Note: Descriptions are shown in the official language in which they were submitted.
CA 02474878 2004-07-29
WO 03/068468 PCT/N003/00049
A Method and Equipment for Compacting Materials
The present invention concerns a method and equipment for compacting
materials.
More precisely, the present invention concerns vibration of "green mass" in a
moulding
process for the creation of mould bodies for the production of electrodes for
the melting
industry, in particular the aluminium electrolysis industry.
Such electrodes, in particular anodes, are created by the "green mass" being
subjected
to compaction in a vibration device, which may consist of a moulding box with
a base
and side walls mounted on a table, plus a plumb that is allowed to slide down
between
the mould walls (the side walls of the moulding box). There are primarily two
types of
vibration equipment for moulding anodes available on the market, equipment
with plumb
vibration and equipment with table vibration. The main difference between them
is the
location of the vibration unit that generates the dynamic vertical input force
for the
equipment. For equipment with plumb vibration, the vibration unit is fixed
to/integrated in
the plumb. For equipment with table vibration, the vibration unit is fixed
to/integrated in
the table.
NO patent no. 132359 concerns vibration equipment with plumb vibration for the
compaction of mould bodies for the production of anode and cathode blocks. The
specification states that plumb vibration offers many advantages over table
vibration, in
particular with regard to simplification of the equipment. By moving the
vibration unit to
the plumb, the claim was that the vibration principle could be simplified, as
the base
would be stationary, fixed to the floor. In accordance with the reference, the
compression effect is achieved by one or more vibration generators being
arranged only
on the cover weight or the plumb, the base being stationary and the mould
walls being
fixed to the base during the creation process. In accordance with the solution
stated in
the reference, the table is to be the stationary base in order to avoid a
coupled
mechanical system with several vibrating masses, which is also illustrated in
the figure
attached to the reference.
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2
The present invention will be described in further detail in the following by
means of
examples and figures, where:
Fig. 1: shows a simplified diagram of improved vibration equipment,
Fig. 2: shows a simplified diagram of a first embodiment of vibration
equipment in
accordance with the present invention,
Fig. 3: shows a simplified diagram of a second embodiment of vibration
equipment
in accordance with the present invention,
Fig. 4: shows a simplified diagram of a third embodiment of vibration
equipment in
accordance with the present invention,
Fig. 5: shows a simplified diagram of a fourth embodiment of vibration
equipment
in accordance with the present invention,
Fig. 6: shows a diagram of a mechanical realisation of the principle in Figure
4.
The figure also shows a proposal for how the anode mass can be vibrated
with a vacuum, where a vacuum chamber encloses the anode mass and
part of the entire plumb.
The mechanical system as stated in NO 132359 has been tested in experiments,
but
the experiments showed that vibration equipment containing one vibrating mass
did not
produce the expected result. The reason for this was propagation of dynamic
energy to
the environment, and the equipment was also unstable. The table was
subsequently
improved in the experiments and converted into a mass that could be vibrated
by
placing a spring k1 and a damper d~ between the table mb and base U, see Fig.
1. In the
figure, the anode mass m~ is shown as a complex spring that may also consist
of a
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JP-A-i 1 226698 discloses an upper vibration pressing apparatus in a vibration
moulding machine for green sand mould. The principles for vibration is similar
to that of
the above mentioned reference, and is.not based upon the principles in
accordance with
the present invention.
'the present invention will be described in further detail in the fvllvwing by
means of
examples and figures, where:
to
Fig, i : shows a simplified diagram of improved vibration eguipment,
Fig. 2: r~ ~ shows a simplified diagram of a first embodiment of vibration
equipment in
. accordance with the present invention,
Fig.3: shows a simplified diagram of a second .embodiment of vibration
equipment in accordance with the present invention,
Fig, 4: shows a simplified diagram of a third embodiment of vibration
equipment
in accordance with the present invention,
Fig. 5: , shows a simplified diagram of a fourth embodiment of vibration
equipment
in accordance with the present invention,
Fig. 6: shows a diagram of a mechanical realisation of the principle in Figure
4.
The figure also shows a proposal for how the anode mass can be vibrated
- with a vacuum, where a vacuum chamber encrases the anode mass and
;.
part of the entire plumb. !
