Patent Publication Number: US-2002006075-A1

Title: Tireless rotary mixer

Description:
[0001] This application claims the benefit under 35 U.S.C. Section 119( e ) of prior U.S. Provisional Patent Application No. 60/192,970, filed Mar. 29, 2000, the disclosure of which is incorporated herein by this reference. 
    
    
     
       TECHNICAL FIELD  
       [0002] This invention relates to drum mixers for asphalt plants. More specifically, the invention is directed to a novel, improved drum mixer in which the drum is not driven or supported by tire type drive mechanisms.  
       BACKGROUND  
       [0003] Many types of process equipment designs have been provided or taught for the preparation of asphaltic compositions, often called HMA or “hot-mix” by those in the trade. However, the prior art designs utilized for achieving rotary motion in mixing drums have repeatedly been directed toward the use of double or single tire drive designs. Such designs have been inherently troublesome and are prone to need a lot of maintenance attention, particularly with respect to trunnion adjustments and with respect to limited tire life. This is undesirable, since the preparation of asphaltic compositions often occurs under extreme time and schedule pressures, due to the need for coordination of the application of such compositions with crew schedules, road closure schedules, and suitable weather conditions. Downtime for maintenance can quickly become a major cost concern in the projects which require reliable preparation of HMA; in some projects, damages resulting from schedule delays can carry heavy penalties. Consequently, there remains an as yet unresolved need in the HMA preparation business for provision of a rotary drum mixer (a) which have inherently trouble free rotary drive components, and (b) which allow contact between asphalt cement, aggregate dust, and aggregate under optimum conditions, with respect to product composition and air quality concerns.  
       OBJECTS, ADVANTAGES, AND NOVEL FEATURES  
       [0004] A primary object of our invention is to provide a rotary drum mixer which has a reliable, tireless support or drive mechanism, and which is economical to operate.  
       [0005] Another object of the invention is to provide a rotary drum mixer that is supported from each end by a weight supporting shaft that is mounted on bearings for rotary motion, rather than using a conventional trunnion and drive tire arrangement.  
       [0006] In conjunction with the preceding object, an additional object of the present invention is to eliminate alignment and wear problems as are commonly experienced in conventional drum mixer designs, by providing a novel support and drive mechanism.  
       [0007] To achieve the just mentioned objectives, a novel feature and advantage of the present invention is that a separate thrust bearing is used to accommodate the thrust generated due to inclined mounting and heating during use; this is preferably accomplished by using one fixed pillow block bearing (non-expansion) and once sliding pillow block bearing (expansion) to accommodate movement of the rotary drum dryer during use.  
       [0008] Another object of the invention is to provide a rotary drum mixer that allows contact between heated aggregate, asphalt cements and aggregate dust under optimum conditions, to minimize or avoid air pollution or loss of product concerns.  
       [0009] An additional object of the invention is to provide a means for heating and mixing recycled asphalt pavement (“RAP”) with heated aggregate, asphalt cement, and aggregate dust.  
       [0010] A still further and additional object of the invention is to provide an apparatus and method for removing hydrocarbons generated by contact of asphalt cement with hot aggregate and routing the same to the heat source (burner) for combustion, in order to eliminate objectionable air pollution.  
       [0011] A still further and important additional object of the invention is to provide the capability of insulating 100% of the mixer shell over its entire length.  
       [0012] Other and further objects of the invention will be understood by those in the art by examination of the drawing in conjunction with this specification. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
     [0013] In the description provided by the drawing, like reference numerals are employed to indicate like parts in the various figures, without the need for further mention thereof. The figures provided are as follows:  
     [0014]FIG. 1 is a partially broken side view of our novel asphalt plant drum mixer, constructed in accordance with the teachings herein, shown with aggregate inlet, first and second shaft portions supported for rotary motion by first and second supports via pillow block bearings, and also showing the motor, gear reducer, chain sprocket and final drive mechanism for effecting rotary motion of the mixer.  
     [0015]FIG. 2 is an end elevational view of the feed end of the drum mixer, showing the aggregate in-feed hopper, the inlet pipe for the asphaltic cement, the inlet pipe for aggregate dust, and additional asphalt cement inlets.  
     [0016]FIG. 3 is an end elevation view of the outlet end of the rotary drum mixer, showing the HMA discharge chute, the drive motor and frame, the chain and sprocket drive, and the support for the pillow block bearing on which a first shaft portion is mounted.  
     [0017]FIG. 4 is a cross-sectional view, taken across section line  4 - 4  of FIG. 1, showing the internal support bracing or “spider” for internal support of shaft portions about which the rotary drum mixer is rotated.  
     [0018]FIG. 5 is an end view of the rotary mixer just set forth above, now showing the unique rotary elbow which provides an effectively sealed conduit from a stationary asphalt source, such as through the flexible hose shown, to the internal rotating asphalt outlet pipe.  
     [0019]FIG. 6 is a side view of the rotary mixer and rotary elbow just illustrated in FIG. 5, showing how the rotary elbow is affixed to and effectively sealed with respect to the rotating asphalt outlet pipe.  
    
