Note: Descriptions are shown in the official language in which they were submitted.
V~ t7
The present invention relates to the degassing and
iltration of molten metal, and particularly to the treatment
of said metal with a fluxing gas.
Molten metal, particularly molten aluminum, in practice
generally contains entrained and dissolved impurities, both
gaseous and solid, which are deleterious to the final cast
product. These impurities may affect the final cast product
after the molten metal is solidified, whereby processing may
be hampered or the final product may be less ductile, or have
poor finiqhing and anodizing characteristics. The impurities
may originate from several sources. For example, the impuri-
ties may include metallic impurities such as alkaline and al-
kaline earth metals, and occluded hydrogen gas and dissolved
surface oxide filmq which have become broken up and are en-
trained in the molten metal. In addition, the inclusions may
originate as insoluble impurities, such as carbides, borides
and others or eroded furnace and trough refra~tories.
It is naturally highly desirable to improve the de-
gassing and filtration of molten metals in order to remove or
minimize quch impurities in the final cast product, particu-
larly with respect to molten aluminum and especially, for ex-
ample, when the resultant metal is to be used in a decorative
product, such as decorative trim or sheet, or products bearing
critical specifications, such as aircraft forgings and extru-
~ions, and light gauge foil stock. Impurities as aforesaid
cause loss of properties such as tensile strength and corro-
sion resistance in the final solidified alloy and lead to de-
gradation of processing efficiency and loss of properties in
the final product. For example, one type of finishing flaw
which is particularly significant in decorative trim or sheet
is a stringer defect known as a linear defect.
,.~ S!
--1--
~V~ 7
Conventionally conducted gas fluxing processes, such as
general hearth fluxing, have involved the introduction of the
fluxing gas to a melting or holding furnace containing a quan-
tity of molten metal. This procedure required that the furna-
ce be shut down while the fluxing gas is circulated, so that
the metal being treated would remain constant and treatment
could take place. This procedure had many drawbacks, among
them, the reduced efficiency resulting from the prolonged
idleness of the furnace during fluxing, as well as the lack of
efficiency due to the low surface area to volume ratio between
the gas flux and the molten metal. Further factors comprised
the reqtriction of location to the furnace which permitted the
re-entry of impurities to the melt before casting, and the
high emissions resulting from both the sheer quantity of flux
required and the location of its circulation.
A~ an alternative to the batch-type fluxing operations
employed as set out above, certain fluxing operations were
employed in an in-line manner, that is, the operation and as-
sociated apparatus were located outside the melting or holding
furnace and often between the melting furnace and either the
holding furnace or the holding furnace and the casting station.
m is helped to alleviate the inefficiency cauRed by furnace
shut-down, but was not a~ ~uccessful in improving the effi-
ciency of the operation itself, in that undesirably large quan-
tities of fluxing gas were often required per unit of molten
metal, which was both costly and detrimental to air purity.
Some of these processes utilized in conjunction therewith con-
ventional filter media such as open-weave glass cloth screens,
and bed filters made up, for example, of tabular alumina, which
both exhibit as a primary disadvantage the inability to main-
tain a uniform pore size.
10~0~ 7
Porous ceramic foam materials are known in the art,
for example, having been described in U.S. Patents 3,090,094
and 3,097,930. mese porous ceramic foam materials are known
to be particularly useful in filtering molten metal as des-
cribed in U.S. Patent 3,893,917 for "Molten Metal Filter" by
Michael J. Pryor and momas J. Gray, patented July 8, 1975,
and also as described in our copending Canadian Patent Appli-
cation No. 249,110 filed March 26, 1976. Said Canadian Patent
Application also describes an apparatus and method for the fil-
tration of molten metals which employs filter plates preparedfrom said porous ceramic materials.
Porous ceramic foam materials are particularly useful
for filterin~ molten metal for a variety of reasons included
among which are their excellent filtration efficiency resulting
in part from their uniform, controllable pore size, and low
cost, as well as ease of use and replaceability. me fact
that these ceramic foam filters are convenient and inexpen-
sive to prepare and use has prompted the development of means
for easily and conveniently employing these porous, molten
metal filters in an in-line degassing and filtration unit
which provides a highly efficient assembly.
Accordingly, it is a principal object of the present
invention to provide an improved method and apparatus for the
degassing and filtration of molten metal which employs filter-
type plates of uniform porosity.
