Note: Descriptions are shown in the official language in which they were submitted.
07~1382
t9e~Y~3!~ Y~___ __nve
This invention relates to ex~avation with drag cutters
(i.e., cutters that operate with a scraping action, like saw
teeth). The invention is particularly applicable to excavation
of soft to medium non-abrasive materials such as coal, potash,
or trona, and even such materials as oil shale which, although of
moderate compressive strength, are~non-ahrasiv~.
Summary of the Invention
.
The invention provides for improved excavation with
efficient use of power and low cutter wear. In preferred embodi-
ments a large fraction (preferably at least 2/3~ of the material
being excavated is broken out in large pieces, rather than being
sawed or crushed. Existing openings can be enlarged, or new
openings cut. The same device can be used to repeatedly enlarge
an opening on successive passes, and can even be adjusted during
operation to following varying seam heights. Cutter velocity,
noise, and fines generation are all low.
In general the invention features a core extending along
an axis, a bit carrier supported on the core, cutter bits supported
~0 by the carriex along a three dimensional spiral having a constant
pitch P and increasing radius along at least a portion of the axis,
the carrier being relieved to provide radially extending spaces be-
tween the turns of the spiral, a frame supporting the core, carrier,
and bits for rotation about and advance along the axis, a drive to
provide rotation and advance at the rate of one pitch P per revolu-
tion, and means including bits for cutting in the material to be ex-
cavated a slot of depth that increases with the advance, while leav-
ing between portions of the slot and extending into the spaces, to
be subsequently broken away, the major portion of the material to
be excavated. In preferred embodiments, the bits are arranged
in a single spiral; the carrier is relieved at least to a depth
having a predetermined radial spacing from the axis along all
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said portion of the axis to permit the material to extend into
the spaces to said depth all along said portion without being
broken away; each bit is wider than the carrier in the direction
transverse to the bit's instantaneous direction of motion in
operation, to permit the carrier to extend into the slot; the
carrier is relieved to the core along said axis portion, and the
core is of constant cross-section along said axis portion,
to permit thef~aterial to extend into the spaces to a constant
depth therealong; the pitch is at least 3 times as great as the
width of the bits, where the width of a bit is taken in the
direction transverse to its instantaneous direction of motion in
operation; the radial distance between the core and the bits at
the maximum radius portion of the carrier is at least 3 times as
great as the width of the bits; means are carried by the core to
break away the material extending into ~he spaces, the means com-
prising in some embodiments cutting edges mounted on a continua-
tion of the carrier to make a generally cylindrical cut transverse
to the slot, and in other embodiments an arcuate wedge mounted on a
continuation of the carrier; at least some of the bits having cut-
ting edges at an angle (opening away from the direction of theadvance) to a line perpendicular to the instantaneous direction
of motion of the respective bit, to produce a reaction force of
the material against the cutting edges having a component in
thè direction of the advance to propel the device along the
axis, the angle preferably being greater than the mean
value of the helix angles of the respective paths followed by
the bits in operation; multiple cores with their respective
carriers and bits are mounted in a common framework with
counter-rotation to balance tor~ue or horizontal or vertical
reaction forces, the framework preferably being adjustable for
varying the spacing between the cores; boring means are carried
by the device forward of the~bits to bore a hole in solid
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material to admit the core, and a system is provided for forcing
flushing fluid through the core to the boring means to flush
the material removed thereby; and the material extending into the
spaces and broken away has at l~ast twice the volume of the
material cut by the bits to form the slots.
The invention also features supporting a plurality of
the above cutting elements in an array sloping along a plane
with their respective axes parallel to each other, the plane slop-
ing in a direction transverse to the axes, the axes being spaced
along the plane in the direction of slope, the elements having their
drives arranged so that each core, carrier, and bit assembly ro-
tates clockwise when viewed along its axis with the plane sloping
upwardly toward the right. In preferred embodiments the elements
are staggered along the direction of the axes so that cuttings
produced by one element do not drop on another element, and
upper and lower support vehicles are provided at the upper and
lower ends of the support means.
Other advantayes and features of the invention will be
apparent from the description and drawings herein of a preferred
embodiment thereof.
Brief Description of the Drawings
_
Fig. 1 is a partially schematic top view with the
~aterial being excavated shown in section;
Fig. 2 is a rear view of an assembly of two of the
elements of Fig. 1;
Fig. 3 is a rear view of an assembly of four of the
elements of Fig. 1;
Fig. 4 is a perspective view of the embodiment of
Fig. l;
Fig. 5 is a fragmentary view similar to a portion of
Fig. 4 but showing another embodiment;
Fig. 6 is a view similar to Fig. 5 showing yet another
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embodiment;
Fig. 7 is a detailed view of an individual cutter bit and
the adjacent portion of the carrying web, looking radially
inwardly;
Fig. 7a is a vector diagram illustrating instantaneous
tooth motion;
Fig. 8 is a side view of the tooth of Fig. 7;
Figs. 9-10 correspond respectively to Figs. 7-8 and
show another embodiment;
Fig. 11 is a partially-sectioned view o~ another embodi-
ment of a screw element; and
Fig. 12 is a rear view of an assembly o four of the
elements of Fig. 11;
Fig. 13 is an end view of an assembly of four of the
elements of Fig. 1 embodying the invention;
Fig. 14 is a perspective view of the assembly o Fig. 13.
