GB2134929A

GB2134929A - Degassing molten metal

Info

Publication number: GB2134929A
Application number: GB08328156A
Authority: GB
Inventors: Thomas Steinhauser; Thomas Buch
Original assignee: Honsel Werke AG
Current assignee: Honsel Werke AG
Priority date: 1982-12-22
Filing date: 1983-10-21
Publication date: 1984-08-22
Also published as: BR8306983A; GB2134929B; DE3247457C1; GB8328156D0; FR2538409B1; FR2538409A1

Abstract

The invention relates to a method and a device for the degasification of molten metals in a melt container, with a cover, in particular an aluminium melt, using reduced pressure between the container cover and the melt level. The melt container has a porous wall, through which gases surrounding the container e.g. combustion products pass into the melt. The container may be a crucible.

Description

SPECIFICATION A method and container for the degasification of molten metals, in particular of an aluminium melt The invention relates to a method and a device for the degasification of molten metals, in particular of an aluminium melt, in a melt container with a cover, using underpressure between the container cover and the melt level.

For the degasification of aluminium melts different methods are known, such as chlorinating or scavenging with dechlorinating agents or gases, flushing with inert gases, degasification by tapping, ladle degasification i.e. degasification by passing through a ladle, single billet degasification and continuous degasification. These methods of degasification have the disadvantage of toxicity, of forming aggressive compounds and of burning off Mg, Sr and Na. The use of inert gases is usually expensive (use of noble gases) or much waste metal is formed. When transferring the melt container into a vacuum chamber, a heat loss occurs and relatively high-powered pump is required to ensure degasification, whether of the ladle or of the chamber.

For degasification of aluminium casting alloys in mould casting, essentially degasification by means of a container and a ladle is used. In the first-mentioned degasification, when using a crucible as the melt container, the wall and the base of the crucible have a porosity of 5 to 50 I/m2 per min.

Furthermore, the porous base of the crucible can rest on a gas-permeable base plate.

The fact that no aggressive compounds are released because these can be removed by suction from the space between the cover and the melt surface, and furthermore the fact that it is not necessary to remove the crucible from the furnace, so avoiding temperature losses during degasification, are to be considered as advantages of the method according to the invention and of its device. In addition, however, a good scavenging effect is crucial as the melt is scavenged on all sides and uniformly by gas, and also no Mg-burnoff and only a small amount of Na-burn-off is to be noted as a result of which degasification is still possible even after refining.Finally, the device does not require a lance and a corresponding supply line for the blow gas with pump in order to carry out the method, as a result of which it is not necessary to remove the lance when emptying the crucible and to seal the lance in the cover.

The invention is based on the concept of using the porous wall of the melt container as a diaphragm, so that the furnace atmosphere surrounding the melt container penetrates the wall substantially uniformly and penetrates the melt from the bottom towards the top or radially upwards. The furnace waste gas which occurs in the form of microbubbles produces a particularly finely distributed and intensive scavenging of the melt by means of which both the hydrogen and the melt impurities are carried to the bath surface.

Oxides which occur are also flushed to the surface by the rising gas bubbles, so that with a treatment time of 10 minutes and less, a gas-free and oxidefree melt is obtained. The metallurgical effect of the method according to the invention is equal to chlorination in the gas of an aluminium melt.

In the drawing, a melt container of the device according to the invention is represented with its cover.

Being a crucible T, the stationary melt container has a known shape with a cylindrical side wall 1 and a base 2. Towards the top the crucible can be sealed tightly by means of a cover 3, for which purpose a corresponding seal 4 can be provided between the edge 1 a of the wall 1 and the opposite section 3a of the cover. The cover 3 itself has a vacuum pipe 5 which projects process, the melt is brought in a crucible into an evacuated space, through the cover of which a blow lance projects to the crucible base. In contrast, degasification by means of a ladle provides a crucible which can be closed by means of a detachable cover, again a blow lance being used, which penetrates the cover and reaches the crucible base.In the space between the crucible cover and the melt level a vacuum < 130 mbar is formed, at which point the bubbles begin to form (German "Giesserei" (Casting), 66-1 979-, No. 3, p. 56-62).

In contrast to this, the object of the invention is to produce a static degasification method with an increased degasification effect with respect to known methods and using a simplified degasification device avoiding the disadvantages of the known degasification methods mentioned initially.

In order to achieve this object the invention provides for the use of a melt container with a porous wail, through which gases surrounding the container pass into the melt. In this connection, preferably an absolute pressure of 50 to 500 mbar is produced between the cover and the melt level, into the intermediate space 6 between the cover 3 and the melt level 7.

The wall 1 and the base 2 of the crucible T consist of a material with a porosity of 5-50 I/m2 per min. In this way it is possible for atmospheric air to pass through the wall 1 in the direction of the arrow 9 out of the furnace space 8 which surrounds the melt container and to penetrate the melt upwards in the direction of arrow 10, in order to be collected in the space 6 and to be removed through pipe 5. Preferably, the crucible rests on a gas-permeable base plate 11, as a result of which furnace air can also permeate the base 2 of the container in the direction of the arrow 12 and penetrate the met S from the bottom towards the top.

The pump connected to the pipe 5 produces an absolute pressure 50-500 mbar in the space 6 between the melt level 7 and the cover 3.

