Abstract:
A warp resistant fuel feed door assembly for use in injecting supplemental fuel into a high temperature combustion chamber such as a rotating cement kiln without substantial loss of heat or combustion gases. The apparatus, which is positioned on the exterior side of a fuel passage transecting the wall of a rotating kiln, opens to receive fuel and then seals during the balance of the rotation of the kiln. Warping, bearing fracture, shaft distortion and jamming due to exposure to extreme heat and cooling are minimized by the sectional construction of the doors. The door includes a plate positioned over the mouth of the passage, a plurality of support arms attached to the plate and a hinge shaft attached to the arms. Stresses on the door structure from inconsistent expansion of the plate are reduced due to symmetrically spaced oblong and oversized bolt attachment bores in the support arms. Synchronous opening of the feed doors is achieved by levered rotation of the hinge shafts by an electric motor. Selective introduction of supplemental fuel into a rotating kiln can be controlled by electrical actuation of the feed doors.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority from, and is a 35 U.S.C. §111(a) continuation of, co-pending PCT international application serial number PCT/US00/35563 filed on Dec. 28, 2000 which designates the U.S., which is a continuation-in-part of U.S. application Ser. No. 09/477,918 filed on Dec. 31, 1999 from which priority is also claimed. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable 
     REFERENCE TO A COMPUTER PROGRAM APPENDIX 
     Not Applicable 
     NOTICE OF MATERIAL SUBJECT TO COPYRIGHT PROTECTION 
     A portion of the material in this patent document is subject to copyright protection under the copyright laws of the United States and of other countries. A portion of the material in this patent document is also subject to protection under the maskwork registration laws of the United States and of other countries. The owner of the copyright and maskwork rights has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the United States Patent and Trademark Office file or records, but otherwise reserves all copyright and maskwork rights whatsoever. The copyright and maskwork owner does not hereby waive any of its rights to have this patent document maintained in secrecy, including without limitation its rights pursuant to 37 C.F.R. §1.14. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention pertains generally to high temperature kiln access door assemblies, and more particularly to a warp resistant supplemental fuel feed door assembly for a rotating kiln. 
     2. Description of the Background Art 
     Rotating cylindrical kilns are frequently used in the production of cement. Because such kilns operate at extremely high temperatures, it is possible to burn various forms of liquid and solid combustible waste materials as a source of supplemental heat. Waste materials tend to completely combust at the high operating temperatures found in such kilns, which are on the order of 3400 degrees Fahrenheit and above, while producing little or no undesirable gaseous or solid emissions. Therefore, these waste materials can serve as a form of supplemental fuel, thereby reducing the demand for and cost of the primary fuel. 
     Worn rubber vehicle tires are particularly suited as a supplemental fuel for a rotary cement kiln. The extremely high temperatures within a cement kiln will cause the rubber tires to burn without any significant liquid, solid or gaseous waste byproducts which might otherwise be detrimental to the environment. Since worn out tires currently present a disposal problem, burning the tires in rotary kilns helps alleviate the growing problem of disposal without impairing the environment. 
     Various secondary fuel feed mechanisms have been developed to introduce fuel through a kiln wall into the interior of a rotating cylindrical kiln. Typically, these feed systems have an entrance chute which transects the kiln wall with an outer portion protruding through the outer wall of the kiln and an inner portion protruding into the interior of the kiln. The outer portion of the chute normally includes a feed door which opens to allow passage of the secondary fuel into the kiln. Some feed systems positively inject the supplemental fuel into the kiln using a ram or advancing screw mechanism. Other feed systems known tend to use gravity to inject the supplemental fuel into the kiln. A kiln feed door is utilized in both systems to prevent the escape of heat and combustion gases when the supplemental fuel is fed into the interior of the kiln. 
     The repetitive opening and closing of the kiln feed door results in the exposure of the door to higher temperatures when closed and lower temperatures when open. Such heating and cooling of the door results in expansion and contraction of the door surfaces and warping of the door over time. Warped doors do not properly seal against the entrance chute and allow heat and combustion gases to escape when the door is closed. Replacement of the warped kiln feed door can be costly requiring the kiln to be shut down during the time a new door is installed. 