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The mechanical system as stated in NO 132359 has been tested in experiments,
but
the experiments showed that vibration equipment containing one vibrating mass
did not
produce, the expected result. The reason for this was propagation of dynamic
energy to
the environment, and the equipment was also unstable. The table was
subsequently
improved in the ~ experiments and converted into a mass that could be vibrated
by,
placing a spring ki and a damper d~ between the table mb and base U, see Fig.
1. In the
1Q figure, the anode mass ma is shown as a complex spring that may also
consist of a
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CA 02474878 2004-07-29
WO 03/068468 PCT/N003/00049
3
spring and damper element k2, d2. It is expedient for the anode mass or spring
damper
system between the table and floor to be expressed as complex springs since
complex
springs have a real spring element and a hysteresis damper element. The anode
mass
may, of course, have other forms of damping than hysteresis damping, such as
friction
damping, etc. In the same way, different forms of damping may occur in a real
damping
element such as rubber dampers mounted between the table and the base. In
Figure 1,
the vibrating plumb is shown as m,. The dynamic input force Fdyn ~n against
the
equipment is a vertical periodic force. In accordance with the above
adjustment, the
improved equipment will consist of a coupled mechanical system with two
vibrating
masses. A coupled system with two vibrating masses can also be established by
vibration being applied to the table instead of the plumb.
As a consequence of the above improvement, the noise to the environment was
considerably reduced. There were many reasons for this:
~ With 2 vibrating masses and by selecting a frequency range in which the
table
and the plumb will vibrate in virtual phase opposition (towards 180°),
the dynamic
gain of the compression force against the anode mass increased since the table
also accelerated and contributed to the compression force. This meant that the
dynamic input force against the equipment could be reduced to achieve the same
dynamic compression against the anode mass. In turn, this led to the
dynamically
transmitted force against the base U being reduced since the dynamic input
force
was reduced.
~ The damper d~ between the table mb and the base U dissipated dynamic energy.
~ The base U was protected against shocks from the plumb. A shock contains a
range of frequency components. The dynamic energy against the floor could be
very high and random if the energy came directly from the plumb. The table was
given a protective role so that the floor experienced a continuous sinusoidal
force
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4
from the table with the same frequency component as the dynamic input force
had, rather than shocks from the plumb.
~ The equipment was stabilised on account of the damper element d1. Low-
frequency unstable fluctuations of the equipment were damped.
In connection with the development of the equipment in accordance with the
present
invention, it was decided, on the basis of the above knowledge, that the
equipment
would not comprise a base or foundation (the large passive mass under the
equipment).
It was found that optimal equipment should, as far as possible, be able to
insulate the
dynamic energy itself, so that it is absorbed in the equipment and, as far as
possible, in
the mass to be compacted/moulded, and so that a minimum quantity of it is
emitted to
the environment. In the improved equipment, a foundation under the floor on
which the
vibration equipment may rest has the sole task of damping the rest of the
dynamic
energy that is emitted from the vibration equipment.
In the aforementioned patent NO 132359, it is also proposed that a "constant
compressive force, for example by means of a hydraulic cylinder" (reference
number 16
in the figure) be applied to the plumb. The intention was to reduce the weight
of the
plumb. This is a very unfortunate way of applying external static force to the
plumb.
Firstly, the hydraulic cylinder was connected in stationary fashion to the
base. Dynamic
energy will then be propagated via this connection to the base. Secondly, the
hydraulic
cylinder contains damping and will directly dissipate dynamic energy that was
intended
for the anode mass. The dynamic gain towards the anode mass was reduced.
Experiments with a hydraulic cylinder were carried out, but failed for the
above reasons.
The present invention concerns further improvements to the prior art by means
of a
method and equipment for compacting materials, in particular vibration of
"green mass"
in a moulding process for the creation of mould bodies for the production of
electrodes
for the melting industry. The equipment comprises two mould parts, at least
one of
CA 02474878 2004-07-29
WO 03/068468 PCT/N003/00049
which has vibration applied to it during the compaction process. Moreover, the
mould
parts, for example the table and plumb, are mutually physically integrated
during
vibration by means of a static compressive force, which may consist of at
least one
spring k3. The vibration equipment may be designed as a closed system in which
the
5 vibration energy is emitted to the environment as little as.possible. Four
embodiments of
the equipment, which are closed systems, are shown in Figures 2-6. A
fundamental
difference between the embodiment shown in Figure 1 and those shown in Figures
2-6
is that the table in the latter is connected to the plumb via one or more
springs ks, or an
arrangement equivalent to a spring k3.
