US2253421A

US2253421A - Method and apparatus for deoxidizing and degasifying liquid steel

Info

Publication number: US2253421A
Application number: US295491A
Authority: US
Inventors: Mare Baltzar E L De
Original assignee: Individual
Current assignee: Individual
Priority date: 1938-09-20
Filing date: 1939-09-18
Publication date: 1941-08-19
Anticipated expiration: 1958-08-19

Description

METHOD AND APPARATUS FOR DEOXIDIZING AND DEGASIFYING LIQUID STEEL Filed Sept. 18, 1939 lvwe 712 52" Marl l aQ/far y with the cast iron mould, chills rapidly and I the gases to the top of the ingot being formed Patented Aug. 19, 1941 METHOD AND APPARATUS FOR DEOXIDIZ- ING AND DEGASIFYIN G LIQUID STEEL Baltzar E. L. de Mare, Philadelphia, Pa.

Application September 18, 1939, Serial No. 295,491 In Sweden September 20, 1938 3 Claims.

This invention relates to the treatment of liquid steel, to improve the quality thereof by eliminating the two chief causes of defects in articles formed therefrom, namely the elimination of products of oxidation, chiefly silicates of manganese and aluminum which cause nonmetallic impurities in the articles; and the elimination of occluded gases, such as hydrogen, nitrogen and carbon monoxide which cause seams.

The object of the invention is to provide a thoroughly practical method for such treatment, to replace methods hitherto known or proposed which have proven to be, in one or more respects, commercially impractical, ineillcient, or unadaptable and have therefore been discarded.

For instance, it has previously been proposed to pour molten metal into a mould placedin an airevacuated chamber, to give the vacuum a chance to eliminate gases occluded in the metal. Thus, for instance, a whole electric furnace and one or more moulds have been placed under one large bell for evacuation. The bell therefore, was necessarily large in size, heavy, and unwieldy. Incidentally, the means for handling the furnace and the mould, or moulds, were complicated and expensive.

It has also been proposed to arrange the moulds alone, with a distributing arrangement for the metal, in'a vacuum chamber, and to employ a special ladle as a cover for the chamber, above the distributing arrangement. This arrangement is necessarily diiiicult to handle, bulky, and complicated and suffers further from the disadvantage that the evacuation of the vacuum chamber cannot begin until the ladle has been placed in position.

Normally the pouring of liquid metal directly into a mould under vacuum involves the disadvantage that the metal, upon making contact solidifies before the vacuum can become effective to extract all the occluded gases and before the slag and impurities can be carried upwards by in the mould.

It has been proposed to provide a ladle or similar receptacle with a tight cover connected with an evacuating arrangement, and on this cover to out breaking the connection with the evacuating arrangement.

Both of the last named arrangements have an additional disadvantage in that the ladle in which the vacuum treatment is being carried out is surrounded by air, therefore the radiation of heat from the ladle becomes considerable. For that reason the metal cannot'be permitted to remain for any prolonged period of time in the ladle. Therefore, the vacuum treatment cannot be continued for a sufficient length of time to be thoroughly efiective.

It has also been proposed to treat the liquid metal with deoxidizing slag to remove oxides and other impurities from the metal, by causing the metal to fall from a great height into a receptacle containing such slag, to cause a violent impact therebetween for creating an intermixing of the two. This involves the'disadvantage that oxidization of the metal and loss of heat by radiation and convection increase in proportion to the height of its fall.

The several disadvantages pointed out above in regard to the heretofore known methods and arrangements are avoided in the invention at hand, according to which the treatment can be carried out in a practical way by the use of ordinary ladies and with the greatest possible efiectiveness.

The present invention also ensures that the Pouring can be done conveniently in the usual way and under atmospheric pressure, after the deoxidizing and degasifying treatment has been finished.

