US1829290A - Electric kiln - Google Patents

Description

J. L. MERRILL Oct. 27, 1931.

ELECTRIC KILN Filed June 5, 1929 2 Sheets-Sheet l Oct. 27, 1931. J. L. MERRILL` 1,829,290

ELECTRIC KILN Filed June 5, 1929 2 Sheets-Sheet 2 4 ing zones, t

Patented 27, 1931 PATENT oEFlcE JOBIAH L. ILRBILL, Ol' MEDIA, PENNSYLVANIA i ELECTRIC KILN Application `liell June 5, 1929. Serial No. 388,678.

This invention is a kiln for firing porcelain and other ceramic articles.

In neral, kilns of the continuous type for firing ceramic products to be economical must not only be designed for'large capacity, but it is very essential that they e o erated at full capacity. In those insta lations where the naturalradiation of the ware in cooling is depen ded upon, the preheating and cooling chambers normall incorporated in kilns of this ty e necessari y have to be very lon This is ecause such ware should not ordlnarily leave the kiln at a temperature above 400 F.' In kilns of this character, employing hard fuel, oil or gas as the firing medium, the total length is normally between 200 feet to 300 feet, or over. The extreme length of these kilns is due to the necessity of providin space for preheating and coollie actual firing chamber occupying a com ratively small portion of the total lengtlh. It has been demonstrated, however, that kilns need not be nearly so long if electricity is utilized as the heating medium. In fact, kilns of the electrical type now in commercial use run from 104 feet to 140 feet.

One of the objects of the invention is to provide an electrically heated kiln' of the counter-flow ty e, so constructed as to transfer heat by radiation from the out oing hot ware to the incoming coldware. further object is to provide an electrically heated kiln equi ped with means to articiall accelerate t is heat exchange, so that pre eating and cooling zonesmay be shortened to such an extent as to materially reduce the cost of installing and maintainin the furnace, making it possible to buil kilns of smaller size for more economical operation -than is possible where this forced method of heat transfer is not used. A further object is to provide a kiln of the character referred to of a plurality of sections, so constructed and arranged that the sections may be constructed as independent units and readily assembled at the site of installation.

vThe invention will be hereinafter fully set forth and particularly pointed out in the In the accompanying drawings Figure 1 is a vertical longitudinal sectional view of a kiln constructed in accordance with the invention. Figure 2 is a transverse sectional view on the line 2--2 of Figure 1. Figure 3 is a similar sectional view on the line 3--3 of Figure 1. Figure 4 is a detail View illustrating the Inutile. Figures 5, 6 and 7 are sectional Views illustrating slight modifications.

Referring to the4 drawings, the kiln therein illustrated comprises three sect-ions, to Wit, a middle or muiile section A and two end sections B and C.v The walls of these chambers are formed of any suitable or 'desired refractory material in a ,manner which is well understood in the art and need not here be explained in detail. The sections are su ported in alignment with each other by sultable frameworks D.

As illustratedin the drawings, the kiln is constructed so as to provide two complete but independent passages for the ware to be heated. Each middle section A is provided with two parallel mulile portions 10, and each end section B and C is provided with an initial or preheating chamber 1v1 extending from one end of the muiiie in one direction, combined with an annealing or cooling chamber 12 extending from the other end of the muiile portion in the other direction.l The double form illustrated is desirable for many reasons, but obviously the kiln may be conv structed of a single passageway arranged with the preheating, muiiie and coollng chambers mentioned, without departing from the spirit of the invention.

Each muilie 10 may be constructed of any desired material. but preferably consists of a refractory tube 13, upon which is exteriorly wound a conduct-or 14, inthe form of a relatively wide ribbon extending helically around the tube. It is preferred to construct the ribbon 14 of platinum because of high melting point and inertness at high tempera'- tures, and in order `to obtain the best resistance effects the l.tape or ribbon form is employed. The ends of the ribbon 14 are fastened in suitable manner so as to be connected with the terminal block 15 in the reterminal on the side of the kiln.

fractory brick lining of the kiln. From said terminal block a conductor 16 is taken to the This last mentioned conductor is made of any desired type of heat resisting metal, but it has a very large cross section to make the resistance through the insulation as low as possible.

