Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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TITLE : BUTT AND THIMBLE PRESS
Background of the Invention
This invention relates to a method and apparatus for the removal of anode
butts or anode remnants and stripping anode thimbles from anodes such as those
used in the electrolytic smelting of aluminiums.
In the electrolytic smelting of metals such as aluminium, the cathode is
located in the bottom and lower side regions of the cell and a carbon anode
block
is suspended or supported by yoke stubs attached to the anode rod. The yoke
stubs
have cast iron thimbles fitted at their lowermost end and the thimbles are
cast within
recesses in the carbon anode block. During operation of the smelting cell the
carbon anode is consumed requiring regular replacement of the anode block.
To replace the anode block, it is necessary to remove the anode remnants or
butts and the cast iron thimbles from the anode yoke stubs. For the economics
of
the smelting operation, it is highly desirable that the anode butts are
removed,
crushed and the carbon reclaimed for use in replacement carbon anode blocks.
In the prior art, the thimbles and anode butts are removed by a downwardly
acting stripper. Since the main support for the anode rod and anode butt is
the
overhead transport crane; additional clamping device have been employed to
resist
the downward forces required to strip the anode butt and thimble from the
anode
yoke stubs.
In GB 1269809, an anode stripping apparatus is disclosed in which the anode
rod is clamped in a clamping device consisting of two hydraulically operated
pistons.
Hydraulic strippers act vertically downwardly on the anode butt to strip the
butt from
the stub. Scrappers are provided on the downwardly acting strippers to remove
the
thimble from the stub.
During the downward operation of the stripper, the anode rod is held in
position and supported by the clamping device acting laterally on the rod.
Since a
large force needs to be applied by the clamping device to resist the downward
forces
of the stripper, damage to the anode rod and a shortened operating life is
inevitable.
The apparatus as disclosed in EP 191,954 and US 4,442,593 also rely on
downwardly acting hydraulic rams to break the anode, butt from the anode stub.
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Australian Patent No. 565330 and GB 2,108,530 relate to holding devices for
an anode stub to secure the anode in position during cleaning of the anode.
In other prior art methods, the steps of anode block removal and thimble
stripping have been carried out in separate operations, on separate apparatus
and at '
separate locations thereby increasing the space required for the operations
and the
capital cost of equipment.
Brief Summary of the Invention
It is an object of the present invention to provide an apparatus and method
for the removal of the anode butt and thimble from the anode yoke stub without
some of the problems of the prior art.
The invention provides an apparatus for breaking the anode butt and stripping
the thimbles from the stubs of an anode including a support frame, a fixed
plate
assembly substantially secured to said support frame, and a ram assembly
extendible
towards said fixed plate assembly for contacting and breaking the anode butt
and
stripping the thimbles, said fixed plate assembly comprising a substantially-
rigid
fixed plate and having recesses to receive the anode stubs of said anode, said
thimbles abutting said fixed plate assembly during the extension of said ram
assembly to contact and break said anode butt.
By securing the substantially rigid fixed plate to the support frame in line
with the ram assembly, the fixed plate becomes the load bearing surface and,
substantially all of the loads applied by said ram assembly are transferred to
the
fixed plate and support frame during the breaking and stripping operation.
The ram assembly may comprise an hydraulic ram with stripping means to
protrude into the anode butt during the movement of the hydraulic ram and
thereby
break the anode butt. The stripping means is preferably also able to strip the
thimbles from the yoke stub after the bulk of the anode butt has been removed
from
the thimbles. Preferably the stripping means are rock bits mounted on a platen
attached to the uppermost surface of the ram.
The apparatus may also include locating means which aligns the anode stubs
with the recesses in the rigid fixed plate. The locating means are preferably
opposed
locating arms positioned in line with the fixed plate assembly and the ram
assembly.
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In a preferred form of the invention, the ram assembly is positioned below the
fixed plate assembly and the breaking and stripping operation is performed by
upward movement of the hydraulic ram towards the fixed plate assembly.
The substantially rigid fixed plate is preferably provided with an aperture to
separate the fixed plate assembly and fixed plate into two sections. When the
anode
butt is moved into position between the fixed plate assembly and the ram
assembly,
the anode stem passes through the aperture until the stubs are aligned with
the
recesses in the fixed plate.
