US2093212A - Muffle construction - Google Patents

Description

3 Sheets-Sheet 1 www. kw

H. M. ROBERTSON MUFFLE CONSTRUCTION Filed 061;. 3l, 1955 Sept. 14, 1937.

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Sept. 14, 1937. H. M. ROBERTSON 2,093,212

MUFFLE CONSTRUCTION 5 Sheets-Sheet 2 Filed Oct. 3l, 1955 H. M. ROBERTSON MUFFLE CONSTRUCTION Sept. 14, 1937.

5 sheets-sheet s Filed oct@ 51, 1955 l /A/l/E/v 70H 7 /71- KM?? Patented Sept. 14, 1937 gaaanz MUFFLE CQNSTRUCTION Harry M. Robertson, Cleveland, Ohio, assignor to Electro Refractories &

Buffalo, N. Y.

Alloys Corperation,

Application October 31, 1935, Serial No. 47,657

3 Claims.

f as are used in annealing and heat treating of metals, drying and calcining of minerals, salts and other materials, enamelling of steel, iron and other ware, drying, calcining, vitrifying and glazing of pottery, china, clay, porcelain, refractory and similar ware.

One of the objects of this invention is to provide a mufe of improved construction which results in a more uniform heating of the material under treatment. Another object of this invention is to provide a muille of improved construction which will increase the eikziency of a furnace or kiln in the utilization of heat, and capable of giving long service. Another object of the invention is to provide a muflle of increased strength and having greater radiation surface per lineal foot. Another object is to provide a muflie in which the heating of the material by radiation and by convection currents is so controlled as to produce improved conditions under which the material is treated. Another object of the invention is to provide a muille capable of withstanding high temperatures for long periods of time and having long life. Another object is to provide a muffle in which the concentration of radiation on any one portion of the material is avoided. Other objects of the invention will appear from the following description and claims.

In the accompanying drawings, which illustrate several of many possible embodiments of this invention:

Fig. 1 is a fragmentary transverse sectional elevation of a kiln or mufe furnace embodying this invention.

Fig. 2 is a face view of a muflle used in the furnace shown in Fig. 1 on an enlarged scale.

Fig. 3 is a transverse sectional view thereof on a still larger scale on line 3-3, Fig. 1.

Figs. 4, 5 and 6 are fragmentary transverse sectional elevations of a kiln or furnace showing mufiles of modified constructions.

Fig. '7 is a fragmentary transverse sectional view of still another type of muflle construction.

Figs. 8, 9 and 10 are respectively face views of muiiles shown in Figs. 4, 5 and 6, respectively.

Fig. 11 is an enlarged transverse section on line II-I I, Fig. 6.

Fig. 12 is a face view of a mufile of still another modified form.

Fig. 13 is a sectional view thereof on line |3-I 3, Fig. 12.

Fig. 14 is a top plan View thereof.

Fig. 15 is a longitudinal section on the l 5-I 5 of Fig. 16, showing a different form of construction.

Fig. 16 is a section on the line lli-I6 of Fig. 15.

In Fig. 1 is illustrated a part of a tunnel kiln of the type in connection with which muiiies embodying my invention may be used. It will be understood, however, that it is not intended to limit this invention for use in connection with the particular type of furnace or kiln illustrated. In this kiln, upright structural members 20 are provided, the lower ends of which are connected in any suitable manner not shown and the upper portions of which are connected by means of tie rods 2|. These upright structural members 20 and the tie rods are spaced at intervals lengthwise of the kiln and collectively hold together the side walls of the kiln. The walls of the kiln may include an outer facing including plates 22 and 23 which may be of metal or other suitable material. 25 represents the usual benches which are made of refractory material, such as re bricks or the like, and 26 represents an arch connecting the upper ends of the side walls 24 and suitably braced laterally by the structural side members 20. In order to provide additional heat insulation, suitable insulating material 2l, such for example, as diatomaceous earth, may be placed between the side walls 24 and benches 25 and the outer facing 22, and similar insulating material may also be placed over the arch 26 and the upper ends of the side Walls 24. This construction pro-vides a pair of combustion chambers 35 with a single treating chamber 36 arranged between them. The benches, as is usual in furnaces of this kind, form, between them a space `for a car 31 including a platform 38 supported on girders or frame members 39 which are suitably mounted on wheels 42 operating on tracks (not shown) to carry the materials to be treated through the furnace or kiln past the various zones of heat in the treating chamber 36. wheels and lower part of the car may be provided, such as labyrinth seals 46 formed by cooperating recessed and projecting portions of the benches 25 and platform 38 and also by depending flanges 49 secured to the girders 39 of the car, which run in sand in stationary troughs 50.

