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Description  |
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BACKGROUND OF THE INVENTION
The present invention relates to screw-type cutter drums for mining
machines, and more particularly to cutter drums of the type having cutter
picks carried on helical ribs on the body of the drum and additional
cutter picks on the end face of the drum adjacent the working face.
Drum cutters for mining coal, or other minerals, are known having helical
ribs on the circumferential surface of the drum body which function to
convey the coal away from the working face and which have cutter picks
mounted on their outer surfaces. Cutter picks have also been mounted on
the end of the cutter drum in a radial line and spaced at varying radial
distances from the axis, as shown, for example, in German Pat. No.
1,216,821.
Cutter drums are also known as shown, for example, in German
Gebrauchsmuster No. 1,993,515 in which cutter picks are mounted on the
circumference and surface of a mounting disc attached to the working face
end of the cutter drum. The circumference of such a mounting disc has
interruptions or gaps corresponding in position to the channels between
the helical ribs on the drum body and the radial projections between these
gaps coincide in position with the end surfaces of the helical ribs. The
cutter picks are mounted on the radial projections and the end surface of
the mounting disc and are arranged in radial rows with non-uniform radial
spacing between picks. Such an arrangement of cutter picks could, of
course, also be attached directly to the end surface of the drum and the
end surfaces of the helical ribs.
To improve pickup of the coal or other material being mined by the cutter
drum, the channels between the helical ribs should terminate at the
working face end in openings of the largest possible cross section in
order to facilitate pickup of the mined material without further breakage
and to minimize the formation of dust. This, however, results in a large
space, or circumferential distance, between the cutter picks on opposite
sides of each such opening. Since the cutter drum is continuously moved
transversely of its axis by the mining machine, the cutter picks adjacent
the openings are always required to make the deepest cuts, and smooth
operation of the cutter drum is difficult to obtain.
SUMMARY OF THE INVENTION
In accordance with the present invention, a screw-type cutter drum is
provided having cutter picks arranged on the working face end of the drum
in such a manner that in spite of the different circumferential spacing
between picks in different parts of the drum, due to the large required
area of the conveyor channels, each cutter pick always operates at the
same depth of cut.
This result is obtained in cutter drums of the general type described above
by arranging the cutter picks on the end of the drum in sets spaced apart
in correspondence with the ribs on the drum and with the picks of each set
arranged so that successive cutter picks in the direction of rotation of
the drum are angularly spaced apart at equal angles and their radial
distances from the axis decrease by a constant amount .DELTA. r' defined
by the following relation:
##EQU1##
where: V.sub.M = the rate of advance of the mining machine in meters per
minute;
n.sub.W = the cutter drum speed in RPM;
.beta. = the angle between the first cutter pick of one set and the last
cutter pick of the adjacent set;
z = the number of cutter picks in each set; and
a = the depth of cut in millimeters.
The number z of cutter picks in a set and the angle .beta. are determined
in the design of the cutter drum and depend on the dimensions of the end
face of the cutter drum, while the maximum depth of cut a is determined by
the type of cutter pick to be used. The dimension .DELTA. r' can readily
be calculated, therefore, from the rate of advance of the mining machine
V.sub.M and the cutter speed n.sub.W. If the cutter picks are arranged as
described, the depth of cut for each cutter pick will not exceed the set
dimension a, even at the maximum speed of advance of the mining machine
and in spite of the large space between adjacent picks of different sets.
This is because the first cutter pick of each set is at a substantially
smaller radial distance from the axis than the last cutter pick of the
preceding set, so that all cutter picks on the end of the drum are equally
loaded, and the pick life and the smoothness of operation of the drum are
greatly improved. The cutter picks may be mounted directly on the end
areas of the helical ribs of the cutter drum, or they may be mounted on an
end plate suitably shaped and attached to the end surface of the drum.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be more fully understood from the following detailed
description, taken in connection with the accompanying drawings, in which:
FIG. 1 is a somewhat diagrammatic side view of a cutter drum embodying the
invention, with cutter picks mounted directly on the end areas of the
helical ribs;
FIG. 2 is an end view showing the arrangement of the sets of cutter picks,
and showing them mounted on a separate end plate;
FIG. 3 is a diagram showing the components of motion of a cutter pick
moving in its circular path; and
FIG. 4 is a diagram showing the arrangement of sets of cutter picks on the
end of a cutter drum.
DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1 shows a screw-type cutter drum 1 of typical construction but with
the cutter picks arranged in accordance with the present invention. The
cutter drum 1 has a cylindrical body or drum member 2 with two helical
ribs 3 extending around the body 2 and terminating at the right-hand end
approximately 180.degree. apart. The ribs 3, as can be seen in FIG. 1,
have relatively wide channels between them which serve as conveyors for
removing the coal, or other material, from the working face which would be
at the right as seen in FIG. 1. The cutter drum is provided with cutter
picks 4 mounted in pick holders 5 attached to the outer surfaces of the
helical ribs 3. In addition, cutter picks 4 are mounted at the working
face end of the cutter drum. The cutter picks 4 on the end surface are
disposed in circumferentially-spaced sets corresponding in position to the
ribs 3, and they may be mounted directly on the end areas of the ribs
themselves, as shown in FIG. 1, or they may be mounted on a separate end
plate 6, as shown in FIG. 2, which is mounted on the end of the drum 2.
The cutter picks may be mounted on, or attached to, the cutter drum in any
desired manner and the mounting means have not been shown in detail as
they are not a part of the invention. In either case, the cutter picks 4
of each set are spaced circumferentially from each other with equal
angular spacing and are arranged with their cutting edges at different
radial distances from the axis of the drum in accordance with the relation
mentioned above and which is more fully described below.
FIG. 3 shows the path of travel of a cutter pick 4 about the axis of the
cutter drum, the position of the pick at any time being defined by its
angle .theta. with respect to the vertical or Y axis. The peripheral
speed, or cutting speed, of the pick is represented at V.sub.S and the
speed of advance of the mining machine which carries the cutter is
represented at V.sub.M and is transverse to the axis of the cutter drum.
The instantaneous components of motion of the picks 4 in the X and Y
directions, for different positions of the pick, are seen to be as
follows:
______________________________________
.phi. = 0.degree.
V.sub.X = V.sub.S + V.sub.M
V.sub.Y = 0
.phi. = 90.degree.
V.sub.X = V.sub.M V.sub.Y = V.sub.S
.phi. = 180.degree.
V.sub.X = -V.sub.S + V.sub.M
V.sub.Y = 0
.phi. = 270.degree.
V.sub.X = V.sub.M V.sub.Y = -V.sub.S
.phi. = 360.degree.
V.sub.X = V.sub.S V.sub.Y = 0
______________________________________
These limiting conditions are satisfied by the following relations for the
instantaneous components of motion:
V.sub.X = V.sub.S cos .theta. + V.sub.M (1)
v.sub.y = v.sub.s sin .theta. (2)
If S.sub.X represents the travel of the pick 4 in the X direction,
dS.sub.X /dt = V.sub.X
and from Equation (1)
dS.sub.X = (V.sub.S cos .theta. + V.sub.M) dt (3)
where .theta. is measured in angular measure (radians). Furthermore, if the
cutter diameter is D.sub.W, then
V.sub.S = D.sub.W .omega./2 where .omega. = d.theta./dt
and
V.sub.S = D.sub.W d.theta./2dt (4)
From this
dt = D.sub.W d.theta./2V.sub.S
if n.sub.W is the speed of rotation of the cutter,
V.sub.S = D.sub.W .pi. n.sub.W /10.sup.3
substituting this value of V.sub.S and integrating
t = 10.sup.3 .theta./2.pi.n.sub.W (5)
since the initial conditions are t.sub.o = 0 and .theta..sub.o = 0, the
constant of integration is also zero.