     In addition, most door actuating mechanisms are mechanically controlled by the use of cams or rollers and operate within a fixed operating cycle. Such mechanical mechanisms must open the door on each revolution of the kiln and can not skip a cycle. Thus, the rate of secondary fuel introduced into the kiln can not be modified efficiently. 
     Accordingly, there is a need for a kiln feed door that is resistant to warpage when repetitively exposed to hot and cold temperatures, and which can be opened and closed such that the rate of secondary fuel can be varied. The present invention satisfies those needs, as well as others, and generally overcomes deficiencies found in convention kiln feed door assemblies. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is a kiln feed door assembly that restricts the loss of heat and combustion gases when feeding tires and other combustible materials into a rotating kiln as a source of supplemental fuel. By way of example, and not of limitation, the apparatus comprises a kiln feed door assembly that preferably includes two feed doors pivotally mounted to a baseplate on the exterior entrance of a chute which transects the wall of the rotary kiln. Each door includes a pivot shaft which preferably pivots within two high temperature pillow block bearings. Preferably four door plate mounting arms are attached to the pivot shaft and extend radially from the center of the pivot shaft. Planar rectangular door plates are mounted to the mounting arms with bolts secured through bores or apertures in the mounting arms. 
     In the preferred embodiment, there are at least two apertures in each mounting arm. The apertures are matched in pairs in each mounting arm. Some apertures are oblong in shape with the lengthwise portion of the aperture aligned with the direction of the width of the mounting arm. Other oblong apertures are aligned such that the lengthwise portion of the aperture is in the direction of the length of the mounting arm and perpendicular to the length of the pivot shaft. Still other apertures are circular. Each aperture may be sized to receive a bushing. 
     The bushings and linear alignment of the oblong apertures allow the door plates to expand and contract inconsistently without causing stress or otherwise warping the door. An efficient seal against the loss of heat and combustion products is maintained when the door plates keep their planer shape. 
     The two kiln doors pivot outwardly from the base plate and center of the kiln. One door assembly has a lip on the outer surface of the door. The lip is positioned to cover and seal the small space between the doors when the doors are in the closed position. 
     Each kiln feed door of the door assembly is preferably counterbalanced on the pivot shaft, preferably with two counterweights, one disposed near each of the block bearings. The door and counterweights are equally balanced with respect to the pivot shaft allowing for the opening and closing of the doors with little effort. 
     In one preferred embodiment, the kiln doors synchronously open and close using an electric motor, gearbox, actuating arms, rods and transfer arms. An actuating arm is radially mounted to one end of the pivot shaft of one door and a transfer arm is radially mounted to the other end of the shaft. The actuating arm is connected by an actuating rod to a rotating armature from the gearbox. This portion of the mechanism translates the rotational motion of the armature to oscillating motion of the actuating arm and partial rotation of the pivot shaft. Rotation of the pivot shaft results in movement of the transfer arm. An elongate transfer rod is pivotally connected to the transfer arm on one end and to an arm mounted to the pivot shaft of the opposing door on the other. Therefore, both kiln feed doors open simultaneously when the electric motor is activated. 
     In one embodiment, the actuating rod that is coupled with the door actuating arm on one end and the rotating linkage of the gearbox on the other includes a dampening member which tempers the impact of the closure of the doors against the rim of the opening to the kiln thereby reducing stress on the doors and linkage. 
     In another embodiment, the activity of the motor is regulated during various times of the cycle of the rotation of the gearbox armature with sensors thereby regulating the rate of movement of the door-actuating rod. When the motor is momentarily turned off just before the doors are fully closed or opened, the stress on the seals, doors and linkage of impact against the kiln opening under power is eliminated. 
     In operation, tires or other combustible materials are presented to a feed ramp or injection platform. As the kiln rotates, the feed door assembly eventually comes into proper alignment with the feed ramp. The kiln feed doors are mechanically or preferably electrically opened to allow the kiln to receive the combustible materials from the ramp. The doors are closed after the combustible material enters into the kiln to eliminate the loss of heat and combustion products from the kiln during rotation. 