The recesses in the fixed plate axe sized to enable the stripped stubs to pass
therethrough but sufficiently small to prevent the passage of the thimbles.
Therefore,
if the relative positions of the stubs on the anode yoke remain substantially
constant,
the size and shape of the recesses will allow the thimbles to abut directly
onto the
fixed plate to transfer the load from the ram assembly to the support frame.
In operational situations, a number of anodes are used and maintained and
there may often be variations in the relative position of the anode stubs on
each of
the anode yokes. In these situations where the variations are considered
large, the
size and shape of the recesses required to enable the stripped stubs of the
anodes
to pass vertically through the fixed plate may result in only a small portion
of the
top flange of the thimble contacting or overlapping the bottom of the fixed
plate.
Consequently accurate locating of the stubs relative to the fixed plate may be
required.
The fixed plate assembly may further comprise a stub locating mechanism.
The stub locating mechanism may be either a clamp or claw assembly which
secures the yoke stub in position minimizing lateral movement of the anode
relative
to the fixed plate.
In another aspect of the invention, there is provided a method for the removal
of an anode butt and thimbles from the stubs of an anode yoke of an anode on
an
apparatus including a fixed plate assembly having a substantially rigid
apertured
ftxed plate and an ram assembly for contacting and breaking said anode butt,
said
method including the steps of positioning the anode butt between the fixed
plate
assembly and the ram assembly, moving the anode to receive the anode stubs
within
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recesses in the fixed plate, extending the ram assembly towards the fixed
plate to
contact and break the anode butt against the fixed plate assembly and strip
the
thimbles from the anode stubs, retracting the ram assembly and withdrawing the
stripped anode from the fixed plate assembly. '
The step of extending the ram assembly may further comprise the steps of
initially, extending the ram assembly to contact and break the anode butt,
retracting
the ram assembly to allow the larger pieces of the butt to be cleared, and
extending
the ram assembly to strip the thimbles and remaining anode pieces from the
anode
butts. .
The ram assembly may be provided with a stripping means to protrude into
the anode butt during the breaking operation. The stripping means which is
preferably in the form of rock bits mounted on a platen attached to the ram,
is able
to strip the thimble from the yoke stub to allow it to be removed.
The step of positioning the anode between the fixed plate assembly and the
ram assembly may also include an additional step of locating the anode rod
using
a locating means. Once the anode has been moved into position and the stubs
are
received within the recesses of the fixed plate, a stub locating mechanism may
be
activated to locate the stubs in position such that the respective thimbles
are
positioned relative to the recesses to upward movement of the thimbles beyond
the
fixed place.
Movement of the ram assembly towards the fixed plate assembly ensures
that substantially all of the load from the hydraulic ram is transferred to
the
substantially rigid support plate during the butt breaking and thimble
stripping
operation.
Brief description of the drawing
Figure 1 is a plan view of a typical anode used in the invention,
Figure 2 is a sectional view through line A-A of Figure l, '
Figure 3 is a sectional view through line B-B of Figure 1,
Figure 4 is an enlarged view of region C of Figure 2,
Figure 5 is an elevational view of an embodiment of the apparatus of the
invention,
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Figure 6 is a side view of the embodiment shown in Figure 5,
Figure 7 is a sectional view of the embodiment of Figure 6 through line D-D
of Figure 6,
Figure 8 is a sectional view of the embodiment of Figure 6 through line E-E
of Figure 6,
Figure 9 is a sectional view of the embodiment of Figure 6 through line F-F
of Figure 6,
Figure 10 is an elevational view of the of the embodiment of Figure 5 with
a section of the shedder plate removed,.
Figure 11 is a plan view of the fixed plate showing the arrangement of
recesses for a four stub yoke,
Figure 12 is schematic view showing an example of the shape of a recess in
the fixed plate,
Figure 13 is a plan view of a clamp assembly,
Figure 14 is a sectional view of an embodiment of the clamp mechanism
positioned in the fixed plate,
Figure 15 is a plan view of the clamp mechanism in the open position,
Figure 16 is a plan view of the clamp mechanism in the closed position,
Figure 17 is an enlarged view of a claw assembly of Figure 9 in the closed
position,
Figure 18 is an enlarged view of the claw assembly of Figure 9 in the open
position,
Figure 19 is a sectional view through Line A-A of Figure 17,
Figure 20 is a sectional view through line B-B of Figure 18,
Figure 21 is a sectional view through line C-C of Figure 18,
Figure 22 is a plan view of the anode rod locating means, and
Figure 23 is a section view through line A-A of Figure 22.
