TECHNICAL FIELD

This invention relates to tools for cutting rock and hard soils, and more particularly, to improvements in disc cutters and cutterheads for use in drilling, boring, and tunneling machines. BACKGROUND

Rolling disc cutters are well known in the art of mechanical excavation. Such cutters operate on the principle that by applying great thrust on the cutter, and consequently pressure on a rock face to be cut, a zone of rock impinged by the cutter is crushed. The crushed zone forms a pressure bulb of fine rock powder which exerts a hydraulic like pressure in the cutting direction and thence outward against adjacent rock which then cracks, so that chips spall from the rock face.

The present invention is directed to a novel disc cutter which dramatically improves production rates of disc cutter excavation, which also allows reduced thrust requirements for cutterhead penetration, which in turn reduces the weight of the structure required to support the cutters. Such reductions also allow disc cutter technology to be applied to novel, small diameter cutterheads for excavation equipment. Additionally, the relatively light weight of our disc cutters provides dramatically decreased parts and labor costs for the maintenance and replacement of cutterhead wear parts.

BRIEF DESCRIPTION OF THE DRAWING

For a better understanding of the general principles of our invention, reference should be had to the following detailed description, taken in conjunction with the accompanying drawing, in which:

FIG. 1 is a vertical cross-sectional view of present invention, showing the rolling type disc cutters in use cutting a rock face.

FIG. 2 is a rock face view showing the pattern left in a rock face when a rotary cutterhead with rolling disc cutters is employed.

FIG. 3 is an exploded vertical cross-sectional view of the novel rolling type disc cutter of the present invention, revealing (a) a shaft, (b) wear ring, (c) seal, (d) cutter ring or blade, (e) bearing, (f) bearing retainer, and (g) hubcap, all assembled on a pedestal mount.

FIG. 3A is a cross-sectional view of a shaft for a rolling disc cutter, were the hardened washer surface is provided as an integral part of the shaft structure. FIG. 3B is an enlarged vertical cross-sectional view of a substantially semi-circular shaped disc cutter ring as may be employed on our novel disc cutter.

FIG. 4 is an exploded perspective view of the disc cutter assembly of the present invention, showing (a) a shaft, (b) wear ring, (c) cutter blade, with seal (not visible) and bearing assembled, (d) bearing retainer, and

(e) hubcap, all assembled on a pedestal mount.

FIG. 5 is vertical cross-sectional view of an assembled disc cutter as earlier illustrated in FIGS. 3 and 4 above.

FIG. 6 is a schematic illustrating the forces acting on a disc cutter and key measurements in relation thereto.

FIG. 7 is an axial cross-sectional view of an unused disc cutter utilizing a hard metal cutting blade insert. FIG. 8 is an axial cross-sectional view of an used disc cutter utilizing a hard metal cutting blade insert, showing the self sharpening cutter blade described herein.

FIG. 9 is a transverse cross-sectional view of our novel disc cutter design with a hard metal segmented cutting edge, using twelve hard metal inserts.

FIG. 9A is an enlarged transverse cross-sectional view of a hard metal segment as used in one embodiment of our novel disc cutter, showing three critical radii which when properly sized will achieve desired reliability of hard metal segment inserts.

FIG. 9B is an axial cross-sectional view, taken along the rolling axis, of a hard metal insert segment as used in one embodiment of our novel disc cutter, illustrating one critical radius which when properly shaped will achieve desired minimum lateral forces necessary to achieve the desired reliability of of the disc cutters.

FIG. 9C is a transverse cross-sectional view of our novel disc cutter design with a second embodiment of our hard metal segmented cutting edge design, utilizing four hard metal segments.

FIG. 10 is an axial cross-sectional view of a second embodiment of our novel fully assembled disc cutter, shown utilizing a hard metal insert cutting edge.

FIG. 10A is a partial axial cross-sectional view of the disc cutter ring first shown in FIG. 10, now

illustrating the technique used for brazing the hard metal inserts to the cutter ring.

FIG. 11 is a top view, looking downward on a disc cutter ring as set forth in FIG. 10, showing a twelve segment hard metal insert design in its operating configuration.

FIG. 12 is a side perspective view, looking slightly oblique to the face of a cutterhead designed using the novel disc cutters disclosed herein. FIG. 13 is a front view, looking directly at the cutterhead design first illustrated in FIG. 12.

FIG. 14 is a vertical cross-sectional view, taken through section 14-14 of FIG. 13, illustrating the cantilever mounting technique for employing the novel disc cutter of the present invention in a cutterhead.

FIG. 15 is a cross-sectional view of one embodiment of the cutterhead first set forth in FIG. 12 above, illustrating use of a central drive shaft with drilling fluid (slurry) muck removal. FIG. 16 is a cross-sectional view of one embodiment of a cutterhead using with central drive shaft and drilling fluid (slurry) muck removal.

FIG. 17 is a cross-sectional view of another embodiment of a cutterhead using the novel disc cutter disclosed herein.

FIG. 18 is a vertical cross-sectional view of the disc cutter of the present invention, showing another embodiment utilizing a journal type bearing.

FIG. 19 is a vertical cross-sectional view of the disc cutter of the present invention, showing our novel disc

cutter being utilized in a saddle mounted shaft type application.

FIG. 20 is a vertical cross-sectional view of the novel disc cutter disclosed herein, showing a saddle mounted shaft type application, and employing journal bearings.

In order to minimize repetitive description, throughout the various figures, like parts are given like reference numerals.

THEORY Although the fundamental operational principles involved in using a disc cutter for rock excavation are well known, a significant improvement in the state of the art is provided by our novel disc cutter design, and by cutterheads which use the same. Attention is directed to FIG. 1, wherein a hard rock 40 is being cut by disc cutters 42 and 44 of the type disclosed and claimed herein. By applying pressure downward from adjacent cutters 42 and 44 toward rock 40, a zone 46 of rock directly beneath each disc cutter is crushed. The force required to form the crush zone 46 is a function of both cutter geometry and characteristics of the rock, particularly the compressive strength of the rock. Zones 46 provide a pressure bulb of fine rock powder which exerts a downward and outwardly extending hydraulic-like pressure into the rock 40. This pressure causes cracks 48a, 48b, 48c, 48d, etc., to form in the rock 40. When the cracks 48a and 48b contact each other, for example, a rock chip 50 spalls off the surface 52 of the rock 40. The objective of efficient rock cutting is to crush a minimum of rock 46 and to spall off chips 50 which are as large as possible, thus maximizing the volume of rock chips 50

produced .

To form a maximum volume of large chips, the lateral spacing S should be maximized. The present invention enables an increase in the mean particle (rock chip) size, thus allowing a reduction in the amount of energy required to excavate in a given rock 40. Also, cutter performance is greatly enhanced, when used at the same horsepower input, due to increased mean particle size.

