Abstrict A coal crusher roll includes a smooth tubular cylindrical back-up
roll having a series of regularly spaced tapped radial holes to
receive bolts by which eight identical shell segments may be fastened
on the back-up roll. The holes at the axial ends of the segments
are undercut to provide a rabbet into which fits the tang of a special
lifting hook by which the segment can be easily handled by a lightweight
crane. A recess in the central part of the segment defined by a
peripheral berm around the backside of the segment reduces the weight
of the segment, provides a place for receiving balancing weights,
and simplifies the face fit machining for the segment with the back-up
roll.
Claims I claim:
1. A removable segment for a coal crusher having a cylindrical
back-up roll adapted to receive a plurality of said segments, said
segment comprising:
a curved metal member in the form of a sector of a cylindrical
tube having inner and outer cylindrical faces, and having teeth
formed on said outer cylindrical face;
a recess in said inner cylindrical face for weight reduction, for
simplifying the face fit of the segment on the back-up roll, and
for receiving balancing weights; said recess defined by a raised
peripheral berm on all four sides of said segment;
radial holes in said segment around the periphery thereof through
said berm for receiving bolts which thread into tapped holes in
said back-up roll for attachment of said segment to said roll, said
segment having a coaxial counterbore at said outer face for receiving
the heads of said bolts.
2. A removable segment for a coal crusher having a cylindrical
back-up roll adapted to receive a plurality of said segments, said
segment comprising; a curved metal member in the form of a sector
of a cylindrical tube having inner and outer cylindrical faces,
and having teeth formed on said outer cylindrical face;
a recess in said inner cylindrical face for weight reduction, for
simplifying the face fit of the segment on the back-up roll, and
for receiving balancing weights; said recess defined by a raised
peripheral berm on all four sides of said segment;
radial holes in said segment around the periphery thereof through
said berm for receiving bolts which thread into tapped holes in
said back-up roll for attachment of said segment to said roll, said
segment having a coaxial counterbore at said outer face for receiving
the heads of said bolts, and at least two rabbets in said inner
face where at least two of said holes open in said inner face, said
rabbets in said two holes facing in opposite directions so as to
be engaged by hooks inserted through said two holes and used to
lift said segment.
3. The segment defined in claim 1 further comprising a substantially
central circumferentially extending berm connecting the sections
of said peripheral berm on exially extending leading and lagging
edges of said segment, said peripheral and central berms being configured
to lie flush against said back-up roll said connecting berm also
including radial holes for receiving bolts which thread into tapped
holes in said back-up roll.
4. The segment defined in claim 3 wherein the berm on one axial
end of said segment is substantially wider than the berm on the
other axial end of said segment, and said recess is divided into
two substantially equally sized substantially square recesses by
said central berm, said segment subtending an angle of 90.degree.
whereby the breaker roll made by said segments and said back-up
roll may be dynamically balanced.
5. A removal shell segment for a back-up roll of a coal crusher,
comprising:
a curved metal member in the shape of a sector of a cylindrical
tube having a concave face on the inside, facing toward said back-up
roll when mounted thereon, and a convex face on the outside, facing
aay form said back-up roll when mounted thereon;
a plurality of radial holes in said member for receiving fasteners
by which said member may be fastened to said back-up roll;
at least one recess in said concave face defined by an axially
extending raised berm along each leading and lagging axially extending
edge of said member and a circumferentially extending berm along
each circumferentially extending edge of said member;
said holes extending through said berms and opening on said convex
face in cylindrical counterbores;
at least four of said holes being through said circumferentially
extending berms at the axial ends of said member, said end holes
having means at the opening thereof in said concave face defining
a rabbet extending from said hole toward the adjacent circumferentially
extending edge;
said four end holes being aligned in two circumferentially extending
end columns adjacent the axial end edges of said member, said columns
being spaced from their adjacent edges a combined axial distance
equal to 1/4 the axial distance between said columns.
