Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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SHELL LINER ASSEMBLY
Technical Field
The invention relates generally to ore pro-
cessing, and is specifically directed to an improved
liner assembly for the cylindrical shell of an ore
grinding machine.
Background of the Invention
Ore grinding or comminuting machines have long
been used to reduce the size of ore fragments to small
particles for further processing.
One type of commonly used machine comprises a
cylindrical shell in which ore particles enter through
an opening in one axial end and reduced particles are
discharged from the opposite end. Comminution occurs by
rotating the shell, causing the ore fragments to tumble
on one another, resulting in grinding and a reduction in
size.
Typically, the inner cylindrical surface of
the shell is lined with a plurality of thick liner
segments that cover substantially the entire shell sur-
face. The exposed grinding surface of the liner
assembly is configured to carry the ore fragments
upwardly as the shell rotates, causing them to tumble
back into the charge of ore fragments, resulting in
comminution.
It is well established that, in any rotary
grinding mill, a portion of the tumbling charge of ore
fragments consists of a relatively inactive region that
is generally kidney shaped. In the "kidney", there is
very little movement of the particulate matter, and as
a result, very little useful grinding takes place.
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The size of the "kidney" is dependent on a
number of factors including shell diameter, to what
extent the mill is filled, rotational velocity of the
shell, liner configuration, ball size (if balls are used
to assist in comminution) and percent moisture in the
ore charge. However, in any tumbling charge of ore par-
ticles, a kidney exists which adversely affects ore com-
minution.
With increased sizes of ore grinding mills,
useful grinding work appears to be limited to and depen-
dent upon a maximum depth of the ore charge (as measured
from the bottom of the shell to the top of the charge at
rest).
Grinding efficiency drops as the ore charge
depth is increased beyond an upper limit. It is
believed that this efficiency loss is related to an
increase in the size of the ore charge kidney, which is
accompanied by increased slippage of the active outer
charge layers and the inactive layers in the kidney.
Grinding efficiency refers to the volume of
reduced particles discharged from the mill in a given
unit of time. If the size of the charge is increased,
it is potentially possible for more reduced particulate
matter to be discharged from the mill in a given unit of
time. However, the larger the ore charge, the greater
the size of the kidney, which significantly reduces the
overall efficiency. Consequently, even though the
charge may be larger and the mill capacity increased, it
takes a greater period of time to reduce the charge to
ore particles of a predetermined size, and mill effi-
ciency is therefore reduced.
The charge may be decreased in volume, which
reduces the size of the kidney and comminutes the ore
more quickly. However, with a reduced input of the
charge, this necessarily limits the volume of ore par-
ticles to be discharged in a unit of time, and grinding
efficiency is decreased in this manner.
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Summary of the Invention
It has been found that, by configuring the
liner assembly in a particular manner, activity within
the charge can be increased with a commensurate decrease
in the size of the kidney by breaking it up to an
extent.
More specifically, this is accomplished by
creating a plurality of ramp-like surfaces that extend
circumferentially to present sequential steps to the ore
charge as the shell rotates. Advantageously, the liner
assembly includes a plurality of axial sections with
each section defining its own sequence of ramp-like sur-
faces, and with the ramp-like surfaces staggered relati-
vely from section to section.
Rotation of the mill is such that any given
point in the charge which is disposed in engagement with
the liner surface is moved progressively closer to the
center of the drum as it travels up the ramp, but then
abruptly steps radially outward at the end of one ramp
and the beginning of another. It will be appreciated
that, since this occurs over and over as the ramp moves
sequentially by the charge, the charge is "pulsed" at a
rate which is a function of the effective circumferen-
tial length of the ramp and the rotational velocity of
the shell.
It is the repeated impartation of "pulses" to
the charge that produces directional physical forces and
creates additional action within the kidney, thus
serving to break it up. With the increased activity,
there is a commensurate increase in total useful work
done by the charge, resulting in increased grinding
efficiency.
In addition to increased activity within the
charge, the improved liner assembly can also result in
secondary benefits of increased retention time and
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segregation of the charge based on size. Both of these
benefits further enhance performance of the mill.
Where a plurality of axial sections are used, we
have found that variation in the circumferential position of
the ramps of one section relative to those of adjacent
sections (i.e., "staggering" of the sections) will produce
different desired results; e.g., retarding or advancing the
rate of flow of the charge through the mill.
With the improved liner assembly, overall efficiency
in terms of volume of reduced throughput per unit of time is
increased. Because ore grinders are typically operated on a
twenty-four hour per day basis, increased comminution efficiency
results in significant economic advantages to the user.
