US1416726A - Burning ceramic wares and apparatus therefor - Google Patents

Description

T. G. lVIDOUGAL.

BURNING CERAMIC WARES AND APPARATUS THEREFOR.

APPLICAUON FILED JULY I8, V921.

Patented May 23, 1922.

E Emhmqu T. G. IVICDOUGAL.

BURNING CERAMIC WARES AND APPARATUS THEREFOR.

APPLICATION FILED Juv/18,1921.

Suva/wko@ 7547?@ Gf azyal PATENT @FFICEO AN, ASSIGNOR TO CHAMPION IGNITION COMPANY, 0F FLINT, MICHIGAN, A CORPORATION OF MICHIGAN.

Specification of Letters Patent.

Patented May 23, 19532.

Gontinuation of application Serial No. 329,705, filed October 1 0, 1919. This application led July 13,

1921. Serial No. 485,784.

To all 107mm t may concern.'

'Be it known that I. TAINE (i. MCDOUGAL, a citizen of the United States, and a resident of Flint, county of Genesee, and State of Michigan, have invented certain new and useful Improvements in Burning Ceramic vares and `Apparatus Therefor, of which the following is a full, clear, concise, and exact description, such as will enable'others skilled in the art to which the invention relates to make and use the same` reference being made therein to the accompanying drawings, which form a part of this speci- .ication In the firing of clay wares as generally conducted, the burning takes place in large periodic units in which the wares are placed in saggers or fire-clay boxes that are stacked up anywhere from ten to thirty or more high, depending on the height of the partioular ware. For the cruder wares such as bricks, the furnace 0r kiln is usually rectangular, whereas for dish-ware and porcelain and other products of a better class the kiln is round and of from eight to thirty or more feet in inside diameter.

Because it is necessary to heat so large a mass of material from" normal temperatures l to the temperature required to properly bake orvitrify the Ware, it is necessary:y

1.7"That these large units be burned at a very slow rate in order to insure the proper even distribution of heat throughout the great mass. From 24 to 144 hours are required to complete a cycle consisting of placing ware in the kilns, raising the heat slowly to the proper temperature, holding at this temperature until the whole mass is uniformly heated, cooling the large mass, and finally emptying the oven.

2. That a loss be expected and provided for on account of over-fired and under-fired ware due to uneven heat distribution throughout the large mass.

To provide and maintain a department for manufacturing saggers which have an average life of four or live successive burns. These saggers are necessary to allow the ware to be stacked in the ovens, and also to protect it, in the case of coal fuel being used, from the dirt in the combustion gases. In the case of all fuels the saggers also afford a protection for the ware from too sudden heat directly in front of the spaces through which the combustion gases enter the kiln.

4. To employ labor to enter hot chambers of the kiln for unloading and loading the saggers of ware.

For the purpose of eliminating the diiiiculties inherent to the use of periodic kilns, a

continuous process has been developed heretofore which provides for the placing of the saggers or fire-clay slabs upon a refractory car-top and passing the cars through a tunnel from three hundred feetto six hundred feet long, comprising a pre-heating, a hightemperature, and a cooling zone. With this method the saggers or slabs which support the ware are piled in 4mass four to eight feet high on the cars, which travel the length of the tunnel-kiln in not less than twenty-four hours. This method of mass-burning, While it eliminates the necessity of workmen entering the kiln for loading and unloading purposes` and while it reduces the time of firing' somewhat, is nevertheless subject to the loss incident to over-firing and under-firing growing out of the uneven distribution of heat, especially from top to bottom of the mass, and to the expense of forming and handling the saggers.

A leading object of the invention is to provide for both a more rapid and a more uniform burninor of the `ware than has been attained heretofore, whereby the quality of the goods is improved and the percentage loss incident to Veven the most approved prior practice is substantially avoided. rl`o'this end it resides in an improved method for burning ceramic wares or silicate bodies in a kiln of the continuous type, said method consisting in exposing them openly, preferably while in a single-tier only, to the intense heat of a substantially llameless combustion of pre-mixed air and fuel directed against the closely adjacenttop or dome ofthe kiln and refiected thereby down onto the ware. In this manner the individual articles are each subjected to the direct intense heat of say 2300o F. or thereabouts to 2650J F. or possibly higher, as distinguished from the previous practice of piling in mass either with or without saggers; and the time necessary for firing is reduced from twentyfour hours or more in the case of spark plug porcelains to as low as six hours or even less, and a more uniform grade of product is se- .closed spaces from cured. In connection with articlessuch as small floor tile, the temperature may be somewhat lower than stated heretofore.

