US1567023A - Continuous drying kiln and method of drying ware - Google Patents

Description

Dec. 22 1925- T. LARSSON CONTINUOUS DRYING KILN AND METHOD OF DRYING WARE Filed Oct. 30, 1920 3 Sheets-Sheet 1 Tin/re Lanna/7.

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Filed Oct- 30, 1920 7 CONTINUOUS DRYING KILN AND METHOD OF DRYING WARE Dec. 22.1925- Methods of Drying Ware,

PATENT OFFICE.

THUBE LAR SSON, OF WOBCESTER, MASSACHUSETTS, ASSIGNOB TO NORTON COMI- PANY,

OF WORCESTER, MASSACHUSETTS, A CORPORATION OF MASSACHUSETTS.

CONTINUOUS DRYING KILN AND METHOD OF DRYING: WARE.

Application filed October 30, 1920. Serial No. 420,606.

To all whom it may concern:

Be it known that I, THURE LARSSON, a citizen of the United States of America, residing at Worcester, in the county of Worcester and State of'Massachusetts, have invented certain new and useful Improvements in Continuous Drying Kilns and of which the following is' a full, clear, and exact specification. My invention relates to the art of drying green ceramic articles and more particularly to a progressive drying kiln structure and a method of drying ceramic ware therein.

Iuthe manufacture of ceramic ware, such as a grinding wheel, it is customary to make a plastic mixture of the abrasive grain and clay materials with water, shape this mixture in a mould and then fire it in a kilnto vitrify or fuse the clay materials into bonding-contact with the abrasive granules. It has been found that before the articles can be subjected to high heat, the moisture which has been added to give desirable plasticity to the moldable mass must be removed, in order to prevent the fragile wheel structure from being cracked or otherwise injured; The methods heretofore employed in this art have involved wheels on fixed racks in a steam heated drying room, butno adequate provisions have been made for carefully regulating the temperature and humidity vconditions of the drying atmosphere and otherwise insuring that successive consignments of wheels be subjected to the same drying operationin order thatuniformity tained. p v The principal objects of my invention are to improve and simplify the procedure of drying ware, such as green ceramic articles. to' ehmmate unnecessary manual control of e dry room operations and render the vdrying process substantially automatic in its action,

= thus obviating accidental variations in the humidity and temperature conditions of the drying air to provide a method of drying wherebv all ware'may be'subjected to substantially uniform initial and final treat-. ments andto avoid using theexpensive ro'-',

oedure heretofore employed fori conditlon-i ing the drying: air in acontinuous drying With these and other objects in view, as

I llb madfly apparent in' the; following and placing the green humidity in order to in results may be obcirculate the air in the d with the ware and regulate-its forward movev its drying capacity.

an'd forwar the description and covered section of one form of tunnel kiln embodying my invention;

Fig. 2 is a sectional detail of the air inlet pipes and damper mechanism;

Fig. 3 is a transverse section of the kiln near the ware entrance;

Fig. 4 is a longitudinal section of the kiln partly broken away, taken on the line 44= of Fig. 3, to' show the entrance and exit portions of the kiln;

Fig. 5 is a horizontal plan partly in section showing the arrangements of the fans,

heaters and thermostat controlling devices;

Fig. 6 is a diagrammatic sketch of the vehicles and subjecting them initially asthey progress to circulating air currents of hlgh temperature and practically 100% heat the articles to a drying temperature without permitting drymg action to take place;'then to treat them wlth air currents which are of progressively decreasing temperatures and moisture content and finally to dry them inan atmosphere which is maintained at a constant tem erature and is provided with a practlca 1y uniform moisture content, whereb'y all the were will be dried under the same conditions. I To effect this procedure, I pass the green ware in one direction through the kiln and the circulating drying air in the o posite direction, and in order that the goods may v be subjected under uniform conditions to large volumes of'heate'd air,

room in contact men: in accordance with and effect u on theware. This circulating causing. the air to move repeatedly in a circuitous' ath' transversely; of the; dry room I propose .to