An aspect of this invention is a follows:
An improved liner assembly for the cylindrical
shell of an ore grinding machine comprising:
a plurality of individual liner segments covering
substantially the entire inner cylindrical surface of said
shell;
means for mounting the liner segments to said
shell;
the liner segments being arranged in a plurality
of axial sections commonly centered on the shell at rotational
axis and disposed in side-by-side relation;
each section being generally annular in configuration
and comprising a plurality of ramp-like surfaces that extend
circumferentially and define sequential steps with the
lowest point of one ramp-like surface adjacent the highest
point of another;
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the ramp-like surfaces of each axial section being
circumferentially staggered with respect to the ramp-like
surfaces of an adjacent annular section.
Brief Description of the Drawings
Figure 1 is an exemplary view of a portion of a
liner assembly embodying the invention and installed in the
shell of an ore grinding machine as viewed in a transverse
sectional plane perpendicular to the axis of the cylindrical
shell;
Figure 2 is a reduced perspective view which is
schematic in nature showing a plurality of separate axial
sections making up the inventive liner assembly and the
relationship of these axial sections to each other;
Figure 3 is a view similar to Figure 2, and showing
an alternative relationship of the axial sections of the
liner assembly;
Figure 4 is a view similar to Figures 2 and 3
showing another alternative relationship between the axial
sections of the inventive liner assembly;
Figure 5 is a generated fragmentary plan view of
the specific structural configuration of a first embodiment
of the inventive liner assembly;
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Figure 6 is a sectional view taken along the
line 6-6 of Figure 5;
Figure 7 is an enlarged fragmentary sectional
view taken along the line 7-7 of Figure 5;
Figure 8 is a view similar to Figure 7 of a
slightly modified version of the liner assembly shown in
Figures 5-7;
Figure 9 is an end sectional view of a second
embodiment of the inventive liner assembly as installed
in the shell of an ore grinding machine;
Figure 10 is a generated fragmentary plan view
of the second embodiment as viewed along the lines 10-10
of Figure 9;
Figure 11 is a sectional view taken along the
line 11-11 of Figure 10; and
Figure 12 is an enlarged fragmentary sectional
view taken along the line 12-12 of Figure 10.
Detailed Description of the Invention
Figure 1 shows one of a plurality of axial
sections of a liner assembly which is represented
generally by the numeral 11. Each axial section com-
prises a plurality of individual liner segments which
are installed in such a manner as to cover the entire
inner circumferential surface of the cylindrical shell
12 of an ore grinding machine. One circumferential row
of liner segments is shown in Figure 1. As will be
discussed below, the liner segments also extend in axial
rows within the cylindrical shell 12 so that substan-
tially the entire inner cylindrical surface of the shell
12 is covered by the liner assembly 11.
In Figure 1, the individual liner segments are
secured to the shell 12 by suitable means not shown,
such as nut and bolt assemblies.
With continued reference to Figure 1 r there
are four different structural configurations of liner
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segments used, which respectively bear the reference
numerals 13-16. As is apparent in Figure 1, the primary
difference between the segments 13-16 is in their
thickness or radial height, and a description of the
structural details of one segment will otherwise be
exemplary of all of the segments.
Segment 16 has a bottom surface 16a that is
slightly convex to correspond to the inner cylindrical
surface of the shell 12, and a top or grinding surface
16b which defines two axially extending ridges which
serve to carry particles of the ore charge upwardly for
subse~uent tumbling upon rotation of the shell 12 in the
direction shown in Figure 1.
Liner segment 16 has sides 16c, 16d, with the
latter having a greater thickness or radial height than
the former. Accordingly, the thickness or radial height
of the segment 16 increases gradually from the side 16c
to the side 16d.
Each of the liner segments 13-16 is structured
with the same gradual increase in thickness, and the
segments are interrelated in size so that together, the
four grinding surfaces of the segments 13-16 generally
define a ramp-like surface, but with undulations as
defined by the axially extending ridges.
As shown in Figure 1, there are six groups of
segments 13-16 extending circumferentially around the
inner cylindrical surface of the shell 12, with the
lowest point (the shortest side of segment 13) of one
segment group disposed adjacent the highest point (side
16d of segment 16) of another segment group. As such,
this defines a plurality of circumferentially extending
sequential steps to which the ore charge is exposed as
the shell 12 rotates.
While six groups of segments 13-16 are shown
in the preferred embodiment, it will be appreciated that
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the number of groups is variable depending on the mill
diameter and bolt hole pattern.