6. A removable segment for a coal crusher having a cylindrical
back-up roll adapted to receive a plurality of said segments, said
segment comprising:
a curved metal member in the form of a sector of a cylindrical
tube having inner and outer cylindrical faces, and having teeth
formed on said outer cylindrical face;
a recess in said inner cylindrical face for weight reduction, and
for simplifying the face fit of the segment on the back-up roll,
said recess defined by a raised peripheral berm on all four sides
of said segment;
radial holes in said segment around the periphery thereof through
said berm for receiving bolts which thread into tapped holes in
said back-up roll for attachment of said segment to said roll, said
segment having a coaxial counterbore at said outer face for receiving
the heads of said bolts.
Description Coal crushers have been available and in use for many years for
breaking coal into small pieces suitable for handling and burning.
The best crushers available are capable of breaking the coal into
precisely the desired range of particle sizes which are best for
the particular application such as pipeline transportation or particular
coal preparation plants. The breaking of the coal into precisely
desired sizes is done by passing the coal between two crusher rolls
which have intermeshing teeth which are spaced apart a certain distance
axially and circumferentially so that the coal is broken to the
desired size, with minimal production of "fines."
After a period of use, the chisel teeth on the crusher rolls wear
down to the extent that the coal pieces passing through the crusher
exceed the desired size. When this happens, it is necessary to correct
the situation either by building up the teeth on the crusher rolls
by welding or by replacing the rolls altogether. In either case,
it is necessary to remove the roll and replace it with a new or
repaired roll while the worn roll is being repaired or replaced.
Removal of the roll from the coal crusher necessitates that the
crusher be taken out of service while the rolls are being replaced.
It is therefore desirable that the roll replacement process be as
fast as possible to reduce the amount of time that the coal crusher
is out of service. However, coal crusher rolls are extremely large
and heavy, especially for large, efficient machines, and the process
of removing a roll is a lengthy one. It requires the disassembly
and/or disconnection of the roll bearings and the drive mechanism
and requires very careful and precise manipulation of the large
heavy roll by a large crane. Because of the size and mass of the
roll, the process of removing a roll must be done with great care
to prevent damage to surrounding equipment, to the roll itself,
and to the workers in the vicinity. The replacement of the roll
is just as difficult and ticklish a business as the removal of the
roll and the entire roll replacement process could take several
days. In the time that this work is under way, the coal crusher
is out of operation with resulting economic loss and loss of production.
It has been proposed in the past to make coal crushers with removable
roll segments. The removable roll segments of the prior art have
suffered from numerous disadvantages which have retarded their acceptance
by the industry. One problem is the achieving of a close face fit
between the roll segment and the roll on which it is mounted. Unless
this face fit is extremely precise, the cyclic forces on the roll
segment can cause it to fret and abrade the roll on which it is
mounted and can also cause fatigue of the fasteners by which the
segment is attached to the roll. The prior art has attempted to
solve that problem by various strategems, such as zinc coating and
precision machining, but these strategems are expensive and not
always successful.
Because of the extreme vibration encountered in a coal crusher,
the fasteners which hold the segments to the roll must be extremely
resistant to becoming loose under vibration. This problem has been
recognized in the past and has been approached by using lock nuts
on the attachment bolts to lock the nut in place, by cotter pins
through the end of the bolt or other similar techniques. These are
undesirable because of the greatly increased time required to secure
the fastener and also because, while these techniques prevent the
attachment bolts from falling out of the machine altogether, they
do not always prevent them from becoming loose. The loose bolts
are useless to hold the segment in place and allow it to flex and
fret against the support roll.
Prior art coal crushers with removable segments have utilized ribs
or splines in the backside of the segment which fit into corresponding
grooves running axially along the roll face to prevent circumferential
forces exerted on the segments during crushing from shearing the
attachment bolts. The cost of special machining in the support roll
and corresponding difficulties in ensuring the correct placement
and size of the ribs in the segment casting has greatly increased
the cost of the removable segment system, but it or some variant
of this scheme for carrying circumferential stresses has usually
been considered necessary because the shearing of the attachment
bolts on the segments can result in catastrophic failure of the
crusher and require replacement of the entire crusher.
