Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
_ CA 02097261 1998-OS-06
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PROCESS FOR TREATING MOLTEN METAL DURING A CASTING
OPERATION USING A FILTER AND FILTER FOR IMPLEMENTING THE
PROCESS
BACKGROUND OF THE INVENTION
Field of the invention
The present invention concerns a process for
treating a molten metal during a casting operation into a
mold using a filter, the process including the step,
prior to casting the molten metal, of placing a material
for treating said metal at a point or_ the channel adapted
to guide said metal to the filter.
The invention also concerns a filter for
implementing the process in accordance with the
invention.
Description of the prior art
The treatment agents are usually merely placed in
the channels for the molten metal, which is time-
consuming.
It is also known to distribute products for
treating the metal by placing the treatment products in
destructible sachets which are disposed in a corner or a
cul-de-sac of the channels for the metal upstream of the
filter; this process has the drawback that it does not
guarantee that all of the metal comes into contact with
the treatment agents.
Because of turbulence caused by the flow of the
metal in the casting channels the destructible sachets
are sometimes dislodged from where they are placed and
travel upstream into the funnel into which the molten
metal is poured. This results in wastage of the unused
treatment material and rejection of the cast parts
because the metal is insufficiently treated. Also the
molten metal does not enter fully into contact with the
treatment material and the metal cast in the mold may not
be homogeneous.
2
It is also known to treat the liquid metal by placing on
the upstream side of the filter pastilles of treatments products
held together by a binder or by pressing and/or sintering and/or
molding them: once again, there is no guarantee that all of the
metal has been treated. Also, this represents a further handling
operation.
An object of the present invention is to remedy of the
aforementioned type whereby all of the cast molten metal is
treated as regularly and as homogeneously as possible and the
treatment material is entirely used to treat said metal.
Another object of the invention is to propose a filter for
implementing said process.
SUMMARY OF THE INVENTION
An apparatus for filtering and treating molten metal
adapted to implement a process for simultaneously filtering
and
treating a molten metal during an operation to cast said molten
metal into a mold, said apparatus comprising a series of at
least
two refractory mineral material filtering plates in contact
with
each other at their periphery and defining between them at
least
one cavity, said filtering plates each having a series of
filtering holes through which said molten metal flows and by
which said molten metal is filtered, the dimensions of the
filtering holes and the number of the filtering plates being
selected so as to eliminate from the molten metal solid
inclusions likely to affect the quality of the cast metal,
said
apparatus containing within said at least one cavity an inorganic
treatment material for treating said molten metal flowing through
the cavity, said treating material being in the form of one
of
solid compressed or molded or sintered treating plate positioned
in said at least one cavity and extending over substantially
the
length and the width of said at least one cavity, said treating
plate having when viewed in the direction of metal flow, a
shape
such that one or more passage holes are arranged in or around
said treating (or inoculating) plate for said molten metal
to
pass through said passage holes and through said apparatus.
In this way it is certain that the treatment material will
not be expelled from the cavity by turbulence caused by the
flow
of the molten metal, as it is retained between two plates,
and
that it will all be used to threat the metal. This eliminates
any risk of rejection of the cast parts because of defective
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treatment of the metal.
Furthermore, all of the molten metal passing through the
filter is brought into contact with the treatment material and
this contact takes place within the cavity of the filter where
the metal travels at a lower speed than in the channels.
It has been found that metal cast by the process of the
invention has a better distribution of the treatment product and
improved treatment homogeneity as compared with the prior art
processes.
Without wishing to claim that this is the only possible
explanation of this unexpected and surprising result, it is
thought that he result is due to the very slow speed at which the
metal travels in the filter cavity compared to the much higher
speeds at which it passes through the holes in the plates. This
causes energetic and very regular mixing of the untreated metal
reaching the interior of the cavity at high speed and the already
treated metal remaining in this cavity before it is evacuated
through the holes in the second plate, this. mixing continuing
throughout the duration of casting.