movement may be obtained by ers; soythat if the airmisjnot saturated a 1 ,Lecaoaa and through 'a'return passage andvto pro return passage above the. drying room.. grass in a slow helix-like motion end iSQ/Qhese fans, 'the construction-of which is no through the kilnwhile thus-circulating transpart of myinvention', may be suitably. :versely. Furthermore, in order that the, mounted .to be driven from shafts 26 prowater'content of the circulating air entering jecting through the outside wall. thedry ro'om may be properly regulated, 1- which in turnare driven by ulleys andpropose a, utilize the moisture evaporated belting from an outside shaft-2 connected from the Wheelsthemselves bymixing satu- With-anyllesired-source ofpower. By conrated air-drawmfrom the gas exit with a nectin all of the fans with the one drive.

suitable amount of drier air from the outshaft side atmosphere as determined by the conthe drying room.

ditions of humidity at the particular time! T of operation and thus avoid such variations g "in drying action as would becauseol by cli- 15' matic changes. To obviate the necessity for.

' manual control of the kiln and to provide for uniform emperature and humidity conditions, '1 'ma yutilize; thermostatically controlled heaters located at intervals throughout the kiln, andcirculate the air the'reover at a uniformate by suitable means. The rate of progre s of the air through the dry room, or-the itch of the helix .as it were,

' is determined ythecondition of the drying air and is regulated v automatically if desired, by thermostatically operatedjdampe rents to different temperatures at difi'erent parts of the kiln,-I rovide a seriesof independently controlle heaters spaced longitudinally of the kiln and preferably located in the openings=20 so that all the movingv 'airmust come into. close proximity with the heating elements. Each heater may comprise, as showmaset of steam pipes 28 connected.) with an, outside source A of steam through the transverse pipe 29, the inflow ,of steam to these pipes being ,separatel y-- feg'ulatable. l 4

With the construction so far explained, tliejair may be circulated repeatedl I transv fv'ersely; .ofthe'drying room so t at the; i f at the gasexit the,Iongitudinalinovement of the air will be retarded vvhi-le its transverse motion-is maintained. In this way, fthe'wa-re willalwaysbe' subjected to dr. ing

;curre:uts of air of substantially uni orm velocity-but of variable absorption capacity as may be found suitable togive proper ry in? actionto difierent batches-,otwareflf '1 norder that this 'i ven 'tioil ay,be-.clearyunderstood,. refer'ence i'sf 'tobehad toflthe a v ,drawingsl in which l have I illustrated one. embodiment of this jinvention, The kiln 91-10, which ma be constructed of anyfsuitable material. an ';in accordance lwitlrfany-g approved architecturalplan, is prqvidedfvvith parallel; sets of tracks .1. upon, which; cars; 12 of suitable design m y nror; transportin'gthe} goods; through 'the'ikilmq To provide. K foraftransverse circulationoftheheatedair, l l J intermediate partitionsj13 and f 14 gspaeed, the'kilm; this passa e 5 from the side fwall'sj' 15 'andglfi respectively ;34 'builty'ibetweenfii v arelliuilt. to? extendfthelengthof the kiln cand-yspaced .from,,jtheffioor517;."

. fromthe floor'17 toaifalseceilingfi Is aced nded pipe35ipassingth 'ou'ghj theikilnwall-- gfrem the top 19ofthe'kilm'thereby a 0rd,.- n'g an 1 air passage about; three sidesfof' the *mnerj drvingjroom. The circuit rot theair i amputee; "in the" form. illustrated,. by means of a series of spaced-openings, 20 and 21 formed in the partitions13 and-14- re-v spectively, these openings preferably being.

site 'eachother and oisuch -sizes as to] it the air currents to travel as uniformpo'ssible inl parallel paths through. the The airis circulatedhy means' ably located fans 23,f'24:and "mountedin the openings, w lades facing outwardlytodraw [the irfron'r the' rooi'n'Tand direct it into the i a r- 'thierethroughl Inorder to regulate the ";,a1rflow, I preferably have two separate exits othe,liln, one to the. outside airand the other. commun cating through a return pipe withfthe air. inlet tothe kiln. 101m; exit pas-1 32 opposite'ltlie fan 24v between theiwal s "14' that ,oithe fan openingini orderlthat ajpor'.