The combustion chambers 35 are separated from the treating chamber 36 by muffles 5l. The combustion chambers may be heated in any suitable or desired manner by means of hot gases conducted to or generated in the combustion chambers and any suitable means may be pro- Suitable sealing means for protecting the.

vided for heating the combustion chambers, such for example as have heretofore been employed in similar kilns.

Referring to Fig. 1, slabs or abutments 52 of refractory material are inserted in the arch 26 and project downwardly beyond the lower surface of this arch. The mufiles I rest against the slabs 52 and are sealed to the slabs by any suitable means such as a refractory cement. The lower ends of the muiiles 5i preferably rest in depressions or grooves 53 in the benches 25 and may be sealed thereto by means of a similar refractory cement.

The mules illustrated in Figs. 1 to 3 are formed in sections or units, each of which is provided with a corrugated back wall 55 facing the combustion chamber 35 and a corrugated front wall 56 facing the treating chamber 36, which walls are joined or connected by means of spaced webs, the latter being preferably formed integral with the front and back walls. For example, upright end walls or webs 51 and 58 connect the ends of the front and back walls, and these webs are preferably provided with interlocking parts adapted to connect with adjacent muflle sections. For this purpose, the end wall 51 may have a projecting tongue 59 and the other end wall 58 may have a complementary recess or groove Si). When the muflle sections are installed in a furnace or kiln, the tongue of one muille interts with the groove in an adjacent muflie, as indicated in Fig. 3. The front and back walls of the muflle may also be joined intermediate of their ends by additional vertical conlnecting webs 5|, thus producing a strong and highly eiective structure. By having the corrugations of the front and back walls arranged as shown in Figs. 1 to 3, the webs extend from an inwardly extending trough of one wall to a crest of another wall.

It will be noted too that in the construction shown in Figs. 1 to 3, the front wall 5B of each section is not coextensive with the back wall, but terminates at its upper and lower ends respectively below and above the corresponding ends of the back wall. This provides for'the admission of air or kiln atmosphere into the lower end of the space between the two walls of the muile, for the upward passage of the air in the space between the two walls, and for the discharge of this air at the upper end of this space.

Muilles constructed as described are very effective in the heating of the material under treatment for several reasons. The amount of radiation of heat depends upon the surface area from which the heat is radiated, and since a corrugated siuface has much larger area than a flat surface, a correspondingly increased radiation of heat results. Radiation of heat is generally in a direction perpendicular to the surface from which it is radiated. By using a corrugated surface, the heat is radiated from this surface in a number of different directions, so that it is not concentrated upon the material under treatment to the extent that would happen if a flat radiating surface were used. Furthermore, with the muiile described, convection currents of gas or air are produced within the treating chamber, which have the advantage of distributing the heat through the material under treatment rather than concentrating it upon the outer surface thereof. By providing a muffle in which the cooler air can enter between the two walls of the muiile at the lower end thereof, become heated during its passage between the walls, and then discharged at the upper ends thereof, strong convection currents are produced. This form of mule is, consequently, particularly desirable for use in treating certain types of material such, for example, as china or porcelain ware in which the separate pieces are spaced from each other so that convection currents can flow readily through the spaces between the individual pieces of the ware.

The corrugations of the muiile also materially strengthen the same. A corrugated muflie wall is far less likely to buckle than a straight walled mullie and a double walled corrugated muffle has a still greater resistance to buckling or other deformation. A mufle of this kind has been found to be capable of withstanding higher temperatures for longer periods of time than a single wall mule. The upright Webs also greatly strengthen the mufe in that they enable each wall of the mufe to reinforce the other wall.