Combined with the fact that the treatment product is
trapped within the cavity and cannot be expelled from it under
any circumstances, this mixing probably explains the very regular
distribution of the treatment product in the metal of the cast
part and the excellent homogeneity of the result of treating said
metal within said part.
An apparatus for filtering and inoculating molten metal
adapted to implement a process for simultaneously filtering and
inoculating a molten metal during an operation to cast said
molten metal into a mold, said apparatus comprising a series of
at least two refractory mineral material filtering plates in
contract with each other at their periphery and defining between
them at least one cavity, said filtering plates each having a
series of filtering holes through which said molten metal flows
and by which said molten metal is filtered, the dimensions of the
filtering holes and the number of the filtering plates being
selected so as to eliminate from the molten metal solid
inclusions likely to affect the quality of the cast metal, said
apparatus containing within said at least one cavity an inorganic
inoculating material for inoculating said molten metal flowing
through the cavity said inoculating material being in the form
of one of solid compressed or molded or sintered inoculating
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plate positioned in said at least one cavity and extending over
substantially the length and the width of said at least one
cavity, said inoculating plate having when viewed in the
direction of metal flow, a shape such that one or_ more passage
S holes are arranged in or around said treating (or inoculating)
plate for said molten metal to pass through said passage holes
and through said apparatus.
This enables the preparation of prefabricated filters
containing a predetermined dose of the treatment product:
filters of this kind are highly suited to mass production,
facilitate the work of the casting shop and reduce the problems
associated with management of consumable materials and products
for such shops.
In one beneficial embodiment of the invention the filter
comprises at least two plates joined together along their
periphery, the cavity formed between said two plates is filed
with said powdered treatment material and said holes in said
plates are blocked k.~y a film of a material adapted to melt,
carbonize or calcine in contact with the molten metal to be
treated, said film being disposed on the inside or the outside
surface of each plate.
In this way the treatment material can be easily sealed by
an insulated film of this kind against moisture in the atmosphere
so that it remains perfectly dry, enabling problem-free storage
of prefabricated filters.
The filters are used to eliminate from the liquid metal any
solid inclusions such as metal oxides likely to affect the
quality of the metal which is cast into a container such as
a
mold or a mold for ingot.
The effectiveness of any such filter depends essentially on
the diameter of the holes and the number of plates constituting
it. The smaller the diameter of the holes the greater the
ability of the filter to hold back fine inclusions and the more
effective the filter action.
If the holes have a diameter less than 1 mm filtration
takes a very long time (because the liquid metal passes through
holes this size with great difficulty) and the holes rapidly
clog.
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If the number of plates is increased the cost of
the filter is increased.
In one advantageous embodiment of the invention
said treatment material is an inoculating material in
5 plate form optionally comprising one or more holes for
said liquid metal to pass through.
This inoculating material improves the
characteristics of the metal.
Thus the inoculating material makes it possible to
increase very significantly the effectiveness of the
filter by virtue of a barrage effect. Also, the cavities
in the filter plates form receptacles which are
particularly well suited to receiving the inoculating
material with the result that use of this material does
not require any modification of the filter.
When the liquid metal enters the filter it laps the
surface of this plate which treats the metal with the aim
of improving it.
In one advantageous embodiment of the invention at
least the side of said plate adjacent the bottom of the
cavity comprises a series of recesses.
These recesses increase the area of contact between
the liquid metal and the inoculating material which
increases the effectiveness of the inoculation reaction.
In one embodiment of the filter in accordance with
the invention said inoculating material is in the form of
spaced bars extending across substantially all of the
length and the width of a cavity.
Such bars are simple to manufacture and also make
it possible to obtain a large area of contact between the
inoculating material and the liquid metal without
impeding the passage of the latter through the filter.
In another embodiment of the invention at least one
of the cavities is filled with a filter material.
This filter material comprises refractory fibers,
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for example, and further increases the effectiveness of
filtration.