     An object of the invention is to provide secondary fuel access doors for a rotating kiln that can expand linearly or laterally without warping. 
     Another object of the invention is to provide kiln feed doors that will efficiently prevent the escape of heat and combustion products from the interior of the kiln yet allow the efficient entry of tires or other combustible material into the kiln. 
     Another object of the invention is to provide a kiln feed door that can be repetitively exposed to heat extremes and cooling and maintain its shape. 
     Yet another object of the invention is to provide a door actuating mechanism that efficiently and reliably allows momentary access to the interior of the kiln without releasing large amounts of heat or combustion gases. 
     Still another object of the present invention is to provide a kiln supplemental fuel feed door assembly that can be programmed to open and close at desired times and is capable of skipping cycles. 
     Further objects and advantages of the invention will be brought out in the following portions of the specification, wherein the detailed description is for the purpose of fully disclosing preferred embodiments of the invention without placing limitations thereon. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be more fully understood by reference to the following drawings which are for illustrative purposes only: 
     FIG. 1 is a perspective view of a feed door assembly according to the present invention showing the warp resistant doors in the open position. 
     FIG. 2 is a side view of the feed door assembly of the invention with the doors shown in the open position, and showing the feed door assembly in relation to the fuel guide of a rotating kiln and a feed chute. 
     FIG. 3 is a top view of the warp resistant doors of the present invention showing the positioning of the bores in the arms and pivot shafts, and showing one of the doors partially cut away for clarity. 
     FIG. 4 is a front view of the feed door assembly of FIG. 1 with the warp resistant doors shown in the closed position. 
     FIG. 5 is a rear view of the feed door assembly of FIG. 1 with the warp resistant doors shown in the closed position. 
     FIG. 6 is a perspective view of a rotating kiln with the attached feed door assembly of FIG. 1 shown the warp resistant doors in the open position to receive secondary fuel from the feed chute. 
     FIG. 7 is a side view of an alternative embodiment of the motor and gear mechanism of the feed door assembly of FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring more specifically to the drawings, for illustrative purposes the present invention is embodied in the apparatus generally shown in FIG.  1  through FIG. 7, where like reference numbers denote like parts. It will be appreciated that the apparatus may vary as to configuration and as to details of the parts without departing from the basic inventive concepts disclosed herein. 
     Referring first to FIG.  1  and FIG. 2, the invention comprises a kiln access door assembly  10  that is used to allow the injection of combustible material into a rotating kiln of the type that is commonly used in the production of cement. The invention includes a pair of outwardly opening warp resistant feed doors  12   a ,  12   b  which provide access to a feed opening  14  in the side wall of a kiln  16 . It will be appreciated, however, that the present invention can be used with any combustion chamber such as a stationary kiln, furnace or boiler that exposes an access door to high temperatures. As can be seen, feed opening  14  is at the exterior end of a fuel feed inlet tube  18  which transects the sidewall of the kiln. 
     In the configuration shown in FIG.  1  and FIG. 2, the feed door assembly  10  of the invention is supported by a baseplate  20  mounted on the exterior end of feed tube  18 . Feed opening  14  is an opening in baseplate  20  that allows the passage of combustible material to the interior of the kiln through feed tube  18 . 
     Doors  12   a  and  12   b  include door plates comprising planar members  22   a  and  22   b , respectively, which face the interior of the kiln when the doors are in the closed position. Preferably, the periphery of feed opening  14  has a lip  24  that engages the face of planar members  22   a  and  22   b  sealing the opening when doors  12   a  and  12   b  are closed. 
     A fuel guide  26  is mounted on the baseplate  20  such that the plane of surface  28  of the guide is perpendicular to the baseplate. Preferably door  12   a  opens to a position that is perpendicular to the baseplate and then stops. Fuel guide  26  is positioned such that guide surface  28  is substantially contiguous with the inner surface of planar member  22   a  when the door is open. In this manner, tires and other combustible materials can be deposited on the surface  28  of fuel guide  26  and slide by the forces of gravity along the guide and the surface of door member  22   a , and through the interior of feed tube  18  into the interior of the kiln as the kiln rotates. 
