US3384362A - Apparatus for adding heat to flowing metal - Google Patents

Description

May 21, 1968 H. s. PHILBRICK, JR 3,384,362

APPARATUS FOR ADDING HEAT TO FLOWING METAL 2 Sheets-Sheet 1 Filed March 4, 1965 INVENTOR.

Walk/1 f (2/2 llzfwwgyn y 1968 H. s. PHILBRICK, JR 3,384,362

APPARATUS FOR ADDING HEAT TO FLOWING METAL 2 Sheets-Sheet 2 Filed March 4, 1965 //l l I m r J Rm 1 g m W M r a a x 67/ n W M 2 WM 7 H M M w ||H%%%\ M W w w 1| J m y m%\\ H I United States Patent 3,384,362 APPARATUS FOR ADDING HEAT T0 FLOWING METAL Herbert S. Philbrick, Jr., Chicago, Ill., assignor to John Mohr & Sons, Chicago, Ill., a corporation of Illinois Filed Mar. 4, 1965, Ser. No. 437,132 8 Claims. (Cl. 266-39) ABSTRACT OF THE DIECLOSURE An apparatus for stream degassing of molten metal, including a ladle positioned above a receptacle which is, in turn, positioned above a gathering receptacle located in a vacuum tank. The receptacle is formed with a bottom and a multi-layer, non-metallic sidewall. An inductive heating element is located adjacent the receptacle sidewall.

This invention relates to the treatment of molten metal, and particularly to a method and apparatus for counteracting heat loss and subjecting the molten metal to a vacuum treatment in the time interval between tapping and teeming.

One of the most efficient ways of improving the quality of steel during the steel making cycle is to subject it to vacuum treatment, either alone or in combination with other operations such as purging, while it is in a molten condition. The time interval available for treatment is rather short however. This is because metal, particularly low carbon steels, must be teemed into an ingot mold at a temperature no lower than about 2850 degrees F. Steel which has been degassed will generally be more fluid than non-degassed steel, and accordingly teemable at a somewhat lower temperature. For purposes of convenience however, it will be considered that the lower teeming temperature limit is on the order of about 2850 degrees F. It is also well established that it is not feasible to tap molten metal from a steel making vessel, such as electric furnace, at temperatures appreciably higher than 3100 degrees F. This is because relatively small increases in temperature above 3100 degrees F. result in relatively large increases in the rate of refactory erosion in the steel making vessel. The economics of the steel making process therefore may require that the tapping temperature be on the order of about 3100 degrees P. so that only a relatively narrow temperature range is available for treatment of the molten metal between tapping and teeming. The time therefore left for treatment is the time it takes the metal to cool from about 3100 degrees to about 2850 degrees. This time may vary somewhat with the size and configuration of the tapping vessel, but in general it can be characterized as a matter of minutes.

Stream degassing processes for the treatment of steel have recently begun to gain favor in the steel making industry on a commercial scale. In this process dispersion of a downwardly falling stream of molten metal into droplets exposes a maximum surface area to the vacuum and therefore provides a maximum opportunity for removal of included deleterious gases from the metal. This dispersion of the stream has the attendant disadvantage however that heat loss from radiation is maximized.

The concept of stream degassing has been before the art for some time. It is only recently, however, that stream degassing has begun to be successfully practiced on a commercial scale. Numerous possible drawbacks to the earlier proposed processes are immediately obvious to one skilled in the art, not the least of which is Patented May 21, 1968 the inflexibility of the equipment from the standpoint of inability to correlate the rate of heat input to the quantity flow-rate of metal past a given point in the system at any given instant of time, and the every-heat replacement of the intermediate ladle.

Accordingly, a primary object of this invention is to provide a method of compensating for temperature loss in the time interval between tapping and teeming in a steel making process.

Another object is to provide a method as described above in which there is simultaneously provided a good mixing action to the metal.

