US3236636A

US3236636A - Method of treating molten metal

Info

Publication number: US3236636A
Application number: US176493A
Authority: US
Inventors: Charles W Finkl
Original assignee: Finkl A and Sons Co
Current assignee: Finkl A and Sons Co
Priority date: 1962-02-26
Filing date: 1962-02-26
Publication date: 1966-02-22
Anticipated expiration: 1983-02-22

Description

Feb. 22, 1966 c. w. FINKL METHOD OF TREATING MOLTEN METAL 4 Sheets-Sheet 1 Filed Feb. 26, 1962 Feb. 22, 1966 c. w. FINKL 3,236,636

METHOD OF TREATING MOLTEN METAL Filed Feb. 26, 1962 4 Sheets-Sheet 5 Feb. 22, 1966 c. w. FINKL 3,236,636

METHOD 0F TREATING MOLTEN METAL Filed Feb. 26, 1962 4 Sheets-Sheet 4.

INVENTOR.

United States Patent O 3,236,636 METHOD F TREATING MOLTEN METAL Charles W. Finlrl, Chicago, Ill., assignor to A. Finkl & Sons Company, Chicago, Ill., a corporation of Illinois Filed Feb. 26, 1962, Ser. No. 176,493 Claims. (Cl. 75-49) This application is a continuation-in-part of applications Serial Numbers 777,664; 27,826, now Patent 3,071,- 458; 54,745, now abandoned; 340,594; 805,927, now Patent 3,083,422; and 855,442, now Patent 3,084,038.

This invention relates generally to methods and apparatus for degassing molten metal, more specifically it relates to method and apparatus for adding alloys to molten metal under vacuum, and particularly to a method and apparatus whereby the Iadmission `of the alloys to the molten metal can be made at will.

More and more steel is being vacuum degassed as steel consumers realize the many advantages such steel possesses. Among these Iadvantages are increased ductility by reason of a decrease in dissolved hydrogen, and fewer oxide inclusions resulting in a cleaner steel giving better tool life.

Degassing by subjecting the surface of a melt to a vacuum or by bubbling a purging gas upwardly through the melt under non-vacuum conditions has been known -for some time. Recently, however, a new method has been developed in which a purging gas is bubbled upwardly through a melt while the melt is exposed to a vacuum. Exceptionally good results have been attained by this new procedure. For a more complete description of the advantages and means whereby heats of molten metal may be purged under vacuum, reference is made to copending application Serial No. 777,664 assigned to the assignee of this application.

Adding alloys to melts before conventional vacuum degassing treatments has presented serious problems because of the inhibitory effect of some alloys on the degassing. This problem has even persisted to some extent in the simultaneous vacuum purging process. Aluminum for example is desired in many alloy steels becausev of its ability to control grain structure. It is, however, a highly deoxidizing alloy so that -degassing is markedly inhibited if it is added to the melt too soon in the vacuum degassing operation. This follows because the aluminum combines avidly with the oxygen in the melt to form alumina and this combined oxygen cannot, of course, be removed as readily as when it is simply dissolved in steel. Other alloys such as vanadium may be added as a substitute for aluminum to rene the grain, but the results are not substantially better than those obtained with the use of aluminum and most of the other substitute alloys, including vanadium, are substantially more costly than aluminum.

Another problem that has bothered alloy steel makers who utilize the vacuum degassing process is the inhibiting eifect that the presence of slag has on the degassing operation. It is highly desirable that the surface of the melt be covered with a layer of slag between the time the melt is transferred from the vacuum treating chamber to the teeming station, and during teeming. The slag acts as a blanket which substantially reduces temperature loss during this period, and of course the more fluid the steel, the better the casting and the lower the permissible teeming temperature.

Adding the slag to the melt at the start of the operation raises several difficulties. First and foremost the presence of the slag reduces the degassing effect 'because the slag itself has mass and must itself be degassed. In addition, it covers the surface of the melt so that the action of the vacuum on the surface is considerably reduced. Secondly, the slag attacks the ladle refractory and the stopper rod, and the longer the slag is in con- 3,236,636 Patented Feb. 22, 1966 tact with these refractories the greater will be the erosion of these parts. Thirdly, the slag itself liberates a considerable amount of gas which is evolved under vacuum. This excess gas may overload the ejectors at the commencement of operations with attendant disastrous effects. Fourthly, the presence of slag during the entire operation creates a substantial amount of dust which must be cleaned up eventually to insure proper functioning of the apparatus and to maintain a clean working area. Finally, the slag may create an explosion hazard.

Additions of lime or insulating covers to the melt at the end of the degassing operation reduces the rate of heat loss while teeming and transfering from the degaslsing station to the teeming station fbut its presence at this point may considerably reduce the overall effectiveness of the degassing operation. The slag or insulation may contain a substantial quantity of moisture which reacts upon contact with the melt to form hydrogen and oxides which diffuse into the melt. The effect of the just completed degassing operation is thereby partially nullied to the extent these gases are dissolved in the melt.

Another drawback with present vacuum alloy addition systems is the fact that none of them is automatic. To add alloys to a melt, the vacuum treatment must be interrupted while the alloy material is maneuvered into dumping position and the addition made. This results in an increase in the treatment time which results in an increased heat loss. An increased heat loss, of course, requires 4higher tapping temperatures which carries with it attendant disadvantages such as higher oxygen and greater attack on furnace refractories, Perhaps even more important is the fact that since the furnace time is lengthened, production is reduced.

