US2493623A - Manufacture of ceramic articles - Google Patents

Description

Jan. 3, 1950 M. E. GATES MANUFACTURE OF CERAMIC ARTICLES Filed Aug. 27, 1946 2 Sheets-Sheet 2 J? 0747 @afes Patented Jan. 3, 1950 UNITED STATES PATENT OFFICE MANUFACTURE OF CERAMIC ARTICLES Major E. Gates, Crystal Lakes, Ill. Application AugustZ'i, 1946, SerialNo. 693,235

10 Claims.

This invention relates to the manufacture of ceramic articles, such as brick, block, etc. Among other objects the invention aims to improve the quality and reduce the cost of manufacture of ceramic products.

The nature of the invention may be readily understood by reference to one illustrative method of manufacture and one illustrative apparatus for practicing the method, described in the following specification and illustrated in the accompanying drawings.

In said drawings:

Fig. 1 is a fragmentary plan section through a tunnel kiln, and showing the ware therein in plan View; 7

Fig. 2 is a diagrammaticview. on a smaller scale of the kiln and ware as arranged in Fig. 1;

Figs. 3 and 4 are similar diagrams showing a different arrangement of ware;

Fig. 5 is a transverse section of a tunnel kiln showing the ware in elevation; and

Fig. 6 is a fragmentary perspective view of a bench or stack of ware.

The illustrative method is shown applied to the making of brick, but it will be understood that it is applicable to other articles which are stacked or associated for processing in rather close relationship. Processing, which includes oxidation and subsequent burning or firing, is carried on in a tunnel kiln Iii which may be either of the circular or straight type. The traveling floor ll embodies .a refractory top l2 whose margins [3 travel in grooves I 4 in the kiln walls 15, thereby to protect the floor rolling and supporting structure from the heat of the kiln. Continuous circular baflles l 6 traveling in a bed of sand I! assist in protecting this structure from high temperatures.

In the straight type the ware is passed through the kiln on a succession of separate cars or floor sections which are introduced at one end and removed from the other end of the kiln. In the circular type the cars or floor units are connected together to form a continuous circular platform surrounded by the kiln Walls except for a small sector where the ware is removed and unburned ware is introduced. Each car carries a bench or stack of ware which is separated by a substantial space (much wider than the passages between the pieces of ware) from the stacks on adjacent cars. In general the ware is arranged so as to provide transverse and longitudinal passages or flues through the bench of such size as to conduct an adequate volume of heating gases. In

the case of brick or similar ware it is advantageously stacked in checker brick fashion comprising superimposed tiers l8 of spaced rows 19 of brick running alternately transversely and longitudinally 'of the kiln. "This spacing thus provides alternate tiers or series of longitudinal gas flues or passages 20 and transverse flues or passages 2|. Even in those circular kilns which .have a continuous type of 'fioor 'or platform (except for expansion joints therein), the circular character of the floor (wherein the circumference of the inner periphery of the 'jflOOI.iS less than the outer) makes it necessary to arrange the ware in separate stacks or benches separated by a space. This is because it would be diificult to stack the ware in a continuous stack due to difference in spacing necessitated by the unequal lengths of the inner and outer portions of the kiln floor. The space between benches is as narrow as practicable but it nevertheless provides a substantial passage through which an excessive volume of heating gases can short circuit.

In tunnel kilns whether they be of the straight or discontinuous type, or the circular type, the heat exchanging gases travel counter to the travel of the ware. Thus cool air is drawn in adjacent the exit end of the kiln picking up heat from (and thereby cooling) the burned ware.

The gases continue to the firing or burning zone Where the temperature reaches that necessary to effect burning of the ware, i. e., 1800 F. to 3000* F. depending on the character of the clay and results desired. These very hot gases then traverse the ware in the oxidation zone of the kiln, i. e., the ware approaching the burning zone. They are gradually reduced in temperature as they approach the entrance end of the kiln, and the pieces of ware are correspondingly increased in temperature from the entrance end of the kiln to the burning zone.

