CA1048751A - Continuous tunnel kiln for curing molded concrete products - Google Patents

Abstract

CONTINUOUS TUNNEL KILN FOR CURING MOLDED

CONCRETE PRODUCTS

ABSTRACT OF THE DISCLOSURE
A system for curing molded concrete products, such as green concrete blocks supported on pallets, wherein a carousel chassis mounting circumferentially spaced carriers, with generally radially extending, vertically spaced shelf members for supporting the products, is disposed for indexing rotary travel in a circular kiln tunnel, the carousel carriers comprising racks with substantially imperforate inner and outer end walls, a substantially imperforate bottom wall, a substan-tially imperforate radial wall, and a substantially imperforate top wall, but being sidewisely open at at least one side. Cir-cumferentially spaced groups of rack surrounding seals compris-ing circumferentially spaced resilient wiper blades are mounted to form sealed compartments between the groups as a result of carriers being stopped in indexed position at a series of cir-cumferentially spaced locations in the tunnel, and means is provided for introducing heated air with entrained steam into certain compartment, recirculating it, and entraining added steam in the recirculated flow. At least one carriage mounted for reciprocatory movement on the tunnel floor indexes the carousel chassis which is supported on rollers which adjust in posi-tion automatically to accommodate variations in chassis level.

Description

1()487S~L
This invention relates to kilns for curing molded concrete products, and particularly green cement blocks supported on pallets, in much shorter time periods than has been possible heretofore.
In production plants producing quantities of cementitious blocks in production lines having automated machinery for making and handling the block produced, it is important to cure the green blocks produced at an accelerated rate which does not require the many hours of steaming and soaking which have been deemed necessary in past systems.
Recently, designers have sought to build systems in which block can be continuously processed under well-controlled conditions and some have utilized circular tunnels which are open at one side to permit blocks to be automatically loaded and unloaded from the racks which travel in the circular kiln tunnel. I refer particularly to the Anderson United Statespatent No. 3,545,733 and the LaForest patent No. 2,969,577 which are typical of prior art structures. Rack carriers, which substantially engage the walls of the tunnel in which they move, so as to provide isolated treating compartments within the tunnel in which they move, have also been used (see Nerge United States patent No. 3,234,661) and more recently such racks for carrying cement block have been used in a circular - tunnel of the Anderson type in several commercial appli-cations. The present invention relates to certain im-provements in such systems which will be described and are delineated in the claims.
One of the prime objects of the present invention is to provide a superior kiln which is capable of producing high quality products in a relatively short curing time such lV9~87Sl as 5 hours, using available aggregates and cements (i.e. type I) in the area in which the kiln is to operate.
A further object of the invention is to provide a continuous and uniformly controlled curing kiln, particularly for the concrete block industry, wherein novel blade assembly seals are provided at predetermined circumferentially spaced locations within a circular processing tunnel to cooperate with carousel chassis-mounted racks which engage these seals to provide isolated sections or compartments within the tun-nel whose recirculated atmosphere is so eontrolled that thehydration of the cement is accomplished, in a manner to pro-vide uniformly high quality products.
A further object of the invention is to provide an automatic system of the character described which permits the high speed operation of the associated block-making and other handling equipment in an economic manner.
Still another object of the invention is to design a kiln of the type indicated which requires substantially no re-pair or maintenance and operates completely automatically to process the blocks on a first in - first out basis, through a controlled atmosphere in aceordanee with the eomposition of the bloek being proeessed.
Another objeet of the invention is to provide an improved earousel strueture wherein a ehassis made up of areuate seetions, having spaeed apart raek mounts, is pro-vided for supporting the raeks whieh travel in the kiln system.
Still another objeet of the invention is to provide a system of the eharaeter deseribed wherein heated air with entrained steam is introdueed into steam eompartments, reeir-eulated, and wherein added steam is entrained in the reeir-eulated flow dependent on eonditions measured within the partieular eompartment.
A still further objeet of the invention is to design a kiln system of the character described wherein an improved carousel indexinq mechanism is employed.
Still another object of the invention is to provide a continuous kiln of the type mentioned wherein the rack carousel is supported on an automatically self-aligning sys-tem of independent rollers which can individually accommodate to the carousel surface which they support at a given moment.
Other objects and advantages of the present inven-tion will become apparent to those of ordinary skill in the art as the description thereof proceeds.
An improved carousel comprising a chassis with spaced apart rack carriers mounted thereon is moved on guides, such as guide rollers, provided in a circular kiln tunnel.
The rack carriers, while sidewisely open, have substantially imperforate end and top and bottom walls, and a substantially imperforate radial wall, and cooperate with circumferentially spaced groups of seal blades mounted in the tunnel to form sealed compartments between the groups as a result of the carriers being stopped in indexed position at predetermined locations in the tunnel. Hot air with entrained steam is introduced into certain of the compartments and recirculated continuously.
Figure 1 is a schematic top plan view of the kiln with portions of the annular tunnel roof and carousel racks removed in the interest of clarity;
Figure 2 is an enlarged, fragmentary, transverse, sectional view taken on the line 2-2 of Figure 1, and illus-trating the mechanism for introducing heated air with en-trained steam to those portions of the kiln tunnel which employ it in the processing operation;
Figure 3 is an enlarged, fragmentary, transverse, sectional view taken on the line 3-3 of Figure 1, and particu-larly illustrating the construction of a rack carrier, and mechanism for indexing the carousel and racks around the kiln;
Figure 4 is an enlarged, fragmentary side eleva-tional view taken on the line 4-4 of Figure 3 to particularly illustrate the carousel indexing mechanism, the chain lines illustrating a tilted, inoperative position of the rack engaging dog;
Figure 5 is a top plan view thereof;
Figure 6 is an enlarged, top plan schematic view of several racks illustrating the manner in which products are supported by the shelves of the rack carriers;
Figure 7 is an enlarged, fragmentary, transverse sectional view, taken on the line 7-7 of Figure l, and par-ticularly illustrating the tunnel seal blade assemblies which define the kiln processing compartments;
Figure 8 is a sectional plan view taken on the line 8-8 of Figure 7;
Figure 9 is a top plan view of a carousel chassis section;
Figure lO is an end elevational view thereof, taken on the line lO-10 of Figure 9;
Figure 11 is a perspective, plan view of a wiper pan which is mounted on the underside of the chassis section under each rack mount fabrication which is provided thereon;
Figure 12 is a schematic, electrical control system diagram;
Figure 13 is a transverse sectional view, similar to Figure 3, illustrating a preferred form of carousel sup-port system;
Figure 14 is an enlarged fragmentary view of a sup-port element used in the system; and Figure 15 is a side elevational view thereof.

