US3337201A - Vacuum degasser - Google Patents

Description

Aug. 22, 1967 J. A. SNYDER VACUUM DEGASSER 2 Sheets-Sheet 1 Filed Aug. 28, 1964 FIG. 1

INVENYLOR. John A. Snyder ATTORNEY Aug. 22, 1967 Filed Aug. 28, 1964 FIG.2

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35A no.4

J. A. SNYDER VACUUM DEGASSER 2 Sheets-Sheet 2 &

United States Patent tion of New Jersey Filed Aug. 28, 1964, Ser. No. 392,801 3 Claims. (Cl. 266-13) The present invention relates generally to the production of high purity steel, and more particularly to an improved apparatus for purifying steel by the vacuum degassing method.

In order to meet the modern specification requirements for steel products, such as bearing parts, that are to be used to near the limit of their physical characteristics, it is necessary that the steel from which these products are made be as pure and free from solid or gaseous inclusions as possible. Vacuum degassing is a process used between the melting and ingot pouring steps in the steel making process to remove gaseous materials, particularly oxygen, hydrogen, nitrogen and their compounds, from the molten steel. In vacuum degassing, the free surface of the molten steel contained in a vessel is subjected to a high vacuum, i.e., less than an absolute pressure of 100 microns of mercury, and the body of molten metal is then stirred or otherwise agitated to expose the entire mass of metal to the free surface whereby the gases included in the metal are drawn from the free surface due to the difference between their pressure and that of the vacuum. It will of course be recognized that the vacuum degassing of large masses of molten metal, e.g. batches of 50 tons or more, at commercial rates requires the use of extremely large and expensive equipment.

The large vacuum degassers built prior to the arrangement of the present invention employed a pit-type chamber having a removable top cover. The ladle or vessel containing the molten steel to be degassed was first lowered into the chamber by means of a crane. Then the top cover was placed in position, and the vacuum applied to the chamber. Suitable means, such as an induction stirring device, were permanently mounted within the chamber for agitating the mass of metal to expose it to the vacuum conditions maintained within the chamber. After the desired degree of degassing'was accomplished, the chamber top cover was removed and the ladle lifted out of the chamber by the crane and removed to the ingot pouring area.

Although this arrangement proved to be satisfactory insofar as accomplishing the desired degree of degassing was concerned, the expense of the equipment and the chiciency with which it could 'be utilized were found to be considerably less than ideal. Since the degassing operation is accomplished between the melting and ingot pouring stages of production, it is absolutely essential that a minimum amount of time be used in performing the degassing operation so that the heat loss and temperature decline of the molten metal may be kept to a minimum. Because of the handling problems associated with pit-type degassers, the time consumed in degassing was marginally close to the allowable limit. Moreover, the handling procedures employed were not readily adaptable to the flow-through production methods of modern steel mills.

Since the present steel producing capacity in the United States is considerably greater than the market demand, very few new steel mills are being erected. Vacuum degassers, a relatively recent innovation, are therefore usually incorporated into an existing steel making plant or facility. Although high capacity cranes are a normal part of the equipment in a steel melting and pouring plant, when considering the large size of a vacuum degasser installation, there is rarely available space in which the chamber can be located in an existing facility with complete access to a crane of suflicient capacity. Thus, in inice stances where a pit-type or top loading degasser is to be installed, the degasser installation almost invariably necessitates the concurrent installation of a degasserservice crane, the initial cost of which is about 15% of the cost of the degasser itself.

Thus, it can be seen that the pit-type of degassing chamber has apparent shortcomings making its incorporation into the usual steel mill production scheme both awkward and expensive.

It is therefore an object of the present invention to provide a vacuum degassing apparatus which may readily be incorporated into the flow-through production schemes of a modern steel mill. It is a further object to provide a vacuum degasser arrangement which may be installed integrally into an existing steel melting and pouring facility while requiring a mini-mum amount of space, outlay of capital and disturbances of the normal production arrangement. It is a still further object of the present invention to provide a vacuum degasser chamber arrangement in which the complete degassing operation may be accomplished with a minimum amount of material handling in a lesser amount of time than has heretofore been possible.