Description of the Preferred Embodiment
The basic mining element is a screw-like, tapered saw
as illustrated in Figure 1. The spiral saw assemhly 108 con-
sist~ of a bit carrier in the form of a three-dimensional spiral
web 110 of constant pitch P mounted on a central cyli~drical
core 112. The outer radius of web 110 increases monotonically
from the leading end 114 to a maximum at 116 near the trailing
end, and from that point rearward the web radius remains con-
stant. The outer edge of web 110 is equipped with a plurality
of cutter bits or teeth 118 arranged to cut into the rock 50.
Teeth 118 are wider than the thickness of web 110 (in the direc-
tion transverse to the instantaneous direction of the movement of
the bits in operation) and thus cut spiral slot 120, wider than
web 110 in rock 50 so that upon rotation of core 112 and web 110,
the latter does not rub against the sides of slot 120. In
operation the assembly 108 advances parallel to core axis 113
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exactly one p~tch P for each revolution. As illustrated in
Figure 1, assembly 108 engages rock 50 along one side only and
although slot 120 appears to be several slots, it is actually
segments of a single slot, like a screw thread, which has been
interrupted by the absence of rock on the opposite side of
assembly 108.
Core 112 is at its forward end supported for rotation
by bearing 122 in frame 124, and at its rearward end by bearin~
126, also in frame 124. Rearward shaftsextension 127 extends
through bearing 126 to be driven by motorized drive assembly 128
(e.g., hydraulic, using fluid supplied through suitable hoses,
not shown) attached to frame 124.
Figure 2 illustrates a pair of assemblies 108, 208
mounted on frame 124~ The right hana assembly 108 corresponds
to that of Figure 1, while the left hand assembly 208 is its
mirror image, with 200 series numbers identifying points corres-
ponding to those of the 100 series in 108. Note that assembly
108 rotates clockwise while assembly 208 rotates counterclock-
wise--the counter rotation being for the purpose of cancelling
net torque on the overall assembly. This device excavates rock
from both~-side walls of opening 40, moving original right hand
wall 52 (see also Figure 1) to 54, and left hand wall 252 to 254.
Material between surfaces 52 and 54 and 252 and 254 falls to the
floor to be picked up by.ianother device (not shown).
Figure 3 shows four rotatable assemblies of the type
described above, carried on frame 124. In this device the screws
on opposite sides are~counter-rotated as in Figure 2, and screws
on the same side are also count~r-rotated to cancel any net verti-
cal force on the overall assembly. An uncut web of rock 56 and
256 is left between the screw~ on each side, to be broken off by
auxiliary means (not shown). Frame 124 is adjustable to allow
variation of the vertical space between the screws on each side,
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and hence the thickness of webs 56 and 256; thus, the overall
assembly can be used to excavate to variable overall heights,
e.g., for excavation of seams of various thicknesses. Variation
of the width of frame 124 permits excavation of openings 40 of
variable width, usually in multiple passes from an initial
narrow opening to the maximum width (for mining applications)
permitted by roof stability limita~ions.
Teeth 118 cut spaced sections of slot 120, leaving
therebetween rock webs 58 which, because carrier web 110 is
relieved all the way to core 112, extend into the spaces between
the carrier turns all along the spira~. Cylindrical section 130
of assembly 108 is arranged to break out~ithese "quarter moon"
shaped webs. In one configuration (Figs. 1, 4) the cylindrical
extension of web 110 is e~uipped with a rearward extending wedge-
shaped protrusion 132 which in turn is tipped with teeth 134.
Upon rotation of core 112 and web 110, protrusion 132 enters
slot 120, cutting and wedging rearwardly into rock web 58, with
the result that a crack 60 appears, and rock web 58 breaks off,
creating new rock surface 54.
Figure S, illustrates an alternate construction fox
excavating weak material such as coal: a simple wedge 136 is
shown without teeth. Figure 6 illustrates still another con-
struction: a cylindrical (i.e., not wedge section like 132) saw
138 equipped with teeth 139 for sawing out rock web 58 and, op-
tionally, a ramp surace 140 on!~web 110 to assist by bending
rock web 58 to the rear.