Directing attention again to FIG. 1, when cutter 42 or 44 is cutting rock 40, the cutters 42 and 44 penetrate into rock 40 by a depth Y. A relationship known as the spacing ratio exists between the depth of penetration Y into the rock 40 and the the spacing or width S between the cutter 42 and the cutter 44; that ratio is determined by dividing the distance between kerfs S by the depth of penetration Y. Parameters which affect penetration Y are (1) characteristics of the rock being cut, (2) thrust of the cutter blade against the rock, (3) the diameter of a selected cutter, and (4) blade width of the cutter. The latter two parameters, taken together, are frequently referred to as the cutter "footprint." PRIOR ART

The method which has heretofore been employed by others in the art to exploit the relationship has been to use larger and larger diameter disc cutters which are adapted to accommodate high thrust forces by provision of larger and larger bearings. Such bearings have been used to allow rotation of the cutter at the increased thrust force on the rock as necessary in order to achieve deeper penetration Y. In so far as we are aware, tunnel boring

machine manufacturers have heretofore generally employed a disc cutter configuration with a diameter D of 17 in.

(43.18cm), 18 in. (45.72cm) and 18.25 in. (46.36cm) , 19 in.

(48.26cm), and 20 in. (50.8cm). Such cutters have typically been saddle mounted with the shaft supported at both ends, to minimize shaft deflection, at the high thrusts required for rock penetration. Cutter blade widths W at the cutter tip or rim of 0.5 in. (1.27cm) to 0.8 in. (2.03cm) are most common. The largest cutters of which we are aware have a claimed thrust capacity of up to about 75,000 pounds force. Typical designs use a high percentage of the total radial space in the design as bearing space. Shaft diameters in such designs are insufficiently large for use in cantilever mounting. Such prior art designs of large size, heavy weight cutters and accompanying saddle type shaft mounts make modern single row, rotating disc cutters useable only in conjunction with large diameter cutterheads. Due to the size and weight of the prior art large diameter disc cutter designs, it is not practical (or even possible, in many cases) to use such disc cutters in smaller diameter cutterheads, much less in drilling bits. As a result, in so far as we are aware, rotating disc cutters have generally not been provided in such applications.

Also, prior art cutters are heavy, complex, and contain many parts. When such prior art cutters require maintenance, such as replacement of the blade or cutter ring the entire cutter assembly is removed from a boring machine and carried away from the point of excavation. Generally such cutters are too heavy for manual removal and carriage

by workmen, and therefore must be removed with the help of lifting equipment and transported by conveyance to a cutter repair shop outside of the tunnel or excavation site, in order to be repaired or rebuilt. Such prior art large disc type cutters are described in various patents; U.S. Patent

No. 4,784,438, issued Nov. 15, 1988 to Tyman Fikse for

TUNNELING MACHINE ROTATABLE MEMBER, is representative.

Other types of drilling applications can benefits from use of our novel disc cutter, since it may be advantageously applied in relatively small diameter drilling applications. Heretofore, for example, tri-cone type drill bits with carbide inserts have been commonly used in drilling holes up to about 23 in. (58.42cm) in diameter. The specific energy expended in using such tri-cone bits is in the range of approximately 80 horsepower-hours per ton (HP-hr/ton) and upward. However, by use of our disc cutter design in cutterheads in this size range, the specific energy required for such drilling operations can be dramatically reduced. In conclusion, insofar as we are aware, no bearing and structural support configurations have heretofore been provided or suggested (1) for small diameter disc cutters (i.e. preferably in the range of about 14 in. (35.56cm) diameter and smaller, and more preferably in the range of about 10 in. (25.4cm) diameter or smaller, and most preferably in the 5 in. (12.7cm) diameter range or smaller) with the structural capability to reliably endure the high thrusts required to meet and exceed the critical pressure required for rock excavation, or (2) are of a size which can advantageously applied to small diameter cutterheads.

SUMMARY OF THE INVENTION

The present invention relates to an improved rolling type disc cutter and to a method for mounting the cutter in a cutterhead assembly. Our novel rolling disc cutter is designed for use in a mechanical excavation apparatus to exert pressure against substantially solid matter such as rock, compacted earth, or mixtures thereof by acting on a rock face being cut, where the cutter is of the type which upon rolling forms a kerf by penetration into the face so that, when two or more cutters are used, solid matter between a proximate pair of kerfs is fractured to produce chips which separate from the face. Our disc cutter comprises (a) a relatively stiff shaft having a proximal end and a distal end with an axis for rotation thereabout, (b) a washer having a sealing surface, (c) a cutter ring assembly, wherein the cutter ring assembly further comprises an annular cutter ring having an interior annulus defining portion and an outer ring portion, with the outer ring portion including a cutting edge having diameter OD and radius R- _j _. Also included is a bearing assembly which is adapted to substantially fit into the annulus of the cutter ring, and to sit in a close fitting relationship with the shaft, so that the cutter ring may rotate with respect to and be supported by the shaft. The bearing assembly comprises a bearing and a seal, with the seal adapted to fit sealingly between the washer sealing surface and the cutter ring, so as to form a lubricant retaining seal for the interior annulus portion of said cutter ring. A retainer assembly is provided which is adapted to retain the cutter ring assembly onto the shaft. A cap with an interior

surface portion and adapted to seal the interior annular portion of the cutter ring assembly is provided, so that, in cooperation with the seal and the cutter ring, a lubricant retaining chamber is provided. In one embodiment, the cutter ring further includes a pair of laterally spaced apart support ridges, wherein the ridges have therebetween a groove forming portion, with the groove forming portion including a pair of interior walls , and an interior bottom surface interconnecting with the interior walls. The interior walls outwardly extend relative to the interior bottom surface to thereby define a peripheral groove around the outer edge of the outer cutter ring. Two or more, or as many as twelve or more hardened, wear-resistant and preferably hard metal inserts are substantially aligned within and located in a radially outward relationship from the groove. The inserts further include a (i) substantially continuous engaging contact portion of radius R-^, wherein the contact portion on the outer side of said inserts are adapted to act on said face, (ii) a lower groove insert portion, which has a bottom surface shaped and sized in complementary matching relationship relative to said bottom surface of said groove, and first and second opposing exterior side surfaces which are shaped and sized in a complementary matching relationship relative to the interior walls, (iii) a rotationwise front and rear portion. The lower groove insert portion of the inserts fit within the groove in a close fitting relationship which defines a slight gap between the inserts and the interior walls. A somewhat elastic preselected filler material such as a braze alloy is

placed between and joins the inserts in a spaced apart relationship to the groove bottom and to the interior sidewalls. The preselected filler material is chosen so that it has a modulus of elasticity so that in response to forces experienced during drilling against a face, the inserts can slightly move elastically relative to the cutter ring so as to tend to relieve stress and strain acting on the insert segments.

The novel disc cutter and cutterhead designs provide improved disc cutter geometries, high footprint pressure, improved hard metal insert configurations, improved disc cutter bearing designs, more robust structural supports for the cutter, simplified cutter mounting apparatus and methods, small diameter cutterheads with disc cutters, and improved cutter rebuilding methods.

In addition, the disc cutter of the present invention provides higher penetration into any given rock at lower thrust than conventional disc cutters. This performance factor at lower thrust is very significant in many types of excavating machinery design. The lower thrust requirements possible by use of our designs allow lighter excavating machine structural components, as well as lower operating power requirements for a given excavation task. Moreover, this combination makes feasible the design of significantly more mobile excavating equipment.

