4378
The invention relates -to a process for decreasing the
contaminant content of aluminium melts or of aluminium alloy
melts, characterized by leading into the aluminium melt or
aluminium alloy melt isolated from the air an inert gas of a
pressure below 2 atmospheres, and at a temperature of 670-860C.
Various processes are known for the purification of
metals. Of these processes, the more effective ones are
carried out with use of an active gas: chlorine gas or salts
which develop chlorine gas: halogenides. By means of rinsing
with chlorine gas (Tomany, J. P.: The control of aluminium
chloride fumes. - Light Metal Age, 1968. 26, No. 9-10,
p. 19-20) the content of gaseous hydrogen, of oxide and of
alkali metal of most alloys is decreased but at the same time
most part of the gas (introduced into the melt through graphite
pipes or steel pipes protected by resistant coat) does not
participate in the purification process and causes severe
problems of neutralisation and absorption. In the workshops
of the plants where chlorine gas is used, the iron structures
are exposed to corrosion, and in the course of the handling,
storage and neutralisation of chlorine gas, the hazard of
intoxication is continuous (N~lting, P.: Betriebliche
Erfahrungen mit der Chlorbehandlung von Aluminiumlegierungen.
Giesserei. 61, 1974. No. 1, p. 7-10).
Solutions of this problem are known where the gas
blown-
-- 2
.~
~1~4~78
- 3 _
-~n for rinsing consists of a mixture of chlorine gas and
nitrogen gas or of one of the noble gases: argonJ! helium~
neon,J krypton,! xenon alone or of a mixture of these noble
gases.
Also nitrogen is a gas which does not react with alu-
minium.
The generally used composition of chlorine-nitrogen gas
mixtures isi:
10~35 % by volume of chlorine gas ~ 65-90 % by volume
of nitrogen gas.
The hydrogen-gas removing effect of this gas mixture is
lower than ~hat of pure chlorine gas but higher than that of
pure nitrogen gas tPrescheO~ P. ~ Wulmstrof~! N.~ sehandlun9 von
Aluminiumschmelzen mit Gasgemischen. Aluminium. 48. 1972. No.
10. p. 677_678). Of $he gases inert towards aluminiumrl argon
decreases the hydrogen content of the melt more effec~ively
than nitrogen ~Ginsberg.j H. - Agrawal~, A.N.: ~berprufung der
Wirkungsweise gebrauchlicher Entgasungsmethoden fur Metall-
schmelzen aus Reinaluminium und Aluminium-Magnesium-Legierungen
unter Anwendung der neuen Gasbestimmùngsapparaturen. III~
Aluminium. 41~ 1965. No. 11. p. 683-687). At the same time
argon and the other noble gases are rather expensive~i and thus
their use has not been introduced into the aluminium industryO
By the liquefaction and separation of air great amounts
of nitrogen gas can be produced cheaply. However~l rinsing with
nitrogen gas has the drawbaclc that in case of melts of alloyed
aluminium the degree of degasification is low~! and at the
same time on the surface of the metal bath a slag containing
1~ ~4378
~ 4 --
a relatively high amount of metals and hardly treatable is
formed and this increases the loss of metal. Nitrogen gas
does not decrease the content of alkali metals of the melt,l
either,J and thus nitrogen alone is not suitable for the purifi-
cation of melts contaminated by alkali metals,J and it must
be applied only when mixed up with chlorine gas ~Szél<ely~
A.G.,: The Removal of solid particles from Molten Aluminium
in the Spinning No~zle Inert Flotation Process. Metallurgical
Transactions. 7B. 1976. p. 259-270). Sodium content is
decreased the most effectively by chlorine gas ~Lagowski,
S.~: Magnesium loss during chlorination of aluminium melts~
Les Plaines III.~J Trans. Amer. FoundrymenJ!s Soc. 77. 1969.
p. 206-207).
On t~e effect of chlorine gas introduced into the
melt AlC13 is formed,3 and thus sodium is bound:
AlC13 + 3 Na ~ 3 NaCl + Al
NaCl + AlC13 ---~ tAlC13.NaCl)~
Of the gas-developing salts~j the chlorides e.g. manganese
chloride and zinc chloride are reacting with liquid aluminium
and they form aluminium chloride which latter is in a gaseous
state at the temperature of the treatment (Marienbakh~ L.M. -
- Sokolovskii.J L. 0.: Plavka slavov tsvetnykh metallov dlya
fasonnogo litya. Moscow~j 1967~ p. 184-189~.
