US3598383A

US3598383A - Method and apparatus for incorporating additives in a melt

Info

Publication number: US3598383A
Application number: US791062A
Authority: US
Inventors: William H Moore; Harry H Kessler
Original assignee: Individual
Current assignee: MEEHANITE WORLDWIDE Corp
Priority date: 1969-01-14
Filing date: 1969-01-14
Publication date: 1971-08-10
Anticipated expiration: 1988-08-10
Also published as: ES372561A1; FI50345C; FR2028243A7; NL6918061A; SE375794B; CH542930A; FI50345B; JPS504161B1; GB1281233A; DE1941760A1; BR6912880D0; BE737059A

Abstract

A method and apparatus for incorporating a normally oxidizable and/or volatile additive into a molten metal bath disposed in a vessel with a relatively gas tight cover thereover. A gas which is normally nonreactive with the additive is introduced, in one form of the invention, through a porous refractory plug in the bottom of the vessel and this gas bubbles up through the molten metal agitating the metal and fills the space above the metal and under the cover with at least a small positive pressure of the gas. This gas substantially excludes air from the space above the metal. A gas outlet is provided in the cover and is controllable for the purpose of regulating the outflow of gas to atmosphere thereby regulating the gas pressure above the metal surface. An additive container or hopper directly communicates by way of a valve with the space above the metal so that when desired an additive can be introduced into the molten metal. Cooling means are disclosed to condense any volatilized additive.

Description

United States Patent [72] Inventors William H. Moore Meadow Laue, Purchase, N.Y. 10577; Harry H. Kesler. 7 Dromara Road. Ladue,

Mo.64758 2n AppLNo. 791,062 1221 Filed Jan. 14,1969

[4S] Patented Aug-10,1971

[54] METHOD AND APPARATUS FOR INCORPORATING ADDITIVES IN A MELT FOREIGN PATENTS 555,980 4/1958 Canada 898,986 6/1962 Great Britain Primary Examiner-Gerald A. Dost Anomey-Woodling. Krost, Granger and Rust thereover. A gas which is normally nonreactive with the additive is introduced, in one form of the invention, through a porous refractory plug in the bottom of the vessel and this gas bubbles up through the molten metal agitating the metal and fills the space above the metal and under the cover with at least a small positive pressure of the gas. This gas substantially excludes air from the space above the metal. A gas outlet is provided in the cover and is controllable for the purpose of regulating the outflow of gas to atmosphere thereby regulating the gas pressure above the metal surface. An additive container or hopper directly communicates by way of a valve with the space above the metal so that when desired an additive can be introduced into the molten metal. Cooling means are dis closed to condense any volatiiized additive.

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METHOD AND APPARATUS FOR INCORPORATING ADDITIVES IN A MELT Our invention relates to an improved method of introducing volatile, oxidizable and combustible alloys into-a ferrous or nonferrous metal. For example, it relates to the introduction of magnesium, calcium, lithium, aluminum, antimony, zinc, sodium and other alloys, for the purposes of deoxidation or other special effects, in such a way that the additive alloy is readily incorporated in the melt without excessive loss due to volatilization, oxidation, etc.

Our invention is more particularly directed towards incorporating elemental magnesium or concentrated magnesium alloys into cast irons for the purpose of making nodular graphite cast iron.

An object of this invention is to provide a means and method of incorporating alloys into the melt so as to increase the efficiency of recovery.

Another object is to allow the use of concentrated magnesium alloys or even metallic magnesium by addition directly to the melt, for the purpose of making nodular irons.

Another object is to allow other highly oxidizable alloys to be used effectively in both ferrous and nonferrous melts.

Another object is to allow volatile alloys to be used effectively in ferrous and nonferrous melts.

Still another object is to decrease the degree of oxidation of the metal bath during the process of degassing or purifying of the melt.