Detailed description of the preferred embodiment
While the invention will be described with reference to four stub anode yokes,
it would be appreciated by those skilled in the art that the apparatus and
method can
easily be adapted to anode yokes with a different number of stubs (such as
2,3, 6 or
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8 stub yokes) which can be found in the industry by increasing or decreasing
the
number of rock bits (to correspond with the number of stubs) and making other
minor non-inventive modifications.
Referring to Figures 1,2,3 and 4, a typical anode for use with the apparatus
and method of the invention as shown. The anode consists of an anode rod or
stem
connected to a yoke 11. The yoke stub 12 of the yoke 11 is fitted with
thimbles
13 which are received within wells 8 formed within the upper surface of a
carbon
anode block 14. The anode rod 10 is coupled overhead to a conveyer for
transport
around the rodding room (not shown).
While the apparatus in accordance with an embodiment of the invention will
now be described with regard to an upwardly acting ram assembly and a
substantially vertically aligned anode rod, it would be appreciated by those
skilled
in the art that other alignments of the ram assembly and anode rod (eg.
horizontal)
can be assumed without departing from the scope of the invention.
The apparatus shown in Figures 5 and 6 for removing the anode carbon butt
and thimble 13 from the yoke stubs 12 includes a support frame 20 to which is
substantially secured to a fixed plate assembly 21 and further includes an
upwardly
acting hydraulic ram assembly 22 for contacting and breaking the anode butt 15
and
stripping the thimbles 13.
The fixed plate assembly 21 shown in Figure 8 includes a substantially rigid
fixed plate 23 having an aperture 24 to enable the anode butt to be positioned
between the fixed plate assembly and the ram assembly and recesses 24a to
receive
the yoke 11 and yoke stubs 12 of the anode. The aperture in the fixed plate 23
preferably separates the fixed plate assembly 21 and fixed plate 23 into two
sections.
When the anode yoke is moved horizontally into position beneath the fixed
plate
assembly 23, the anode stem 10 passes through the aperture 24 until the stubs
12 are
below the recesses 24a in the fixed plate. The size and shape of the recesses
24a
are such that the stripped anode butts are able to pass vertically through the
fixed
plate 23 but prevent upward movement of the thimbles beyond the fixed plate
23.
In this way, the force applied to the anode by the ram assembly during the
action
of breaking the butt and stripping the thimbles is transferred directly to the
fixed
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plate 23. The fixed plate 23 is rigidly secured to the support frame 20 to
provide
adequate resistance to those forces.
When the anode reaches the apparatus in accordance with the embodiment of
the invention, the anode rod is moved into the aperture 24 along guide rails
38, 39
and preferably located in position by means of an overhead locating means
shown
in Figure 7 and 22. Stub guides 38a and 39a are also provided to assist
positioning
of the anode. The locating means comprises two stops 40,41 which separately
engage the anode rod 10. The two stops are each pivotally mounted on swing
arms
42 and pivotally mounted air rams 43 are provided to control the position
thereof.
The anode is lifted into position by a lifting assembly (not shown) such that
the anode stubs are received within the recesses 24a in the rigid fixed plate
23.
To facilitate the breaking of the butt 15 and stripping of the thimbles 13,
the
hydraulic ram assembly 22 shown in Figure 5 is preferably provided with
stripping
means illustrated as rock bits 25 mounted on a stripper plate 26. The number
of
rock bits equates with the number of yoke stubs and thimbles. These rock bits
25
penetrate into the anode butt 15 during the upward movement of the hydraulic
ram
to split the butt. The rock bits 25 are positioned on a stripper platen 26
(shown in
Figure 10) so that upward movement of the ram assembly 22 will fracture the
carbon
butt 15 and bring the rock bits 25 into contact with the thimbles 13 to crush
the
bottom of the thimble. Further application of the load strips the thimble from
the
yoke stubs 12 enabling the thimbles to fall away. The rock bits are preferably
provided with knife edges to aid crack propagation in the wall of the thimble.