    
     DETAILED DESCRIPTION  
     [0020] Attention is now directed to FIG. 1 of the drawing in which a cylindrical drum  20  is shown oriented along an axis of rotation, designated by the dashed line marked with “C L ” as indicated along the centerline of the drum  20 , between a first shaft portion  22  at first end  24 , and a second shaft portion  26  at second end  28 . The cylindrical drum  20  is mounted above base support frame  30  by first structural support  32  at the first end  24 , and by a second structural support  34  at second end  28 . A first bearing  36 , preferably but not necessarily of the pillow block type, is mounted on first structural support  32  for rotary support of first shaft portion  22 , which is affixed to first end  24  of drum  20 . A second bearing  40 , preferably but not necessarily of the pillow block type, is mounted on second structural support  34  for rotary support of second shaft portion  26 , which is affixed to second end  28  of drum  20 .  
     [0021] First shaft portion  22  includes an outer end  50  that is mounted in bearing  36 , and an interior end  52  that protrudes into the interior  53  of drum  20  and which is supported by a structural steel spider  54  of the general design indicated in FIG. 4. Ideally, as seen in FIG. 4, the spider  54  design includes a pair of cross braces  56  extending outward to the periphery of drum  20 , and a strengthening frame brace  58 .  
     [0022] Second shaft portion includes an outer end  60  that is mounted in bearing  40 , and an interior end  62  that is mounted in and which is supported by a second structural steel spider  54 ′ of the general design indicated in FIG. 4. The second shaft portion  60  is hollow, and at the distal, exterior end  62 , a flange  70  is provided for affixing an outlet pipe  72  of variable length L.  
     [0023] The mixer  20  is driven via a non-weight supporting driver mechanism, such as via electric motor  80 , which acts through an appropriate gear reducer  82 , to turn drive toothed sprocket  83  and thus energize a linked chain  84  or other suitable linkage for driving a thrust purchase mechanism on drum  20  such as toothed  85  drum sprocket  86 . It should be recognized that sprocket  86  may be advantageously affixed to the outer surface or shell  89  of drum  20  via use of aligned, segmented portions, such as  86   A  and  86   B  as shown in FIG. 2.  
     [0024] Hot air is brought into the mixer drum  20  through the inlet chute  140  (further described below), and travels through the drum  20 , for discharge out the air outlet duct  160  and thence to the exhaust fan  162 .  
     [0025] At the outlet end  90 , optional internal paddles  92  scoop the hot-mix asphalt (HMA) outward and thence downward through discharge chute  94 , in the direction of reference arrow  96 . When, as is illustrated in FIGS. 1 and 3, the discharge chute  94  is centered, paddles  92  may be omitted; however, when the discharge chute  94  is located off-center, then such paddles  92  are desirable for transfer of the finished product to the discharge chute  94 .  
     [0026] Returning now to FIG. 1, the rotary mixer is provided with at least one asphaltic inlet tube  72  having an in-mixer length L T , and where in said length L T  is less than the L O  of said mixer drum  20 . Ideally, as shown in FIG. 1, the asphaltic inlet tube  72  is provided, at least in part, concentrically within the first support shaft portion  26 . Further, it can be seen that the asphaltic inlet tube  72  has an inlet end  100  and an outlet end  102 . As shown in FIG. 5, the inlet end  100  of asphaltic inlet tube  72  is sealingly mounted to a stationary rotary elbow  110 . A flexible inlet hose  112 , having an inlet end  114  and an outlet end  116  at the stationary rotary elbow  110  is used to provide an asphaltic composition A (see FIG. 1) to an interior space  53  in said rotary drum  20 .  
     [0027] As also seen in FIG. 5, the mixer drum  20  ideally has a stationary first or inlet end wall portion  120 . At this stationary end wall portion,  120 , additional, such as second  122  or more asphaltic inlet tubes  72 ′ can be provided.  20 . Also, an inspection manhole  130  can be provided to allow access, through the stationary inlet wall  120 , to the interior space  52  within the rotatable mixer drum  20 .  
     [0028] Also seen in FIGS. 1 and 5 is an inlet chute  140 . The inlet chute  140  is provided with a support  142 . The inlet chute  140  is hopper shaped for receiving incoming material such as aggregate or RAP, and directing the same to said interior space  53  within said rotatable drum  20 .  
     [0029] The rotary drum  20  also normally utilizes a stationary second our outlet end wall  150 . A seal  152  is provided between the rotatable drum  20  and the stationary discharge end  150 . Also at the discharge end of the rotary drum  20 , an outlet air duct  160  is provided sealingly affixed to the discharge end  150  of the rotatable drum  20 . An induced draft fan  162  is provided, having an impeller portion  164 , an impeller housing  166 , and an air discharge plenum  168 . The fan  162  is configured to pull air hot and commingled hydrocarbon contaminated gases outward in the direction of reference arrow  170 , i.e., through said outlet air duct  160  and discharge such gases outward through said air discharge plenum  168 . A motor  174 , preferably electric drive type, is provided to drive fan  162  impellers  164  via gear or pulley drive mechanism  176 .  
     [0030] During operation, it is to be appreciated that due to thermal effects, the overall length L O  will change due to thermal expansion on heating, and thermal contraction on cooling. To accommodate this effect, the first bearing  40  is preferably fixedly mounted to the first support shaft portion  60 , so that the first support shaft  60  cannot move longitudinally with respect to the first bearing  40 . However, the second bearing  36  is mounted in a manner which allows the second support shaft portion  50  to expand or contract, longitudinally along the centerline C L  of the mixer drum  20 , with respect to the location of the second bearing  36 . While it is preferred to use pillow block type bearings for bearings  36  and  40 , other types may be utilized and accomplish the same design feature.  
