center of hub 26, which opening 56 is reduced in size at the hub front wall 8 by window 60. Also, two circular holes 62 extended through opposite portions of the peripheral edges of hole structure 26.

Each radial spoke beam 28 includes a pair of side plate members 42, 44 disposed in spaced parallel relation¬ ship to each other by a plurality of partition or cross walls 63 which transversly connect and are spaced along the length of said side plate members 42, 44. The inner end of each of the side plate members 42, 44 fixedly abuts against hub peripheral walls 54 at the corners of said peripheral walls 54 so that adjacent side plate members 42 and 44 of adjacent spoke beams 28 intersect each other at such corners. Each member 42, 44 includes a forward section 64, 66 re¬ spectively, that radiates outwardly from hub structure 26 while lying in a plane perpendicular to the tunnel axis, FIGS. 3 and 4. At their outer ends, each side plate member 42, 44 curves rearwardly to form outer end sections 68 and 70, respectively, which outer end sections fixedly abut against frustro-conical shaped forward wall 72 of annular box beam 30. However, the location of the foreward sections 64, 66 and the outer end sections 68 and 7*0 corresponds to the front or forward portion of cutterhead 20 which front or forward portion includes both the generally vertical face portion and the peripheral or gauge portion of said cutterhead 20. As best shown in FIG. 1, the front edges of side plate members 42 and 44 generally follow the desired contour of the tunnel face which is preferably cut in a relatively flat crown shape with a generally circular curvature existing at its outer circumference.

In addition to forward wall 72, annular box beam 30, has illustrated in FIGS. 1, 3 and 4, also includes frusto-

conical peripheral first wall 78 and second wall 8θ. Se¬ cond wall 80 intersects the outer or circumferential edge of forward wall 72. A frustro-conical outer rear wall 82 extends radially, inwardly from the rear edge of peripheral second wall 80 to intersect mounting ring 84, which ring serves as a lower rear wall. Lastly, a cylindrical inner wall 86 interconnects the radially inwardly edge of forward wall 72 and the front face 88 of mounting ring 84.

Constructing main frame 24 with rearwardly curving spoke beams 28 and annular box beam 30 provides a sufficient amount of interior space I.S. within cutterhead 22 to al¬ low workmen to enter into interior space I.S. to install and remove all of the cutters 32, 34 and 36 from behind said cutterhead 20.

Referring now to FIG. 1, cutterhead 20 is support¬ ed for rotation by a large diameter bearing 90 that is mount¬ ed on cutterhead support 92. Dirt seals 94 and 96 are pro¬ vided between the rotating and non-rotating parts at each end of bearing 90« Furthermore, the cutterhead support 9 includes a central, axial passageway 98 through which pas¬ sageway extends the front portion of a conveyor assembly 100, including its associated hopper 102. Hopper 102 collects the ground material fractured by cutterhead 20 and then de¬ posits such ground material on conveyor belt 104 for removal rearwardly through tunneling machine 22 and tunnel T.

As best shown in FIG. 1 and 2, the center cutter assembly 32 is mounted within hub opening 56 from the rear of hub structure 26. The center cutter assembly 34 in the embodiment illustrated includes four aligned disc cutters 105. Clearance space exists between each disc cutter 105 and the perimeter of hub window 60 to permit ground material, which is fractured and cut by said disc cutters 105 to pass rearwardly through opening 56.

Single intermediate disc cutter units 34 and sin¬ gle gauge disc cutter units 26 are mounted within their

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corresponding mounts 38 and 40. Mounts 38 and 40 in turn are fixedly positioned between spoke beam side plate mem¬ bers 42 and 44 so that the peripheral cutting edges 106 of said cutters 34 and 36, and of center cutters 105, co¬ operate to cut concentric kerfs in the tunnel face as cut¬ terhead 20 rotates. Each disc cutter 34, 36 and 105 also includes sloping breaker surfaces 108 flanking said circum¬ ferential cutting edge 106 for fracturing the rock material at the tunnel face.

