US2320172A - Tunnel kiln - Google Patents

Description

May 25, 1943. F.W. BROOKE ETAL TUNNEL KILN Filed June 19,

1939 5 Sheets-Sheet 1 & ATTORNEY 5 Sheets-Sheet 2 INVEN TUNNEL KILN Filed June 19, 1939 May 25, 1943. F. w. BROOKE ETAL May 25, 1943. F. w. BROOKE ETAL TUNNEL KILN 5 Sheets-Sheet 5 Filed June 19, 1939 May outrun srA'rss raraur or ies Frank W. Brooke and r Pittsburgh, lPa., assignors Corporation, Pittsburgh, Pa

Kennsylvania 13 Claims. (Cl. 13

The present invention comprises improvements in continuous tunnel kilns.

A primary object of the present invention is to provide a continuous tunnel kiln having two side by side goods passages, with separate walking beams at the bottom of two passages and means for giving said beams the movements necessary for the intermittent advancement of goods in opposite directions along the two goods passages, and having means for supplying to a central section or" the kiln, all, or the major portion, of the total amount heat supplied to the kiln, so that in each end section of the kiln,

heat may be transferred from the outgoing to the incoming goods, whereby the incoming goods are preheated, while the outgoing goods are cooled.

Prior continuous tunnel kilns include one type provided with a single goods passage and with a walking beam at the bottom of the passage for intermittently advancing goods in one direction through the kiln, include another type having two side by side passageways along which goods are moved in opposite directions by corresponding trains of kiln cars. So far as we are aware, however, we are the first to provide a kiln comprising two side by side goods passages along 1 ch goods are moved in opposite directions by walking beams at the bottoms of the respective passages. The use of walking beams to move goods along the two passages in opposite directions, has a number of advantages, including a reduction in the kiln heat losses, a reduction in kiln construction and operating costs, and the possibility of supplying heat at the bottoms of the goods passageways, by desirable kiln heating means not usable in kilns through which goods are moved on kiln cars.

A further main object or" the invention is to provide improved kiln heating means, adapted to supply sufficient heat to the goods from beneath the latter, so as to thereby avoid the tend ency, experienced in the operation of most existing continuous tunnel kilns, to the undesirable maintenance of lower temperatures at the bottoms, than at the tops of the goods masses or columns moved through the kiln chamber. Our improved kiln heating means comprise heating elements located below the bottom of the goods passage or passages and each extending transversely oi the kiln structure through an opening or chamber formed for the purpose in the refractory body portion of each kiln walking beam. Preferably, each of said chambers is open at its upper side so that the corresponding heating eleknown as globars.

hiilp diluc Dressier,

to Swindell-Dressler corporation or? ment may radiate heat at all times to the goods, or goods supporting tray or box, above it.

For certain kiln uses, in which relatively moderate maximum kiln temperatures are required, the heating elements may be of any usual or suitable form, and in particular may be tubular cornbustiou chambers of the general character now extensively used in heating intermittent furnaces of the removable bell type. Our improved kiln is well adapted, and of especial utility, for use in firing porcelain and for other purposes requiring relatively high maximum kiln temperatures, and for the maintenance of such rna"'inum tom eratures, we consider it desirable,

indeed practically necessary, to employ heating elements of the electric resistor type. For some uses, the electric heating elements may comprise the special silicon carbide resistors For use in firing porcelain and analogous high temperature operations, however, we consider it desirable to use heating elements of a type now known, in which each heating element comprises a resistor body in form 01 an elongated rod of graphite, graphite end members connected to the ends of the resistor body and substantially larger in diameter than said body and. a tube of silicon carbide surrounding the end members and resistor body, and in the ends of which the resistor end members fit snugly. Furthermore, in accordance with a method now known to the art, we advantageously pass gas into the space which surrounds the resistor body or" each heating element to thereby seal joints or cracks in the heating element, to protect the latter against oxidation.

Heretoiore, so far aswe are aware, electric heated kilns had been used in firing ceramics only to a small extent, and at relatively low ternperature, such as those employed in certain decorative processes, and in kilns, such as those in which the goods are moved through the kiln chamber on a roller hearth or by conveying means including work supporting parts extending through a slotv in the kiln chamber roof, so as to make it possible to locate electric heating elements below the ware, while at the same time avoiding the necessity of heating up large masses of refractory ware supporting material, such as refractory bodies of ordinary kiln cars.

