US3735011A

US3735011A - Circular refractory brick construction

Info

Publication number: US3735011A
Application number: US00218340A
Authority: US
Inventors: F Soykan
Original assignee: Special Metals Corp
Current assignee: Special Metals Corp
Priority date: 1972-01-17
Filing date: 1972-01-17
Publication date: 1973-05-22
Anticipated expiration: 1990-05-22
Also published as: JPS4881711A; IT976911B; CA973356A; GB1392011A; SE400118B; DE2302205C2; DE2302205A1; FR2168806A5; ES410717A1; BE794147A

Abstract

Circular crucible or the like constructed from arcuate refractory bricks wherein the mating edges of the bricks are at uniform acute angles with respect to the radius of the furnace. This permits each brick to slide on the mating edges of adjacent bricks such that circumferential or tangential thermal expansion forces will not materially increase the radius of the crucible.

Description

Elited States Patent Soykan [451 May 22, 1973 CIRCULAR REFRACTORY BRICK [56] References Cited CONSTRUCTION UNITED STATES PATENTS 75 Inventor: Ferhun H. S k New Hartford, 3,140,333 7/1964 Tredennick et a1 ..263/46 X N Y 3,401,226 9/1968 Renkey 3,603,050 9/1971 Coleman .52/249 73 Assignee: Special Metals Corporation, New 3,635,459 l/ 1972 Marc ..266/43 Hartford, N.Y. Primary Examiner-Roy N. Envall, Jr. 1 Flledi J 1972 Attorney-Vincent (j. Gioia and Robert F. Dropkin [21] Appl. No.: 218,340

[5 7 ABSTRACT Circular cmcible or the like constructed from arcuate refractory bricks wherein the mating edges of the bricks are at uniform acute angles with respect to the radius of the furnace This permits each brick to slide on the mating edges of adjacent bricks such that circumferential or tangential thermal expansion forces will not materially increase the radius of the crucible.

5 Claims, 5 Drawing Figures PATENTEU MAY 2 2 I975 SHEET 2 OF 2 FIG. 2.

CIRCULAR REFRACTORY BRICK CONSTRUCTION BACKGROUND OF THE INVENTION While not limited thereto, the present invention is particularly adapted for use in induction heated circular crucibles and the like. In a crucible of this type, an induction coil surrounds the refractory wall of the crucible such that when an alternating current is caused to flow through the coil, magnetic lines of flux will pass through the refractory wall and induce eddy currents in the metal within the crucible, the eddy currents acting to rapidly heat and melt the metal charge.

In the past, it has been common to construct a refractory wall of a crucible of this type from arcuate bricks having mating edges extending along the radius of the crucible. That is, the edges of the bricks were essentially flush, one against the other. When bricks of this type are heated, they are subject to thermal expansion, generating tangential or circumferential forces which expand the radius of the furnace in much the same way that the radius of any ring will expand when heated. This compresses ramming and insulation material against the surrounding induction coil which can cause the induction coil to warp permanently and cause cracks which permit molten metal run-outs.

SUMMARY OF THE INVENTION In accordance with the present invention, a generally circular furnace or crucible construction formed from arcuate refractory bricks is provided wherein cracks in the furnace wall and radial expansion due to thermal forces is minimized by the use of bricks having mating edges which are at uniform acute angles with respect to the radius of the furnace.

Specifically, there is provided in a generally circular vessel for molten metal or the like a wall construction formed from arcuate refractory bricks stacked one upon the other. The abutting edge surfaces of the refractory bricks at the opposite ends of their arcuate configurations are at uniform acute angles with respect to the radius of the vessel whereby thermal expansion forces generated in the bricks will cause the edge surface of at least one brick to slide on the abutting edge surface of an adjacent brick without materially increasing the radius of the wall. The edges at opposite ends of the arcuate configuration of each brick are sloped in the same direction, each edge surface being defined by a line drawn from the inner radial end of one edge surface of a brick to a point on a circle which lies intermediate the center of the vessel and the inner periphery of the wall, the aforesaid point on the circle being defined by the intersection therewith of a radius which intersects the inner radial end of the other edge surface of the brick.

In the preferred embodiment of the invention, the aforesaid circle has a diameter equal to one-half the diameter of the inner periphery of the vessel; however the only limiting factor is that the circle must have a diameter greater than zero and less than that of the inner periphery of the crucible wall.

The above and other objects and features of the invention will become apparent from the following detailed description taken in connection with the accompanying drawings which form a part of this specification, and in which:

FIG. 1 is a top view of a prior art induction-heated crucible;

FIG. 2 is a vertical cross-sectional view of the prior art furnace shown in FIG. 1;

FIG. 3 is a top view of the improved furnace construction of the present invention;

FIG. 4 shows the manner in which the slope at the opposite ends of arcuate bricks is determined in the crucible construction of the invention; and

FIG. 5 is an enlarged view of the assembly shown in FIG. 4, illustrating the forces which occur at the abutting edge surfaces of the arcuate bricks used in the construction of the invention due to thermal expansion.

With reference now to the drawings, and particularly to FIGS. 1 and 2, the furnace shown includes a cylindrical wall 10 formed of refractory bricks 12 and having a bottom formed from a slab 14 of refractory material. Surrounding the wall 10 is an induction coil 16 adapted to be connected to a source of alternating current voltage, not shown. Surrounding the coil 16 is a supporting structure which, in the illustration shown, comprises a cylindrical shell 18 which rests on a bottom plate 20. Between the bricks 12 and the inductive coil 16 is a layer 15 of ramming mortar.

