Note: Descriptions are shown in the official language in which they were submitted.
~7~6
.
~`his invention relates to refrclctory materials and,
more especially, to ~e~ractory mcl~erials intended to
withstand contact with moltell met~llic masses o aluminium
~nd its alloys, ~oth for use in the cons~ruction of smelting
fu~naces and for the manufacture of fittings for ~urnaces of
this kind, such as ducts, chutes, transfer ladles or casting
ladles, which remain ln con~act with molten alumini~n, often
~or prolonged periods.
Refractory compositions o the type uscd in the smelting
of metals contain silica, generally in the ~onm of various
silicates. The proportion of silica varies according to the r
type of composition. It c~mounts to approximately 60% by
- weight in so-caLled argillaceous or silico-aluminous products
- (35% of alumina) and to 35% i.n aluminous products (60% of
alumina) based on sillimanite, bauxite) mullite or others.
The "alumina" itself contains of the order of 1~'7/o o~ silica.
The magnesia or chrorne-magnesia products often contain close
t~ 10% o silica.
This silica tends to react with the r~ducing metals,
- 20 such as alumini~n, in accordance with the ~ollowlng scheme:
-
4 Al ~ 3 SiO~ 2 3 3 Si ~ 000= -150.020 cal
This reduction o~ the silica or silic~tes by the reducing
me~al liberates a ~onsiderable amount of energy. Th~xetically,
i~ could be contlnued until one of the two starting produrts
-2-
~ .' ~ '
-~
.
~ 6
has been completely conswned. I~ practice, the reaction
velocity is slow enough for lightweight reducin~ metals
and their alloys to be melted in furnaces made o materials r
containing silica. ~lowever, various phenomena are encountered,
S as a result o wllich ~he furnaces or t~leir fi~tings soon have
to be taken out of service. rl`he re~ractory ma~erial grad~lally
becomes impregnated. ~s a result, i~ changes into a black,
extremely hard mass ~hich is ~n aggre~ate of corund~ and
alumini~ll. This mass conducts both heat and electricity
which can have serious consequences for an electric furnace
and ~ives rise to significant losses of energy. Swelling
and cracking occurs t above all when tlle alwnina content of
the refrac~ory composition is low. Particles of refractory
material become detached from the furnace and reappear in
the aluminium àrticles in the fol~ of hard inclusions.
- "Mushrooms'7 o oxides are formed both on the hearth and
- - above all on the walls of the furnace in contact with the
; bath. These mushrooms grow until they o~struct a large
part of the furnace. They are extremely hard and, in
practice, cannot be detached from the walls~
~ritish Patent Specification No. 1,135,147 and the
ar~cle by W. Helling and E. Kistermann entitled "Salzimprag-
nierverfahren fur Zustellung von Aluminium-Schmelz und
Warmhalteofen" published in the Journal 'IAluminium" 33 (1957)
No.8, pages 514 to 520, recall these serious dif~iculties o
the aluminium industry and suggest overcoming them by coating
the inner walls of the furnace wi~h a mixture of 8~/o o
- -- sodium chloride and 20~/~ of cryolite. The melting point o~
this mixture is 795C. Because it is very fluid, it p~netrates
readily into the surface pores of the chamotte-based refractory t
- . -3
- .',, . , . 1
1: ................. . . . .
-
- . - - . - - . . - - : -: . ~
material. Generally, it has a visible thickness of 1 to 2 mm,
although the depth of penetration into the refrac~ory material
- reaches 6 m~. The high sodiuln con~ent: of this so called
glazing flux and its resulting relatlvely low mel~ing poin~
make it substantially non-re~rac~ory and rela~ively weak.