DESCRIPTION

The present invention will now be described by way of illustration, it being understood that a small diameter rolling type disc cutter with a long wearing blade, and cutterheads advantageously employing the same, may be provided in a variety of desirable configurations in accord with the exemplary teachings provided herein.

Attention is now directed (a) to FIGS. 3, where our novel disc cutter is shown by way of an exploded cross- sectional view, (b) to FIG. 4, where the same embodiment is shown in a perspective view, and (c) to FIG. 5, where the same embodiment is shown in an assembled cross-sectional view. Our novel cutter will be easily understood by evaluation of these three figures. The cutter 120 is comprised of five (5) major parts:

First, a large diameter shaft 122 is provided. Second, a washer surface 123, preferably hardened, is required. (Washer surface 123 is here shown as provided by optional ring type washer 124 rather than provided as an integral washer surface 125 as part of the shaft 122 structure, as seen in FIG. 3A.)

Third, a cutter ring assembly 126 is provided. When assembled, nested within the cutter ring assembly 126 are the cutter ring 128, bearing 130 (including inner 132 and outer 134 race) and seal 136 (here all shown individually in exploded view) . The cutter ring 128 is the ring which runs against a rock to be cut and imparts the cutting action described above.

Fourth, a retainer 138 retains the ring assembly 126 onto the shaft 122. Retainer 138 is secured in place by

fasteners such as machine screws 140, which in turn pass through fastener apertures in retainer 138 and are received by threaded receptacles 142a, 142b, and 142c (see FIG. 4) in the end 144 of shaft 122. Fifth, a hubcap 146 is affixed to the outer side 148 of cutter ring 128 by securing means such as threads 150 (on hubcap 146) and 152 (in cutter ring outer side 148)

Although threads 150 and 152 are shown, alternate securing means such as a snap ring arrangement may also be utilized. The hubcap 146 rotates with the cutter ring 128 and thus eliminates the need for an outer seal. The clearance between the interior wall 154 of hubcap 146 and the outer end 156 of fasteners 140 is minimal and prevents the fasteners 140 from backing out should they happen to loosen. The hubcap 146 also serves as a cover for an interior oil or grease reservoir 158 (see Fig. 5 ) .

Thus, the overall cutter assembly 120, contains but five (5) major parts. This is a significant reduction in parts when compared to many conventional prior disc cutters heretofore known which contain as many as twenty (20) or more parts. Moreover, the parts provided are at greatly reduced weight when compared to prior art disc cutters.

The hard washer 124 described above is utilized as a replaceable wear surface on which the seal 136 rubs. However, it is to be understood that washer 124 is an optional part depending upon the selected use and desired economic life cycle of the disc cutter or body 120. However, in the embodiment as illustrated in FIG. 3, when a ring assembly 126 is replaced, the bearing 130 and seal 136 are replaced as well. All wear components, except the above

described hard washer 124, are thus contained in the single ring assembly 126. Yet, even the hard washer is easily accessed when the ring assembly 126 is changed, thus easy maintenance of the disc cutter 120 is achieved. Disassembly of cutter 120 can be accomplished with use of simple, common hand tools. Reassembly of cutter 120 is accomplished with equal ease. The worn cutter ring assembly 126 which preferably weighs less than 40 lbs. (18.14kg); more preferably the cutter ring is provided in a weight less than 20 lbs. (9.07kg.); most preferably the cutter ring is provided in the range of 3 lbs. (1.36kg) to 8 lbs. (3.63 kg) (for a 5 in. (12.7cm) diameter disc cutter). Therefore, the cutter assembly 126 weighs in the range of approximately one tenth (1/lOth) or less of the weight of conventional prior art disc cutters. Cutter ring assembly 126 is thus quite portable, even in quantity, and is easily handled in the field by a single workman without need of power lifting or carriage tools. Also, the cutter ring assembly 126 is sufficiently inexpensive that a worn ring assembly 126 may be simply discarded, rather than rebuilt. To install a new ring assembly 126, the ring assembly 126 is slid onto the shaft 122, the retainer 138 is secured, and the hubcap 146 is installed.

Further details of the cutter 120 may also be seen in FIG. 3. At the inward 160 side of shaft 122, a retaining wall 162 is provided. When a wear ring 124 is utilized, the outer edge 164 of the wall 162 is provided with a shoulder portion 166 sized in matching relationship with the inner wall 168 diameter of wear ring 124. Also, retaining pins 170 are provided to insert through apertures 172 provided in

wear ring 124, to secure wear ring 124 against rotation.

Seal 136 is sized to fit within a seal receiving portion 174 of cutter ring 128. An outer shoulder 176 of cutter ring 128 extends inwardly in the axial direction to the above (toward the outside) seal receiving portion 174.

The outer shoulder 176 includes a lower seal portion 178 and an inward surface 180.

Below the seal receiving portion 174 of cutter ring

128 is a bearing retainer portion 182 which extends radially inward at least a small distance so as to prevent the advance of bearing 130 all the way through cutter ring 128 upon assembly. An interior sidewall 184 of ring 128 is sized in matching relationship to the outside diameter of the outer race 134 of bearing 130, so that the bearing 130 fits snugly against interior sidewall 184.

Retainer 138 may include an inwardly extending outer edge portion 186 which is sized and shaped to match the appropriate portions of the selected bearing 130 so as to allow proper freedom of bearing movement which securing the bearing 130 in an appropriate operating position. Also, one or more lubrication apertures 189 may be provided to allow lubricant to migrate to and from lubricant reservoir 158 (see FIG. 5) .

Hubcap 146 may include a threaded plug 188 for use in providing lubrication as selected depending upon the type of service of the disc cutter 120. As more clearly visible in FIG. 4, hubcap 146 may be provided with a purchase means such as slot 190 for enabling application of turning force as necessary to turn the hubcap through threads 150 and 152 so as to tighten the hubcap. Also, hubcap 146 may also

include a shoulder 191 or other diameter adjusting segment to allow internal clearance with retainer 138.

For underwater applications, a grease type lubrication system is normally provided with a pressure compensation membrane 192 and interconnecting lubricating passageways 194 defined by lubricating passageway walls 196. Also seen in any of FIGS. 3, 4, or 5, a pedestal 198 is provided for integral attachment of the cantilevered shaft 122. It is important to note that shaft 122 is of large diameter SD in proportion to the outside diameter OD of the cutter 120. For example, with a 5 in. (12.7 cm) diameter OD disc cutter, the shaft 122 diameter SD would preferably be at least forty percent (40%) of the cutter 120 diameter OD, or at least 2 in. (5.08 cm) diameter. A large ratio of shaft 122 diameter SD to cutter diameter OD ratio is important to provide a sufficiently stiff shaft to minimize possible deflection of shaft 122.