According to our information and belief, the kiln disclosed and claimed herein is the first practical kiln adapted for use in firing ceramics at the relatively high temperatures of 2600 F. or so, required in the production of porcelain and certain other ceramic products. We believe, also,

our kiln is the first comprising refractory ware supporting means beneath the ware, and com prising heating elements also located below the ware, but so associated with the refractory ware supporting means as to avoid the necessity for highly heating large ware supporting masses of refractory material.

A further object of the invention is to provide our improved kiln with provisions whereby atmospheric conditions in the kiln can be controlled, and different atmospheric conditions can be maintained, when necessary, in different longitudinal sections of the kiln, so that in firing porcelain, for example, the kiln atmosphere may be oxidizing in the end portions of the kiln, and reducing in the central high temperature portion of the kiln.

' A further object of the invention is to provide simple and effective means for giving the two walking beams their movements.

The various features of novelty which characterize our invention are pointed out with pariicularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, however, its advantages, and specific objects attained with its use,

reference should be had to the accompanying drawings and descriptive matter in. which we have illustrated and described a preferred embodiment of the invention.

Of the drawings:

Fig. 1 is a somewhat diagrammatic sectional plan of a kiln;

Figs. 2 and 3 are longitudinal sectional elevations through central and end portions of the kiln, respectively taken on the line 2-2 and on the line 33 of Fig. 1;

Fig. 4 is a transverse section through the kiln on the line d-t of Fig. 2;

Fig. 5 is a diagrammatic sectional plan of aportion of a kiln including a modified form of electrical heating means;

Fig. 6 is a partial sectional elevation, taken similarly to Fig. 4, illustrating the use of fuel burning kiln heating elements;

Fig. '7 is a fragmentary sectional elevation, taken similarly to Fig. 4 of a kiln in which an electric heating resistor is mounted in and shares the movements of a walking beam;

Fig. 8 is a horizontal section on the line 8-8 of Fig. 7 and Fig. 9 is a diagrammatic plan view of a kiln oi modified form.

The kiln structure A shown in the drawings, is formed with two elongated side by side goods assageways B and b, which may be, and are shown as in free communication at their adjacent sides along the entire length of the kiln structure, except for a short portion adjacent each end of the structure, at which the passageways are separated by a central vertical partition wall A. The goods passageway B comprises a central high temperature portion between preheating and cooling end sections B and '3 respectively extending to the entrance and exit ends of the passageway from the adjacent ends of the high temperature section. The sections B and B are shown as of equal length and normally, each is longer than the central high temperature section. The goods passageway b comprises a central high temperature section, a preheating end section b, and a cooling end section 13 respectively, similar to the central and end sections B and B of the passage 13.

of passageway b. are respectively alongside the cooling and preheating sections B and B of passageway B, so that as goods are moved in opposite directions along the goods passageways B and b, heat is transferred to the goods passing through and preheated in the preheating section of each passageway, by goods which are passing through the cooling section of the other passageway and are thereby cooled.

At the bottom of each goods passageway, the kiln structure is formed with a corresponding slot A which is somewhat narrower than the goods passageway above it, and there are kiln bottom wall portions or ledges A and A at the inner and outer sides, respectively, of each slot A The slot A beneath the passageway B receives a walking beam structure D for intermittently advancing work supporting trays or boxes C, along the passageway B from its entrance to its exit end, and the slot A beneath the passageway b receives a walking beam structure d, which may be identical with the structure D, and is employed to intermittently advance the set of goods supporting members C in the passageway b, from the entrance to the exit end of the latter. The said bottom wall portions A and A at the sides of each slot A form shoulders or ledges which during recurring The preheating and cooling sections b and b periods in the kiln of the work supporting trays or boxes C extending across the slot.

As shown, each walking beam comprises a body portion, formed of blocks or bodies of refractory and heat insulating materials, specially shaped in accordance with the present invention, to provide passages or chambers D through which heating elements I, extend, as hereinafter described. Said blocks or bodies are supported on a heavy channel bar D forming a bottom sill or base portion of the beam. As shown, also, the refractory side walls of the kiln structure are supported on longitudinally extending metallic beam members E, and the refractory central pier A separating the two bottom wall slots A is supported by a series of metallic beam or pier members E. The members E'and E are supported in turn on transversebeams E resting on longitudinally extending pier portions E? of the masonry kiln foundation. The space between the beams E and above their lower edges, is sealed against communication with the external atmosphere by means including a sealing plate E interposed between the beams E and the superposed beams E and E.