3 MeC12 + 2 Al --~ 2 AlC13 1 3 Me
Aluminium chloride in a gaseous state decreases also
the sodium contamina~ion of the melt.
Aiso hexachloroethane is used for decreasing the
content of contaminants in aluminium mel~ or aluminium alloy
11~43~78
melts ~Marienbalch~l L.M. - Sokolovskii~l L.O.: Plavka slavov
tsvetnykh metallov dlya fasonnogo litya. Moscow. 1967. p.
184_189).
Reactions of hexachloroethane in the aluminium melt
are as followslO
3 C2C16 _ 3 C2C14 ~ 3 C12
2 Al ~ 8 C12 --- 2 AlC13
3 C2C16 ~ 2 Al ~-~ 3 C2C14 ~ 2 AlC13
Owing to the violence of the reactions taking place and to
the hazard of explosion the amount of treating material
reguired to attain the desired effect canno~ be added at
once to ~e liquid metal. Some processes are known wherein
hexachloroethane is added in smaller portions into the melt.
This means surplus costs~ and at the same time the powder
packed in ~oils or capsules or the compressed compact tablets
must be-introduced into the melt by means of dipper bells
by a tlresome manual operation which cannot be mechanizedD
In case of furnace units having a large bath ~urface
20 the feeding will not be uniform and thus the degree o~ utiliza-
tion of hexachloroethane is low and a significant portion
of the treating material is lost quite unused with the waste
gases.
Also the vacuum treatment is applied for the purifica~
25 tion of the liquid metal ~Alker,~ K.~ Aluminiumentgasen im
Vakuum. Vakuumbehandlung be~riebssicher und umweltfreund~
licher als Chlorierungsverfahren. VDl~Nachrichten 27~ 1973.
No. 22~ p~ 12)o The drawback of this process is that only
~ 7 8
the upper part of the melt layer is degasified ~Mal<arov~
G~S.: Zalconomernosti udaleniya vodoroda pri vakuumnoi
obrabotlce rasplavlennogo alyuminiya. Tekhn. Legk. Splavov.
1970. No. 4,, p. 37-42)~ The process is expensive because the
construction and operation of the vacuum furnaces require
high investment and maintenance COStS-
Also the ultrasonic treatment belongs to the physicalprocesses by which the hydrogen content can be decreased
~Livanov,J V.A. et al.: Rafinirovaniye alyuminiya i ego splavov
ul~ltrazvul<ovymi kelebaniyami. Tsvetnye Metally~ 19680 No. 60
p. 82-84). The process has not been applied on an industrial
scale.
A common drawback of the physical processes is that
they do not decrease the all<ali metal content of the aluminium
melt.
In the last 15 years the equipments for carrying out
the treatment of metals in a continuous operation outside
the furnace passed through a significant development. These
equipments are being described below.
The equipment of the trade nanie FILD of the firm
Gautschi combines the rinsing with nitrogen gas by filtra-
tion through activated alumina balls ~Entgasung und Reinigung
von Aluminiumschmelzen. Gautsch folder. Aluminium 50. 19740
No~ 4,~ p. 297).
The firni BASF applies a continuous equipmen~ based on
petroleum coke. This equipment combines the rinsing with
neutral gases by filtration through a surfactant mechanical
filter bed (Bohm,l G0 Das Filtrieren und Entgasen von Alumi~
~ 37 8
niumsch~elzen im Durchlaufverfahren. ~luminium. 1973. No.
11. p. 743-747)-
In the equipment produced by the firm Carborundum the
main filter element ~8 an inser~ecl filter composed of porous
6 tubes o~ the trade-mark AloxitO Thls inserted filter is locat-
ed in a filter ves~el equipped with an electric roof heater
ln a way that the metal inflltrates on the effsct of the
mstflllostatic pressure through the mantle o~ the tubes and
belongs into a collector space ~hesfi~J C. Mangalick: The
Rlgid Medls Filter - Princlples and Appllcations. Manuscript
presented on the 102nd Annual Meeting of the AIM~. Chicago.
1972).