t ou h he-,i y'r arrows are shown in F of. the kiln,

insure a uniform draftthroughout I Inorder to heat'the circulating air cu p'e'isite;v thorn-'24 near the were entrance sage .31 is formed by: providing lailiafiie late and- 16. That portion-of'the fan-opening beneath the battle communicatesvvith; a as--. :sage z33 extendingv to the warefexit en ,of i being formedby ayiall I e'flkiln'walls 1.473116, 3161 Aniilopenr to the fan opening abovethe-balflle' fplate 32 furnishesegress. directly "from the "d rying .r iroo nto the outside atmosphere; "l-iThecapac-lf" 'ity of these {exits {is} 'considerably""less than": tion only of the l'circulating gas may be discharged from thekilnandthe}reinainclenbe fo'rcedt to yrepeatjy its t ansverse, i-p-motion t fyvill "be; noted.- that, H 3 '5lto'represei bthejglZfi air currents diagrammatically,- those: in .-fullexternal atmosphere. 7, formed at the junction of the passage 33 with the pipes 41 and 42 may be controlled by a su1table damper to permit the introduction 1nto the kiln room of desired proportions of water saturated air and the drier air from 'the external atmosphere.

The damper may be formed, as illustrated in Fig. 2, of a member 43 havlng a surface like a portion of a sphere which is mounted to swing about the pivot 44 in the axis of its position controlled by means of a suitable crank 45 on the end of the pivot outside the pipe operated by a thermostat device to be presently described. The ends of the conduits at the junction are suitably shaped relaj atmosphere at various points, I each heater and the dampers 43 and 46.

While various types of thermostats may obtive to the form of the damper so that the damper may close 011? either the passage 33 or the pipe 42 or leave each partially open. Thepipe- 35 is also provided with a suitably shaped damper 46 which is pivotally hinged within the pipe and may be controlled by means of the crank 47 to close off entirely the opening to the external atmosphere or permit a portion of the gas issuing through the end fan 24 to pass outside of the kiln.

If it is desired that my method be carried on automatically so that the temperature and humidity conditions in the kiln roomneed not be manually controlled, I provide a series of thermostats which are exposed to the kiln for controlling viously be employed, I have illustrated, somewhat diagrammatically, a Well known pneumatic type which comprises two sets of heat measuring instruments, one a wet bulb thermometer 51 and the other a dry bulb thermometer 52. Each wet bulb thermometer is kept moistened by suitable means,such as a Wick 53 surrounding the thermometer and dipping in a receptacle 54 which is supplied with water. These thermostats, as will be understood by one skilled in the art, com-- prise control instruments 55 which areeach adapted to be set for any temperature within the desired range, whereby, when the particular temperature 'has been reached, com- .pressed air from the supply pipe 56 Will flow through the thermostatically controlled valves in the instrument to a device 57 adapted to operate the valves in the steam pipes 29 or the air dampers 43 and 46. This device 57 comprises in general a stem 58 connected at one end with an inside diaphragm and at. the other with the valve in the steam pipe or the damper operating linkage, wherepipe 41 and have air pressure admitted through the pipe 59 may operate this diaphragm and move the stem 58 outwardly, the return movement being caused by a helical spring surrounding the stem 58.

As shown particularly in Fig.6, the two end wet bulb thermostats 60 and 61 are utilized'to operate the dampers 43 and 46. The two end steam pipes 29 supplying the two end steam heaters in the tunnel kiln are operated by the dry bulb thermostats 62 and 63, while the remaining steam heaters supplied by the remaining steam pipes 29 are controlled by thermostats in which the dry and wet bulbs 51 and 52 have -a combined effect, that is the wet bulb thermometers control the humidity conditions in the different parts of the drying room and the dry bulb thermometers the temperatures. The mechanical connections between the end thermostat 60 and the damper 43 may be of any suitable construction but, as illustrated particularly in Fig. 2, may comprise a bell crank lever 64 pivoted at 65 to a-fixed member. one end of this lever being connected to the valve stem 58, and the other to the damper operating linkage 66. The air passes from pipe 56 through the thermostatic device and through pipe 67 to the valve control mechanism 57. The damper 46 in pipe 35 may be controlled similarly, as shown in Fig. 3, the air passing through pipe 68 from the wet bulb thermostat 61 to the valve control mechanism, in which the stem 58 connects through a linkage with the damper crank 47.