Referring now more particularly to the accompanying drawings, and in the first instance particularly to Figure 1, 7S~
a letter K generally designates the kiln or kiln frame which includes octagonal inner and outer siae walls 10 and 11, re-spectively, covered by a top wall 12. The walls 10 - 12 are of insulated character, comprising, for example, a foam plastic core sandwiched between inner and outer metal sheets, and the walls 10 - 12 together form an enclosure open along its bottom which can rest on the concrete floor 13 of a concrete block manufacturing plant (see Figure 3).
The inner and outer walls 10 and 11 have a break or opening lOa and lla respectively, provided for purposes of permitting access for a loader machine, generally designated L, and an unloader machine generally designated U, which load palleted blocks to, and unload palleted blocks from, the kiln K. As Figure 1 indicates, bulkheads 14 - 22 divide the en-closure K into a series of arcuate compartments 23 - 30, the purpose of which will presently become apparent.
Provided within the enclosure K and extending through the compartments 23 - 30, are a series of pedestals 31 (Figure 3) which bolt to plates (not shown) embedded in the floor 13. The pedestals 31 are bifurcated at their upper ends and mount cross pins 33 on which guide rollers 34 are freely rotatable. Also provided on like pedestals 31, are horizontal rollers 35, journaled on vertical pins 33a which are operative to engage the chassis assembly of a carousel generally designated C, which will now be described.
The chassis assembly (Figures 3 and 9 - 11), which forms the base framework for the carousel, comprises circum-ferentially abutting arcuate sections A (one section and a fragmentary portion of the next adjacent section being shown in Figure 9) each consisting of arcuate inner and outer tubular members 36 and 37, respectively, joined by pairs of radially extending channel members 37a and by end members 37b.

