COMPOSITE STEEL CLADED MILL LINER
This invention relates to an effective tool for grinding of ore minerals, rocks and
other materials. Particularly, this invention relates to a liner to be used in the Mill
for grinding in course of mineral Processing Operations. More particularly, this
invention relates to a composite steel clad mill liner for use in AG and SAG mills.
Background of the Invention
Grinding mills are typical Equipments for mineral Processing as mentioned
above. A standard grinding mill generally has a drum shaped shell connected to
conical/vertical Mill heads with integral or bolted trunious and the assembly is
mounted on the journal bearings for its rotation. Semi-Autogenous Grinding Mill
or SAG is a typical mill which uses steel balls to break large rocks in grinding
operations. The rotating drum continuously throws the rocks and the balls in a
Cataracting motion causing breakage of the bigger rocks primarily by impact. It
also causes compressive grinding of the rocks to finer materials. Attrition in the
charge causes grinding of finer particles. SAG mills has, in its inner surface, lifter
bar & shell plates to carry the ore/rocks inside up and from there the ore/rocks
along with balls are thrown tangentially. Subsequently they all fall downwards
due to gravity facilitating grinding.
In contrast, Autogenous mills or AG mills do not use steel balls. The rotating
drum throws the ore /rock in a cataracting motion which causes impact breakage
of the ore and also cause compressive grinding of the finer particles. Attrition of
rock media charge causes grinding of finer particles.
The significant impact forces generated during the operation of the grinding
mills, due to continuous collision between the steel balls, ore and the inner shell
liners of the rotating drum while comminuting the ore to finer particles also
causing degradation of the grinding media and the liner of the drum. In view of
the wear life cycle of the lining system being used, operation downtime for the
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machine along with a vital segment of the OPEX is manifested at the user's end.
More the wear life of the liners better is the availability of the machine which is
desired.
In order to decrease the rate of deterioration and to prolong the life of the liners,
various types of liners have been used. Normally, complete cast alloy steel
liners, composite metal liners or polymet lining system and only rubber liners are
used in the AG / SAG Mills. Magnetic liner materials are also known to be used
retain in place chip or flakes of the liner generated due to severe impact in the
grinding process. However, the above various liner materials have short comings
and do not provide very satisfactory results so far as the life of liner is concerned
against aggressive operating conditions.
Further replacement of inner lining of the Mill is a cumbersome procedure and
the types of liner mentioned above are operation specific and cannot be
retrofitted, in the grinding mills. Also, the constructional design of the liners
used in the state of the art is dependent on the drilling patterns of the mill.
Moreover, the total cast metal liners being heavy, it is not easy to be fitted /
replaced in the grinding mills. It calls for some other facilities to be inducted in
the system during capital expense of the project.
So, there was a constant need of an improved liner for the inner shell of
grinding mills which can overcome the above mentioned shortcomings.
Objects of the Invention
Therefore, it is an object of the present of invention to provide a liner, which is
more resilient and with greater wear life cycle for inner wall of the shell of
grinding mills.
It is another object of the invention to provide a liner for the shell of grinding
mills, which can be easily retrofitted in a mill having some different lifter pattern
not conducive for a particular application.
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It is yet another object of the invention to provide a liner for inner wall of the
shell of grinding mills which is relatively light weight than the cast steel liners,
thereby reducing the inertia effect of the Mill and delivering comfort to the motor
in terms of starting time.
It is a further object of the invention to provide a liner for the shell of the
grinding mills which is independent of the drilling pattern of the existing shell in
terms of fixing.
It is another object of the invention to provide a liner for the shell of the grinding
mill based on this concept which can be manufactured in a tailor made fashion
for different milling application.
These and other objects of the invention will be apparent from the description of
the exemplary embodiments of the invention described hereinafter. Of course,
the present invention is not limited to such embodiments or to the drawings with
the help of which the embodiments are described, purely for explaining the
invention, by way of example.
Summary of the Invention
To achieve the above and other objectives, the invention provides a liner made
of symmetrically distributed soft rubber backing against the partial steel profile
on a composite lining system.
Brief Description of the Accompanying Drawings:
Fig 1 is a cross -sectional view of an exemplary grinding mill according to the
invention.
Fig 2 is a graph showing the relative wear of the mill liner over time.
Fig 3, Illustrates a preferred embodiment of the mill liner according to the
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invention.
Fig 4, Illustrates another preferred embodiment according to the invention.