Each walking beam is moved at alternate intervals, the frequency of which varies with the rate at which the goods are moved through the kiln, between a lower position. In its lower position shown in Fig. 3. each walking beam is below and out of engagement with the corresponding set of trays C above it, which then rest on the adjacent bottom wall portions or ledges A and A In its upper position, the upper edge of each beam is above the bottom wall portions A and A and supports the corresponding set of trays C, the weight of which is transferred from the corresponding bottom wall portions A and A to the beam on each up movement of the beam, and is transferred back from the beam to said bottom wall, portions, on each down movement of the beam. While each beam is in its elevated position, it is moved longitudinally of the kiln chamber in the direction to advance the trays then supported by the beam, toward the discharge end operation support the edges.

position and an upper of the kiln and when the beam is in its lower position, it is given longitudinal movement in the opposite direction.

The means employed to give each walking beam the above described movements may take various forms, but in the preferred construction illustrated, the walking beams are given their up and down movements by a common lifting mecha- I nism, and separate mechanisms are employed to give the beams their horizontal movements. As shown the bottom channel D of each walking beam rests at all times upon a series of rollers F distributed along the length of the kiln in pairs, each pair of rollers having a common axle F transverse to the kiln length. The rollers F underlying each walking beam are connected into one or more beam supporting units, by side bars i to which the ends of the roller axles F of the unit areconnected. As shown, the rollers F supporting each walking beam rests upon a corresponding track plate G which is supported by track girders G. Thelatter are connected at their ends to, and are supported by columns or posts G carried by lifting beams G As shown, there are two end to end lifting beams G underlying each walking beamand spaced away from one another at the center of the kiln, for a short distance to accommodate the operating mechanism. Each pair of side by side beams G are rigidly connected by cross beams G The parts (3, G G and collectively form a vertically movable platform structure, including an individual track plate G directly beneath and parallel to each walking beam. The platform is guided in its up and down movements and held against longitudinal movements by a pair of transverse frame members G connecting each side by side pair of lifting beams G As shown, the members G are of angle bar cross section and have parallel vertical flanges spaced apart to provide guides at opposite sides of a stationary guide member G shown as a channel bar, which may be connected in any suitable manner into the metallic frame work of the kiln.

Objectionable leakage through the vertical joint spaces between-the sides of the walking beams and adjacent side walls of the slots A is prevented by sealing means including the previously mentioned sealing plate E sealing provisions for preventing gas flow through openw ings E formed in that plate for the passage of the columns G Said seaiin provisions, as shown, comprise a casting E secured to the underside of the sealing plate at the margin of each opening E and including a depending tubular fiange portion surrounding the corresponding post G The lower edge of each flange extends into a sealing medium, which may be water or oil, held in corresponding pan-like receptacle G open at its top, which is at a-level well above the lower edge of the part or parts E I extending into the receptacle. In the construction shown, each post G forms part of a casting which also includes a second post G alongside the first mentioned post and beneath the other walking beam, and also includes a common scal ing receptacle portion G" receiving the lower ends of the tubular members E which surroundthe two integrally connected posts.

The lifting platform is adapted to be engaged and lifted by a plurality of crank arms El directly beneath each lifting beam G and carried by horizontal crank shafts H journalied at intervals along the length of the beam in a subjacent supporting sill H and each provided with an oper= ating arm H angularly displaced from the arm H, and pivotally connected at its upper end to a corresponding pull rod H As shown, each crank arm H carries an anti-friction roller i 1 directly engaging the corresponding beam.

The pull rods H are given longitudinal movements to thereby turn the crank arms H and. raise and lower the lifting platform, by means including a transversely extending rock shaft H6 at the center of the kiln structure and having a crank arm H connected to the plunger of a hydraulic cylinder H At each end, the shaft H has secured to it oppositely extending crank arms H and H The two crank arms H extend downwardly, and are respectively connected, by connecting rods H, to the two pull rods H associated with the right hand half of the kiln structure as seen in Fig. 2. The two crank arms H extend upward, and are connected by corresponding connecting rods H to the two pull rods iiassociated with the left hand half of the kiln structure. As will be apparent, angular movement of the rock shaft H in one direction will operate through the various crank arins H to simultaneously raise the two walking beams D and d from their lower positions shown in full lines in Fig. 3, to their elevated positions shown in dotted lines in that figure, and an opposite, angular movement of the shaft will return the beams to their lower full line position.