If the speed of advance V.sub.M of the mining machine is constant,
substitution of Equation (4) in Equation (3) and integration yields
dS.sub.X = (D.sub.W d.theta./2dt) cos .theta. dt + V.sub.M dt
.intg.dS.sub.X = D.sub.W /2.intg.cos .theta. d .theta. + V.sub.M .intg.dt
Performing the integration and substituting the value of t from Equation
(5) gives
S.sub.X = D.sub.W /2 sin .theta. + 10.sup.3 V.sub.M .theta./2n.sub.W
.pi.(6)
if the cutter drum diameter D.sub.W, the speed V.sub.M and the speed of
rotation n.sub.W are constant, the position of maximum depth of cut as a
function of the angle .theta. is given by
dS.sub.X /d.theta. = 0
Using the value of S.sub.X from Equation (6)
##EQU2##
If the speed V.sub.M is taken as 15 meters/minute, the cutter drum speed
as 44 rev./minute, and the diameter D.sub.W as 1600 millimeters, then from
Equation (7) the maximum depth of cut occurs when cos .theta. = -0.06782,
that is, when the angle .theta. is 93.89.degree..
Referring now to FIG. 4, which shows diagrammatically the positions of two
sets of cutter picks 4 on the end of a cutter drum which is moving to the
left and rotating as shown by the arrow, and substituting R for D.sub.W
/2, the depth of cut a is (see also FIG. 2)
a = S.sub.X - (R - .DELTA.S)
s.sub.x = a + R - .DELTA.S (8)
converting the angle .theta. to degrees, .theta. = .pi.
.theta..degree./180.degree.
and from Equation (5)
t.sub.S = 10.sup.3 .theta..sub.S.degree. /n.sub.W .multidot. 360.degree.
since .DELTA. S = V.sub.M t.sub.S,
.DELTA. s = 10.sup.3 v.sub.m.theta.s.degree. /n.sub.W .multidot.
360.degree.(9)
where .theta..sub.S must be expressed in degrees and represents the angular
movement of the cutter drum corresponding to the time t.sub.S.
From Equations (8) and (9)
##EQU3##
If .theta. = 90.degree. or .pi./2 radians and sin .theta. = 1, then from
Equation (6) for the radially innermost picks 4 of FIG. 4,
##EQU4##
In this equation r is the radius in millimeters to the point of the cutter
pick 4 in FIG. 4 and its value can be obtained by equating the right-hand
sides of Equations (10) and (11)
##EQU5##
The angle .beta. is the angle between the positions of the last pick of one
set of cutter picks and the first pick of the next set, and from FIG. 4
the angle .theta..sub.S = .beta. -90.degree.. Substituting in Equation
(12)
##EQU6##
The value of r, that is, the radius from the axis to the points of the
cutter picks 4, can be determined for given depths of cut a and for known
speeds of rotation n.sub.W and speeds of advance V.sub.M, the angle .beta.
being fixed in the design of the cutter drum.
From FIG. 4
.DELTA. r = R - r Substituting in Equation (13)
##EQU7##
If Z is the number of cutter picks in each set, the radial difference
.DELTA. r' between adjacent picks 4 and 4', or 4' and 4", is
.DELTA. r" = .DELTA.r/Z - 1 (16)
or
.DELTA. r' (Z-1) = .DELTA.r
That is, as seen in FIG. 4,
r' = r" - .DELTA.r'
r - r' - .DELTA.r'
From Equation (15), therefore,
##EQU8##
The depth of cut of the individual cutter picks is determined by the
dimension .DELTA. r' and by the speed of advance V.sub.M of the mining
machine.
If .DELTA. .theta. in degrees is the angular distance between adjacent
picks of each set, then the distance .DELTA.S is the travel of the mining
machine during the time t .sub..DELTA. .theta. required for the picks to
move through the angle .DELTA. .theta. and .DELTA..sub.S = V.sub.M t
.sub..DELTA. .theta.. Therefore (see Equation (9))
t .sub..DELTA. .theta. = 10.sup.3 .DELTA. .theta./n.sub.W .multidot.
360.degree. (18)
the depth of cut a = .DELTA.S + .DELTA.r'
or
a = V.sub.M t.sub..DELTA. .theta. + .DELTA. r/Z - 1 (19)
Substituting Equations (15) and (18) in Equation (19)
##EQU9##
From Equation (20), the depth of cut a can be calculated for a given number
of cutter picks per set, or for a known depth of cut the number of cutter
picks and angle .DELTA. .theta. are determined.
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Description |
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