Each cutter mount 38, as illustrated in FIGS. 9-H _> includes a box shaped structure which is welded in place be¬ tween the side plate members 42 and 44 and between adjacent partitions 63 to form a cutter compartment or well 109. Clearance exists between each cutter 34 ^" and its correspond¬ ing well 109 to permit fractured ground material to pass rearwardly therethrough. Each cutter well 109 is constructed to receive cutter 3 from behind cutterhead 20 and also to retain said cutter 34 within said well 109 through the use of load transferrinf blocks 110. Blocks 110 are positioned between the rearwardly directed face 112 of each cutter end member 114 and a corresponding forwardly directed face 116 of channels 118 formed in each end wall 120 of each well 109. Once load transferring blocks 110 are in place, capscrews 122 can be inserted through clearance openings provided said blocks 110 and then engaged with threaded blind holes pro¬ vided in end walls 120. Thus, since each end wall 120 forms an integral portion of the main frame 24, thrust loads im¬ posed on cutters 34 are transmitted in compression through load transfer blocks 110 directly to said cutterhead main frame 24.

Furthermore, the construction of each gauge cutter 36 and its associated mount 40 is similar to the construction of the above described intermediate cutter 34 and inter¬ mediate cutter mount 38.

As shown most clearly in FIG. _, a plurality of auxiliary disc type roller cutters 124 are located within

the region of cutterhead 20 between adjacent spoke beams 28. In a manner corresponding to the above described intermediate cutters 34 and gauge cutters 36, each auxiliary cutter 124 is mounted within its corresponding mount 126, which is il¬ lustrated as including a box shaped well 127 fixedly pos¬ itioned within a correspondingly shaped framed opening 128, FIG. 5. Opening 128 is formed in part by a pair of side walls 130 spaced apart in parallel relationship. Each of said side walls 130 extends rearwardly to abut against annular box beam forward wall 72 in a manner similar to side plate member outer end sections 68 and 70. Furthermore, each framed opening also includes an outer end wall 132 and an inner end wall 134, which two walls are spaced apart in par¬ allel relationship and are disposed perpendicularly to a ra¬ dius line beginning at the rotational center of main frame 24 and extending radially outwardly through the center of each framed opening 128.

In a manner similar to cutters 34 and 36, aux¬ iliary cutters 124 can be removed from, and replaced within, well 127 from the back side of main frame 24. Corresponding¬ ly, clearance space exists between each auxiliary cutter 126 and its corresponding well 127 to permit fractured material to pass rearwardly through said space. Furthermore, each auxiliary cutter 124 has a peripheral cutting edge 106 and sloping breaker surfaces 108 flanking said peripheral cutting edge 106 to cooperate with disc cutters 34, 36 and 105 to cut concentric kerfs within the tunnel face.

As shown in FIGS. 2 and 3, cutterhead 20 includes a plurality of radially extending cut-ground-material passage ways 46 extending transversly through said cutterhead 20 in the regions between adjacent radial spoke beams 28. Each passageway 46 initiates from a central location near hub structure 26 and then extends generally radially outwardly to terminate at the outer circumference of annular box beam 30. Each of said passageways 46 includes a leading wall 137 formed by an outward segment 138, an intermediate segment

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l4θ and an inward segment 142, which inward segment 142 is disposed substantially parallel to the adjacent spoke beam side plate member 42. Each passage way 46 also includes an outward trailing wall 144, which wall 144 is disposed sub¬ stantially parallel to leading wall intermediate segment l4θ. The inner end of each trailing wall 144 diagonally inter¬ sects with a corresponding spoke beam side plate member 42, which side plate member 42 also forms an inward section of the trailing wall of each passageway 46. The depth of pas¬ sageway leading wall 137 and outward trailing wall 144 is equal to the depth of spoke beam side plate members 42 and 44; thus the rearwardly directed edges of leading wall seg¬ ments 136 and 140 and the rearwardly directed edge of trail¬ ing wall segment 144 intersect the forward wall 72 of annular box beam 30 in a manner similar to spoke beam side plate mem¬ bers 42 and 44.

