US2874201A - Segmented casing for kaolin melting furnace - Google Patents

Description

' Feb. 17, 1959 J -rw e 2,874,201

SEGMENTED CASING FOR KAOLIN MELTING FURNACE Filed Nov. 8, 1955 FIG.2

United States Patent SE GMENTED CASING FOR KAOLIN MELTING FURNACE Frederick J. Hartwig, Alliance, Ohio, assignor to The Babcock & Wilcox Company, New York, N. Y., a corporation of-New Jersey Application November 8, 1955, Serial No. 545,590

3 Claims. (Cl. 13--23) This invention relates to electric resistance furnaces for melting refractory mineral materials and, more particularly, to an improved construction of such furnaces providing for easy disassembly of the furnace for'inaintenance, inspection and repair of replacement of parts.

The melting of such refractory mineral materials is a prerequisite for forming mineral wool. The minerals commonly employed for the manufacture of mineral wool are natural wool rock (calcareous shale or argilaceous limestone), common shale, and combinations of calcareous and siliceous materials, such as metallurgical furnace slag. All such materials have a fusion point in the range of l500-2500 F.

One of the principal uses of mineral wool of the character described is for heat insulation. The upper use temperature limit for such material is determined by the temperature'at which recrystallization occurs therein to an extent that embrittlement and loss of strength in the fibers result. At this temperature, known as the devitrification temperature, the material changes from a'glassy to a crystalline structure. Tests of the best known commercial brands of mineral wool have shown none in satisfactory condition after a twenty-four hour exposure at 1350 P. due to excessive recrystallization at that temperature. The manufacturers recommended upper use temperature limits for these mineral wools are therefore in the range of 900-l200 F.

As disclosed in Patent No. 2,467,889, a mineral wool having an upper use temperature limit in the range of l50(l2300 F. can be formed by using kaolin as a starting material. Kaolins have a fusion point of about 3245 F. The mineral wool is formed by melting the kaolin, which may be initially in the form of pieces of grog or clinker made from calcining the raw material to eliminate the water of combustion. The molten material is withdrawn from the furnace as a stream or a series of droplets and subjected to a high velocity jet of air or steam which blows the droplets into long fibers.

In the production of mineral wool from molten refractory materials, it is desirable to tap the furnace continuously, rather than to tap intermittently, as in batch melting. This is particularly true in the case of high melting point refractory materials, such as kaolin, as the periodic shutting down of the furnace heating in order to pour batches of the molten material results in solidification of the charge in which the electrodes or other heating elements may be imbedded. In turn, this introduces operating difficulties in re-starting the furnace.

In addition, it is difficult, if not impossible, to pour the molten material at a precise location when pouring by tilting the furnace, as well as being very difficult to precisely control the pour rate. All these criteria dictate the need for a type of furnace construction in which the refractory material, such as kaolin, can be continuously and progressively melted and tapped at a uniform rate over as long a period of time as possible.

In accordance with the present invention, the kaolin,

or other refractory material to be used to form a mineral wool, is melted in an electric resistance melting furnace. This furnace comprises a generally cylindrical metal shell having a metal bottom and an open top, the interior of the shell being lined with refractory brick, for at least part of the distance from its bottom plate toward its open top. Three main electrodes are mounted through the walls of the furnace, and are connected to a threephase supply of alternating current of the required capacity. The bottom plate has a central opening through which the molten kaolin may be tapped.

After a production run of a given duration, the time length of which is variable from several hours to several days or weeks, it is generally necessary to shut down the furnace for inspection, maintenance or repair. When the furnace is thus shut down, themolten kaolin solidifies, generally making a solid mass of refractory including the solidified kaolin and the lining of the furnace. It is necessary to disassemble the furnace in order to recover usable portions of the electrodes and tapping assembly.

The furnace construction of the present invention is particularly designed to facilitate such disassembly and subsequent re-assembly of the furnace. To this end, the metal shell or casing is formed of a plurality-preferably three-of upright segmental cylindrical sections joined, with their adjacent edges in circumferentially spaced relation, by bolted connectors. This provides upright slots through which the main electrode assemblies may be mounted radially of the furnace. Each segment has a horizontal flange adjacent its lower edge, these flanges forming a shelf supporting an annular metal bottom plate.

The tapping assembly is-supported through the bottom plate-by mounting it detachably to the undersurface of the bottom plate. The interior of the furnace is partly or completely lined with built up refractory shapes supported on the bottom plate.

For an understanding of the invention principle, reference is made to the following description to a typical embodiment thereof as illustrated in the accompanying drawing. In the drawing:

Fig. 1 is a diametric sectional view of the furnace;

Fig. 2 is an elevation view of the furnace casing;

Fig. 3 is a diametric sectional view of the furnace casing; and

Fig. 4 is a partial axial sectional view of the furnace illustrating the support for the bottom plate.