It is a particular object of the present invention to
provide an apparatus and method as aforesaid which achieves
improved degasæing by counter-current contact between molten
metal and fluxing ga~ taking place within and above one of
the filter-type plates.
It i~ a still further object of the present invention
10~VS~7
to provide improvements as aforesaid which are convenient and
inexpensive to utilize and which result in highly efficient
metal degas3ing and filtration.
Further objects and advantages of the present inven-
tion will appear hereinbelow.
In accordance with the present invention, the foregoing
objects and advantages are readily attained.
The pre~ent invention comprises a highly efficient de-
gassing and filtration apparatus comprising a chamber having
respective metal inlet~ and outlets, and wall ~urfaces for the
support of at least a first and a second removable filter-type
medium in sequential spaced-apart relationship, and at least
one conduit providing at least one fluxing gas inlet port
positioned between said first and said second medium, wherein
said port is so positioned that fluxing gas issuing therefrom
is capable of disper~ion and percolation through said first
medium. The filter-type media differ in pore size and permea-
bility whereby said first medium possesses a relatively coarser
pore structure, higher permeability and larger available flow
area than said second medium. In a preferred embodiment,
filter-type media are provided which posses~ an open cell
structure characterized by a plurality of interconnected voids,
and are preferably prepared from a ceramic foam wherein said
voids are surrounded by ceramic material. Ihe filter media
may comprise plates having bevelled peripheral surfaces adapt-
ed to mate with bevelled wall surfaces on said chamber. A
resilient sealing means is provided on each of said bevelled
filter plate surfaces which is resistant to said molten metal
to sealably engage the bevelled wall surface~ of said chamber
upon installation of the filter plates.
In accordance with the method of the present invention,
--4--
lt)~t~ff7
degassing and filtration of molten metal is conducted by the
passage of a melt through a chamber wherein said melt travels
through at least two sequentially placed, spaced-apart filter-
type media, whereby said melt is brought into counter-current
contact with a fluxing gas while within and above the first of
said media, said fluxing gas, having issued from at least one
inlet port provided within said chamber between the first and
second of said media, dispersing and percolating up into con-
tact with said melt within said first medium.
During the operation of the present method, the surfa-
ce of said first filter-type medium is maintained below the le-
vel of the melt. The method may employ a fluxing gas such as
an inert gas, preferably carrying a small quantity of an active
gaseous ingredient such as chlorine or a fully halogenated car-
bon compound. Optionally, a supernatant salt cover comprised
of alkali and alkaline earth chlorides and a fluoride may be
located on the surface of said melt residing above the first
of said filter-type media.
The present apparatus and method provide a considerable
increase in productivity in the degassing of molten metal as
degassing is conducted without interruptions of the melting
furnace. Further, the design of the apparatus enables its
placement near to the casting station, whereby the possibility
of further impurities entering the melt is substantially eli-
minated.
me employment of the filter-type medium of the present
invention in the above apparatus enables the gaseous flux to
achieve a greater dispersion throughout the melt whereby
greater surface areas of flux contact with a unit of melt volu-
me is achieved. me improved kinetics attributable to the pre-
sent invention contribute to its greater efficiency.
lO~S~
In addition, the efficiency of the present invention
permits degassing to be conducted with a sufficiently lowered
amount of flux material whereby the level of effluents result-
ing from the fluxing operation is greatly reduced.
The present apparatus and method provide considerable
increase in productivity in the degassing of molten metal as
degassing is conducted without interruption of the melting
furnace. Further, the design of the apparatus permits its
placement near to the casting. me present invention enables
the operation of a fluxing and filtering process which achieves
significant reduction in the level of effluents normally result-
ing from processing of this kind.
By virtue of the employment of conveniently removable
filter-type media possessing a carefully controlled gradation
of filter properties, the apparatus and method of the present
invention are capable of achieving levels of melt purity here-
tofore attainable only with the most rigorous of processing.
Also, the employment of a relatively coarse first filter-type
medium to abstract larger entrained non-metallic particulate
before the melt reaches the second fine filter greatly extends
the useful life of the latter. In addition, these high levels
of purity are attained utilizing inexpensively manufactured
filter-type media.
The invention will now be described with reference to
the accompanying drawings which show a preferred form thereof
and wherein:
Pigure 1 is a side sectional view of the apparatus of
the present invention depicting the filter-type plates in pla-
ce therein substantially horizontally disposed.
Figure 2 is a perspective view, partly broken away, of
a filter-type medium illustrative of the present invention.