As most clearly shown in FIGS. 2 and 3, the outer radial end of each passageway 46 is open to permit entrance of fractured ground material which may be located about the circumference of cutterhead 20. The inner end of each pas¬ sageway 46 is formed by a sloped inner end wall 146 which is disposed perpendicularly to leading wall intermediate segment 140 and which intersects the inward end of the in¬ ward segment l42 of leading wall 136 and a corresponding spoke beam side plate member 42.

As most clearly shown in FIG. 5, almost the en¬ tire rear of passageway 46 is closed off by plating 148, with the exception of a circular segment shaped opening 150 for¬ med by leading wall inward segment 142, inner end wall 146 and arcuate edge 152 of plating 148.

A large portion of the fractured ground material which travels rearwardly through passageways 46 reaches the interior of cutterhead 20 while the particular passageway 46 is in the upper part of its rotation; thus, the material drops directly into hopper 102. Most of the remainder of

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the cut ground material reaches the interior of cutterhead 20 when its corresponding passageways 46 is in the lower part of the rotation of said cutterhead 20 and thus is scoop¬ ed or carried upwardly along the inside perimeter of said cutterhead 20 by a series of scoop walls 154, FIGS. 1, 4 and 4. Said scoop walls 154, as best illustrated in FIG. 1, has a front edge 156 and an outward edge 158, which two edges abut against adjacent edges of a corresponding spoke beam side plate member. Each scoop wall 154 also includes a rear edge l6θ which abuts against the adjacent portion of forward wall 72 of annular beam 30. Thus, it can be seen tha each scoop wall 154 lies essentially coplanar with a corres¬ ponding spoke beam side plate wall 42. A lip 162, constructe of flexible, resiliant material, is sandwiched between the inward edge portion of each scoop wall 154 and a rectangularl shaped plate 164 through the use of capscrews 166 which ex¬ tend through clearance holes provided in said plate 164 and then tread into aligned, tapped through holes provided in such inward edge portions. Lips 162 function to provide a seal between it associated wall 154 and the corresponding stationary portions of tunneling machine 22 which partially surrounds the hopper 102 to there by prevent fractured ground material from sliding inwardly off said scoop wall be¬ fore reaching an elevation high enough to drop into said hop¬ per 102. The portion of the tunneling machine which lips l62 wipe against do not form part of the present invention. Now referring specifically to FIGS. 1 and 2, al¬ most the entire front and circumferential faces of main frame 24 are covered by plating 52. The only areas not covered by plating 52 are the areas within central hub open¬ ing 56; cutter mounts 38, 40 and 126, cut-ground-material passageways 46, rectangular shpaed front opening 168. Open¬ ing 168 is provided to permit workmen to crawl through to the front side of cutterhead 20, for instance, in an emergenc situation. The overlying portion of face-support-ring mem¬ ber 48 will, however, first has to be removed. Also, there

are three generally rectangularly shaped circumferential openings 170 within plating 162. Said openings 170 as ilustrated in FIG. 5, are spaced around the circumference of cutterhead 20 and extend through the portion of cutterhead 20 corresponding ^' to first peripheral wall 78 and the outer rear wall 80 of annular box beam 30. Furthermore, a plate 172 is ^' positioned at the trailing edge of each circumferen¬ tial opening 170 to extend slightly rearwardly of the rear surface of outer rear wall 80 of annular box beam 30 FIG. 5- Circumferential openings 170 permit material which has col¬ lected at the rear side of cutterhead 20 to enter into the interior of said cutterhead as such material is pushed ahead by forward facing wall 173 of cutterhead support 92.

Referring now to FIGS. 1-3, 7 and 8, a plurality of concentric, radially spaced apart face support-ring mem¬ bers 48 overlie almost the entire front and circumferential or gauge regions of the cutterhead main frame 24 except in the center area of said main frame near hub structure 26. Thus, said face-support-ring members 48 are located in at least the radial region of cutterhead 20 in which the cut- ground-material passage ways 46 are located, including re¬ gions in which gauge cutters 36 are positioned. Ideally it would be preferable to place face-support-ring members 48 even in the central area of the cutterhead main frame 24. However, placement of such ring members 48 in the central area of main frame 24 would not be beneficial unless the cut- ground-material passageways 46 could also be extended radial¬ ly inwardly a corresponding amount. Extension of passageways 46 in the typical cutterhead 20 illustrated was not possible because of the presence of a rather large central hub struc¬ ture 26 which is required to provide adequate structural sup¬ port for the center of said cutterhead 20.