With reference to Figure 2, it will be seen
that, in the preferred embodiment, the liner assembly 11
comprises four individual sections lla-lld, each of
which is structurally identical to the section shown in
Figure 1. These axial sections lla-d are commonly cen-
tered on the rotational axis of shell 12 and are
disposed in side-by-side relation.
Broadly speaking, each of the axial sections
lla-d is annular in configuration, and as discussed in
connection with Figure 1, each section defines a plura-
lity of ramp-like surfaces that extend circumferentially
and define sequential steps with the lowest point of one
ramp-like surface adjacent the highest point of another.
Further, and as shown in Figure 2, the ramps of each
axial section are circumferentially staggered with
respect to the ramps of an adjacent axial section.
More particularly, and as shown in Figure 2,
the axial section llb is staggered or advanced in the
forward or clockwise direction (as viewed from the left
end of the liner assembly 11) by a distance X. In the
preferred embodiment this staggering is followed uni-
formly throughout the axial sections lla-lld, so that
each of the sections llb-d is advanced by a distance of
X relative to the section which immediately precedes it.
With reference to Figure 3, which shows an
alternative form of staggering, the staggering distance
between the adjacent sections lla-d is 2X in the forward
direction, and this spacing is uniformly followed
throughout the liner sections.
In Figure 4, which represents another alter-
native, the distance of staggering is 3X in the forward
direction, and in the preferred embodiment this
staggering is also uniformly followed from section to
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section. This alternative may also be viewed as
staggering each of the succeeding sections llb-d by a
distance of X in the rearward direction, or counter-
clockwise as viewed from the left end of the liner
assembly 11.
As will be discussed below, different handling
of the ore charge is accomplished with different
staggering arrangements, and other variations are
possible to accomplish desired functions. The distance
"X" is based on the circumferential spacing of mounting
holes in the cylindrical shell 12, and this distance is
not critical. Neither is absolute uniformity of
staggering between adjacent sections, although unifor-
mity is preferred.
Figures 5-7 disclose a first specific struc-
tural embodiment of the liner segments of the inventive
liner assembly. This liner assembly bears the general
reference numeral 21, and in the generated plan view of
Figure 5, three axial liner sections 21a-c are shown.
In this embodiment, the length (i.e., the dimension
extending in the direction of the rotational axis of
shell 12) of the individual liner segments in liner sec-
tions 21a and 21c is the same, and the liner segments of
section 21b are somewhat shorter. This dimensional
variation may be carried out as one of several
approaches to accommodating the liner segments to a par-
ticular mill, and demonstrates that the axial length of
the liner segments in all of the axial sections 21a-21c
need not be identical.
With additional reference to Figures 6 and 7,
axial sections 21a and 21c are made up of three dif-
ferent individual liner segments 22-24, and axial sec-
tion 21b is made up of individual liner segments 25-27.
Each of the segments 22-27 is secured to the cylindrical
shell 12 by two or three conventional tapered head bolt
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and nut assemblies that extend through mounting openings
29 in the individual segments and registering mounting
openings 30 in the shell 12. As best appears in Figure
5, the mounting openings 30 in the shell 12 are uni-
formly disposed in axial and circumferential rows, and
the mounting openings 29 in the segments 22-27 must be
appropriately disposed to register therewith. Also as
shown in Figure 5, the cylindrical shell 12 of the pre-
ferred embodiment is provided with one or more "manhole"
access openings 31. In the embodiment shown in Figure
5, the access opening 31 is covered by one of the liner
segments 26.
With specific reference to Figure 7, each of
the liner segments 22 defines a bottom mounting surface
22a that is slightly convex to conform to the inner con-
cave surface of the shell 120 Segment 22 further
comprises unequal sides 22b, 22c that reflect the
increasing thickness of the body of segment 22 from left
to right as viewed in Figure 7.
Each of the segments 22 further comprises an
upper or comminuting surface defined by axially
extending, elevated ridges 22d, 22e, each of which has
a rounded top. With reference to Figure 5, each of the
segments 22 includes three spaced, colinear ridges 22d
and 22e which are of different length and staggered
relative to one another. The number of ridges 22d, 22e,
and their length and spacing is not critical. Of impor-
tance is the performance of a lifting function to the
ore particles as the shell 12 moves in the clockwise
direction as shown in Figure 7.
With continued reference to Figure 7, each of
the segments 23 also comprises a similar mounting sur-
face 23a, but which also includes axially extending
recesses 23br 23c facing the shell 12 that conserve
material without affecting the strength and wearability
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of the segment 23. The recesses 23b, 23c are of gra-
duated depth, corresponding to the increased thickness
of the body of segment 23.