In the devices described thus far elements have cut an
interrupted thread against one side only of an existing opening--
hence each cutting tooth 118 enters and leaves slot 120 once per
revolution. Upon leaving slot 120, each tooth 118 thus has a
chance to discharge its load of cuttings picked up in deepening
slot 120.
07~38~32
Figure 11 illustrates a device capable of completely
excavating its own hole. Parts corresponding to those of the 100
series in Figure 1 are numbered in the 300 series in Figure 11.
Cylindrical core 312 is hollow and carries spiral web 310 which
in turn is tipped with teeth 318. The forward portion of web 310
is tapered while rearward portion 330 is cylindrical in outer
diameter. Rearward web portion 330 is equipped with rearward
pr~truding wedge 336 ~see Fig. 5) to break formation left between
slots to the rear. Cylindrical core 312 contains hollow shaft
368 which is connect~d at its leading end, and the leading end
of core 312, to an auger head 370 equipped with teeth 372. Shaft
368 is xotated ~by means not shown) so that head 370 can auger
hole 374 in formation 350 as the assembly advances ~from left to
right in Fig. 11). The diameter of hole 374 is sufficient to
clear cylindrical core elemént 312 with sufficient space to permit
cuttings flow in annular spaces 376 between hole 374 and core 312.
In operation core 312 and web 310 rotate (in the same or opposite
direction as head 370) at a much slower speed than head 370.
One means for rearward flushing of cuttings is to force
fluid (~ypically water) in through hole 380 in core 312 (or
hole 378 in shaft 368 or both) to enter the hole through orifices
(not shown) in cutter head 370. This fluid then picks up cuttings
from the excavation of hole 374 and flows rearwardly in annulus
37`6. Cuttings produced by teeth 318 are also picked up by this
rearward flow. To enhance the flushing of cuttings from teeth
318 (deep in a spiral slot 320 (not shown)) radial holes 382 in
web 310, communicating with inflowing fluid inside core 312, can
carry flushing fluid directly to the teeth 318.
Figure 11 i~lustrates another flushing system. Fluid
(water) enters from line 384 into non-rotating gland 386, around
core 312. Seals 388 and 389 rotatingly seal against core 312.
Fluid enters annular space 380 inside core 312 through radial
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ports 390. This inflow enters the region around head 370 just asbefore (including some radial outflow through holes 3821. Some
flows rearward in annulus 376, while some flows rearward through
hollow shaft 368 (through bore 378).
The entir~ rotating assembly is carried in bearings
(only one is shown) 326 in frame 324. Frame 324 is sufficiently
distant fxom splitter 336 to avoid jamming of excavated material
therebetween.
An assembly of four elements of the Figure 11 type is
shown schematically in Figure 12. Separate elements 308 are
counter-rotated as in Figure 3, for the s~ne reason. All four
elem~nts are mounted on a single frame 324~ Unexcavated material
between elements, as at 394, may be trimmed from surrounding
formation by trimmer means (e.g., chain saws) shown schematically
as at 3g6. Unexcavated material in the center 398 is unsupported
and will fall to the floor easily. Note that the elements ex-
cavate all material within their circular cross-qe~tions by
augering a relatively small center portion, spirally slitting
the remaining material, and breaking out the slit material to
the xearO The operation of such an assembly of four elements is
relatively slow, permitting ample time for rearward flushing
of directly excavated (i.e., pilot hole 374 and spiral slot 320)
material. For example, four elements assembled to mine a 6 by
7 foot heading in coal at 6 tons per minute would advance at
about 5.6 feet per minute~ Assuming a 6 inch screw pitch ta
reasonable value for coal) the rotational speed of each screw
element would be only 11.2 rpm. Tip speed on 3 foot diameter
screws would be only 106 feet per minute--far less than typical
~lushing fluid velocities.
Figure~7 shows in detail an individual cutter tooth 118
and the adjacent local portion of web 110. The instantaneous
path of the tooth 118 is shown as the sides 120' and 120'' of
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slot 120 illustrated in previous Figures. As shown in Figure 7a,
a development of the moti~n of a single tooth 118 duriny one -
revolution of the spiral saw assembly 108 consists of a com-
ponent P (the screw pitch) in the direction of the assembly axis
113, and a circumferential component equal to 2~R, where R is
the local radius from axis 113 to the tip of the tooth 118. The
resultant motion describes a helix at angle ~ with the tangential
direction where
tan ~ = P
2~R
For example, for a tooth at the rear of a 2-foot radius unit
having a 6-inch pitch, thP helix angle would be
tan ~2 = 2 x 3 14 x 2
~2 = 2.3
For another tooth further forward on the same unit,,say at a
radius of l-foot, the local helix angle would be
tan ~ 2-x 3 14 x
' ~1 = 4.5
Note that, whatever the local radius R, the pitch P is the same
for all teeth on a given unit; hence helix angle Q varies with
radius.