In cross section, each ring member 48 includes an outwardly projecting face section in the form of flange mem¬ ber 172, which flange member is disposed tangentially to the

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envelope defined by the peripheral cutting edges 106 of disc cutters 34, 36, 105 and 124, which envelope corresponds to the desired profile of the tunnel face. Each ring member 48 also includes an integral, inwardly directed shank section in the form of web member 174, which web member cooperates with its corresponding flange member 172 to form identical T-shaped cross sections. Constructing each ring member 48 in this manner with a flange member 172 which is wider than the corresponding web member 174 provides an enlarged space into which cut-ground-material can expand. Thus, it is to be understood that all of the face-support-ring members 48 do not have to be of the same cross-sectional size or even of the same cross-sectional shape, as long as each individu¬ al ring member 48 is of uniform cross-sectional size and as long as the face portion of each ring member 48 is wider than its shank portion. The free or inward edge portion 178 of each web member 174 is fixedly attached to corres¬ ponding portions of spoke beam 28, front plating 52 and cutter mounts 38, 40 and 126 which directly underlie said edge portion 178.

The ring members 48 are positioned outwardly of front plating 52 a distance sufficient to permit the peri¬ pheral cutting edge 106, which encircles the annular rim 182 of each disc cutter 34, 36, 105 and 124, to project slightly forwardly of ring members flange sections 172 as shown in FIG. 1. Face-support-ring members 48 are spaced a- part so that the annular openings between them are of con¬ stant width so that chunks of rock which are too large to pass directly through cut-ground-material passageways 46 can freely slide along adjacent ring members 48, while mak¬ ing only line contact with flange members 172, until such chunks are broken up into smaller pieces by disc cutters 34, 105 or 124 by scraper cutters 50. Preferably the spacing between adjacent ring members 48 progressively decreases as the radial distance from the center of cutterhead 20 in-

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creases. This change in spacing is required to compensate for the fact that due to the force of gravity, more rock ma¬ terial tends to fall downwardly into the peripheral regions of cutterhead 20 than in the central portion of said cut¬ terhead 20. Thus, the narrower spacing between the peri¬ pherally located face-support-ring members tends to force some of the rock material to migrate toward the center of cutterhead 20 whereat such material can be accommodated. As illustrated, ring members 48 are spaced apart a distance suf¬ ficient to permit from two to three peripheral cutting edges 106 to be disposed between adjacent ring member flanges 172 which thus also limits the size of fractured particles which can pass between said adjacent ring members 48. Preferably the size of such particles should be large enough so that ex¬ cessively repetitious cutting by cutters 34, 36, 105 and 124 is not required while small enough to permit conveyor 104 to handle such particles without being damaged.

Ring members 48 also function to support the tunnel face to thus prevent loose material from falling away from the tunnel face at a rate faster than at which such material can pass rearwardly through cutterhead 20 or at a rate faster than such material can be handled by conveyor 104. Corres¬ pondingly, each ring member 48 is constructed to be substan¬ tially circumferentially continuous except where continua¬ tion of a ring member 48 would interfere with proper place¬ ment of a disc cutter 34, 36, or 124. Where possible, ring members 48 are only notched a minimum amount which is suf¬ ficient to permit clearance for the interferring disc cut¬ ter peripheral cutting edges 106. Also, instead of discon¬ tinuing a ring member in the areas shown in FIG. 2, said ring members could be provided with a close fitting hole through which peripheral edge 106 of said disc cutters 43, 3 or 124 could protrude. Thus, as cutterhead 20 rotates, fragments of ground material that have only partially passed through the openings between adjacent ring members 48 are

free to slide along between the edges of ring member flanges members 172 until they are broken up into a size which are small enough to pass between said adjacent ring members 48. Furthermore, material which does not fall between adjacent ring members 48 ^"' is free to ride along over the face of flange members 172 until such material encounters and is fractured by a disc cutter 36, 105 or 124. Since flange mem¬ bers 172 are relatively narrow, they do not impart a large frictional resisting force against the tunnel face thereby permitting unrestricted relative movement between fractured material and the front face of said flange members 172.

