US2021742A - High temperature furnace insulated wall construction - Google Patents

Description

Nov. 19, 1935. A. s'. NICHOLS 2,021,742

HIGH TEMPERATURE FURNACE INSULATED WALL CONSTRUCTION Filed June 18, 1934 gil Patented Nov. 19, 1935 UNIT ED STATES PATENT GFFICE HIGH TEMPERATURE FURNACE INSULATED WALL CONSTRUCTION Application June 18, 1934, Serial No. 731,029

4 Claims.

This invention relates to wall constructions for high temperature furnaces and the like involving the use of insulating material, among. other objects aims to provide a durable construction of this character capable of resisting the disintegrating forces to whichv a structure of this character is subjected.

` The invention may be readily understood by reference to one illustrative construction embodying the invention and shown in the accompanying drawing;

In said drawing:

Fig. 1 is a sectional elevation of a portion of a furnace wall; and

Fig. 2 is a plan section of aportion of such wall taken approximately on the plane 2-2 of Fig. 1.

The construction of insulated walls for high temperature furnaces and the like involves problems not encountered in ordinary insulated structures. In an open hearth furnace, for example, the expansion of the refractory side Wall material (usually silica brick above the charging floor) is about three-sixteenths of an inch per foot. The ensuing movement of the walls has made it difficult to prevent separation of the refractory wall from the insulating wall under the methods heretofore employed for supporting the insulating material. Owing to the high temperatures developed and for other reasons, the insulating material has not generally been anchored to the refractory material but is supported by external means independent of the refractory wall. Moreover, the insulating materials heretofore available which are capable of resisting high temperatures (2000 F. and up) cannot satisfactorily withstand disintegration by the crushing stresses developed by the expanding refractory walls or are' otherwise not suitable for conditions present in the construction and' operation of high temperature furnaces.

The present invention enables the construction of an insulated high temperature furnace wall wherein the insulating material is of a character which will resist disintegration under the aforesaid compressive stresses and is otherwise appropriate for high temperature furnace conditions and wherein the insulating wall is safely and permanently anchored to the refractory wall so as to provide a durable unitary structure.

The illustrative construction comprises a wall l0 of refractory material herein consisting of a plurality of courses of refractory brick Il whose character and dimensions depend largely upon the type of furnace and operating temperatures. For walls above the charging floo-r of an open and hearth furnace, silica brick are generally employed to form a wall thickness of about eighteen inches,generally formed by two thicknesses of brick. Variation in refractory wall thickness may be secured by changing the method of laying the 5: brick. For lower temperature furnaces, thinner Walls may be employed and in some cases the typical clay fire brick may be used. As here shown, the refractory brick wall and the insulating wall l2 have been combined in a unitary 10 structure by the use of high fusion point, corrosion resisting metallic ties I3. An appropriate alloy steel for such ties is a chromium alloy steel which has a high corrosion resisting or scaling temperature of about 2100 F. and a melting 15` range of 2710 F. to 2750 F., thereby enabling the4 ties to resist disintegration by corrosion (i. e. scaling) at the high temperatures to which they are subjected. An alloy steel of this character is procurable on the open market; it is 20 made for example by the United States Steel Corporation and identified as U S S 27 stainless and heat resisting steel. 'I'hese ties are advantageously flat in character so as to pass through the joints between the brick without increasing 25 the joint thickness. It will be understood that in high temperature furnace walls the joint thickness between brick is minimized because of the relative lack of stability of the fire clay mortar generally employed, and only sufficient mortar is used to level off the inequalities of contiguous contacting brick faces. Of course the tie may have mechanical anchoring means such as perforations, notches, tongues, etc., and if the mortar joint be relatively thick, the tie may advantageously be distorted transversely of the mortar joint by corrugations, etc. As here shown, the tie i3 extends to an inner face of a refractory brick and has an angularly bent portion I4 engaging such inner face to anchor the tie in place. For refractory walls of double thickness (usually employed in furnaces developing exceedingly high temperatures) the tie preferably extends only to the inner face I5 of the outer thickness I6 and is protected by the inner thickness ll. Ink single thickness refractory walls (usually used for the lower temperature furnaces) the tie may safely extend to the inner face of the wall since it will resist corrosion up to temperatures of 2l00 F. (whereas ordinary iron and steel corrode rapidly at about 1000" F.). Generally the prong of the tie is coated over by deposits from the furnace and is thereby additionally protected. It is not necessary therefore to 55- rely upon the strength of the mortar between the bricks to hold the tie in place.

It is desirable that the horizontal brick joints I8 and i9 of the refractory brick and insulation brick frequently align to permit the ready application of ties; and therefore the vertical thickness of the insulation brick and refractory brick should either be the same or their relative thicknesses so proportioned that joint alignment willl occur every few courses. The tie may extend to the outer face of the insulation brick to be anchored there by another angularly bent portion or if, as in the present instance, the brick may be readily penetrated without disintegration, the tie may have a pronged extremity which may be easily pressed into the brick as at 20. The latter arrangement is preferable since the construction is not affected by variations in transverse brick thickness.

The number of ties employed in each course as Well as the vertical spacing ties is generally determined by the character of the Wall and the stresses imposed by expansion under heat.