In order that the kiln may be closed to external atmospheric conditions, I provide suitable doors, such as the sliding doors 70, at each end of the kiln. The cars are loaded and unloaded outside of the kiln. While the mechanical constructions of these load ing and, unloading mechanisms are not a part of my invention, they .may comprise, as shown in Fig. 4, suitable uprights 71 and 72 supporting a travelling crane 73 for lifting the ceramic articles. and an endless chain mechanism 74 at the ware entrance which is adapted to engage a dog 75 on the car and push it into the kiln, this chain being moved by any desired type of motor. A portion only of this external construction is shown at the exit end of the kiln in Fig. 4. I have furthermore illustrated the ceramic articles as grinding wheels which are supported on separate batts 76 spaced apart so that air may be freely circulated between and around the wheels. If desired, the carriers 77 for these batts may have legs 78 to permit movement by means of motor trucks. Two of these carriers may be placed on the car, one being supported directly on the car body and the other above the first on legs 7 9 attached to the car.

In accordance with my invention, the kiln 1' trolledthat' it has asubstantially constant tissoo ea -a thatjtheair at the lefthand end the kiln 1 (Fig. 4) where-the ware.

l entersis saturatedwith moisture and heldat a uniformly high temperature which, for example, may be considered to be 120 F. In

, order that the ware leaving the kiln may be exposed to air of uniform drying characteristics, the temperature of the entering air is held at a lower tem erature, for example 100 F. ,.and the humi ity of this air so'conmoisture content, .as, for example, 0.03

po'und' of water per cubic-foot of airs. To provide automatic regulation forfithe humosp'here'until the vwet bulb temperature is mi-dity conditions, the wetbulb thermostat controllin the damper 46f is sosetthat the damper s all be closed to the external at-- about that which represents a saturated con dition of air for 120. F. ;At the righthand end-of the kiln where the air enters,'. the

damper 4:3 is similarly controlled by the wet bulbs thermostat, so that if the latter is set for a temperature of, say, 89v R, which represents; approximately a humidity condition of- 70% for'100 F. dry bulb tempera ture, and if the temperature of the wet bulb thermostat rises above 89 F., thus indicating that the moisture content is increasing, the thermostat operates to close 03 the passage 33 and open the entranceto pipe 42 so;

that drier air will be drawn'from the ex{' ternalatmosphera As aresult, andsin'ce the first heater at this end of the chamber is controlled-by the dry bulb temperature to maintain a temperature of=100 F., the' humiditycondition of the air'will fall and the wet bulb thermostat will become lower in temperature and so operate to, open the damper again -to the: passage 33 and close it to the outside air through pipe 42. This damper will thus hunt-or swing back and through the dry I y I by the drying wareuntll it becomes a: maxianiount of Water mum about fourYor five heaters from'the along'is being heatedjto a higher temperavtureto. keep it below thesaturation point.

ware entrance. The 'dryin'gg;goperationre sults from the fact that while. in:-

creasing in moisture contenfias i it moves If the water content of the whole, kiln is too low, as when the drying operationis start ed, the dampers 43 andn46. close the passages to the external atmosphere so thatno air I can leave"- orenter the kiln and-"the airmust cir culate "longitudinally of the kiln and throughsthe .ret urnpassage 33 until it be-= memes comesi'suiiiciently moist. At 'other times, 1

the rateofflow of the air. longitudinally of i the kiln varies fromzero'to a'maximum de- 1 pending" upon the positions of the two dampers, it being noted that if damper 46 closes pipe 35 the forward movemen'tof the air is permitted only when damper 43 swings to-let a little more moisture into the entemn' air. --Hence, irrespective ofa the. type 0 were being dried orthe variable humidity and temperature of the external atmosphere, the'drying air is so conditioned sons; I a