A grid of wear beads 184, as shown in Figs. 2-4, is deposited, for instance by welding, in a cross-hatched pattern over the entire outward surface of each ring flange member 172 to form diamond shaped patterns. Said wear beads 184 are composed of material which is substantially harder than the material from which the ring members 48 themselves are constructed to thereby protect flange members 172 from abrasion by rocks when the cutterhead 20 of the present in¬ vention is in use.

Now referring to FIGS. 2, 6 and 7, a plurality of scraper cutters 50 are positioned along the trailing edge of the forward opening of each passageway 46. Said scraper cutters 50 are mounted on a mounting plate 186; one each of said mounting plates 186 are disposed along the trailing edge of each passageway 46. Furthermore, each mounting plate 186 extends outwardly from front plating 52 and is canted forwardly toward the direction of rotation of cutter¬ head 20 to intersect the rearward surfaces of overlying face-support-ring members 48 to thereby form a stop or bar¬ rier -for materials which may be sliding along the annular opening between adjacent ring members 48 and to direct such material into a passageway 46, FIG. 7 and 8. Each scraper cutter 50 is closely receivable between adjacent face-support-ring members flange members 172 and projects

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forwardly of said flange members 172 but rearwardly of cut¬ ter peripheral edges 106.

Furthermore, each scraper cutter 50 has a shank portion 190 which overlaps the corresponding leading sur¬ face of mounting plate 186, and a pointed tip or blade por¬ tion 192 which projects outwardly of and overlaps the lead¬ ing edge portion 194 of each mounting plate 186 FIGS. 6-9. Each of said scraper cutters 50 is detachably mounted on mounting plate 186 by capscrews 196 which extend through clearance holes provided in said mounting plate 186 and then thread into aligned, tapped through holes provided in shank portion 190 of each of said scrapers cutters 50 thereby per¬ mitting said scraper cutters to be replaced when required. However, since the blade portion 192 is constructed of har¬ dened material and is considerably thicker than, for in¬ stance the peripheral cutting edges 106 of disc cutters 34, it is contemplated that cutters 50 will have to be seldom replaced, if ever. Moreover, cutters 50 can be removed when, for instance, the particular characteristics of the ground material being bored does not require their use.

As best shown in FIG. 2, cutterhead 20 also in¬ cludes a plurality of forwardly directed nozzles 198 position¬ ed adjacent oppositely extending spoke beams 28 for dis¬ charging or spraying water forwardly toward the face of tun¬ nel T to minimize the dust generated during operation of said cutterhead 20. Nozzles 198 are interconnected in fluid flow communication with each other through the use of hoses 200, which hoses 200 are covered for protection by angle members 202. It is to be understood that other types of conduits, such as pipes, could be substituted for hoses 200.

In operations, as cutterhead 20 is rotated and simultaneously advanced by tunneling machine 22, disc cutters 34, 36, 105 and 124 cut concentric kerfs into the tunnel face so that the sloping breaker surfaces 108 flanking the circumferential cutting edges 106 fractures and dislodges

the rock material located between the kerfs. The fractured rock material then travels rearwardly through cutterhead 20 by passing between adjacent face-support-ring members 48 and then through passageways 46.

Material which is too large to pass directly be¬ tween adjacent ring members 48 can slide along the annular opening defined by said adjacent ring members 48 until such material reaches a scraper cutter C Scraper cutter 50 thereupon fractures the material into a small enough size to pass between said adjacent ring members 48. Furthermore, said ring members 48 serve to support loose, large chunks of rock material against the face of the tunnel until such material can be broken up by disc cutters 3 , 36, 105 and 124 and by scraper cutters 50. When the rock material reache the interior of cutterhead 20, such material either drops directly into hopper 102 or is lifted or carried upwardly a- long the inside perimeter of cutterhead 20 by scoop walls 154 until such material is raised high enough to slide down¬ wardly into hopper 102 and then onto conveyor 104 to be transported rearwardly through tunnel T.

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