In time the impregllation has to be rep~al:ed, wllich the
au~hors have recogllis~d. A tec~lnical le~El~t for co~nmercial
cons~nption issued by Soclete Servimetal ~ncien department,
fonderie soudure Otalu, 87 Rue Pierre Joigneaux, 92 Bois- ~
Colombes, France, entitled "Les ProccJ~s ~e glacage des r
garnissages refractaires des fours de fusion et de coulee
utilises dans les fonderies d'aluminium" [Methods of Glazing
the ~efractory Linings of Smelting furnaces and Casting Furnaces
used in Al~niniurn Foundries3, is more explicit. After having
~` 15 recalled the'detrimental effect of molten aluminium on the
furnace, it proposes two glazing techniques using a mixture
of 8~/o of NaCl and 20% of AlF3 - 3 NaF. The deep impregnation
; techniquet corresponding to that described ln the above-
mentioned Gennan Article, has given way to a so-called
I'sur~ace impregnation" method which is more advantageous
because it is simpler and ~uicker, using less glazing flux
' and requiring lower working temperatures. Ater the furnace
has been dried and fired, this improved method comprises
regulating the surface temperature of the re~ractory lining
~5 to between 750 and 780C, spraying the hearth with a quan~y
o flux amounting to between'7 and 10 ~ per cm using a
compressed-air projection apparatus, charging al~ninium,
- preerably ordinary alumini~n, approximately 1 hour after
the beginning of melting, the charge being calculated in
30 - such ~way that it represents only one third of the normal
'
_4_
.
~ '' ' " ;
capacity of ~te furnace3 distributing from 2 ~o3 kg of flux
-- per square metre of hearth over the ~ath when the charge is
half melted, distributing another ~lux over the dross at
the end o~ melting, the temperature oE the bath being o~
the order of 730 to 750C, this o~ller 1ux making ~he dross
dry and pow~ery and hence easy ~o remove by drossing after
4 to 5 minutes' reaction, ~egassing and puddlirlg in the
us~lal way, completely emptying the furnace and carefully
~ soraping the hearth, applying another glaze in the same way
as described above, except that the second charge of metal
is calculated to amount to half the normal capacity of the
furnace, followed by a third glaze applied in the same way
as described above except for a ew modifications~ and renewing
the glaze five days later. Since the furnace is thus prepared
lS once and for all, it is sufficient to apply an interim glaze r
once a month. The comple~ty and labour costs, the general
immobilisation and materials involved in these initial and
subsequent glazings have prevented the development of these
techniques, especially since the addition of relatively
volatile flux continuously contaminates the alurninlurn treated.
In fact al~ninium founders continue to work in thP same way æ
bPore and include in their manufacturing costs the investment
required for the frequent replacement of the urnaces 9 their f
! rapid reduction in capacity, their immobilisation or cleaning
purposes after each batch and the costs attributable to losses
of alwninium, still with the fear that a "hard spot" in the
molten al~ninium will not damage an expensive tooL downstream
- of the furnace. These techniques have failed because they
have been unable to escape from the following dilemma~ If
a low melting point flux ,s used or impregna~ion, impregnation
~5_
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, - .
.
~ ~ 7 ~
can readily be carried out, but unÇortunately the flux
- evaporates rapidly. If a re~ractory iux is used for
- 'impregnatlon, the urnace has to be heated to a high
temperature in order both to make the 1ux L~Iid and
to enable it to be effectively applied. Unfortunately, r
the furnace is inc~pable or substantiaLly incapa~le o~
withstanding this temperature and is pennatlently damaged.
In the article by Michel Drouzy and ~lichel Richard
entitled " oxydation des alliages ondus, reaction avec les
reractaires" [Oxidation of Molten Alloys, ~eaction with
Refractory ~laterialsJ, published in the Journal r;onderie 332,
pages 121 to 128' in l~arch 1974, it was recalled that
J,W. ~`ruehling and J~D. I~anawalt demonstrated that a
fluorine-containing atmosphere protected a furnace of
refractory material intended for the treatment of liquid
magnesium (Atmosphere protectrice pour la fusion des alliages
du magnesium [Protective Atmosphere ~or Melting ~lagnesium
Alloys], Modern Casting 56, August 1969, pages 159 to 164),
and it was $ound tllat this fluorine-containing atmosphere
was also suitable for protecting a refractory material of
¦ - an aluminium bath.
! - The protection obtained is temporary ~a ~ew days at the
' most~ and is governed by the quar~ity of fluorine which the
- ' refractory composition is able to adsorb in its pores once j'
~5 the fluorine-containing compound placed in the furnace has
been consumed. In the case of a furnace or ladle which does
not work in a confined atmosphere~ the pennanent renewal
of the atmosphere virtually prevents correct protec~ion from
being obtained. In addition, the removal of large quantities
of fluorine-containing gases is too dangerous for adoption
;
t
- . ' , , ~.