Other objects of this invention will become readily apparent on reading the specification and drawings in which:

FIG. 1 is a diagrammatic view of the apparatus of the preferred embodiment of this invention in which 1 is a refractory-lined vessel for holding molten metal, the surface of which is indicated at 6. A cover 2 is held in position by clamps 3 fitted with an alloy hopper 9 having'a cover 11 and a controllable valve 10. A controllable outlet 7 is fitted with a valve control 8 and a cooling coil 20 surrounds the outlet. A porous refractory plug assembly 4 is supplied by a gas line 5. A pressure guage 12 for the purpose of ensuring a positive pressure in the chamber is attached to the core;

FIG. 2 is essentially the same arrangement as FIG. 1 showing a metal inlet 14 and a metal outlet 13, enabling metal to be introduced and exhausted from the apparatus continuously. A cooling gas supply 21 is provided in the cover for introducing a gas under pressure which upon expansion creates a cooling effect in the chamber above the molten metal;

F IG. 3 is another arrangement of a suitable apparatus for this invention, having the same features, but introducing the gas directly through the cover through the gas pipe and being fitted with a refractory rotatable paddle 22 driven from a motor 23 -through two gears 24; and

FIG. 4 is still another suitable apparatus for this invention comprising a refractory-lined vessel 1 with a porous plug 4, a gas inlet 5 and a cover 2 with a refractory bottom 25 projecting into and below the surface of the metal 6. An alloy hopper 9 is provided which has a cover 11, and a valve 10. A gas outlet 7 is located in the cover 2 and also has a controllable valve 8. In this embodiment the cover 2 may be carried by a hoist or other suitable means so it can be removed readily from the vessel 1.

The addition of certain alloys to molten metal for the purpose of deoxidation, as with phosphorus in bronzes; or nudularization, as with magnesium in nodular iron; or deoxidation, as with aluminum and calcium in steels, has always been a matter of extreme difficulty. Usually, alloys or elements which are strong deoxidants, by virtue of the fact that they combine readily with oxygen, also tend to burn directly in the air at the temperature of the metal to which they are being added; thus, their effectiveness in deoxidizing the melt is hampered by the fact that they burn at the surface, where the melt is exposed to air.

In the case of making nodular iron, for example, by adding magnesium to the melt an attempt has been made to overcome this problem of magnesium loss by various means; for example, it is common to use a diluted alloy of magnesium, such as nickel magnesium or magnesium ferrosilicon, in an effort to slow down the rate of magnesium oxidation and thereby obtain more recovery of magnesium in the melt. This has the disadvantage that the elements that may or may not be required were always added with the magnesium and larger alloy additions had to be made, whereas, in actual fact, only a relatively small amount of magnesium was actually required to be retained in the melt. For example, a recovery of magnesium of 10 percent or 20 percent is quite common in the normal procedures used for making nodular cast iron.

Other methods have been used, which consist of placing the magnesium alloy in the bottom of the ladle and covering it with steel chips or ferrosilicon, in such a way that the surface .of the alloy may be rapidly covered with molten metal and,

therefore, decrease the burning or oxidation in the air. In such a case the magnesium volatizes in the bottom of the bath and rises through the metal, where it burns quite violently at the point where the metal bath surface comes in contact with the oxygen in the air.

Another popular method is to inject metallic magnesium or magnesium alloy under the surface of the melt by using a suitable lance or tube. Here again, magnesium rises through the metal to the surface in the form of vapor and burns at the surface of the metal, where it contacts the oxygen in the air. Recovery by this method is usually on the order of 10 percent of the magnesium added.

Another method is to use magnesium alloys which are relatively dilute and place these into a refractory bell, which is then plunged under the surface of the metal. This method also allows magnesium vapor to rise through the metal bath but here again, this magnesium burns violently on contact with the air at the surface of the metal bath.

The usual method preferred by those skilled in the art in adding any oxidizable low-melting point and perhaps volatile alloy to the bath, is to somehow plunge it under the surface or cover it quickly with metal, so as to prevent undue loss of the alloy.

We have discovered a means of introducing alloys of this type into melts in such a way that oxidation is entirely eliminated or is reduced to the extent where the alloy addition is considerably more effective. We do this by special means and method, whereby we provide for agitation in the metal bath, exclusion of oxygen or air from the surface of the bath and a means for introducing the alloy into the melt through an atmosphere which is essentially inert or nonreactive with the materials being added.

in the preferred embodiment of our invention we introduce the inert gas through a porous plug or a lance, which allows the gasto enter the metal at the bottom of the bath and provides for agitation of the bath with the inert gas.

