US3215423A - Degassing system for metal alloy furnace - Google Patents

Description

Nov. 2, 1965 y K. c. TAYLOR 3,215,423

DEGASSING SYSTEM FOR METAL ALLOY FURNACE Filed Aug. 1, 1962 3 Sheets-Sheet 1 INVENTOR KE/VO/P/C/f C. TAYLOR ATTORNEY Nov. 2, 1965 K. c. TAYLOR DEGASSING SYSTEM FOR METAL ALLOY FURNACE 3 Sheets-Sheet 2 Filed Aug. 1, 1962 INVENTOR. Kf/VD/P/C/f C. TAYLOR @Zapz w ATTORNEY Nov. 2, 1965 K. c. TAYLOR 3,215,423

DEGASSING SYSTEM FOR METAL ALLOY FURNACE Filed Aug. 1, 1962 I 3 Sheets-Sheet 3 Q a, Q s 2 \l r E Q a 1' Q f a 2 c INVENTOR. KE/VDR/CA C. TAVL 0R ATTORNEY 3,215,423 DEGASSING SYSTEM FOR METAL ALLOY FURNACE Kendrick C. Taylor, Oreland, Pa., assignor, by mesne assignments, to Pennsalt Chemicals Corporation, Philadelphia, Pa., a corporation of Pennsylvania Filed Aug. 1, 1962, Ser. No. 214,031 12 Claims. (Cl. 266-34) In general, this invention relates to a new system for applying chamber degassing to a metal alloy furnace and, more particularly, to the application of vacuum degassing to electric furnaces.

In the past, vacuum degassing of a molten metal alloy bath was accomplished after the alloy had been produced in a furnace. Degassing equipment was placed over a ladle which had received the molten alloy from the furnace. This created problems as the molten alloy lost heat in the transfer between the furnace and the ladle. It has been suggested that the loss of heat be rectified by inductively heating the molten metal as it moves through a conduit between the ladle and the vacuum chamber. This system of reheating was found to unsatisfactory because it resulted in superheating the molten metal which changed its metallurgical properties, was very expensive, and was difficult to control.

Additionally, contamination often occurred in the metal alloy between the transfer from the furnace to the ladle and the degassing therein. The chamber in which the degassing is accomplished requires valuable floor space in the craneway in a mill which is extremely expensive. Furthermore, since the alloy additive was supplied to the molten metal charge before it was degassed, elements in the molten metal bath such as oxygen combine with the alloy addition to form undesirable compounds which change or damage the metallurgical properties of the resultant alloy metal.

[It is the general object of this invention to avoid and overcome the foregoing and other difiiculties of the prior art practices by the provision of a better and more simple vacuum degassing system for a metallurgical furnace.

'Another object is to provide a better method of manufacturing metal alloys in which oxides and other contaminates in the molten bath are reduced during vacuum degassing prior to the addition of the alloying material.

Another object of this invention is to provide a new and novel metallurgical furnace having an integral vacuum degassing unit attached thereto.

Another object of this invention is to provide a unitary heater and vacuum degassing chamber combination which may be utilized with a plurality of metallurgical furnace hearths.

Other objects will appear hereinafter.

For the purpose of illustrating the invention there is shown in the drawings forms which are presently preferred; it being understood, however, that this invention is not limited to the precise arrangements and instrumentalities shown.

FIGURE 1 is a cross sectional view of an electric arc furnace embodying the principles of the present invention. FIGURE 2 is a partial cross sectional view of the furnace of FIGURE 1 taken along lines 22.

FIGURE 3 is a partial cross sectional view of the degassing chamber shown in FIGURE 2 taken along lines 3-3.

FIGURE 4 is a top plan view of the electric arc furnace shown in FIGURE 1.

FIGURE 5 is a cross sectional view of a second embodiment of the present invention.

FIGURE 6 is a cross sectional view of an electric arc furnace with a portable vacuum degassing chamber in United States Patent as to receive the molten metal charge.