To accomplish these objects, according to the present invention there is provided an apparatus for degassing a body of molten metal contained in a large ladle and having a free liquid surface, which apparatus includes upright side walls and a roof defining an enclosed degassing chamber. The chamber walls are provided with a side opening through which the ladle, carried on a wheeled carriage, may be admitted into the chamber, and a slidably movable door is arranged to cover and seal the door in gas tight relationship to the boundaries of the opening during the degassing operation. Pump means, such as a jet injector system, are connected with the chamber for evacuating substantially all the atmosphere from the chamber to form and maintain a vacuum therein. Tracks on which the carriage is adapted to move extend between the steel melting and steel pouring facilities and into and outwardly from the chamber through the opening formed in the chamber walls. A detachable prime mover, which is located outside the chamber when the door is closed, is provided for moving the carriage along the tracks into and out of the chamber. An induction stirring device, powered through a detachable connector located within the chamber, is permanently mounted on the carriage and is constructed and arranged to circulate'the metal within the carriage with a horizontal and vertical component of movement so that substantially all the metal is exposed at the liquid surface to the vacuum conditions within the chamber during the degassing operation.

The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawing and descriptive matter in which there is illustrated and described a preferred embodiment of the invention.

In the drawings:

FIG. 1 is a perspective view of a vacuum degassing apparatus according to the present invention;

FIG. 2 is a floor plan showing the incorporation of the vacuum degasser of FIG. 1 into a steel melting and pouring plant;

FIG. 3 is a side elevation view of a movable track section at the entrance and exit of the degassing chamber;

FIG. 4 is a sectional end elevation taken along line 4-4 of FIG. 3; and

FIG. 5 is a sectional view showing the door seal arrangement taken along line 5-5 of FIG. 1 when the door is closed.

Referring to FIG. 1, the degassing chamber 16 is formed of a roof 12 and side walls 14 which are reinforced with structural steel members 14A so that the walls 14 can withstand the inward force of the atmosphere when the chamber is evacuated. The chamber walls are formed with opposed entrance and exit side openings or doorways which are sufficiently large to pass the ladle carried on the transfer car or Wheeled carriage 25. As shown in FIGS. 1 and 2, the carriage operates on rails 35 which extend through the doorways of the chamber 10. It should be recognized that the carriage 25 may readily be pushed or pulled along the tracks 35 into, through and out of the chamber 10 by a suitable detachable prime mover generally indicated at 24 in FIG. 2.

A air of covers or doors 16 (one of which is open and one of which is closed in FIG. 1) are provided for purposes of closing the doorways during the degassing operation, and are also suitably reinforced by structural steel members 16A. The doors 16 are each hung by rollers 17 which are arranged to roll along the channel shaped track 18 overlying and extending laterally beyond the respective doorways. During the degassing operation, the doors 16 are rolled into place over their respective doorways and are engaged in gas-tight sealing relationship to the doorway boundaries by a sealing arrangement to be described hereinafter.

A control room 50 is arranged atop and to the one side of the chamber 10, the control room being thus disposed to afford an operator the best possible view of the overall operation. Roof sighting tubes 51 are provided with transparent covers to allow viewing of the ladle 20 and the metal contained therein when the doors 16 are closed. Additive bins 52 disposed on the roof 12 of the chamber 10 are provided for purposes of adding pre-measured quantities of alloying materials to the metal in the ladle 20 during the degassing operation.

The required vacuum (usually less than 100 microns of mercury) is imposed in the chamber 10 by pump means or multi-stage steam injector jet system 301 which communicates via conduit 34 with the chamber 10 through an opening 33 formed in one of the side walls 14. In FIG. 1, the five serially arranged injector jets of the system are designated 30A, 36B, 30C, 30D, and 30E in the order of their serial arrangement. Condensers 31A and 31B are respectively interposed between the third and fourth stage jets 30C and 30D, and between the fourth and fifth stage jets 30D and 30B.