Our novel cutter 120 design can also be described in terms of the minimal radial space required for bearing purposes. Again, for an exemplary 5 in. (12.7 cm) diameter OD cutter, when using a needle type bearing as illustrated in FIGS. 3, 4, and 5, the total bearing space (B ₂ + B ₂ ) would occupy about twenty percent (20%) of the total diameter OD (or also about twenty (20%) of the total radial space) . The ratio of shaft diameter SD to cutter ring diameter OD is preferably over 0.4 (i.e, the shaft diameter is at least 40% of the cutter ring diameter) . More preferably, the ratio of the shaft diameter to cutter ring diameter is in the range of 0.4 to 0.5 (i.e., the shaft

diameter SD is forty to fifty percent (40-50%) of the diameter OD of the cutter ring 128. Using the desired shaft size or better in conjunction with the other design features illustrated provides extreme rigidity to the shaft 122, thus substantially minimizing shaft deflection when the cutter

120 is under load and thrusting against a rock face. This is a major improvement in the art, as shaft deflection has historically been a major cause of early bearing failure in disc cutters, particularly when roller bearings were used. With respect to the desirable size of cutters 120 in the design just illustrated, we can provide cutter rings 120 in various sizes. However, cutter rings of less than about 20 in. (50.80 cm) diameter, and preferably in the range of about 14 in. (35.56 cm) diameter and smaller, and more preferably in the range of about 9 in. (47.29 cm) diameter or smaller, and most preferably in the 5 in. (12.70 cm) diameter range or smaller, are desirable. These sizes are considered practical for currently known applications, although our disc cutter design could be provided in any convenient size.

Turning now to FIG. 6, tests of our 5 in. (12.7 cm) diameter cutter were conducted on a linear cutter machine (LCM) at the Colorado School of Mines. That test machine simulates the cutter action of an excavating machine by passing a rock sample 204 beneath the test cutter 200. Depth of penetration Y and spacing S can be set, while forces in three axis are measured (rolling force 206, normal force 208, and side force 210). Multiple cuts were made across rock sample 204 at spacing S, with penetration Y; each complete pass resulted in removal of a thickness Y.

Initial results are shown in TABLE I and TABLE II.

The first rock sample 204 used was an extremely hard gneiss

(about 43,000 psi compressive strength) rock. The second rock 204' was a 23,000 psi compressive strength welded tuff. The thrust and side forces of our novel disc cutter, as set forth in the test data in TABLE 1 and TABLE 2, are extremely low in comparison with those forces which would be experienced with a conventional large diameter saddle mount type disc cutter, for example. TABLE III below shows comparison results in the same rock (23,000 psi welded tuff) between our disc cutter design and a conventional disc cutter designed by the Robbins Company of Kent, Washington, U.S.A., when both cutters operate at a spacing of 3 in. (7.62 cm). As is evident from TABLE III, our novel cutter achieves the same penetration with substantially reduced thrust. Also, our cutter accomplishes the same penetration with substantially reduced side loading, here measured for our disc cutter at a a little less than three (3) percent of thrust, as compared to about ten (10) percent on the prior art Robbins Company cutter.

The significance of this thrust reduction can be readily understood by considering a nominal 6 ft. (182.88 cm) diameter cutterhead. If a 3 in. (7.62 cm) kerf spacing across a rock face were desired, a typical 6 ft. (182.88 cm) cutterhead would have fourteen (14) cutters and might rotate at about twenty (20) revolutions per minute ("rp ") . If the Robbins Company conventional 17 in. (43.18 cm)

TABLE I

Five inch (12.70 cm) Diameter Cutter Performance

43,000 psi Rock

Pene¬ Spacing Avg . Thrust Avg. Side Specific tration Force Force Energy

( inches (inches) (lbs) (lbs) HP-hr/yd3

0.075 0.75 8,515 332 31.9

0.075 1.00 9,613 599 29.1

0.100 0.75 9,968 533 30.5

0.100 1.00 10,347 721 24.4

0.125 0.75 10,878 828 30.2

0.125 1.00 11,103 834 23.7

TABLE II

Five inch (12.70 cm) Diameter Cutter Performance

23,000 psi Rock

Pene¬ Spacing Avg . Thrust Avg. Side Specific tration Force Force Energy

(inches (inches) (lbs) (lbs) HP-hr/yd3

0.10 1.5 8,062 316 11.08

0.10 2.5 8,217 367 7.79

0.10 3.0 9,102 384 7.43

0.15 1.5 8,845 566 10.2

0.15 2.5 11,379 762 7.04

0.15 3.0 11,956 302 6.61

cutters were used, as based on the data shown in TABLE III, total thrust on the cutterhead would be calculated as 14 x 42,200, or 590,800 pounds force. On the other hand, if our novel disc cutter as described herein were used, the total thrust would be calculated at 14 x 11,956, or 167,384 pounds force. In both cases, the boring machine penetration rate through the rock would be equal, at 0.15 in. (0.38 cm) per revolution, or 15 ft. (457.2 cm) per hour. Therefore, it can be appreciated that substantial reductions in excavation equipment structure, weight, thrust cylinder size, and operating power requirements are made possible by use of our novel disc cutter design.

TABLE III COMPARISON WITH PRIOR ART CUTTERS

Cutter Type Penetration Thrust Side Force (inches) (lbs. force) (lbs)

New 5" (12.70cm) 0.15 (0.38cm) 11,956 302

Robbins Co.

17" (43.18cm) cutter with 0.5" (1.27cm) 0.15 (0.38cm) 42,200 4,200 wide blade

Note: Spacing ("S") = 3.0 in. (7.62 cm)

Referring now to FIG. 3B, preferably our novel disc cutter ring 240 is provided with a blade width W of less than about 0.5 in. (1.27 cm), and more preferably, our novel cutter ring 240 is provided with a blade width of less than about 0.4 in. (1.02 cm), and most preferably, a relatively thin blade (0.32" to 0.35", or 0.81 cm to 0.89 cm width) is provided. The most preferred blade width penetrates into a rock with less thrust force requirement than conventional prior art disc cutters which are typically of 0.5 in. (1.27 cm) and larger width (0.5" to 0.8", or 1.27 cm to 2.03 cm blade widths are believed most commonly used in the prior art) .

Also, our relatively small cutter blade ring 240 outside diameter OD - preferably in the 5 in. (12.7 cm) range. Importantly, a substantially smooth transverse cross-sectional cutter blade tip shape, more preferably a sinusoidal cross-sectional shape, and most preferably semi¬ circular transverse cross-sectional shape of the cutter blade tip (here shown with a radius R ₇ ) , is employed in order to reduce side loading. Whereas conventional cutters normally exhibit side loading of about one tenth (0.1) of the thrust loading, our novel cutter ring, exemplified by cutter 240, and similar cutter ring discussed herein, provide a side load which is normally somewhat less than one tenth of thrust load, and generally provide a side load of about 0.06 times thrust load, or less.

The reduced side loading in our cutters is the key to allowing the use of a novel bearing design. While the bearings utilized can be any one of a variety of bearings selected with regard to cost and load capability. We have found that with the relatively low side loads encountered, a

needle type bearing provides sufficient bearing capability at relatively low cost. The needle type bearing accepts a high thrust load at low speeds (generally under 200 RPM) but is not tolerant of high side loading or axial loads. Therefore, our cutter design which minimizes side load is significant in reducing bearing costs and important in attaining adequate overall reliability of the bearing. One bearing make and model which has proven to provide satisfactory service during our testing has been a Torrington model 32 NBC 2044 Y2B needle bearing, which is used with a Veriseal teflon type seal manufactured by Busak+Shamban, model S 67500-0177-42.

