FR2529230A1 - METHOD AND APPARATUS FOR DEGASSING METAL FUSION BATH AND / OR REMOVING NON-METALLIC IMPURITIES FROM THESE BATHS - Google Patents

Abstract

THE SUBJECT OF THE INVENTION IS A PROCESS AND APPARATUS FOR DEGASING METAL FUSION BATHS AND REMOVING NON-METALLIC IMPURITIES. THE PROCESS CONSISTS OF SENDING SCAN GAS 5 UNDER THE LOWER OPENING (S) OF ONE OR MORE CRANKCASE DUCT (S) 2 CONTAINING ONE OR MORE STATIC MIXING ELEMENT (S) ALSO GIRATORY ELEMENTS FILLED WITH METAL MASS IN FIXED OR MOVING MELTING AND ALSO, OPTIONALLY, AT LEAST PARTLY BY SPACE FILLING PRODUCTS; THE MELTED METAL IS OPTIONALLY SET IN MOTION OR ITS SPEED IS MODIFIED BY THE UPWARD GAS CURRENT IN DUCT 2 OR ON STATIC ELEMENTS OR BY INDUCTION OF AN INDUCTION CURRENT 12.

Description

The present invention relates to a degassing method and apparatus

  metal melting baths and / or removal of non-metallic impurities from these baths. Several methods of degassing metal fusion baths during which

  the partial pressure of the gases to be eliminated in the atmosphere

  gaseous sphere that is in contact with the melt,

  to promote, in this way, by a change in the state of

  equilibrium, their exit from the melt So, for example, oxygen is removed from the molten metal baths

  belonging to Group VIII of the Periodic Classification

  The reduction of the partial pressure can be done, for example, by reducing the atmospheric pressure, that is to say by applying the vacuum or by

  letting in a stream of an inert gas This last

  operation can be done, for example, by bubbling

through the inert gas.

  When using an inert gas, the efficiency

  removal depends on the size of the surfaces in

  the phases as well as the duration of the phase contact In order to obtain maximum efficiency and

  minimum consumption of inert gas, one must be sure

  that the gas to be removed from the melt and the gas

  inert environment are in equilibrium.

  free or at least in a state close to equilibrium.

  The introduction of as little as possible of inert gas is of paramount importance because this introduced gas, if it is not preheated, risks

cool the melt.

  A method and apparatus for introducing

  In accordance with the first of these patents, a compressed inert gas is introduced (US Pat. No. 3,227,547, US Pat. No. 3,743,263 and US Pat. No. 3,870,511). argon, -2-xenon, helium, nitrogen or krypton) below the surface of the molten metal at a rate to exceed the feed rate of 0.3 m 3 / h through the opening having a smaller diameter at 20 mm, while maintaining between the gas leaving the opening and the molten metal mass a relative movement of at least 0.9 m / s and up to 9 m / s as a result of the shearing effect that develops, so that the gas is dispersed in bubbles having 10 mm in diameter and this gas back into the melt The last two patents cited describe equipment that is suitable for the implementation of said

  process, that is, they describe a similar process

  wherein in a closed vessel, which may be under pressure, a rotor having blades or vanes is stably connected to the rotating shaft in the vessel. The rotor comprises a series of vertical channels between the blades. compressed on the upper part of the rotating tree, arrives by

  vertical rotor channels immersed in the metallic mass

  as molten, in the form of small bubbles on the metal melt while the relative velocity, from 0.9 to

  9.0 m / s between the introduced inert gas and the metal mass

  melting, is obtained by the rotary motion of the

  at the same time as the blades on the rotor produced

  have an intense current so that almost

  the mass comes into contact with the gaseous bubbles.

  In the processes and materials described, the specific requirements for inert gas are 0.3 to 2.5 Nm 3 for

  1 ton of molten metal mass.

