US1931144A

US1931144A - Treatment of metals

Info

Publication number: US1931144A
Application number: US487776A
Authority: US
Inventors: Gilbert Harvey Nicholas
Original assignee: EI Du Pont de Nemours and Co
Current assignee: EIDP Inc
Priority date: 1930-10-10
Filing date: 1930-10-10
Publication date: 1933-10-17
Anticipated expiration: 1950-10-17

Description

1933- H. N. GILBERT TREATMENT OF METALS Filed Oct. 10 1930 2 Sheets-Sheet 1 FIG.1

F i VENTOR BY ATTORNEY Oct. 17, 1933. H. N. GILBERT 1,931,144

TREATMENT OF METALS Filed Oct. 10 1930 2 Sheets-Sheet 2 l 2 24" I j 4 4 ATTORNEY Patented Oct. 17, 1933 UNITED STATES" PATENT OFFICE slgnor, by mesne assignments, to E. I. du Pont de Nemours and Company, a corporation of Delaware Application October 10,

5 Claims.

This invention relates to the treatment of molten metals and more particularly to the introduction of a metal into the molten bath of another.

Certain light metals such as aluminum are commonly used to treat other molten metals, for instance, molten steel. The result of such treatment is the removal of objectionable elements, such as sulfur, oxygen, etc. It has been proposed to use certain reactive metals, for instance the alkali metals for this purpose. However, use of these metals has not been found practical because of the great difference between their boiling points and the temperature of the molten metal being treated. This difference in temperature causes sudden vaporization when the reactive metal is added to the metal being treated, which results in much of the reactive metal being thrown out of the treating vessel as vapor before it has an opportunity to react with the undesirable constituents of the metal being treated. Furthermore, this sudden vaporization often causes dangerous explosions.

In the preparation of alloys, the common practice is to add solid metal to the molten bath of another, or to mix the molten metals. Such processes have not been heretofore easily and economically carried out without exposure of the molten metals to the atmosphere, with resultant loss by oxidation. Such loss is especially significant when working with reactive metals, for instance, alkali metals. These procedures also involve danger to workmen, for instance by explosions caused by rapid oxidation of analkali metal or poisoning caused by the fumes from open pots of metals such as lead or mercury. Furthermore, oxidation of the metals usually result in a certain amount of oxide inclusion in the product.

One object of my invention is to provide a method and means for introducing a metal having a low boiling point into a bath of molten metal whereby danger of explosions and loss of the low-boiling metal are eliminated. Another object is to provide method and means of introducing a metal or alloy into a molten bath of other metal or alloy whereby loss of metal and other disadvantages caused by oxidation are eliminated.

Other objects will be hereinafter apparent.

These objects are accomplished according to my invention by introducing metal vapor into a body of molten metal.

Figures 1 and 2 show forms of apparatus suitable for practicing my invention. In Figure 1, 8

1930. Serial No. 487,778

is a cylindrical steel tank, mounted in a furnace 13, made of refractory material. A cover 4 is screwed on the tank 3 and is fitted with meal inlet tube 1, gas inlet tube 5 and vapor exit tube 6. Tube 1 is fitted with a closure cap 2 at the upper end. The tube 6 is covered at its extremity by a refractory coating 10. Tube 5 is connected by means of the T-joint 1'? to gas supply line 12. A safety release valve 9 is connected to line 12. One arm of the T-joint 17 is connected to the side of the metal inlet tube 1 by means of the tube 16. 7 and 8 are valves in tubes 5 and 16 respectively. 15 is a gas burner fitted with gas and

air inlet lines

21 and 22 and their

respective control valves

23 and 24. 14 is a rocker element of which there are two. 19 is a container for molten metal, having a refractory lining 11.

In Figure 2, like reference numbers refer to similar elements. Gas inlet tube 16 is connected to the tank 3 through the side wall outside the furnace 13. 20 is a union connection in gas inlet tube 5'. Tube 6' is connected to the tank 3' through the side wall of tank 3. 18 is a circular cover fastened to tank 3 by means of bolts 25 am. the flange 26.

One method of carrying out my invention may be described by reference to Figure 1. A quantity of low-boiling metal, for instance an alkali metal, is charged into the tank 3 through tube 1, which i. then closed with cap 2. The tank is heated by means of the burner 15 until the alkali metal reaches a temperature of about 30130 C. below its boiling point. The apparatus is then ready for use.