1050S~7
Figure 3 is a side sectional view of an alternate em-
bodiment of an apparatus in accordance with the present inven-
tion wherein the second filter-type medium is disposed in
substantially side-by-side relationship to the first medium.
Referring to Figure 1, an apparatus is illustrated in
location within a molten metal transfer system which may inclu-
de pouring pans, pouring troughs, transfer troughs, metal
treatment bays or the li~e. As will be discussed later on,
the apparatus and method of the present invention may be em-
ployed in a wide variety of locations occurring intermediatethe melting and casting stations in the metal processing sys-
tem. m us, Figure 1 depictq apparatus 10 in location adjacent
the exit port 11 of holding furnace 12. The rate of flow of me-
tal from holding furnace 12 is controlled by a valve means com-
prising a check rod 13. Metal flows into apparatus 10 via
a short transfer pasqageway 14 leading to chamber 15 wherein
the de~assing and filtration operations of the present inven-
tion take place. By the control of metal flow into transfer
passageway 14 by the positioning of check rod 13, melt level
16 is maintained at a point above the first of said filter-
type media, at a level depicted in Figure 1 selected for pur-
poses of illustration only.
Chamber 15 is illustrated as roughly bowl-shaped and
is disposed with its bottom recessed below the level of trans-
fer passageway 14 so that molten metal travelling thereto will
flow downwardly through the filter-type media. Chamber 15 is
characterized by the provision of at least two peripheral
rims 17 and 1~, comprising, respectively, a first and a second
peripheral rim. First peripheral rim 17 is located at the
upper portion of chamber 15 and, in Figure 1 is positioned at
a level continuous with the bottom of transfer passageway 14.
109~S~ ~'
Second peripheral rim 18, as depicted in Figure 1, is disposed
within chamber 15 so as to effectively divide it into sub-cham-
bers 19 and 20. As with the first peripheral rim 17, second
downwardly converging bevelled surface which enables the ex-
peditious installation and replacement of appropriately con-
figured filter-type media. Though rims 17 and 18 are illus-
trated as having bevelled surfaces, the invention is not li-
mited thereto, as rims possessing other means for retaining
in place the filter-type media of the present invention may
be employed as will be noted later on. Rim 18 is shown to be
reduced in size from first rim 17 to enable the unobstructed
manipulation of the filter medium located therein.
First sub-chamber 19 comprises the area residing ~et-
ween the first and second filter-type media labeled 21 and 22,
respectively. As illustrated herein, filter-type media 21
and 22 may likewise possess bevelled peripheral surfaces 23
adapted to mate with correspondingly configured peripheral
rims 17 and 18. me bevelled peripheral surfaces 23 when em-
ployed are provided with resilient sealing means 24 thereonwhich are resistant to molten metal, and the respective fil-
ter media 21 and 22 including sealing means 24 are sequential-
ly inserted into chamber 15 so that sealing means 24 in each
instance engages the respective bevelled surfaces of rims 17
and 18.
As noted earlier, the provision of peripheral rims 17
and 18 supporting respective filter media 21 and 22 effective-
ly divides chamber 15 into sub-chambers 19 and 20. Referring
again to Figure 1, in accordance with the present invention
sub-chamber 19 is provided with at least one inlet port 25
comprising the opening or openings of a conduit 26 or mani-
5~3~
fold through which a fluxing gas may be introduced to the meltfrom an outside source, not shown. The flux material which may
be employed in the present apparatus and method comprises a wi-
de variety of well-known components including chlorine gas
and other halogenated gaseous materials, carbon monoxide as
well as as certain inert gas mixtures derived from and includ-
ing nitrogen, argon, helium and the like. A preferred gas mix-
ture for use in the present invention comprises a mixture of
nitrogen with from about .1 to about 5% by volume dichlorodi-
fluoromethane, wherein the inert gaq component may further in-
clude an inert carrier such as helium, argon and mixtures
thereof, and dichlorodifluoromethane may be replaced in whole
or in part by chlorine or fully chlorinated or chlorofluorina-
ted lower hydrocarbon components containing one to six carbon
atoms and free of hydrogen. In conjunction with this gas mix-
ture, a liquid salt mixture may be employed on the surface of
the melt residing within transfer passageway 14 which would
compri~e mixtures of alkali and alkaline earth chlorides and a
fluoride. A specific such formulation may, for example, inclu-
2~ de 40-50% NaCl, 45-55% KCl and 5% Na3AlF6. me foregoing flux
materials are fully disclosed in U.S. Patent No. 3,854,934, by
James E. Dore et al,, commonly assigned, the disclosure of
which is incorporated herein by reference. As indicated above,
the foregoing compositions are presented for purposes of illus-
tration only and do not form a material limitation on the pre-
sent invention.