Each walking beam while in its elevated position, and the trays C then supported by it, is given a longitudinal movement in the direction in which the goods are moved through the corresponding passageway B or b, and while in its lower position and out of supporting engagement with the slabs C, each walking beam is given a return longitudinal movement by means comprising a corresponding rock shaft H extending transversely of the kiln structure adjacent the center of the latter and provided with a crank arm H connected by a link H to a bracket 13 secured to the underside of the bottom sill or channel beam D of the corresponding walking beam. Each of the two rock shafts H one for each of the beams D and d, is oscillated by means of a corresponding individual hydraulic cylinder H having its plunger connected to an operating crank arm H" carried by the rock shaft H Advantageously, each walking beam is given a cyclic set of movements to effect each inter mittent goods advancing movement, and to return the walking beams to the positions respectively occupied at the beginning of the cycle, during one oi a series of periods, which alternate with other periods in which the walking beams are stationary. line periods during which the walking beams remain stationary, may well be of considerably greater duration, than the alternating periods in which the beams are given their cyclic movements. For example, in a kiln m which a goods advancing movement is efiected once every five to twenty minutes, depending on the rate of kiln op ration, each cyclic set of movemerits may well be effected within a period of one minute or so. advantageously, moreover, be cause of the character of the hereinafter described kiln heating means, it is advantageous to have each walking beam held in its lower pcsition, and midway of its range of horizontal movement, during the periods between successive sets of cyclic movements. In consequence, during each set of cyclic movements, each walking beam is given its horizontal return movement in two stages or sections, one at the beginning and one at the end oi the cycle, and each of a length equal to half the length of the opposite goods advancin horizontal movement of the beam.

In the kiln structure shown in Figs. 1-4, heat is supplied to the central high temperature portion of each goods passageway by lower and upper? electric heating units I and i. The heating units I and i may be identical in construction but are diii'erently disposed in the kiln structure. The elements a extend transversely across the upper portions of both of the goods passageways, and are distributed along the length of the central high temperature portion of the kiln and have their ends supported in the side walls of the kiln structure. The lower heating units I are similarly distributed along the lengthof the intermediate high temperature portion of the kiln, and also have their ends supported in the side walls of the kiln structure, but are located at a level below the floor of the goods passageways and extend through the previously mentioned chambers or passages D in the refractory body portions of the walking beams, and through chambers or passages A formed in the central bottom wall pier portion A The chambers D ordinarily are larger than the chambers A so as to provide suitable clearance between the chamber walls and stationary heating elements I, in all positions of the beam. Each of the chambers or passages D and A is open at its upper side, so that the elements I radiate heat at all times against the underside of the work supporting slabs or body 0.

In the preferred construction shown, the heating elements I are of the character disclosed in the O'Neil and Callahan Patent No. 1,947,793, Feb. 20, 1934, each comprising a heating resistor proper in the form of a rod 1 of graphite having its ends screwed into axial sockets formed in the ends of graphite terminal bodies I, which are substantially larger in diameter than the resistor rod 1, and which have the latter terminal members l secured to their outer ends. Each element I includes a tubular outer wall or shell I which surrounds the graphite terminals I and rod I of the element, and is formed of silicon carbide or other suitable refractory material. The graphite terminal bodies I are of a diameter to fit snugly in and reinforce the ends ofthe tube 1 which are anchored in the side walls of the furnace structure, the graphite terminal bodies being ordinarily to the thickness of the furnace side walls. As shown, each metallic terminal I is screwed into the outer end of each graphite terminal body 1 Ordinarily and as shown, each metallic terminal I is formed with a space I through which a cooling fluid may be circulated to keep the temperature of the terminal suitably low.

As shown, a gas supply pipe I extends axially through each terminal part 1*, and is in communication at its inner end with a passage 1'' formed in the corresponding terminal body I and opening to the annular space 1 within the tube 1 and surrounding the resistor body I'. By passing a hydrocarbon gas, for example, propane,'into the space I of each heating element through the corresponding passages I and I during an initial operating period, joints or cracks in the heating element may be sealed as described in the patent of Gould No. 2,095,977, granted October 19, 1937. Such sealing action results from the deposit within-the cracks and joints of carbon liberated from the gas by a cracking action. The carbon thus cracked out of the gas and deposited in the cracks or joints, not only seals the cracks or joints, but also forms a good mechanical and electrical conducting bond between the opposing wallsof the cracks and joints. While hydrocarbon gas is being supplied to the heating elements, the latter are protected against oxidation, and after the joints and cracks are sealed, the element space may be kept filled with some inert gas, as nitrogen, supplied through the passages I and 1", thereby protecting the heating elements against oxidation.