Although the figures show that the plumb is vibrated, the principles of the
present
invention can also be implemented by the table being vibrated. The principles
of the
present invention may also be utilised by horizontal vibration of the mould
parts. The
mould parts may then be mounted in such a way that they can slide across a
mainly
horizontal base, for example by the mould parts being supported by a support
that is
able to slide in a horizontal direction (not shown).
With the present invention, materials can be compacted faster and more
precisely with
a higher degree of compaction and with less loss of energy to the environment
than is
possible with prior art equipment. Figure 6 also shows how it is possible to
realise such
equipment mechanically in such a way as also to achieve vibration with a
vacuum,
where the vacuum chamber is as small as possible and the gas evacuation time
is
minimal. These and other advantages can be achieved with the present invention
as it is
defined in the attached claims 1-18.
The attached Figures 2-5 are simplified diagrams of vibration equipment during
vibration
when a mass ma is compressed or compacted. Figure 6 is a realisation of the
simplified
diagram in Figure 4. Figures 2-6 will be explained using the following
definitions:
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6
Definitions:
U: The base.
ma: The mass to be compressed by the vibration equipment.
k2: The spring constant of the mass ma.
d2: The damping of the mass ma. The damping may be in the form of hysteresis,
viscous
damping, friction, etc. (only one symbol is used for damping in the figures
although we
may have combinations of different forms of damping).
m,: The mass of the plumb or the mass that oscillates between the mass m~ and
the
body with spring constant k3. The vibration unit for plumb vibration is
included in this
mass. In some setups, there may also be a yoke included as the plumb mass, as
shown
in Figures 3, 4 and 6. As we see in Figure 6, only part of the plumb's total
mass is in the
vacuum chamber. The yoke and the vibration unit are outside, but are
permanently
connected with bolts to the part of the plumb that is inside the vacuum
chamber.
mb: The mass of the table. The mass that oscillates between the mass ma and
the body
with spring constant k~ or the body with damper element d~.
k~: One or more bodies with a total spring constant k~, placed between the
table with
mass mb and the base U.
d~: One or more bodies with a total damping d1, placed between the table with
mass m,~
and the base U. The damping may be in the form of hysteresis, viscous damping,
friction, etc. (only one symbol is used for damping in the figures although we
may have
combinations of different forms of damping).
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k3: A body with spring constant k~. The plumb must be connected to the table
via
equipment with properties equivalent to those of a spring k~. The equivalent
spring must
be progressive in the sense that the static force through it must be
independent of how
much the mass ma is compressed. With k~ it must be possible to vary the static
force
from the table to the plumb or keep it constant regardless of the compression
of the
mass ma. At the same time, the equipment that is to represent k3 must have
minimum
damping since it takes dynamic energy from the equipment as a whole. One
example of
such equipment may be air pressure adjustable bellows, as shown in Figure 6,
where
one set of bellows is placed at each end of the yoke. The bellows "press" the
plumb
towards the mass ma during vibration. The bellows receive the compressive
force from
the table mb.
As an exception, the body with spring constant k3 may also have a fixed spring
characteristic if the table's "side legs" can be height adjusted during
vibration, as shown
in Figure 5, so that the static force through k3 is independent of how much
the mass ma
is compressed. Such height adjustment can be implemented by the side legs
being
telescopic, for example by using screw jacks or hydrauliclpneumatic cylinders.
Fdyn_in: The mechanical dynamic input force to the vibration equipment. A
periodic force
with one or more frequency components. The vibration unit fixed to the plumb
for plumb
vibration generates the dynamic input force. Fdyn in has the same direction as
the mass
ma that is compressed. In Figure 6, the vibration unit is integrated in the
yoke.
The parameters' effect during vibration for plumb vibration:
k1: The vibration equipment was a coupled mechanical system with 2 vibrating
masses,
an active mass m, and a passive mass mb.