As shown in FIG. 1, the bricks 12 are arcuate in configuration and have opposing end surfaces which abut each other along the radius of the circular wall construction 10. That is, the abutting surfaces lie along lines which extend through the center of the circular configuration. With an arrangement of thisgsort, the heat generated within the crucible or furnace will cause thermal expansion forces in the bricks l2; and since the end edges of the bricks are essentially flush with each other, tangential or circumferential forces which are generated at the interface between adjacent bricks cause the entire circular configuration to expand in diameter, forcing the ramming material 15 against the coil 16. As was explained above, this can cause permanent deformation of the surrounding induction coil 16, damage to the ramming material, and possible cracks in the furnace wall with a resultant metal spill out.

A top view of a crucible or furnace constructed in accordance with the present invention is shown in FIG. 3. It will be noted that it is similar to FIG. 1 except that the abutting surfaces of the bricks 22 now lie along lines 23 which are at an acute angle with respect to the radius of the circular configuration. This is perhaps best shown in FIGS. 4 and 5. The radius of the crucible is indicated by the line 24. Note that the abutting surfaces 23 are at uniform acute angles 0 with respect to the radius 24. When bricks expand due to the heat, each brick becomes subjected to thermal expansion which generates tangential or circumferential forces F, (FIG. 5) and compressive stresses between the bricks. The tangential force F can be broken down into two components F,- and F,,. The force F, is normal to the end surface or junction 23 between two bricks; while the force F, is along the interface between the two bricks. Whenever the force F, reaches a value where the force F,- is greater than the frictional force on the interface between bricks, a sliding motion occurs between the bricks, and each brick is forced to rotate in a clockwise direction. That is, the upper and lower edges of the brick are forced to move a very small amount to the dotted-line positions 26 shown in FIG. 5, this being exaggerated for purposes of explanation. This rotation tends to minimize the gap between the bricks and any diametrical or circumferential growth of the original circular configuration.

It can be seen from FIG. 5 that conventional bricks have comers defined by points a, b, c and d. Under these circumstances, the forces F and F do not exist since the force F, is perpendicular to the line b c which is on the radius of the circular configuration. Therefore, it is necessary to generate a shape where the forces F, and F, are present, the brick configuration then being defined by the comers A, B, C and D. Furthermore, it is necessary that the edges of the bricks at the opposite ends of the circular configuration defined by lines A-D and B-C do not pass through the center of the circular crucible, identified by the reference numeral 28 in FIG. 4.

The angular relationship of the lines A-D and B-C is determined by first establishing a circle identified by the reference numeral 30 in FIG. 4. This circle must have a radius greater than zero and less than the radius R, of the inner periphery of the wall formed from the bricks 22. Preferably, the radius of the circle 30 is onehalf the radius R at the inner periphery of the crucible, or R /2. In designing the bricks, and assuming that twenty bricks are to be used in the furnace wall, the circle 30 is divided into equal circular arcs, four of which are shown in FIG. 4 and identified as 32A, 32B, 32C and 32D. By drawing radii through points 34 at the ends of each

equal arc

32A, 32B, etc. the inner edges C-D of each circular brick can be established. Thereafter, by drawing a line from the inner radial end D, for examplel of one edge surface of a brick to a point 34 on the circle (which point 34 is defined by the intersection of a radius which intersects the inner radial end C of the other edge surface of the brick), then the slope of the edges 23 is determined. When this procedure is repeated, centers of

resolution

36 and 38, for example, will be generated and these points will be on a circle 40 which is concentric with the circle 30.

As was explained above, the circle 30 need not have a radius equal to one-half the radius of the inner periphery of the crucible wall; however this is desirable. As the radius of the circle 30 is increased, so also will the slope of the edges 23. Conversely, as the radius of the circle 30 decreases, so also does the slope in the angle 6 shown in FIG. 5.

Although the invention has been shown in connection with a certain specific embodiment, it will be readily apparent to those skilled in the art that various changes in form and arrangement of parts may be made to suit requirements without departing from the spirit and scope of the invention.

I claim as my invention:

1. In a generally circular vessel for molten metal and the like, a wall construction formed from arcuate refractory bricks stacked one upon the other, the abutting edge surfaces of said bricks at opposite ends of their arcuate configurations being at uniform acute angles with respect to the radius of said vessel whereby thermal expansion forces generated in said bricks will cause the edge surface of at least one brick to slide on the abutting edge surface of an adjacent brick without materially increasing the radius of said wall.

2. The wall construction of claim 1 wherein the edge surfaces of each brick are sloped in the same direction.

3. The wall construction of claim 2 wherein said edge surfaces are defined by lines drawn from the inner radial end of one edge surface of a brick to a point on a circle which lies intermediate the center of the vessel and the inner periphery of the wall, said point on the circle being defined by the intersection therewith of a radius which intersects the inner radial end of the other edge surface of said brick.

4. The wall construction of claim 3 wherein said circle has a diameter equal to one-half the diameter of the inner periphery of the vessel.

5. The wall construction of claim 3 including an induction coil surrounding said wall, and ceramic ramming and insulation material embedded around said induction coil.