FIG. 2 indicates that the vacuum degassing chamber 10 may be conveniently located between an existing melting area or bay 40, and one or more melting furnaces 41 located therein, and a teeming bay or pouring area 45 in which a multiplicity of ingot molds 46 are located. The rails on which the ladle-bearing carriage 25 is arranged to operate, extend through the chamber 10 between the melting bay and the teeming bay 45, so that the carriage 25 is accessible to the ladle handling crane facilities (not shown) in each of the bays 40 and 45. Thus, it can be seen that the installation of the vacuum degassing apparatus into an existing plant as shown in FIG. 2 eliminates the necessity of adding crane facilities for handling the ladle 20. Also it is obvious from FIG. 2 that the vacuum degassing operation, which is performed between the melting and ingot pouring stages of production, can be accomplished in the disclosed apparatus with a minimum of ladle handling and lost time because of the flow-through arrangement of the degasser chamber 10 and its relative location with respect to the melting and pouring areas 40 and 45.

The carriage 25 has permanently mounted thereon a stirring device or induction stirrer 26 for magnetically circulating the molten metal within the ladle 20 to effect exposure of substantially all the molten metal to the vacuum conditions existing at the free surface of the molten metal and to insure thorough mixing of any additives charged to the ladle 20 via the bins 52 during the degassing operation. The induction stirrer 26 includes a series of vertically stacked separately operable coils 26A each of which circumscribes the ladle 20 when it is positioned on the carriage 25. The coils 26A may be of downwardly diminishing diameter so that they generally conform to the slightly inwardly tapering sides of the lower portion of the ladle 20. With this arrangement of coils 26A, a horizontal component of circulation results from the normal operation of the individual coils; moreover, a vertical component may be afforded the stirring action by sequentially firing or energizing the individual coils 26A. The induction stirrer is powered through a detachable electrical connection (not shown) located within the chamber 10.

The ladle 20, which is usually of about ton capacity, is preferably made of a non-magnetic material such as stainless steel to avoid its becoming magnetized due to the operation of the stirrer 26. Diametrically disposed outwardly extending trunnions 21 are provided on the sides of the ladle 25 for crane handling, and positioning lugs 22 welded to the upper sides of the ladle 20, are arranged to engage with a mating support frame 29 on the carriage 25 to insure the proper positioning and support of the ladle 20 thereon. During the degassing operation, the top of the ladle is covered by a heat shield 27 having a reflective refractory inner surface to prevent the unnecessary loss of radiant heat from the free molten metal surface within the ladle 20. Charging holes 28 are provided in the heat shield 27 so that the additive material may be charged from the bins 52 to the ladle 20 during the degassing operation.

In order to prevent the leakage of outside air into the chamber 10, it is necessary to provide a seal for the doors 16. The sealing problem created by the rails 35 is resolved by providing movable rail sections 35A (to be described hereinafter) at the entrance and exit of the chamber 10. With the track sections 35A removed all four boundaries of each doorway are accessible for use as sealing surfaces. The door sealing arrangement is shown in FIG. 5 in which 16 is representative of a door and 14B represents a structural steel member forming one of the boundaries or sides of a doorway and having a sealing surface 14C that is in a plane parallel with the plane of the door 16. Welded peripherally around the door 16 in a common plane are a pair of spaced pipes or rigid tubular members 56. A sealing tube 57, made of a suitable resilient material such as rubber, is suitably affixed to the door 16 between the pipes 56. The cross-sec tional area of the sealing tube 57 is such that it substantially fills the space between the pipes 56 when compressed by the door 16. In operation, when the jet injector system 30 starts to pull a vacuum on the chamber 10, the door 16 is urged, by suit-able means such as hydraulic cylinders 58, toward the sealing surface to establish contact of the sealing tube57 with the doorway sealing surface 140. Thereafter, the vacuum within the chamber 10 will cause the sealing tube 57 of the door 16 to remain firmly engaged with the sealing surface 14C, thereby effecting a substantially gas-tight seal. The pipes 56, arranged as shown, prevent the sealing tube 57 from lateral displacement and also provide a protection to the tube 57 from any molten metal that may be splashed from the ladle 20 during the degassing operation. m