  According to said descriptions, the rotor is

  truit preferably of a stainless or resistant material

  heat, such as graphite or carbide

  In general, in industrial circumstances,

  a rotor made of a stainless material has a

  However, in order to purify the metal-melt bath simultaneously with its degassing, chemically active gases which react with the impurities, for example chlorine gas, are frequently used. In this case, it is impossible to use a stainless material. as structural material because of the temperature of the molten metal mass it does not

  not withstand the chlorine atmosphere, it becomes

  ingrained, strongly deteriorated and corrosion products also contaminate the molten metal A graphite rotor or other heat resistant material can withstand the chlorine atmosphere but does not withstand the loads developed in some cases extremes of an industrial operation (sudden thermal fluctuations, etc.) and, according to practical experience, a graphite rotor is

  destroyed in a few weeks or months.

  The present invention aims to develop

  a process and apparatus whose performance

  would be free from the aforementioned drawbacks.

  The method and the apparatus according to the invention are based on the fact that, if one introduces a gas of

  sweep under the casing duct containing the ele-

  in static mixing or swirling elements

  known, the gas passing through this area becomes

  During its rise, it causes the molten metal mass to rise upwards. The current of the molten metal which starts in this way is so intense that the mixing stages previously described can be abandoned. melting can also be enhanced by a different process, without the use of mechanical stirrers, for example

  producing an induction current in the metal mass

  melting liquor; as a result of the turbulent movement of the bubbles, the metabolism between the active gas and the metal salt on the gyratory element increases to a degree of

  such that a mixing and purifying effect can be achieved

  cation, respectively, surprisingly using

  a much smaller amount of gas.

  Consequently, the process according to the invention can be summarized by the following characteristic: the flushing gases are admitted under the lower opening of the casing duct or ducts containing the static mixing element or elements and / or the whirling elements filled

  with the molten metallic mass in motion or in

  also optionally filled at least by

  With space filling profiles, and optionally, the molten metal mass is driven into a flow movement or its speed.

  of flow is modified by the gaseous flow of

  up in the crankcase or on the static mixing elements and / or

induction flow.

  According to a preferred embodiment of the invention,

  the ascending gas stream is dispersed in

bubbles.

  According to another preferred embodiment of the invention, the gas stream passes through one or more

  openings having a diameter of less than 10 mm.

  It is also advantageous to pass the gas stream upwards through the casing pipe containing the elements in static mixture or the gyratory elements which define, alternately,

  strangled spaces and flaring spaces.

  According to another preferred embodiment of the method according to the invention, the ascending gas stream is directed through a casing duct formed with a narrowed section of convergence at the bottom and / or a

  diffusion section with flaring on the top.

  The method according to the invention can be carried out

  regulating the flow of the molten metal bath against

  current relative to the introduced gases.

  -5- The essential characteristic of the equipment

  according to the invention is that in the metallic mass

  due to movement or flow, provision is made for one or more crankcase ducts enclosing one or more static mixing elements and / or gyratory elements mounted above the gas inlet opening (s).

  and, optionally, provision is made for

  space crimping which at least partially fill the crankcase ducts containing the static mixing elements and / or the gyratory elements and optional means are also provided for creating an induction flow.

  According to a preferred embodiment of the appa-

  according to the invention, the axis of the crankcase is oriented vertically or deviates towards

  the bottom of the vertical at an angle less than 50.

  According to another preferred embodiment of the apparatus according to the invention, between the casing duct and the rotating elements mounted therein, spaces which narrows and widens in

alternation are formed.

  Another preferred embodiment of the apparatus

  according to the invention, consists in that the

  crankcase containing the gyratory elements

  feels a narrower convergence portion at the bottom and / or a diffusion portion that flares upwards. According to another preferred embodiment of the invention, between the static elements in mixture and the wall or walls of the apparatus, there are

  spaces that narrow and flare, alternately.

  According to another embodiment of the

  reillage of the invention, the filling elements

  of space are preferably formed with the same material

  than the static mixing elements or the gyratory elements, this material being a metal, a metal alloy or a ceramic material which resists

to the molten metal mass.