Referring further to Figure 1, one of the primary fea-
tures of the present invention comprises the location of the
flux inlet comprising port 25 as illustrated herein in rela-
tion to the first filter-type medium comprising filter plate
21. Specifically, the placement of port 25 is such that flux-
ing gas issuing therefrom is capable of percolating up through
_g_
~0~0 ~'7
the melt residing within sub-chamber 19 to pass through first
filter-type medium 21 where it is broken up and dispersed, and
makes counter-current contact with molten metal flowing in the
opposite direction through said filter-type medium. It is at
this point in filter 21 that the unexpectedly efficient impu-
rity removal takes place whereby relatively coarse undesirable
particulate inclusions,undesirable gases and certain dissolved
metallic elements are separated from the melt and then percola-
te up to the melt surface by the counter-current action of the
fluxing gas, where the particulate material may be subsequent-
ly removed if so desired by conventional surface treatment
techniques, such as skimming and the like. The action of the
fluxing gas is schematically illustrated in Figure 1 wherein
the gas is depicted as a plurality of bubbles 27 issuing
from inlet port 25 and passing through and above filter medium
21 to the melt surface or level 16. Further, though not illus-
trated herein, melt surface 16 may optionally possess thereon
the liquid salt cover noted earlier in conjunction with a pre-
ferred fluxing material useful with the present invention.
After contacting the fluxing gas upon passage through
filter medium 21, the molten metal flows through sub-chamber
19 and continues through filter medium 22 comprising in the
illustration a filter plate possessing a relatively fine pore
size. Whereas the primary purpose of first filter-type medium
21 is to break up the fluxing gas into a fine dispersion to
assure intimate and extensive contact with the melt, the pur-
pose of second filter-type medium 22 is to remove any remaining
non-metallic particulate material from the melt as it passes
therethrough. mus, the molten metal issuing from filter me-
dium 22 into second sub-chamber 20 is purified and is ready
for transfer to either a casting station or, if desired, fur-
ther processing, through exit trough 28.
--10--
~O~V~8~
A further primary feature of the present invention re-
sides in the provision of filter-type media of uniform, close
tolerance at a significant reduction in cost. Accordingly, the
filter-type medium of the present invention comprises a filter
plate such as that illustrated in E~igure 2. Filter plate 29
possesses an open cell structure, characterized by a plurality
of interconnected voids, such that the molten metal may pass
therethrough to remove or minimize entrained solids from the
final cast product, or to facilitate the exchange of impurities
between the melt and a fluxing gas. Such a filter may comprise,
for example, a solid filter plate made from sintered ceramic
aggregate, or a porous carbon plate. In the preferred embodi-
ment, a ceramic foam filter is utilized as described in the
aforesaid copending application. In accordance with the teach-
ing of said copending application, ceramic foam filters may
be prepared which have an open cell structure characterized
by a plurality of interconnected voids surrounded by a web of
said ceramic material. The ceramic filters have an air permea-
bility in the range of from 400 to 8000 x 10 7 cm2, preferably
from 400 to 2500 x 10 7 cm2, a porosity or void fraction of
0.80 to 0.95 and from 5 to 45 pores per linear inch, preferably
from 20 to 45 pores per linear inch. ~he molten metal flow
rate through the filter may range from 5 to 50 cubic inches
per square inch of filter area per minute. The ceramic foam
filter described in said copending application is particularly
suitable in the present invention since it is of low cost and
may be readily employed on a throwaway basis. Furthermore,
this filter is surprising effective in the filtration of mol-
ten metal, especially aluminum, at a low cost achieving sur-
prising filtration efficiency with considerable flexibility.
In accordance with the present invention, first filter-type
--11--
~v~s~l~
medium 21 may be prepared of a relatively coarse pore size
ranging from 5 to 20 ppi, which possesses an air permeability
ranging from 2500 to 8000 x 10 7 cm2, while second filter me-
dium 22 would comprise a relatively fine filter possessing a
pore count of from 20 to 45 ppi and an air permeability from
400 to 2500 x 10 7 cm2. Naturally, as noted earlier, both
permeability and pore size of the respective filter-type media
may be varied to suit the particular material being filtered,
and the present invention should not be limited to the afore-
noted exemplary ranges.