The refractory tubes 13 may be supported in any suitable or desired manner, but it is referred to mount them on refractory sadilles 17, preferably a material which has a ver small co-eiicient of expansion over a wi e range of heat. The tubes are so --supported that their ends are free to permit unrestrained expansion and contraction. The ends of the tubes 13 communicate with extension chambers 18 of refractory material formed in section A adjacent the ends of the tubes 13 and positioned to coo erate with said tubes so as to complete the eating section A.

The portion of the kiln 'containing the muiiles is so constructed that the tubes 13 may be lifted out and replaced if necessary. For this purpose, the space immediately above said tubes is bridged b a metal shell 19 hinged to the supports ofy the kiln as indicated at 20, and s urmounted by an arch 21, of refractory blocks superposed by a filling of refractory material.

The sections B and C are of similar construction and a description of either will apply to both. At both ends of each Inutile, i. e. the outer ends of each of the extension chambers 18, are located upper batlies 22 and lower baiiies 23, so positioned as to confine the heat as much as possible within the muiiles. The chambers 11 and 12 at their outer ends are also provided with baffles 24, depending from the roofv of each and said chambers are also provided with similar intermediate baiiles 25.

All of said batlies together with the radial forced circulation serve to retard the escape of. heat as much as possible, so as to confine said heat within the respective chambers and thereby prevent any sudden lowering of the temperature to which the ceramic articles are to be treated. It is preferred to provide vents V for allowing escape of gases given oif by the incoming ware.

The ware to be fired may be transferred through the kiln in any suitable or desired manner. For the purpose of illustration, refractory tracks 26 are mounted upon refractory track supports 27 in the chambers 12 and 13, and slidably mounted upon reduced portions 28 of said refractory tracks are ware-carriers 29. Refractory tracks 30 are also mounted on` track supports 31 `arranged in the muilies, so as to connect the tracks of the respective sections 12 and 13 and thereby p rlovide continuous tracks throughout the The carriers may be caused to travel through the kiln in any suitable or desiredA manner, but for purposes of illustration an endless drive belt 31 1s shown operated from a source not shown, said belt bem equipped with carrier pushers 32 positione to engage the carriers as they are placed by o rators upon the tracks at the entrance to eac initial heating chamber 11. the belt operates, pushers 32 s ucceively engage the carriers and push them alon in a succeedin train, passing from the initial heating chamber 11 through the munie and out through the cooling chamber 12.

The tracks are so arranged that as the ware is introduced through the initial heating chamber it is greatly raised in tem erature 'as it approaches the muille cham er,.the

operation of the driving chain being regulated to propel the ware at the desired speed for effective firing. In other words, the speed at which the ware travels through the inutile is regulated to insure the completion of the firing step while passing through the mullle. As it leaves the Inutile the ware enters the cooling chamber 12 in line with the initial heating chamber through which it was introduced, and gradually cools as it approaches the outlet end of said chamber 12. As the fired ware asses through the cooling chamber 12, the iieat radiated during the cooling process is transferred to an incoming train of unired ware which is being in troduced in the initial heating chamber 11 which lies beside the said cooling chamber 11. In this manner there is a heat exchange from the outgoing hot ware to the incoming cold uniired ware, so that by the time said unfired ware reaches the muiiie it has absorbedquite a substantial degree of heat and is thus-gradually brought up to the firing temperature. In a similar manner, as this ware moves out into its cooling chamber its heat is transferred to the incoming ware of the adjoining preheating chamber.