Yet another object is to provide a stream degassing process in which the molten metal may be vacuum degassed in stages and heat simultaneously added to the metal without the complications of operating induction coils in a vacuum environment.

A further object is to provide a method and means for varying the rate of heat input to molten metal in response to a change in the system conditions thereby providing great flexibility to the system.

Another object is to provide a method and means for vacuum degassing, on an economical basis, low carbon steels which comprise a large percentage of the steels currently poured, and for which no commercially feasible system has heretofore been developed.

Another object is to provide structure to accomplish the above objects including a special receptacle so con structed as to provide a highly effective magnetic window effect when induction coil means associated with the receptacle are operated.

It is another object to provide a heat addition unit for an intermittent flow process in which the metal holding receptacle and the heat generating means are located in close physical proximity to, but spaced from, one another whereby rapid assembly or disassembly of the heating unit may be accomplished without causing prolonged shutdown of the system.

Another object is to provide a continuous flow stream degassing system of great flexibility in which variable quantities of heat can be imparted to the molten metal so as to enable degassing procedures to be employed within a reasonable margin of safety above the critical teeming temperature.

Yet another object is to provide a continuous flow stream degassing system which may be quickly and easily adapted to existing plants yet which will enable the system operator to have control over system conditions at any given instant.

A further object is to provide a metal holding receptacle having a heat conversion efficiency on the order of about percent, or more, and which may be used numerous times between overhauls thereby reducing auxiliary equipment costs to a minimum.

A further object is to provide a stream degassing system which requires no alteration of conventional shop ladles or other expensive equipment.

Other objects and advantages will become available from the reading of the following description .of the invention.

The invention is illustrated more -or less diagrammatically in the accompanying figures wherein:

FIGURE 1 is an elevational view, with parts in section, illustrating the physical arrangement of the present invention;

FIGURE 2 is a sectional view through the receptacle to a larger scale; and

FIGURE 3 is a detail view of a portion of the intermediate receptacle of FIGURE 2 to a larger scale illustrating both the construction of the wall and temperature gradients through the wall.

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

The stream degassing system of the invention is shown in FIGURE 1. The system includes a tapping ladle *1, a treatment receptacle unit 2, and a vacuum chamber 3 within which is placed a receptacle 4. The system is of the continuous flow type in the sense that metal may, if desired, be continuously passed from ladle 1 into receptacle 4, which may be a shop ladle identical in all respects to ladle 1.

The upper or tapping ladle 1 can be the conventional bottom pour shop ladle presently used in many melt shops. Discharge from the ladle may be controlled by the illustrated stopper rod mechanism which may be controlled from a remote point by any means well known in the art. Overhead crane 5 suspends shop ladle 1 during pouring in a position such that its outlet 6 discharges directly into the treatment receptacle unit 2.

Treatment receptacle unit 2 rests directly upon the upper portion 7 of tank 3. The treatment receptacle support structure is a ring 8 whose construction is illustrated in greater detail in FIGURE 2. The treatment receptacle is removable and positionable by trunnion means 9 which likewise is shown in greater detail in FIGURE 2.

The treatment unit 2 consists of a special ladle 10, illustrated best in FIGURES 2 and 3, and a ladle cover 11, the ladle and cover being sealed as by O-ring 12 to form a vacuum tight enclosure. A streaming collar is indicated at '13 and a sealing plate at 14, the sealing plate including suitable seal means such as an O-ring seal which, when in abutting engagement with a sealing surface 15 surrounding the discharge outlet of ladle 1, forms a vacuum tight seal between the shop ladle 1 and treatment unit 2. A flexible vacuum conduit is indicated at 16.

The upper half 7 of the vacuum chamber or tank 3 is lifted and lowered into place upon the lower portion 21 of the tank by any suitable means such as the hydraulic cylinders 22 carried by the cover bridge crane 39. A charge material addition hopper at 23 and viewing ports may be provided in both ladle cover 11 and tank cover 7.