As mentioned above, movable track sections 35A are provided immediately adjacent the doorways to the chamber 10 so that there are suitable parallel sealing surfaces around the entire peripheries of the doors 16 and their respective doorways. As shown in FIGS. 3 and 4, movable track sections 35A are connected by hold-down lugs 63 and supported on a rectangular frame consisting of a pair of spaced I-beams 61 extending parallel to the track sections 35A and another pair of spaced I-beams 62 extending perpendicular to and having their ends connected with the I-beams 61. The rectangular frame thus formed is supported on four wheel assemblies 65 connected to the undersides of the I-beams 61 and arranged to engage the inverted angle tracks 66 which are suitably anchored to the foundation 67. The movable track sections 35A are urged into and out of position through a rod 70 which interconnects the I-beam 61 that is nearest the door 16 to the lower corner of the door 16. A spring assembly 71 is attached to the rod 70 and serves to prevent the transmission of shock forces between the door 16 and the wheeled frame to which the track sections 35A are attached. Since the track sections 35A and the door 16 are substantially rigidly interconnected, means are provided for adjusting the length of the rod 70 so that the lateral position of the track sections 35A may be adjusted to be in alignment with the tracks 35 when the door 16 is in its fully opened position. Thus, it can be seen that when the doors 16 are opened, the track sections 35A will be moved into alignment with the tracks 35A so that the carriage 25 may be moved into, through or out of the chamber 10. Conversely, when the doors 16 are closed, the track sections 35A are moved laterally out of alignment with tracks 35 so that the doors 16 may be engaged around their entire peripheries in sealing relationships with the boundaries of the doorways as described above.

As shown in FIG. 3, the floor 13 of the chamber is supported from the foundation 67 by a support beam system SQWhlCh also supports the portions of the rails 35 within the chamber 10. A refractory pan or reservoir 85 is built up between the tracks 35 Within the chamber 10 and serves to catch any molten metal which may leak from the ladle 20 while it is in the chamber 10. Thus, if a minor leak does develop, the leakage may be confined to the pan 85 until the ladle 20 can be removed from the chamber 10.

To further demonstrate the utility of the invention disclosed herein, a complete degassing operation will be described. The molten metal to be degassed is poured from the melting furnace 41 into the ladle 20 in the pouring bay 40. The crane in the pouring bay 40 is then used to position the ladle 20 on the carriage 25. After the heat shield 27 has been placed on top of the ladle 20, the carriage 25 is pulled by the prime mover 24 along tracks 35 into the degassing chamber 10. The prime mover 24 is then detached from the carriage 25 and moved out of the chamber 10, and the power connection for the induction stirrer 26 is made within the chamber 10. The doors 16 are then closed, which closing action also moves the track sections 35A out of their normal position so that the peripheral sealing surfaces around the doors 16 may be aligned. The doors 16 are then urged into engagement with their respective seals and the jet injector system 30 is activated to produce the desired level of vacuum within the chamber 10. During the time when vacuum conditions are maintained within the chamber 10, the induction stirrer 26 is operated to effect circulation or agitation of the molten metal within the ladle 20, and the desired additives may be added to the laddle 20 from the additive bins 52. After degassing has been completed, the vacuum in the chamber 10 is reduced, and the doors 16 are opened, the opening of the doors 16 serving additionally to reposition the movable track sections 35A. Induction stirrer 26 is then disconnected from its power source, and the prime mover 24 is coupled with the carriage 25. The ladle 20 may then be transferred to the pouring area 45 where, utilizing the crane facilities of the pouring bay 45, the molten metal from the ladle 20 is poured into the ingot molds 46.

From the above, it can be seen that the vacuum degasser arrangement disclosed herein necessitates a minimum amount of ladle handling and time and utilizes existing crane facilities to a maximum extent.

While in accordance with the provisions of the statutes there is illustrated and described herein a specific embodiment of the invention, those skilled in the art will understand that changes may be made in the form of the invention covered by the claims, and that certain features of the invention may sometimes be used to advantage without a corresponding use of the other features.