     Door  12   b  preferably opens to a position approximately one-hundred and ten degrees from horizontal and then stops. This positioning effectively directs stray fuel into the feed opening  14  as it slides down the guide and into feed opening  14 . 
     In FIG. 2, a tire  30  is shown positioned in a feed chute apparatus  32  for delivery into the kiln. In operation, the timing of the release of the fuel from the feed chute should be coordinated with the opening of the doors  12   a  and  12   b  when in the proper position to receive the fuel. In this regard, it will be appreciated that it is important that the tires not be released from the feed chute apparatus until the feed doors on the kiln are in position and opened to receive the tires. In addition, to ensure that the tires will be gravity fed into the kiln, the feed chute is oriented on the support frame such that the plane of the internal ramp (bottom wall) has an angle of inclination between approximately 33 degrees and approximately 60 degrees, and preferably 47 degrees. The feed chute apparatus with rate regulation capability described in detail in co-pending application Ser. No. 09/448,570 filed on Nov. 23, 1999, which is incorporated herein by reference, can be used for this purpose. It will be appreciated, however, that the feed door assembly of the present invention can also be used with other feed mechanisms known in the art that actively inject the fuel into the kiln without the assistance of gravity. 
     Referring also to FIG. 3, the preferred embodiment of the warp resistant feed doors are shown in greater detail. It will be appreciated that the various components described herein can be attached using conventional fastening techniques, such as welding, bolts, pins or the like, as appropriate for the type of attachment made. In the embodiment shown, doors  12   a  and  12   b  each have a pivot shaft, a plurality of support arms mounted to the shaft and a planar member secured to the arms. Specifically, door  12   a  includes a pivot shaft  34  which functions as a hinge and which preferably has grooves to receive splines at both ends. A plurality of arms  36 ,  38 ,  40 , and  42  are oriented substantially parallel in the same direction and are securely mounted to shaft  34 . Each arm preferably has a horizontal anchor  44 ,  46 ,  48  and  50 , respectively, which serves as an attachment point with planar member  22   a . Each horizontal anchor is supported by a vertical upright which is perpendicular to the horizontal plane of the anchor. Vertical uprights  52 ,  54 ,  56  and  58  are attached to pivot shaft  34  as well as to its respective horizontal anchor. Each vertical upright has a top plate  60 ,  62 ,  64 , or  66 , respectively, attached on the side opposite the anchor. 
     Top plates  60 ,  62 ,  64 , and  66  are also attached to pivot shaft  34  providing additional strength and rigidity to the door. Further rigidity for door  12   a  is provided by a cross-brace or beam  68  which cross-links the vertical uprights of the anchor arms. 
     Each of the horizontal anchors has one or more pairs of apertures that receive bolts or the like to secure the planar members to the anchors. For example, horizontal anchor  44  has a pair of apertures  70   a  and  70   b  that have a generally oblong shape with the lengthwise portion of the oblong oriented substantially parallel to the length of shaft  34  and substantially perpendicular to the length of anchor  44 . In other words, the longitudinal axis through the oblong portion of the aperture is generally aligned with the longitudinal axis of the shaft and generally offset with the longitudinal axis of the anchor by approximately ninety degrees. 
     Horizontal anchor  46  has two pairs of apertures  72   a ,  72   b  and  74   a ,  74   b  that are preferably disposed on either side of vertical upright  54 . Apertures  72   a  and  72   b  are oversized and circular in shape. In contrast with apertures  70   a  and  70   b , apertures  74   a  and  74   b  have a generally oblong shape with the lengthwise portion of the oblong oriented substantially perpendicular to the length of shaft  34  and generally parallel to the length of the anchor. In other words, the longitudinal axis through the oblong portion of the aperture is offset in relation to the longitudinal axis of the shaft by approximately ninety degrees and is generally aligned with the longitudinal axis of the anchor. 
     Apertures  76   a  and  76   b  in anchor  48  have the same oblong dimensions as apertures  74   a  and  74   b  and are oriented in the same direction generally perpendicular to the length of the shaft  36  and aligned with the length of the anchor. Likewise, apertures  78   a  and  78   b  are circular and preferably have the same dimensions as apertures  72   a  and  72   b.    