For many uses for which the kiln construction illustrated in Figs. 1-4. is especially adapted, the kiln chamber will be provided at its ends with doors, but the latter may be of customary type and therefore need not be described herein,

Under conditions of operation making such heating desirable, special heating means may be provided to heat the goods moving through each of the preheating sections B and 12', toward the central high temperature portion of the kiln. For example, metallic electric resistor ribbons J may be disposed along the outer vertical wall of the preheating section of each goods passage as indicated inv Fig. 1. When conditions require, also, the kiln may have special cooling provisions, which may comprise vertical channels K in the outer side wall of the cooling .section of each goods passage as shown in Fig. 1. We have found,

of a length substantially equal use. the special kiln however, in practical operation of one kiln of the type and form shown in Figs. 1-4, employed in firing ceramics, with a temperature of about 2600 in the central high temperature portion of the kiln, that the heat transfer from the outgoing to the incoming goods in kiln is so effective, as to make special preheating and cooling provisions unnecessary, and the channels K of that kiln have been filled with suitable refractory heat insulating material. When it is desirable to cool the goods discharged from the kiln to a lower temperature than is readily obtainable with the kiln shown in Figs. 1-4, we may construction shown in Fig. 9.

In a kiln having the above described heating provisions the kiln atmosphere taminated by the discharge, or leakage, of products of combustion into the kiln chamber. consequence, it is readily feasible to accurately and is immediately beneath, and extends for substantially the full width of the kiln chamber roof.

the vertical outer walls of the section. To prevent the gaseous media passed into the kiln chamber through the nozzles L and inlets M, from createach end portion of the is not con- By passing air into each of the kiln chambers through the corresponding nozzle L, and passing a suitably reducing gas into the kiln chamber through the inlets M, and suitably regulating the vents N, we have found it possible to continuously maintain an oxidizing atmosphere in each end portion of the kiln and a reducing atmosphere in the central portion of the kiln, as is needed ior the production of high grade porcelain.

The heating elements extending through the walking beams or passages A may vary widely in form and type. For example, a separate set of heating elements IA may be provided for each walking beam as shown in Fig. 5. Each element IA comprises a casing body 1 of silicon carbide or other refractory material, in the form of a flattened tube which is closed at the inner end of the element. Mounted in the outer end of each casing is a plug like part I of silicon carbide, or the like, formed with two side by side passages. each receiving a corresponding graphite terminal body 1 To the inner end of each terminal body is secured the adjacent end of a corresponding resistor body or rod I of graphite, and at the inner end of the element, the two bodies 1 are connected by body 1 In Fig. 6, we illustrate the use of fuel burning kiln heating elements 1B disposed in a kiln struca heavy transverse graphite ture of the type shown in Figs. 1-4, in the same 1 general manner as the electrical heating elements I are disposed in those figures. merit 113 comprises a tubular casing or body, which may be a tube or pipe formed of metal in some cases, and in other cases of silicon carbide or other refractory material. The ends of said tubular body are mounted in the portions of the kiln structure at the outer sides of the two slots A At one end, the element IB is provided with a burner 1 shown as receiving fluid fuel and combustion air through pipes I and 1, respec tively. As the burner may be of conventional type, it need not be further described than to note that it is preferably so disposed in the element IB that combustion will be initiated at about the plane of the outer wall of the adjacent slot A. At its discharge end, each element 113 is connected to an uprising pipe 1 through which products of combustion leaving the heating element are passed to astack, directly, or prefer ably after passing through heat recovery means..

which, in some cases, may serve to preheat the air for combustion supplied through one or more connections I To assure similar heat supplies to the two goods passages B and b of the kiln,

heating elements 113 having their burner ends at one side of the kiln, may alternate with heating elements 113 having their burner ends at the 0pposite side of the kiln.