' as to give substantially; the sametreatment "to the ware fthroughont*themhanging' sea-' Having thus' described a ihv'enu ii; I

what I claim as new and desireto secure Letters Patent is: i

com ris-' 1. The method of dryingware ing; continuously-moving ware to be ried through a drying kiln,

over the were at a uniibrm 'veloclty', and

eriy conditioned to" givea desired .dryin action.

reg!'llating the rate: offflow'ofairpassing" through the kiln to maintainthe-same prong W 2. The meth0d; 0f dryingwa-re comprise I ing passing theware progressively through a n a kiln, circulating'conditioned air in one dis rection over the ware and back in a substantially helical path and varying the'fon Ward movementof theair through the kiln to control its drying action on the, ware.

3."The method of, drying ware comprising continuously moving the ware through a,

drying" kiln, repeatedly -circulating heated air over a given ieceorware, moving the air longitudinally through the kiln, progressively heating vthe air in its forward move fnent, and rgulatinglthe rate of its longitudinal flow so as to subject the continuously moving ware to air containingpredeter-f molstur'e at definite": lQ.-

mined amounts of calities inthe I ",4. The method of drying warecomprising passingjthe ware progressively through a dry room in'one direction, moving a heated air current in the opposite direction in contact with the ware, repeatedly circulating the drying air in contact with a given piece drying. y.

5. he method of drying ware comprising-l passing air progressively through a one direction, passing the were in the oppo-tfif 1 site direction, progressively heating said airin itspassage through the kiln, repeatedly circulating kiln airof a given't'emperatpre over a piece of wake to IIICIGaSG IiZS dr mg action thereon, regulating'the rate 0 air I movement through the kiln sothatthe air ined moisture cone tent at the ware entrance, and maintaining 5 will have a predete i if of wareand varying thelrate of flow of the; air through the dry r'o'o'mfto re late the 'moistu'recontent of the air andt e rate of Q substantially uniform moisture content in.

. ingpassing thee- Ware progressively througha drying kiln, repeatedly circulating heated air ata uniform velocity in contact with the Ware, moving the circulating air for ward through the kiln in a direction oppo-' site to that of the aware and varying the 'rate of such forward. movement so as to keep the air. saturated at the, ware entrance and thereby'heat the ware initially without drying it.

7. "The method of drying ware comprising' passing the ware rogressively through a drying kllIl, repeate ly circulating heated air at a uniform velocity in contact with the ware, movin the circulating air forward through the 'ln in a direction opposite to that of the ware at such a rate as to keep the air saturated at the ware entrance and thereby heat the ware initially Without drying it and-maintaining the moisture contegt a su 8. The method of drying ware comprising passing the ware in one direction through a drying kiln, movin a body of air-over the ware in the opposite direction,

progressively raising the temperature'of the air as it travels through the kiln, repeated- 1y circulating the air over the ware to increase its drying action until the air has a fixed moisture, content at theqware entrance returning kiln air'fro'm the air outlet to the air inlet and maintaining the temperature and humidity ofthe entering air constant to subject successively treated wares to the same drying trea ment.

' -9. The method of drying ware comprising passing the were progressively through a drying kiln in one direction and a drying a1r 1n the opposite direction,'.circulating the air at anniformvelocity over the ware, heating the-entering air and maintaining its moisture content substantially uniform, progressively raising the temperature of the air to a desired maximum as it passes through the kiln and maintaining the air throughout-an extensive zone adjacent the ware entrance in "a substantially saturated condition to heat the ware initially without drying it. I

10. The method of drying ware comprlsing passing the ware progressively througha drying kiln in one-direction and a heated a1r current in the opposite direction, maintain- 'ing the entering air at a substantially uniform temperature and moisture content,

progressively heating the air as it passes through the kiln, regulating the temperature of the air at the ware-entrance to a substantially uniform degree higher than that of the entering air' and moving the air kiln to provide it with a ing passing in the other direction. progressively raising the temperature of the air as it passes through the kiln, independently regulating the temperatures of the air at spaced points in the kiln to maintain a desired drying rate at each point, circulating the air through. the klln at such a rate as to maintain a uniform humidity conditionat the ware entrance and regulating the temperature and humidity of the air at the ware exit to provide a substantially uniform drying treatment for successive batches of ware.