A penetrable insulation brick of the character above referred to may be formed from granules of exfoliated vermiculite mixed with a small quantity of plastic clay bound together superficially to provide a firm reinforcing shell for the brick. Exfoliated vermiculite is an alteration product of particles of certain micaceous minerals, such as biotite, which exfoliate or expand to many times their original size upon the application of heat to produce a granular insulating material both highly refractory and extremely light in weight (about six pounds per cubic foot). Heat causes the multitude of micaceous laminae of the vermiculite to separate minutely, thus providing a multitude of substantially parallel planes of highly polished surfaces which not only make transfer of heat extremely diiiicult, but substantially reflect heat waves. The particles are readily compressible in the direction of their expansion, thus rendering the interior of the brick compressible and making it capable of absorbing without disintegration the compressive forces which develop in the operation of high temperature furnaces and preventing their transmission to retaining structures, as presently explained. The plastic clay in this case serves somewhat as a matrix to protect the compressible particles of vermiculite but is preferably not used in such quantities as to substantially increase the weight of the brick or impair its insulating efficiency. The

exfoliated vermiculite is both extremely refractory and a highly efficient insulator which does not lose its insulating efficiency when subjected to the high temperatures encountered adjacent the refractory wall of an open hearth furnace.

To facilitate formation of the brick, a liquid binder is used to form a plastic mass which is molded into brick form and thereupon dried. The drying action causes the binding material to migrate to the surface of the brick to form a hard durable shell on the brick. Even though the binder be destroyed after the brick is in place and subjected to high temperature, disintegration does not result since the clay material thereupon serves as a satisfactory binder. While the surface of the brick is hard, it can be easily penetrated by a prong of the metallic ties I3 since the interior of the brick is quite compressible.

The above described compressible character of the brick makes it particularly advantageous for use in the typical furnace construction wherein the insulatingwall is either enclosed by a metallic shell or abuts in places the typical buck-stays 2| used in open hearth and other furnace constructions. It will be understood that the buck-stays extend vertically on opposite sides of the furnace and are connected together by tie rods extending across the furnace above its roof. Upon expansion of the furnace wall the outer wall of insulating material yields (i. e. compressed) under the forces developed and thereby protects the buck-stays or other surrounding metal retaining structure from disruption and distortion. A hard and incompressible outer layer of brick would of course transmit the expansive forces to the outer retaining structure and there- -by distort or seriously damage it. On the other hand, bricks or blocks made from friable insulating materials such as diatomaceous earth and ceramic bonded materials would be crushed and would disintegrate under the aforesaid compressive stresses and the powdered insulating material would eventually sift down and expose the refractory wall. This is quite serious particularly where the furnace wall is enclosed in a metallic shell and the absence of insulation is not immediately visible. The compressible character of the exfoliated vermiculite in the insulation brick above described enables the brick to be compressed without disintegration, There is no danger therefore of developing exposed points in the furnace wall. Upon cooling of the furnace and contraction of the refractory wall, the metallic ties prevent the separation of the insulating wall which would otherwise ensue. The wall structure therefore is unitary in character under the expanding and contracting movel 45 1. A high temperature furnace construction comprising in combination a refractory wall formed of a plurality of courses of refractory brick, an outer wall in contact with said refractory wall and formed of a pluralityr of courses of compressible insulating brick, a metallic retaining structure bearing against the outer face of said outer wall, said insulating brick being compressible and adapted to be compressed by the expansion of the refractory brick wall against the metallic retaining structure and to be compressed thereby without disintegration, certain joints between the brick ineach wall being in alignment, and ties extending between said joints and having projections in engagement with the brick in each of the walls to tie the walls together, said ties being formed of flat strips of high temperature corrosion resisting steel to withstand the high temperatures in said furnace.

2. A high temperature furnace construction comprising in combination a refractory wall formed of a plurality of courses of refractory brick adapted to expand substantially under heat, a separate outer wall of, brick having different expansion characteristics from said refractory brick, said outer wall being independent of said refractory brick wall so that each wall may move independently under expansion or contraction, and flexible metallic ties made of high temperature corrosion resisting alloy steel and having angular projections engaging the brick in each Wall thereby to hold the Walls against substantial separation under the disruptive forces developed in the operation of the furnace.

3. A high temperature furnace construction wherein the high temperatures involve substantial expansion of the furnace structure comprising in combination a refractory lining Wall made of refractory brick, an outer insulating Wall made of brick having different expansion characteristics from said refractory brick, said Walls being unconnected except by flexible metallic ties made of a high temperature corrosion resisting alloy, said ties having angular projections adapted to engage brick in each of said Walls to tie the walls together.

4. A high temperature furnace construction wherein the high temperatures involve substantial expansion of the furnace structure comprising in combination a refractory wall formed of a plurality of courses of refractory brick, an outer Wall in contact with said refractory wall and formed of a plurality of courses of brick formed of particles of exfoliated vermiculite, said brick having a penetrable outer shell, certain joints between the brick in each Wall being in alignment, and high temperature alloy steel ties extending between said joints to tie the Walls together, said ties having prongs which penetrate the outer shell of said insulating brick.

ARTHUR S. NICHOLS.

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