3,215,423 Patented Nov. 2, 1965 ICC accordance with another embodiment of the present invention.

in FIGURE 1, there is shown one embodiment of the present invention utilized in conjunction with an electric arc furnace. The electric arc furnace shown in FIG- URE 1 is generally designated by the numeral 10.-

The furnace 10 has a steel outer surface 12 surrounding a refractory hearth 14. The hearth 14 is shaped so The furnace 10 has a pivotal roof 16 through which extend electrodes 24, 26 and 27. The electrodes 24, 26 and 27 are adapted to be connected to a three-phase Y-A connected transformer. In larger sized electric arc furnaces, six such electrodes could be utilized.

' Metal is placed in the furnace through the open roof or the sliding door 18 and is poured from the hearth 14 through a spout 20 on the side opposite the door 18. The roof 16 is pivotally mounted about an axis '22 located on top of the furnace. If necessary, the roof 16 can be pivoted to a position as shown in phantom in FIG- URE 4. In this position, the roof 16 has been numbered 16', and metal can be added to the hearth.

The molten metal 28 is placed at the bottom of the furnace 10 in the hearth 14. A layer of slag 30 forms on top of the molten metal 28. The slag normally consists of combinations of acid, neutral and basic oxides, and other non-metallics.

{1" he metal 28 is heated by supplying current to the electrodes 24, 26 and 27. The electrodes extend into the molten metal 28. The electrical current will strike an are between the electrode and the molten metal 28. The slag 30 offers a higher resistance than the molten metal. The power input to the electrical arc furnace is controlled by the distance between the electrodes and the molten steel. The selected voltage is normally taken care of by automatic adjustment. The slag, by its presence, shields the molten metal from the atmosphere and conserves the heat thereof. There is a slight motor or stirring effect produced in the bath by the current, and this also helps in distributing the heat.

The vacuum degassing chamber 44 is provided to be utilized with the electric arc furnace 10. The vacuum degassing chamber 44 is connected from ports 38 and 40 below the level of molten metal in the hearth 14 through pipes 42 and "60 to ports 62 and 64 in the bottom of the degassing chamber 44. Heater means 43 which may be electric coils or a gas burner is provided on chamber 44.

A pump 48 is also in communication with conduit 42 through a pipe 46 located below the port 62. An alloy material hopper 50 is also in communication with the degassing chamber 44 through a port 58 in the wall of the degassing chamber 44. Supply valves '52 and 54 control the feed of alloy material from the hopper 50. Additionally, a vacuum port 66 in communication with the interior of the chamber 44 connects a vacuum pump 74 to the chamber 44 through a rigid pipe 68, expansible bellows 70, and rigid pipe 72.

The operation of the degassing chamber 44 is as follows: The chamber 44 is preheated by heater means 43 so that there is little difference between the temperature in the furnace and the temperature of the chamber. Vacuum pump 74 evacuates chamber 44 through conduits 68, 70 and 72. This causes molten metal to rise in conduits 42 and 60. Pump 48 is then turned on to supply a gas under pressure through conduit 46. This gas may be hydrogen, methane, carbon monoxide, other carbonaceous gases, hydrides, halogens or volatile halides, vapors of strongly reducing volatile and relatively insoluble metals or metalloids, such as sodium zinc and phosphorus, inert noble gases, or active gases. The particular gas used depends upon the effect desired upon the molten metal. For instance, if it is desired to de-oxidize the molten metal, a reducing gas such as carbon monoxide would be pumped through conduit 46. The gas in conduit 42 lowers the density of the resultant mixture in the conduit. This causes the molten metal in conduit 42 to rise to a higher level than the molten metal in conduit 60. Thus, the molten metal acts upon the well-known principle of the gas lift and ultimately overflows the top of conduit 42. This action is accentuated by the reduced pressure created by the pump 74.

The gases which have been introduced into the tube 46 bubble upwardly through the metal in the conduit 42 and in the course of this operation, they become intimately mixed with the liquid metal. The conduit 42 is preferably provided with internal turbulence causing projections which will insure active mixing and provide a more active flow of the metal.

The gases cause the liquid metal to spill over at the upper end of the riser conduit 42 from which the metal gravitates into the open end 64 of the return tube 60. The gases and all other gases which are separated from the metal are then carried away through the vacuum conduit 68, 70 and 72 by vacuum pump 74.

The metal which is delivered into the return conduit 60 passes downwardly into the molten charge 28 through port 38. The conduits 42 and 60 form barometric columns which are continuously maintained by the vacuum in the chamber 44.