The oxidation zone is of great importance where the clay contains a substantial amount of oxidizable substances and where it matures at relatively low temperatures. In this zone oxida tion of impurities and perhaps other chemical changes takes place, preceded by drying out of traces of water. The temperatures range from 700 F. to 1500 F. depending upon the nature or the material to be oxidized. Very often such 'material as coal or other matter of a vegetable source is found in the clay. It is not uncommon to find very thin strata of vegetable matter or coal in clay beds which cannot by any practicable means be separatedirom the strata of clay. It is important that this matter be oxidized before the ware is raised to burning temperatures, otherescape of gases.

in the kiln. A wreck is obviously serious since it requires shutting down of the kiln and a long delay while the kiln and ware cools sufficiently to permit workmen to remove the ware. Much of the ware will be damaged and defectively burned.

' The result is that the great majority of the gases travel on the outside of the stack of ware where only the exterior pieces of ware are heated.

the exterior of the ware. In such cases relatively less of the kiln length can be devoted to burning, and it is therefore of even greater improtance (than for purer clays) that the ware be efficiently and uniformly raised to burning temperatures. The temperature gradient, preferably, should be 1inear,'i. e., the temperature should rise at a uniform rate, as the ware approaches the burning zone. Thisis desirable not only to provide an opportunity for distribution-of heat throughout the ware and to secure efficient and complete oxidation, but to avoid the sudden increase in temperature which would otherwise occur as the ware entered the hot burning zone. This would result in excessive burning and vitrification of the ware on the exterior of the stack, and insufficient heating of the interior of the stack, no mat ter how efficient the distribution of heating gases throughout the benches. V r

Optimum results, i. e.,maximum speed of travel through the kiln and the best quality of product,

can be secured only if all portions-of the stack of ware be heated uniformly and at the same rate at all points in the oxidation and burnin g'cycles. Uniformity of heating throughout the stack of Ware permits effective control of temperatures which has not heretofore been possible. This in turn makes it possible not only to improve the quality of the ware but to increase the production by increasing speed of travel through the kiln. Ware on the outside of the stack will not be damaged because of the difficulty in-heating the ware on the interior of the stack. Conversely the Ware on the interior of the stack will not be underheated.

Since heating for oxidation and other ment of the ware on the interior of the benches must be effected almost entirely by convection, i. e., circulation of hot gases, it is therefore of the utmost importance that the hot gases circulate efficiently and uniformly throughout the interior of the stack of ware. This has presented a difficult problem and unsuccessful attempts have been made to solve it. Instead of passing through the stack of Ware, the hot gases have heretofore tended to short circuit or take the path of least resistance through spaces around the exterior'of the ware. These spaces are unavoidable since the ware cannot be stacked so as to travel too closely to the surface of the walls or roof of the kiln. These surfaces warp, buckle and expand in unpredictable ways under the high temperatures existing in the kiln so that even if originally built to very close tolerances, they cannot be depended on to retain their original positions. Moreover the ware itself may expand at certain points in the cycle to reduce the, initial clearance. Hence it is the practice to allow a space of about 4 be-. tween the exteriorof the stack and the kiln surfaces, to avoid possibility of a wreck ofthe ware treat- Some gases travel longitudinally through the interior of the stack of ware but since these are isolated from the exterior gases, they soon lose their heat and soon serve no useful purpose. Travel of gases transversely, i. e., from side to side of the stack has been negligible. Various attempts in special kiln design and by the use of fans have been made to improve the transverse flow of gases through the stack of ware but these have been unsuccessful for various reasons, among those being the short circuiting of the gases through the spaces between adjacent benches of ware. Fans are not effective in producing efficient transverse flow at all points in the kiln.

posite points in the stack or bench, thereby causing hot gases to travel through the transverseflues in the stack and to mingle repeatedly not only with the gases traveling through the longitudinal flues but those which travel through the spaces along the exterior of the stacks. This results in an efficient heat exchange which raises the temperature of the longitudinally and transversely traveling streams of gases and corre produce transverse pressure differentials. Preferably the benches 22 are slightly skewed relative to the direction of travel of the ware (indicated by arrow 23), repeatedly to restrict and enlarge the clearance passages 24 along the sides of the benches. In the illustrative method the passages are sharply restricted at 25 at the outermost corners of the bench. Where, as illustrated in Figs. 1 and 2, the benches are similarly skewed, this results in a sharp enlargement of the passage at 26 at one side of the kiln and a gradual enlargement as at'2l of the passage along the other side. This produces pressure differentials transversely of the benches which cause the heating gases to travel through the transverse passages 2! as well as through the longitudinal passages 20 inside the benches. In this connection it should be remembered that the flow of gases through the kiln is counter to the travel of the ware. The term "transverse as applied to flow is used in a broad sense to include diagonal or other flow from side to side of the kiln.

