US2600306A - Kiln for heat-treating materials - Google Patents

Description

June 10, 1952 c, UPSCOMB 2,600,306

KILN FOR HEAT-TREATING MATERIALS 4 Sheets-Sheet 1 Filed May 28, 1948 Pair/ck C. L/ scomb Q I VENTOR. Q Q Wm B ATTORNEYJY June 10, 1 P. c. LIPSCOMB KILN FOR HEAT-TREATING MATERIALS 4 Sheets-Sheet 2 Filed May 28, 1948 m N wm m Lm w A w k m W T. o P

a BY

HIM I June 10, 1952 P. a LIPSCOMB 2,600,396

I KILN FOR HEAT-TREATING MATERIALS Filed May 28, 1948 4 Sheds-Sheet 3 [Iil Mum E Pafrvc/r C. L/ 500mb 1 VENTOR.

Arrok/vz m June 10, 1952 P. c. LIPSCOMB 2,600,306

KILN FOR HEAT-TREATING MATERIALS Filed May 28, 1948 '4 Sheets-Sheet 4 Lo It) ATTORNfVS Patented June 10, 1952 KILN FOR HEAT-TREATING MATERIALS Patrick C. Lipscomb, Bellaire, Tex., assignor of one-half to The Featherlite Corporation Application May 28, 1948, Serial No. 29,841

1 Claim. 1

This invention relates to improvements in kilns for heat treatment of materials such as clay, shales and the like and a kiln therefor.

Heretofore in kilns for treating materials at very high temperatures wherein the kiln employs an endless conveyor for conveying the material to be treated through the kiln, it has been thought necessary to employ a conveyor surface composed of slabs of refractory material and usually a thin film of sand or other suitable granular material is spread over the refractory slabs to serve as a parting compound. These refractory slabs have not proven entirely satisfactory, but it has been thought necessary to use such materials because.

of the deleterious effect that high temperatures have upon metals. It has also been considered necessary in the past to pre-dry clays, shales, and the like at temperatures ranging up to 900 F. before subjecting'the material to higher temperatures required in the treatment in order to prevent portions of the material from popping or exploding off the main body of the clays or shales. This pre-heating treatment is both expensive and time consuming. In addition when it has been desired to treat clay products, shales and the like to provide a bloated material, it has been deemed necessary to spread a thin layer of granulated clay or the like upon the conveyor and pass this thin layer of material through the kiln where it i subjected to bloating temperatures ranging from 1900 F. to 2200 F. This treatment is so slow that rotary kilns have been resorted to for the purpose of forming light weight or bloated materials and even then the results have not been satisfactory. I I

It is an object of this invention to provide a kiln for treating materials such a clay, shale, and the like at elevated temperatures in which a metal conveyor may be employed for conveying thematerial to be treated through the kiln. 7

Another object is to provide a kiln for treating materials at high temperatures wherein an endles metallic conveyor carries the material through the kiln and a means is provided for protecting the material of the conveyor from ex posure to the temperature within the kiln.

Still another object is to provide a kiln with a conveyor for conveying material to be treated through the kiln in which a flat supportsurface i closely associated with the conveyorfor supporting a layer of granular insulating material.

covering the portion of the conveyor which extends through the kiln and means is provided for continuously applying a layer of insulating material to the surface.

2 Other and further objects of this invention will appear from the following description. 4

The accompanying drawings, which form a part of the instant specification, are to-be read in conjunction therewith, and wherein like reference Fig. 4 is a view taken along the line 4-4 in' Fig. 3 in the direction of the arrows;

Fig. 5 is a side view of one of the links from which the chain shown in Figs. 3 and 4 is fabricated;

Fig. 6 is a detail or fragmentary view of the discharge end of the kiln shown in Fig. 1;

Fig. 7. is a side elevational View upon a fragmentary scale illustrating the stacked arrange- 25 ment of material to be treated upon the insulation layer which covers the conveyor;

Fig. 8 is a plan view of the kiln shown in Fig. 1; Fig. 9 is a view illustrating a modified form which the material to be treated may assume;

Fig. 10 is an enlarged front elevational view of the shoe for regulating the thickness of the layer veyor in the kiln of Fig. 1; and,

of granular insulation material covering the con-Q Fig. 11 is a graph the curves of which may be employed to determine the required thickness of the layer of granular insulation material.