1. A method for the degasification of a molten

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION A method and container for the degasification of molten metals, in particular of an aluminium melt The invention relates to a method and a device for the degasification of molten metals, in particular of an aluminium melt, in a melt container with a cover, using underpressure between the container cover and the melt level. For the degasification of aluminium melts different methods are known, such as chlorinating or scavenging with dechlorinating agents or gases, flushing with inert gases, degasification by tapping, ladle degasification i.e. degasification by passing through a ladle, single billet degasification and continuous degasification. These methods of degasification have the disadvantage of toxicity, of forming aggressive compounds and of burning off Mg, Sr and Na. The use of inert gases is usually expensive (use of noble gases) or much waste metal is formed. When transferring the melt container into a vacuum chamber, a heat loss occurs and relatively high-powered pump is required to ensure degasification, whether of the ladle or of the chamber. For degasification of aluminium casting alloys in mould casting, essentially degasification by means of a container and a ladle is used. In the first-mentioned degasification, when using a crucible as the melt container, the wall and the base of the crucible have a porosity of 5 to 50 I/m2 per min. Furthermore, the porous base of the crucible can rest on a gas-permeable base plate. The fact that no aggressive compounds are released because these can be removed by suction from the space between the cover and the melt surface, and furthermore the fact that it is not necessary to remove the crucible from the furnace, so avoiding temperature losses during degasification, are to be considered as advantages of the method according to the invention and of its device. In addition, however, a good scavenging effect is crucial as the melt is scavenged on all sides and uniformly by gas, and also no Mg-burnoff and only a small amount of Na-burn-off is to be noted as a result of which degasification is still possible even after refining.Finally, the device does not require a lance and a corresponding supply line for the blow gas with pump in order to carry out the method, as a result of which it is not necessary to remove the lance when emptying the crucible and to seal the lance in the cover. The invention is based on the concept of using the porous wall of the melt container as a diaphragm, so that the furnace atmosphere surrounding the melt container penetrates the wall substantially uniformly and penetrates the melt from the bottom towards the top or radially upwards. The furnace waste gas which occurs in the form of microbubbles produces a particularly finely distributed and intensive scavenging of the melt by means of which both the hydrogen and the melt impurities are carried to the bath surface. Oxides which occur are also flushed to the surface by the rising gas bubbles, so that with a treatment time of 10 minutes and less, a gas-free and oxidefree melt is obtained. The metallurgical effect of the method according to the invention is equal to chlorination in the gas of an aluminium melt. In the drawing, a melt container of the device according to the invention is represented with its cover. Being a crucible T, the stationary melt container has a known shape with a cylindrical side wall 1 and a base 2. Towards the top the crucible can be sealed tightly by means of a cover 3, for which purpose a corresponding seal 4 can be provided between the edge 1 a of the wall 1 and the opposite section 3a of the cover. The cover 3 itself has a vacuum pipe 5 which projects process, the melt is brought in a crucible into an evacuated space, through the cover of which a blow lance projects to the crucible base. In contrast, degasification by means of a ladle provides a crucible which can be closed by means of a detachable cover, again a blow lance being used, which penetrates the cover and reaches the crucible base.In the space between the crucible cover and the melt level a vacuum < 130 mbar is formed, at which point the bubbles begin to form (German "Giesserei" (Casting), 66-1 979-, No. 3, p. 56-62). In contrast to this, the object of the invention is to produce a static degasification method with an increased degasification effect with respect to known methods and using a simplified degasification device avoiding the disadvantages of the known degasification methods mentioned initially. In order to achieve this object the invention provides for the use of a melt container with a porous wail, through which gases surrounding the container pass into the melt. In this connection, preferably an absolute pressure of 50 to 500 mbar is produced between the cover and the melt level, into the intermediate space 6 between the cover 3 and the melt level 7. The wall 1 and the base 2 of the crucible T consist of a material with a porosity of 5-50 I/m2 per min. In this way it is possible for atmospheric air to pass through the wall 1 in the direction of the arrow 9 out of the furnace space 8 which surrounds the melt container and to penetrate the melt upwards in the direction of arrow 10, in order to be collected in the space 6 and to be removed through pipe 5. Preferably, the crucible rests on a gas-permeable base plate 11, as a result of which furnace air can also permeate the base 2 of the container in the direction of the arrow 12 and penetrate the met S from the bottom towards the top. The pump connected to the pipe 5 produces an absolute pressure 50-500 mbar in the space 6 between the melt level 7 and the cover 3. CLAIMS

1. A method for the degasification of a molten metal in a melt container with a cover, wherein the melt container has a porous wall, through which gases surrounding the container can pass into the melt, and an under-pressure is applied in the space between the container cover and the melt level.

2. A method according to claim 1, wherein an absolute pressure of 50 to 500 mbar is maintained between the cover and the melt level.

3. A method according to claim 1 or 2, wherein the molten metal is an aluminium melt.

4. A device for carrying out a method according to claim 1 with a crucible as the melt container, characterized in that the wall and the base of the crucible have a porosity of 5 to 50 I/m2 min.

5. A device according to claim 3, wherein the porous base of the crucible rests on a gaspermeable base plate.