In order to make a tight seal between the corrugated back wall 55 of the muiiie and the downwardlyV extending abutment or slabs 52 of the furnace or kiln, the upper edge of the rear face of the back wall of the muille is provided with a rib or reinforcing beadV 64 which extends into the troughs of the corrugations of the back wall and the rear face of 'which forms a at surface extending parallel to the front face of the slab 52 with which the muflle cooperates. This rib or reinforcement 64 may be cemented to the slab 52 to form a substantially air-tight joint. vvThe reinforcing part 64 also increases materially lthe' strength of the muiile andreduces the danger of breaking of the upper end of the same.

In the particular construction shown in Figs. 1 to 3, the combustion chambers are sealed in such a manner that no products of combustion enter into the treating chambenrso that all heat passing into the treating chamber from the combustion chambers must pass through'the muffles. In the modified construction shown in Figs. 4 and 8, the mules are substantially identical in construction with the vmuillesv shown in Figs.-` I to 3, except that the back wall of the muffle is provided with holes', theseholes being preferably formed in the back wall below the lower edge of the front wall of the mufllef 'These holes may be of a`desired sizeand number to admit the required amount 4of combustion gases into the treating chamber 36. It isdesirable in some cases to have an oxidizing atmosphere in the treating chamber and in other cases, a neutral atmosphere is desired, while in still other 'cases,it maybe desirableto have areducing atmosphere in the treating chamber. 'Ihese varied' conditions depend, of course, upon the material which is being acted upon in the treating chamber and upon the results desired. By means of the construction shown in Figs. 4 ar`1d'8,l a neutral or reducing atmosphere may be provided inthe treating chamber' 36 by'- controlling combustion in the combustion chambers.

In cases where it is desired to' convey AAa lesser amount of heat to the treating chamber -36 from the combustion chamber or chambers, and where long life of the muflle is of primary importance. the construction shownv in Figs. 5 and 9 may be provided'in which the front wall 56hl of the mule isof the same or substantially the' 'same length as the back wall 55. The front wall 5619 of the muiile, consequently, extends to the bench 25 and prevents' thev ventranceof air'or gas into the lower end of the space between these two walls so that no convection currents through the muille itself are produced. In this construction, however, the radiation of heat is directed in a large number of different directions because of the use ofthe corrugated front wall 56h so that the radiation of heat is distributed over a large area. This construction, consequently, eliminates excessive concentration of radiation on that portion of the ware or material which is nearest to or faces the mulfle.

A further modification is shown in Figs. 6, 10 and ll, in which the muliles have a flat back wall 61 'and in which the front wall 68 is corrugated. This muifle incorporates many of the advantages of muffles having both front and back walls corrugated and yet is somewhat less expensive to manufacture, since the cost of manufacturing a flat wall is less than that of a similar corrugated wall. This muilie is also shown with a forwardly extending reinforcing rib or projection 89 which reinforces the upper edge of the muflie. It will be noted also that in this construction, the front wall terminates at a distance below the upper end of the munie, thus permitting direct radiation from the flat back wall into the treating chamber above the portion thereof in which the material under treatment is located. In this manner, a large amount of heat is radiated above the upper end of the front wall 68 of the muifle against the arch 26, by which it is reflected downwardly upon the material under treatment.