.
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~ ~ 7 ~ 6
on a wide scale in foundry ~ork.
It had not been considered to overcome these difficulties
by incorporating fluorine-containing compounds in the actual
mass of the re~r~c~ory composit~;on because it was kno~l that
the fluorine-containing colnpounds are fluxes wllich at~versely
affect the re~ractory qualitles of the ~,roducts to which they
are addecl. Ilowever, the addition o fluorine derivatives to
construc~ion ma~erials which are not intended to corne into r
contact wi~h molten alumini~n has already been carried out
to the detriment of their refractory qualities essentially
under two types o~ specific conditions. On the one hand,
it has been proposed to mix a little fluoride with refractory
compositions bonded by a phospllate (cf. inter alia the
Article by ~erbert D. Sheetsg Jack J. ~ulloff and Wisto~
H. Duckworth of the Batelle Memorial Institute entitled
"Phosphate Bonding of ~efractory Compositions" published
in Brick and Clay Record in July, 1958, or the Article
published in ~erichte der ~eutschen Keramischen Gesellschaft,
Vol.37 (1960), No~8, pages 362 to 367 by ~ etchel and
G. Ploss entitled "Uber das ~bbinden von Keramischer Ruhstoffen
mit monoal~niniumphosphate Losung ~Feuerfestbinder 32)".
Thus, an attempt was made to improve the setting o concrete
~ by the addition of fluoride. It was hoped that the formation
of fluophosphates would promote this effect. In order to
2~ offse~ ~he adverse effect upon refractory properties, use
was made according to the first ~rticle of expensive
refractory cons~tuents such as tabular aLumina, zirconia,
etc. whert?as according to the second Article there is a
- - warning that3 in practice, it is-generally not possible tc
30 ~ obtain a high pyroscopic resistance if the presence of
- ,
.~
, . ' ' ' i
1~7~106
fluorine can be tolerated with a view to forming a
vitreous fluophosphate phase to accelerate setting.
On the other hand, attempts have been made to produce
vitreous sodi~n-containin~ products referred to as
refractory concretes in the book entitled "tllt~ebestallcliger
Beton" by Nekrassow (~auverl~g G~l~ll Wies~aden~~erlin 1961),
especially in the third and four~h cha~l~rs, by tlle use of
soluble glass and sodium ~luosilicate. 'rhe high sodium
contents of these gla~es adversely affect their reractory
quallty. A chamotte fire resistant up to 15~0C withstands
a temperature of only 900C when a soluble glass and
` fluosilicate, ~oth po~erful 1uxes, are added to it. In
order to withstand a temperature of 1000C, a chromite has
to be used (cf. the Table on page 239). None of these
publications reers to the particular case of a furnace
or molten aluminium.
US Patent Specification No. 3,261~699 describes bricks
intended for ~urnaces ~or the electrolysis of aluminiwn.
.....
The inventive idea of this patent is to make the furnace
of the same constituents as the electrolysis bath, n~mely
cryclite and A1203. As a result, the bath is never polluted,
- even if the furnace is as it were attacked during electrolysis.
To obtain this result, it is specifically pointed out in
column 5j lines30 to 32 of the above-mentioned Patent
Specification that, if additives are used9 they must be t
used in relatively small quantities, i.e. in-quantities
~f less than 1%. This is so true that the Patentee
recommends using synthetic alumina, namely alumina produced
by the Bayer process, whilst the cryolite is also artificial
cryolite. AccordinglyJ the product in question is a very
_ ~ .
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.~ . , .
expensive product o~ synthetic origin.
On the other hand, it has been found in accordance with
the present invention that it is possible to use a re~ractory ma- -
terial which is relatively inexpensive because it is produced from
natural materials and which is sufficiently resistant to molten
aluminium even when it contains an appxeciable quantity o~ silica.
By virtue o~ the present inventlon, it is possible to
produce an object, such as a furnace or ~urnace fitting, intended
to be in contact with molten aluminium which is substantially una~-
f~ected both chemically and physically by the bath o~ aluminium andwhich withstands the high temperatures whilst at the same time
being of ralatively low cost because it does not involve the use
of special or synthetic refrac-tory products, such as tabular alu- .:
mina zirconia or synthetic alumina.