Ingeneral this invention is concerned with the heat treatment of materials, such as clays, shale or the like at elevated temperatures. The invention is especially adapted but not limited to the treatment of bloatable ceramic materials such as certain clays and shales or cintered material to form light weight expanded objects. By way of illustration and not by way of limitation the invention will be described in conjunction with its 7 application to the bloating of clay and the like. The material to be treated is preferably formed into objects having sufiicient strength to support their own weight and having substantially uni-.

form wall thicknesses. These objects are placed upon a moving hearth and pass through a kiln within which the temperature is maintained at bloating temperatures usually within the range of 1900 F. to 2200 F. 0

During this bloating period, the material aswithin the kiln. For this reason a layer of granular or finely divided insulating material is placed over the conveyor and supported on a flat surface which is associated with the conveyor. Of course the insulating material should have a fusion point greater than the temperatures to. which" it will be exposed within the kiln. It has been found that the thickness of the layer of insulatingmaterial required for given conditions of time oi treatment, permissible temperatures of the'conveyor, and temperature within the kiln can be determined experimentally-- ora' safe thickness may be determined'by use of a-mathematical exe pression hereinafter more fully developed.

It is well known that practically all clays" or shales; under ordinary conditions, if rapidly heated to temperatures exceeding 900 F. will have fragments exploded off probably due to theformation ofsteamwithin the materialitself. It has been found, however, that if the clay or shale is quite moist so-as tocontain free water=that= this spoiling, exploding, or popping off-'of-the material-is eliminated. If the moisture-content-of the clay orshale is-adjustedtopermit 1 forming of the material under pressure, such as in what is commonly-known to the industry as pug-mill where the material is extruded through dies, these forms or objects may bepassed directly and quickly into a kiln at temperaturesbetween-1900 and 2200" F. for.

the purpose of bloating the material. Thelcus tomary pre-drying at relatively low temperaures may be dispensed with, thus eliminating the expense' involved in the pro-heat treatment .and also reducing the time oftotal treatment.

Usually-in the. adjustment -of the moisturecontent of the material, particularly where the:

material-has been dug for several daysandlhas lain exposedto the'atmosphere, it is necessary to addwater-to-the-clay; or shale inorder togive it sufiicient plasticity to be formed i into self-supporting forms whensubjected to pressure On the-other-hand; if the material is taken directlyfr'ommarshy-or as in a pug mill.

swampyground; the material may contain such a highdegree; (if-moisture: as to require some drying before itis introduced into -theforming machinery. In any event; themoisture must be adjusted and it has been found that when thisrelative moist material, as it extruded from the pug --mill,'- is subjected to the. elevated temperatureseven as high as bloating temperatures, thatquite-unexpectedly no explosion takes place.

Afgreat number of claysand shaleshavebeen treated in this fashion; including ashaleobtainedat- Strawn; Texas; and several I varieties of Beaumontclays and in no instance have these clays-hada--tendency to s pop or explode when subjected in'the moist-state directly to the intense heat ofthe-kilnfor the-purpose of causing theclays to bloat. Thesesamematerials, on-theother hand;- are-vry; bad about spoiling and exploding; or-pcpping-oifunless this moisture content adjustment is first" made -01 unless the clays are first subjected to'a -p'rehe'ating' treatment: at temperatures preferably 4 between 400 F. and 800 F. for some one to six hours.

Referring now to the details of the kiln shown generally at In in the drawings, the kiln proper is a furnace having Walls made of refractory material 3| or having refractory material lining. The upper portion of the kiln may carry a layer of sand or the like 32 for added insulation. The kiln l6 has a fire. box H with suitable openings i2' therein communicatingwvith' pipes l3 for supplying fuel such as gas, powdered coal, oil, or the like. This fire box extends substantially the full length-of the kiln and is separated from the heat treating chamber l4 by a perforate wall or partition 15. The heat treating chamber from the fire box through the chimney causing the heated gaseous medium from the fire box to passthrough the. heating chamber substantially normally tothe. direction of travelof the (3011-.- veyor [8 through the. heat chamber.

The structure just above described may. be supported on suitable supports l9 which may carry-a. metallicplate or the'like' 28 upon which the kilnrests. heat treatment chamber is somewhat lower than the, bottom .of the fire box II, as is'shown at 2|.