The end members 37b may be bolted or otherwise secured together ~048751 to fix the arcuate sections A in circular formation. Welded in position radially intermediate the tubular members 36 and 37 are arcuate bar members 38 and 39 which secure to the undersides of members 37a and 37b. It is to be understood that the pairs of channels 37a function as mount plates for rack carriers, generally designated R, which bolt to their upper faces as at 40. Welded in position between the bars 38 and 39 are thrust blocks 41, which in a manner to be de-scribed, are engaged by indexing mechanism (to be described) for moving the carousel C around the kiln enclosure K.
As Figures 3 and 6 indicate, each wedge-shaped rack R includes sets of outer, upright angle members 42, inter-mediate angle members 43, and inner butting angle members 44.
Welded to the upper and lower ends of the angle members 42, 43 and 44 are solid, imperforate upper and lower walls 45 and 46, respectively, which completely cover the upper and lower ends of rack R, and it will be observed that it is bottom walls 46 which bolt to the chassis members 37a. While the radial sides of racks R are open, imperforate solid end walls 45a and 46a completely cover the ends of each rack R as indicated in Figures 3 and 6. Also, a solid, imperforate, radially extend-ing partition 47 effectively segregates one side of the rack R from another. Welded to the angles 42 - 44 are vertically spaced, horizontally disposed, radially extending angle bars 47a which provide a designated number of shelf members 47a (in this instance nine) as predetermined by kiln requirements.
In a typical installation, the shelf members 47a will support a series of pallets P (such as six) which may typically sup-port three concrete blocks apiece, the pallets and products being supported between the opposing shelves 47a of adjacent racks R as particularly indicated in Figure 6. Provided on the chassis assembly below each rack R is a wiper pan member, generally designated 48 (Figure 11), which is intermediately 1~4~751 recessed as at 48a to accommodate the bars 39. The pans 48 are welded to the members 37a and 39 to further seal the bottoms of racks R.
Provided at each of the bulkheads 14 - 22 are rack-surrounding wiper blade assemblies generally designated W
(Figures 1, 7 and 8) which are shown in detail in Figures 7 and 8. Each of the wiper assemblies W includes four separate side, bottom and top wiper units 49a, 49b, and 49c respec-tively, which are so positioned as to each be engaged by a rack R passing therethrough. The construction of the wiper units 49a - 49c is identical so the construction of only one will be described-in detail. In Figure 8, one of the bulk-heads 16 is shown as supporting a vertical plate 49 ha~i~g spaced apart angle members 50 fixed thereto. Opposite angle members 50 are supported by a like frame strip or wall 49.
Each of the angle members 50 supports a resilient rubber wiper blade 51, which, for example, may be made of a flexible resilient neoprene material. The spacing between blades 51, which typically might be eight inches, for instance, is some-thing less than the distance _ (Figure 6) constituting thewidth of each rack R at its inner end (which might typically be ten inches) so that there will always be at least one blade 50 (and preferably two) in contact with the end surface of the indexed rack R when the rack is halted in indexed position.
Further, the over-all depth b of each wiper unit 49a - 49c is so predetermined as to be always greater than the space c (Figure 6) between racks R. This, with proper indexing, assures that, when the racks R are stopped in indexed position, there always will be a rack R at each wiper unit W, thus effectively isolating each of the compart-ments 23 - 30.
Provided to index the racks R of the carousel C a predetermined distance d (Figure 6), which insures that a '' :.
.