Again, certain ceramic mixtures of more recent development, which require very rapid and careful cooling to prevent crystallization of the porcelain to an extent sufiicient 'to render it worthless for spark plug insulators, posses, when properly burned and cooled, exceptional toughness coupled with highly desirable electrical properties; these mixtureshave not heretofore gone into extensive use for the reason that no process or means was available by which they could be economically produced.

The invention further consists in a process wherebyv wares formed of mixtures having these characteristics may be produced on a commercial scale, said process consisting in passing the articles through a continuous kiln in the manner stated in the preceding paragraph at a speed such that the cooling takes place in less time than would enable the formation of the objectionable crystalline structure. The equivalent of this process could not be attained with the wares stacked up in saggers for the reason that the necessary rapid and uniform cooling could not then be attained, but by exposing the wares in single tier formation all cool quickly and at substantially the same rate.

Again, vthe invention consists in a continuous kiln of the type set forth wherein the Ware is placed directly on the upper surface of the car or other carrier or in 'open trays as distinguished from saggers,

Which latter are so designed that they may be placed one on another to form enwhich the combustion gases are more or less excluded, and in which spaces cooling is more difficult and less eicient.

- The invention also provides trays or other ware supports, the only permanent sides of which are positioned along the outer side of the. car or carrier to prevent the spark plug porcelains or other wares being treated from fallin off, the other sides of the tray or support eing preferably provided with temporary retaining strips of metal or of some combustible material such as cardboard, whereby the ware is prevented from falling off when the trays are being handled prior to being placed on the cars or other carriers. In this manner an increased carrying surface is secured and the wares, particularly when small, are more fully exposed to the direct heat.

A further important object is to enable the heating and cooling steps to be effected at an increased rate as compared with that necessitated by the use of cars on which both the Wares and a large mass of refractories are necessarily carried. While this may be accomplished in various ways, I prefer to.

form the ware-supports as thin slabs or trays of highly refractory material which themselves ride on suitable, conveyor-elements of heat resisting and insulating material, the necessarybod or backing of fire brick and insulating )rick (heretofore carried on the cars) being stationary. In this manner the very large quantity of heat necessarily -wasted in the cooling of the large moving mass of the kiln as heretofore constructed is saved, and the time element incident to heating up and cooling down is further reduced.

An additional object is to prevent the` current-of air to which the Wares are preferably finally subjected for cooling from passing into the highly heated zoneV of the "kiln, this being accomplished by means of a movable baille which conforms to the upper surface of the carrier without interfering with the passage of the wares.

As stated heretofore, the present invention differs from prior practices in that mass-firing is avoided, and for this purpose the wares are placed on the movable car tops, trays or other carriers in a single open tier or so arranged as to be directly subjected to the downward radiation or reflection of heat from the over-lying arch wall of the tunnel, this wall being in turn intensely heated by blasts from burners wherein air and gas fuel or air and oil are premixed in the proper proportion to produce substantially flameless or surface combustion, that is, wherein there is substantially no excess of either air or fuel, or wherein a small excess of oxygen is' admitted for the purpose of burning out organic matter con- -tained inthe raw porcelain. Thev articles, for example spark plug porcelains, are thus subjected directly to the intense heat and vitrify substantially uniformly without the loss,I or variation in product incident to the previous continuous kiln practice. spark plug insulatorcompositions as require it may be subjected to controllable neutral or reducing atmospheres for the purpose of developing finished structures best obtained under such conditions..

In the manufacture of certain small articles, such, for example, as thin units of mosaic tile fiooring, butter pats, saucers, plates, etc., it is found that the article may Such be stacked in more than one layer or tier,

other so as to form vertical columns, (or otherwise piled in such manner that the several sides of the articles are exposed) these individual columns in effect being the same as the individual porcelains more particularly shown in the drawings. It is evident that the multiple tier formation so defined is nothing more or less that a modification of the single tier open formation.