This, bottom may be formed of refractory ma-- terial supported. byplate 22 but this isnotessential. whenthe kilnis tobe operated and constructedin accordance withthis invention, for the insulating material that protects the conveyor from the extreme temperatures of thekiln also will protect. the, bottom of theheatr treating. chamber-and ametallicr structure or surface :may be employed. alone.

Referring; to; the conveyor 18,- it-will beseen that. the. endless conveyor extends sprockets 23 andflZdat-opposite endsof the kiln. The sprocket 24:.is, the driven sprocket and. has a drive connection with driven sprocket 25 ineluding. shaft. 26 upon which both sprockets 2 4 and 25. are. mounted. Sprocket 25 -has:a suit.-

able drive connectionzthrough chain 21,- sprocket 28 and. gears, not shown in:thedrawings with a, suitable prime mover/29.

has ahat top surface.

provides a support surfacel ins close'proxhnity tothe conveyor. and'associated: with the conveyor for supporting alayenofsand 33. or other suitable granular material. above the. conveyor. This insulating material has aiusion or melting point greater thanthe temperature to:b e..encountered within the kiln. Av trough is 1 provided within the kiln and: through the heat. treating chamber thereof; by.thev offset; position. .of the bottom 2|, relative toiztherefractoryrbot?- tom of the adjacent-firebox .andchimney. This:

trough isextended;from..the;.entrance Illa; of

the kiln toward sprocket:;23- byproviding; side; wall members. for thepart-ofbottom 2tthat extends from the .kiln. Theseside'wall mem-. here are supported by plates a .mounted on uprights l 9. These plates also:suppOrt the-shaft for sprocket 2 3;

The layer 33 of granular.;insiilating ;.material,-, i such as sand, diatomaceous earth,-silicon;carbid;.

Preferably the bottomof the about pulverized fire brick, is distributed upon the fiat top surface 2| to cover the conveyor by hopper 34. The hopper is supported adjacent sprocket 23 by legs 34a footing on plates 30a. Hopper 34 has an adjustable shoe 35 which may have its vertical position adjusted to determine the thickness 'of the layer of insulated material to be deposited over the conveyor. This shoe is detailed in Fig. and has slots to provide for bolting the shoe to the hopper in a selected position. The layer 33 of granular material is carried along by the conveyor. The conveyor chain shown in the drawings pulls the material through the heat treating chamber with practically no disturbance to the upper surface of the sand. The speed of the conveyor is relatively slow and depends upon the length of the heat treating chamber and the time of treatment required. At such slow conveyor speeds, the body 33 of insulating material behaves substantially as a continuous slab of material.

As the chain moves through the trough formed by bottom 2| the chain apparently floats in the sand and it has been found that there is extremely little or practically no wear either of the chain or the support surface provided by the top of bottom surface 2|. Preferably the sprockets 23 and 24 which carry the conveyor should have their upper peripheries, at the valleys between the teeth, slightly above the end portions of the bottom member 2| and inch has been found satisfactory. This allows the conveyor to sag down onto the support surface and materially reduces the wear.

It is contemplated that in lieu of the support surface 2| a conveyor may be employed of the type which carries its own support surface. It is difficult to provide a seal between the support surface carried by the conveyor and the side walls of the trough and for this reason the arrangement shown in the drawings is preferred. With this arrangement there is no possible way for the sand or other granular insulating material to leak from operative position.

A means is provided for distributing the sand from the exit end of the conveyor adjacent sprocket 24 into hopper 34. This means includes chute 36, endless conveyor 31 supported on sprockets 38, 39 and 40, and laterally extending chutes 4| and 42. A drive means such as prime mover 43 is associated with one of the sprockets as 39 in the drawings. By this arrangement the sand or other granular insulating material drops through the conveyor and from the support surface at the end of the bottom 2| adjacent the exit of the kiln, upon laterally extending chute 4|. This chute distributes the sand into chute 36 where it is moved along by conveyor 31 and carried' to the upper end of the chute. At this position it falls into the laterally extending chute 42 and drops into hopper 34. This means for moving the sand is external of the kiln and the heat accumulated by the sand in the kiln is dissipated to the atmosphere.

Also associated with the conveyor I8 adjacent the exit of the kiln is a chute 44 residing just beneath sprocket 24 and communicating with a hopper 45. The material discharged from the kiln falls over the end of the conveyor at the discharge end and drops into the chute 44 and drops into receptacle 45 where it may be disposed of in the manner desired.