Referring to the drawings, the electric resistance melting furnace comprises a generally cylindrical and upright metal casing 15 comprising three cylindrical segments 15A, 15B and 15C detachably interconnected at their adjacent upright edges to leave longitudinal slots therebetween to receive the main electrodes 30. Casing 15 has an angle 16 welded to its inner surface adjacent its bottom edge, this angle comprising separate arcuate angles on each of the three cylindrical segments. Angle 16 serves as a shelf to support a flat annular metal bottom plate 17 of the furnace, plate 17 having a central circular opening 18 therein. It will be noted that the furnace casing is thus an easily assembled and disassembled composite structure of the casing segments and the bottom plate.

The interior of the metal casing is lined by built-up refractory shapes providing a relatively thick refractory lining 21 on bottom plate 17 and a relatively thick wall lining 22. The wall lining may be carried to the upper end of furnace 10, but it is usually terminated just above the main electrodes with the slots between the casing segments, above the Wall lining, being suitably closed, as by removable metal strips.

The main electrods 30 may be mounted through special shape refractory brick guides 25 aligned through each of the three slots in casing 15. The tapping assembly is mounted coaxially with the bottom furnace opening 18.

The construction of electrodes 30 and of the tapping assembly forms the subject matter of my co-pending application Serial No. 547,917, filed IJovernberfZl, 1955, now'Patent N0. 2,817,695,.issued December 24, 1957.

Referring more particularly to Figs. 2 and 3 each casing section 15A, 158 or 15C is in the form of an are or segment of a cylinder, and has an arcuate length of substantially 120. The casing sections are bent from relatively thin steel plate, and each section has a relatively thicker steel flange 26 welded to its upper end and angles 27 welded along each edge and braced by vertically spaced stiifeners or supports 28 extending between the outer surface of the section and the inner surfaces of the angle and welded thereto. At'its lower inner edge, each section has an angle 16 welded thereto to removably support bottom plate 17.

Adjacent the top and bottom ends of the casing section vertically spaced stops 31 are welded to the outer leg of angles 27 to act as locators-for straps 32 secured by bolts 33 to flanges 27. These straps detachably secure the casing sections together in circumferentially spaced relation with slots 34 between adjacent sections to receive electrodes 30 mounted in guides 25. After the sections are thus interconnected, plate 17 is positioned on flanges 16 and refractory lining 21, 22 put in place.

After completion of a run, the power is turned off, and after the furnace has completely cooled, any water and electrical connections are disconnected from electrodes 30 and the tap assembly. Casing 15 is then disassembled from the refractory mass and the solidified melt is split with a sledge hammer or the like. Usable portions of the electrodes and tapping assembly may then be recovered.

While a specific embodiment of the invention has been shown and described in detail to illustrate the application of the invention principle, it will be understood that the invention may be embodied otherwise without departing from such principle.

What is claimed is: v p

1. In a furnace for melting refractory material, an outer casing comprising a plurality of separate segmental upright metal sections; means disengageably interconnecting said sections with their upright edges spaced circumferentially from each otherrto form elongated slots; a lining of refractory material enclosed by the interconnected sections; and electrodes mounted to extend through the slots between such upright edges into the furnace and supported by said lining; whereby said sections may be disconnected and removed for access to the refractory material without disturbance of the electrodes.

2. In a furnace for melting refractory material, an outer casing comprising a plurality of separate segmental upright metal sections; means disengageably interconnecting said sections with their upright edges spaced circumferentially from each other to form elongated slots; a flange on the inner surface of each section adjacent and above its bottom edge; a metal floor plate removably mounted on said flanges; a lining of refractory material enclosed by the interconnected sections and supported by said floor plate; and electrodes mounted to extend through the slots between such upright edges into the furnace and supported by said lining; whereby said sections may be disconnected and removed for access to the refractory mate rial without disturbance of the electrodes.

3. A furnace casing as claimed in claim 2 in which each section has an angle secured along each edge; each angle having the outer edge of one leg secured to the section with the other leg extending inwardly from the edge of the section; said interconnecting means comprising straps bolted to the outer legs of adjacent angles.

References Cited in the file of this patent UNITED STATES PATENTS 1,626,000 Kay Apr. 26, 1927 1,737,566 Brown Dec. 3, 1929 2,280,101 Slayter Apr. 21, 1942 2,340,601 Langford Feb. 19, 1944 2,493,939 Ames Jan. 10, 1950 2,538,811 Triggs Jan. 23, 1951

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