A shedder plate 27 shown in Figure 5, is mounted to the stripper platen 26
and is apertured to allow the rock bits 25 to protrude through its upper
surface. The
shedder plate 27 moves vertically with the extension of the hydraulic ram
cylinder
22A. The purpose of the shedder plate 27 is to deflect pieces of the broken
anode
butt to either side of the ram to be collected in conveyors (not shown) which
convey
the pieces of anode butt and split thimbles away from the apparatus.
A fixed shedder plate 27A may also be provided fixed to the hydraulic
cylinder of the ram assembly to cover the cylinder at all times. The angle of
the
shedder plate and fixed shedder plate to the horizontal is sufficient to shed
the
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broken butts and thimbles and would typically range between 30°-
60° depending
on the anticipated sizes of the broken butts. A. cylinder bellows connected to
the
underside of the moving shedder plate and to the top of the cylinder flange
may be
provided to protect the cylinder from particles scoring the hydraulic ram rod.
The shedder plate 27 is preferably arranged across the narrow side of the
machine to minimise the height lost by the broken butts and thimble pieces as
they
clear the apparatus. The broken butts and thimble pieces are then conveyed
away
from the apparatus.
Referring to Figure 11, the distances 18,19 between the centres of the
recesses
24a in the fixed plate 23 are substantially the same as the respective average
distances between the centres of the stubs 12 of the anode yoke 11.
The recesses 24a in the fixed plate 23 are shaped and sized to enable the
stripped stubs to pass vertically therethrough but sufficiently small to
prevent the
passage of the thimbles. An example of the shape of a recess is shown in
Figure
12.
In an operational situation, a number of anode rods are used to enable fresh
anodes to be installed into the smelting pot while the butt and thimbles are
stripped
from the rods of the used anodes.
Where the relative positions of the anode stubs on the anode yoke remain
substantially constant, the size and shape of the recesses 24a are designed to
enable
a high proportion of the upper flange 16 of the thimble to abut against the
fixed
plate 23 and transfer the load from the ram assembly 22 directly to the fixed
plate
23.
In many operations and in particular older operations, there may often be
variations in the relative position of the anode stubs on each of the anode
yokes in
operation. Where the variations are considered large, the size and shape of
the
recesses required to enable the stripped stubs 12 of the anodes to pass
vertically
through the fixed plate 23 may result in only a small portion of the top
flange 16 of
the thimble 13 overlapping with the bottom of the fixed plate 23. Consequently
a
stub locating mechanism may be provided on the fixed plate assembly 21 to
position
the stubs 12 relative to the fixed plate 23 and ensure that the load from the
hydraulic
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ram assembly is transferred through the thimbles to the fixed plate 23.
The stub locating mechanism which may be in the form of either a clamp or
claw assembly which positions the yoke stub 12 prior to the breaking and
stripping
operation. The clamp or claw assembly is preferably secured between a bottom
plate
29 and the fixed plate 23.
As shown in Figures 14,15 and 16, the clamp assembly which is sandwiched
between the fixed plate 23 and a bottom plate 29 consists of a central rod 30
actuated by a pneumatic cylinder 34 at the rear of the clamp assembly which,
when
extended, acts on cam surfaces 31 of clamp 32. The clamps 32, pivot around a
clamp pivot shaft 28 to clamp or grab the stub. A sandwich plate 33 maintains
the
distance between the fixed plate 23 and bottom plate 29 and is recessed to
house the
clamp mechanism between the fixed plate 23 and bottom plate 29.
When using the clamp mechanism, the clamps 32 clamp the stub 12 of the
anode above the thimble 13. During the butt breaking and thimble stripping
operation, the thimbles 13 abut directly against the underside of the clamps
of the
fixed plate assembly 21. As a result of the close proximity of the clamps to
the
fixed plate 23, the load which is applied by the hydraulic ram assembly 15 is
transferred to the fixed plate through the thimbles 13 and clamps 32.
Since the clamps are much wider than the thimble flanges 16 and the clamps
surround a large proportion of the anode stub, a much larger surface is
provided to
transfer the loads through the thimbles to the fixed plate via the clamps.