Use of the needle type bearing achieves one key design objective of our cutter because it requires a very small amount of radial bearing space, noted, for example, as B ₂ above in FIG. 3. The needle type bearing is particularly an improvement over the double row, tapered roller bearings design used in most prior art cutters. The radial space thus saved by our bearing design allows the use of a relatively large diameter shaft, thus enabling achievement of another key design objective. The large shaft minimizes shaft deflection when under load, to a degree which easily permits the use of a cantilever mounted cutter assembly, rather than saddle mounted cutter assembly. The cantilever shaft (axle) arrangement also helps achieve another key design objective, namely simplified assembly and disassembly of the cutter. Finally, the cantilever axle mounting arrangement allows the disc cutters to be mounted in a closely spaced pattern which provides close kerf spacing, as frequently desired in rock drilling type applications.

The cutter ring 128 is the component which is pushed with great force against the rock face, and which causes the rock chipping action. The cutter ring 128 (or similar ring

240 as in FIG. 3B) is thus subject to wear, which is greatest when the cutter ring 128 attacks a rock containing quartz and other hard crystalline minerals. Nevertheless, a simple alloy steel ring 128, as illustrated in FIGS. 3, 4, and 5, when hardened to 57 - 60 Rockwell "C", is satisfactory in limestone, for example. However, such a hardened cutter ring 128 shows signs of rapid wear in a welded tuff material containing 25 - 30% quartz. Therefore, when excavating such materials, a much harder, wear resistant cutter ring material is highly desirable.

FIG. 7 shows a cross-sectional view of another embodiment of our novel disc cutter in which a cutter ring 250 is provided which has a hard metal insert 252 as the cutting edge, or blade 254. This cutter blade 250 design not only wears longer than the above described alloy blade 128, but it is also "self sharpening." As the hard metal insert 252 wears, the metal walls

256 and 258 which support the insert 252 also wears, to shapes shown as 256' and 258-' in FIG. 8. However, the blade 254 width W remains constant, as is illustrated in the worn blade 254' illustrated in FIG. 8 FIG. 10 shows an axial cross-sectional view of our novel disc cutter design (here shown in vertical position with cutter ring 280 ready to cut at the bottom position 281) which was successfully tested at the Colorado School of Mines Laboratory. This embodiment is essentially the same as the embodiment first illustrated in FIGS. 3, 5, and 5

above, except that prior cutter ring 128 is here replaced by cutter ring 280. The cutter ring 280 includes a disc shaped body 282 having an outer edge 284. The body 282 includes opposing outer side wall portions 286 and 288. The opposing outer side wall portions 286 and 288 each further include an interior wall, 290 and 292, respectively, and an exterior wall, 294 and 296 respectively. The body 282 also includes a bottom edge surface 298 which interconnects with the interior walls 294 and 296 of the opposing outer side wall portions 286 and 288. The opposing outer side wall portions 286 and 288 extend substantially radially outwardly relative to the bottom edge surface 298 to thereby define a peripheral groove 300 penetrating the outer edge 284 of the disc shaped body 282. The interior walls 294 and 296 are spaced above the bottom edge surface 298, preferably so that the walls 294 and 296 extend adjacent in close fitting fashion alongside of preferably more than half and more preferably about seventy five (75) percent of the height (R-^ -R ₂ ) of the hard metal insert 302. With respect to materials of construction, the hard metal inserts 302, as better shown in FIG. 9, can be made with current tungsten carbide manufacturing methods or other wear part materials that are known to those skilled in the art. However, with respect to the exact shape required for hard metal inserts 302, it is to be understood that inserts 302 must be carefully configured in order to achieve long service life, as the precise size and shape of the inserts have considerable influence upon their longevity. To that end we have done considerable work and investigation, the

results of which are set forth herein, in order to determine an exemplary insert 302 shape which results in an acceptable service life. Set forth in the transverse cross-sectional view of FIG. 9 is one possible configuration for providing hard metal inserts 302. In FIG. 9, it can be seen that twelve (12) inserts 302, each substantially in the shape of a segment of an annulus having an outer diameter R^ and an inner diameter R ₂ can be provided for mounting on a cutter ring 280 with shaft radius of size Rg and insert slot radius R ₂ ^, » While it may be desirable to have the inserts 302 built in circumferentially larger angular segments, or even as a single annular piece, in view of current tungsten carbide insert manufacturing techniques, extremely large angular segments would be rather difficult to produce. However, a hard metal insert design with at least as few as four segments 302*', as illustrated in similar transverse cross-sectional view FIG. 9C, is believed feasible utilizing current manufacturing technology and the design techniques taught herein. The precise configuration of each segment 302 is important in order to avoid their premature failure. We have discovered that is is significant in the design of the outer surface 310 of each hard metal insert segment that careful attention be paid to three or more important radii. Referring now to FIG. 9A, R-^ is the desired radius of the cutter disc 280 (for example, 5 in. (12.7 cm) outside diameter OD in one tested embodiment) . The bottom 312 of insert 302 has a radius R ₂ , which is sized and shaped to match groove 300, formed by bottom 298 wall of radius R ₂ ' and side walls 290 and 292 of radius Rg. With cutter

rotating in the direction of reference arrow 314, a trailing edge 316 of the segment 302 is provided with a curvature R ₃ which is slightly reduced from radius R-j_. At the end 318 of insert 302, another well rounded radius R ₅ is required. We have found that it is desirable that R ₅ be no less than about 0.065 in. (0.17 cm) when R-^ is 5 in. (12.7 cm).

Normally, segments 302 are manufactured symmetrically, and therefore leading edge 320 is provided with radii R ₄ and

Rg, which preferably correspond to radii R ₃ and R5, respectively. Without use of curved portions including each of the mentioned radii, any insert segments superficially similar to exemplary segments 302 have been found subject to premature cracking or catastrophic failure.

In addition to the just described radii, it is important to provide a slight gap 322 between hard metal segments 302. Because the co-efficient of thermal expansion of steel alloy cutter ring 280 and the hard metal inserts 302 are different, temperature cycling will crack the segments 302 unless slight relative movement is allowed between the segment 302 and the cutter ring 302. The selected fabrication method must allow for this minute movement to occur.

Also, the finite thickness T (R ₂ - R ₂ ') and ductile composition (modulus of elasticity) of the braze alloy or solder 330 used to secure the segments 302 is significant. This finite thickness T and ductile composition both cushions the hard metal inserts 302 and allows the small relative movement between the hard metal inserts 302 and the base cutter ring 280 material.