     Anchor  50  has apertures  80   a  and  80   b  which are oblong oriented in a direction substantially parallel to the direction of length of shaft  34  and substantially perpendicular to the length of the anchor. Preferably, apertures  80   a  and  80   b  have the same dimensions as apertures  70   a  and  70   b  in anchor  44 . 
     One skilled in the art will appreciate the symmetry of the placement of apertures  70   a  through  80   b . While this symmetry is preferred, other combinations and placements are anticipated. The orientation and placement of the apertures  70   a  through  80   b  allow the expansion and contraction of planar member  22   a  due to the high temperature gradients associated with opening and closing the doors to occur without causing significant deformation to the door assembly. In addition, appropriately sized bushings may alternatively be placed in the apertures to further reduce stresses. Thus, expansion and contraction of the inventive door assembly from exposure to extreme temperatures does not create sizeable stresses in the door assembly causing warping and a loss of door seal to escaping combustion gases. 
     Kiln feed door  12   b  has essentially the same structure as feed door  12   a  as can be seen in FIG.  3 . Pivot shaft  82  preferably has four mounting arms  84 ,  86 ,  88 , and  90  which are secured to pivot shaft  82 . Each arm has horizontal anchors  92 ,  94 ,  96 , and  98 , respectively, which are ultimately secured to planar member  22   b . Each anchor has a vertical upright  100 ,  102 ,  104  and  106 , respectively, mounted radially to shaft  82  and perpendicularly to horizontal anchors  92 ,  94 ,  96 , and  98 , respectively. The vertical uprights are preferably cross-linked by beam  108  to provide strength to the mounting arm assembly. Top plates  110 ,  112 ,  114  and  116  are mounted to the vertical uprights on the side opposite the horizontal anchor as well as shaft  82  providing further rigidity to the assembly as shown in FIG.  1 . Note that cross beam  108 , cover  130  and top plates  110 ,  112 ,  114  and  116 , can be seen in FIG. 1, but have been omitted from FIG. 3 for clarity. 
     The apertures in the horizontal anchors of arms  92 ,  94 ,  96  and  98  share the same shape, symmetry, placement and orientation as those apertures in anchors  44 ,  46 ,  48  and  50  of door  12   a . Apertures  118   a  and  118   b  in anchor  92  are oblong shaped with the lengthwise portion of the oblong oriented in the direction of the length of shaft  82 . Apertures  120   a ,  120   b  and  122   a  and  122   b  are disposed in anchor  94 . Apertures  120   a  and  120   b  are circular in shape, and apertures  122   a  and  122   b  are oblong in shape with the lengthwise portion of the oblong perpendicular to the length of shaft  82 . 
     Horizontal anchor  96  has apertures  124   a  and  124   b  which are oblong in shape and  126   a  and  126   b  which are circular in shape disposed on either side of upright  104 . The lengthwise portion of oblong apertures  124   a  and  124   b  is perpendicular to the length of shaft  82 . 
     Anchor  98  has apertures  128   a  and  128   b  which are oblong in shape and oriented so that the lengthwise portion of the oblong is parallel to the length of shaft  82 . As can be seen, therefore, door  12   b  preferably maintains the same symmetry with respect to the apertures as door  12   a  as seen in FIG.  3 . 
     Referring to FIG. 1, FIG.  4  and FIG. 5, there is a cover  130  that is attached to the outer edge of planar member  22   b  and covers the gap between planar members  22   a  and  22   b  when doors  12   a  and  12   b  are in the closed position. Cover  130  acts to seal the gap between the doors to prevent the escape of significant amounts of combustion gases and heat from the kiln. 
     The door assembly of the present invention has a front or drive side as seen in FIG. 4 and a rear side as shown in FIG.  5 . In the embodiment shown, the ends of pivot shafts  34  and  82  rotate in high temperature pillow block bearings  132   a ,  132   b  and  134   a ,  134   b , respectively. The pillow block bearings  132   a ,  132   b ,  134   a  and  134   b  are preferably mounted on baseplate  20 . 