The firm Unio~ Carbide Corporation uses a flotation
process instead of f1ltration ~or the separation of the solid
contaminants while applying a SNIF equipment ~Szbl<ely,J A.G.:
The Removal of Solid Particles from Molten Aluminium in the
Spinning Nozzle Inert Flotation Process. Metallurgical
Transactions 7~. 1976. p. 259-270).
The equipment developed by the firm Alcoa contains tWO
filter beds through which a mixture of chlorine and argon
gases is allowed to pa99 ~Blayden~J L.C. - BrondykeJIi<,~
Alcoa 469. Process. Low costi,J non-polluting,l continuous metal
fluxing. 30urnal of Metals. 1974. February. p. 25-28).
The above described processe~ are advantageous in
~5 continuous foundries where the cas~ing period is long and
the non~recurrent treatment in the furnace is not sufficient
to keep the hydrogen gas content o~ the charge at the desired
.
3~8
- 8 -
.
low level till the end of casting. However7l a common draw-
back of these processes is that the gaseous reaction products
owing to the rather hlgh flow-through outputs ~3-20 t/hour)
and to the short residence times~J cannot be lifted cDmpletely
to tha surface. To compensa~e this drawbacl<,J reactors with
several chambers have been developed~i but the dimensions and
the heating system of these are similar to those of the fur-
naces and thus they hardly can be fi~ted between the existing
foundry and furnace.
-10 The invention is aimed at eliminating the above draw-
backs and at developing a continuous process for the decrease
of the contaminant content of aluminium melts and aluminium
alloy melts by the use of which proces~ the utilization of
the treating material is increased to a great exten~ and the
purification process becomes weli regulable and controllable.
We were surprised to experience that on introducing
into the aluminium melt or aluminium alloy melt7l isolated
from the air?l ~ powder which develops chlorine gas~l expedient-
ly zinc chlorideJ~ magnesiùm chlorideJ! hexachloroethane or
manganese chloride mixed up with an inert gasrl expediently
with nitrogen gas~l the amount of the powder developing the
chlorine gas required for the removal of a certain amount of
contaminant can be decreased in the process according to the
invention by about 60 % referred to the processes known up
to the present.
The advantages of the process according to the invention
are summarized below.
1. By the use of the process according to the invention
378 '`
_ g _
the amount of the powder developing the chlorine gas
required fDr the removal of the given amount of contaminants
is decreased to a great extent i.e~ the utilization of
ma~erial is improved end the amount of non-utilized treat-
ing material is reduced. From a~ e~onomical aspect this 1s of
quite unest~mable importance.
2. The process according tD the invention can be
operated con~inuously and controlled automatically at a
high precision. Thus the purification process can be carried
out by less physical power in a well controlIable way.
3. Purification is carried out under exclusion of
air.J and thus any further oxide contaminations can be eliminat~
~d. Namely,l in the presence of atmospheric oxygen additional
oxide contaminants could be formed.
4. A further advantage of the process according to
the invention is that on applying ~his process the aluminium
content of ~he slag formed during the treatment is essen-
tially lower than e.g. the aluminium content on treatment
with nitrogen gas only.
The process according to the invention is carried,
out in the equipment shown schematically in Fig. 1.
The pressurized container denoted in Fig. 1 by (1)
which can be filled up after opening the cover ~9) serves
as a recipient of the'treating material. The feeder ~4)
forwards the treating matenal to the mixing ~pace ~5).'The
velocity of feeding can be varied ungradually and it is
' stabilizad by the driving unit ~3) at a high ac'curacy.
The filling~up of the container wlth the treating material
.
. .
-- lo --
is controlled by a signal induced by the signal device (2).
The carrier gas enters the mixing space ~5) through
pressure regulator and stabilizer t7)~ The volume of the
gas can be controlled by the flow meter ~6). The mixture of
gas and treating material prepared in the mixing ~ace flows
through the flexible tube t8) to the treating pipe ~lo). The
material of the treating pipe is resistan~ to the effect of
the liquid metal. Metal purification by means of a mixture
of gas and treating material is applied under plant conditions
at the treatment of aluminium and aluminium alloy melts. The
treating material is hexachloroethane,J the carrier gas is
nitrogen.
The process according to the invention is elucidated
in detail by the following non-limiting examples.