7Sl rack R Will always be disposed in radial confronting position with relation to each of the wiper units W, are a pair of carousel indexing units I. Figures 1, 4 and 5 particularly illustrate the indexing units I which are utilized, as shown in Figure 1, at generally radially opposite locations. Fixed in position at the bottom of compartment 24 and the loading-unloading zone, are frameworks generally designated 52, Figures 4 and 5, which include a bottom plate 53, and a top plate 54, connected by spacer members 55, the spacers 55 being spaced apart for a purpose which will presently be described.
The top plates 54 include openings 56 with arcuate walls 56a and 56b (Figure 5) conforming to arcs taken on the axis of revolution of the carousel C. Mounted to move back and forth along opening 56 is a carriage 57 mounting dependent, horizontally disposed, rollers 58 which engage the walls 56a and 56b of the opening 56 and assure that the carriage 57 will be moved in an arcuate path corresponding to the arcuate path in which the carousel chassis thrust blocks 41 (Figure 9) are moved. Also provided on the carriage 57 are sets of upper and lower guide rollers 59 and 60, respectively, which travel along the plate 54 at the edges of opening 56.
Mounted on a platform 61, atop each carriage 57, is a carousel pusher assembly comprising support bars 62, journal-ing a pin 63 on which a dog member 64 is eccentrically pivotally mounted. The dog member 64 has a locating key 65 for engage-ment with platform 61, as shown in Figure 4, when the dog is in rack indexing position, and also includes a stop member 66 which limits the extent of its movement beyond the inoperative position (shown in broken lines in Figure 4). It will be ob-served that the dog 64 is mounted off-center so that it will always be gravity-returned to the position in which it is shown in Figure 4.
Provided to reciprocate each carriage 57 is a 7S~
double acting, hydraulic cylinder 67, disposed inside the inner wall 12 as shown, so as to separate the cylinder 67 from the atmosphere of the kiln treating compartments. Each cylinder 67 includes a piston rod 67a, to which a chain 68 is connected which passes through an opening 74 in wall 12 around a sprocket 69 journaled on a pin 70 provided on the platform assembly 52. The chain 68 is connected to the indexing car-riage 61 by a suitable coupling member 71. Also connected to the piston rod 67a is a return cable 72 which passes around an idler pulley 73 mounted within the inner enclosure wall 12 and which extends through a similar opening 74 in inner wall 12 to a series of idler pulleys 75, 76 and 77, and finally connects to the carriage at 78.
Figures 1 and 2 illustrate the mechanism for sup-plying hot air, or hot air and steam, to the treated compart-ments. In Figure 1 an oil heater unit 79, which supplies hot - oil to the heating system now to be described is shown. Hot oil from the heater 79 is pumped via supply lines 80 to a circular manifold 81 and via lines 80a to a series of fin tubes or coils 82 (Figure 2) disposed in the vertical air supply heater assembly H, which is depicted in Figure 2. The oil returns through a manifold 81a and return lines 80b and 80c.
The assembly in Figure 2 provides a tubular vertical duct 83 to receive air from a blower fan 84 which moves it to a lower manifold 85, connected with a duct 86 which, as Figure 1 in-dicates, extends radially to the inner side of the indexing pathway of the racks R. At the upper end of the unit, a re-turn duct 87 receives the atmosphere of the particular com-partment and returns it to fan 84 for recirculation. The units H in compartments Z3 and 24 are constructed as described thus far. In those compartments 25 - 28 which also require the injection of steam under pressure, a steam pipe 88, sup-plied with steam from a suitable source such as a steam boiler 1~875~
which may be disposed within the inner wall 12 adjacent to oil heaters 79, has nozzle ports 89 which inject the steam S in a countercurrent direction to the air which is being forced through the system in the direction of arrows x by fan 84.
Alternatively, pipe 88 might be a water pipe releasing water under tap pressure in a fine stream through the fine nozzle ports 89 into the heated air stream for instant vaporization to provide the requisite entrained steam. In compartments 29 and 30 no unit heater H is utilized and, rather, cooling fans 90 are provided to introduce ambient air at room temperature to compartment 30 (which then is exhausted through ducts provided in the roof of the enclosure). Com-partment 29 is a bleed off chamber from which steam vapor may be removed by roof fans.
Figure 12 illustrates a typical circuit in which a circuit line 1-1 connected across a power source represented by lines L-l and L-2 includes a fan motor 84 and a thermostat T. There would be such a line 1-1, including the components described, for each of the compartments 23 and 24, which utilize heated air only (no steam) and comprise presetting compartments in which the blocks take a preset at elevated temperatures which typically might reach llO~F. When the thermostats T in either of chambers 23 and 24 indicate that the temperature is falling below such a preset level, the fans 84 in these compartments will be turned on to blow warm air past the fin tubes 82 and raise the temperature to the desig-nated level once again. The oil heater 79, which includes a continuously operated pump, supplies hot oil to all of the fin tubes 82 in the system.
Lines 1-2 are utilized for each compartment 25 - 28 which receive entrained steam in the heated air, and a humidi-stat ~ is utilized in each compartment to operate a solenoid-opened valve V, when the humidity falls below the designated 1~87Sl level. A parallel line 1-3 for each line 1-2 includes the thermostat T provided in each compartment 25 - 28. It will be noted that the valve V can be opened to provide entrained steam only when the fan 84 is operating, whereas the fan 84 in each of these compartments can supply heated air without steam, when so directed by the thermostat T in the particular compartment. The temperature may be gradually increased to 190F as the blocks proceed from compartment 25 to compartment 28, with the thermostats being set in compartments 25 - 28 to maintain typical intermediate levels therein respectively.
At the right end of the kiln in Figure 1, the loader L loads the palleted blocks sequentially to the shelves 47a of adjacent racks R to dispose them in the supported posi-tion illustrated in Figure 6 at a time when the carousel C is halted in an indexed position. At the same time, the unloader U unloads pallets sequentially from the racks R which have moved into the unloader zone from the compartment 30. Such loading and unloading equipment is commercially available and need not be described here.