After the molten metal has been completely treated with the gas from the pump 48, an inert gas such as argon is introduced in place of the active gas, if such was used. The inert gas does not react with the molten metal, but instead continues the metal flow through the degassing chamber. At this point, the alloying material which may be silicon, carbon or the like, is fed into the chamber 44 from the hopper 50. The alloy feeding is done through the use of a trap valve system including valves 52 and 54. Valve 52 is first opened with valve 54 closed to place a given amount of alloy material between the two valves. Then valve 52 is closed and valve 54 opened and the alloy material allowed to flow into the chamber 44. The vacuum system will aid in the flow of the alloy material into the chamber 44. Since the molten metal is flowing continuously in the bottom of the chamber 44, the alloy material will be given a large surface area to combine with the molten metal. Additionally, since the contaminating gases have been removed from the molten metal, there will be no undesirable chemical reaction between such gases and the alloy mate-rial before the metallurgical combination with the molten metal.

The alloying agents which might be utilized could be silicon, chromium, aluminum, manganese, titanium, vanadium, etc. These metals in their pure form can dissolve in the alloy solution without forming contaminating oxidation by-products. The turbulence of the flowing metal as it leaves port 62 increases the area of contact with the dissolving alloy materials. An inert gas may be utilized to protect the molten metal charge at the base of the hearth from contact with the air. This can be done by the introduction into the furnace of a blanket of gas which is inert to the metal being treated and which is relatively insoluble in the collected met-a1.

The furnace 10 has two arcuate gear members 32 on the base thereof on either side of the furnace 10. These arcuate gear members 32 mesh with similarly spaced gears 34 fixedly supported on the floor of the mill. A

motor (not shown) drives a connecting arm 36 rotatably secured to the base of the furnace 10. Movement of the arm 36 causes tilting of the furnace 10 in one of two directions. When it is necessary to pour the molten metal from the furnace 10,.the connecting arm 36 is moved to the right tilting the furnace and allowing the metal to flow out of spout 20. When the slag 30 need be removed, the furnace is tilted in the other direction and the door 18 opened so as to allow the slag to be removed.

A new charge of metal can be fed to the furnace through door 18 or by rotating roof 16 to the position indicated in FIGURE 5.

The degassing chamber 44 and hopper 50 are mounted directly on the furnace 10 and move with it. Vacuum pump 74, however, is mounted separately and therefore, it is necessary to have the flexible bellows 70 which connects the two pipes 68 and 72. Thus, when metal is poured, the bellows contracts and when slag is removed, the bellows expands without loss of vacuum.

, -In FIGURE 5, there is shown a second embodiment of the present invention. In this embodiment, the furnace has molten metal 82 and slag 84 in the bottom thereof. The furnace 80 is also rotatable about curved gears 86. The furnace 80 has a spout 88 and a gate 90.

A degassing chamber 92 is mounted directly on the roof 108 of the furnace 80. The roof 108 is removable from the furnace 80. A hopper 94 feeds the degassing chamber 92 through a port 96. The vacuum pump 98 is connected through a flexible conduit 100 to a port 102 in the degassing chamber 92.

Electrodes 104 and 106 are also mounted on the roof 108. Riser tube 112 is connected from a point below the level of the molten metal 82 to a port 116 in the chamber 92. A return tube is connected from a port 114 lower in level than the port 116 to the molten metal bath 82. A pump 118 supplies gas under pressure to riser tube 112.

The operation of the electric arc furnace and degassing unit shown in FIGURE 5 is in all ways similar to that shown in FIGURES 14. However, the unit in FIG- URE 5 has one distinct advantage. In this unit, the degassing chamber 92 and its auxiliaries may be lifted from the furnace 80 and placed on a different furnace while furnace 80 is cleaned and refilled. Therefore, chamber 92 and its associated apparatus may be utilized by more than one furnace and effect a considerable saving for the user.

In FIGURE 6, there is illustrated the furnace 10 and a portable vacuum degassing unit associated therewith for degassing the molten bath 28 therein. The unit 130 includes a vacuum chamber 132 having a preheater 134. A hopper 136, identical with hopper 50, is associated with the chamber 132. Conduits 138 and 140 extend from chamber 130 into the bath 28. The conduits 138 and 140 are parallel to each other and are connected to chamber 130 in the same manner as conduits 112 and 110, respectively, are connected to chamber 92. Hence, the bath 28 will flow up leg 138 through chamber 132, and down leg 140.