The lower portion 21 of the vacuum tank rests upon a plurality .of inverted T-beams 25 which in turn rest upon foundation 26. An outlet pipe 27 is connected to any suitable vacuum means, such as a multiple stage steam ejector system.

The tank ladle 4 rests upon a bottom ring 30 which in turn rests upon a low platform 31 within the vacuum tank. In this instance, a conventional bottom pour shop ladle having a stopper rod 32 has been illustrated. Means for admitting a purgent to the melt are indicated at 33. It should be understood however that the invention does not require the use of any particular supplemental purging system. Furthermore a tank receptacle of substantially any configuration may be employed, its only requirement being that it have a sufficiently large opening to catch all of the molten metal streamed downwardly into the tank. In this instance, an extension conduit or streaming collar 34 is aligned with the bottom discharge port 35 of treatment receptacle unit 2 to insure that dispersion of the molten stream upon exposure to the vacuum will not be so widespread as to cause droplets of metal to fall outside the gathering receptacle ladle 4. As best seen in FIGURE 1, the conduit 34 has an upper bearing flange ring 36 which forms a support base for treatment receptacle unit 2, and which, in turn, carries combination sealing and supporting plate 8. A shield is indicated at 38 which functions to reduce heat loss and prevent splash.

A cover bridge crane is indicated at 39, the crane being movable along tracks 40 and 41. The crane carries induction heating means indicated generally at 42, the induction heating means in this instance being supported by a base which may be a circular ring 43. As best seen in FIGURE 1, the induction heating means is in close physical proximity to, but still physically separated from, the treatment receptacle unit 2 so that it is possible to lower the special ladle 10 into place, and lift it, without dis tunbing the induction heating means.

Means for regulating the current input, and therefore the heat generated by the induction heating coil means are indicated at 44 and 45.

The treatment receptacle 2 is illustrated in greater detail in FIGURES 2 and 3. The receptacle consists essentially of an upwardly open shell structure which includes an outer, relatively thin layer 48 of non-magnetic, relatively low heat conducting plastic material. The shell may be on the order of about .5 inch thickness and may be formed over a mandrel and autoclave cured.

The shell may be composed of a glass fiber reinforced plastic. A composition consisting of glass fibers conforming to the descriptive standard 184/150 and sold by B. F. Goodrich Company of Akron, Ohio, which are reimpregnated with a phenolic resin conforming to the descriptive standard 37-9X, and available from the US. Polymeric Chemicals Co., Inc., of Stamford, Conn. under the trademark Poly-Preg is quite suitable. Alternately, a material available from the J-ohns-Manville Company of New York, N.Y., under the trademark Thermomat and consisting of asbestos fiber, phenolic resin, and alcohol is also quite suitable. The material may be formed in a warm state either from large sections or from tape. In tape form it is composed of percent ASTM Grade AAAA long, oriented Chrysotile asbestos fibers saturated with a phenolic resin conforming to military specification MlL-R9299. Various inorganic fillers may be incorporated for improved thermal performance. The material may be formed by lay-up, vacuum-bag molding, low and high pressure laminating, and molding. Alternately, a similar compound sold under the trademark Trevarno F- and available from the Coast Manufacturing and Supply Company may be employed, said compound having the properties mentioned in the publications of said company.

The shell insulation lining 49 is composed of a material having a very low thermal diffusivity and functions to maintain a relatively low temperature at its outer face. A material currently available from the Iohns-Manville Company under the trademark Min-K is quite suit-able. This material has a service temperature of about 2000 F., a normal density of about 20 pounds per cubic foot, satisfactory transverse and comprehensive strength, low linear shrinkage and a thermo-conductivity in Btu. inches per square foot-Fahrenheit of .27 to .46 in the range of 800 F. to 1600 F. The specific heat varies from about .23 to .27 B.t.u.s per pound degree Fahrenheit over the temperature range of about 400 F. to 1600 F. It may include an asbestos-reinforced plastic laminate. This material has a thermo-conductivity well below the conductivity of still air and has good erosion resistance and high strength. A thickness on the order of about 1 inch may be employed to advantage.