The clearance between the outer corners 28 of each bench is sufficient to avoid contact with any bulging kiln walls, but with the present arrangement contact is not nearly so serious as when the benches are generally parallel with the kiln walls and all portions of the sides of the 1. bench are likely to contact with a bulging wall. In the present case even if the outer corners In the illustrative method the ware 1s soari ranged as to produce pressure differences on op- I should. contactwith a kiln wall, it is not likely o cau a-wreck s nce a d p aced b c o ot e pie ef wer w l fall into t en ar d space behind the corner where it is much less likely towedge between the falls and the. :bench to dis.- place other .br-ick. The result isthat if desired, the clearance at the corner 28 may be reduced withou nc e ing the danger o pa alyz n wreck. The narrower the space ,25 the greater the pressure different als cre ted thereby and the greater the transverse circulation through the :benches.

The dimensions of the ware in relation to the width of the kiln floor determine to some extent the amount of clearance at the corners 28, par,- ticularly if, asis generally the case, the pieces ofware are identical in length. The capacity .of the kiln is therefore not reducedxover the previous square arrangement of benches because the decreased width of the latter arrangement is not sufficient to accommodate additional ware in the bench with safe clearance. Indeed; as presently explained the capacity of the kiln is greatly increased through the ability to increase the speed of travel through the kiln.

.In the illustrative kiln wherein the inner faces of the walls are 55apart, benches of fire brick (which a e 1 n len th), are app xim tely i dth. us n only 'svh le fi ic T length of the bench also 43". The minimum l r nce at he c ne s :28 ma be om 0 and the maximum clearance at the opposite 00rnor-will thus be from 1 0 to .6". The space between adjacent benches, which as stated above.

is generally determined by practical-considerations, is about 4- Fire brick are about 2% in thickness and the spaces between adjacent brick forming the longitudinal and transverse gas passages are about 1 in width. The dimensions of :benches for other differently .d-imensioned ware will of course vary depending upon the wars itself and the relation between the width .of the kiln and the length of .a multiple of the length of the individual pieces of ware which can be accommodated in the kiln. Flues between rows ,of ware vary somewhat as the mass .of the ware so as to carry enough heat in the volume of gases passing throu h the flues, to secure the necessary treatment of the ware.

As illustrated in the arrangement shown in igsndfl a e ra in th o h a ve se passages '21 issue in the diverging longitudinal passage 21 through which they reach the discharge end 29 of such passage. A major part of these gases then travel across the kiln through 5 the gap '30 between adjacent benches. As the transversely flowing gases respectively-reachgeach of the spaces24 at the sides of each bench, they intermingle with and pick up heat from and correspondingly reduce the temperature of the hot gases which short circuit along thesides of the kiln through the spaces 24. Over-heating of the exterior of the benches is therefore prevented. In-the successive gaps 30 the transversely traveling gases also contact with the streams of gases issuing'from the longitudinal passages '20 into the space 3,0 providing an opportunity for heat exchange so that all gases entering the next bench have substantially the same temperature.

It is no longer possible for the longitudinally traveling. gases to cool to a point where they are inefiective.

C ross travel between the benches is caused ;of ours b th pre e di e i l ex st n :be-

twcen the outlets .29 and the inlettl of the .con-

vergin passa e :82 .onthe opposite .side of= the ne t tench, Bctwcenrassa es :2 and 2.1 or the me bench the e a further pressure hcehsesmost or t e as s o th ou h he t ansverse passa es 2. of hat be c issu ng.

n th spawn. cycle i repea ed o each ch. and in the side p s ges Hand c ss pas: sages 30 at the end ofeach bench there is the above described heat exchange with the short cincuiting gases and the longitudinally traveling as s espectivelmth r by equalizing t hea ing effect of all thegases.