The inoculating material is preferably selected
from the following substances: alloys of iron, magnesium
and magnesium compounds, calcium and its compounds,
lithium compounds, strontium and barium compounds,
silicon, zirconium, aluminum, rare earth, graphite and
carbon.
- Other features and advantages of the invention will
emerge from the following description given by way of
non-limiting example and with reference to the appended
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a view in cross-section on the line I-I
in figure 2 of a two-stage filter in a first embodiment
of the present invention.
Figure 2 is a plan view of the filter from
figure 1.
Figure 3 is a view similar to figure 1 of a filter
comprising only one cavity.
Figure 2 is a view to a larger scale and in cross-
section-of a filter in a second embodiment of the present
invention.
Figure 5 is a view similar to figure 4 comprising
two adjoining half-views of respective variants of the
filter shown in said figure.
Figure 6 is a view in cross-section on the line
VI-VI in figure 7.
Figure 7 is a plan view with the top plate removed
comprising two adjoining half-views of respective
variants of a third embodiment of the present invention.
Figure 8 is a view in cross-section of a fourth
embodiment of the filter in accordance with the
invention.
Figure 9 is a partially cut away plan view of the
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filter from figure 8.
Figure 10 is a view in cross-section of a fifth
embodiment of the filter.
Figure 11 is a plan view of the filter from
figure 10.
Figure 12 is a partial view in cross-section of a
sixth embodiment.
Figure 7 is a view in cross-section of a seventh
- embodiment.
DETAILED DESCRIPTION OF THE INVENTION
As shown in the figures, the process with which the
invention is concerned for treating molten metal during
an operation of casting it in a mold using a filter 1,
la, lb, lc, ld, le comprises the step, prior to casting
the molten metal, of placing a material 12, 22, 23, 24
for treating said metal at a point on the channel -adapted
to guide said metal to said filter.
In the process of the invention a filter 1, la, lb,
lc, ld, le for liquid metal is used which comprises a
series of at least two refractory mineral material plates
2, 2a, 2b in contact with each other at their periphery
and defining between them one or more cavities 4, 5, 6,
each plate 2, 2a; 2b comprising a series of holes 3, 3a,
3b through which the liquid metal passes and by which it
is filtered, and the treatment material 12, 22, 23, 24 is
introduced into at least one of the cavities 4, 5, 6
before the filter 1, la, lb, lc, ld, le is placed in a
mold (not shown) such as a cylindrical sleeve.
The treatment material 12, 22, 23, 24 is selected
from desulphurizing, thermogenic, inoculating,
spheroidizing, recarburizing, refining and modifying
products and additive alloys.
The weight of the treatment material 12, 22, 23, 24
may vary between approximately 0.001% and 1°s of the
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weight of the liquid metal depending on the nature of the
treatment to be applied.
The filter la shown in figure 1 comprises three
plates 2, 2a, 2b. The plates 2 and 2a each have a
projecting peripheral rim 11 adapted to come into contact
with the respective adjacent plate 2a, 2b which is thus
spaced from it to form a respective cavity 4, 5. The
plate 2b has no such rim, as this would increase the
height of the filter 1 with no benefit.
The upper plate, which is normally on the upstream
side, has progressively increasing diameter holes 3, 3a,
3b in it. The plates 2a, 2b also have holes in them, of
the same diameter or different diameters. The holes in
the intermediate plate 2a are arranged in a quincunx
arrangement relative to the holes in the outer plates 2
and 2b. The holes 3, 3a, 3b may be non-circular. -
In the known way the plates 2, 2a, 2b are made from
a ceramic refractory mineral material such as silica, for
example, and are able to withstand the temperature of the
cast metal without distortion.
The filter 1 shown in figure 2 comprises a plate 2
with holes 3 of substantially the same diameter.
The filter lb shown in figure 3 comprises two
plates 2a whose peripheral edges 11 are adjacent and
fastened together by an adhesive 10. The heights of the
rims 11 are shown the same but they could be different.
The two plates delimit a cavity 6.