The invention relates to a solid material having a de-
flection temperature under load above 1000C, a content by weight
of aluminium, expressed as A1203, of from 10% to 60% and, better
still, from 30% to 50% and a content by weight of ~luorine of from
0.1% to 10% and bet*er still from 0.2 to 5%, the fluorine forming
part of the structure of the material, wherein it has a content
by weight of silicon, expressed as SiO2, of from 5% to 85% and, : .
better still, from 20% to 60%.
The invention is also directed toward a process for in-
hibiting the effect of molten aluminium on an object with which
it is intended to come into contact. The process comprises making
ths object of a concrete which has a de~lection temperature under
load above 1000Cg a content by weight of aluminium, expressed as
A1203, of from 10 to 90%, a content by weight o~ calcium expressed
as CaO of from 4 to 14% and a content by weight of fluorine form- .
ing part of the structure of the concrete of from 0.1 to 10%.
The very small proportion of ~luorine incorporated in
the mass has proved to be sufficient to prevent the material from
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l~r78~
being ehem~cally or physicochemically at~ackad by the aluminium,
and insufficient for adversely affecting the refractory properties
o~ the material to an unacceptable extent. The incorporation of
fluorine, even in small proportions, radically modifies the phe-
nomenon of the wetting of the refractory material by the molten
aluminium The refractory material is neither wetted nor attacked
by the aluminium
The fact that it is possible to produce a matexial with
properties such as these is surprising in view of U S. Patent
Specification No. 3,261,699 not only because this publication spe-
ci~ically states that silica or any other additives must no$ be
used in significant quantities, but above all because it was not
foreseeable that the addition o~ silica, a fairly reducible mate-
rial, would nevertheless be tolerated for a material intended to
be in contact with molten aluminium on the conditivn that fluorine
was added to the material. In the case of the U.S. Patent Speci~
fication, the addition of ~luorine to the alumina is motivated by
the composition of the electrolyte and not by the need to protect
the rest o~ the material consisting of Bayer alumina which is a
non-reducible material. By contrast, the role and function of
the fluorine are entirely different in the material according to
the invention. They prevent the SiO2 from being attacked by the
molten aluminium.
The deflection temperature under load (To 53 charact r-
ises the refractory quality and the mechanical strength of the
re~ractory material. It is det rmined in accordance with the
Standard ISO R 1893 (F) of October, 1970. The test ess~ntially
comprises placing a cylindrical test specimen 50 mm in diameter
and 50 mm tall made of the material tested in a furnace between
th~ compression rods of a
~ -- 1 0
. ~ Q~
compress on devic~ capable of applying a constant lo~d o
2 kgf/cm to the test specimen, and recor~ing the temperature
~ached on defonnation to 0.5~/O of the initial height o~ the
test specimen for a given hea~ing rate of the furnace o 10oC
S~ per minute to 500OC, and then 5OC pcr Ininute beyon~ 500C~ ;
The statemell~ tllat the fluorine ~onns part of the
structu~e is meant to show that the fluorine is not present
in the form o~ a gas adsorbed in the pores a~ a basic
aggregate or in the Çorm of a coating applied to the surace
10 ` and in the pores of that aggregate. The fluorine is present L
in and distributed throughout the mass in a solid form,
combined with the aggregate, or in the ~orm of a solid
fluorine compound associated with tlle aggregate. In general,
the fluorine is uniformly distributed throughout the mass.
lS Analysis of samples taken a~ points situa~ed at different r
distances from the surace intended to come into contact
with the molten aluminium reveals the presence of fluorine.
` The 1uorine is virtually only desorbed at temperatures above
the service temperature.
~`he invention also relates to a solid maErial having
a deflection temperaturè under load above 1000oC, a content
by weight of sodium, expre~sed as Na20, of less than 5% and
better still less than 2%, a content by weight of aluminium,
zirconium, beryllium, chromium and carbon, expressed
respectively as A1203, Zr02, BeO, Gr2O3 and SiC, of less r
- than 60% and a content by weight of fluorine of from 0.1%
- to l~io and better still from Or 2% to 5%,
The invention also relates to a solid material having L
a deflection ~emperature under load above 1000C, a content
by weight of alkali metal, éspecially sodiwn expressed a~ Na20,
.