Variations in the size of the hard metal insert 302, but still showing the overall desired smooth, rounded, preferably sinusoidal, and most preferably semi-circular

(with radius R ₇ /) transverse cross-sectional shape of insert 302, are shown in FIGS. 9B and 10A. A cutter 280 which is ready for rock cutting operations is illustrated with an external view in FIG. 11 (here considered as a top view in comparison to the side view provided in FIG. 10) . Hard metal insert segments 302 in cutter ring 280 are illustrated in their working position, ready for rock cutting operations.

During tests, a disc cutter 400 with cutter ring 280 having hard metal insert segments 302 installed as shown in FIGS. 9 and 11 exhibited virtually identical performance to a new, solid steel cutter ring (ring 128 above) . The continuous blade formed by hard metal inserts 302 performs as the principal contact surface between the disc cutter 400 and the rock being cut, without significant gaps in contact between the rock and the hard metal inserts 302 during rolling action of the disc cutter ring 280.

Unlike conventional cylindrical "button" inserts to cutter blades which perform in an impact mode, and penetrate rock in a cratering fashion to produce smaller average chip sizes, our hard metal insert 302 design preserves the efficient cutting action of a true rolling disc cutter over the working life of the cutter, (i.e., as insert 302 wears, the cutting radius R ₇ shape is substantially preserved during wear thereof to maintain a substantially uniform cutter footprint) . Thus, we prefer using such hard metal insert type blades for most rock excavation applications.

To confirm the durability of our insert segment type cutter blade design, we conducted tests on the LCM

(described above) at Colorado School of Mines. The insert segment cutter 400 of FIG. 11 was tested using carbide inserts 302 on a hard rock sample (43,000 psi unconfined compressive strength) at increasing penetration depths until failure of the segments 302 occurred. Finally, at an average thrust load of nearly 30,000 lbs. (and peak load of over 50,000 lbs.) and at a penetration of 0.30 in. (0.76 cm) , a hard metal insert 302 failed.

To illustrate the significant improvement in the state of the art which is provided by our novel disc cutter design, a computer simulation was used to estimate the force which would be required on a standard prior art 17 in. (43.18 cm) disc cutter to achieve 0.30 in. (0.76 cm) penetration in 43,000 psi rock. The computed force is over 100,000 lbs. thrust. However, on a prior art disc cutter, such thrust cannot be achieved using currently available materials of construction. Therefore, it can be appreciated that our disc cutter can provide the superior wear characteristics of a hard metal cutter (usually tungsten carbide) at rock penetration depths superior to any rolling disc cutter heretofore available. The ability of our novel disc cutter design to provide superior rock penetration at reduced thrust levels directly translates into the ability to cut rock at advance rates (i.e. lineal feet of rock cut per hour) superior to any disc cutter or cutterhead apparatus currently known to us.

In further confirmation of the excellent, and indeed striking improvement in the state of the art provided by our

novel cutter design, the computer simulation further showed that at 30,000 lbs. thrust load, the standard prior art 17 in. (43.18 cm) cutter would penetrate only 0.03 in. (0.08cm), or about one tenth (1/10) of the rock penetration of our new disc cutter 400 design. Thus, our new cutter 400 design has the potential of increasing penetration Y on a cutterhead or drill bit by a factor of 10, when operating at a comparable thrust loading.

This superior performance was demonstrated in the Colorado School of Mines laboratory on a full scale (32 inch diameter) drill cutterhead 420, of the type illustrated in FIGS. 12 and 13. Cutterhead 420 is mounted on shaft 421 to provide rotary motion to the cutterhead 420. As shown, cutterhead 420 contains twelve (12) of our 5 in. (12.7 cm) diameter cutters 422. With 82.1 HP and 65,752 lbs. of thrust on the cutterhead 420, an advance rate of 33.6 ft/hr (1,024.13 cm/hr) was achieved in 23,000 psi rock. Specific energy was 11.8 HP-hr/yd3 of rock excavated. This is the best rock cutting performance in hard rock of which we are aware, and to the best of our knowledge, it is the best rock cutting performance ever witnessed in the Colorado School of Mines laboratory on a cutterhead or drill bit.

Although above in FIGS. 3, 5, and 10 above, our novel disc cutter 120 is shown mounted on pedestal 198, it is advantageous in some applications to avoid the use of a pedestal and instead directly affix the cutter 120 to a cutterhead. In FIGS. 12 and 13, the advantage of such an integral mounting technique can be seen in the construction of a protected, inset cutter arrangement which is particularly useful for drilling in broken ground or

boulders. Cutterhead 420 is provided, and cutters 422 are mounted to body 424 via aft portions 425 of shaft 122. A cantilever mounted shaft 122 supports cutter 422 at or near the distal end of shaft 122. As illustrated in FIGS. 12, 13, and 14, a further unique feature of a cutterhead 420 with integral shaft mounted cutters 422 is that cutter 422 to cutter 422 (kerf- to-kerf) spacing S can be varied on a given cutterhead 420. This is made possible (1) because the shaft 122 occupies a small frontal area on the body 424 of cutterhead 420, (in contrast to the total area required for use of a typical prior art saddle type cutter mount) , and (2) because small diameter disc cutters are utilized, which enable the designer to incorporate a large number of shafts 122 in the cutterhead body 424, including shafts 122, for use in adding additional cutters 422. Therefore, when it is desired to decrease kerf spacing S, additional disc cutters can be mounted on such extra shafts 122, and, in combination with the use of spacers 430 of width Z on existing cutter shafts 122, a new smaller kerf spacing S can be achieved.

In FIG. 14, it can be seen that a clearance H is left between the cap 146 of the cutter 422 and the cutterbody 424, so that cap 146 and retainer 138 may be easily removed and the cutter ring assembly 126 replaced as necessary. With our novel cutter design, this replacement is easily accomplished with common hand tools.

Muck (cuttings) handling in our cutterhead designs is also simplified. That is because by placing muck scoops 426 on the front 427 of the cutterhead body 424, as well as side scoops 428 on the sides 429, the muck is picked up almost

immediately, as it is formed. Thus, the regrind of the cuttings is substantially reduced, and therefore the efficiency of the cutter is greatly enhanced. With forward scoops 426, it is possible to gather up to 75% or more of the muck immediately, thus substantially improving cutter efficiency.

For micro-tunneling, box (blind) raising, raise drilling and tunnel boring, the problem of broken rock falling in on a cutterhead is a common and serious matter. Shielded face cutterheads, where the rolling disc cutters are recessed, and in some cases can be removed from behind the cutterhead, have been known and have been developed by others for large diameter tunnel boring. Such prior art designs have been shown to be very effective in poor ground conditions.

Attention is now directed to FIG. 15. Our disc cutter and cutterhead designs permit a dramatic improvement in shielded face cutterhead technology. Namely, we have been able to extend the use of shielded face cutterhead technology to much smaller diameter cutterheads. Thus, shielded cutterheads with a novel and much simplified structural design are possible when using our disc cutter technology. One exemplary version of our novel shielded cutterhead designs, which is configured so as to allow the loading, repair, or replacement of our disc cutters 422 from either the front (i.e, toward rock 448 face 449) or back (i.e., from behind the cutterhead), is shown in use in FIG. 15 (cutterhead 450) . Configuration of cutterhead 450 was designed specifically for micro-tunneling in varying applications, ranging from solid rock 448 to soft ground

with boulders.