  The invention will now be described in detail with reference to the accompanying drawings, in which

  Figure 1 is a schematic view of a

  discontinuous operation and used for the purification of a metal melt, driving

  crankcase containing the converging and diffusing parts

  sion, while the static elements of mixing create alternating spaces that shrink and widen; Figures 2 and 3 are schematic views of the continuous operation molten metal purification equipment, the static mixing elements alternately forming narrowing and widening spaces, while the filler elements space according to the invention are also shown in Figure 3; and

  Figure 4 is a schematic view of a

  purification network of the continuously operating molten metal mass, comprising two

  crankcase containing the gyratory elements provided with

  convergence and diffusion, respectively, the molten metal mass and the flushing cleaning gas

by equicurrent.

  As can be seen in Figure 1, in a discontinuous open apparatus for

  to purify a metal melt, the metal mass

  The molten liquid 6 is introduced through the inlet 4 into a container 1.

  casing 2 vertically mounted is filled with the ele-

  3 and a convergence part 13 and a diffusion part 14 This housing duct can occupy a position deviating -7-

  from the vertical but at an angle not exceeding 500.

  Below the lower opening of the pipe of

  casing, is provided an inlet 5 for the flushing gas.

  On the outside of the container, a coil of

  duction 12 is optionally installed.

  In the container of the apparatus with

  Continuously for the purification of the molten metal (Figure 2), the molten metal mass 6 is divided into two halves by a partition 9 The container 1 is provided with a lid 7 On the container, the inlet 4 is provided of the molten metal mass and an outlet 8 for the discharge of the purified molten metal mass On one side of the partition 9, are arranged the static mixing elements 3 while on the other side of the partition, is installed the inlet 5 of the flushing gas. The container shown in FIG. 3 is an open U-shaped container having a shrinking and widening shaft. In the narrowed shaft, there is the inlet 4 of the molten metal, the mixing elements 3

  static and space filling elements; au

  below the static mixing elements 3, an inlet is provided for the admission of the purge gas. In the larger shaft of the container, the

  discharge 8 for the purified metal melt.

  In the container 1, according to Figure 4,

  green by the converge 7 and divided in two by the

  9, there is provided on both sides of the partition 9 a casing duct 2 Above one of the ducts 2 is arranged the inlet 4 of the molten metal, said casing duct being provided with a diffuser 14 on the top and being filled with gyratory elements 11 arranged coaxially with respect to the axis of the pipe

  The other crankcase 2 comprises the

  converging element 13 and the axes of the rotating elements -8- inside the pipe defining an angle with the axis of the casing duct 2 above; the discharge 8 of the purified molten metal is also provided at this location. Below the two casing ducts 2, the inlet 5 for the flushing gas is arranged. In the spaces of the container divided in two by the partition

  9, is placed the molten metal mass 6.

  In the case of open equipment operated

  intermittently to clean the metal mass

  due, this molten metal mass to be cleaned

  is introduced through the inlet 4 into the container 1.

  The inlet 5 for introducing the purge gas, below the lower opening of the casing duct 2, allows the admission of an inert and / or active gas to the molten metal mass 6 The flushing gas flows upwards in the pipe 2 through the static mixing elements 3 and, during this time, this gas is dispersed in tiny bubbles. The stream of bubbles which progress upwards entralne the metal mass

  melted and it follows that this melt is also

  In the casing duct 2, outside the casing duct 2, a slower flow of molten metal directed downwards is established, which can cause the smaller bubbles.

  current of the molten metal mass can be

  due to the current caused by the induction coil

  12 Under the effect of narrowing and widening spaces, respectively, in the conduct of

  crankcase in acceleration, slow currents are

  therefore, and as a result of the location of the contact of the currents, a strong turbulence may be

  observed whose bubbles are disintegrated and provoked

  Instead of a relatively intense sweeping effect from the downwardly directed melting stream containing minute bubbles of non-metallic impurities, these impurities form a sediment or float at

  the surface together with the tiny metallic bubbles

  By means of the current flowing in the induction coil 12, the molten metal stream can be maintained after stopping the inlet of the balancing gas.

  So we can promote the floating of impure-

nonmetallic tees.