.
,
~ . . . - . . . . . . . . , ~ . - .. .
~ 7 ~ 1 0 ~ -
of less than 5% and better still less than 2~/o J a content
by weight of phosphorus, expressed as 133P04, of less than
5~/0 and better still l~ss than 2% and a content by weight of
fluorine of the same order as indicated a~ove.
S Other materials accorcling to ~he inven~ion have a
con~ent by ~eigllt o~ phospllorus expresse(l as ~l3P04 o~ less
than 5% and ~etter sti~l less ttlan 2n/o.
Prefera~ly, these materlals which gener~lly contaln
- oxidised silicon, have an average content ~y weight o~ 1
aluminium, expressed as A1203, of for example more than P
l~to~ better still more than 30% or even better more than
40%, but Less than 60%, better still less than ~% and even
better less than 50/0.
Apart from the fact that it is surprising that a
material of the kind in question has both the required
- refractory quality and also the property of not being
wetted by the molten aluminium for such low ~luorine
contents and such high silicon contents1 its production
has given rise to unexpected dif~iculties, because it has
been ~ound that the fluorine compounds and the alumina,
which are known to retard ~he setting o~ conventional
cements and concretes, play a different part with the
~ reractory aggregates with which they are associated to
- - form a material according to the invention. The presence
of ~luorine gives rise to a ~alse setting phenomenon. r
Accordingly~ special procedures have to be adopted.
According to the first of these procedures9 the
aggregate, the fluorine compound, a hydraulic binder and
wa~er have to be stirred for a sufficient period after they -
have been combined in order to avoid this false setting
.
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~971~3106
phenomenon. A stirring time o approximately 10 minutes
is generally sufficient. It is also advisable to select
a fluorine content for the final material which is as low
as possible within the effective range. It is also advisable
to add a setting retar~r.
The ~irst stage of this me~hod compris~s mixing an
aggregate and a hydraulic binder.
Products o high alumina content, for ex~mple with ~n
alumina conten~ of more than 45% or even more than 55/0 by
weight, may be used as aggregate.
Thus, it is possible to use an aggregate oomprising
cyanite, siLimanite, ~auxite, ~iaspore, corundum, andalousite,
gibbsite, synthetic mullite.
It is also possible to use aggregates lncorporating
special refractory products, such ~s products of magnesia, t
chromite, chrome-magnesia, orsterite~ dolomite, carbon
products based on graphite or coke, silicon carbide products,
zirconia products, zirconium silicate, nitride-containing
products. I~owever, it is possible by virtue of the invention
not to use th~ expensive products mentioned above, and to
obtain satisfactory results with more common aggregates.
Aggregates such as these are in particular th~se with
~ a content by weight of alumina of from approximately 35%
to 45%, which are often referred to as argilaceous products,
~5 and those with a content by weight of alumina of from 10/~
to 35%, which are known as silico-argilaceous products, the
complementary contents of the alumina bein~ fonmed by silica
aside from a few impurities.
The grain size distribution of the aggregate is
conventional. For example, the following distribution may be
adopted:
-13-
.
O to 0.2 ~m5 to 25 %
0.2 to 2 mm20 to 50V/o
2 to 5 ~n5 ,:o 35%
5 to 10 t~n20 to 60%
,: r
Suitable ~inders are the conventio~ ydraulic binders,
especially al~ninous and silico-aluminous binders. Their
alumina content is with advanta~e equal to at least ~O% by
weight. It is possible to use in particular "Lafarg~" alumina
S ` ~ement which is a calci~n alwninate containing 40% o-al~nina9
- ` Seca~ 162 ~hich contains 40% of alumina) Secar~250 which
contains 70% of al~nina and Sup,_rsec~r~hicll contains 80%
o f alumina.
In general, the binder makes up from 10 to 35% of the t
;10 weight of the aggregate.