     Doors  12   a  and  12   b  are preferably counterweighted to create a zero lift weight and reduce the stress on the door actuating mechanisms. Shaft  34  has a counterweight  136   a  on the drive side and a counterweight  136   b  on the rear side of the apparatus. Similarly, shaft  82  has a counterweight  138   a  on the drive side and a counterweight  138   b  on the rear side of the shaft. The counterweights are preferably placed on the shaft such that the pillow block bearings are between the door and the counterweight. 
     Referring more particularly to the drive side of the apparatus as shown in FIG. 4, armature  146  is connected to an output shaft  150  (FIG. 5) of gearbox  152  and rotated by the output shaft at a desired speed. Output shaft  150  and gearbox  152  are preferably driven by an electric motor  154 . The proximal end of push rod  142  is rotatably connected to rotating arm  146  by bearing  148 . The distal end of push rod  142  is pivotally coupled to actuating arm  140  by bearing  144 . Thus, it will be seen that the rotation of armature  146  and movement of push rod  142  forces actuating arm  140  to oscillate. Consequently, the force applied to actuating arm  140  will cause pivot shaft  34  to rotate around its axis in block bearings  132   a  and  132   b  preferably to a point that door  12   a  is opened to a vertical position. 
     Push rod  142  is preferably coupled to a resistive plunger or spring assembly  156  that will allow the length of pushrod  142  to compress or shorten slightly while resisted by spring assembly  156 . This serves to temper the force applied to arm  140  and shaft  34  by pushrod  142  when door  12   a  is opened or closed. 
     In one embodiment, the spring assembly  156  includes a spring loaded cylinder with one end of pushrod  142  fixed to actuating arm  140  and the other end of pushrod  142  sliding within the cylindrical body of assembly  156  and resisted by a spring within the body (not shown). The fixed end of the cylindrical assembly  156  is connected to the rotating arm  146  on the output side of the gear box  152  and the sliding pushrod  142  is connected to the actuating arm  140  on the lower kiln door. Thus, when the fixed end shaft of the cylindrical assembly is pushed, the sliding end of pushrod  142  preferably bottoms at the opposite end of the cylindrical body of assembly  156  creating a full positive force. Additionally, when the fixed end of the cylindrical spring assembly  156  is pulled the sliding end of rod  142  extends, thereby compressing the cylinder spring. The strength of the spring determines the force created. Preferably, an internal sleeve on the sliding pushrod  142  limits its travel (not shown). 
     Motor  154  may be activated by any number of timing mechanisms known in the art that allow the doors to be opened at the proper position to receive fuel during rotation of the kiln. The opening and closing of the feed doors can be timed for every cycle of rotation of the kiln or for alternate cycles. Alternatively, the doors may be opened more than one time during any one rotation of the kiln. Thus, it will be seen that a kiln mounted, low voltage electrical motor and linkage allows total operational flexibility to control when and where the doors are open and the duration of closure thereby eliminating cumbersome mechanical linkages known in the art. 
     Referring now to FIG. 5, the rear side of the inventive apparatus is shown. A transfer arm  158  is mounted to pivot shaft  34  and rotates with shaft  34  in pillow bearings  132   a  and  132   b  when the shaft is rotated by actuating arm  140 . Transfer arm  158  is pivotally connected to one end of transfer rod  160  by transfer arm bearing  162 . The other end of transfer rod  160  is pivotally connected to arm  164  through bearing  166 . When shaft  34  is rotated, counterweight  136   b  rotates downwardly, transfer arm  158  moves upwardly about the axis of shaft  34  and transfer rod  160  forces arm  164  to rotate pivot shaft  82 . Rotation of shaft  82  causes door  12   b  to open upwardly and counterweight  136   b  to rotate downwardly around the axis of shaft  82 . It is preferred that door  12   b  open beyond vertical to approximately one hundred and ten degrees from horizontal. 
     In operation, the opening of doors  12   a  and  12   b  is preferably coordinated with the release of fuel from feed chute  32 . It is also preferred that the doors do not open when the assembly is below forty degrees from horizontal. 