As shown in FIG. 15 , our novel disc cutter - see for example cutters 422a and 422b - can also be mounted by directly welding the cutter shaft 122 into a cutterhead 450. In that case, no saddle or pedestal is used, and the shielded , recessed cutter conf iguration , heretofore successful almost exclusively in tunnel boring applications can, by use of our novel cutterhead and small diameter rolling disc cutter design, be applied to much smaller micro-tunneling and drilling applications . Shielded cutterheads even in the 2 ft. (60.96 cm) to 4 ft. (121.92 cm) diameter range are feasible, with about 3 ft. (91.44 cm) s l ightly less diameter shielded cutterheads easily achievable . Thus , our unique shielded cutterhead design greatly simplif ies how broken ground ( shielded type) cutterheads are fabricated, since easy rear (behind the shield) access to the disc cutters can be provided.

Another important design feature of our cutterhead 450 design is that it is hollow: it is built like a one- ended barrel. Gusset plates (braces) 460 , located inside cutterhead 450 , also function as internal buckets . A disc cutter mounting saddle, as used by others heretofore, can be advantageously eliminated by use of our pedestal mount type disc cutter design , or by direct attachment to the cutterhead body , as noted above for our stiff shaft cant i lever des ign . This combinat ion of f eatures dramatically simplifies fabrication as compared with typical prior art shielded cutterheads, which have heretofore been designed with box section type or frontal plate type construction.

Also in FIG. 15, shielded type cutterhead 450 is shown set up for use in a drilling fluid application. The cutterhead 450 is rotated against face 449 by shaft means 464, which is in turn affixed to cutter head body by braces 460. Cutterhead body 424 also includes a rear flange portion 466 which has an outer shield accepting flange 468. The shield accepting flange 468 rotates within the forward interior wall 470 of shield 472. A shield bulkhead 474 and shaft seal 476 prevent leakage of drilling fluid from flooded compartment 477 on the face 449 side of shield to the space rearward of the bulkhead 474. Drilling fluid indicated by reference arrow 478 is provided through bulkhead 474 to cutterhead 450 via inlet 480. In the hollow cutterhead 450 and through the cutterhead body 424, fluid picks up cuttings 482 and thence exits in the direction of reference arrow 484 past bulkhead 474 through outlet 486. The shield 472 and cutterhead 450 are advanced in a manner so that the forward interior wall 470 of shield 472 and the shield accepting flange 468 are maintained in shielding engagement with respect to the sides 488 of bore 490.

Another configuration for an exemplary broken ground cutterhead is shown in FIG. 16. A nominal 32 in. (81.28 cm) diameter cutterhead 452 is illustrated with hollow construction that allows a muck removal system (not shown) to be inserted forward in the cutterhead 452, perhaps all the way to the inside 494 of cutterhead body 424, to a point as little as 8 in. (20.32 cm) or so from the rock face 449. The cutterhead 452 is compatible with a pneumatic muck system, or an auger, or a conveyor system. If an auger is used with a sealed bulkhead and water injector, the

cutterhead 452 can be used as an EPB (Earth Pressure

Balance) type drilling apparatus, and in such cases, the hollow cutterhead 452 becomes the essential muck chamber.

Cutterhead 452, is thus suitable for drilling situations with high water inflow and in hydraulic soil zones. The design is is also easily switched back and forth between the

EPB drilling mode and an atmospheric or open drilling mode.

The cutterhead 452 set forth in FIG. 16 uses a downhole gear drive mechanism for providing rotary motion to cutterhead 452. The drive shaft 500 turns against a ring gear 502 which is affixed to cutterhead 452, and which, when rotated, rotates the cutterhead 452. A roller type radial bearing 504 separates the ring gear 502 and the shield support flange 506, to which shield 508 is attached. A roller type thrust bearing 510 is located between the shield support flange 506 and the bulkhead 512, to allow rotation of cutterhead 452 against the bearing 510, so that cutterhead 452 freely turns within the shield 508. Gear 502 and bearings 504, operate within an oil filled compartment 514, which is sealed by shaft seals 516 and by lip seal 520 between rotating bulkhead 518 and fixed bulkhead 522. For most applications, a chevron type muck seal 524 is provided between the forward interior wall 470 of shield 508 and bulkhead 512, and/or the adjacent axially extending outer shield accepting flange 468 the rear flange portion 466 of cutterhead body 424.

Attention is directed to FIG. 17, where one embodiment of our novel drill bit 530 design is illustrated. As shown, the bit 530 is suitable for small bit sizes such as those in about the 13.75 in. (34.93 cm) in

diameter range or so. The bit 530 incorporates six (6) of our novel 5 in. (12.7 cm) diameter cutter discs 422. This bit 530, similar bits which are somewhat smaller, or those which are larger and range in size up to about 23 in. (58.42 cm) or so in diameter (about the largest standard size prior art tri-cone bit) , can advantageously replace conventional tri-cone drilling bits.

The design of bit 530 is nevertheless quite simple, due to use of our unique small diameter cutters 422. In the version of bit 530 illustrated in FIG. 26, six (6) of our novel disc cutters 422 are used to simultaneously cut into rock 448, at face 449, a bore 531 defined by borehole edge 532. Disc cutters 422 are outward (cutters 422i, 422j , 422k, and 422m) , to provide the cut; those familiar generally with use of prior art rolling cutters will recognize that the exact placement of cutters 422 may be varied without departing from the teachings of our novel bit design. Usually a drill string 533 (shown in phantom lines) is provided to provide rotary motion to the bit 530 by connection with drill head 534 of bit 530. The drill head 534 is connected to a downwardly extending structure 536 (normally steel) . The exact configuration of structure 536 is not critical, but may consist of a top plug structure 537, downwardly extending sidewalls 538, and the cutterhead assembly 539. Affixed below the cutterhead assembly 539 are disc cutters 422. Although we presently prefer to use a cutter pedestal 198 for each cutter 422 in order to maximize flexibility in number and location of cutters 422, other mounting configurations, such as described elsewhere herein, are feasible. Stabilizers 540 are affixed to the outward

edges 541 such as at sidewalls 538 of structure 536 to position and secure the bit 530 with respect to borehole edge 532.