Alternately, a material known as Thermoflex which is also available from lohns-Manville Company, may be employed. This material is composed of a mass of uniform ceramic fibers, predominately alumina and silica. The fibers average about 3 microns in diameter and the material has an unusually low K factor at elevated temperatures due to the opacity of its fibers to infra-red radiation. It is non-alkaline and contains no sulphur.

The next innermost, or safety, lining 50 may be composed of conventional Dando ladle brick sold by H. K. Porter Company and widely used in the steel industry today.

A layer on the order of about 2 inches thick may be employed to advantage. The next innermost, or insulating, lining 51 may be composed of a brick sold by the Babcock and Wilcox Co. under the trademark K-28. Again a layer on the order of about 2 inches thick may be employed to advantage.

The innermost, or working, lining 52 may be composed of a high alumina brick containing approximately 80- 85% alumina and sold by the Richard C. Remney Son Company under the trademark DV-38. A layer on the order of about 4 inches thick may be employed to advantage.

The bottom is formed by stainless steel inverted head 60, the flange portion of the head being mechanically fastened to the shell as by fasteners 61. The bottom lining may be composed of materials similar to the wall lining.

A trunnion ring is indicated at 63 and trunnions at 64. In this instance the trunnion ring is fastened to the shell structure by tapered band 65 which enables the ring to be removable if it becomes necessary to replace the wall.

A stopper rod assembly, not shown, may be mounted on the ladle in such fashion as to clear the induction heating coil means 42. Alternately, other means well known to the art may be used to open and shut off flow through the discharge opening. There is thus no problem occasioned by replacement and removal of the treatment receptacle from the supporting platform 37.

The use and operation of the invention are as follows:

Assume that a reservoir or tapping ladle 1 contains approximately 60 tons of electric furnace steel at a temperature of approximately 3100 F. The ladle is placed in the position of FIGURE 1 and a vacuum tight seal formed between bearing plate 15 and sealing plate 14. O-ring 12 forms a vacuum tight seal between ladle cover 11 and the sealing flange encircling the upper edge of the ladle 10. As soon as molten metal fills in the discharge part 35 a vacuum tight enclosure is formed. A vacuum sufiiciently low to effect an initial, or primary, degassing is then drawn in treatment receptacle unit 2 through vacuum conduit 16. This vacuum may be on the order of about 2 to 20 mm. of Hg absolute for example.

Molten steel streamed into ladle through streaming collar 13 disperses into droplets upon which the vacuum acts. The streaming collar however confines the dispersion such that all metal reaches the surface of the metal in ladle 10.

When the level of molten metal reaches approximately the height indicated in FIGURES 1 and 2, the discharge opening 35 is opened and metal streamed into tank 3. By suitable proportioning of the bottom discharge openings 6 and 35, and regulation of the flow control means of ladle 1, a substantially constant rate of inflow into and overflow from the treatment receptacle can be maintained.

Assume then that a steady state metal flow condition has been established and that the treatment receptacle 2 holds approximately 20 tons of molten metal. If the pouring rate is about 10 tons per minute, each increment of metal will remain in the treatment receptacle approxi mately two minutes. The induction heating coils are .operated to generate enough heat to meet the required predetermined desired rise in temperature which may for example be on the order of 50 F.

The unique treatment ladle 2 enables the system to be kept in uninterrupted operation for extended periods of time, as contrasted to earlier proposed systems. The particular multi-layered wall and bottom construction of the ladle, illustrated best in FIGURE 3, contributes significantly to the success of the system in the following manner.

No commercially acceptable metal holding vessel, such as a ladle, of a size sufficient to hold several tons of molten steel has gone into commercial usage because of the problem of over heating of the ladle shell. Nearly invariably the ladle shell has been composed of stainless steel because this material enables a considerable quantity of the heat generated by the coils to pass through it and into the melt. Substantial heating losses in the shell were always encountered, however, and these losses have been such as to reduce the efficiency of the process to a point where the process became commercially uneconomical. Further, the possibility of dangerous overheating of the shell is always present. No acceptable system has been proposed which enable a stainless steel shell ladle to function on a commercial scale.