Figs. '7 and 8 illustrate a modification in which the refractory upper portion DA of a walking beam D or d is formed with a longitudinal heater chamber D in which is mounted an electrical heating resistor P. The latter may be in the form of a ribbon of a suitable metallic alloy, looped about projections D at the upper sides of rei ractory supports I) mounted in the lower portion of the heater chamber D. In practice, the

supports D may be vertically disposed refractory slabs serrated at their upper edges to provide the projections D and intervening resistor receiving notches. The chamber D which is more or less open at its upper side, and the resistor P may extend along the length of the entire per- Each heating eletion of the walking beam within the high tem perature portion of the kiln.

At each end, the resistor P is connected to a vertical terminal rod or cable Q, shown in Fig. 7

as extending downward through the walking beam ture and having its upper end in the chamber D and has a lower portion extending through an opening formed for the purpose in the bottom channel bar D of the walking beam. At its lower end, the terminal Q is connected to the inner end of a flexible copper cable R, which extends outwardly through openings G and E in the adjacent girder members G and E, into engagement with a terminal end member R. The latter is mounted in a disc E of insulating material which closes the outer end of a tubular metal part E secured to the outer side of the vertical web of the member E and sur rounding the corresponding aperture E A resistor P formed of an alloy comprising 80 parts of nickel and 20 parts of chromium can safely withstand a temperature of 2100 F. That temperature is not high enough to produce the maximum kiln chamber temperature needed in firing hard porcelain, but is adapted to produce the maximum kiln temperature needed for various industrial processes in which continuous tun nel kilns may advantageously be employed.

The modified kiln arrangement AA illustrated in Fig. 9, need not differ from that shown in Figs. 1-4, except in that at each end, the kiln structure AA comprises a portion A enclosing a discharge end portion of the corresponding goods passage cooling section B or 12 which extends beyond the inlet end of the adjacent preheating sections 1), B, respectively. Each such cooling section extension A of the kiln structure may include special cooling provisions, which may take any of the forms customarily employed in the goods cooling end of a continuous tunnel kiln having a single kiln passage. With the arrangement, shown in Fig. 9, the temperatures to which the outgoing goods are cooled prior to their discharge from the kiln is not limited by the need for maintaining a temperature differential or heat head between the entering and outgoing goods, as is needed with the kiln shown in Figs. 1-4.

While in accordance with the provisions of the statutes, we have illustrated and described the best forms of embodiment of our invention now known to us, it will be apparent to those skilled in the art that changes may be made in the form of the apparatus disclosed without departing from the spirit of our invention as set forth in the appended claims and that in some cases certain features of our invention may be used to advantage without a corresponding use of other features.

Having now described our invention, what we claim as new and desire to secure by Letters Patent, is:

l. A continuous tunnel kiln comprising two side by side goods pathways, a walking beam at the ing means adapted to maintain temperatures substantially higher in the central section of the kiln than in its end sections comprising a set of transverse stationary electrical heating elements extending through said transverse passage.

2. A continuous tunnel kiln comprising two side by side goods pathways, a goods advancing walking beam at the bottom of each pathway, a common means for raising and lowering the two walking beams, separate means for giving each walking beam longitudinal movements relative to the other and to said lifting means, whereby each walking beam is adapted to intermittently advance goods along the corresponding pathway in a direction opposite to that in which they are advanced by the other beam along the other pathway, and kiln heating means adapted .to maintain temperatures substantially higher in the central section of the kiln than in its end sections. I

3. A continuous tunnel kiln comprising two side by side goods pathways, a Walking beam at the bottom of each pathway, a common mechanism for raising and lowering the two beams, separate means for giving each beam a longitudi-= nai movement in one direction when raised and a longitudinal movement in the reverse direction when lowered, and kiln heating means adapted to maintain temperatures substantially higher in the central section of the kiln than in its end sections.

4. A continuous tunnel kiln comprising two side by side goods pathways, a walking beam at the bottom of each pathway, a common mechanism for raising and lowering the two beams, separate means for giving each beam a longitudinal movement in one direction when raised and a longitudinal movement inthe reverse direction when lowered and simultaneously with each such longitudinal movement giving the other beam a longitudinal movement in the opposite direction, and kiln heating means adapted to maintain temperatures substantially higher in the central section of the kiln than in its end sections.

5. A continuous tunnel kiln comprising two side by side goods pathways, a walking beam at the bottom of each pathway, beam raising and lowering mechanism comprising a platform portion beneath and extending longitudinally of each beam, supporting rollers interposed between each beam and the subjacent platform portion and having horizontal axes transverse to the kiln, and separate means for giving each beam a longitudinal movement in one direction when raised, and a longitudinal movement in the reverse direction when lowered, and kiln heating means adapted to maintain temperatures substantially higher in the central section of the kiln than in its end sections.