Segment 23 further comprises a short side 23d
that is slightly greater in height or radial dimension
than the adjacent side 22c oE segment 22, and a long
side 23e.
The top or comminuting surface is also defined
by axially extending, elevated ridges 23f, 23g that, in
the preferred embodiment, are structurally similar to
the liner segments disclosed in the commonly owned U.S.
Patent No. 4,270,705, which issued on June 2, 1981 in
the name of Darrell R. Larsen, and U.S. Patent No.
4,295,615, which issued on October 20, 1981 in the name
of James E. Mishek. Axially extending longitudinal
channels 23h, 23i having closed ends and tapered sides
that converge toward the mounting surface are formed in
each segment 23. Inserts 23j, 23k are subsequently cast
in the respective longitudinal channels. The resulting
elevated ridges 23f, 23g are flat topped in this embodi-
ment.
Alternatively, the longitucinal channels 23h,
23i may be open ended and extend over the entire length
of the associated segment, and the inserts 23j, 23k may
be of commensurate length and inserted by sliding in
from one end thereof, as disclosed in U.S. Patent Nos.
4,270,705 and 4,295,615.
Preferably, the body of segment 23 is cast
from a material which is softer and less brittle than
the material of the inserts 23j, 23k, which are pre-
ferably cast from an extremely hard, long-wearing
material such as martensitic white iron. Other
materials are suitable.
The structural configuration of segment 24 is
the same as that of segment 23 except for its thickness,
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which increases from the largest radial dimension of
segment 23.
Mounted together, the liner segments 22-24
define a ramp-like surface that increases in dimension
from the shortest side of segment 22 to the longest side
of segment 24, then stepping off to the short side of
another segment 22 in a sequential manner.
With the exception of axial lengths and the
number of axially extending elevated ridges, the liner
segments 25-27 have the same structure as the segments
22~24 as shown in Figure 7.
With specific reference to Figure 6, the ends
of segments 22-27 are disposed in parallel, spaced rela-
tion. However, just above the inner surface of the
shell 12, these mutually parallel sides diverge from
each other in the direction of the shell 12, and define
a pocket in which an insert 32 is retained. The func-
tion of the insert is to prevent the entry and com-
pacting of ore particles between adjacent liner segments
to the extent that removal of the segments for replace-
ment purposes becomes extremely difficult.
In the preferred embodiment, the insert 32 is
made of rubber and is generally triangular in con-
figuration and dimensioned to be loosely retained within
the pocket. Reference is made to the commonly assigned
' U.S. Patent No. 4,165,041 for further structural details
and features of the insert and pocket.
In the preferred embodiment of liner assembly
21 as shown in Figure 5, the liner segments 25-27 of
axial section 21b are advanced by a distance of one
axial row of mounting openings 30 in the shell 12 by
advancement of one axial row of mounting openings 30.
Liner assembly 21 thus generally conforms to the embodi-
ment shown in Figure 2.
Figure 8 discloses a liner assembly 21' that
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is quite similar to liner assembly 21 with one varia-
tion. The individual segments 22', 23', 24' are dif-
ferent than their counterparts in liner assembly 21 in
that each has a substantially constant thickness or
radial dimension (aside from thickness variations due to
the elevated ridges). However, the overall thickness of
the segment body of liner segment 23' is greater than
that of liner segment 22' and less than that of liner
segment 24'. Consequently, each of the ramp-like sur-
faces is defined by incremental steps. These steps
do not adversely affect comminution and function in
substantially the same manner as the elevated ridges
themselves.
Liner assembly 21' offers certain advantages
because the individual liner segments 22'-24' are sym-
metric. These include less difficulty in manufacture
and reversability of the liner section within the shell
when the leading edges of the elevated ridges become
worn.
Liner assembly 21' may also be configured to
receive rubber inserts 32 in a similar manner to liner
assembly 21.
Figures 9-12 disclose a second specific struc-
tural embodiment of a liner assembly 41 embodying the
invention. Liner assembly 41 utilizes the general
inventive concept of plural axial sections each of which
defines a plurality of ramp-like surfaces that extend
circumferentially in sequential steps. However, most of
the liner segments of liner assembly 41 are of a com-
posite rather than an integral structure. Consequently,
and as best shown in Figures 9 and 12, a single wear cap
42 may be commonly utilized throughout the assembly 41.
With reference to Figure 10, liner assembly 41
comprises two circumferential rows 41a, 41b of liner
segments that together comprise a single axial section;
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i.e~, there is no staggering of adjacent liner segmen-ts.