Applicant believes himself to be the first to employ the open small mass formation, as distinguished from the usual closed or protected mass formation; the absence of anything in the nature of saggers or other kiln refractories interposed between the source of heat and the wares to be fired, together with the continuous nature of the furnace, permits direct application of the heat and' gives rise to results and economies not heretofore attained.

In the drawings,

Figures 1 and 1a are central vertical longitudinal sections each showing substantially7 one-half the length of the kiln, Figure 1 beinnat the charging end;

Figures 2, 3, 4 and 5 are sections on the lines 2 2, 3 3, 4 4 and 5 5, respectively, of Figure 1; v i

Figure 6 is an enlarged vertical transverse section showing the article retaining sides or elements of the trays which are preferably used when the latter are of less width than the carrier;

Figure 7 is lan enlarged vertical section through the adjacent end portion of two of the cars appearing in Figure 1, showing the preferred manner of placing the trays the-reon to prevent the combustion gases from gaining access to the iron wheels and other parts; and

Figure 8 is an enlarged transverse cross-- section showing a modified construction whereon the wares are carried.

The actual construction of the kiln is subject to considerable variation. As shown in Figures .1, 1, 2, -3, 4 and 5, it is built up on a concrete foundation 1 whereon are supported suitable tracks or the equivalent 2 along which the cars 3 are slowly moved from left to right, Figures 1 and 1a, by suitable propelling means, not shown. To seal the joints between the brickwork 4 and the cars, the former is extended inwardly to form ledges 5 beneath which sand boxes 6 are provided, as by means of the angle irons 7, and the cars are equipped with depending plates 8 that drag in the sand. The car bodies conform fairly closely to the walls,

including the ledges 5, so that but little space exists through which the subjected to heat.

It will be seen that the kiln comprises three zones, namely, a pre-heating zone, a high-temperature zone, and a cooling zone. The pre-heating zone is preferably provided sides of the car are with a series of overhead baiiies 9 which reach down nearly to the wares on the cars and thereby divide, the structure up into a plurality of chambers 10. 10', 10, etc., in which the temperature increases from left to right, Figure 1. A suitable outlet.12, that may be closed by a damper or slab 13, is provided for the waste gases. The temperature of the wares and cars is thus gradually raised in the pre-heating zone to a point where they will safely withstand the highest temperature available, whereupon they pass into the high-temperature zone.

Both walls of this zone are provided throughout their length with upwardly and inwardly inclined passages 15 directed substantially toward the longitudinal mid-line of the tunnel dome or arch 16, which is here formed of material of the highest refractory nature; and through these passages gaseous or oil fuel and air pre-mixed in substantially such relative proportions that there is enough air, and practically no more than is required to completely burn the fuel is directed in blasts which may easily be made to maintain the dome substantially white hot in the event spark plug porcelains are being treated, or at a lesser temperature when such is desirable by reason of the nature of the ware, as in the case of enameling or coating iron ware This flameless combustion generates unusually high heat in an exceedingly small space and has substantially no coloring infiuence on the ware, although the latter `is fully exposed.

From the high-temperature zone, the cars pass closely under the fiat lower surfaces of a baffle arch or space made up preferably from highly refractory blocks 20 of carborundum or the like backed by some cheaper insulating filling 21, whereupon they emerge into an area in which they are subject to indirect cooling brought about by a circulation of air through the kilnwalls, preferably in the manner best indicated in Figures 1a and #1. As shown therein, the air is admitted to the interior of the tunnel wall through a passage 23 and from there iows upwardly, transversely across the kiln, and downwardly, back and forth in a series of passages, or rather in a continuous passage 24 that leads toward the highly-heated zone and communicates with a stack 25. ln this manner the coolest portion of the air current is opposite the cooler portions of the tunnel which tends to prevent warping and cracking of the walls. The moving cars next enter a water cooled section of the tunnel wherein water is circulated through suitable piping 28 disposed just above the level of the wares, the flow preferably taking place toward the middle of the tunnel. ln this manner the wares are very gradually and definitely cooled down and might in some instances then be removed immediately from the kiln, but it is preferred to continue the cooling process through the medium of an extension chamber or jacket 30 to which air is supplied by means of the pipes 31. It will be understood that the construction of the cooling zone is subject to considerable variation.