.Thus, while a .substantial.yolume of gases still travels through the side pa sages 24 and thr ug the res trictecl .thr oats.. 25, their over-heatingefiect as een liminated. Moreover, the v um so traveling is not as reat as what would travel if he passages er unif m in s o b cause th energy of the gases is dissipated to .a greate e 'i the p sent ar n men T is ene gy can be further dissipated by making the kiln walls rough, as by slightly skewingthe brick of thekiln walls so that their'inner corners are 01;!- setas air-32' (see Fig. 1)

The passages 21 advantageously increase in section so as 'at'least'to equal-the progressive aggregate of the sections of the transverse passages 2| cpening into the diverging passage 121.

There-is then no tendency to convert the -velocity-head of-the gases into pressure head-and thereby reduce-the .pressuredifierential on the transverse passages 21 W-hercgasyelocities do notexceed 5 to 7 miles per'hour, the laws governing flow are not the same as for more rapid-flow. Low flow is sometimes termed' viscous flow as distinguished from tiu'bulentflow -by which gases traveling at higher velocityis characterized. For viscous how the pressure head or zdifierential-required to produce flow varies directly as the velocity and not as the square of thevelocityz-for turbulent flow. A-tilow velocities itiS thus possible to have a greater flow n opo n to higher .yelocitiesj. At some restricted points, such as:25. al ng thes dc o he kiln. the velocities in ordinary kiln operation are probably in excess of 5 ,to 7.,miles per hour, but transversely through th passages 21 the now probably may be characterized as low.fi ow and respond to the laws governin low flow.

Other arrangements of ware than that illus.- trated in Fig.1 will produce similar results. .For example, in Fig. 3 thebenches are skewed in alternate directions. In such case transverse ow from one-b n h to th ex is indicated by the arrow .33 There is little or no cross flow h ou the spaces 3. ween the bench since there is no pressure drop or differential across these passages. Hence there is no opportunity for efficient heat exchange with the longitudinally traveling gases. Furthermore this arrangement more wasteful of .ki ln space. Better results could be obtained by more complex bfinchesi. e. of non-rectangular sections suchas illustrated in Fig. 4 where each row of wareiis.. laterallyoirset from the next. This 101T- settlng :could also be varied considerably as by simulatin the arrangement in Fig. 1. A11 of thesespecialarrangements require vastly more skill in setting and therefore greatly increase costs without compensating advantages.

A further advantage of the rectangular-or duarehenchpfor tr ck and s m rwar is he-b nc can h handled by mech ni a rick oad rs now in use, thus a oiding "the lab rer;

pressure diiferential than at 7 stackingone brick at a time. The brick can be stacked in bench format the brick press, carried through the dryer, and then mechanically'transferred as a unit to the kiln floor. I r The same result I can be accomplished without-the brick loader if the kiln be built with removable car or floorsections each of a size to hold one bench. The bench is then built at the brick press on a floor section which is carried throughthe dryer and then transferred bodily with the bench to the kiln to replace another section removed from, the kiln with its burned brick.

Summarizing: substantial improvement in quality and reduction in cost of production can be effected by the aforesaid method because it permits eflicient temperature control and increase in speed of travel through the kiln. The temperature gradient, .being substantially linear, brings the ware uniformly throughout the bench to desired temperatures in a minimum time. Heretofore ware on the interior of the bench, was insufficiently heated. to complete oxidation at the proper stage, with the result that the gases developed on the interior at a later stage. in the-cycle under higher tempera. tures had difiiculty in escaping because of reduction in porosity of the surface of the ware under such higher temperatures, thereby bloating the ware. Ware with black centers also is chargeable to the action of the high temperatures on incompletely oxidized interiors of the ware. To overcome this speed of travel through the kiln was reduced but with the risk of over-burning the ware on the exterior of the bench. Uniform heating throughout the bench according to the present invention therefore not only makes it possible to increase production by increasing speed, but at the same time to produce more perfect ware.