It is preferred to fabricate conveyor l8 from mild steel for the reason that the conveyor of this material has great strength, is economical, and

when protected by the layer of granular insulating material from the extreme temperatures of the kiln may be maintained at a temperature below the temperature at which it would be deleteriously affected. It is contemplated that high temperature alloy steels may be employed for this purpose and that when so employed the thickness of the sand can be substantially reduced. Of course if the kiln is to be operated at relatively low temperatures, that is, temperatures at which the alloy steel conveyor is able to withstand, no sand need be used at all, as long as the character of the material to be treated would permit it to be placed directly upon the alloy steel conveyor. However, due to the great cost of these alloys it is not preferred at this time to use a conveyor fabricated of such alloys. Of course, alloy steels presently known may not be heated to the temperature range required for bloating ceramics.

The chain I8 is made up of a plurality of links 46 detailed in Fig. 5, having apertures 46a. These links are strung on rods 41 with spacer washers 48 holding the links in proper spaced relation upon the rods. This arrangement of parts for the conveyor has been found entirely satisfactory for advancing the bed of insulating material over the support surface 2|. With this arrangement it has been found that the bed 33 moves substantially as a solid body with practically no vibration or movement of the surface of the insulating material other than in a forward direction. I

It is contemplated that other forms of conveyor arrangement may be employed, such as wire meshes and the like.

In operation, the kiln is fired up until the desired temperature within the heat treatment chamber has been obtained. During the heating up operation or at least the last stages thereof. the chain or conveyor should be covered with the insulating material to protect it from overheating as the temperatures rise within the heat treating chamber. Preferably as the temperature within the chamber commences to rise the prime mover 29 is tsarted in order to advance the conveyor through the heat treating chamber reducing any likelihood of over-heating the conveyor. The arrangement of the shoe 35 upon the hopper makes it possible to selectively gauge the thickness of the layer of insulating granular material to be deposited upon the conveyor. Prime mover 43 is started to drive sprocket 39 and thus drive conveyor chain 31 to distribute the sand from the discharge end of conveyor l8 to the hopper 34. The chain 31 carries the granular material along chute 3'6 and it falls into the lateral chute42-and thence is deposited within the hopper 34.

When the proper treating temperature has been reached within the kiln, the material to be treated is deposited upon the upper surface of the insulating granular material or bed 33. In the operation to be carried out is to treat a bloatable ceramic material the material may be deposited upon the bed 33 of insulating material in the usual fashion in granular form in a thin layer. B

but due to the slowness of this operation it is much preferred to place pre-formed objects upon the bed of sand 33 in the manner shown in the drawings.

Fig. 7 shows the preferred open ended form of the material at 49 but it is to be understood that other forms may be employed. The thickness of the wall affects the time required to complete the treatment and in the interest of high c eeses rate of production, a thickness of 17.5. inch. is usually the thickest wall that should. be used. A wall thickness: of /8 of; an. inch. is preferred. A tubular form with. aninternal. diameter of one inch and an outside diameter of one and three.- fourths inchesv has been foundentirely. satis.- factory and such forms. are capable of. maintaining their shape when. stacked eight high. upon the moving hearth.

' The forms should be distributed upon the bed 31 of insulating material? in such fashion as to provide passageways ft and 51' through the stacked: material. These passageways extend substantially normal to the direction of travel of-the conveyor and are provided by the. spaces between. adjacent tubular objects-l9 and by the openings. through the objects 49 themselves. These objects. are open-ended hollow objects in the forms of tubes and may be formed by the. usual pug mills well known to the art but. not shown intlledrawings. These tubes or pipesare placed hand upon .the bed of insulating sand but mas be. distributed thereon by machinery. The plasticity of, the clay or shale. is such that the objects are, not only self-supporting but also will support the layer of several other such objects when-.instacked relation.

The conveyor l8 with the superimposedioover. of. insulating granular material 33. provides in effect a. moving hearth for carrying the. material to. b e treated through the kiln. Material passes slowly, through the heattreating chamber of. the kiln and the heated gas or gaseousmedium from the fire box circulates-through and past: the objectscontinuously passing through the passages 50 and 5| subjecting the objects to-betreateduniformly to the heat. treatment. By this; method the: rate of production of the kilnis: greatly. increased over the methodof depositing a. thin lay erof a granular.- material to be treated; upon a moving; hearth and carrying'it throughthe. kiln. Thisis true because the thicknessofgsuclra film oimaterial to be; treated preferably should. not be; greater than about three-eighths ofan. inch.