Returning to Figure 7 a "square" tooth having a face 119
at 90 to the instantaneous tooth path is illustrated. Figure 8
shows the side of tooth 118 and web 110. Line 120''' indicates
the constant radius depth of groove 120 produced by this particu-
lar tooth 118 as the assembly rotates about tand advances along)
axis 113. Note that the groove depth 120'''' ahead of this tooth
left by a preceding tooth at lesser radius, is less and that the
30 illustrat~ ~ooth increases the groove 120 depth by a constant ~ '
increment ~, in saw-like fashion. Figure 8 also illustrates a
1~78i5 1 3~
tooth "rake angle" ~ (which is illustrated in the conventional
"positive" form but which may advantageously be "negative" for
some materials) and "relief angle" ~, both in keeping with con-
ventional practice (and to avoid interference with curved sur-
face 120'''').
The motion of the square tooth 118 in the helical
direction is resisted by force F which is generated by the
material (of thickness ~) removed by this tooth~ In general, for
a square tooth as illustrated (or for any other tooth form sym-
metric about the tooth central plane 121), the force F will beparallel to and opposite to the direction of instantaneous motion
of tooth 1180 In particular, this resistive force F will have ~;
a rearward axially directed component which must be overcome by
the mechanism driving the tooth 118. For the plurality of teeth
118 in contact with the rock, then, a net forward force must be
provided to propel assembly 108 forward as it rotates. This
force may come from an external source such as a tractive vehicle
carrying the assembly, or it may arise locally as the rearward
flank 123 of tooth 118 rubs against and follows the side 120'
groove 120. This latter operation, however, would cause excessive
wear of tooth flank 123, and it would consume excessive power.
Figure 9 illustrates a tooth 118' having a face 119'
which is skewed at angle ~ (cpening in the direction o advance
along axis 113~ relative to the "square tooth" (i.e., relative
to a line pexpendicular to the instantaneous direction of tooth
motion). In this case, resistance F' being at roughly 90 to
face 119', has a orward component if skew angle ~ is greater than
the local helix angle ~. Thus a skewed tooth face can be used
to provide an axial propelling force component, avoiding both
an external means, such as a tractive vehicle, or rubbing against
the flank of the tool. Since ~ varies with tooth radial position,
a practical design may use a ~ value that is greater than the
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maximum ~, thus providing an excess forward force component
(and resulting in rubbing on the tooth forward flank) or,
preferably, a ~ value that is greater than the mean ~ value for
all the teeth.
Preferably both pitch P and the radial distance
between the cylindrical surface o core 112 and the cutting edge
of tooth 118 at the maximum radius portion of web 110, are at
least 3 times, and most preferably at least 5 times as great as
the width of ~eeth 118 in the direction transverse to the instant-
aneous direction of tooth motion in operation. Thus, wellover 2/3 of the excavated material will be broken off in large
chunks rather than being directly sawed by the teeth~
Figures 13 and 14 show four elements 108, each with their
individual frame l24 and drive (not shown) arranged in a common
framework 200 according to the invention, to excavate on the
sloped face of an exposed coal seam. The horizontal offset
from screw to screw, with all screws rotating in the same direc-
tion (clockwise when viewed axially with the slope extending
upwardly to ~he right) as shown, provides the necessary horizontal
force to crowd the vehicle against the face, while the weight of
the machinery holds it down. The self~advancing screws of course
require no force in the traverse direction, although traverse
would in all probability be controlled by ordinary traction means
via the support vehicles 202 and 204 at the top and bottom of
the screw assembly.
Each screw is mounted to the rear of the one immediately
below in the assembly. This permits identical screw elements
~i.e., all of the same "hand") to rotate in the same direction
without clashing, and it also permits cuttings from each screw
to fall freely down the face without interfering with the lower
screw elements.
Seams of widely differing thicknesses can be accomodated
1{~7~81!~2
by varying the number of screws in an as5embly while re~aining the
convenience and economy of a single standardized screw element
design. Variations in seam thickness along the length of a single
pit are easily accomodated by simply allowing the angle of the
face slope to vary as necessary. Note also that, within reason~
curved pit plans would present no problems.
A conveyor 20~ extends the length of the pit along the
base of the coal face. Coal either falls onto or is directed onto
this conveyor, thence out to the end of the pit to another con-
veyor that delivers coal r~m the pit. The face conveyor ismoved laterally as the face recedes, as in l~ongwall mining.
The arrangement shown advantageously permits an ex-
tremely narrow pit floor. The minimum possible floor width
would be that required by the lower support vehicle, although i~
would probably be advisable to leave a slightly wider floor to
permit access by maintenance vehicles alongs-ide the conveyor.
As is apparent, the above arrangement could be used
to simultaneously excavate the opposiAg sloping forces of the
shaped pit, by moun~ing separately sloping assemblies of screw
elements side by side on a common framework.
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