Accordingly, the primary object of this invention is to provide a method of adding charge materials including alloys and slag forming materials to molten metal at a preselected time in a vacuum degassing cycle to thereby realize the full advantages of vacuum degassing to obtain a cleaner steel and a high recovery of alloys.

Another object is to provide a method of adding, by single or multiple additions, alloying materials and/or slag-forming materials sequentially or simultaneously to molten met-al at a preselected time or times in a vacuum `degassing cycle.

Another object is to provide a method of treating molten metal which reduces the included deleterious gas content of the molten metal to extremely low levels and substantially prevents reabsorption of deleterious gases prior to and during the pouring operation.

Another object is to provide a unique arrangement for protecting degassed molten metal between the cessation of a degassing operation and the completion of a pouring operation.

Yet another object is to provide a method of creating and maintaining a protective atmsophere in a plurality of ingot molds which eliminates delays, and therefore cooling of the degassed metal while filling the molds.

Yet another object is to provide a method of adding highly deoxidizing alloys such as silicon and aluminum to steel at a point in the vacuum degassing cycle of operations which will not inhibit degassing.

Yet another object is to provide a method of automatically adding slag forming material, such as burnt lime, toward the end of the vacuum degassing cycle to thereby reduce the overloading of the gas ejection system when slag is initially present and to provide an insulating blanket which considerably reduces the heat loss subsequent to the degassing operation and during teeming.

Yet another object is to provide a method of adding alloys to heats of molten metal which is completely contained so that treatment time is not increased and heat loss over the whole cycle is kept at a minimum.

Another advantage is to provide a method of adding alloys to heats of molten metal in which the time of addition of the alloys to the heat can be controlled to the second.

Yet another object is to provide structure suitable for accomplishing the above-described process and advantages.

Other objects and advantages will become apparent upon reading the following description.

The invention is illustrated more or less diagrammatically in the accompanying drawings, wherein:

FIGURE l is a sectional view, partly diagrammatic, with parts omitted for clarity of a combination vacuum and purging degassing apparatus illustrating the novel alloy addition system of the invention;

FIGURE 2 is a detailed view to an enlarged scale of the alloy addition container illustrated in FIGURE l;

FIGURE 3 is a sectional view similar to FIGURE 2 of a modification of the invention;

FIGURE 4 is a reproduction of a variable scale pressure-time chart showing the time of addition of slag and alloy to the melt;

FIGURE 5 is a sectional view partly diagrammatic with parts submitted for clarity as a combination of a variant embodiment of the invention;

FIGURE 6 is a sectional view to an enlarged scale of certain parts of FIGURE 5;

FIGURE 7 is a schematic flow diagram showing the complete treatment of a melt of molten metal including the provision of a protective covering on the melt and other protective measures after degassing;

FIGURE 8 is a perspective view of the unique mold sealing arrangement; and- FIGURE 9 is a sectional view taken substantially along the line 8 8 with the flap door or closure member in its sealed` position.

Like reference numerals will be used to refer to like parts throughout the following description of the invention.

A combination vacuum and gas purging degassing setup is illustrated in FIGURE 1. The apparatus consists essentially of a vacuum chamber or tank indicated generally at 10 resting on any suitable support, such as the I-beams 11, which in turn rest on bearing pads 12 secured to a suitable foundation 13. The chamber is shown in this instance as composed of an upper vertically and horizontally movable section 14 and a lower stationary portion 15. The lower, permanent portion 15 consists of a circular wall section 16 secured about its lower periphery to a base plate 17 which in turn rests upon the supporting beams 11. The upper periphery of the tank wall terminates in a bearing ring 18 whose upper surface is recessed to receive a suitable Oring seal 19. An annular layer of refractory 20 overlies base plate 17 to protect it from excessive heat and spillage.

The upper or movable half of the vacuum chamber is a composite structure including a wall portion 21 formed roughly as a 10p-sided frustum of a cone. The lower edge of cone 21 terminates in a bearing ring 22 which mates with and overlies the bearing ring 18 so that when the two rings are in engagement, the O-ring 19 forms an air-tight seal between the upper and lower sections of the chamber. The upper edge of cone 21 terminates in another bearing ring 23. A downwardly dished cover plate 24 is welded at its upper edge to the lower inner edge of the upper bearing ring 23 to complete the vacuum chamber.

The downwardly dished cover includes a projection 25 which provides clearance for a stopper rod 52 and an aperture ring 26 which will be described in detail hereinafter.

A charge container is indicated generally at 27. The container forms an air-tight seal with the aperture ring 26 and will be described in detail hereinafter.

The upper portion of the chamber is lifted by a lift and swing device indicated generally at 30. This device consists essentially of a hydraulically actuated piston and cylinder assembly 31 secured to the crossbeams 11 by an anchoring structure indicated generally at 32. A vertically reciprocable piston 33 travels between its lower retracted position, shown in FIGURE l, to an upper operative position in which it abuts seat 34 of a collar member 35. Collar member 35 in turn is connected to the cone wall section 21 and bearing ring 23 by a suitable arm 36. The piston and cylinder assembly 31 is maintained vertically aligned by a yoke structure 37 secured to the exterior of the lower wall 16 by suitable bolts, not numbered. Any suitable mechanism may be utilized to swing the upper portion 14 `horizontally once it has been elevated by piston and cylinder assembly 30.

A ladle for treating molten metal is indicated generally at 40. The ladle consists essentially of an outer metallic shell 41 and an inner layer of refractory material 42. An extra reinforcing plate 39 is positioned across the bottom of the ladle. A plurality of feet 43, 44, are secured to the ladle bottom so that it may be rested upon any suitable supporting surface when not positioned within the vacuum chamber.