The present invention makes use of a plastic ladle shell which forms a magnetic window between the coil and the hot metal contained within the ladle. The plastic shell is made from one of the re-inforced plastic materials discussed heretofore. The re-inforced plastics which comprise the shell present no opposition to the passage of magnetic flux therethrough and therefore the magnetic flux does not generate induced currents in the shell.

Since plastic materials are generally limited to operating temperatures substantially below those of stainless steel, an important part of the invention is the employment of the very efiicient shell insulation layer of the type discussed earlier. By employing this special shell insulation material, and the conventional safety, insulating and working linings now conventionally employed in the steel industry, a design operating temperature of about 300 F. may be realized, with reduced life resistance up to 700 F.

Referring now to FIGURE 3, steady state condition temperatures are indicated by the solid curve 54. This curve represents the theoretically highest temperatures obtainable in a system such as that described here. Even if the same ladle is used for several successive heats, the illustrated steady state values will not be reached because establishment of steady state conditions will require a long period of continuous exposure. This will seldom, if ever, occur in practice. An additional safety factor is provided by the fact that the insulating materials in the plastic shell are capable of withstanding substantially higher temperatures than the temperatures associated with steady state conditions for a relatively long period of time.

The particular multi-layer construction also has the great advantage that the efiiciency may be increased 50% or more as contrasted to present systems. That is to say, the efliciency of the illustrated system may be on the order of 77% as contrasted to present efiiciencies of only about 50%. This is because no metallic material, not even stainless steel, is interposed between the induction coils and the molten metal in the ladle. Since the metal level in ladle 2 may be maintained at approximately the level of the upper end of induction coil 42, an ideal magnetic couple is made.

After the addition of heat the metal passes downwardly through streaming conduit 34 and eventually is dispersed into a spray of fine droplets 70 in the ladle 4. Once in the ladle 4 the metal may or may not be subjected to further treatment such as gas purging.

A great advantage of the system is that the sensible heat added to the metal in the treatment receptacle can be varied with extreme accuracy. Thus, at the beginning of pour the discharge from the reservoir 11 will tend to be at a higher rate than towards the end of the treatment since the metal head in the ladle will decrease and fine control is not always possible, especially if the conventional stopper rod assembly is used. The amount of heat added can likewise be varied with the decrease in flow rate from the shop ladle from a maximum level at the commencement of operations to a minimum level at termination merely by operation of the variable heat input means 44, 45.

At the same time, the induction heating coils means are so disposed that considerable internal agitation is created within the metal in the treatment receptacle. This action promotes mixing thereby improving the homogeneity in the product. Should charge materials such as alloys or deoxidizers be required, they may be added either to the stream passing into tank 3 or the ladle 4, but in any event they will be added after an initial degassing which, as is now well known in the art, greatly reduces the final number of oxide inclusions. This is of particular advantage in the low carbon grades of steel,'.especially the types that go into the automotive industry, and perhaps structural steels as well. As a general rule, the lower the carbon the higher the oxygen content and it is very advantageous to add oxide prone alloys such as aluminum and silicon after removal of as much oxygen as possible to reduce the formation of oxide inclusions. This system is therefore particularly applicable to the low carbon steels, which are the large tonnage steels.

In tank ladle 4, the metal may be subjected to a second degassing at a vacuum as low as about microns Hg absolute.