Detailed Description of the Invention:
According to the invention, a symmetrically distributed soft rubber backing on a
composite liner system, as shown in figure 1 is disclosed. The inside wall of the
shell of the grinding mill 1 is retrofitted with a rubber backed composite mill liner
3. The liner has a top layer made of cast steel and back layer is rubber. Natural
rubber can be used to make the rubber layer. These two layers make an
integrated system of rubber backing and composite lining. The two layers may
be joined together by hot vulcanization in the mould.
Due to presence of symmetrically distributed and soft rubber backing in the liner,
the wear rate of the steel surface will be less compared to that in the Polymet
lining system or in the composite metal liner. Due to this unique metal rubber
distribution system in the liner as the metal wears down, liner becomes more
resilient and its relative wear rate decreases. The effect becomes much more
significant after the liner has attained its half life period. This effect is shown in
figure 2. The slope of the curve clearly radically that the relative wear rate
sharply decreases after the half life TH line. The TD line shows the time for
discarding the liner.
On the liner further arrangement necessary for the grinding operation such as
lifter profile can be arranged, by known means as may be necessary.
Figure 3 shows the cross sectional view of the composite liner system with one
lifter and having two point fastening system with the shell. Hatched section
represents solid steel casting. On top of the casting, a bidirectional cast metal
grid system is shown. Grid section has been provided a retardant to the in
process wear. Integral anchors of the metal section has been shown at the two
ends embedded in rubber to ensure adequate protection against rubber metal
separation due to the force encountered by the liner which negotiating its
movement across the pressure charge to regions in the mill. Two aluminum
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clamps are also shown at the point of fixing. All remaining un-shaded zone
represents rubber.
Figure 4 shows a cross section of a composite liner profile with one lifter and
with a single point fastening system. Hatched section represents solid steel
casting having bi directional grid system on top, integrated anchor system and
aluminum clamp are also shown as in Figure 3. Un-shaded area represents
rubber.
The liner of the invention can be produce in a tailor made arc lengths and fixing
arrangements to make retro fitment in any mill much easier and faster.
It will be apparent to a person skilled in the art that due to the above
characteristics of the liner the drilling pattern of the mill shell is not significant.
Number of lifts or number of rows of lifter in the shell can be altered without
changing the shell. This flexibility will help the user to use any ball mill in SAG or
FAG mode.
Due to less weight in comparison to equivalent steel liner, GD2 value of the mill
will also decrease significantly.
Specific Gravity of cast steel would be in the range of 7.6 to 7.85 kg/dm3.
Whereas Specific Gravity of rubber used in the composite liner would be 1.14 to
1.16kg/dm3. As the cross section of the composite liner has some cast steel &
some rubber, for a given shape of the liner of occupying volume V, weight of the
steel liners would be (7.6 - 7.85) x V kg. Whereas, the weight of the composite
liners would be {x*(1.14 - 1.16) + (V-x)*(7.6 - 7.85)} kg.[ x: volume of
rubber.] From the above expressions, it is clear that the weight of steel liners
would be more than that of the composite liners for any given shape and
volume.
GD2 value of a rotary equipment is its inertia effect automatically narrated as: 4
*WK2 (W: weight of the rotating mass and K : radius of Gyration).
As the liner weight with the composite lining system would be less compared to
that of the complete metal lining system, rotary mass of the grinding mill with
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the liners would be less with the composite lining system.
Starting time of the drive motor is = K.GD2/ Ta (when Ta = average acceleration
torque and K = const).
As the GD2 value referred to the motor becomes less, starting becomes easy and
the time required to effect the same is also lesser. Thus, thermal withstand time
for each start would be less for the driver motor giving it the relief which is
manifested in terms of working life of the motor.
Cataraction of charge induces large impact on the lining system in a cyclic
pattern. This in turn causes lot of chipping wear along with abnormal stresses in
the fixing fasteners. With the inventive resilient composite system, the
magnitude of impact reduces by 5 to 6 times of its real intensity, hence the
chances of damage becomes less. Therefore the efficacy of the inventive liner
will be far superior to all other types of liner for the conditions where
applications calls for partial cataraction of change in the mill to deal with the
materials having high front end competency. Thus difficult FAG/SAG operation
can be addressed with this type of liners.
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It is to be understood that the inventive concept has been described with the
help of non-limiting exemplary embodiments. Various alterations, modifications
and improvements may be made without departing from the scope and spirit of
the invention.

The invention discloses a composite liner for ball mills comprising an upper layer of alloy cast steel bonded on a symmetrically
distributed lower rubber surface, said cast steel layer is prefabricated so as to form the desired profile on the upper surface of the
said liner required for specific grinding operation. The present invention also discloses a method of manufacturing composite mill
liner.