An alternative stub locating mechanism shown in Figures 7,17,18,19,20 and
21 uses a claw design which allows for stub variations and provides a close ~t
around the stub in any location. The claw arms 45, 46 simply open and close
around the stub 12 above the thimble 13. Claw linkages 47 which are pivotally
attached to claw arms 45,46 are pivotally attached at pivots 48 to pneumatic
cylinder
housing 49. The claw arms 45,46 are actuated by a pneumatic cylinder 50 within
housing 49 which drives an actuation rod 51 mounted behind pivotal connection
pins
52 connecting claw arms 45,46. The claws 45, 46 are normally held open against
the walls of the sandwich plate 53 which may be formed in segments to house
the
claw mechanism between the fixed plate and bottom plate and on actuation by
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retracting rod 51 the claws 45, 46 close, self centering about the stub 12.
The
bottom plate 29 is mounted on the fixed plate 23 to retain the claw assembly
and a
sandwich plate in position. During and after butt crushing, the anode bar is
raised
so that the top of the thimble flanges 16 rest against the underside of the
claws of
claw arms 45,46. The underside of the claw arms 45,46 may be provided with a
rebate 54 to seat the flange of the thimble to be stripped.
In respect of both designs, since the stub locating mechanisms are mounted
directly under and against the fixed plate 23 substantially all of the load
provided by
the hydraulic ram is still transferred to the fixed plate 23 of the fixed
plate assembly
as discussed in an earlier paragraph.
The support frame 20 of the apparatus shown in Figure 5 is essentially a
gussetted fabricated structure in the shape of a C section consisting of a
press frame
floor base 55 and two side frames 56,57. The support frame is mounted on a
base
frame 58 which is fixed to the floor of the rodding room.
To remove the butt and thimble from the anode in accordance with the
invention, the anode is transferred by the conveyor into the position shown in
Figure
5. The anode butt is then raised so that the anode stubs 12 pass through the
recesses
24a in the plate 23 as shown in Figure 8 with the thimble flanges 16 against
the
bottom of the fixed plate assembly. If no stub locating mechanism is provided,
the
flanges 16 of the thimbles bear against the fixed plate 23.
The hydraulic ram 22 is then raised so that the stripping means contact and
penetrate the anode carbon butt 15 to a sufficient depth to fracture the butt
15. The
carbon block has a nominal compressive strength of 35 MPa and it is assumed
that
the carbon block will fail at the compressive stress limit in a brittle (or
exploding)
manner. As the compressive strength of the carbon block is dependant on the
thickness and nature of the carbon, these limits should be determined and
allowances
to the design made in accordance with the circumstances prevailing. It is also
assumed that the rock bits 25 will indent into the carbon block up to the full
diameter of the rock bits main shaft although this may vary depending on the
butt
depth. The applicants estimate that a load of up to 200 tonnes will be
required for
four rock bits to crush a carbon block. This estimate incorporates a safety
factor of
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1.5 since the nominal carbon block strength may also vary.
The hydraulic ram 22 is then retracted to allow the anode butt pieces to
fall away from the thimbles 13 onto the shedder plate 27 which guides the
carbon
pieces to conveyors to be conveyed away from the apparatus by conveyors. Once
the
pieces of anode butt have been cleared, if the thimbles have not been stripped
from
the stubs, the ram is then raised to contact and strip the thimbles on the
yoke stubs.
Based on a series of tests, the applicants have found that, in situations
where the thimble has not been fused to the yoke stubs, the maximum load
required to
strip a thimble is up to approximately 150 tonnes. Consequently for a four
stub carbon
to block and yoke assembly, the hydraulic ram 22 must provide a load of up to
G00
tonnes to simultaneously strip the four thimbles from their stubs.
The thimble metal then is directed by the shedder plate into conveyors
to be carried away from the apparatus.
As clearly illustrated, in order to break the anode butt and strip the
is thimble, it is necessary for substantially all of the load to be
transferred to the fixed
plate 23 during the breaking and stripping operation so that the fixed plate
acts as
anvil against the force applied by the hydraulic ram.
Once the thimble has been stripped the yoke is removed from the
apparatus.
2o Those skilled in the art will appreciate that the invention described
herein is susceptible to variations and modifications other than those
specifically
disclosed. It is to be understood that the invention is considered to
encompass all such
variations and modifications that are all within its spirit and scope.