The ceramic foam filter preferably utilized in thepresent invention is prepared from an open cell, flexible foam
material having a plurality of interconnected voids surrounded
by a web of said flexible foam material, such as polyurethane
foamq or cellulosic foams. m e ceramic foam filter may be pre-
pared in accordance with the general procedure outlined in U.S.
Patent 3,893,917 wherein an aqueous ceramic slurry is prepared
and the foam material impregnated therewith qo that the web
thereof is coated therewith and the voids substantially filled
therewith. me impregnated material is compressed so that a
portion of the slurry is expelled therefrom and the balance
uniformly distributed throughout the foam material. The coat-
ed foam material is then dried and heated to first burn out
the flexible organic foam and then sinter the ceramic coating,
thereby providing a fused ceramic foam having a plurality of
interconnected voids surrounded by a web of bonded or fused
ceramic in the configuration of the flexible foam. Naturally,
a wide variety of ceramic materials may be chosen depending
upon the particular metal to be filtered. Preferably, a mixture
of alumina and chromia is employed, however, these materials
may naturally be utilised separately or in combination with
other ceramic materials. Other typical ceramic materials
109~ '7
which may be employed include zirconia, magnesia, titanium
dioxide, silica and mixtures thereof. Normally, the slurry
contains from about 10 to 40% of water and one or more rheolo-
gical agents, binders or air setting agents.
As shown in Figure 2, the filter plate of the present
invention 29 may have a bevelled peripheral surface 30 adapted
to mate with the similarly bevelled rims of the filter chamber
illustrated in Figures 1 and 3. Naturally, variations in
design are contemplated within the scope of the present
invention and thus a wide variety of geometric configurations
may be contemplated within the scope of the apparatus disclosed
herein, and the illustration of Figure 2 is not meant to be li-
miting thereto.
In the instance where the filter plate of the present
invention is designed to be a throwaway item, it is essential
to provide an effective means of sealing the filter plate in
place in its holder which is easy to assemble, disassemble and
clean up. The holder or filter chamber itself is normally an
integral part of a trough, pouring pan or tundish, etc. and
should be constructed of refractory materials resistant to the
molten metal similar to those used in standard trough construc-
tion. It iQ greatly preferred to seal the filter plate in pla-
ce using a resilient sealing means or gasket type seal as il-
lustrated and discussed earlier, which peripherally circum-
scribes the filter plate at the bevelled portion thereof. The
gasket type sealq ensure a leak free installation and also pro-
vide an effective parting medium which is essential for ease of
disassembly. In addition, since the gaskets or sealing means
prevent ingress of metal to the sealing faces of the holder
unit, their use considerably eases clean up and effectively
prolongs the life of the unit by eliminating problems of metal
-13-
0~
attack. Furthermore, because of its resiliency, the gasket
may provide sufficient frictional force to hold the filter body
in place in the holder or filter chamber without resort to
other types of hold down devices. The resilient sealing means
should be non-wetting to the particular molten metal, resist
chemical attack therefrom and be refractory enough to withstand
the high operating temperatures.
Plate type filter units of the present invention may
be sealed by gaskets around their edges and/or at the periphe-
ry of their large faces. The plate type filter units of thepresent invention are preferably sealed by an edge type seal
along the peripheral surface of the filter plate thus provid-
ing a positive seal and, in conjunction with the gasket, a
mechanical advantage to hold the filter in place. In the event
that a simple press fit is insufficient to hold the filter in
place, naturally a variety of mechanical devices such as wed-
geq and hold down weights may be employed. Alternatively,
apparatus 10 in Figure 1 can be made to be split at rims 17
and 1~, in a manner not shown, ~o that pressure can be applied
to the sealq by the vise-like action of closing the split unit.
The bevelled angle of the filter chamber and corresponding be-
velled angle of the filter plate tends to form a positive seal
and hold the filter in place against buoyancy forces acting
thereupon. Naturally, as indicated above, the gasket or seal
should be resistant to the molten metal utilized. Typical
~eal materials utilized in aluminum processing include fi-
brous refractory type seals of a variety of compositions, as
the following illustrative seals: (1) a seal containing about
45% alumina, 52% silica, 1.3% ferric oxide and 1.7% titania,
(2) a seal containing about 55% silica, 40.5% alumina, 4%
chromia and 0.5% ferric oxide, and ~3) a seal containing about
53% silica, 46% alumina and 1% ferric oxide.