Once loading and unloading has been accomplished, the pair of cylinders 67 are concurrently activated to move carriages 61 in a clockwise direction in Figure 1, to the end position in which they are shown in Figure 1, dogs 64, being in the upright position shown in Figures 4 and 5, and engag-ing one of the thrust blocks 41 to move the carousel C clock-wisely an increment such as to advance the carousel the distance d. The indexed distance d is predetermined to halt the follow-ing rack R in each instance in a position radially opposite a wiper assembly W so that when the carousel C is halted in indexed position, there will always be a rack R sealing each of the wiper units W and effectively isolating each of the compartments 23 - 30. The double acting cylinders 67 are then immediately reversed, so that cables 72 return the ~)487Sl carriages 61 in a counterclockwise direction. When the in-dexing dogs 64 contact the following thrust block 41, their cam surfaces 64a will move them to the tilted, inoperative position shown in chain lines in Figure 4, so that they pass beneath the following thrust block 41 to the opposite side (counterclockwisely) thereof. Finally, when the carriages 61 are in halted, return position, the dogs 64 will have been moved counterclockwisely slightly beyond the following thrust blocks 41 and will be gravity restored to the solid line posi-tion illustrated in Figure 4. The spacer blocks 55 (seeFigure 4) are so spaced apart that the carriage 61, sans lower wheels 60, can be readily assembled (and lower wheels 60 then readily engaged).
The carousel C is indexed through identical distances d in a uniformly timed manner, such that èach product processed requires the same amount of time to proceed from the loading machine L to the unloading machine U, and since conditions in the kiln K are rigidly controlled, it should be clear that the blocks will all be subjected to identical curing conditions and will be cured uniformly.
It has been determined in practice that a carousel cannot be fabricated so precisely, on a production basis, that its lower, roller engaging surface extends in a common horizontal plane. With the structure disclosed in Figure 3, carousel breakdown problems have occurred because of minimal differences in the level at which rails 36 and 37, for instance, ride, and because the lower surfaces of rails 36 and 37 themselves do not uniformly lie in a common horizontal plane. This misalignment, due to irregularity in the fabrica-tion of the carousel, tends to force the carousel off centerand tends to produce a ride condition in which the edges of the rollers 34 and 35 are in engagement with the rails 36 and 37, and tend to score them. Moreover, the life of rollers 34 1~4~Sl and 35, with the heavy load carried by the rack carriers undermisaligned conditions, has been found to be short.
To obviate these difficulties, an improved version of the invention includes a series of circumferentially abut-ting arcuate wear strips 100, welded to the lower surfaces of rails 36 and 37. It is to be understood that the entire kiln structure remains the same in this modified embodiment of the invention, except for the changed construction (including wear strips 100) which will now be described, wherein the rollers 34 are supported for restricted universal movement as well as rotation.
In the modified embodiment, the rollers 34 are used in pairs, as indicated particularly in Figure lS, and they are journaled on bushings 101 provided on transversely or radially disposed pins 102. The bushings 101 may suitably be bronze bushings of a type which may be readily procured in the marketplace.
The pins 102 are supported by a generally box-like roller mount frame structure, generally designated 103, which 20 i5 itself pivotally supported by a pivot pin 105 which extends transversely or radially as indicated. The pin 105 is sup-ported by an intermediate frame mount 106, journaled by similar bushings 107 provided for a pin 108 supported by the fixed base mount structure, generally designated 110, which is fixedly supported on the bed 13.
Each of the pins 102, 105, and 108 is notched or flatted as at 99 and each is prevented from rotating by a keeper plate 109. As Figures 14 and 15 indicate, the base mount 110 includes a bottom anchor plate 111 which may be bolted or otherwise fixed to the concrete floor 13.
The base structure 110 includes a pair of end walls 112 and a pair of side walls 113 and the roller mount 103 includes side walls 114 joined by end walls 115. Supports 116 87Sl are fixed on side walls 114 and include lower portions 117having openings 118 for journaling the roller mount structure 103 on the pin 105.
Each of the pins 102, 105, and 108 includes a suitable cotter pin "c", and a grease filling "g" to provide proper lubrication. The intermediate frame structure 106 comprises side plates 119 with end members for supporting bushings 107. Pivoting movement of the intermediate frame structure 106 on bushing 107 is limited by the engagement of the lower surfaces of plates 119 with the upper surfaces of base plates 113 and typically a space of about 1/16" is left between these members. This permits a limited pivoting of frame structure 106 and the structure 103 and wheels 34, which it carries, in a radial plane or direction as indicated by arrow "a".
The pivoting of intermediate frame structure 103 ; on pin 105 in what may be termed a generally circumferential plane, or a vertical plane, as indicated by arrow b, is limited by engagement of the side plates 114 with the end plates 112 of base structure 110, and typically a 1/16" space is also provided between members 114 and 112.
The wear strips 100 are preferably constructed of "jalloy" plate of 400 to 500 Brinell hardness and these are engaged by the wheels 34 which typically may have a hardness factor of 360 Brinell. Shims are, in some instances, used between the base plates 111 and the floor 13.
In practice, each pair of rollers 35 has essentially a restricted universal pivoting movement with relation to either the rail 36 or the rail 37 which it is supporting, and is capable of universally rocking to accommodate to irregu-larities in carousel chassis construction, to the extent that - line contact across the width of wheels 34~ as indicated in Figure 13, is maintained by these load-bearing surfaces. ~ith 87~il the structure described, down-time is not a material economic factor in the operation of the circular kiln systems which have been described.
It is to be understood that the drawings and descriptive matter are in all cases to be interpreted as merely illustrative of the principles of the invention, rather than as limiting the same in any way, since it is contemplated that various changes may be made in various elements to achieve like results without departing from the spirit of the invention or the scope of the appended claims.