12. The method of drying ware comprismg passing the ware progressively through a drying kiln in one direction and a heated air current in the opposite, direction, re-

peatedly circulating the heated air current adjacent a piece of the ware transversely of the kiln, moving the air longitudinally of the drying kiln at such a rate as to keep the air saturated at the ware entrance and there by heat theware initially without drying it and progressively heating the air currentas it moves through a portion of the kiln.

13. The method of drying ware comprising passing the Ware progressively through adrying kiln, passing a heated current of air in the opposite direction, maintaining the air at the ware entrancein a saturated condition to heat the ware initially without drying' it, returning a portion of the moisture laden air to the opposite end of the drying kiln and conditioning the air entering the substantially uniform moisture content.

14. The method of drying ware compris-' 'ing passing the ware at a uniform rate through a drying kiln, moving a heated current of a1r m the opposlte direction in contact with the ware, mixing a moisture saturated air with air from the outside atmos- 1 moisture content for a fixed temperature condition, passing this air into the kiln for the final drying operation, progressively heating this air as it passes through the kiln to cause of flow of the air through the kiln to mainphere to provide a substantially uniform the ware to be dried and varying the rate tain a uniform humidity condition adjacent the wareentranCe.

15. The method of drying ware compristhe ware progressively in one direction through a kiln and drying air in the opposite direction, heating the air as it passes through the kiln. withdrawing the moisture-laden heated air and returning a portion of the same to the ware exit, mixing unsaturated air therewith and conditioning the" mixture asrequired to provide an initial drying current of uniform temperature and moisture content. I v

16. The method of drying ware comprising passing the wareprogressively in one direction through a kiln and drying air in the opposite direction, heating the air as it passes through the kiln, regulating the kiln conditions to provide a saturated air of a substantially uniform temperature at the ware entrance, returning a portion of this Cheated saturated air to the ware exit, mixing unsaturated air therewith and conditioning.

the mixture to provide an initial drying air of substantially uniform temperature and absorption capacity.

17. The method of drying ware comprising passing the ware progressively through a drying kiln, passing a heated curent of air through the kiln in the opposite direction, repeatedly circulating the air at auniform velocity transversely of the kiln through the ware, returning a portion of the moisture laden air to the air entrance, mixing this moisture bearing air with air from the external atmosphere and conditioning the same to maintain a substantially uniform moisture content at a fixed temperature, progres sively heating the air current in the kiln and maintaining a substantially saturated condi- 1 a room, an air inlet and an air outlet at opposite ends of the kiln, means to heat a suppl of air for said kiln, means to circulate t e air at a uniform velocity repeatedly transversely of the drying room and means to move the airlongitudinally through the kiln at a variable rate or to prevent such movement.

20. A continuous drying kiln comprising a room having air inlet and outlet openings, a series of heaters within said kiln, means to circulate air transversely of the kiln at a uniform velocity and repeatedly in contact with said heaters and means to move the circulating air at a variable rate longitudinally through the kiln.

21. A continuous drying kiln comprising a room having closures at its ends and a passageway for conveying ware therethrough, means to circulate air past said ware, controllable heating devices in said kiln, means to maintain the moisture content of the air entering the kiln room at a unimemes form amount and means .to vary the rate of flow of the air through the kiln to subject the were entering the kiln to a drying atmos phere of substantially uniform moisture content and of a high temperature.

22. A. continuous drying kiln comprising a room having closures at its ends and a passageway for conveying ware therethrough a series of independently controlled heaters spaced in the kiln, means to circulate air repeatedly transversely of the room in contact with said heaters and the ware, thermostatic devices. to regulate said heaters and means comprisin regulatable inlet and outlet openings to an from the kiln to cause a controllable drift of the transversely circulating air-from one'end of the kiln to the other.

