US3472503A

US3472503A - Vacuum degassing apparatus for molten metals

Info

Publication number: US3472503A
Application number: US612131A
Authority: US
Inventors: Erich Breuer
Original assignee: Bbc Brown Boveri & Cie
Current assignee: BBC Brown Boveri AG Germany
Priority date: 1966-02-01
Filing date: 1967-01-27
Publication date: 1969-10-14
Anticipated expiration: 1986-10-14
Also published as: DE1281466B; CH476845A; GB1108029A

Description

Oct. 14, 1969 E. BREUER VACUUM DEGASSING APPARATUS FOR MOLTEN METALS ,Filed Jan. 27, 1967 2 Sheets-Sheet 1 Fig. 1

Erich Brewer l md $1 M W W Oct. 14, 1969 BRE E 3,472,503

VACUUM DEGASSING APPARATUS FOR MOLTEN METALS I Filed Jan. 27, 1967 2 Sheets-Sheet Erich Brewer United States raemomce H 3,472,503 Patented ot.'14, 1969 Int. Cl. C21c 7/10,- Hb 3/52 US. Cl. 266-34 1 Claim ABSTRACT OF THE DISCLOSURE A vacuum degassing apparatus for melted metals, particularly steel, includes a vessel in which the degassing takes place, the upper portion of the vessel including a vacuum g'as takeoff space and one or more electrically heated rods for maintaining temperature of the melt during the degassing phase. The melt itself is not poured into the degassing vessel until the vacuum has been established, and enters the top of the vessel through a tubular connection piece associated with a supply tank for the melt such as a converter. As the melt discharges from the lower end of the connection piece, the flow widens out in a funnel-shaped manner in the form of a spray which facilitates release of the gas from the melt. The tubular connection piece through which the melt flows into the vessel is electrically conductive and serves as one current supply contact to the resistance heating rods which are secured at the inner ends to the connection p1ece.

FIELD OF THE- INVENTION The present invention relates to the art of vacuum degassing melted metals and is particularly concerned with an improvement in the construction of the degassing vessel which minimizes the tendency of the molten metal to splash against and adhere to the vessel walls.

DESCRIPTION OF THE PRIOR ART It is known to degas melted metals, particularly steel, by subjecting them to the effects of a vacuum in a closed vessel. The gas which escapes from the melt causes a splashing of the liquid steel whereby the splashes can partly reach the refractory lining of the vessel. Since the degassing operation takes some time during which the temperature of the melt sinks appreciably (for instance 30 to 50 C.), splashes of metal can easily adhere to the lining of the vessel. These particles of steel which adhere to the lining have a detrimental effect on the efficiency of the degassing process. In order to prevent the melt from cooling during degassing, it is known to provide heating resistors, particularly graphite resistances, underneath the cover of the vessle. With such an arrangement the liquid steel is introduced through the bottom of vessel. The gas bubbles which occur when the degassing operation is undertaken with such an arrangement result, however, in a considerable amount of splashing. To prevent the heating device from becoming inoperative after a short time it is necessary to have a considerable empty space above the level of the melt in the vessel. This necessitates a large heating power and a considerable overall height for the vessel, this being a disadvantage particularly when the device has to be used in connection with continuous casting plants which already are of a considerable height.

The relatively large heating power makes it necessary to cool the contacts of the graphite rods which have been used up to now for the heating, the cooling water coming within close proximity of the melt chamber.

There is therefore a considerable danger that in the event of a leak, water may enter the vacuum chamber containing the melt.

SUMMARY OF THE INVENTION The object of the invention is to achieve a fundamental improvement as regards degassing devices of the aforesaid type. It has been found that when a stream of liquid metal falls into a vessel evacuated to a pressure of about 0.8 torr, it immediately spreads out in a funnel-shaped manner and forms a spray consisting of finely divided drops. When this descending fog impinges on the surface of the melt no appreciable splashing occurs.

In order to utilize this phenomenon in a degassing apparatus, it is necessary to provide an arrangement so that the degassing action is already effective when the melt flows from the storage vessel into the crucible-like pouring vessel.

In a degassing apparatus of this kind for liquified metals, particularly steel melts, comprising a cruciblelike ladle with a cover-shaped headpiece containing an electrical resistance heating device, an opening is provided for filling in the melt which on the one hand is in vacuum-tight communication with, the ladle and on the other hand with the storage vessel for the liquified metal in such a manner that the closeable outlet in the storage vessel is above the filling opening in the covershaped headpiece.