The present invention is chiefly distinguished from the prior art in that the liquid metal, tapped from a converter or melting furnace into a ladle, is pouredfrom said ladle into a smaller open vessel or pouring box arranged the shortest possible distance below the ladle and having controlled communication with a vacuum chamber; in that the metal, while in this vessel is subjected to electric heating and cleaning by a suitable deoxidizing slag; in that the liquid metal is permitted to flow from this vessel in a stream place a receptacle from which liquid metal con-' top; and that the cover cannot be removed withdown into a ladle removablyv enclosed in the vacuum chamber; inthat during its pouring into the enclosed ladle the liquid metal is exposed to the action of a high vacuum; in that after' the pouring is completed the exposure'of the liquid metal to said high vacuum is continued for adesired period of time; and in that the last named ladle,after the vacuum treatment has been finished and atmospheric pressure restored, is taken out of the vacuum chamber and its content poured oil into moulds. Further distinctive features and advantages of the invention will be made evident by the following description and appended claims.

In the accompanying drawing is shown a design or an arrangement for carrying out the method according to the invention, the single figure of the drawing being a vertical section of the preierred arrangement for the vacuum treatment of liquid steel.

In the drawing, I denotes a vacuum chamber formed within a suitable structure placed in the ground, such as a concrete pit 2, which may be reinforced with an outer air-tight casing 3, and provided with a refractory lining, as shown at l.

The vacuum chamber I is covered with a convex lid Ii, which is provided with a suitable heatinsulating lining, for instance concrete, and with lifting clevlses 6 for the handling thereof. The lid 5, at its under edge, is provided with a laby rinth packing I, which consists of a number of concentric ridges with sharp edges, which edges rest on a machine "finish bottom of a troughshaped channel 8 covered with a suitable plastic material into which said edges are pressed. The sloping inside wall 9 of the trough 8 forms a irusto-conical guide for the lid 5.

n the lid 5, a small open vessel or pouring box Ill is mounted and suitably secured. The vessel I0 communicates with the vacuum chamber I through a nozzle I I disposed in the bottom of the vessel II). The opening or hole of the nozzle II can be closed .or' opened by means of a stopper rod II. The entrance of air into the vacuum chamber I is at first prevented by the stopper I2 and alter the level of the metal in the vessel III is raised to a predetermined height the liquid metal in the vessel III forms the necessary seal.

In the construction shown, the vessel I0 is surrounded by an electric coil I3 and is designed as a high frequency electric furnace of the Northrup type, for example. A

The lid of the vacuum chamber I can be provided with an air-admission valve 25 and a sight glass III for observation and for use of an optical pyrometer for determining the temperature of the stream 28 in comparison to the temperature 0! the stream 24, also determined by optical py" rometer, or with other arrangements, by which the course oi treatment in the vacuum chamber I can be regulated or controlled, and according to which the strength of the electric current in coil It can be suitably regulated.

A ladle I8 is shown above the vessel III, by

which ladle the liquid steel is carried from the converter or melting furnace to the vacuum apparatus, I1 denotes the removable ladle in the vacuum chamber I, into which the metal is poured and in which the treated metal is collected as the vacuum treatment is being carried out. Both the ladles I8 and II can be constructed identically, so that exchanges can be made.

In the vacuum chamber I, there is a plurality of supports or piers I8, which are provided with sonically shaped attachments I! to serve as guides and supports tor the ladies and which cooperate with attachments ZII on the ladles for that purpose. The ladies may be provided with an insulating space between the outside plate shell and the lining of the ladle. The ladles are also provided with stopper rods 22 for controlling the flow of the liquid steel through the nozzles 23.

The vacuum chamber I is connected by means of a heavy duty pipe 21 and pipe-fitting assembly with any suitable air evacuating apparatus, for

instance, a steam-Jet air-ejector of such capacity as to quickly evacuate the vacuum chamber and reduce the pressure in the vacuum chamber to a minimum low value, approximating zero.

The vacuum treatment is carried out in the following way: Liquid steel from a Bessemer converter, or melting furnace is tapped into the ladle I6, which is then taken to and supported above the vessel III. The liquid steel is permitted to flow through the nozzle 23 of the ladle I6 into the vessel III. The nozzle II in the bottom of the vessel III is opened, after the vessel III has been filled to a suitable height with liquid steel. From the vessel III, the steel is permitted to flow as a stream 28 into the preheated ladle II in the vacuumchamber I.

The metal in the stream 28 will, during its passage through the vacuum chamber I, previously evacuated, become degasifled, and the degasification continues afterwards with respect to the liquid mass of steel 29 which collects in the ladle I1.