The rate of movement of. conveyor l8 is-.ad lustedto provide a pr per th. of; heattreatmentof the material so that it is; discharged: at the expiration of the proper heat treatment. The treated; material is permitted to fallifrom; the. conveyor on to chute M and into; a suitable-receptacle 45. Howevenbefore the treatedjmaterial is discharged the granular insulating material isdischarged intolateralchute H and is conveyed back to the hopper 3-4.- for. re.-use-,. cooling en route.

Wherethe material is bloated .andis tobe; used forlight. weight aggregatein making light weight concrete and. the like the bloated objects A'Qrare removed from the container 45. anditaken to a suitable mill for, breakingintothe-proper size.

Itis contemplated that-the forms-ofithe-material to betreatedmay be adjusted-intoeany-suitable shape or desiredshape'so 10ng .-as;the shapes mayxbe. arranged upon the moving hearth :insuch manner as to provide for substantially even heat treatment. In other'words, so as to provideipasasages for circulating: a heated gas between; surfaces of. adj acentobjects and if: desired. through passages formed in the objects themselves.v Pref.- erably these flow passages for heated gasashould be. in a direction substantially normal to; the direction of travel of .the conveyor.

A modified f0 rm-in which the material. to; be treated may be shaped in apugmillis. shown-in 10 at. 52.' Inthisformrthematerial hasr plurality of passages53' therethrouglr andthe wall thicknesses of. the solidv portion of the honeycomb. as shown at 54 are substantially uniform. The advantage of this shape or form. is; in the handling and stacking of the material upon the hearth.v

Referring to the layerof insulating. material 33 the thickness. of this, layer must be selected. to providesuflicient. insulation to protect the con-' veyor from the extreme heat: of the kiln and to prevent it from rising, to such a temperature that it would be deleteriously affected. Of course; the temperature which .the conveyormaybe" subjected to will depend upon the materials from which the conveyor is constructed. Formost mild: steel construction the conveyor may-safely be subjected to temperatures in the. order of 700 F., but in order to provide a safety factor it is preferred that the thickness of the layer of sand be sufilcient to prevent the material. of: the conveyor from attaining a, temperature. greater than 500 F. Also, it is desirable to maintain the thickness of the layer of granular insulating material sufliciently great to protect the conveyor in the event of break-downs for a period of time at least as great as thirty minutes over the: time of the pass through the kiln. Thisreduces the necessity of shutting on the heat in the. firebox of the furnace which would otherwise Ice-required by shortinterruptions of the heat treating operation.

Under some-conditions it is contemplated. that special alloy steels capable of withstanding relas tively high temperatures may be employed. Alloy steels are now available which may be safely-operated at temperatures up to 1700 F. However, these alloys are-expensiveand-at the present time it is preferred to use the mild steel materials for theconveyor for this reason. For some operations it may be necessary to heat certainclays; shales or other ceramics at temperatures under 1700 F. If this is true of course the-layer of sand'need not beemployed and the. formed objects of the material to be treated may be. stacked directly uponthe conveyor.

The thickness of the layer of insulatinggranular material may be determined by experimentation and has been experimentally determined for mild. steel conveyors wherein the temperature to be encountered in the kiln is in the neighborhood of 2150 F. This temperature is preferred for most. bloating operations. The initial temperatureofthe granular insulation material was F. and the time. within the furnace was one hour, the normal bloating. operation requiring thirty minutes-and thusproviding for' a thirty, minute. safety factor. The. conveyor was fabricated of; mild steel and the permissible tempera ture was: considered to be 590 F. to provide. an additional safety factor. It wa found that asand layer 1.24 1 inches thick was sufficientunder these conditionsto maintain the temperature of the conveyor'below 500" F. With these same" condi* tions, but with the time within the kilnof' only 3.0 minutes, the sand layer. needbe. only .88 inch With thekilntemperature of 2200 F.) which is. the maximum. bloating. temperature usually en'counteredzin a'kiln,.a..sand layer. 1.2.6 inches deep with-the other conditionsuas set forth-above was found satisfactory. It ispreferredto: use this thickness of sand. in order to provide for a safety factor when materials are. to be bloated.