Figures 4 and 5 on the one hand and figures 6 and 7
on the other hand respectively show a filter lc, ld
comprising two plates 2a in contact at their peripheral
edge 11 to delimit a cavity 6.
In the embodiment shown in figures 8 through 12 the
liquid metal filter comprises three refractory material
plates 2, 2a, 2b in contact with each other at their
periphery and defining between them a plurality of
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cavities 5, 6, 7. The plates 2, 2a, 2b each comprise a
series of holes 3 through which the liquid metal passes
and by which it is filtered as it passes through the
filter in the direction of the arrow D.
As shown in figures 1 through 12, and in accordance
with the invention, at least one of the cavities 4, 5, 6
of the filter 1, la, lb, lc, ld, le contains a material
for treating the molten metal.
In the embodiment of figures 1, 3, 4 and 5 the
treatment material 12 is in powder form and is retained
by a film 13 of a material adapted to melt, carbonize or
calcine in contact with the liquid metal to be treated.
The particle size of the powder material is
selected in accordance with the required treatment
conditions.
The film 13 of a material adapted to melt,
carbonize or calcine in contact with the metal to be
treated is an aluminum or paper or plastics material or
composite film, for example.
In the embodiment of figures 1 and 3 the treatment
material 12 is contained in sachets 8, 8a, 8b made from
said film 13 and placed in said cavity 4, 5, 6.
The cavities 4 and 5 in figure 1 each contain a
respective sachet 8, 8a which fills the respective cavity
4, 5 partially or almost completely. The sachets 8, 8a
may be identical or have different capacities.
The cavity 6 in figure 3 contains a sachet 8b
disposed eccentrically in said cavity 6, for example.
In the embodiment of figures 4 and 5 the cavity 6
formed between the two plates 2a is filled with powdered
treatment material 12 and the holes 3 in the plates 2a
are blocked by a film 13 of the aforementioned type
disposed on the inside or outside surface of each
plate 2a.
In the figure 4 example a film 13 is fixed (for
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example glued) to the inside surface of the upper plate.
Another film 13 is fixed to the outside surface of the
lower plate, the holes 3 being filled with treatment
material 12.
5 In the figure 5 example the films 13 are fixed to
the inside surfaces of the plates in the lefthand half-
view and to the outside surfaces of the plates in the
righthand half-view. This latter case represents the
- maximum volume of treatment material 12 that can be
10 contained in the filter lc.
In the embodiment of figures 6 and 7 the powdered
treatment material 12 is pressed or sintered to form
plates 14a, 14b or bars. The dimensions of the plates
14a, 14b or-bars are less than or equal to the inside
dimensions of the cavity 6 so that as soon as casting
begins the plates or bars can move inside the cavity 6
due to the turbulence caused by the arrival of the molten
metal in the cavity 6.
The lefthand half-view shows, by way of example, a
hexagonal contour plate 14a whereas the righthand half
view shows an annular plate 14b. Plates 14a, 14b of this
kind are pressed with a binder such as stearate or the
like, for example; the treatment material 12 prepared in
crystallized form, for example, can also be bound
together under high pressure. The plate 14a includes a
central hole 15 through which the metal passes. It could
comprise other holes of various shapes and sizes.
The treatment materials may be desulphurizing
agents, for example magnesium and/or calcium carbide,
and/or thermogenic agents, for example calcium carbide,
and/or inoculation and/or post-inoculation agents and/or
spheroidizing agents, for example magnesium and/or rare
earths and/or ferrosilicomagnesium, and/or additive alloy
agents, for example molybdenum, boron, silicon,
ferrosilicon, manganese, chromium, titanium,
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ferroaluminium, silicomishmetal alloys, recarburizing
agents, for example based on carbon or graphite, or
fluxes for modifying the structure of the metal, such as
sodium, phosphorous, boron, titanium, strontium, etc
salts.