Fig. '7 illustrates another embodiment of this invention which includes a four-piece muflle constructed so that the combustion chamber is formed within a space confined by the four pieces of the mullie. In this construction, a mufile 5H) is employed, facing the treating chamber and this muffle may be identical in construction with the one shown in Figs. 5 and 9, except that the muflle 5lb is of less height than the one shown in Figs. 5 and 9. The passages between the inner and outer walls of this muiile communicate with a hole 18 in the top wall 'H of a bottom muffle member l2, the bottom wall 73 of which may rest upon the bench 25. This bottom muifle member 'I2 may be of plain at walled construction, but may be reinforced by means of a plurality of transverse webs 14 corresponding to the webs 6| and the end walls shown in Fig, 3, thus leaving passages which communicate at their opposite ends with similar passages in the front muflle member 5|b` and a back mulile member l5. The bottom mullle member 'l2 may be attached to the back muffle member 'I6 whichin turn is attached to a top mufllemember Ti. All of these muffle members are of the double-Walled construction, and are so formed as t be fitted together as clearly shown in Fig. '7 to form continuous passages 18 having an opening 19 adjacent to the platform member 38 of the. car and another opening 39 near the arch 26. This causes convection currents to be set up in the treating chamber 35 through the bottom, back and top sections of the muflie as well as through the front section. The front section also directly transmits heat to the treating chamber by radiation through the corrugated walls thereof. The spaces between the walls of the front mulfle member lb preferably terminate in holes or openings in the bottoms and top muifle members to enable this member to transmit heat both by convection and radiation,

In Figs. l2 to 14, still another modif-led form of muiile is illustrated. This muille is similar to the one shown in Figs. 1 to 3y except that the corrugations are differently formed and the connecextend to the bottom of the backwall but terminate at the upper end of the front wall. From about the level of the top of the front wall to the top of the back wall short ribs or webs 86 extend forwardly from the troughs of the corrugations approximately to the plane ofthe crests thereof as plainly shown in Fig. 14. The tongues and grooves B1 and 88 in the opposite webs or end walls are formed -in the portions of these end walls below the upper edge of the front Wall and are only partially formed in the upper ends 86 of these webs. By means of this construction, muflles of great rigidity and strength are produced without waste of material. By forming the webs on the portions of the corrugations of the back wall which extend farthest into the combustion chamber, a more uniform heating of the corrugated back Wall is produced, since the most rearwardly extending portions of the corrugations are, of course, heated to the greatest extent by the combustion gases in the combustion chamber. By forming the webs 85 and 86 integral with these portions of the corrugations, heat is conducted forwardly by the webs 85 to the front wall of the muftle, which tends to reduce the temperature ofthe rearwardly extending portions of the corrugations of the back wall. Consequently, the temperature of the back Wall is rendered more uniform throughout and is, consequently, less liable to damage. mufile is, consequently, desirable under some conditions of use.

Figs. 15 and 16 show a slight modification of the invention in which the end walls and connecting webs, which are formed integral with the front and back walls, have a joint which extends completely from one end to the other of these end walls and webs.

The muflies hereindescribed are thoroughly practical and are of greater rigidity and strength than muffles heretofore produced. The modulus of rupture of the walls of the muflie is improved by making the same in corrugated form and the corrugated walls provide from 25% to 40% greater radiation area than corresponding flat walled muflles would have. By means of the double walled muflie, a greater proportion of the heat is conducted to the material under treatment by means of convection currents, and a lesser amount by radiation, and the heat which is transferred by radiation is distributed or broken up in such a manner as not to be excessively concentrated upon the portion of material or ware which is nearest to the mulfles.

'I'he word kiln is herein employed to desig- This type of nate any type of furnace or heating device in said end walls and webs extending from the bottom to the top of said outer wall. 1

2. A muie adapted to be incorporated lwith the walls of a kiln and .co-operate therewith to form a combustion chamber, said muilie compris.- ing an outer wall corrugated on vertical lines from side edgefto side edge thereof, websextend-k ing longitudinally of said outer wall and disposed at right angles to said outer wall and in spaced relation between the side edges thereof, said webs being formed integrally-with said louterwall, and an inner wall corrugated-on vertical lines from side edge to side'edge thereofrand integrally connected to said webs, said inner wall having a length less than that ofY said webs.

3. A muiiie adapted to be incorporated with the walls of a kiln and cooperate therewith to form Va combustion chamber, said mufile comprising spaced inner and outer walls each corrugated on vertical lines, the corrugations on one wall being related to those on the other wall to dispose all portions of said walls in parallel relation, each corrugated wall being provided on its inner side with integral, vertically extending walls disposed at right angles thereto and in alinement with the vertically extending walls on the inner side of the other corrugated wall and arranged to cooperate therewith to reinforce said inner and outer walls.

HARRY M. ROBERTSON.

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