~ Increase in dynamic gain of dynamic forces against the mass ma.
The compression force against the mass ma increases since the
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8
mass mb also contributes to a great extent to the dynamic
compression force.
~ Reduced noise to the environment since the table and plumb in
virtual phase opposition cancel each other out to a great extent
against the base. The transmitted dynamic force against the base is
therefore less.
d1:
~ Higher stability since d~ filters out low-frequency unwanted
fluctuations in the vibration equipment on the table and plumb and
thus prevents the equipment from becoming unstable.
~ Less noise to the environment since d~ dissipates energy and
functions as a buffer against the base.
~ However, reduced dynamic gain of dynamic forces against the
mass ma may occur if the damping is too high or the fundamental
frequency of the compression force is too low so that it is in the low-
frequency range that d1 has the task to damp.
k3: Introduction of k3: with static force from the table to the plumb.
~ Further increase in dynamic gain of dynamic forces against the
mass ma on account of a higher compression amplitude of the
mass ma and a higher frequency. Since it is possible to increase the
static force against the mass ma with ks, the dynamic force against
the mass ma will also increase. The vibration unit is also indirectly
connected to the table via k3 so that this contributes to increased
acceleration of the table and thus also to increased dynamic force.
Another reason for higher dynamic gain is that the static force
through k3 leads to the dynamic fluctuation of the mass ma
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approaching the total dynamic fluctuation of the table and plumb.
The plumb's dynamics are thus "pressed" further down in the mass
ma to be compressed. This leads to a higher compression
amplitude of ma. The working frequency of the equipment also
increases because the mass ma accelerates the table and plumb to
a greater extent because it is in longer contact with the plumb over
an oscillation period. The higher dynamic force will contribute the
possibility of a higher degree of compaction of the mass ma to be
compacted.
~ Reduced vibration time on account of a higher frequency and
higher compression amplitude of ma. This leads to higher capacity.
Measurements show that the time can be reduced from a vibration
time of approximately 60 seconds to approximately 20 seconds.
~ Reduced noise since k3 stores dynamic energy inside the
equipment and thus emits less to the environment. Stored dynamic
energy in k3 is emitted to the mass ma at the time in the vibration
when k3 is extended or ma is compressed. The equipment becomes
more of a closed system. If the spring rigidity in k3 is increased, the
equipment can store more dynamic energy.
~ Higher stability since d~ can be increased further without the
compression force against the mass ma being reduced. One of the
advantages of the present invention is that it is possible to set the
vibration frequency of the equipment with just the vibration unit. The
working frequency can thus be moved to a greater extent out of the
low-frequency range so that it is easier to damp low-frequency
signals with d~ without damping the compression signal that has a
higher frequency (easier to introduce a high pass filter). It is
therefore easier to increase the damping d~ without any negative
impact on the dynamic gain against the mass to be compressed.
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~ Flexibility. Since the static force against the mass ma can be
adjusted via k3, it is possible to adjust the size of the dynamic force
against the mass ma. In Figure 6, the air pressure in the bellows can
be optimised to determine the size of the force. With the vibration
5 unit, the amplitude [mm]/frequency ratio [Hz] of the dynamic
fluctuation of the table and plumb is set. If the equipment is to
function more as a beat oscillator, the frequency is reduced with the
vibration unit to increase the amplitude [mm] of the dynamic
fluctuation of the table and plumb. If the equipment is to function
10 more as a "vibration press", the frequency is increased with the
vibration unit so that the amplitude [mm] of the dynamic fluctuation
is reduced. Such a setting also reduces the noise to the
environment since impacts are reduced if we keep the same
dynamic size of the force with the compressed air in the bellows.
The optimal ratio here depends on the mass to be compacted, its
dimensions and whether it is vibrated with a vacuum or not.
~ Maintenance and robustness. The flexibility stated above can
lead to a reduction in impacts. This reduces the wear on the
equipment and considerably reduces the noise level.
Reduced dynamic energy to the environment:
The vibration frequency is adjusted as with the modified equipment towards the
frequency at which the dynamic gain against the anode mass is greatest. This
is also
the frequency at which the table and plumb approach phase opposition. Because
the
plumb and table are connected to each other via the spring k3, the plumb will
contribute
to pressing the table up when the table is on its way down towards the floor.