  The molten metal mass to be purified and which is introduced through the inlet 4 into the container 1 of the continuously operating apparatus for purifying the metal mass, the container being divided in two by the partition 9, flows from first upwardly against the current relative to the static mixing elements 3 opposite the flushing gas stream which

  is admitted through entry 5 and flows upwards

  following, the molten metal mass 6 flows into the

  space of the container 1 on the other side of the partition 9 and begins to descend slowly During this time, the non-metallic impurities float at the top of the

  melt The purified metal melt

  out of the installation by the discharge 8.

  The outward flow of the flushing gas

  is not represented on the drawing -

  In open equipment with

  In order to purify the molten metal mass (FIG. 3), between the static mixing elements 3 space filling elements are arranged on which the non-metallic impurities of the melt can be deposited. the same way that was described about

Figure 2.

  The molten metal mass loaded into the

  continuous closed fencing to purify the molten metal mass (Figure 4) through the inlet 4 of molten metal, arrives at a half of the container 1 - having the partition 9 and begins to descend around the casing pipe 2 The gas The sweep admitted into the line 2 through the inlet 5 rises through the gyratory elements 11 where a considerable separation of the gaseous bubbles occurs. In the case line, the flow of the metal melt is slower than in the case of an equidient flow and therefore the contact time is also longer; the prolonged contact time as well as the greater interface between the molten metal mass and the gas, an interface formed by the tiny gas bubbles, cause a relatively intense and rapid degassing of the molten metal mass On the other side of the partition 9, the molten metal mass 6

  As a result, under the influence of

  In this space, an accelerated flow of the melt in the casing duct 2 is achieved. The shortest contact time is compensated by the fact that, due to their geometric

  gyratory elements 10 cause greater turbulence

  increased by the more turbulent turbulence

  tense under the effect of the faster flow of the

  molten metal mass The current around the con

  2 down casing is almost completely

  This is compensated by the upward movement of the molten metal mass in this half of the space, and hence the flotation of non-metallic impurities.

is extremely effective.

  The following examples will provide further practical details of the process and apparatus

according to the invention.

11 -

EXAMPLE 1

  In a continuously operating closed vessel having a crankcase conduit having an inside diameter of 50 mm, having a converging portion which tapers at the bottom and a diffusing portion which widens at the top, accommodating 650 kg of molten metal, during a purification performed at a rate of 4 tons / hour, the impurities contained in the starting virgin metal (99.5% Al) can be reduced as follows: Na of 0.005% to 0 , 0001% Li of 0.006% to less than 0.001% H 2 of 0.28 cm 3,100 g of metal at 0,05-0,1 cm 3,100 g of metal. The purification is carried out at a temperature of 700 to 800 ° C using nitrogen gas (99.995% 1 m 3 / tonne), the chlorine content of which

  between 0 and 3% by volume.

  The calculated amount of chlorine introduced and the exhaustion of the confined space allow the absence of harmful gases.

in the working premises.

  With a pair of elements (gas line and a crankcase), about 4000 to 5000 tons of

  metal; in a known method, if a

  graphite, one can purify 1000 to 1500 tons

  virgin metal With other known processes

  as many ceramic fillers, one can purify in a single filling about 3000 tons of virgin metal (aluminum) The consumption of sweep gas represents 3 to 5 m 3 per ton of virgin metal when using one of the known methods By reducing the gas consumption to about 1/3, and also extending the useful life of the mixing elements, the costs of the metal purification can be reduced to 30 to 40% by comparison with the direct costs of the metal cleaning equipment currently used, that is to say using a mechanical stirrer, to get closer

  of the purification efficiency indicated above.

EXAMPLE 2

  By carrying out the purification process described above with an aluminum alloy of Al Mg Si quality, the Applicant reduced the impurities as follows: Na from 0.0092% to 0.0001%, Li from 0.0005% to 0.0001%; H 2 0.42 cm 3/100 g metal 0.12-0.16 cm 3/100 g metal; Purification was carried out at 700-800 ° C with 99.995% purity nitrogen gas (1.3 m 3 / ton) containing 2.5 vol% chlorine. In both cases, a coarse yarn is obtained from the purified hot-rolled metal; tearing of the threads and cracking during the

  hot rolling can be entirely removed.