The ladle rests on a support ring 45 extending upwardly from the base plate 17. The ring terminates in a ladle bearing ring 46. An annular bearing ring 47 is welded or otherwise suitably secured to the shell 41 of the ladle. A layer of refractory 48 protects the base plate 17 within the ladle support ring 45 from excessive heat and spillage. The interior of the vacuum chamber is connected to a source of vacuum through an outlet 50 surrounded by a suitable hood structure 51.

Apparatus for bubbling a purging gas upwardly through the melt is indicated generally at 52. The purging apparatus consists essentially of a source of purging gas 53 under a pressure greater than the static head of the metal in the ladle and is connected by a gas line 54 to the upper end of a combination purging and stopper rod 55. The rod is so constructed that gas passes downwardly through a longitudinal passage, and is then directed radially outwardly into the melt. For further details of the structure of the purging-stopper rod, reference is made to co-pending application Serial Number 805,927, now Patent Number 3,083,422, assigned to the assignee of this application. The combination purging-stopper rod seats in a suitable nozzle assembly 56, described in detail in copending application 855,442, now Patent Number 3,084,038 also assigned to the assignee of this application. Any suitable actuating mechanism 57 may be utilized to raise and lower the rod from the illustrated seated position.

The charge container 27 is illustrated in detail in FIG- URE 2.

In this embodiment, the time of addition of the charge materials to the melt can be controlled to the second.

Charge container 27 consists essentially of an upper expanded section 60 and a lower composite section 61. A positioning flange 62 welded to the upwardly outwardly inverted conic section 63 rests upon bearing flange 64. The lower section 61 consists of a shell 65 to which a continuous circular L channel 66 is welded about its inner periphery at its bottom. The channel supports a layer of refractory 67 which protects the shell 65 from melt radiation internally after the plate is dropped. The upwardly inwardly inclined conic section 69 terminates in a neck 7d which receives the closure mmeber of

composite cover

71, 72. The cover or plug forms an airtight seal with the upper flange 73 which is welded to neck 70. The overhang of plate 71 rests upon and makes the airtight seal with O-ring 74 in aperture 75 in the top surface of cover flange 73.

A circular steel plate 76 is held in snug engagement against the bottom of circular channel 66 by a rod 77. The rod is secured to plate 76 at its lower end by a nut and washer 78 threadably received on the lower end of the rod. The outer end of a short shaft 79 is received in an eyelet 80 formed at the upper end of rod 77.

Shaft 79 is rotatably received in bearing journal block 81 which is welded to the upwardly inwardly conic section 69 of the container. A pin 82 projects downwardly a slight distance into a helix 83 milled in the shaft. O-ring 84 between the shaft and its bore completes the air-tight seal. The outer end of the shaft 79 terminates in an eyelet 85 to which a suitable handle 66 is connected. Helix 83 is so located that clockwise rotation of shaft 79 will cause this shaft to move to the right as viewed in FIGURE 2.

The steel bottom plate 76 supports a quantity of charge material indicated generally at 87.

A variant form of charge container having a heat destructible bottom is indicated generally at in FIGURE 3. In this ligure, the container consists of .an outer tubular shell 91 to which is welded a positioning flange 92. The flange rests upon a bearing flange 93 welded to the internal surface of collar 26 which in turn is welded to the dished cover 24. An air-tight seal is formed between the positioning flange 92 and bearing ange 93 by an O-ring 94 received in a recess in the upper surface of the bearing flange.

A cover flange 95 whose upper bearing surface is recessed as at 96 to receive another O-ring seal 97 is welded to the outside of the tubular shell 91 at its upper end.

The interior of shell 91 is protected from the heat in the Vacuum chamber by a layer of refractory 98 held in place by a plurality of studs 99 welded at appropriate intervals about the internal surface of the shell. An annular ring 100 is welded to the bottom of shell 91, and an annular layer of refractory 101 supported by downwardly projecting studs 102 protects the ring from the heat of the melt. The radial depth of ring 100 is somewhat greater than the thickness of composite wall 91, 98 so that an annular shoulder 103 is formed about the bottom of the container. A closure member, which in this instance is illustrated as a plug, 71, 72, similar to the plug of FIGURE 2, forms an air-tight seal with the upper flange 95.

A heat destructible or disintegratable bottom for the container is indicated at 104. It rests upon the shoulder 103 to form a support for a quantity of charge material. Its thickness will depend upon the length of time it is desired to hold olf addition of the alloys and/ or slag forming material to the melt.

In the variant form of FIGURE 5, a double addition charge container 114 is illustrated. The container consists essentially of a lower portion 116 and an upper portion 115.

Lower portion 116 includes a lower section 117, an expanded midsection 118, and an upper section or neck 119. A positioning flange 120 is welded to the lower section 117 of the container. Flange 120 rests on a bearing ange 121 which in turn is welded to a collar 122 which in turn is welded to a dome 123 of a vacuum degassing tank. The various welds are -airtight and an O-ring seal 124 provides an airtight seal between the abutting anges 120, 121. A refractory lined heat shield is indicated at 125 and a reinforcing plate at 126. The refractory heat radiation shield 125 is apertured as at 127 to receive lower section 117 of the charge container.

Charge material is indicated at 128. As in the FIG URE 2 embodiment, the bottom of the container is formed by a plate 129 which is bolted to a rod 130i, the rod in turn being suspended from a supporting structure indicated generally at 131, the details of which will be described later.