To facilitate introduction of the conduits 138 and 140 in the bath 28, the door 18 on furnace 10 has been moved to an open disposition. The chamber 132 is mounted on a carriage having wheels 142 and 144 which ride on an inclined track 146. Track 146 is parallel to conduits 138 and 140. If desired, an inclined rack and pinions may be substituted for the track 146 and wheels 142 and 144. The ends of track 146 are supported by standards 150 and 152 on platform 148.

A vacuum pump 154 is supported by platform 148. Pump 154 is in communication with port 158 in chamber 132 by flexible conduit 156. The chamber 138 is selectively reciprocated along track 146 by a cable 158. One end of cable 158 is secured to chamber 132. Cable 158 extends around pulley 160 and is wound on spool 162. Spool 162 is selectively wound or unwound by operating motor 164.

The above mentioned elements of the unit 130 are supported by a portable wheel mounted dolly 166. Platform 148 is adapted to be raised or lowered by hydraulic jacks 168 and 170 and pump 1'72. Dolly 166 is provided with suitable guides to limit movement of the platform 148 to vertical reciprocation.

Thus, it will be seen that the unit 130 is portable and may be moved from furnace to furnace. The jacks 168 and 170 enable the chamber 132 to be raised or lowered to accommodate the unit to different makes of furnaces. When chamber 132 is at the proper height and supported at the top of track 146, door 18 is opened. Thereafter, conduits 138 and 140 are introduced into the bath 28 by reciprocating chamber 130 toward furnace 10. Degassing of the bath 28 and addition of alloy metals are accomplished as set forth above. If desired, unit 130 may be suspended from an overhead track.

The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof and, accordingly, reference should be made to the appended claims, rather than to the foregoing specification as indicating the scope of the invention.

I claim:

1. A method of forming a metal alloy comprising the steps of heating metal in a furnace to form a molten metal bath, lifting metal from below the surface of the metal bath into a vacuum chamber, feeding alloy agents into the molten metal to form an alloy with the molten metal, returning the metal from the vacuum chamber to a point below the surface of the metal bath, and effecting said lifting and returning steps in a continuous metal flowing cycle, said lifting step including the step of forcing an active gas through the metal to act on the metal, and stopping the forcing of the active gas through the metal prior to the step of feeding the alloy agents into the metal and forcing an inert gas through the metal during the alloy feeding step.

2. The method of forming a metal alloy of claim 1 wherein the step of feeding alloy agents includes the step of measuring a desired amount of alloy agent in a closed receptacle connected to the vacuum chamber prior to opening the closed receptacle to the vacuum chamber to feed the alloy agents to the molten metal in the vacuum chamber.

3. A metal furnace comprising a hearth for receiving metal to be heated, heating means for heating metal in the hearth, a vacuum degassing chamber spaced from and higher than any metal in the hearth, vacuum degassing means for circulating metal from said hearth through said chamber and back to said hearth for degassing the metal, a roof mounted on said hearth, said chamber being mounted on said roof, said vacuum degassing means including a vacuum pump mounted exterior from said hearth and roof, and flexible conduit means connecting said vacuum pump to said chamber.

4. A metal furnace comprising a hearth for receiving metal to be heated, heating means for heating metal in the hearth, a vacuum degassing chamber spaced from and higher than any metal in the hearth, vacuum degassing means for circulating metal from said hearth through said chamber and back to said hearth for degassing the metal, a roof on said hearth, and means for mounting said heating means and said chamber on said roof.

5. A metal furnace comprising a hearth for receiving metal to be treated, heating means for heating the metal in the hearth, a vacuum degassing chamber spaced from and higher than any metal in the hearth, vacuum degassing means for continuously circulating metal from said hearth through said chamber and back into said hearth for degassing the metal, said last-named means including first and second conduits connected to said hearth below the surface of the metal in said hearth, said first and second conduits also being connected to said chamber, said first conduit having its chamber end higher than the chamber end of said second conduit, said vacuum degassing means including a vacuum pump connected to said chamber, and a gas supply means connected to said first conduit between said chamber and said hearth.