Ne contain the bath in a suitable vessel, which is fitted with a relatively airtight cover and a gas escape valve, with a controllable outlet.

This cover effectively encloses the area above the bath, which would normally be in contact with air. The gas bubbling through the bath, ejects air from the enclosure at the top of the bath and replaces it with an inert atmosphere, such as nitrogen, argon or with any other gas which may be used, such as natural gas, carbon monoxide, etc., which does not contain oxygen. Gases which provide special atmospheres. such as chlorine, fluorine, etc., may also be used. We find that a positive in the chamber of at least l-inch water gauge is usually sufficient to ensure removal of all air from the chamber. We prefer to work in the pressure range of a 1-24 inches of water but may go higher particularly where volatile alloys are involved. ln practicing our invention we start the gas flow setting up agitation and allow sufficient time for the atmosphere pocket above the metal to be exhausted and replaced by the inert gas we are using. We then add the alloy to the surface of the bath, through a hopper which we attach to the cover, above the bath, in such a way that the alloy never contacts any air. The alloy, thus added, falls to the surface of the metal and is incorporated in the melt, without any opportunity for it to contact air and, therefore, become oxidized.

If the alloy is excessively volatile, we supply cooling means at the controllable exhaust, so as to condense the alloy and allow it to fall back into the bath, much as would be the case with a reflux condenser. We have also found that the injection of a cooling gas under pressure such as CO or liquid nitrogen in the upper part of the chamber causes vapor to liquify and drop back into the molten metal.

While we prefer to use gas for agitation, we find that we are also able to provide agitation by mechanical means by oscillating or shaking the ladle with the airtight covers or by means of a rotating refractory paddle immersed into the bath.

Where we use such mechanical means, we replace the air in the compartment above the metal by injecting inert gas into this compartment and allowing it to escape through the escape vent.

By maintaining positive pressure in this compartment, either through direct injection of inert gas or by injecting inert gas through a lance or a porous plug, we are able to effectively exclude air from the compartment and thereby promote conditions necessary for efficient incorporation of the alloy or ele ment into the melt.

' While the subsurface injection of inert gas as a carrier into the melt or the use of inert gas for agitation through the porous plug are both methods known to those skilled in the art, it has never been realized that it is necessary to confine this inert gas to the surface of the metal, so as to effectively exclude air particularly for additives to be introduced through direct addition to the molten metal surface. Common usage of all these' methods has neglected the surface of the metal bath, which is invariably in contact with the air and, because of this, it has never been possible to obtain fully effective incorporation of oxidizable alloys into the bath.

In the practice of this invention we would refer to FIG. 1 of the drawings. A melt, to which the oxidizable alloy is to be added is placed in the refractory-lined vessel 1 and the cover 2 is clamped into position with'the clamps 3. The alloy to be added is placed in the hopper 9 with the valve 10 in the closed position and with the cover 11 in place.

Gas is introduced through the metal by means of the porous refractory plug 4 and by opening the control on the gas inlet 5. The metal surface 6 is brought to a suitable degree of agitation and valve control 8 is partially opened, so as to leave a positive pressure by gauge 12) in the chamber formed between the cover 2 and the ladle 1.

Gas is blown for a period of l to 2 minutes, to completely replace the air in the aforesaid chamber. At this time the valve 10 is opened and the additive alloy is allowed to fall on the surface of the metal 6, whereby it c becomes effectively incorporated into the melt. As soon as sufficient time has occurred for incorporation, which is usually from ten to 30 seconds, the gas flow through the gas inlet pipe 5 is stopped, the cover 2 is removed from the refractory-lined vessel and the metal is ready for casting. The cooling coil may be utilized if it is necessary to condense any vaporized additive.