-14-
)$~7
In accordance with a further embodiment of the present
invention, an apparatus 31 is depicted in Figure 3 which com-
prises a transfer passageway 32 leading to a continuous filter
chamber _ . Chamber 33 differs from chamber 15 of Figure 1 in_
that it is continuous rather than partitioned into sub-chambers.
In this embodiment, coarse filter-type medium 21' is located in
essentially side-by-side relationship with fine filter-type me-
dium 22'. The respective filter-type media are separated by
partition wall 34 which is integral with and of identical
height to transfer passageway 32 and exit trough 35. As in
the apparatus of Figure 1, a flux inlet port 25' is located in
chamber 33 adjacent and below filter medium 21' and is fed in a
similar manner by conduit 26'. Thus, flux material comprising
a gaseous fluxing agent may issue from port 25' and will perco-
late through filter medium 21' to achieve the desired counter-
current contact and exchange with the downwardly moving melt.
me difference in the configuration of chamber 33 dictates that
the melt will flow downward around partition wall 34 and will
receive its final filtration aq it passes upward through filter
medium 22' on its way to exit trough 35. As in the illustra-
tion of Figure 1, apparatus 31 is provided with bevelled peri-
pheral rims to accomodate the placement and support of the res-
pective filter media. Likewise, the filter media are provided
with resilient sealing means to effect the desired securement
of the filters within the rims.
A wide variety of instances exist where the apparatus
and method of the present invention in all of the above dis-
closed variations may be employed. Specifically, in the ins-
tance of a continuous casting operation, a pair of flux fil-
tration chambers may be employed in parallel arrangement. Insuch an operation, the great length and associated total flow
of metal involved may require the frequent changing of filter
lO~VS~
media in mid-run. Such changes may be facilitated by the em-
ployment of parallel flow channels each containing a filtration
chamber, together with a mean~ for diverting flow from one
channel to the other, by valves, dams or the like. Flow would
thus be restricted to one filtration chamber at a time and
would be diverted to an alternate channel once the head drop
across the first filtration chamber became excessive. It can
be seen that such a switching procedure could supply an end-
less stream of filtered metal to a continuous casting station.
In addition to the above, the present apparatus and
method are capable of several modifications within the scope
of the invention to accomodate variations in operating proce-
dure. For example, in the instance where small, individual
lots of molten metal are prepared and cast, it is desirable
that the filter-type media remain operable for s~veral such
lots. To this end, the filter media may be recessed somewhat
from the levels of the transfer passageway and exit trough
whereby, after melt flow has ceased, residual melt remains
which fill~ the chamber and covers both filters. In conjunc-
tion with this modification, at least one cover unit may be
employed which would reside above the remaining melt, and would
be provided with heating means such as a plurality of radiant
heaters to keep the melt in the liquid state. In the event
that such modifications are employed with the apparatus of
Figure 1, peripheral rim 17 would be recessed and the cover
member, not illu~trated herein, would be placed thereover.
Likewise, the bottom of exit trough 28 would be brought into
alignment with the bottom of passageway 14 and a similar cover
member would be employed at the location where the exit area of
sub-chamber 20 abuts with trough 28. In the illustration of
Figure 3, filter-type media 21' and 22' could simply be re-
-16-
05~3~7
cessed to permit the residence of melt thereover, and appro-
priately configured cover members could be located thereat.
Other modifications contemplated within the scope of
the invention include the provision of a plurality of inlet
ports surrounding the respective chambers immediately below the
respective first filter-type media. In addition, and likewise
not illustrated herein, the inlet ports could be extended to
the center of said chambers by the extension of the respective
conduits thereinto, whereby fluxing gas may enter the melt
from a point centrally located within the chamber. Both the
provision of a manifold of fluxing gas inlet ports, and an in-
let port or ports centrally located within the chamber, neither
of which illustrated herein, comprise modifications which are,
themselves, subject to alterations of design, etc., and accord-
ingly, the invention should not be strictly interpreted
thereby.
It is to be understood that the invention is not limi-
ted to the illustrations described and shown herein, which are
deemed to be merely illustrative of the best modes of carrying
out the invention, and which are suitable of modification of
form, size, arrangement of parts and details of operation.
m e invention rather is intended to encompass all such modi-
fications which are within its spirit and scope as defined
by the claims.