Claims (19)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An apparatus for curing molded concrete products such as uncured concrete blocks supported on pallets; com-prising a circular tunnel structure having inner, outer and top walls defining an essentially closed passageway except for ends at which loading and unloading can be ac-complished; a turntable means mounted for travel about an axis of revolution, comprising circumferentially spaced carriers, with vertically spaced generally radially ex-tending shelf members for supporting the products, dis-posed for indexing rotary travel in said passageway; said carriers having substantially imperforate inner and outer end walls, a substantially imperforate bottom wall, a sub-stantially imperforate radial wall, and a substantially im-perforate top wall, but being open on each side of the radial wall; circumferentially spaced seals mounted to form sealed compartments as a result of carriers being stopped in indexed position at a series of circumferen-tially spaced locations in said tunnel; means for intro-ducing heated air with entrained steam into certain com-partments, recirculating it, and entraining added steam in the recirculated flow; and means for indexing the turn-table means in increments to dispose carriers radially op-posite said seals at said spaced locations.

2. An apparatus as claimed in claim 1, in which said means for introducing heated air with entrained steam includes a fan and ducting for housing heating elements con-nected with a supply duct leading to certain compartments, and a return duct leading therefrom, and a fluid supply nozzle to entrain steam in the hot air circulated by the fan is disposed to direct the fluid in a counterflow direction to the air flow.