Each of the rows 41a, 41b comprises three liner segments
represented generally by the numerals 43-45. As shown
in Figures 10 and 11, the liner segments 43-45 are of
the same length or axial dimension.
In addition, to compensate for the manhole
access openings 31, each circumferential row 41a, 41b
further comprises a liner segment 43' of reduced length.
The liner segment 43'' is sized to cover the manhole
access opening 31 and fits between liner segments 43'
as shown.
With reference to Figure 12, and as briefly
discussed above, each of the liner segments 43-45 is of
composite structure, comprising carrier or holder
segments 43a-45a, respectively, with wear caps 42
respectively superimposed thereover. Each of the holder
segments 43a-45a increases in thickness, with wear
segment 43a the lowest of the three. As shown in Figure
12, the increasing thicknesses of the holder segments
43a-45a are dimensioned so that, with the wear caps 42
attached, a ramp-like surface is defined extending in
the circumferential direction in sequential steps as
described above.
To resist shear stresses on the mounting bolt
assemblies (discussed below), and to resist relative
movement, each of the wear caps 42 of the preferred
embodiment is cast with three circular, downwardly pro-
jecting bosses 42a. As shown in Figure 10, the holder
segment 43a is cast with three corresponding recesses
43b to receive the associated bosses 42a. As shown in
Figures 11 and 12, registering mounting openings for
mounting bolt assemblies 46 extend through the bosses
42a and recesses 43b. The mounting bolt of assembly 46
is a standard oval-head bolt that is recessed below the
grinding surface of the wear cap 42 for protective pur-
poses. The mounting bolt assemblies 46 commonly secure
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both the wear cap 42 and holder segment 43a to the
cylindrical shell 12. The mounting arrangement of the
holder segments 44a and 45a and their respective wear
caps 42 is the same, although the mounting bolt
assemblies 46 are somewhat longer due to the increased
thickness of the holder segment bodies.
With reference to Figures 10 and 11, each of
the holder segments 43a-45a is formed with four equi-
distantly spaced mounting openings. Liner segment 45 is
exemplary, and these mounting openings bear the
reference numeral 45c. The circular recesses 45b
register with three of these openings 45c to receive the
associated bosses 42a. The mounting opening 45a for
which there is no recess 45b receives a short bolt
assembly 46 the head of which is recessed within this
mounting opening, as shown in Figure 11. As such, one
of the four mounting bolt assemblies 46 secures the
holder segment 45a directly to the shell 12 indepen-
dently of the associated wear cap 42, whereas the other
three mounting bolt assemblies 46 extend through both
the wear cap 42 and underlying holder segment 45a to
commonly secure both to the shell 12.
The same mounting arrangement exists for all
of the liner segments 43-45. With such construction, it
is possible to remove the wear caps 42 for replacement
without removing the underlying holder segments 43a-45a.
With continued reference to Figure 11, the
opposed ends of adjacent wear caps 42 diverge toward the
bottom or mounting surfaces to receive an insert 32. As
exemplified by the holder segments 45a in Figure 11, the
ends of the holder segments 43a-45a also diverge to
receive an insert 32, such construction being similar to
that shown in the embodiment of Figures 5-7.
With reference to Figures 10 and 12, the liner
segment 43' is of single-piece construction, but has the
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same thickness and grinding surface as liner segment 43.
Liner segment 43'' is also of single-piece construction,
and aside from its shorter length, is otherwiss struc-
turally the same as liner segments 43'.
The composite approach to the liner segments
43-45 is advantageous in that the wear caps 42 and
holder segments 43a-45a may be cast from different
materials appropriate to their respective functions.
For example, the wear caps 42 are continuously and
directly exposed to the ore comminution process, and in
the preferred embodiment are cast from material having a
high resistance to abrasion, such as martensitic white
iron or martensitic steel. The holder segments 43a-45a
are not directly exposed to the comminution process, and
their primary function is to support the wear caps 42 in
the ramp configuration. Consequently, they can be cast
from a material which is less hard and less brittle,
such as pearlitic chrome-molybdenum.
The composite approach and the mounting con-
figuration also enable the wear caps 42 to be replaced
when worn without replacement of the holder segments
43a-45a.
Summarizing, each of the embodiments disclosed
utilizes a plurality of ramp-like surfaces extending
circumferentially to present sequential steps to the ore
charge as the shell rotates. The repeated impartation
of "pulses" to the ore charge decrease the size of the
kidney by breaking it up, increasing the total useful
work done by the charge and grinding efficiency.