Asis best indicated in Figure 6, the wares, particularly when in the form of small articles such as spark plug insulators 35, are

` only on one side of the trays, and to prevent the articles from falling ofl' the other three sides, when the trays are being handled, by means of suitable thin retainers such as the rectangular loop 39, one edge of which fits over the rib 87'. IVhen these loops are made of card-board or the like they burn away and leave the porcelains fully exposed; if constructed of metal they are removed after the trays have been placed on the cars or conveyor and before the car or conveyor enters the kiln. By allowing the trays of one car to bridge the joint between it and the next, the combustion gases are prevented from passing down about lthe wheels and other iron work of the car and kiln. The joint may bejfurther sealed and the refractories relieved of direct pressure on one another by facing the joint, preferably along its lower edge, with an lasbestos rope or the like 40 secured to one of the cars in any suitable manner; for example, each car may be provided with an angle facing 41 to onel or both of which the rope facings may be ato tached.

In order to prevent the air which enters through the pipesl from passing into the hotter portion of the kiln, I preferably provide a baille plate 42, Figure l, pivoted at 43 and having its lower edge arranged to drag`over the porcelains as they pass into the air cooled space.

It will be observed that the cars 3, which may be of the conventional type, necessarily include, as a protection for the wheels and .other metal Work thereof, a large mass or body of refractory and insulating material which must be heated up and cooled down at each passage of the car through the kiln, thereby causing costly losses both in time and heat. In order to effect a saving in these particulars, I preferably construct the kiln in the general manner shown in Figure 8,2Wherein 50 indicates suitable conveyor elements-as shown, rollers-constructed of refractory material such as silicon carbide yzirconium compounds, corundum, etc., upon which the thin refractory carriers or trays 51, also preferably of the same materials,

are carried, it being understoodthat there are a series of`such rollers spaced from each other longitudinally of the tunnel distances considerably less than the length of the carriers. The floor of the tunnel is built in close to the over-hanging sides of the trays and between the lines of conveyor elements Awith fire brick and insulation brick or material 52-53, so that the heat which would pass into a car body of the conventional type is absorbed by the stationary mass and made .use of to heat up the thin on-coming refractory slab or tray. In this connection, it 'will be understood that the drop in temperature throughthe tray or carriers 50 is relatively small, the temperature immediately beneath the carrier being too high to permit the use of metal rollers in the high heat zone espe- Acially, although metal rollers or conveying mechanism could be employed in parts of the pre-heating and cooling. In the construction shown, the refractory rollers are of sufficient diameter to protect the shafts 54 on which they are secured, and the 'latter extend outside the furnace to lubricated bearings 55. By forming the carriers or trays' and the wheels with associated bearing and guiding surfaces 56-57, the former are guided properlyfrom end to end of the kiln. Obviously, the rollers may either be of the driven or of the free running type, in which latter case any suitable means for pushing or propelling the slabs may be provided. Again, while I have shown the refractory conveyor elements in the form of rollers, it is clear that heat insulating con'- veyors of different construction, such, for` example, as the reciprocating or step-bystep type, might be used.

uF rom the foregoing it will be understood that the wares in all cases travel'. through the kiln continuously from end to end whether the movement be constant or stepby-step, and it is in this sense that the term continuously is employed in some of the claims. i

' This application is a continuation of my application for United States Letters Patentl Serial No. 329,705, filed October A10, 1919.

I claim: 4

1. That improvement in the art of burning ceramic Wares which consists in continuously passing said wares throu h a kiln having a pre-heating zone, a hig -temperature zone and a cooling zone, and maintaining said Wares openly exposed to radiation from the under surface of the ceiling of the kiln in the high-temperature zone fora period suiiicient to insure thorough burning throughout the whole mass of said wares, said under surface being intensely heated by combustion in the space between it and the wares.