SUMMARY OF THE INVENTION
Accordingly, it is an object of this invention to provide a roll
for a coal crusher having removable segments which are easily and
quickly removed and replaced without removal of the crusher roll
from the machine.
It is another object of this invention to provide a segment for
a coal crusher roll which is inexpensive to produce but reduces
or eliminates circumferential shear forces from acting on the attachment
bolts.
It is another object of this invention to provide a segment for
a coal crusher roll which has an attachment which locks into a receptacle
on the segment which is protected from wear in use.
It is a further object of this invention to provide a segment for
a crusher roll having a reduced weight, a simplified system for
ensuring a precise face fit to the support roll, and a simple and
effective means for balancing the crusher roll.
It is yet another object of this invention to provide a removable
segment suitable for use in roll crushers generally suitable to
crush hard or rock-like materials which are equivalent to coal,
for example, coke, stone or ores or other material that may be crushed
by means of a roll crusher.
The objects of the invention are attained in the preferred embodiment
of a coal crusher roll having a smooth tubular cylindrical backup
roll having a series of regularly spaced radial holes drilled through
the roll and tapped to receive bolts. A series of identical segments
may be mounted on the back-up roll with machine screws provided
on their threads with an anaerobic adhesive. The segments are provided
with counterbored holes which align with the holes in the back-up
roll to receive the screws and attach the segments to the roll.
The holes at the axial ends of the segments are undercut to provide
rabbets that enable special lifting hooks to be placed in the bolt
holes while the segment is still fastened to the back-up roll with
the other bolts. The lifting hook enables the segment to be easily
handled by a lightweight crane, and the undercut rabbet and tang
arrangement makes it possible to insert or remove the hooks when
the segment is attached to the backup rolls so that the segment
may be supported by the hooks while the bolts are being removed,
and may also be maneuvered into position and bolted in place without
first removing the hooks. A recess in the central part of the segment
defined by a peripheral berm around the backside of the segment
reduces the weight of the segment, provides a place for receiving
balancing weights, and simplifies the face fit machining or casting
for the segment with the backup roll. The peripheral berm also reduces
the surface area contact with the back-up roll so that the force
exerted by the attachment screws is concentrated over a smaller
area and, therefore, the pressure between the segment and the back-up
roll in the region of the attachment bolts is much greater than
would otherwise be the case, thereby providing a greater force to
resist the circumferential force exerted on the segment in use so
that the attachment bolts are subjected to a reduced shear force.
DESCRIPTION OF THE DRAWINGS
The invention and its many attendant objects and advantages will
be better understood upon reading the following description of the
preferred embodiment in conjunction with the following drawings,
wherein.
FIG. 1 is a perspective view of a crusher roll made in accordance
with this invention showing one segment attached to the roll and
a second segment being removed by the special lifting hooks made
for this purpose;
FIG. 2 is a sectional elevation of the back-up roll for the crusher
roll shown in FIG. 1;
FIG. 3 is a plan view of one of the segments shown in FIG. 1;
FIG. 4 is a sectional elevation of two meshing segments of the
type shown in FIG. 2;
FIG. 5 is a perspective view of the backside of the segment shown
in FIGS. 3 and 4; and
FIG. 6 is a perspective view of the lifting hook shown in FIG.
1.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the drawings wherein like reference numerals identify
identical or corresponding parts, and more particularly to FIGS.