6. The metal furnace of claim 5 wherein said hearth is arcuately movable to receive and pour out molten metal, said chamber and said conduits being rigidly mounted on said hearth, and said vacuum pump being mounted separate from said hearth and flexibly connected to said chamber.

7. A metal furnace comprising a hearth for receiving metal to be heated, heating means for heating metal in the hearth, a vacuum degassing chamber spaced from and higher than any metal in the hearth, and vacuum degassing means for circulating metal from said hearth through said chamber and back to said hearth for degassing the metal, and means supporting said chamber for movement toward and away from said bath along a linear, inclined path.

8. A furnace in accordance with claim 7 including a pair of conduits communicating with said chamber, said conduits having their longitudinal axis substantially parallel to said inclined path and the ends of said conduits extending into said bath.

9. A portable degassing unit comprising a movably mounted support frame, a vacuum degassing chamber reciprocably supported by said frame for movement along a linear, inclined path, means for evacuating said chamber, inlet and outlet conduits communicating with said chamber, said inlet conduit communicating with said chamber at a point higher than the point at which said outlet conduit communicates with said chamber, and the longitudinal axes of said conduits being substantially parallel to said inclined path.

10. A unit in accordance with claim 9 including a preheater for said chamber for preheating said chamber prior to the introduction of molten metal into said chamber.

11. A unit in accordance with claim 9 including a hopper selectively communicating with said chamber and mounted for movement with said chamber.

12. A unit in accordance with claim 9 including elevating means for raising and lowering said chamber.

References Cited by the Examiner UNITED STATES PATENTS 2,054,922 9/36 Betterton et al. 26634 2,528,571 11/50 Babcock et al 26636 X 2,895,820 7/59 Harders 7S---48 2,959,478 11/60 Harders 49 3,042,510 7/ 62 Armbruster et a1. 7549 FOREIGN PATENTS 837,587 6/60 Great Britain.

JOHN F. CAMPBELL, Primary Examiner.

JAMES A. TAYMAN, JR., MORRIS WOLK, Examiners.

Claims (2)

1. A METHOD OF FORMING A METAL ALLOY COMPRISING THE STEPS OF HEATING METAL IN A FURNACE TO FORM A MOLTEN METAL BATH, LIFTING METAL FROM BELOW THE SURFACE OF THE METAL BATH INTO A BACUUM CHAMBER, FEEDING ALOY AGENTS INTO THE MOLTEN METAL TO FORM AN ALLOY WITH THE MOLTEN METAL, RETURNING THE METAL FROM THE VACUUM CHAMBER TO A POINT BELOW THE SURFACE OF THE METAL BATH, AND EFFECTING SAID LIFTING AND RETURNING STEPS IN A CONTINUOUS METAL FLOWING CYCLE, SAID LIFTING STEP INCLUDING THE STEP OF FORCING AN ACTIVE GAS THROUGH THE METAL TO ACT ON THE METAL, AND STOPPING THE FORCING OF THE ACTIVE GAS THROUGH THE METAL PRIOR TO THE STEP OF FEEDING THE ALLOY AGENTS INTO THE METAL AND FORCING AN INERT GAS THROUGH THE METAL DURING THE ALLOY FEEDING STEP.

3. A METAL FURNACE COMPRISING A HEARTH FOR RECEIVING METAL TO BE HEATED, HEATING MEANS FOR HEATING METAL IN THE HEARTH, A VACUUM DEGASSING CHAMBER SPACED FROM AND HIGHER THAN ANY METAL IN THE HEARTH, VACUUM DEGASSING MEANS FOR CIRCULATING METAL FROM SAID HEARTH THROUGH SAID CHAMBER AND BACK TO SAID HEARTH FOR DEGASSING THE METAL, A ROOF MOUNTED ON SAID HEARTH, SAID CHAMBER BEING MOUNTED ON SAID ROOF, SAID VACUUM DEGASSING MEANS INCLUDING A VACUUM PUMP MOUNTED EXTERIOR FROM SAID HEARTH AND ROOF, AND FLEXIBLE CONDUIT MEANS CONNECTING SAID VACUUM PUMP TO SAID CHAMBER.

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