It will at once be apparent to those skilled in the art that various modifications may be made within the spirit of the invention. It is contemplated, for example, that a ladle of the type illustrated in FIGURE 2 may be employed in lieu of the ladle 4 indicated in FIGURE 1, either with or without dwell receptacle 10. In this event the electrical leads would of necessity pass through the vacuum enclosure 3. This variation would provide the added advantage of holding the ladle in the vacuum enclosure for lengthy periods of time to accommodate a slow streaming rate or effect metallurgical reactions therein, or other reasons. It would also enable the metal in the dwell receptacle to be heated to a lower temperature than would otherwise be necessary. Accordingly, it is intended that the scope of the invention be limited not by the scope of the foregoing exemplary description but rather by the scope of the hereinafter appended claims construed in light of the pertinent department prior art.

I claim:

1. A heat additive unit for a continuous flow streaming process, said unit including, in combination,

an induction coil means and support structure therefor,

a receptacle consisting of a multi-ply walled upwardly opening shell structure,

means for discharging molten metal from the shell structure whilst stationary, and

means secured to said shell structure to enable lifting and conveying of said shell structure,

the depth of the metal holding volume of the shell structure being sufficient to span an electrical source of heat and to maintain each increment of molten metal in the shell structure for a dwell period deter mined by the rate of admission and discharge of molten metal thereto,

said coil and support structure being positioned in physically close proximity to but spaced from the shell structure whereby such structure may be freely placed in and removed from the induction coil means.

2. The heat additive unit of claim 1 further characterized in that the induction coil means is so positioned with respect to the receptacle when the components are in assembled, operative condition, that an uninterrupted magnetic couple is provided.

3. The heat additive unit of claim 1 further characterized in that the induction coil means consists of a line frequency induction coil.

4. The heat additive unit of claim 1 further characterized by and including means for varying the rate of heat input from the induction coil means.

5. A system for continuously stream degassing low carbon steel said system including, in combination,

a reservoir,

a receptacle,

said receptacle being so positioned as to receive molten metal discharged from the reservoir, said receptacle including,

a multi-ply walled upwardly opening shell structure,

means for discharging molten metal from the shell structure whilst stationary, and

means secured to said shell structure to enable lifting mined by the rate of admission and discharge of molten metal thereto,

said receptacle being positioned, when in operative posi tion, above a gathering receptacle located within a vacuum tank,

said receptacle being positioned to discharge into the gathering receptacle in the vacuum tank whereby the stream of molten metal discharged from the receptacle may be subjected to the vacuum as it enters the gathering receptacle.

6. A receptacle adapted for use in a continuous stream degassing process, said receptacle including, in combination, a multi-ply upwardly opening sidewall structure composed at least in part of glass fiber, reinforced plastic, and having a metal holding depth sufiicient to span an induction heating coil,

means for discharging molten metal from the shell structure whilst stationary,

means for lifting and conveying said shell structure,

with

the lower surface of said receptacle formed by an inverted stainless steel member, said member being located in a non-interfering position with respect to the induction coil and the molten metal.

'7. A receptacle for holding large batches of molten materials having temperatures up to the temperature of molten steel for extended periods of time, said receptacle including, in combination,

bottom forming means,

wall forming means extending generally vertically upwardly from the bottom forming means,

said wall forming means being composed of non-metallic material and including refractory lining means disposed within a structural plastic member,

said structural plastic member being composed of a material selected from the group consisting of a phenolic resin impregnated glass fiber material, and a phenolic resin and alcohol impregnated asbestos fiber material, with said refractory lining means having the ability to maintain an outer face temperature thereof of less than 700 F.

8. In a vacuum degassing system,

a receptacle having bottom forming means and wall forming means extending generally vertically upwardly from the bottom forming means,

said wall forming means including a plurality of layers of non-metallic material disposed within a structural plastic member,

structure forming a vacuum environment at least above the receptacle,

an induction heating coil surrounding the wall forming portion of the receptacle, with the structure forming the vacuum environment spaced from and surrounding the receptacle and the induction heating coil.

References Cited OTHER REFERENCES Handbook of Reinforced Plastics; Reinhold Pub. Co., 1964, p. 1723.

DAVID L. RECK, Primary Examiner.

N. P. BULLOCH, H. W. TARRING,

A ssislanl Examiners.

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