Because of the relatively low friction between the rolling disc cutters 422 and the rock 448 at face 449, and due to the relatively good heat dissipation by the rolling disc cutters 422, bit 530 can be used "dry", i.e., using only air as the cuttings removal fluid. When used in the dry mode, bottom cleaning of borehole 531 is accomplished by circulating a gaseous fluid such as compressed air. The air functions as both a cooling fluid and a muck or cuttings 542 transport media. Compressed air is supplied through a delivery tube 544 in the direction of reference arrow 546. The fluid enters the face area muck chamber 548 through a "blast hole" orifice or nozzle 550. Fluid is expanded into the face area 548. Cuttings 552 are forced out the muck pick up tube 554, in the direction of reference arrow 555, by air pressure or by vacuum. When desired, by use of both air pressure and vacuum, the pressure P in the face chamber 548 can be controlled. Additionally, it can readily be appreciated that the bit 530 can be converted to "wet" operation simply by supply of a liquid drilling fluid, instead of air, downward through tube 544, and sending the cuttings upward through muck tube 554. The advantage of bit 530 and of our novel small diameter cutterhead design generally for use in conventional drill bit applications can more readily be appreciated by reference to recent test data. A typical tri-cone drilling bit was tested in cutting (a) aged hard concrete and (b) basalt, where, as is typically done, fine cuttings were

produced. In aged hard concrete (about 6,000 psi strength) the tri-cone bit cut at a specific energy of 80 horsepower- hour per ton. In basalt (about 35,000 psi strength) the tri-cone bit operated at 120 horsepower-hour per ton. Referring now to TABLE I, it can be seen that in tests conducted at the Colorado School of Mines, our novel disc cutter design, when operating on 43,000 psi rock at spacings of 1 in. (2.54 cm) achieved a specific energy requirement between roughly twenty four (24) and twenty nine (29) horsepower-hours per cubic yard, (approximately 12 and 14.5 HP-hr/ton) depending upon the penetration Y achieved. In the same tests, when operating on 23,000 psi rock at 1.5 in. (3.81 cm) spacing, our novel disc cutter achieved a specific energy requirement of ten (10) to eleven (11) HP- hour per cubic yard (approximately 5 to 5.5 HP-hr/ton).

Thus, by comparison of the specific energy requirements of prior art tri-cone drilling bits, and the specific energy of required for use of our novel disc cutters and cutterheads, one can readily appreciate that our novel disc cutter, when applied to a small drilling bit body such as bit 530, has the potential of improving the penetration rate by a factor of ten (10) or more at the same power input level.

In addition to the above described performance increases anticipated of about a ten fold drilling rate improvement, drill bits using our novel disc cutters are simple to rebuild. This markedly contrasts to prior art tri-cone bits, well known in the art, which are rebuilt in the following steps: (a) saw the bit body into three

sections; (b) destructively remove the three cutters and pedestals; (c) machine, jig and dowel the three bit body sections; (d) install new cutters and pedestals, one on each section; (e) re-weld the three sections; (f) re-cut the threads; (g) hard face cutting zones as required. The rebuild process of prior art tri-cone bits is time consuming

(several days or more) , and requires a well equipped machine shop. Also, and the refurbished bit sells for about 75% of the cost of a new bit of equivalent size. In contrast, when our novel disc cutter and drill bit design is used, the rebuild may be quickly accomplished in the field. By reference to FIG. 4 above, such a rebuild consists of the following: (a) secure the bit (e.g. bit 600, by mounting the bit in a vise, or leave it on the drill rig; (b) using a hammer, a wooden wedge and a crescent wrench, remove the old cutters ring assembly 126, by (i) removing the cap 146 from the cutter ring 148; (ii) removing fasteners 140 from the retaining assembly 139; (iii) removing the retainer 138; (iv) removing the cutter ring assembly 126 from the shaft 122; (c) clean the unit and replace the hard washers 124 if required (such as if scored) ; (d) replacing the removed cutter ring assembly 126 with a new or reconditioned cutter ring assembly 126; (e) replacing the retainer 138 and said fasteners 140; (f) replacing the cap 146; (g) hard face zones, such as cutter 148 sidewalls, as required.

The operator of the drilling unit does the work with his own field labor, on site, with common hand tools. The work may possibly be done even while the bit is still on the drill rig. Such rebuild can be done in about one hour by

one man. Moreover, if hard facing is not required, total elapsed time is a mere fifteen (15) minutes. For convenience of the operator, a repair kit can be provided which includes one or more of the various wear parts, such as a cutter ring assembly (or its components of a annular cutter ring, a bearing assembly including a bearing, and a seal) , a retainer assembly, a hubcap, or hardened wear ring washer. The most likely replacement part would be the annular cutter ring having hard metal inserts therein. Attention is directed to FIG. 18, wherein the use of journal type bearing 700 is shown. This type of bearing 700 may be of the type with a base 702 and a wear face 704, or may be of unitary design. In some applications use of such a bearing 700 may further reduce the radial bearing space B ₂ required for our novel disc cutter 422, and such bearing 700 is entirely serviceable for certain types of cutter 422 applications. Also, a simple bushing type bearing is of similar appearance to bearing 700 and can be utilized as desired, depending upon loads and service life required. Although the design of our novel disc cutter allows the simplicity of assembly, replacement ease, unique cutterhead design and other benefits of a cantilevered design, our invention of small bearing space B ₂ disc cutters is not limited to the cantilever mount design. Indeed, those skilled in the art will appreciate that by use of our basic cutter assembly design, appropriately modified such as is shown in FIGS. 19 and 20, can be provided in a traditional saddle mount, and still achieve many of the performance advantages set forth hereinabove. Consequently, we do not limit our invention to pedestal or cantilever

mount designs, but also provide a novel disc cutter for saddle mount structures. Also, there are likely applications where our novel disc cutters may may need to be fitted onto conventional or existing cutterheads. By eliminating the hubcap 146, and by providing an extended shaft 700 and employing a second seal 136', a conventional saddle mount is easily provided. Dual mounting pedestals 705 extend from a cutterhead body 706. Pedestals 705 are shaped to accept shaft 700. Caps 707 secure shaft 700 to pedestals 705 via use of fasteners 708. An end plate 710 secures retainer 712 to shaft 700 by way of fasteners 714. End plate 710 also locates and secures retainer 712, which in turn secures one of the two hard washers 124 . Cutter ring 720 rotates about shaft 700 with cutting edge shape and performance as described above; also it is to be understood that the hard metal cutting edge as extensively described above can be adapted for use in an alternate cutter ring similar to ring 720, and need not be further described. Also, as set forth in FIG. 20, journal type bearings 700 can be substituted for the needle type bearing 130 shown in FIG. 19.

Thus our novel small diameter, minimal bearing space, and uniquely shaped cutting head disc cutter is not to be limited to a particular mounting technique, but may be employed in what may be the most advantageous mount in any particular application.

Similarly, although the research connected with the development of our novel disc cutter demonstrated the advantages of using the smallest diameter cutter possible in any given application, our novel cutter could be built in

any desired diameter, including sizes to fit into existing mounts of prior art excavating equipment.

Therefore, it is to be appreciated that the disc cutter provided by the present invention is an outstanding improvement in the state of the art of drilling, tunnel boring, and excavating. Our novel disc type cutterhead which employs our novel disc cutters is relatively simple, and it substantially reduces the weight of cutterheads. Also, our novel disc cutter substantially reduces the thrust required for drilling a desired rate, or, dramatically increases the drilling rate at a given thrust. Also, our novel disc cutter substantially reduces the costs of maintaining and rebuilding of cutterheads or bit bodies.

It will be readily apparent to the reader that the our novel disc cutter and cutterhead may be easily adapted to other embodiments incorporating the concepts taught herein and that the present figures as shown by way of example only and are not in any way a limitation. Thus, the invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The embodiments presented herein are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalences of the claims are therefore intended to be embraced therein.