A particularly expedient form of degassing apparatus in accordance with the invention is obtained when an electrically conductive and interchangeable connection piece is provided which is inserted in the opening of the cover headpiece and extends down into the interior of the crucible-type ladle and serves for filling the melt into the ladle and also acts as a current supply contact for at least one heating resistance which passes from the connection piece through the wall of the cover headpiece in a radially outward direction.

BRIEF DESCRIPTION OF THE DRAWINGS A constructural example of the invention is shown in the drawings where FIG. 1 is a longitudinal section and FIG. 2 a cross-sectional view along the plane A-B of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT With reference now to the drawings numeral 1 indicates a crucible-like ladle and 2 is the cover-shaped headpiece. An electrically conductive tubular connection piece 5 to which the heating resistances 3 are connected is inserted in an opening 4 which is expediently located in the middle of the headpiece. The resistances 3 extend outwards through the wall of the cover-like headpiece and are pressed resiliently against the electrically conductive connection piece 5 by means of a device 13 equipped with a press bolt or spring. The lower, discharge end of the connection piece 5 thus extends below the position of the heating rods 3 so as to prevent damage to the latter by the molten metal. Outside the headpiece, the resistances are connected by way of vacuumtight bushings and current leads 10 to a current supply. Water cooling devices 11 serve for cooling the contact points.

In the example shown, there are three heating resistances 3 which are arranged in a starlike formation with respect to the connection piece 5 and are supplied with three-phase current. A larger number of resistances, namely a multiple of three, can also be provided. Naturally it is also possible to provide only a single resitsance, but this is obviously not so expedient.

The heating rods are preferably made of graphite or a similar resistance material. Connection piece 5 can also consist of the same material.

The upper part of the crucible-like ladle is enclosed by an airtight hood 8 with projections 8a for the resistances, these projections being provided with covers 8b. Inside the hood 8 above the connection piece 5 there is an opening which is closed by a fusible cover plate 9. A pipe connection 7 is provided for the purpose of evacuating the hood and thus also the interior of the crucible-shaped ladle. A flange 80 with a seal enables the storage vessel 14 to be mounted on the hood 8 in a vacuum-tight manner and so that the opening 15, which can be closed by a plug, is in alignment with the connection piece 5. The connection piece 5 which is used for pouring in the melt, can be provided with a removable tubular insert liner 6 consisting of head resistant material, e.g., refractory material, for instance zirconium oxide.

A device 12, shown schematically, serves to discharge the ladle. The height of the apparatus should be selected so that the melt when it emerges from the connection piece 5 and passes into the vacuum forms a funnel-shaped stream which expands as it passes downwards but pnactically does not come into contact with the sides of the vessel.

The apparatus functions in such a manner that after evacuation by way of the pipe connection 7, the discharge opening of the storage vessel, for instance a converter filled with melted steel, is opened. After the cover plate 9 has melted, the liquid metal passes through the connection piece 5 into the crucible-shaped ladle where the flow widens out in a funnel-shaped manner as indicated by the broken lines and in the form of a spray already releases a large part of the enclosed gas.

The apparatus possesses the advantage that it is easy to operate in a quick and reliable manner, and at the same time is very compact. The connection piece 5 in the headpiece moreover provides the possibility of inserting a gas or oil burner as a supplementary heating device for drying and heating the apparatus or holding its temperature.

I claim:

1. Vacuum degassing apparatus for liquefied metals, particularly steel metals, comprising a crucible type ladle having a cover-shaped headpiece, said headpiece containing at least one electrical resistance type heating element in rod form extending radially inwards through the wall of said headpiece, said headpiece being provided with a filling opening communicating said ladle with a storage vessel so located that a closable discharge opening in said storage vessel is above the filling opening in said headpiece, hood means enclosing said ladle in a vacuum-tight manner, means for evacuating said head, an interchangeable tubular connection means located within said opening in said headpiece and which extends into the interior of said ladle to a level below said heating rod, said tubular connection means serving for filling saidladle with melt from said storage vessel and being constituted by an inner tubular member made from a heat-resistant material and an outer tubular member in heat-transfer contact with said inner tubular member, said outer tubular member being made from electrically conductive resistance material, and said outer tubular member being connected to the inner end of said resistance type heating rod so as to electrically heat said inner tubular member.

References Cited UNITED STATES PATENTS 2,133,235 10/1938 Slayter; 3,014,255 12/1961 Bussard et al. 266-344 3,125,440 3/1964 Hornak et a1. 266-344 X 3,137,566 6/1964 Thieme -49 X 3,384,362 5/1968 Philbrick 266-344 X FOREIGN PATENTS 1,192,368 10/1959 France.

I. SPENCER OVERHOLSER, Primary Examiner R. D. BALDWIN, Assistant Examiner U.S. Cl. X.R. 13-33