plot-or graph has been prepared based upon experimentaldata forsfacilitating the calculation 'ofeither the temperature at a point in a 'sandslab rinches below the surface of theslab after anelapsed time ina furnace maintained at "a. constant temperature orthe thickness, .of a

sand layer required for preventing the temperatureof. the conveyor from exceeding apredetermined temperature. V

This graph is shown in Fig. 11 and the data upon which it is based was obtained by a plurality of test runs in a kiln employing a mild steel conveyor chain and employing sand as the granular insulating material. The curve 55 may be used to calculate the sand thickness required with close approximations for furnaces of this general type.

A second curve representing the temperature distribution, neglecting surface resistances to heat transfer and dissipation of heat from beneath the conveyor is given in dotted lines and indicated at 56. By the use of this curve the calculation of the desirable depth of the sand layer which will provide safety for the conveyor may be calculated and will fit any furnace conditions that are likely to be encountered. By experimentation thinner layers of sand or other insulating materials, than those indicated by the curve 56, usually may be found to be satisfactory. Also, by solving simultaneous partial differential equations, the depth of the insulating material may be more closely obtained or calculated. These heat transfer formulae are readily available to those skilled in the art, but their use is so cumbersome or tedious as not to be of practical application.

In using these curves 55 and 56, they should not be exterpolated to long periods of time or to very thin layers of granular insulating material, but these curves will give satisfactory results under average operating conditions.

In the graph the vertical co-ordinate is plotted in accordance with the mathematical expression TI"T T, T

The horizontal co-ordinate is plotted on the mathematical expression In the above expressions, the reference letters have the following meaning:

Ty=temperature of furnace, F.

To=initial temperature of sand. T=temperature of sand at position X at time T. t=time in furnace, minutes.

x=distance below surface, inches.

In the above graph the constant of the equipment, due primarily to the coefficient of distribution of heat of the particular insulation material employed, is introduced into the curve. It is believed that examples will aid in the understanding of the application of the above curves.

Example 1 T =2100 F.; To=100 R; T=400 F.; t=60 minutes; a3=the layer of sand or insulating material above the conveyor.

The expression Solving the expression for is found to equal 1.2 3inches. a

Example Assuming that in the Example 1 conditions, the character and coefficient of distribution of heat of the granular insulating material was unknown, the value of t/x should be obtained from curve 56. In accordance with this, the value of the expression as taken from curve '56 is 11 and solving for :c, a: is equal to 2.33 inches.

By calculations based on curves 55 and 56, thickness of the insulating material may be obtained that will provide adequate protection for the conveyor. This thickness may be adjusted, based upon experience of operation if desired.

It will be seen that the objects of this invention have been accomplished. There has been provided a kiln having insulating means for protecting the conveyor for moving material to be treated through the kiln from the excessive temperatures encountered in the kiln. The arrangement is such that this means for supplying the insulating material to the conveyor may be readily varied to provide proper protection for varied conditions of operation in a kiln.

There has been provided a method for treating material in a kiln by which the rate of treatment of the material may be greatly increased in a given kiln over what has gone before. In accordance with this method all clays, shales and other ceramic materials to be treated may be treated without an expensive pre-heating operation, to prevent spoiling, exploding, or popping off.

From the foregoing it will be seen that this invention is one well adapted to attain all the ends and objects hereinabove set forth together with other advantages which are obvious and which are inherent to the structure and process.

It will be understood that certain features and sub-combinations are of utility and may be employed without reference to other features and sub-combinations. This is contemplated by and is within the scope of the claims.

As many possible embodiments may be made of the invention without departing from the scope thereof, it is to be understood that all matter herein set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.

Having described the claimed is:

In a kiln a furnace with entrance and exit openings, a substantially flat support surface extending through the furnace entrance and exit, a metal chain type continuous conveyor operably mounted with its portion to be loaded extending through the furnace and disposed in close overlying proximity to said surface, and means for distributing at a point exterior of the furnace and adjacent its entrance a finely divided granular insulating material upon the surface in a selected thickness to encompass the conveyor for protecting the conveyor against the high temperature encounted within the furnace.

PATRICK C. LIPSCOMB.

invention, what is (References on following page)

Images