Another advantageous consequence of the foregoing method is a reduction of the undesirable results of the stack action of gases in; the kiln. The very great-difference in temperatures between the gases on the inside of the kiln and the atmosphere on the outside causes the gases to rise in the kiln through displacement by'cold air entering the bottom of the kiln. This is serious at the entrance end of, the kiln since the current of air along the bottom is counter to the current of heating gases and thus tends to neutralise or reduce thecurrent along'the lower portion of the kiln and correspondingly in-v crease it at the top. The arrangement of ware in the kiln according to the aforesaid method very substantially increases the resistance to travel of gases entering along the bottom-of the kiln and correspondingly resists increased travel in the opposite direction of the hot gases at the top of the kiln. Thus the tendency to nonuniformity in heating between the top and the. bottom of the kiln due to the stack efiect, is, minimized; L Obviously the invention is not limited to the details of the illustrative methodor the appa ratus for performing it since these maybe variously modified. Moreover, it is not indispen sable that all features of the invention be used; conjointly since various features may be used to advantage in different combinations and subcombinatior'is'." i v Having described my invention, I claim I U U 1. The method of treating ceramic ware in a tunnel kiln which comprises placing succes sively 'generally rectangular stacksof ware on 7 closer to the kiln walls than the other corners, moving the kiln floor to carry successive stacks and exchange heat with the hot gasestravel-' the kiln floorspaced from the kilnwalls with the stacks skewed to place one pair of diagonally opposite corners of each stack substantially through the kiln, arranging the ware in each stack with longitudinally and transversely extending passages to carry heating gases between the pieces of ware, causing heating gases to pass longitudinally through the kiln through the spaces between the benches and the kiln walls and counter to the direction of travel of the ware, locating said diagonally opposite corners relatively closely to the kiln walls to create pressure differentials at opposite ends of. said transverse passages to cause a substantial por-- tion of the heatin gases to pass through the transverse passages in each stack.

2. The 'method of treating ceramic ware in a tunnel kiln which comprises arranging the ware in stacks on the kiln floor to provide 1ongitudinally' and transversely extending gas fiues through each stack between the pieces of ware and also cross passages between successive stacks, spacing the sides of the stacks'fromthe kiln Walls to provide clearance spaces for the travel of hot gases, moving the kiln floor to carry the stacks through the kiln, causing hot gases to travel through said clearance spaces and longitudinal fiues, and causin streams of hot gases to pass from a clearance space on one side of a stack through said transverse fiues to the clearance space on the opposite side of said stack and thereto mingle with and exchange heat with the hot gases in the latter clearance space, and then causing a portion of the mingled hot gases to return through the cross passage at the end of the stack to the first mentioned clearance space and in so returning to mingle and exchange heat with the gases'issuing from the longitudinal fiues at each of the stack, and repeating said flow of gases for each successive stack.

3. The method of treating ware in a tunnel kiln which comprises building a stack of ware in the kiln with the side walls of the stack nonuniformly spaced from the kiln walls to provide gas flow spaces of varying section between the Ware and the sides of the kiln, arranging the ware so as to provide fiues for gases extending from one side of the kiln to the other, moving,

the stack of ware through the kiln, and causing hot gases to pass longitudinally through said. spaces of varying section anclthereby to create.

pressure differentials at opposite ends of said fiues, said pressure differentials causing a substantial part of said gases to travel through said fiues from one side of the kiln to the other.

4. The method of treating ware in a tunnel kiln which comprises stacking the ware in the kiln to provide fiues for hot gases extending both longitudinally through the stack of wareand from side to side of the stack of ware, spacing the sides of the stack of ware from the kiln walls to provide clearance spaces for the travel of hot gases, moving the stack of ware through the kiln, causing hot gases to pass longitudinally through the kiln through said spaces and also throughthe longitudinal fiues in the stack of ware, creating pressure differentials at opposite ends ofwthe cross fines to cause hot gases to travel back and forth from side to side of the kiln through the cross fiues in the ware to the other side, and causing saidgases to mingle with ing along the sides of the stack of ware and also with the gases traveling through the longitudinal flues thereby to distribute heat uniformly throughout the stack of ware.

5. The method of treating ware in a tunnel kiln which comprises placing pieces of ware in stacks on the kiln floor with the faces of the stacks of ware of varying distances from the kiln walls to vary the area of the spaces between the ware and the sides of the kiln thereby to create pressure differentials between opposite sides of the stack, moving the kiln floor to carry the stacks of ware through the kiln, and causing hot gases to pass longitudinally through the kiln, said pressure differentials causing a substantial part of the gases to travel transversely through the stack of ware.