1 and 2 thereof, the back-up roll 10 for the crusher roll illustrated
is shown as a cylindrical tube 12 through which are drilled a series
of regularly spaced holes 14. The placement of the holes 14 in the
back-up roll will be explained in particular in connection with
a description of removable segments 16 which are fastened by bolts
18 to the back-up roll 10. It will be understood from the following
detailed description of the present invention that the terms coal
crusher, breaker roll and coal crusher roll used herein refer not
only to coal crushers, but include equivalent crusher or breaker
apparatus suitable for use in the crushing of hard or rock-like
materials which are similar to coal, for example, coke, stone or
other ores or material that may be crushed by means of a roll crusher.
As shown in FIG. 2 each end of the cylindrical tube 12 has two
annular recesses machined into the end of the tube. An inner recess
20 is machined to receive an inner end rim 22 of a hub 24. An outer
recess 26 cooperates with a corresponding recess 28 in the rim 22
of the hub 24 to provide an annular groove 30 in which the hub can
be securely welded to the cylindrical tube 12. The outer end of
the hub 24 is provided with peripheral flange 32 by which the hub
can be attached to a suitable bearing and drive structure. A series
of longitudinal vanes or flutes 34 is provided between the rim 22
and the outer flange 32 for additional strength of the hub 24.
A series of radial stiffeners 36 (two being shown in FIG. 2) in
the form of heavy annular rings is provided at approximately 1/3
the length of the tube inside and are welded in place by a peripheral
weld. A diagonal bar 38 is welded across each end of the cylindrical
tube 10 primarily for ease of handling during manufacturing. The
ends of the tube are radially supported by the solid end of the
hub 24 and the radial stiffeners 36 support the tube at the 1/3
positions. The tube itself is extremely strong because it does not
have grooves or other configurations cut into it for circumferential
support of the segments and, therefore, it does not suffer from
the stress peaking problems which such configurations could cause
in a tubular back-up roll. Accordingly, the crusher roll of this
invention provides exceptional strength without undue weight.
Turning now to FIG. 3 a removable segment 16 for the inventive
crusher roll is shown having a series of chisel teeth 40 arranged
in ten columns of six teeth each. The teeth in adjacent rows are
staggered 1/2 pitch so that each tooth 40 is axially aligned with
the space between two teeth in the adjacent columns. Five of the
columns have six complete teeth and the other five columns have
five complete teeth and two partial teeth. As shown, for example,
in the second column from the left-hand edge in FIG. 3 and more
particularly as shown in the same column in FIG. 1 the partial
teeth along the leading circumferential edge 42 match up to the
partial teeth along the trailing circumferential edge 44 of the
adjacent segment to form a complete tooth 40. This preserves the
circumferential spacing between all of the teeth on the breaker
roll and prevents voids while making it possible to have the leading
and lagging circumferential edges be straight.
The axial space 46 between the centerlines of adjacent columns
of teeth 40 is equal to about three times the axial thickness 47
of the teeth. In use, the breaker roll of the coal crusher is placed
parallel to and horizontally spaced from another breaker roll and
positioned so that the teeth of the other breaker roll are positioned
exactly in the center of the spaces 46 between the teeth in this
breaker roll, and vice versa. The breaker rolls are mounted in the
machine so that the horizontal spacing between them is adjustable.
By adjusting the horizontal distance between the two breaker rolls,
it is possible to control the size of the particles of the output
coal stream.
The sum of the distances A+B between the centerline of the column
of teeth adjacent each circumferential edge of the segment and the
circumferential edge of the segment itself is equal to the axial
spacing 46 between adjacent columns of teeth on the segment. In
this way, the segments, when attached to the back-up roll 10 will
continue the same spacing between adjacent columns of teeth as exist
in each segment individually.
Nine holes are drilled in the segment in a uniform pattern as shown.
The holes are in the form of three circumferentially aligned columns
and three axially aligned rows. The sum (C+D) of the distance (C)
between the right-hand column of holes and the right-hand circumferential
edge of the segment, plus the distance (D) between the left-hand
column of holes and the left-hand circumferential edge of the segment
is equal to 1/4 of the distance between the right and left columns
of holes and is equal to 1/2 the distance between adjacent columns
of holes. The spacing of the holes may also be described by referring
to the back-up roll 12 as a cylinder having a circumference, and
each curved segment 16 as comprising a quarter of that circumference.