In order to facilitate the heat exchange which takes place between the unfired ware and the red ware, fans 35 are located in spaced apart positions in the upper part of each of the preheating and the cooling chambers. These fans may be mounted 0n horizontal supporting shafts 36, as illustrated in Figure 3 or on inclined shafts 37, as illustrated in Figure 5, or they may be located at the bottom as illustrated at 38 in Figure 6. These fans by setting up a positive or forced circulation cross-wise of the chambers, as indicated by the arrows invFigure 3, greatly facilitate the heat exchange between the hot and the cold ware. The fans also, by establishing currents of air at approximately right angles to the line of travel of the ware, serve to break up any leakage of cold air into the furnace `through the doors. In other words,

these 'cross currents in effect form a series It is obvious that as' two critical temperatures in cooling the ware, one a little above 1000 F. and one atapproximately 600 F. where the cooling has to be more gradual than at other temperatures; to revent the setting up of cracking strains. `his situation is eiectuall taken care of by the'arrangement of ba es and positive cross currents between them. The

s discharged by the ware during the re- 'minary heating are normally heavier t ank air and there is an advantage 1n also lacing fans at the bottom of the cham r, as shown in Figure 6, because they distribute these ases in the cross currents which are create The fans are operated in any desired manner for instance by means of belts not shown engaging pulleys 39 on their shafts. p

The advantages of the invention will be readily understood by those skilled inthe art to which it belongs. For instance, an imortant advantage is that because of the ibrced heat exchange between the hot and the cold ware, the length of the preheating and cooling zones m'ay be shortened so as to materiall reduce the cost of the furnace. Also, the ki ns may be built of much smaller size for economical o eration than is possible with the old type 'lns which do not employ the forced method of .heat transfer. This not onl reduces the cost of the initial installation, ut also relieves the manufacturer of the necessity of carrying a large stock of finished ware as now has to be done where large kilns have to be operated at full capacity, because the'electric kiln of the invention does not have to be operated at full ca acity where a fluctuating seasonal demand lias to be met. A further advantage lies inthe fact that by shortening the length of the kiln it is possible to push the Ware through the kiln on carriers sliding on refractory tracks. These carriers are constructed of a light refractory material so that the heat carried by them out of the furnace is much less than that carried out by the cars now commonly used in existing types of furnaces. Another important advantage is that the three sections of the kilnmay be constructed as independent units of proper dimensions, so as to provide when assembled, a continuous commercial furnace of the capacity of the 9 and 12 foot standard bottle ilns, said sections being completely constructed at the factory and shi ped to the point of installation as independent sections, and there readily assembled.

Having thus explained the nature of the two'inde ndent parallel muille chambers, and two inde ndent endsections connected each en to the opposite ends ofesaid middle section, l i

section having a single combined preheatln and cooling chamber communi- Vcatin wit the adjacent ends of both mule cham rs, means supporting said muilie 'chambers so that their ends are free to excatin with the adjacent ends of both muillel cham ers, means supporting said muflle chambers so that their ends are free to expand and contract, means for causing the ware to travel inv opposite directions through the kiln, and means within said combined preheating and cooling chambers for creatlng currents of air transversely of said chambers, so as to facilitate temperature exchange between the adjacent hot ware and cold ware.

3. A kiln of the character described com# prising a middle muille section formed with two independent parallel muille chambers, and two independent end sections connected to the opposite ends of said middle section, each end section having a single combined preheating and cooling chamber communicating with the adjacent ends of both muille chambers, means supporting said mule chambers so that their ends are free to expand and contract, means for causing the ware to travel in opposite directions through the kiln, and spaced apart fans mounted on the side Walls of the preheating and cooling chambers and positioned to direct air currents transversely across said chambers, so that air heated by radiation from the outgoing hot ware will be directed against the incoming cold ware.

4. A kiln of the character described comprising two parallel muille chambers and two combined preheating and cooling chambers, each connected with an end of a muiile chamber, so that a preheating chamber and a cooling chamber are connected with the respective ends of each muile chamber, spaced apart bailles depending from the tops of said combined preheating and cooling chambers, and means for creating currents of air transversely of the heating and cooling chambers at positions between the baiiles so as to form a series of air seals between said bales.