The upper portion 115 of the vdouble charge container consists essentially of a substantially uniform diameter cylinder 133 welded at its lower end to a bottom plate 134. Bottom plate 134 rests upon a bearing flange 135 which in turn is welded to the periphery of neck 119. An O-ring seal 136 provides an airtight joint between the abutting surfaces. The upper end of cylinder 133 is closed by a top plate 137 to which is welded a lifting eye 138. A pipe coupling with a pipe plug therein is welded to one 6 wall of the cylinder 133 near its upper end, ras indicated at 139, and a charge dropping mechanism at 140.

Since the charge dropping mechanisms 140- and 131 are substantially identical, a description of one will suffice for both.

Charge dropping mechanism 140 consists essentially of a cylinder 141, a shaft 145, and a sheave shaft 150. Cylinder 141 has a bore 142 therein, the inner end of which is slightly tiared as at 143. The outer end of the cylinder is angled upwardly as at 144.

The shaft 145 reciprocates in bore 142. The shaft consists essentially of an elongated shank portion 146 of uniform diameter which terminates at its inner end at an outwardly flared section 147 and at its outer end in a reduced threaded portion 148. A plurality of grooves 149 are formed along the shank section 146 to receive sealing rings whereby the vacuum within the vacuum chamber may be preserved.

The threaded portion 148 of shaft 146 is received in sheave shaft 150. The inner end 151 of sheave shaft is formed at a angle complementary to the angle at the outer end 144 of cylinder 141. A chain sheave 152, FIGURE 5, is secured by a conventional key, or other suitable securing means, to the sheave shaft. An operating chain is indicated at 153.

A stop 155 is welded to and overhangs the inner end of cylinder 141. The stop consists essentially of a roughly hemispherical plate 156 welded to a bent plate 157 which in turn is welded to the periphery of cylinder 141.

A solid chunk of alloying material is indicated at 158. In this instance a 35 pound aluminum cone has been shown. The aluminum cone rests upon a steel weight 159. A long rod 160 extends through aligned apertures in the steel weight and aluminum cone. The weight and cone are supported by expanded head 161. The upper end of rod 160 terminates in eyelet 162 of a size large enough to receive the flared portion 147 of shaft 146. The parts are so dimensioned that when shaft 146 is in the illustrated position of FIGURE 5, that is with the left end of sheave shaft 150 abutting the right end 144 of cylinder 141, clearance between the extreme left end of shaft 146 and plate 156 is less than the thickness of rod 160.

A gusset plate is indicated at 163.

The charge dropping mechanism 131 is substantially identical to mechanism 140 and accordingly will not be discussed in detail. Substantially the only change is the elongation of those portions corresponding to cylinder 141 and shaft 146 of mechanism 140 to provide the required additional overhang.

In FIGURES 7, 8 and 9 complete treatment system is illustrated including means for protecting the degassed molten metal between the time it leaves the vacuum chamber and the completion of pouring.

A conventional electric furnace is indicated generally at 165. A large quantity, for example on the order of 75,000 pounds, of molten steel 166, such as a nickel alloy or carbon steel, is being tapped into ladle 40 at a tapping temperature of about 3,050 degrees F.

After tapping, the ladle of molten metal is transferred to the degassing station which includes the vacuum tank 10, alloy addition chamber 27, and ejector system 167 which is connected to the vacuum tank 10 by outlet 50.

After degassing, including the addition of slag forming materials, if such an addition is made, the ladle of degassed molten metal is transferred to the teeming station. A protective covering which provides, in essence, an insulating blanket or covering, is indicated at 168. This slag blanket minimizes heat losses and reabsorption of deleterious gases from the atmosphere by the molten metal during the ingot pouring operation. In FIGURE 7, the melt is being teemed into the first ingot mold 169 of a series 169, 170, etc. Each ingot mold includes a lower section 171 and a hot top which may, as

shown, consist of two

collars

172, 173. The annular gap between the mold and the lower hot top 172 is packed with asbestos rope and covered with a mastic, as indicated at 174. Each mold is closed by a unique sealing arrangement indicated generally at 175. A stream protector or collar 176 is attached to the bottom of the ladle about the discharge opening. As best seen in FIGURE 7, the collar extends downwardly below the bottom of the ladle a distance sufficient to enable the collar to be placed very close to the top of the seal 175, for example on the order of about l inch. It will be noted that the length of collar 176 is slightly greater than the feet 177 which are welded to the bott-om of the ladle. A protective atmosphere admission pipe is indicated at 178, and the teeming stream at 179.

In FIGURES 8 and 9, the unique mold sealing arrangement 175 is illustrated in detail. It consists essentially of a cover member 180 which may for example be a sheet of aluminum foil. A flap door or closure member 181 is cut in the center of the cover member 181) for a purpose which will appear hereinafter. The flap door is sealed about its periphery to the cover member with tape 182. A hold down member is indicated at 183. The hold down member in this instance is a steel plate having an opening 184 therein aligned with the flap door 181. The edges of the aluminum foil have been bent upwardly around the edges of the steel plate 183. A suitable sealing material, such as a sealing mud, is indicated at 185 to seal the joint between the top of the hot top section 173 and the sealing arrangement 175. Open bottom molds resting on stools are sealed by water glass, fiber board, or asbestos paper.