In producing nodular iron by using this apparatus and this method, we have been able to obtain recoveries of magnesium as high as 90 percent of the magnesium added. Where this magnesium consists of a relatively dilute alloy; for example, in treating a bath, an addition of 1% percent of a 5 percent magnesium ferrosilicon alloy, giving a total magnesium added of 0.075 percent, resulted in a final treated bath having a magnesium content of 0.06 percent. This corresponds to an 80 percent recovery of magnesium.

During the treatment. no violent flare or burning of magnesium was observed and the gas used for agitation was nitrogen passed through the metal at a pressure of about 30 p.s.i., and at a flow rate of eight cubic feet per ton of metal treated.

In producing nodular iron with a more concentrated magnesium alloy as, for example, a nickel magnesium alloy containing 20 percent magnesium, it was possible to obtain a recovery of 70 of the magnesium added to'the metal. With pure magnesium lumps as the alloy we have obtained recoveries of 50 percent.

In using the apparatus of the invention for nonferrous metals, we have found it possible, for example, to get very close to percent recovery of additives, such as zinc.

ln treating cast iron, we have also found it possible to get very high recoveries with elements such as lithium and calcium. Calcium, we found to be particularly interesting, in that calcium is normally very difficult to add to the metal, because of its tendency to oxidize at the surface, forming refractory slag in the metal. In our invention, the formation of this oxidized slag was completely prevented and calcium was effectively absorbed into the metal.

As mentioned hereinabove, FIG. 2 differs slightly from FIG. 1 in that inlet and outlet passages are provided so as to provide continuous metal treatment and in this embodiment a source of cooling gas 21 is provided to condense any vaporized additive in the space under the cover 2, in addition to the gas supply 5. In FIG. 3 the inert gas atmosphere is provided by gas introduced through conduit 5 directly into the space under cover 2 and mechanical stirring is accomplished by stirrer 22 which extends into the molten metal and driven by motor 23 through gearing 24. The embodiment of FIG. 4 differs from the other showings in the construction of the cover 2. Instead of the clamps 3 the lower periphery of this cover is constructed of a refractory material 25 which can be lowered into the molten metal bath and the airtight seal is thus accomplished. It will be appreciated by those skilled in the art that portions of one embodiment of the invention can be readily incorporated into other of the embodiments.

Although this invention has been described in its preferred form with a certain degree of particularity, it is understood that the present disclosure of the preferred form has been made only by way of example and that numerous changes in the details of construction and the combination and arrangement of parts may be resorted to without departing from the spirit and the scope of the invention as hereinafter claimed.

lclaim:

1. An apparatus for introducing volatile or readily oxidizable additives into molten metal comprising a refractory-lined vessel adapted to hold molten metal, means for introducing additives into the molten metal without substantially breaking the gas pressure in the vessel, conduit means fitted in the refractory-lined vessel below the molten metal level, said conduit means comprising means for continuously introducing a nonreactive or inert gas into the vessel which gas bubbles up through the molten metal and serves to agitate the same, gas outlet means in said vessel which is always in the open condition in operation of said apparatus and is so adjustable as to create a small positive pressure of the gas above the surface of the molten metal with continuous flow of the gas.

2. Apparatus as claimed in claim 1 wherein said vessel is provided with a gastight cover.

3. Apparatus as claimed in claim 2 wherein said conduit means includes a porous refractory plug fitted in the vessel and through which the gas flows.

4. apparatus as claimed in claim 3, wherein inlet and outlet means are provided for continuous introduction and removal of metal from said vessel.

5. Apparatus as claimed in claim I, wherein the refractorylined vessel comprises an upper part, which projects into the molten metal bath, to provide a gastight seal.

Claims

2. Apparatus as claimed in Claim 1 wherein said vessel is provided with a gas tight cover.
3. Apparatus as claimed in Claim 2 wherein said conduit means includes a porous refractory plug fitted in the vessel and through which the gas flows.
4. Apparatus as claimed in Claim 3, wherein inlet and outlet means are provided for continuous introduction and removal of metal from said vessel.
5. Apparatus as claimed in Claim 1, wherein the refractory-lined vessel comprises an upper part, which projects into the molten metal bath, to provide a gastight seal.