6. A continuous tunnel kiln comprising a kiln chamber having a slot in its bottom wall, a walking beam in said slot formed with transversely extending passages, means for giving the beam up and down and longitudinal to and fro movements, and horizontal heating elements mounted in the kiln structure and extending transversely of the latter through said passages and adapted to be heated to a temperature in excess of 2,000 F.

7. A continuous tunnel kiln comprising an elongated kiln chamber formed withtwo side by side slots in its bottom wall separated by a central pier portion formed with transversely extending passages, a walking beam in and substantially filling each slot and formed with transversely extending passages with which the first mentioned passages are in register in all positions of said beams, means for giving said walking beams up and down and horizontal to and fro movements, and heating elements mounted in the kiln structure and extending transversely of the latter each through a passage in said pier portion and through the registering passages in the two walking beams.

8.1%. continuous tunnel kiln formed with an elongated kiln chamber and with a slot in the bottom wall of the chamber, a walking beam in said slot comprising an upper portion of refractory material formed with a plurality of transverse passages distributed longitudinally of the walking beam and each open at the upper side of the latter and heating elements mounted in the kiln structure and each extending through one of said passages, and means for giving said walking beam a cyclic set of movements including an up movement, a longitudinal movement in one direction, a down movement and a longitudinal movement in the opposite direction.

9. A continuous tunnel kiln formed with an elongated kiln chamber and with a slot in the bottom wall of the chamber, a walking beam in said slot and formed with a plurality of transverse passages distributed longitudinally of the walking beam, heating elements mounted in the kiln the charge supporting structure and extending through said passages, and means for giving said walking beam a cyclic set of movements including a longitudinal movement in one direction, an up movement, a. longitudinal movement in the opposite direction, a down movement and a longitudinal movement in said one-direction, each. of said longitudinal movements in said one direction being approximately half as long as each longitudinal movement in the opposite direction. 1 r

10. A continuous tunnel kiln comprising a kiln chamber and having a slot in the bottom wall of the chamber, a walking beam in said slot having an upper portion of refractory material formed with transversely extending passages, means for giving the beam up and down and longitudinal to and fro movements, and horizontal electrical heating elements mounted in the kiln structure and extending transversely of the latter through said passages.

11. In a continuous kiln of the walking beam type for advancing a charge through a chamber consisting of a preheating zone, a high temperature zone and a cooling zone, the combination which comprises a plurality of transverse charge supporting members forming the bottom of the chamber; a vertically and horizontally reciproeating charge advancing beam structure under said supporting members with a plurality .of transverse members adapted to lift and advance members during a portion of the path of travel of said beam structure, and a plurality of transverse channels, extending through said transverse members, below the charge supporting members in the bottom of the high temperature zone defined by the path of travel of said transverse beam structure members; a plurality of transverse stationary exposed elements extending through the top of the high temperature zone and staheating elements extending throu h said transverse channels below the charge supporting members in the bottom of the high temperature zone to uniformly heat the charge on said charge supporting members in said zone.

12. In a continuous tunnel kiln of the walking beam type having two chambers in each 01 which is a preheating zone, a high temperature zone and a cooling zone, with the preheating zone of each chamber adjacent to the cooling zone of the other chamber, a combination which comprises, a plurality of transverse charge supporting members forming the bottom of each chamber; a vertically and horizontally reciprocating charge advancing beam structure under said supporting members of each chamber with a plurality of transverse members of each beam structure adapted to lift and advance charge supporting members during a portion of the path of travel of the respective beam structure, and a plurality of transverse channels through both beam structures below the charge supporting members in the bottom of the high temperature zone common to both chambers, with said channels defined by the path of travel of said transverse members of each beam structure under the high temperature zone; and a plurality of transverse stationary exposed electrical heating elements positioned in the top of the high temperature zone common to both chambers and stationary electrical heating elements extending through said transverse channels below the respective charge supporting members in the bottom of the high temperature zone to uniformly heat the charges on the respective charge supporting members in said zone.

13. A continuous tunnel kiln as specified in claim 1, comprising a set of transverse electric heating elements above the goods pathways.

FRANK W. BROOKE. PHILIP DHUC DRESSLER.

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