What is claimed is:

1. Apparatus for degassing molten metal comprising, upright side walls and a permanently afiixed roof defining an enclosed degassing chamber, pump means connected with said chamber for evacuating substantially all of the atmosphere therefrom to form a vacuum therein, furnace means spaced from said chamber, ingot casting means spaced from said chamber, a ladle, means for pouring molten metal from said furnace means into said ladle, means for pouring molten metal into said ingot casting means from said ladle, a wheeled carriage, means for placing said ladle in and removing the ladle from said carriage, means to form an opening in said chamber side wall sufficiently large so that said carriage holding said ladle can be passed through said opening, track means adapted for the travel of said carriage thereon and extending from said furnace means and said ingot casting means and into said chamber through said opening, an induction stirrer permanently mounted on said carriage and constructed and arranged to circulate said metal within said ladle whereby the metal is exposed to the vacuum within said chamber to effect degassing, a detachable connector within said chamber for energizing said induction stirrer, a movable door arranged to cover said opening, movable track sections connected to and operable with said door to move said sections out of normal track alignment when closing said door, means for moving said carriage along said track means into and out of said chamber, and means for engaging said door in gas-tight sealing relationship to the boundaries of said opening.

2. Apparatus according to claim 1 including means to form openings in opposite upright walls of said chamber, track means which extend through said chamber and opening means for movement of said carriage through said chamber, and a movable door for each of said openings.

3. Apparatus according to claim 2 including means which define a reservoir between the tracks within said chamber for catching any metal leakage from said ladle within said chamber.

References Cited UNITED STATES PATENTS 3,255,897 6/1966 Lacy 214 18 FOREIGN PATENTS 866,928 5/1961 Great Britain.

OTHER REFERENCES High Vacuum Degassing Wit-h Induction Stirring Makes Cleaner Steels, by Thomas E. Perry, vol. 83, Metal Progress, pp. 88-91, August 1963.

JOHN F. CAMPBELL, Primary Eaxminer.

R. F. DROPKIN, Assistant Examiner.

Claims (1)

1. APPARATUS FOR DEGASSING MOLTEN METAL COMPRISING, UPRIGHT SIDE WALLS AND A PERMANENTLY AFFIXED ROOF DEFINING AN ENCLOSED DEGASSING CHAMBER, PUMP MEANS CONNECTED WITH SAID CHAMBER FOR EVACUATING SUBSTANTIALLY ALL OF THE ATMOSPHERE THEREFROM TO FORM A VACUUM THEREIN, FURNACE MEANS SPACED FROM SAID CHAMBER, INGOT CASTING MEANS SPACED FROM SAID CHAMBER, A LADLE, MEANS FOR POURING MOLTEN METAL FROM SAID FURNACE MEANS INTO SAID LADLE, MEANS FOR POURING MOLTEN METAL INTO SAID INGOT CASTING MEANS FROM SAID LADLE, A WHEELED CARRIAGE, MEANS FOR PLACING SAID LADLE IN AND REMOVING THE LADLE FROM SAID CARRIAGE, MEANS TO FORM AN OPENING IN SAID CHAMBER SIDE WALL SUFFICIENTLY LARGE SO THAT SAID CARRIAGE HOLDING SAID LADLE CAN BE PASSED THROUGH SAID OPENING, TRACK MEANS ADAPTED FOR THE TRAVEL OF SAID CARRIAGE THEREON AND EXTENDING FROM SAID FURNACE MEANS AND SAID INGOT CASTING MEANS AND INTO SAID CHAMBER THROUGH SAID OPENING, AN INDUCTION STIRRER PERMANENTLY MOUNTED ON SAID CARRIAGE AND CONSTRUCTED AND ARRANGED TO CIRCULATE SAID METAL WITHIN SAID LADLE WHEREBY THE METAL IS EXPOSED TO THE VACUUM WITHIN SAID CHAMBER TO EFFECT DEGASSING, A DETACHABLE CON-

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