  When we produce fine threads from this pre-

  product, one can reduce rips during production since the old figure of 0.8 to the value

  0.2 tear / ton of coarse thread.

  Improving the casting ability of

  the purified aluminum alloy as described makes it possible to

  old processes of grain refining.

  The methods and fields of application are very large and varied and it goes without saying that they are not limited to the few examples given in connection with the drawings. 13 - Examples show the advantages of the process

  and equipment, which is the suppression of

  preparatory work, reduction of gas consumption, long service life of mixing elements, reduced production prices when the purification and treatment costs of an aluminum alloy can be reduced to 50-55%, with simultaneous improvement

the quality of the purified metal.

14 -

Claims (10)

  1. Process for continuous or discontinuous degassing of metal melts by scanning with a   gas and the removal of non-metallic impurities,   cultally by melting the metal in an open or closed container, introducing an inert gas and / or a chemically active gas below the surface of the molten metal contained in the container and flowing therein and removing the gas who passes through the   melt and non-metallic impurities,   rised by admitting the flushing gases under the opening   lower part of the crankcase duct (s) containing the static mixing element (s) and / or the   gyratory elements filled with the metallic mass   still or moving and optionally and at least partially by space filling profiles, and optionally the metal melt is moved or the flow rate is changed by the gaseous flow flowing upwards in the crankcase line or on the static mixing elements and / or producing a induction current.   2. Method according to claim 1, characterized in that the gaseous stream which tends to flow towards the top is scattered in bubbles.   The process according to claim 1 or 2, wherein   in that the gaseous stream is introduced through one or more openings having a smaller diameter at 10 mm.   4. Process according to any one of the claims   1 to 3, characterized in that the upwardly flowing gaseous stream passes through a casing duct which contains static mixing elements or gyratory elements to form alternating   Strangled spaces and flared spaces. -   5. A method according to any of the claims   1 to 4, characterized in that the upwardly flowing gaseous stream is admitted into a casing duct having a converging portion which narrows at the bottom and / or a flaring diffusion portion. at the top.   6. Process according to any one of the   cations 1 to 5, characterized in that the molten metal mass is allowed to flow countercurrently with respect to introduced gases.   7. Apparatus for carrying out the process according to   any one of claims 1 to 5, comprising a   housing which is resistant to molten metal baths and inert and / or chemically active gases,   or several containers opened or closed with a   discontinuous pleating or continuous flow, in which the pipe assemblies replace the vessel, means being provided for loading and unloading the gas into the molten metal mass and, when it is a closed container for the molten metal, means for discharging the gas, means for removing non-metallic impurities from the surface of the bath of   fusion as well as means for adjusting the temperature   characterized in that in the immobile or moving molten metal mass one or   several crankcase (s) enclosing one or more   static mixing element (s) and / or gyratory elements above the gas inlet opening (s), and optionally   filling space that at least partially fill   the casing ducts containing the static mixing elements and / or the gyratory elements and optionally also means for causing an induction current.   16 - 8. Apparatus according to claim 7, characterized in that the axis of the crankcase is preferably vertical or deviates from the vertical at an angle less than 500.   9 Apparatus according to claim 8 or 9, characterized in that between the casing duct or the rotating elements therein are formed, alternately, narrowing spaces and spaces that flare out.   Apparatus according to any one of   Claims 7 to 9, characterized in that the driving   crankcase containing the rotating elements has a narrowing convergence portion at the bottom and / or an upwardly flaring diffusion portion 11 Apparatus according to claim 7, characterized in that between the static mixing elements and the wall or walls of the apparatus are formed of narrowing spaces and spaces which flare alternately.   12 Apparatus according to any one of   7 to 11, characterized in that the elements   space filling elements are constructed of the same material as the static elements or the gyratory mixing elements, in particular a metal, a metal alloy or a ceramic material which is resistant to molten metal mass.