     Referring also to FIG.  2  and FIG. 6, in operation a tire  30  is placed on feed chute  32  either manually or by using an auxiliary mechanical feed mechanism (not shown). As kiln  16  rotates, sensor  168 , which is a conventional photosensor or the like, senses an actuator key such as tab  170  and activates motor  154  thereby opening doors  12   a  and  12   b . As rotation continues, the doors completely open and fuel guide  26  and feed opening  14  comes into alignment with feed ramp  32 , fuel control sensor  172  detects tab  174  and sends a control signal to feed chute  32 . The tire or other combustible material is timed to slide down the feed chute, along fuel guide  26  and planar member  22   a , and into the kiln since the angle of inclination is sufficient to allow the material to be gravity fed out of the end of the feed chute. 
     The number of times that doors  12   a ,  12   b  open and close may be controlled and coordinated with the release of fuel by feed chute  32  to meter the amount of material injected into the kiln by sensor controllers at the door and feed chute assemblies. (not shown). Accordingly, the door assembly can remain closed until the kiln completes one or more full rotations. 
     Referring now to FIG. 7, an alternative embodiment of the actuating mechanism for opening the kiln feed doors  12   a ,  12   b  is generally shown. In the embodiment shown, the gearbox  152  has an additional mechanism for regulating the activity of the motor through the cycle of the opening and closing of the kiln doors  12   a ,  12   b.    
     The activity of the motor  154  is regulated during various times of the cycle of the rotation of the gearbox armature  146  by sensors thereby regulating the rate of movement of the door actuating pushrod  142 . Preferably the motor  154  is momentarily turned off just before the doors are fully closed or opened thereby reducing the stress on the seals, doors and linkage from the impact of the doors against the kiln opening that occurs under power. 
     Gearbox  152  has a shaft  176  disposed on the side of the gearbox opposite shaft  150  and armature  146  preferably rotates at the same rate as shaft  150 . A rotating disk  178  is coupled with shaft  176  and includes sensor tabs  180  near the periphery of the disk. Detectors  182  are aligned over sensor tabs  180  and activate and deactivate the motor  152 . The input from detectors  182  is preferably coordinated with the input from sensors  168  and  172 . 
     Low voltage motor  154  causes armature  146  to rotate and force pushrod  142  to move actuating arm  140  and open the kiln feed doors  12   a ,  12   b . This may be considered the positive stroke of the door actuating mechanism. When the armature  146  on the gearbox  152  has rotated one hundred and eighty degrees, the lower door  12   a  is preferably perpendicular to the center of the kiln and parallel to the feed chute  32  at the time of material release. It is preferred that a few degrees before one hundred and eighty the disk sensor tab  180  on the disk  178  gear box output shaft  176  align with the detector  182  signifying the proper position. The detector  182 , or other control mechanism associated with the detector, preferably cuts power to the drive motor  154 . As the motor  154  slows to a stop, the doors  12   a ,  12   b  continue to open to the set position and the disk  180  rotates to one hundred and eighty degrees. The doors  12   a ,  12   b  remain in this position until they have aligned with the feed chute  32  and the materials are fed to the kiln. 
     Once the materials have been fed to the kiln  16 , it is preferred that the power to the motor  154  be regained and armature  146  continue rotating clockwise back one hundred and eighty degrees, creating a pulling action on the pushrod  142  and thus closing the doors. This may be considered the negative stroke of the cycle. The linkage is preferably adjusted so that when the armature  146  on the gearbox  152  has reached a few degrees before one hundred and eighty degrees, the sensor tabs  180  on disk  176  aligns with a detector  182  and cuts power to the motor  154 . Consequently the motor  154  is not active when doors  12   a ,  12   b  are in the fully closed position and stresses on the doors and linkage are greatly reduced. 
     Accordingly, it will be seen that this invention provides a simple and effective way of introducing combustible materials such as tires into a rotating kiln using gravity feed or affirmative injection which can skip one or more revolutions of the kiln. The structure of the fuel feed doors allow for exposure to extreme temperatures and inconsistent expansion and contraction without warping, fracturing the bearings, shaft distortion, jamming or significant release of heat or combustion gases. Although the description above contains many specificities, these should not be construed as limiting the scope of the invention but as merely providing illustrations of some of the presently preferred embodiments of this invention. Thus the scope of this invention should be determined by the appended claims and their legal equivalents.