     [0031] Overall, it is to be appreciated that our unique rotary drum mixer has an inlet end for receiving aggregate or RAP, or other suitable materials, an asphaltic cement injection line, a drive means for effecting rotary motion of the rotary drum  20 , usually utilizing a mechanical drive linkage. Importantly, support means such as first and second shaft portions are provided, with extensions into the interior or the drum  20  as necessary to effect adequate structural support. Finally, bearing means are provided to rotationally support the first shaft portion and the second shaft portion.  
     [0032] In summary, it is clear from the foregoing description that a unique asphalt plant rotary mixer is provided. Operationally, the preferably tubular cylinder shaped drum is affixed to shaft portions that are supported at bearing mounts to suspend the drum along an axis of rotation. Each of the opposing shaft end portions are structurally supported at their respective first or second ends of the mixer drum by internal bracing within the mixer, such as with an “X” or “spider” cross-bracing structural support. The drum mixer is driven at a desired rotary speed by use of any convenient drive means, such as an electrical motor, gear driver and reducer, and/or gear drive with sprocket and chain drive mechanism. Overall, the drum and shaft portions of the apparatus are allowed to thermally expand by way of fixing one bearing mount and allowing the other mount to float, in order to accommodate the longitudinal elongation resulting from such thermal expansion. In the mixer, heated aggregate, liquid asphalt cement, and aggregate dust are mixed at about 300° F. or more to produce an asphalt composition. The asphalt cement injection point is adjustable longitudinally along the centerline of the mixer drum, by way of replacement of an asphalt cement injection tube with a substitute tube of different length. Further, multiple asphalt cements of different compositions may be introduced into the mixer by means of additional injection pipes located at the inlet end of the drum mixer. Importantly, Recycled Asphalt Pavement (“RAP”) may be added to the drum mixer along with heated aggregate, through the inlet chute. at the inlet end of the drum mixer. In such cases, the RAP is then heated in the mixer and combined with aggregate, asphalt cement, and aggregate dust, to provide a desired asphaltic composition. Optionally, a plurality of paddles at the discharge end are utilized to urge the asphaltic composition into a discharge chute, particularly chutes which are not centered below the mixer from which prepared asphaltic material is provided. In order to collect the residual hydrocarbons that are generated by the contact of asphaltic cement with heated aggregate, the plant is provided with an outlet air duct and a motor driven, preferably induced draft exhaust fan, having an air discharge plenum that routes contaminated air to a burner (not shown), in order to eliminate objectionable air pollution.  
     [0033] From the foregoing it will be seen that this invention provides an exemplary drive and support mechanism which avoids the use of tires and trunnions. Importantly, the design provided herein avoids wear and tear of prior art tire-type drive mechanisms for heated rotary drums. It is to be understood that various features and subcombinations within the teachings of this disclosure may be utilized and still remain within the scope and meaning of the claims of the invention as taught herein.  
     [0034] It is to be appreciated that the tireless drive system for rotary asphaltic mixers is an appreciable improvement in the art of asphalt equipment. Our novel design addresses the problem of how to avoid additional operational and maintenance costs of conventional drive mechanisms, while minimizing the complexity of an alternative drive mechanism, to provide a significantly improved rotary mixer system. Although only a few exemplary embodiments of this invention have been described in detail, it will be readily apparent to those skilled in the art that our tireless rotary asphaltic mixer may be modified from those embodiments provided herein, without materially departing from the novel teachings and advantages provided.  
     [0035] It will thus be seen that the objects set forth above, including those made apparent from the preceding description, are efficiently attained. Since certain changes may be made in designing the described structures when placing such structures into mass production, it is to be understood that my invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. Many other embodiments are also feasible to attain advantageous results utilizing the is principles disclosed herein. Therefore, it will be understood that the foregoing description of representative embodiments of the invention have been presented only for purposes of illustration and for providing an understanding of the invention, and it is not intended to be exhaustive or restrictive, or to limit the invention only to the precise embodiments disclosed. The intention is to cover all modifications, equivalents, and alternatives falling within the scope and spirit of the invention, as expressed herein, in the various figures of the drawing, and in the appended claims. As such, it is intended to cover the methods, apparatus, structures, and the equivalent methods or structural equivalents thereof. The scope of the invention, as described herein is thus intended to include variations from the embodiments provided which are nevertheless described by the broad meaning and range properly afforded to the language herein, as explained by and in light of the terms included herein, or the legal equivalents thereof.