The aforementioned nine holes may be referred to as being arrayed
in three axially extending rows, comprising a top row adjacent edge
42 a center row and a bottom row, adjacent edge 44. The center
row is spaced about 30.degree. each from the adjacent top and bottom
rows. The top and bottom rows are each spaced about 15.degree. from
the adjacent edges 42 and 44 respectively, of the segment 16. The
purpose of this hole spacing is as follows:
1. Once the back-up rolls are mounted in the machine, there is
only one possible way of mounting the segments. It is impossible
to mount the segments on the rolls backwards or so that the teeth
would interfere because the segments then would be shifted axially
with respect to the backup roll and it would be obvious that they
were being put on incorrectly.
2. It provides an ideal spacing for the holes on the segment so
that they are near, but not too near, the edges of the segment,
and the two center columns of holes in the back-up roll are not
so close together to weaken the back-up roll.
3. A single segment can be used for all positions on both back-up
rolls in the machine and identical back-up rolls can be used in
both positions in the crusher, just switched end-forend. The holes
in the backup rolls are positioned to ensure that the segments are
aligned with the axial ends of the back-up roll and the 1/2 spacing
of the two center columns of holes in the roll ensures that the
teeth on the other roll will be exactly aligned between the teeth
on the first roll when the second roll is switched end for end with
the first roll.
Each of the holes in the two end columns is provided with a special
rabbet 52 where the hole opens on the inside face 54 of the segment
16. The rabbet 52 is formed by counterboring the holes 50 where
they open in the inner face 54 of the removable segment 16. The
counterboring is done with a cutting tool having the same diameter
as the holes 50 but on a centerline which is shifted at least about
1/2 of the radius of the holes 50 in the outward axial direction
only to ensure that the lifting hook will be inserted properly with
the hook tang facing outwardly. This produces an elongated rabbet
having a width equal to the diameter of the holes 50.
A lifting hook 60 most clearly shown in FIG. 6 includes a top
end ring 62 and a bottom end tang 64 at opposite ends of a hook
body 66. In use, two or four of the hooks will be used to manipulate
the segment, two being used as shown in FIG. 1. The orientation
of the hook shown in FIG. 1 will be used to give positional names
to the parts of the hook. For example, in use the end ring will
be facing upward and therefore will be called the top end ring,
and the tang 64 will be at the bottom end and therefore is called
the bottom end tang. The center of the top end ring is displaced
from the centerline of the hook body 66 toward the center or inside
of the segment when the hook is in use and therefore the edge of
the hook toward which the ring is displaced will be called the inside
edge, and the opposite edge will be called the outside edge.
As shown most clearly in FIG. 6 the inside edge of the hook 60
is aligned with the center of the top end ring 62 and the outside
edge of the hook body 66 is tangent to the hole in the top end ring
62. This ensures that the stress lines at the outside portion of
the end ring 62 will be smooth and continuous with no discontinuities
for maximum strength of the ring. The lifting hook 60 may be a one
piece forging or may be cast or flame cut.
The hook body 66 flares smoothly down to a rounded rectangular
base portion 68. A notch 70 is formed in the base portion to provide
a ledge 72 which engages the shoulder formed by the counterbore
of the counterbored holes 50. The tang 64 projects outwardly in
the direction opposite from the offset of the end ring 62. The tang
64 is rounded with a radius of curvature approximately equal to
the radius of curvature of the rabbet s it fits neatly into the
rabbet 52 and the ledge 72 of the notch 70 engages the shoulder
of the top counterbore of the holes 50. When the cable shown in
FIG. 1 exerts an inward and upward pull on the end ring 62 the
tang 64 and the shoulder 72 lock securely in place in the counterbored
hole 50 to secure the lifting hook in place until the cables are
removed. Only by tilting the hook in the same direction in which
it was tilted to insert the hook in the counterbored hole 50 may
the lifting hook 60 be removed from the hole.