,between the battles and positioned to direct currents of air transversely of said chambers so as to form a series of air seals betweensaid bailles.

6. A kiln of the character described comprising a middle mule section formed with two independent parallel muie chambers and with extension chambers at the ends of the mule chambers, and two end sections connected to the respective extension chambers, each end section having a single combined preheat-ing and cooling chamber communicating with the adjacent ends of both muiiie chambers through said extension chambers, said mule chambers each being constructed of a refractory7 tube provided with an exteriorly wound electric heating element, and means for causing the ware to travel in opposite directions through the kiln so that the cold ware travelling in one direction toward a muiile chamber is preheated by radiation from ycooling ware leaving the other muille chamber.

7 A kiln of the character described comprising a middle section havinga tubular mule chamber and extension chambers with which the ends of said muie chamber connect, said muiile chamber being encircled by anelectric heating element, an initial heating chamber connected with one end of the tubular muie chamber, and a cooling chamber connected with the other end of said muffle chamber.

8. A kiln of the character described comprising an initial heating chamber, a muffle supported so` that its ends are free for unrestrained expansion and contraction, and a cooling chamber arranged end for end so as to provide a continuous passageway, and an electric heating element encircling said muffle.

9. A kiln of the character described comprising a structure of refractory material supported so that its ends are free for unrestrained expansion and contraction, said structure being provided with a continuous longitudinal passageway extending therethrough, and an electrical heating element surrounding a portion of said passageway.

10. A kiln of the character described comprising a structure of refractory material supported so that its ends are free for unrestrained expansion and contraction, said structure being provided with a continuous passageway extending therethrough from end to end, and an electrical heatin element helically wound around a of said passageway. l

11. A kiln of the character described oomprising a mulle supported so that its ends are free for unrestrained expansion and contraction, an initial heatin chamber having one end joined to an end o the muille, an an'- nealing chamber joined to the other end vof the muille, a track extending throu h said chambers and muilie, and an electric eating medium encircling said muilie.

12. A kiln of the character described comprising a tubular muille rovided with an axial passageway said mu e being supported so that its ends are free for unrestrained exportion o thefwall 'im pansion and contraction, an initial heatin' 'BB chamber having one end joined to an en: of the muflle and also provided with a passageway, an annealin chamber joined atone ,y end to the other end o the mule and also pro'- vided with a passageway, said passageways t combined forming one continuous passageway, a track extending through the continuous passageway, and an electric heating medium encircling the wall of said muille so as to enclose the bore thereof.

13. A kiln Aof the character described comprising a tubular inutile having extension chambers extending from either end thereof,

an initial chamber' having one end joined to the outer end of one of said extension chambers, an annealing chamber having one end joined to the outer end of the other extension chamber, said muille and chambers being arranged to provide a continuous passageway from end to end, and an electric heating medium encircling said mullle.

14. A kiln of the character described comprising a tubular muiile having extension chambers extending from either end thereof, an initial chamber having one`end joined yto the outer end of one of said extension chambers, an annealing chamber having one end joined to the outer end of the other extension chamber, said muille and chambers being arranged to provide a continuous passage'- way from end to end, and a tape of electro, conductive material wound about said mulflfie so as to provide a heating element there:-

15. A kiln of the character described com prising a middle muille section formed with two independent .parallel muille chambers, and two end sections connected to the opposite ends of said middle section, each end section having a single cmbined preheating and cooling chamber communicatin with the adjacent ends of both Inutile cham ers, spa'cerl apart baiiles Within said combined preheating and cooling chambers, means for caus ing the ware to travel in opposite directions through the kiln, and means for establishing cross currents of air in the spaces between said bales. c a

In testimony whereof I have hereunto set my hand. v

JOSIAH L. MERRILL.

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