A crucible 19, containing molten metal to be treated, is placed beneath the end of the vapor exit tube 6. Valve 7 is then closed and valve 8 opened, thus forcing nitrogen through the system. The apparatus is then tilted on the rockers 1'. until the tube 6 dips to a sufficient distance below the surface of the molten metal bath. The steam of nitrogen flowing through the system prevents metal in the crucible from entering and solidifying in tube 6. Valve 7 is then opened and valve 8 is closed, thus forcing the nitrogen stream through the molten alkali metal in tank 3. Due to the high vapor pressure of the metal at the temperature employed, alkali metal vapors are swept out through tube 6 with the stream of nitrogen and into the metal in crucible 19. As the metal vapors are introduced into the molten metal being treated they are first substantially completely absorbed. In a short time, depending upon the amount of metal being treated and its composition, vapors of alkali metal appear at the surface of the metal bath, indicating that the treatment is nearing completion. Valve 8 is then opened and valve 7 closed thus causing almost pure nitrogen in place of metal vapor to flow through tube 6, and the apparatus is tilted back to remove tube 6 from the molten metal bath.

It the apparatus shown in Figure 2 is used the procedure is substantially identical with that given above, except for a diflerence in the manner of charging tank 3'. This is done by disconnecting gas inlet tube 5' at the union joint 20, and removing the bolts that secure cover 18 to Cover 18, with the section of tube 5' fitted to it, is then removed and alkali metal is charged into the tank 3'. Cover 18 is then replaced, and line 5 is reconnected by union joint 20. The subsequent procedure is the same as when using the apparatus shown in Figure 1.

Example Sixty pounds of molten cast iron was treated with sodium by the method above described, using the apparatus shown in Figure 2. Before passing nitrogen through the sodium the latter was heated to a temperature of about 750-800 C., and

this temperature was maintained during the treating operation. The sodium vapors, when first introduced into the molten cast iron were completely absorbed. After a period of two minutes, vapors were observed at the surface of the cast iron. At this moment a sample of the bath was taken. Analyses of the original iron and this sample showed the sulfur content to have been materially decreased.

' While I prefer to heat the low-boiling metal used as treating agent to a temperature of -130 C. below its boiling point, other temperatures above and below this range may be used without departing from the spirit and scope of my invention. At temperatures below this range, the amount of metal vapor produced by a given rate of flow of nitrogen to the apparatus will be correspondingly less. At temperatures close to the'boiling point of the metal relatively large amounts of vapor are produced by a given nitrogen flow. 11' the temperature is raised above the boiling point of the light metal the nitrogen flow may be greatly reduced or even dispensed with altogether. This method however, has the disadvantage that when treating batches of metal fumes of low-boiling metal vapor are introduced into the atmosphere while the end of tube 6 is being removed from one crucible into another.

One method of operating with a minimum nitrogen flow comprises starting the operation at a temperature below the boiling point, as described above. As soon as possible, after the tube 6 has been dipped into the molten metal bath, the temperature is raised above the boiling point of the light metal and the nitrogen flow either greatly reduced or shut off entirely.

My invention is applicable to the treatment of molten metals with any metal or alloy which possesses an appreciable vapor pressure at the temperature at which it is desired to operate.

The temperature of the molten metal into which the metal vapors are introduced may be either above or below the temperature of the vapors introduced. Thus, by my processysodium vapors at 600 C. may be introduced either into molten lead at 400 C. or molten steel at 1500 C.

Besides nitrogen, other gases which do not react to a material extent with the metals, for instance hydrogen, may be used.

My invention may be used to prepare alloys, where exclusion of air from one or both the metals alloyed is desirable. For instance, by adding sodium vapor to a body of molten lead to make sodium-lead alloy, the formation of sodium oxide is reduced, and the hazard of handling hot sodium in the open air is avoided. If it is also desired to protect the alloy from oxidation, the vessel holding the molten metal may be made part of a closed system, through which nitrogen or other inert gas is circulated to remove all oxygen before the metal is melted.

Other variations of and uses for my invention will be apparent to those skilled in handling metals.

The specific forms of apparatus shown in the drawings are given only by way of illustration and other forms are possible without departing from the spirit and scope of my invention. The essential elements in my apparatus are a container for molten metal with means of heating the same, a means for introducing gas below the surface of molten metal in said container, means for conducting vapor-from the container and means for introducing the vapor below the surface of a second body of molten metal.

I claim:

l. A process comprising passing a substantially inert gas through a body of molten metal to produce a mixture of said gas and vapor of said metal and passing said mixture into a body of other molten metal.

2. A process comprising passing a substantially inert gas through a body of molten alkali through a body of molten sodium maintained at 750-850" C. to produce a mixture of nitrogen and sodium vapor and passing said mixture into a body of other molten metal.

5. A process comprising passing nitrogen through a body oi. molten sodium maintained at ISO-850 C. to produce a mixture of nitrogen and sodium vapor and passing said mixture into a body of molten steel.

HARVEY NICHOLAS GILBERT.