Figures 8 through 13 show other embodiments of the
invention in which the treatment material is a material
22, 23, 24 for inoculating the liquid metal. In the
example shown in figure 8 the cavities 5, 6 each contain
an inoculating material 22.
In the case of figures 8 and 9 the inoculating
material 22 is in the form of a plate comprising holes 25
through which the liquid metal passes and extending over
substantially all of the length and the width of the
cavity 5 or 6.
The side of each plate 22 adjacent the bottom of
the cavity 5 or 6 further comprises a series of recesses
26 made up of a series of parallel dihedra.
In the figure 8 example the other side of the plate
22 also comprises recesses 27. Figures 8 and 9 also show
that the holes 25 in the inoculating material plate 22
have a larger cross-section than the holes 3 in the
refractory material plates 2, 2a, 2b.
When the liquid metal (steel or cast iron) passes
through the filter le shown in figure 8 it first comes
into contact with the upper surface of the inoculating
material plate 22, passes through the holes 25 in this
and then fills the recesses 26 on the lower surface of
the plate 22, thereafter flowing through the filter holes
3 in the plate 2.
Because the holes 3 are smaller than the holes 25
in the inoculating material plates 22 the metal fills the
recesses 26 which achieves a large area of contact
between the liquid metal and the inoculating material
which is beneficial to the metal treatment reaction.
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In this way the presence of the inoculating
material 22 in the filter in combination with the filter
holes 3 makes it possible to improve the metal more
effectively than by means of a simple filtration
operation.
In the embodiment of figures 10 and 11 the
inoculating material 23 is in the form of spaced bars 28,
29 extending over substantially all the length and the
width of the cavities 5 and 6 in the refractory plates
2, 2a.
In this embodiment the bars 28, 29 are disposed in
two superposed and crossed layers, as shown in figure 11
in particular.
During -filtration the liquid metal laps over the
surface of the bars 28, 29 and then accumulates at the
bottom of the cavities 5, 6 before flowing downwardly
through the holes 3.
This embodiment also achieves a large area of
contact between the liquid metal and the inoculating
material enabling the yield from the inoculant to be
improved.
In- the figure 12 embodiment the side of the
inoculating material plate 24 adjacent the bottom of the
cavity 5 of the refractory plate 2 has a recess 30
delimited by a peripheral lip 31 which rests on the
bottom of the cavity 5. This plate 24 has holes 32 in it
through which the liquid metal passes.
As in the embodiments of figures 8 through 11 the
holes 32 in the inoculating material plate 24 are larger
than the holes 3 in the plate 2. Because of this the
liquid metal which is poured onto the plate 24 passes
through the holes 32 and then fills the recess 30 before
flowing through the holes 3 in the plate 2.
By filling the recess 30 the liquid metal is in
contact with a large proportion of the surface of the
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inoculating material 24 so that the inoculation action is
more effective.
In the figure 13 example the inoculating material
is in the form of a plate 2c with holes 3c the same shape
as those of the refractory material plates 2, 2b and is
substituted for one of the latter.
Also, as shown in figures 8, 10 and 13 at least one
of the cavities of the refractory material plates 2, 2a,
2b is filled with a filter material 20, for example with
refractory fibers.
The filter material 20 is preferably disposed in a
cavity 7 on the side of a cavity 5 or 6 containing an
inoculating material 22 or 23 which is the downstream
side relative to the direction D in which the liquid
metal passes through the cavity (see figures 8 and 10).
The filter material 20 is effective in its own
right and further enhances the performance of the filter
in accordance with the invention.
To give a non-limiting example, the inoculating
material is selected from the following substances: iron
alloys (Fe-Si alloy, for example), magnesium and
magnesium compounds, calcium and calcium compounds,
lithium compounds, strontium and barium compounds,
silicon, zirconium, aluminum, rare earths, graphite and
carbon.
Of course, the invention is not limited to the
embodiments that have just been described and numerous
modifications may be made thereto without departing from
the scope of the invention. The pressed or sintered
plates 14a, 14b may be replaced with solid molded plates.