23. In a continuous drying kiln, a series of independently controlled heaters arranged along one side thereot, means including fans to circulate air transversely of the kiln and through said heaters, thermostatic devices cooperating with said heaters to control the temperature and humidity conditions in the intermediate portion of the kiln, means providing inlet and outlet openings at opposite ends of the kiln and means, including a thermostatic device, to move the air longitudinally of the kiln at a variable rate to re ulate the humidity condition of the air a 'acent the exit.

' 24. n a continuous drying kiln, a room havingclosures at its ends and a passageway for conveying ware therethrough, a 100 series of independently controllable heaters in the dry room, means to circulate air through t-he heaters and in contact with the ware, means providing air inlet and outlet openings to and from the dry room, a passsage to the external atmosphere and a return passage from the outlet to the inlet opening and regulatable means for mixin the return air with fresh air to provide t e entering air with a constant moisture content.

25. A continuous drying kiln comprising a room having closures at its ends and a passageway for transporting ware therevthrough, a series of heaters in said kiln,

means for-circulating air repeatedly trans versely of the room in contact with said heaters and the ware, means providing air inlet and outlet passages from the kiln to the external atmosphere and a return passage between the outlet and the inlet openings, means including controllable dampers cooperating with'said passages to move the air longitudinally. through the kiln at a variable rate and to condition the air entering the kiln and means including thermostats to control the amount of'heat admitted to the heaters in order to regulate the humidity conditions in the room.

26. In a continuous drying kiln, a series of thermostatically controlled heaters arranged 1 longitudinally therein, means comprising a 'series of fans to circulate the air transversely through the kiln and over said heaters repeatedly, means providing air inlet and outlet openings at opposite ends of the kiln, means to move the circulating air longitudinallythrough the kiln, means ineluding a wet bulb thermostatic. device to retard the flow of air through the kiln until it becomes sut fiautially saturated at the exit and a Wet bulb thermostatically controlled device to provide the air entering the kiln with a constant moisture content,

27 In a continuous drying kiln, a series of independently controlled heaters arranged along one side of the kiln longitudinally-thereof, a series of fans disposed opposite said heaters and cooperating partitions to circulate the air through the heat -ers and transversely of the kiln, means providing air inlet and outletopenings at opposite ends of the kiln, means tending to circulate the air longitudinally of the kiln room and means to vary the rate of movement of the air longitudinally through the room to provide uniform humidity conditions at a given location in the kiln.

28. In a continuous drying kiln, walls therein forming an inner dry room extending'longitudinally of the kiln and a return passage outside of the room, the vertical walls having openings disposed opposite each other, heaters in the openings on one side of the k1ln room, means to regulate the heaters independently, fans in the openings on the other side to circulate the air transversely of the kiln room and through the return passage repeatedly and means providing regulatable inlet and outlet openings at the opposite ends of the kiln for varying the rate of flow of the air through the kiln.

Moo

29. In a continuous drying kiln, longitudinally extending partitions forming an inner dry room and return passage thereover, the vertical partitions having openings disposed opposite each other. heaters in the openings on one side of the room, fans located in the openings on the other side for circulating the air transversely of the room and through the return passage repeatedly, means providing inlet and outlet passages at opposite ends of the kiln, a passage to the external air and a return passage from the outlet to the inlet, means to move the air lengthwise of the kiln and through the 'eturn passage to the inlet and regulatable dampers cooperating with said passages to, vary the rate of movement of the air lengthwise of the kiln and to condition the air entering the kiln by mixing the returned humid air with fresh air from the external atmosphere.

30. In a continuous drying kiln, a series of heaters arranged longitudinally thereof, thermostatically controlled devices to regulate said heaters independently of each other, means including fans to circulate the air transversely of the'dry room repeatedly in one direction, means providing inlet and outlet openings to and from the kiln to the external atmosphere and a return passage from the outlet to the inlet opening, means for circulating the air longitudinally of the kiln and the return passage to the inlet opening and a thermostatically controlled device to regulate the forward movement of the repeatedly circulating air in said kiln and to condition the air entering the kiln by mixing the return air'with fresh air to obtain a fixed moisture content.

Signed at Worcester, Massachusetts, this 28th day of October, 1920.

THURE LARSSON.

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