In the vessel III may be added preheated or melted slag I5, as for instance an acid reducing slag or any other suitable kind of slag, by which the liquid steel undergoing treatment may be acted on and purified. Theslag I5 also protects the steel against oxidation and radiation of heat. The slag I5 is heated and melted to a substantially liquid state prior to being placed in the vessel I0, such preheating and melting being accomplished by any suitable means forming no part of the present invention.

With the arrangement as shown, an electric heating oi! the steel may be effected while passing through the vessel III. For this purpose the vessel III is designed as an open high frequency electric furnace. All oi! the metal from the ladle I6 is cleansed while passing through the vessel II), by being brought into intimate contact with the slag I5 under a circulating action created in the metal by the heating electric current.

In the present instance, the capacity of the electric furnace I0 is substantially one-tenth the capacity of the furnace or converter from which the liquid metal is drawn into the ladle I8 Ior pouring into the vessel Ill.

After the pouring of the steel into the ladle II has been finished, and the deoxidizing slag in the vessel Ill has also been drained or: into the ladle II, the nozzle II is closed tightly by the stopper I2 to preserve the vacuum in the chamber I, to allow for further vacuum treatment of the steel, and after degasiflcation and deoxidization oi the metal has been continued for the desired length of time, air is admitted into the vacuum chamber, the lid 5 is removed and the ladle I1 is hoisted out of the chamber I and taken to the place where the pouring of the steel into the moulds is to be done.

As it leaves the nozzle I I of the pouring box I I, through the sudden release of the gases as the metal enters the vacuum chamber I, the stream 2| oi liquid steel may assume the form or a spray, providing quicker and greater liberation of the occluded gases.

While the metal is held under the vacuum in the ladle I1, the minute particles oi the impurities coalesce and move upward to and collect at the top of the static body of metal in th ladle II. By being able to hold the metal in a liquid state in the ladle I'I within the vacuum chamber I for a considerable length 01' time, the impurities are given ample opportunity to rise to the top.

The carrying out of the method as described above is, of course, to be considered as an example and the invention can be modified in different ways within the scope of the appended claims.

The process according to the invention can naturally be applied to the treatment of metals other than steel. The apparatus shown admits of many varying possibilities for the treatment of liquid metals.

In addition to the dynamic and static vacuum treatment described above, the apparatus may be used for only static vacuum treatment, and the electrical arrangements shown may be used simply for superheating the metal. Should, for instance, the metal in the ladle l'l, after the vacuum treatment, be too cold, the ladle I! may be hoisted and the empty ladle IE, or another similar ladle, placed in the vacuum chamber, and by again pouring the metal through the vessel in the temperature of the metal may be raised to the desired degree by means of the electric heating arrangements.

I claim:

1. Method to deoxidize and degasiiy liquid steel, characterized by the liquid steel being tapped into a ladle from a Bessemer converter or melting furnace, being then poured from said ladle through a smaller open vessel into a ladle located in a vacuum chamber, wherein the metal during its passagethrough said, vessel is electrically heated and brought into intimate contact with a deoxidizing slag by action of the electric heating currents, and wherein the metal during its passage from said vessel to the ladle in the vacuum chamber is subjected to high vacuum to eifect degasifying of the metal.

2. Method to deoxidize and degasify liquid steel, characterized by the liquid steel being tapped into a ladle from a Bessemer converter or melting furnace, being then poured from said ladle through a smaller open vessel into a ladle located in a vacuum chamber, wherein the metal during its passage through said vessel is electrically heated and brought into intimate contact with a deoxidizing slag by action of the electric heating currents, wherein the metal during its passage from said vessel to the ladle in the vacuum chamber is subjected to high vacuum to effect degasifying of the metal, and wherein the vacuum treatment is continued after the pouring of the metal into the ladle in the vacuum chamber has stopped to continue said degasifying and to permit the impurities to rise to the top of the metal.

.3. An apparatus for the treatment of liquid steel, comprising a vacuum chamber, a ladle in said chamber, a ladle outside and above said chamber, an open vessel between said ladles and in direct communication with the interior of said vacuum chamber, electric means for heating the liquid steel poured from the outside ladle through said pouring boxinto the ladle within the vacuum chamber, and means for drawing a high vacuum in said chamber to efiect said treatment of said liquid steel.

BALTZAR E. L. DE MARE.