Exam ~
An ~luminium_magnesium~silicon alloy melt is treated in
a 15 tons tub-type flame furnace by an equipment of ~he
type shown in Fig~ 1. The flow by volume of the nitrogen
carrier gas used for the treatment is 0.4~0.5 Nm~minute.
Treatment is started at a temperature of 710-720C. In one
half of the cases no salt developing chlorine gas is added
to the nitrogen gas. The amOunt of applied hexachloroethane
is 2 kg/t of melt to. 2 %). The gas content of the melt
before and after ~he treatment is shown in Table 1. The gas
content is determined by the ,~first bubblei~ method. Nitrogen
gas is capable of removing 9-33 % of the hydrogen gas conten~
of ~he melt~ On adding hexachloroethane,l as an agent which
develops chlorine yas,l to the ni~rogen gas,! the content of
37~3
11 -
hydrogen gas can be reduced by 48-77 %. The formed slag'
is drytl powder-lil<e~l having a low aluminium content where-
as on treatment with nitrogen gas alone,l the formed slag is
puLpy. At ths addi~ion of hexachloroethane the temperature
of the melt does not decrease on the effect of the heat of
reaction during the treatment. At the treatment with ni~rogen
gas alone,J in turn~) the temperature decreased by 15C.
Example ,2
An aluminium~magnesium-silicon alloy melt is treated
in the equipment shown in Fig. l in a 15 tons tub-type flame
furnace at the parameters specified in Example l. Powdered
hexachloroethane'serves as a salt developing chlorine gas.
For the salce of comparison on another occasion tablets of
hexachloroethane are introduced into the melt by the dipping
bell method. The amount of the treating material is in both
cases 2 kg/t of melt. The contents of hydrogen'gas are given
in Table 2 for comparison. On feeding in a nitrogen gas
current~ owing to the better reaction conditions,J the gas
content of the melt decreases by 58-70 %ol a value more than
twice as high as the purifying effect attainable by the
tablets of hexachloroethane.
The same effect appears in the oxygen content of the
melt. Whereas the oxygen conce'ntration of the melt is lO,ppm
on blowing~in powdered hexachloroethane,J this value is about q
18 ppm at the treatment with tablets. The variation of oxygen
content in case of a treatment with hexachloroethane tablets
or with powdered hexachloroethane plus nitrogen gas is
shown in Tables 6 and 7.
37 8
- 12 -
Example 3
.
The decrease of the content o~ hydrogen gas in an
aluminium-magnesium-silic4n alloy melt is investigated as a
function of the amount of powdered hexachloroethane introduced
as an agent developing chlorine gas~l with the use of an
equipment of the type shown in Fig. 1.
Figs. 2 and 3 show the efficiency of purification by
comparing the effects of a treatment with tablets of hexa-
chloroethane and the effects of a treatment in 15 ton tub-
-type furnaces with powdered hexachloroethane blown-in by
nitrogen gas. In Fig. 2 the hydrogen gas content of the melt
(ml/100 g) is shown as a function o~ the specific hexachloro-
ethane consumption (l<g calculated for 1 ton of the melt).
In Fig. 3,J in turnr~ the initial hydrogen gas content (denoted
as Sk and given in ml/100 9) is shown as a function of ths
specific hexachloroethane consumption (given as kg/ton of
the melt). Also the hydrogen gas contents at the end of the
treatment ~denoted as Sv) are given. The continuous lines
refer to a treatment with powdered hexachlooethane plus nitrogen
gas whereas the dotted lines relate to a treatment with tablets
of hexachloroethane. The efficiency of powdered hexachloro-
ethane introduced in a nitrogen gas current exceeds that of
the treatment with tablets of hexachloroethane. This is shown
in Fig. 3 for an initial hydrogen gas content of 0.3 ml/100 9
and for a final hydrogen gas content of 0.1 ml/100 9. For ob-
taining an identical purification effect the decrease in the
consumption of hexachloroethane may attain 60 %. On blowing_in
powdered hexachloroethane in a nitrogen gas current the oxygen
~ 37 8
- 13 _
content decreesed in the investigated case to 5 ppmO
Ex~ple 4
By the equipment of the type ~hown in Fig. l a 13 ton
charge of aluminium~magnesium-silicon alloy melt is treat-
ed ~n ~ tub-type flame furnace. Changes in the sodium conten~
occurring on the effect of the blowing-in of 2 kg/ton of melt
of powdered hexachloroethane delivering chlorine gas are
investigated. In Table 3 the sodium contents before and after
the tre~tment ere compared. The decrease is by 27-65 ~.