Alternately, a protective atmosphere may be generated from fluorinated organic compounds, or more specifically, polymerized fluorinated organic compounds, such as the well known products Teflon and Skamex. In this event such a compound or compounds in the form of a suspension such as flakes, chips, turnings, shavings or other form is placed in the bottom of the ingot molds. Actual experience has indicated that a protective atmosphere will be generated if approximately 2 to 8 oz. of material are used per ton. The heat of the molten metal causes the compounds to disassociate, thus generating the required atmosphere. This procedure has the advantage of simplicity, and eliminates the sealing procedure described above.

The use and operation of the invention is as follows:

Molten metal 110 in ladle 40 is subjected to vacuum through vacuum connection 50. Upwardly traveling bubbles of purging gas 111 from the pressurized source 53 set up an internal circulation within the melt which brings virgin metal from the lower portions of the melt to the surface where the occluded deleterious gases such as hydrogen, nitrogen, and oxygen may be removed by the vacuum. The bubbles themselves provide a vehicle for removing the included deleterious gases in that these gases migrate into the bubles during their upward passage.

To add materials to the melt at a preselected time during the degassing cycle, the container of FIGURES 2 or 3 is loaded with alloying materials, or slag forming material, or both, and placed in the

aperture ring

26 or 122 as illustrated in FIGURES 1 and 5.

When using the structure of FIGURE 2, container 60 is loaded with the desired charge before the ladle is positioned within the tank in the usual manner. When the operator wishes to add the alloys to the melt, he rotates handle 86 clockwise which moves shaft 79 to the right due to the action of pin 82 riding in helix 83. As soon as the inner, or left end, of shaft 79 is retracted to `a position within the journal block 81, steel plate 76, rod 77 and the charge materials in the container drop into the melt.

This structure has the great advantage of permitting the operator to add the charge materials at any desired instant. In addition, good mixing of alloyed materials,

even those lighter in weight than steel, is insured because the steel plate and rod will poke a hole in slag that may be present so that the light-weight additions will contact the molten material and not float on top of the slag. There is no possibilty that any portion of the alloyed materials will remain in the container because the entire bottom falls away.

The steel plate 76 and rod 77 should, of course, be composed of a material compatible with the composition of the melt. In general, a low-carbon steel is quite satisfactory.

When using the structure of FIGURE 3, the thickness of heat destructible bottom plate 104 is so correlated to the heat of the melt and the time it is exposed to the heat that it will give way at a predetermined time in the cycle to permit the alloying constituents to pass gravitally downwardly into the melt.

Several materials may be used for this plate. One of the best is plywood, although pine might also be utilized. If the metal is tapped at a given temperature, and that temperature is determined before hand, it is possible to select plywood of a thickness which will burn through within l5 second-s of the desired time. Aluminum could also be utilized. Usually aluminum is one of those alloys which should be added late in the degassing operation because it is rather highly de-oxidizing, but it can be utilized for the bottom plate because it retains its structural shape for several minutes and then gives way suddenly.

With the embodiment of FIGURES 5 and 6, sequential charge and/or alloy additions may be made without vacuum lock arrangements and without inhibiting degassing.

To drop the charge material in lower container 116, chain sheave 152 is rotated in the appropriate direction. As the sheave rotates, shaft 146 will be withdrawn to the right due to the camming action between

faces

144 and 151 of the cylinder and sheave shaft respectively. Movement of shaft 146 to the right draws the outwardly flared section 147 from eyelet 162, and plate 129, rod 130, and the charge materials 128 drop into the melt as in the embodiments of FIGURES 2 or 3.

After the charge materials in lower container 116 have been degassed, or at any predetermined time, upper chain sheave 152 is rotated either way and again shaft 146 is withdrawn to the right dropping the aluminum cone 158, steel weight 159 and rod 160 into the melt. Since the plate and aluminum cone are elevated a substantial distance above the surface of the melt, the charge will penetrate the slag formed from the first hopper addition and drop downardly a substantial distance into the molten metal therebelow. The aluminum cone will melt rapidly and be dissipated throughout the melt. Some of all of the aluminum combines with the oxygen and oats to the surface as oxides but some may additionally remain in the melt as a residual element, the proportions depending of course upon the quantity added. The weight 159 should of course be of a material compatible with the melt so as to avoid the addition of `unwanted alloying elements.

To prepare a subsequent charge, upper sheave 152 is rotated to withdraw shaft 146. An aluminum cone or other solid alloying element suspended on rod 160 with or without a weight at the bottom is then placed substantially in the position of FIGURE 5 and the sheave rotated to move shaft 146 to the left and through the eyelet 162. Once the aluminum or addition cone is in this position there is little danger of the cone accidentially being dropped since the clearance between plate 156 at the left end of the shaft 146 is less than the diameter of rod 160 and, because of the camming surfaces on cylinder 141 and sheave shaft 151, those parts tend to remain in the position of FIGURE 5.

The upper container is then placed upon lower container 116 which has already been placed on bearing 9 flange 121 as described in connection with the FIGURES 2 and 3 embodiments. Since plate 129 does not form an airtight seal with the bottom of lower section 117, a vacuum will be drawn in both upper and

lower charge containers

115 and 116 simultaneously with drawing a vacuum in the main section of the tank.