~ The aggregate and the binder are mixed for at least
; 1 minute and generally for 1 to lO minutes~ ,
- The ~econd phase of the metihod descri~ed above comprises
- adding to the mass of aggre~ate and binder from 0.1 to 10%,
expressed as fluorine, of one or more fluorine compounds,
- followed by further mixing for a few minutesD ~ !
Suitable fluorine compounds include alkali metal and ',
alkaline earth metal fluorides and ~luosilicates.
It is of advantage to use a mixture of two fluorine
Z0 compounds9 one of which is more volatile or more solubLe
than the other in water. ~hus, a system containing ~or
example from 0.8 to 1. 27/~ of sodium fluosilisate and from
0.2 to 0.8% o calcium fluoride gives satisfactory results~
~ The third stage o the process using a hydraulic binder
comprises mixing the mixture of aggregate, binder and fluorine
~ 7~~ '~Y ~ -14~ `
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~ ~ 7 ~
compound with a quantity of water representing from
-- approximately 2 to 20~/o of the weight of this mixture.
A setting retarder is preferably added to the mixin~
water. The setting retarder generally represents rom 0.2
to 2% of the mixture of a~gregate, binder and 1uorine
compound
Suitable retarders are, prefera~ly, ~he "sea1ing
retarders" which render the surace of t~e grains impermeable
to the solubillty reducers.
. Water soluble or surface active se~llng retarders o
- this type include in particular glycolic acid, glycolic
aldehyde, tartronic acid, glyceric aldehyde, glycerol,
pyruvic acid, glyceric aldehyde, dihydroxy acetone, maleic
~ . acid, succinic acid, malic acid, tartaric aci~, erythroI~ ,
,.~ 15 dihydroxy tartaric acid, a- and ~- ketoglutaric acids, rarabitol, gluconic acid, galactonic acid, sorbitol9 citric
. acid, salicylic acid~ diphenols (resorcinol, hydroquinone),
- : benzoquinone, gal1ic acid, dioxane, organic materials which
: flocculate in the presence of Ca , for example digallic acid,
casein, proteins such as albumin, gum, pepsin9 melamine
resin, lignosulphates, Cl2 - Cl8 atty acids; oleic acid, .
naphthenic acids, benzoic acid, pentachlorophenol, dialkyl~ne
. -glycols, mono-and poly-ethanolamines, glucides, glucose,
saccharose, starch, cellulose and other sugars, etc.
- 25 It is surprising that the presence of fluorine, a
conventional retarder used in the hardening of concrete,
necessitates the addition of another retarder to prevent
~alse setting in the particular case of the invention,
whereas above all the alumina itself is also known for its j:
retarding effect on the setting of conventional structural
- .
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-15
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~071~
mortars an~ concretes.
After the mixing water has been added, mixing is con-
tinued for at least 8 minutes and better still for 10 minutes. --
Thereafter a material is obtained which it is suf~icient
to mould and harden and then to heat slowly, ~or example first
to approximat~ly 100 to 120C and then to approximately 700C,
to form the refractory material accordi.ng to the invention.
In a second procedure, the blnder used is a chemlcal
binder~ such as ethyl silicate, sodium silicate, phosphoric acid
or a phosphate. The phenomenon of false setting no longer occurs.
The quantities of chemical binder used are o~ -the same order Or
magnitude as those mentiolled in reference to the hydraulic binders.
In this second process, mixing and cooking are carried out in the
same way as before. The aggregate has a content by weight of
silicon expressed as SiO2, a content by weight of aluminium expres-
sed as A1~03 and/or a content by weight of zirconlum expressed as
Zr2 of from 1% to 99%~
Finally, a ceramlc binder, especially clay, may be used.
The refractory material may be l-sed in the form of a
pourable material or in the form of linings or bricks for the
construction of furnaces and other fittings for the molten alu-
minium. -
The invention is illustrated by the following Examples.
EXAMPLES 1 T0 10 -
..