The inner face 54 of the removable segment 16 is provided with
a circumferential peripheral berm 74 along both circumferential
edges of the segment, and an axial peripheral berm 76 along both
leading and lagging axial edges 42 and 44 of the segment. In addition,
a central berm 78 is provided parallel to the circumferential berms
74 and connecting the leading and lagging axial berms 76. Two square
recesses 80 are defined between the berms. The recesses 80 provide
a means for reducing the metal content of the segment and thereby
reducing its weight and cost, and also they provide a receptacle
for placing balancing weights between the segments and back-up roll
to ensure that the breaker rolls will be balanced in use so as not
to exert undue unbalanced forces on the bearings and run smoothly
with minimal vibration.
The berms are radially aligned with the counterbored holes 50 in
the segment and provide a means for securely fastening the segment
to the back-up roll 10. When the screws are passed through the holes
50 and are threaded tightly into the threaded holes 14 in the back-up
roll, they exert an enormous force on the segment against the back-up
roll. Because of the relatively restricted size of the berm, this
force is carried entirely by a relatively small area and consequently
the pressure at the interface between the berm and the back-up roll
is enormous. Since the segment is harder material than the back-up
roll, the microscopic strain tends to embed the berm of the segment
slightly into the surface of the back-up roll or to closely interengage
the surface aspirities of the facing surfaces of the berms and the
back-up roll so that the frictional force, which is very great in
any case, is actually increased because of the embedding or interengaging
effect. The result is that the frictional force between the segment
and the back-up roll is so great that the circumferential forces
acting on the segment during the crushing process are largely carried
by this frictional force so that little or no shear forces are exerted
on the bolts.
In operation, lifting hooks are placed in the outer circumferential
columns of holes at both ends of the segment and the top end rings
62 of each of the lifting hooks 60 ar connected by cables 82 only
slightly longer than the segment. This ensures that a strong axial
force will be exerted on each hook to securely lock it in place
and prevent accidental disengagement.
The cables 82 are connected in the middle by a ring 84 and lifted
from the ring 84 by a crane. The segment is lifted by the crane
into position on the back-up roll 10 and is secured in position
by two or more screws while it is supported by the hooks. Once attached,
the listing force is relieved and the hooks 60 may be removed by
merely tilting them outward away from each other and lifting them
clear of the hole 50. Each of the other segments is similarly secured
in position. While the segments are being attached to the backup
roll, it is held in angular position against rotation which would
occur because of massive unbalance when some but not all of the
segments are attached to the roll.
When all of the segments are attached, the roll is turned freely
and, if it is unbalanced, a set of test weights is attached by the
screws 18 until the approximate balance is achieved. Then the segments
where the weights are to be attached are removed and the weights
are placed in the recesses 80. A convenient form of balance weight
is a curved plate equal or slightly smaller in size to the recesses
80 so that the plate need merely be placed and fastened in position.
Once the balance weights have been placed, all of the bolts are
coated with an anaerobic adhesive such as Locktite 277 and are threaded
into position. The bolts are then torqued down firmly to provide
the required radial force. Eight hundred foot pounds of torque or
greater on a 11/2 inch screw with six threads per inch has been
found to exert a sufficient radial force on nine equally spaced
positions on a 420 pound segment to hold it securely in position.
Obviously, numerous modifications and variations of the above-identified
invention will occur to those skilled in the art in light of this
disclosure. For example, it will be understood that the present
invention is not limited to use with coal crushers but will be suitable
for use in roll crushers generally suited to crush hard or rock-like
materials which are equivalent to coal, such as, coke, stone, or
other ores or material that may be crushed by means of a roll crusher.
Accordingly, it is expressly to be understood that these modifications
and variations and the equivalents thereof may be practiced while
remaining within the spirit and scope of the invention as defined
by the following claims. |