A complete treatment cycle is illustrated in the system shown in FIGURES 7, 8 and 9. The molten metal is tapped from yfurnace 165 into ladle 40 and then de` gassed in chamber 10. Towards the conclusion of the degassing operation, or at lea-st after the bulk of the included deleterious gases have been removed, a slag :forming and/ or alloy additions are made from

hopper

27 or 116. When slag forming additions are made, a protective covering 168 is provided which, preferably, is itself degased before the ladle leaves the vacuum chamber 10. If for any reason, such as malfunction of the charge dropping mechanism, or by design, a slag forming addition is not made, the advantages derived from protecting the pouring stream (as described below) are still obtained. As described in my co-pending applications, it is desirable to bring the vacuum tank up to atmospheric pressure by flooding it with an inert gas after degassing.

During the just described portion of the cycle, the ingot molds have been iilled and sealed with a protective atmosphere therein. In preparation for argon teeming, the ingot molds receive their regular cleaning and inspection but are then sealed. As illustrated in FIGURE 7, the annular gap between the mold and hot top is packed with an asbestos rope and covered with a mastic. Preferably, the molds are filled with argon gas in the teeming order, and the last mold is filled just before the first ingot is poured. The air is displaced from each mold by argon which flows in from a conventional argon diffuser lowered to the mold bottom. With a flow rate of 3,000 cubic feet per hour of argon, a 23 inch ingot mold for an 8,000 pound ingot may be filled in 30 seconds. When the filling is properly done, experience has shown that residual oxygen at the top of the ingot mold is always below .5%. Experience has also shown that the atmosphere in a well sealedmold will contain less than 1% oxygen until the ingot is poured.

To prepare the mold, the annular setal 174 in between the bottom of the hot top and the top of the ingot mold is put in place and the sealing arrangement shown in FIG- URE 8 is likewise putin place. Flap door 181 is opened, and after the argon has been diffused into the mold, and the argon diffuser removed therefrom, the flap door is closed and sealed by tape 182.

Just before commencing the teeming operation, the stream protector or collar 176 is attached to the bottom of the ladle and argon gas admitted thereto through pipe 178. Immediately after the lling of the last ingot mold with a protective atmosphere, the first ingot 169 is teemed. The impact of the downwardly lowing molten steel will of course immediately rupture the aluminum foil 181.

About ten seconds before teeming, argon is passed into the stream protector 176 at a rate of approximately 800 cubic feet per hour. Experience has shown that about 2O cubic feet of argon is consumed per ingot ton, with a teeming rate of approximately 11/3 tons per minute. Since the bottom of the collar 176 is only approximately 1 inch above the top of the aluminum foil 181, reabsorption of gases by the tight pouring stream 179 during teeming is substantially eliminated.

A comparison of average gas contents between argon and air-teemed steel shows a reduction in the hydrogen, oxygen, andnitrogen contents in the argon-teemed steel as compared to the air-teemed steel. The results definitely show a gas pickup during air-teeming which would be of concern in critical applications.

A typical treating cycle is indicated in FIGURE 4 which illustrates a variable scale pressure-time chart. In this 1nstance, the chart has been calibrated in height of mercury in a radially outwardly direction from a base line 112, and time in minutes is shown as roughly pie shaped truncated sectors extending circumferentially about the base line.

Referring to the graph, it can be seen that the pressure in the vacuum chamber at the start of the operation was approximately 760 millimeters of mercury, or standard atmospheric pressure. The starting point is indicated at point A. After the vacuum system Was turned on, the pressure within the chamber decreased gradually at first and then rather sharply down to point B which was in the neighborhood of millimeters of mercury. From A to B, the chart was calibrated to read pressure over a range of zero to 1,000 millimeters of mercury.

At point B the scale of the chart was expanded ten times so that the chart covers the range of from zero to 100 millimeters of mercury. The stylus or chart indicator jumped immediately to point C. Actually point B and point C represent equal absolute pressure values. The vacuum was then pumped down to point D which was on the order of 10 millimeters of mercury, and then it was again expanded ten times so that the range of the chart now covered a range of zero to 10 millimeters of mercury. The stylus jumped to point E which represents a value of approximately 8.5 millimeters of mercury and pump-down continued until the pressure within the chamber reached a value of approximately one-half millimeter of mercury at point F. By this time, the treatment had been in operation for approximately 6% minutes. At this time, the chart was again expanded ten times so that it covered a range of from zero to 1,000 microns of mercury. The indicating pen then jumped to point G which represents a value of approximately 530 microns of mercury. The pressure in the chamber then gradually decreased to approximately 360 microns, indicated at point H, at which time bottom plate 76 and a charge of burnt lime and aluminum dropped into the melt. In this particular heat of 33 tons of low alloy steel, a charge of approximately 200 pounds of burnt lime and 20 pounds of aluminum was admitted to the melt. As soon as the burnt lime came into direct contact with the melt, the heat caused a considerable quantity of gas to be evolved, and the pressure in the chamber immediately jumped to point I which represented a value of about 700 microns. The gas contained within the burnt lime was then gradually removed from the chamber until the treatment was discontinued at point K, 12 minutes after it started. By the time the charge Was added to the melt, the melt had been substantially completely degassed so that substantially all of the gas evolved from the charge was subsequently removed from the system. When the upper removable portion 14 of the vacuum chamber was swung away, the heat was ready for pouring and contained an insulating blanket of slag which substantially reduced the heat loss between the time the cover was removed and the ingots teemed.

Although the alloy addition method and apparatus has been described in conjunction with a degassing process utilizing both vacuum and purging gas, it should be understood that the invention is equally utilizable in a vacuum degassing process which does not utilize a purging gas. It should also be noted that it is highly desirable that the charge container be so positioned that its upper end forms a portion of the vacuum chamber. The advantages of the invention are just as readily obtained, however, if the container is located entirely within the chamber. The illustrated embodiments takes advantage of existing equipment. Likewise, although the charge container has been shown as positioned substantially directly above the ladle, it should be understood that in some instances it may be advantageous to position the container to one side of the ladle, as when necessitated by equipment design. It is really only essential in the FIGURE 3 embodiment that the bottom of the container be exposed to the heat of the ladle so that its disintegration will be related to the time it is exposed to the heat.