2. That` improvement in the art of burning ceramic wares which consists in slowly Leiavae passing said wares through a continuous kiln while exposed openly in single tier formation to the direct action of the intense heat of substantially flameless combustion of pre-mixed air and fuel and maintaining said waresin the high-temperature zone for a period sufficient yto insure thorough burning throughout the whole mass of said wares.

3. rihat improvement in the art of burning small ceramic wares which consists in passing said wares, while openly exposed to radiation, through a continuous kiln embodying a high-temperature zone having a dome immediately above and closely adjacent the wares, the under surface of said dome being intensely heated by combustion in the chamber through which said wares pass, and maintaininr` said wares in the high-temperature, zone for a period sufficient to insure thorough burning throughout the whole mass of said wares.

4. That improvement in the art of burning ceramic wares which are susceptible to the formation of objectionable crystalline structure on slow cooling, which consists in passing said Wares through a. continuous kiln having a pre-heating' zone, a high-temperature zone and a cooling zone, the time during which the passage of the wares through the `colling zone is effected being less than the period for the formation of said objectionable crystalline structures..

5. In a continuous arched kiln for burning ceramic wares, a car arranged to travel through the kiln, and having a body of heat insulating material, a thin substantially Hat tray of highly refractory material resting on said body and. freely removable therefrom to permit positioning of the wares in a single tier thereon, while the tray is detached from the car, said wares when so positioned bein open, both on top and at the sides, to the direct action of heat reflected from the dome of the kiln and exposed to direct contact with the combustion gases as they travel Atoward the charging end of the tunnel.

6. ln a continuous kiln for burning ceramic wares,

a car arranged to slowly travel through the kiln, and having a body of heat insulating material, a thin substantially flat tray of highly refractory material resting on said body and freely removable therefrom to permit positioning of the wares in a single tierthereon, the trays being provided with thin low edges whereby the wares are p revented from falling ofi" as the trays are placed on the cars.

7. In a continuous kiln for ramic wares, a series of cars arranged to travel through said kiln from end to end, said cars including bodies of heat insulating material each spaced somewhat from the bodies of the adjacent cars, and thin low trays of highly refractory material-resting burning ceon said bodies and therebetween, said for the wares.

8. In a continuous kiln having a preheating zone, a high-temperature zone and a cooling zone, thedatter including a section through which air is circulated, means movable through the kiln for carrying wares being burned therein, and a swingable baffle tending to shut off communication between said section and the rest of the cooling zone and having its free edge movable with the movement of the carrying means to permit the passage of the latter thereunder.

9. That improvement in the art of burning ceramic wares which are susceptible to the formation of crystalline structure on slow cooling, which consists in passing said'wares through a continuous kiln having a preheating zone, a high-temperature zone, and a coollng zone, the time during which the overlapping the spaces trays forming supports passage of the wares through the colling zone is effected being such that the formation of said crystalline structures is regulated by a predetermined manner.

10. That. improvement in the art of burning ceramic wares which consists in contin,

uously passing said wares while openly exposed toradiation through the high-temperature zone and the cooling zone of a kiln, the high-temperature zone having a dome below which said wares pass in close proximity thereto, said dome being intensely heated by heat generated between it and said wares, said kiln also having a pre-heating zone through which said wares are passed before entering the high-temperature zone.

ll. That improvement in the art of burning small ceramic wares which consists in slowly passing said wares through an arched continuous kiln and immediately below the g arch of sa1d kiln while said wares are openly exposed to downward radiation from said arch and while the under surface of the latter is exposed to the direct application of heat of an .intensity at least as great as that of substantially flameless combustion of premixed air and fuel. 12. That improvement in the art of burnlng small ceramic wares which consists in passing said wares, while separated from the laterally adjacent wares so as to be openly exposed to radiation, through a continuous kiln embodying a high-temperature zone having a dome immediately above and closely adjacent the wares, the under surface of said dome being intensely heated y combustion which occurs substantially wholly in the space immediately underneath said surface, and maintaining said wares in the high-temperature zone for a period sufficient to insure throrough burning throughout the whole mass of said wares.

In testimony whereof I affix my signature.

TAINE G. MCDOUGAL.

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