The efficiency of purification attainable by increas
ing the applied amount of the hexachloroethane powder is
shown in Fig. 4 wherein the sodium content tppm Na) is shown
as a function of the specific hexachloroethane consumption
~kg/ton of melt).
Example 5
.
By the e~uipment of the type shown in FigD 1 an
aluminium-magnesium-silicon alloy melt is treated in a 15
ton tub-type flame furnace. The volume flow of the nitrogen
gas used for the treatment is 0.4-0.5 Nm3/minute. The tempe~
rature of the treatment is 710-720C.
Table 4 shows the oxygen content of the melt before
and ~fter the treatment with nitrogen gas. The oxygen content
is determined by the neutron activation method. On average
no decrease of-the oxygen content is experienced. On the
contraryDJ the oxygen content even increased in the majori~y
of cases~
~ . .
In a tub-type flame furnace a 25 ton charge of aluminium-
~4437~3
- 14 ~
-magneslum-silicon alloy melt is treated with hexachloro-
ethane tabletsO Changes ln the sodium content are regist-
rated as a result of mixing up 2 kg/ton tablets of hexachloro-
ethane delivering chlorine gas with the melt. The temperature
of the treatment is 710_720C.
Sodium contents before and after the trc~ment are
given in Table 5 for the sake of comparison. The sodium
content deereases by 14-57 %.
T~ble 1
Hydrogen gas content
Treatment with N2 Treatment with N2~C2C16
., , , ,,,
- Before After Decrease Before After Decrease
t r e a t m e n t t r e a t m e n t
ml/100 9 ml/100 9 ml/100 9ml/100 9
Al A1 ~ Al. ^ A1 %
, ... . ~ _ _ _
0.23 0.21 9 0.20 0.~9 55
0.11 0~08 27 O.z6 0.1~ 62
o.zl 0.14 33 ~.21 0.06 71
0~27 0.24 11 0.23 0.12 48
0.24 0.17 29 0.22 U~05 77
378
~ 15 -
Tabl~e 2
Hydrogen gas content
~ .... ~
Treatment with C2C16tablets Treatment with N2 ~ powdered
. . 2 ~ 6
Before After Dacrease Before After Decreese
t r e e t m e n t t r e a t m e n t
ml/100 ~ ml/100 9 ml/100 g ml/100 g
Al Al % Al Al %
~ . . .._
o.lg 0.16 16 0.20 0.06 70
0.22 0.1~ 14 0.32 0.11 66
0.32 0.23 28 0.23 0.09 61
0.21 Ool9 10 0.2~ o.lo 62
0.32 0.25 22 ¦ b.24 o.lo 5~
Table 3
Sodium content
.. . . _
Treatment with N ~ 2 kg/t of powdered C2C16
Before treatmentAfter treatment Decrease
ppm ppm I %
11 27
6 4 33
7 65
7 30
7 4 43
~ 16 _
T~ble 4
Oxygen content
L ._ -- r _ ~_ _ _ _
Tre~tment with N2 gas
Before tre~tment After treE~tment Ch~nge
ppm ppm
, ,
~ lo
. 65 ~35
26 38 ~13
43 ~ 1~
3e 30 - 8
, 35 - 5
38 40 ~ 2
2~ 30 ~ 5
4 0 35
O
,
378
~ 17 -
Teble 5
Sodium content
. Treatment with 2 kg/t of tablots of C2C16
3efore treatment A~ter treatment Oecrea~e
ppm pp~ %
8 5 37.0
3 40.0
7 4 43.0
8 5 37.0
7 3 57.0
6 4 33.0
9 6 33.0
7 6 .14.0
8 20.0
78
Tab
Oxygen content
Treetment with C2C16 tablet~
~efore tre~tmentAfter treatment Decrease
ppm ppm %
17
5~ 45 1~
3g 30 14
13
22
Table 7
Oxygen centent
Treatment with N2 ~ powdered C2C16
Before treetmentAfter treatment Decrea~e
ppm ppm %
43
33
15 - ~0
17