It is therefore apparent that the invention provides means for adding highly deoxidizing alloys such as laluminum or silicon to a melt at a time subsequent to which degassing operations would be inhibited by the deox'idizing effect of the alloys. The advantages of making additions under vacuum, particularly the production of cleaner steel and a higher recovery of additions are obtained and -of course the advantages of any particular alloy such as aluminum are realized. As discussed heretofore, vanadium could be substituted for aluminum, for example, but the cost of each heat lwould increase considerably. With this system aluminum, with its grain refining properties, may be added at any given point in the cycle.

This system also provides means for ensuring good mixing of the alloys throughout the melt. Since the time of admission of the charge can lbe controlled to the second if desired, ample time may be allowed for purging or carbon Imonoxide boil subsequent to addition, which ensures uniformity.

The system described above makes possible the addition of slag forming materials during the degassing o-peration Which reduces the possibility of inhibiting degassing -by presence of these materials at the start of the operation. Likewise, the corrosive effect of the slag on the refractory parts and the possibility of overlooking the ejectors early in the cycle are overcome. Finally, the explosion hazard resulting from early introduction of the slag is eliminated and the dust is completely controlled.

Other alloys, such as silicon, vanadium, and exothermlc chrome may be added at a later point in the cycle which is an advantage in that a cleaner steel is produced and a better alloy recovery is obtained.

This invention enables steel to be tapped from the furnace at temperatures lower than those required when charge materials are to be added after degassing. A-s a result, furnace life is prolonged. Since the alloy addition is automatic, the treatment time is not lengthened beyond the time necessary to pump out the gas evolved from the added constituents, so that production time is substantially the same a-s for vacuum degassed heats to which no alloy additions are made.

Variations will at once occur to those skilled in the art and those variations are within the broad outline of the invention. For example, it may 'be desirable to make the alloy additions prior to the slag forming addition. In this event a plurality of hoppers, two, three, or perhaps even more, may be positioned one on top of the other. For example, a silicon alloying addition may be made first. Purging may or may not be used after the silicon alloying addition. Next, an aluminum addition may be made either in solid or granular form. After the aluminum addition, which might be made for example by the structure of FIGURES and 6, a purging agent may or may not be employed. Finally, slag forming materials which will eventually form a slag cover may be added by merely placing a charge container similar to that of FIGURE 2 on top of the structure of FIGURE 5. After the addition of the slag forming material, the melt may or may not be purged, at the option of the operator. Likewise, it is within the scope of the invention to utilize a plurality of charge material containers spotted at different locations about the periphery of the tank dome. For example, a charge container similar to that shown in FIGURES 2 or 3 may be positioned on one side of the dome and a substantial distance away a container of the type illustrated in FIGURES 5 or 6 could be employed. Alternately, identical containers could be spotted in the different locations. It is not thought necessary to further describe the possible combinations of containers and their locations, for such combinations will be apparent to one skilled in the art. Sufiice to say that in all embodiments charge material will be added to the melt late in the degassing cycle and, so long as slag forming materials are added at a late point in the cycle, a heat insulating blanket will be provided over the surface of the molten metal between the time the metal leaves the vacuum tank and pouring commences. Further, in all embodiments a vacuum is drawn substantially simultaneously in all charge material containers and the main vacuum chamber without requiring a separate vacuum lock system, with all its attandant disadvantages, such as vacuum valves.

It will be understood of course that vacuum locks could be used, and vacuum lock arrangements are considered to be within the scope of the broad method phase of my invention. One of the great advantages of my invention however is the fact that vacuum locks with their attendant valves, manipulating arrangements and seals are eliminated. Whether vacuum locks are used or not, one of the primary objects, that of making additions to the melt while it is in the vacuum tank, and specifically at a selected time during the cycle, is accomplished.

In the foregoing discussion relating to that part of the total method in which charge additions are made, the addition of a few hundred pounds of charge material to a melt of several' tons has been described. My invention also contemplates the handling of heavy charge additions, say on the order of about 10% of the total weight of the melt. Such an addition requires special precautions, however, because a charge of this magnitude might cool the melt too much or, in other words, cause the melt to drop below its lower permissible teeming ternperature.

To make heavy charge additions, the

charge containers

27 or 116 may be made proportionately larger than shown in FIGURES l and 5, and pre-heated charge materials placed therein.

Alternately, heavy charge additions Imay be made in liquid form. In this event a modified addition container in the form of a small furnace would be located on the

cover

24 or 123, or closely adjacent thereto, and aligned with a pouring collar substantially identical to that illustrated in FIGURE 3 of my co-pending application Serial N0. 855,442, now Patent Number 3,084,038. Conventional electric furnace refractories with induction heating coils may be utilized. A seal would be maintained between the electric charge furnace and interior of the tank by the arrangement described in my aforesaid Patent 3,084,038. The lcharge materials would be stream degassed upon exposure to the vacuum as they pass downwardly towards the melt. The individual droplets of charge material would reach the melt .at a temperature substantially higher than they would if added in solid form. Alternately, if the small furnace is of the lip pour type, the furnace may be tilted `and poured through a more conventional stream degassing seal arrangement.

