WO2000058680A1

WO2000058680A1 - A method and device for transferring metal

Info

Publication number: WO2000058680A1
Application number: PCT/NO2000/000109
Authority: WO
Inventors: Ola GUSSIÅS; Kjell HAFSÅS; Jo Vaagland
Original assignee: Norsk Hydro Asa
Priority date: 1999-03-31
Filing date: 2000-03-29
Publication date: 2000-10-05
Also published as: NO991607D0; AU3577700A; NO991607L; NO308920B1

Abstract

A method and device for transferring metal, for example from a tapping vehicle (9) to a casting furnace or holding furnace (2). The casting furnace or holding furnace (2) is provided with a channel or pipe (1) which extends from the top of the furmace down towards its bottom, below the expected metal level in the furnace, and that, on the outside of the furnace, the channel or pipe (1) is connected to a connection elbow (8) which is designed to be connected to a tapping boss on a tapping vehicle or similar (9). The metal is injected via the channel or pipe directly into the molten metal under the surface of the metal.

Description

A method and device for transferring metal

The present invention concerns a method and device for transferring (tapping) metal, in particular transferring aluminium from a metal crucible on a tapping vehicle to a holding furnace.

The transfer of liquid aluminium, for example by tapping (transferring) the aluminium from an electrolytic furnace to a holding furnace, represents the largest source of slag formation apart from the smelting of cold metal.

The most common methods of transferring liquid metal from a metal tapping crucible to a holding furnace are with the use of compressed air, in which the metal crucible is closed and the metal is pressed over into the holding furnace via a tapping pipe, or with the metal crucible open and the metal being poured over into the holding furnace. With both methods, however, the metal flows in an open atmosphere from the tapping pipe or tapping point on the metal crucible as a "waterfall" down onto the liquid metal in the holding furnace. In this way, the metal is exposed to the oxygen in the atmosphere with the result that a film of oxide is formed on the liquid metal. The film of oxide encapsulates the metal and remains on the surface of the metal as slag. During the transfer of the metal, the free flow of metal ("waterfall") also creates movement in the metal so that the oxide layer cracks and more metal is oxidised while giving off heat. The generation of heat can sometimes cause slag fires in which further metal is lost.

The present invention describes a method and device for the transfer of metal in which the problems of slag formation and slag fire are considerably reduced. More precisely, tests show that slag formation is reduced by 30 to 35%. This represents a reduction in metal loss of approximately 400 tonnes for a casting plant with a capacity of 200 thousand tonnes per annum. In turn, this is equivalent to a reduction in loss of approximately NOK 4 million per annum. The present invention also contributes to increased agitation in the molten metal and thus also to increased smelting of any cold metal which is added. Moreover, the present invention contributes to preventing liquid metal from splashing back so that the surroundings or operators are not exposed to hazards, damage or injury.

The method in accordance with the present invention is characterised in that the metal is transferred through a filling pipe or channel in the wall of the holding furnace and injected into the melt at a level under the surface of the metal. Moreover, the device in accordance with the present invention is characterised in that the holding furnace is provided with a channel or pipe which extends from the top of the furnace down towards its bottom, below the expected metal level in the furnace, and that, on the outside of the furnace, the channel or pipe is connected to a connection elbow which is designed to be connected to a tapping boss on a tapping vehicle or similar.

The dependent claims 3, 4 and 5 define advantageous features of the present invention.

The present invention will be described in further detail in the following using examples and with reference to the attached figure, which shows an elevation of part of a holding furnace and the contours of a tapping vehicle with a metal crucible.

As stated in the above, the procedure in accordance with the present invention consists in liquid metal, which, for example, is transferred from a metal crucible on a tapping vehicle to a holding furnace, being pumped or otherwise pressed through a pipe or channel, the outlet end of which is located under the level of the molten metal in the holding furnace, so that the metal is fed (injected) directly into the melt.

The figure shows an example of a device for transferring metal from a tapping vehicle 9 to a holding furnace 2. The device comprises a filling pipe 1 , which extends from the outside of the furnace 2, through an opening 3 in it and down into the melt 4 towards the bottom of the furnace. The filling pipe is expediently made of a heat-resistant material, for example a ceramic material or cast iron. The filling pipe is otherwise provided with a filling boss 5 and is fixed in the opening 3 in the furnace by means of a flange connection 6. The furnace can be kept tight in this way and thus prevent the inflow of air from the outside atmosphere or metal splashes into the surroundings.

When metal is transferred, a connection elbow 8 on the tapping vehicle 9 is connected to the filling boss 5 on the filling pipe 1. The connection (not shown) between the connection elbow 8 and the filling boss 5 can expediently be a quick-release connection. The upper part of the filling pipe 1 and the filling boss 5 can expediently be covered by a cupular hood 7 which serves to seal them and makes it possible to maintain a vacuum in the furnace 2. The hood 7 is fixed in a rotating arm 10 which is connected to the furnace 2 with an articulated joint and is designed to be swung up or down using a pneumatic piston/cylinder device 11.

Tests have been carried out on the transfer of metal from a tapping vehicle to a holding furnace using a metal transfer setup with a filling pipe as shown in the figures and as described above.

The metal in the tests was taken from aluminium electrolysis production, in addition to some cold metal, and the slag which was scraped off for each charge was compared with the average quantity of slag which was scraped off when filling metal in the traditional manner (by pouring over the melt) in the course of the previous year, i.e. the total quantity of slag which was scraped off with an annual production of approximately 200 thousand tonnes. The results of the tests are shown in the table below.

As the table shows, tests were carried out with three charges. These charges were selected at random. For all three charges, some cold metal was also added. Calculations show a reduction in the quantity of slag of 30 - 35% when the metal is transferred through the filling pipe under the surface of the metal in the casting furnace. The minor variations in slag quantity are due to variations in the quantity of cold metal and differences in metal quality, among other things.

In the example shown above, a filling pipe which extends down into the molten metal in the holding furnace is used.

Alternatively, instead of a pipe, the furnace can be provided with a channel in the furnace wall (not shown) which emerges near the bottom of the furnace. In such case, the tapping boss on the tapping vehicle (metal crucible) should be connected to the channel with an airtight coupling to prevent air from being taken down into the melt.

Claims

1. A method for transferring metal, for example from a tapping vehicle (9) to a holding furnace (2), characterised in that the metal is transferred through a filling pipe (1) or channel in the wall of the holding furnace (2) and injected into the melt (12) at a level under the surface of the metal.

2. A device for transferring metal, for example from a tapping vehicle (9) to a holding furnace (2), characterised in that the holding furnace (2) is provided with a channel or pipe (1) which extends from the top of the furnace down towards its bottom, below the expected metal level in the furnace, and that, on the outside of the furnace, the channel or pipe (1) is connected to a connection elbow (8) which is designed to be connected to a tapping boss on the tapping vehicle or similar (9).

3. A device in accordance with claim 2, c h a ra cte r i s e d i n that the tapping pipe (1) is fixed in the wall of the holding furnace (2) by means of a flange connection (6).

4. A device in accordance with claims 2 and 3, characterised i n that the tapping pipe (1) and the blow-out connection (8) are made of cast iron.

5. A device in accordance with claims 2 and 3, characterised in that the tapping pipe (1 ) and the blow-out elbow (8) are made of a ceramic material.