6. The method of treating ware in a tunnel kiln with a traveling floor which comprises placing pieces of ware in stacks on the kiln floor with passages between the ware in the stacks transversely of the kiln, arranging the stacks of Ware on the kiln floor with the clearance between the side faces of the stacks and the kiln wall repeatedly varying in section to create pressure diiferentials between opposite sides of the stack, and causing hot gases to pass longitudinally through said spaces of varying section, said pressure differentials causing a substantial part of the gases to travel back and forth from side to side of successive stacks through said passages.

7. The method of treating ceramic ware in a tunnel kiln which comprises placing benches of ware on the kiln floor with transversely extending gas passages through the benches, arranging successive benches on the kiln floor with the side faces of the benches longitudinally inclined relative to the kiln walls to form restrictions in the spaces between the sides of the benches and the kiln walls so as to repeatedly to restrict the clearance between each kiln wall and the face of said benches, moving the kiln floor to carry the benches through the kiln, causing hot gases to pass longitudinally through said spaces, the restrictions on opposite sides of each bench being displaced longitudinally thereby to create pressure difierentials between opposite sides of the bench to cause gases to travel through said transverse passages.

8. The method of oxidizing ceramic ware in a tunnel kiln prior to burning which comprises placing spaced benches of ware on the kiln floor with longitudinally and transversely extending passages between the pieces of ware in the bench, arranging successive benches on the kiln floor with the side faces of the benches longitudinally inclined relative to the kiln walls to form restrictions in the spaces between the sides of the bench and the kiln walls so as repeatedly to restrict the clearance between each kiln wall and the face of said benches, moving the kiln floor to carry the benches through the kiln, causing hot oxidizin gases to pass longitudinally through said spaces, said restrictions on the opposite sides of each bench being oiiset longitudinally of the kiln thereby to create pressure differentials at opposite ends of the said transverse passages thereby to cause said hot gases to flow through said transverse passages, said restrictions also causing said gases after issuing from said tranverse passages to return to the opposite side of the kiln through the spaces between said benches, thereby effecting a heat exchange between said gases and those issuing from the longitudinal passages in said benches.

9. The method of treating ceramic ware in a tunnel kiln which comprises placing spaced benches of ware on the kiln floor spaced from the kiln walls with longitudinally and transversely extending passages between the pieces of ware in the benches, skewing said benches on the kiln floor to place diagonally opposite corners of the benches closer to the kiln Walls than the other corners thereby to restrict the spaces between the bench and each kiln wall, causing hot gases to pass longitudinally through the kiln through the spaces between the benches and the kiln Walls, and moving the kiln floor to carry the benches of ware through the kiln in a direction counter to the flow of hot gases through said kiln.

10. The method of oxidizing ceramic ware in a tunnel kiln prior to burning which comprises placing spaced benches of ware on the kiln floor spaced from the kiln Walls and with longitudinally and transversely extending passages between the pieces of ware in each bench, spacing the side walls of the benches relatively to the kiln walls repeatedly to restrict and then to enlarge the spaces between the kiln walls and the benches, moving the kiln floor to carry the benches through the kiln, causing hot oxidizing gases to pass longitudinally through the spaces between the bench and kiln walls, the restrictions in said spaces on opposite sides of each bench being offset longitudinally of the kiln to create pressure differentials at opposite ends of the said transverse passages thereby to cause said hot gases to travel back and forth across said kiln through said transverse passages and to exchange heat with the hot gases passing through the passages between the kiln wall and the benches, said restrictions also causing said transversely traveling gases after issuing from a transverse passage to return to the opposite side of the kiln through spaces between said benches, thereby effecting a heat exchange between said gases and those issuing from the longitudinal passages in said benches, whereby heat is uniformly distributed throughout the benches.

MAJOR E. GATES.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,138,851 Gates Dec. 6, 1938 FOREIGN PATENTS Number Country Date 178,480 Germany 1906 351,070 Germany 1922 564,289 Germany 1932 503,613 Great Britain 1939

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