Since the
transmitted dynamic force against the floor is the sum of the plumb and table
forces,
where the plumb force acts in the opposite direction to the force from the
table, the
transmitted dynamic force to the base will be reduced. This results in the
vibration
equipment emitting less dynamic energy to the environment. In other words,
dynamic
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energy will be stored in the spring k3 when the table is in the low position
and the plumb
is in the high position (spring k3 compressed). The spring then emits energy
to the
anode mass when it is extended (the anode mass is compressed). Dynamic energy
is
stored to a greater extent inside the system and less is emitted to the
environment. Here
it is important for the spring k3 to have minimal damping so that the energy
that is stored
in the spring is used to compress the anode mass and is not converted into
other forms
of energy such as heat, etc.
Increased dynamic Gain against the anode mass:
With increased dynamic gain against the anode mass, there is an increased
possibility
of higher dynamic forces against the anode mass andlor lower dynamic input
force
(eccentric force). This allows for the product to have a higher density and
for higher
capacity.
Stability:
With stable equipment, there are no random fluctuations of the table and plumb
that
disturb the steady supply of energy to the mass ma to be compressed. As the
equipment
in accordance with the present invention has at least one low resonance
frequency in
addition to the working frequency chosen, it is important to prevent the
equipment from
oscillating at these frequencies. It is also important to design the equipment
so that
dynamic gain in these low frequency ranges is minimised. With the present
invention, it
is possible, with the vibration unit, to increase the working frequency of the
equipment.
The damping d1 can thus be increased to minimise low-frequency fluctuations.
An upper
limit for this damping will be where no significant reduction in dynamic gain
against the
mass ma is achieved at the working frequency of the equipment.
By regulating the static compressive force from the spring k3, it is possible
to adjust the
density of the compacted product. The compacting time may also be reduced with
an
increased static compressive force. This means that the capacity of the
equipment can
be increased. With the proposed equipment, the compressive force can also be
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12
adjusted during the compaction process itself if this is required. For
example, it may be
effective to vibrate initially at a relatively high compressive force, which
subsequently
decreases, and to increase it again towards the end of the vibration process.
Vibration equipment built in accordance with the present invention may
comprise means
that make it possible to vibrate electrodes so that they have the same density
or the
same physical dimensions. This can be achieved by the equipment being fitted
with
measuring equipment that registers how far down the plumb goes during
vibration. The
quantity of material placed in the mould before vibration is predefined, and
it is then
simple to establish a value that indicates weight/volume. The vibration may be
terminated when a specific level has been reached so that the physical
external
dimensions are identical.
Moreover, the vibration equipment may have equipment that generates a vacuum
in the
volume that is delimited by the mould parts (the plumb, the table and the
mould walls)
containing the mass ma so that any gas can be removed from the moulds (vacuum
vibration). This will result in increased density, reduced risk of cracks and
vibration at
higher temperatures, etc. Figure 6 shows how this can be realised. Some of the
complete plumb is inside the vacuum chamber Vr formed by the mould walls Fvl,
Fv2
and a vacuum lid Vk. The vacuum lid can be connected via a pipe to equipment
that
generates a vacuum in the vacuum lid such as a fan or similar (not shown). The
rest of
the total plumb mass (the yoke .4 and the vibration unit Ve) is outside, but
permanently
connected with bolts B1, B2 to the part of the plumb Ld that is inside the
vacuum
chamber Vr. This results in the smallest possible vacuum chamber, and the
evacuation
time of the gases can be minimised. The bolts must have the smallest possible
overall
cross-section so that the vacuum has the least possible "suction effect" on
the yoke. At
the same time, the bolts must be sufficiently dimensioned and located so that
the
connection is robust and the torque in the yoke is within reasonable limits.
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As the mass m~ is compacted during vibration, the yoke ~ will approach the
vacuum lid.
There must therefore be a minimum distance to the yoke from the part of the
plumb that
is inside the vacuum chamber. This distance can be reduced if the vacuum lid
also has
telescopic properties. The overall height of the vibration equipment can,
however, be
reduced by integrating the vibration unit in the yoke.