Two pellets wi$h a height of 5 mm and a diameter of
15 ~m of each of three alloys ~ ~
: ''
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V6
graduated from slight to very pronounced, are placed on
the refractory material to be tested, l`lle pieces o
refractory material together with their pellets are then
placed in an electric muf1e ~urnace or 48 llours at a
temperature of 800~C. l'his temperature oE $~0C is the
average telnperature used in alulniniu~li slneltillg or holding
furnaces, an~ the resid~llce tilne selected is suEicient to
provide or clde(luate sensitivi~y to tlle test,
The value of the reaction is detennined by an index
which is the sum of three re~ction indices o each of the
alloys, being de~ined as followsO
0 : no visible reaction or marlc on the refractory
material, , -
1 : slight mark on the refractory material, but volume
of the pellet maintained, the pellet ~eing readily
detached ~y hand.
- 2 : pellet detached from the refractory material, its
- vol~ne having decreased by less than 507/o or the; - "ring" if any not exceeding 22 Inm in its largest
dimenslon or the ~eginning of "mushrooming" on
the refractory material.
3 : pellet detached from the refractory material, its
volume having decreased by more than 50/0 or the
ring formed having a di~neter of 22 ~n in its
largest dimension or significant "mushrooming'~
on the refractory material,
The tests (2 pellets of three alloys) are carried out
twice in each case,
` Since the resuLts are characterised by a certain
disperslon (it is generally accepted that the reaction only r
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``:`
takes pl~ce ~fter an initiation p~riod o~ arbitrary duration),
the maximum index obtained is awarded to each alloy.
The alloys have the following composition:
~lloy A: Zn 0%
Alloy B: 0.22%
Alloy C: Zn 2%
For the three ~lloys, the other elements added to the
aluminium are as follows:
iron 0.33~0 - silicon 8.7% - copper 3.1% - magnesium 0.22%
Table I b~low shows the type o~ ~luorine compound used
i~ the second column~ the ~ontent o~ the fluorine compound in
the third column and the index obtained in the ~ourth column. .
The test marked with an asterisk is a comparison test carried out
on a fluorine-free refractory material. The aggregate is a mix- ::~
ture of chamotte and the binder, which represents 30% of its weight,
is a calcium aluminate containing 40% of A12O3. .
TABLE I . .
20 ¦Example No. Fluorine Compound _ Content ~O Keaction Index -
I 1 Na F 1 0 .;.~
I l* _ _ g ~. .:- -
2 (N~4)2 Si~6 1 0 ~:
. Na2 Sl F6 0.1 8 -~
4 Na2 Si F6. 0.3 6
~ Na2 Si F6 1 0 .. ::~
6 Na2 Si F6 1.5 0 ..
7 Ca Si F6 1 0
8 Ca F2 2 0 .
_ _ ~ Na Si F6 ~ ~ ~ -
- 18 - ~ -
.
78~V6
EXA~E 11
30 kg o chamotte with a grain size of from 2 to 4 ~
22.5 kg of chamotte ~ith a grain size of less than 0.1 mm
and 22.5kg of Secar are mixed ~or 2 minutes ~n a concrete
mixer.
~2 and 1 kg of Na2S']l ar~ tl1 l
followecl by mixi.ng ~or another 2 minll~es.
~ solution o a retarding agent is prepare~ by adding
1 k~ of retardant to 10 l'itres of water.
~1is solution is poured into the concrete mixer~
followed by mixing for 9 minutes.
The mass iS discharged from the concrete mixer and
poured between a male mould and a female mould separated
from one another by an interval of 40 mm. - ~
, ' 15 , m e mass is left to harden and set for 24 hours ,r
,~ without drying. To this end, it is covered with damp
sacks.
,- Th~ female mould is withdrawn, followed by drying inair
j for 48 hours.
, I'he ladle of the material according to the invention
is gently heated for 24 hours at 115C in the absence of
any contact with a flame.
The ladle is then gradually heated to a temperature of
700C by increasing the temperature at a rate of 30C per
hour. It is kept at 700C for a period of 6 hours. ~,
A test ladle of this type withstands' the repeated
attack of molten aluminium for more than 4 monthsO
XAMPLE ?2
The procedure is as in Example 11 except for the
modifications indicated in Table Il-
~19-- ~
.
.
.
~78~
EYAMPLES 13 to 15
The procedure is as in Example 11 except ~or the modi-
fications indicated in Table II. The material is applied to the
mould by tamping in the Iorm o:E a rammed clay.
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-21- ~Q'78~ )6 I I
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