I claim:

1. A method of treating molten metal to reduce the included deleterious gas content, said method including the steps of subjecting a confined volume of the molten metal to a vacuum sufficiently low to effectively degas the molten metal,

simultaneously therewith internally circulating the molten metal within the confined volume to thereby bring molten metal from remote locations in the confined volume to the surface, and

creating a protective atmosphere about the stream of degassed molten metal as it is poured into a receptacle.

2. The method of claim 1 further including the step of providing an insulating covering over the degassed molten metal prior to pouring to thereby protect the molten metal against reabsorption of deleterious gases during pouring.

3. A method of treating and pouring molten metal which reduces heat loss and produces metal having a low included gas content, said method including the steps of,

subjecting a confined volume of the molten metal to a vacuum suthcient to effectively degas the molten metal,

simultaneously therewith passing a sufiicient quantity 13 of a carrier agent upwardly through the molten metal to induce a circulation entirely Within the confined volume which brings substantially undegassed molten metal from remote locations in the confined volume to the surface,

providing an insulating covering over the degassed molten metal prior to pouring `to thereby protect the molten metal against reabsorption of deleterious gases during pouring,

creating a protective atmosphere in a mold into which the molten metal is to be poured by displacing the atmosphere therein with a heavier-than-air inert gas, sealing the mold until pouring commences,

breaking the seal at the commencement of pouring,

and creating and maintaining a protective atmosphere about the stream of degassed molten metal as it is poured into the mold.

4. A method of treating and pouring molten metal which reduces heat loss and produces metal having a low included gas content, said method including the steps of,

subjecting a coniined volume of the molten metal to a vacuum suflicient to electively degas the molten metal,

simultaneously therewith passing a suiiicient quantity of a carrier agent upwardly through the molten metal to induce a circulation entirely Within the confined volume which brings substantially undegassed m01- ten metal from remote locations in the conned 4volume to the surface,

providing an insulating covering over the degassed molten metal prior to pouring to thereby protect the molten metal against reabsorption of deleterious gases during pouring,

creating a protective atmosphere in a plurality of molds into which the molten metal is to be poured by displacing the atmosphere within the molds by a heavier-than-air inert gas,

sealing each mold after the bulk of the atmosphere has been displaced therefrom and maintaining the seal until pouring commences,

pouring the molds in substantially the same order in which they were lled with the protective atmosphere,

5. A method of treating molten metal to reduce the included deleterious gas content, said method including the steps of subjecting a confined volume of the molten metal to a vacuum suicient to effectively degas the molten metal,

simultaneously therewith internally circulating the molten metal Within the confined volume to thereby bring molten metal from remote locations in the confined volume to the surface,

adding charge material to the confined volume of molten metal While maintaining the vacuum,

pouring the degassed molten metal into a mold, and

creating a protective atmosphere about the pouring stream.

References Cited by the Examiner UNITED STATES PATENTS 2,869,857 1/1959 Kopke 266-34 2,872,180 2/1959 Tietig 266-34 2,889,596 6/ 1959 Savage 22-57.2 2,961,722 11/ 1960 Lilljekvist 22-84 2,968,075 1/ 1961 Flickinger 2284 2,994,602 8/1961 Matsuda 75-49 3,026,195 11/ 1962 Edstrom 75-49 3,071,458 1/1963 Finkl 75-49 FOREIGN PATENTS 339,579 12/ 1930 Great Britain.

OTHER REFERENCES Tix et al.: Vacuum Treatment 0f Steel by the Bochumer Verein Stream Degassing Process, J. Iron and Steel Institute, March 1959, pp. 260-265.

DAVID L. RECK, Primary Examiner.

W. C. TOWNSEND, H. W. TARRING,

Assistant Examiners.

Claims

3. A METHOD OF TREATING AND POURING MOLTEN METAL WHICH REDUCES HEAT LOSS AND PRODUCES METAL HAVING A LOW INCLUDED GAS CONTENT, SAID METHOD INCLUDING THE STEPS OF, SUBJECTING A CONFINED VOLUME OF THE MOLTEN METAL TO A VACUUM SUFFICIENT TO EFFECTIVELY DEGAS THE MOLTEN METAL, SIMULTANEOUSLY THEREWITH PASSING A SUFFICIENT QUANTITY OF A CARRIER AGENT UPWARDLY THROUGH THE MOLTEN METAL TO INDUCE A CIRCULATION ENTIRELY WITHIN THE CONFINED VOLUME WHICH BRINGS SUBSTANTIALLY UNDEGASSED MOLTEN METAL FROM REMOTE LOCATIONS IN THE CONFINED VOLUME TO THE SURFACE, PROVIDING AN INSULATING COVERING OVER THE DEGASSED MOLTEN METAL PRIOR TO POURING TO THEREBY PROTECT THE MOLTEN METAL AGAINST REABSORPTION OF DELETERIOUS GASES DURING POURING, CREATING A PROTECTIVE ATMOSPHERE IN A MOLD INTO WHICH THE MOLTEN METAL IS TO BE POURED BY DISPLACING THE ATMOSPHERE THEREIN WITH A HEAVIER-THAN-AIR INERT GAS, SEALING THE MOLD UNTIL POURING COMMENCES, BREAKING THE SEAL AT THE COMMENCEMENT OF POURING, AND CREATING AND MAINTAINING A PROTECTIVE ATMOSPHERE ABOUT THE STREAM OF DEGASSED MOLTEN METAL AS IT IS POURED INTO THE MOLD.