3. An apparatus as claimed in claim 2 in which the fluid is steam.

4. An apparatus as claimed in claim 2 in which the fluid is water.

5. An apparatus as claimed in claim 2, 3 or 4 in-cluding means for sensing the humidity and temperature in said compartments and operating said fan and nozzle ac-cordingly, with said nozzle being operated only when said fan is operating.

6. An apparatus as claimed in claim 1 wherein said seals comprise circumferentially spaced groups of circum-ferentially spaced resilient wiper blades mounted on said tunnel structure along the top, bottom, and inner and outer walls of the tunnel structure along the pathway followed by said rack carriers to extend into the path of said carriers and form sealed compartments between said groups as a result of carriers being stopped in indexed position at a series of circumferentially spaced locations in said tunnel structure, radially opposite said groups, said groups of blades being spaced apart a distance equal to a multiple of the distance between the radial walls of said carriers.

7. An apparatus as claimed in claim 6 in which said groups are of a circumferential extent greater than the cir-cumferential extent of said end walls.

8. An apparatus as claimed in claim 7 in which the circumferential spacing between blades is less than the cir-cumferential extent of said end walls and said inner and outer end walls of the rack carriers are curvilinear and substantially conform to arcs taken from the axis of revo-lution of the turntable.

9. An apparatus as claimed in claim 2 in which said heating elements comprise heated fluid-filled tubes pro-vided in said ducting and past which said atmosphere is moved to the supply duct upstream of said fluid supply nozzle.

10. An apparatus as claimed in claim 1, in which said turntable means comprises a circular chassis made up of joined arcuate sections comprising inner and outer circumferentially extending rails joined by radially extending members forming circumferentially spaced wedge shaped rack mounts, said carriers comprise upstanding racks fixed on said mounts, and rollers are mounted on said tunnel structure to engage and support said chassis for travel in its rotary pathway.

11. An apparatus as claimed in claim 10 in which thrust blocks are provided in circumferentially spaced position on said sections circumferentially intermediate said rack mounts and radially between said inner and outer rails, and said means for indexing the turntable means includes a dog for engaging said thrust blocks and moving the turntable means.

12. An apparatus as claimed in claim 11 in which said arcuate sections have radially extending end rails and thrust blocks are also provided approximately beneath them.

13. The system as set forth in claim 11 in which a guide plate having an arcuate opening with inner and outer marginal sides conforming to arcs taken from the axis of revolution of the carousel is provided on said tunnel struc-ture beneath the path of said turntable means and a carriage mounting said dog moves in a reciprocatory path along said marginal sides.

14. An apparatus as claimed in claim 13 in which said dog is eccentrically mounted on said carriage to be gravity returned from a tilted, inoperative position to an operative upright position in which it can engage and push a thrust block.

15. An apparatus as claimed in claim 1 wherein a radially inner and outer series of circumferentially spaced roller structures receive said turntable means and rack carriers for travel within said tunnel structure; and said roller structures comprise fixed base mounts and rollers mounted for restricted pivoting movement thereon to self-align with said turntable means.

16. An apparatus as claimed in claim 15 wherein said base mounts include a first pivot and a pivot limiting sur-face; and said rollers are mounted on said pivot on an in-termediate frame carrying a second pivot disposed perpen-dicularly to said first pivot and incorporating a roller frame mount on said second pivot journaling a roller; said base mount including also pivot limiting surface for said intermediate frame mount.

17. An apparatus as claimed in claim 16 wherein said roller frame mount journals a pair of rollers, one on either side circumferentially of said second pivot; said second pivot comprising a radially extending pin means.

18. An apparatus as claimed in claim 16 wherein said first pivot comprises a generally circumferentially ex-tending pin.

19. An apparatus as claimed in claim 16 wherein said turntable means mounts roller-engaging wear rails compris-ing abutting strips of greater Brinell hardness than said rollers, for riding on said rollers.