Abstract:
An apparatus and method for fragmenting and re-mixing agglomerated pieces of rubberized asphalt prior to applying same to a road surface. Agglomerated pieces and rubberized asphalt material are delivered to the upper portion of a housing. In a first embodiment, an auger and tine assembly having a common drive shaft, is mounted for rotation within the housing. The assembly includes first and second auger sections, mounted along the shaft in spaced relation and having converging, opposite handedness. A rotating tine section is positioned between the auger sections. A fixed tine section is mounted in the housing in interdigitized relation with the rotating tine section. In a second embodiment, the entire drive shaft includes a rotating tine section, and a corresponding interdigitized fixed tine section is provided within the housing. Passing through apertures defined by the fixed and rotating tine sections, agglomerated pieces are fragmented and re-mixed with the other material.

Description:
BACKGROUND OF THE INVENTION  
       [0001]    1. Field of the Invention 
         [0002]    The invention relates generally to improvements in the field of windrow elevators used in an asphalt paving machine to pick up, process, and provide a ready supply of asphalt-based material. More specifically, the present invention comprises an apparatus and a method, for fragmenting agglomerated pieces of rubberized asphalt material and re-mixing the fragmented pieces with smaller pieces of the same material, to achieve an acceptably homogeneous consistency in the material readied for immediate use by the asphalt paving machine. 
         [0003]    2. Description of the Prior Art 
         [0004]    A material commonly known as Hot Mix Asphalt (“HMA”) is widely used in roadway construction and resurfacing. HMA is comprised of a mixture of asphalt oil binder, sand, small rocks, and other filler material, processed at a batch plant. Ideally, the batch plant is located close to the paving site, so the HMA will stay hot and workable until it is applied on the roadway. A short transportation distance also minimizes the phenomenon known as material segregation. Because HMA is composed of different sized aggregate and fill material, agitation and gravity act on these pieces of HMA differently. The larger, heavier pieces and the smaller, lighter pieces tend to separate and collect in like groups during transport. When the dump trailer deposits the HMA material on the roadway in a windrow, the smaller particles are concentrated in the central, elevated region of the windrow and the larger particles are concentrated in the lateral, lower regions of the windrow. 
         [0005]    U.S. Pat. No. 6,481,922, issued to Boyd, provides a solution to the above-noted material segregation problem. The &#39;922 Patent discloses an apparatus and a method for re-mixing the large particles with the small particles, so that a more uniform mixture of those particles is achieved before the HMA is applied onto the roadway. Through the use of a pair of lateral augers which continuously deliver the larger particles into a centrally positioned stream of the smaller particles, the HMA is re-mixed into a homogeneous mixture before being delivered into a collection hopper for subsequent application on the roadway. 
         [0006]    However, as a roadway material, HMA is not without its faults. The asphalt oil binder used to coat and hold the aggregate particles together, plays a critical role in the performance and longevity of the roadway. The adhesive and agglomerating properties of the binder are affected by temperature, the amount and rate of road loading, and aging. Over a period of time, the surface of well-used roads, particularly in harsh environments, begins to crack and delaminate from lower support layers. To mitigate these effects, various additives have been proposed and tested with existing asphalt binders. 
         [0007]    One of the most promising and successful additives used so far is rubber, recycled from used motor vehicle tires containing a high content of natural rubber. The tires are ground up into small particles known in the industry as “crumb rubber”. Pieces of the steel belts used in the manufacture of tires are removed from the ground up tires, before the crumb rubber is ready for further processing and incorporation into an asphalt based road material. The resultant product is variously known in the paving industry as Rubberized Asphalt, Rubberized Asphalt Concrete (“RAC”), and Asphalt-Rubber. 
         [0008]    Two basic methods have been used to make the rubberized asphalt. The first method, known as the “wet process”, calls for the crumb rubber to be mixed with the binder (approximately 80% asphalt cement and 20% rubber) in a field blending unit. This first step occurs prior to the addition of the mixture to the other materials at a separate hot mix plant. In a second method, rubberized asphalt can be produced directly, using a terminal blended process where the crumb rubber is added at the refinery or at the asphalt cement terminal. The advantage of the latter method is that no specialized and costly rubberized blending plant is required, and the asphalt binder can be shipped to the hot mix plant just as a standard binder would be. 
         [0009]    Irrespective of how it is manufactured, rubberized asphalt has been proven a superior roadway material over unmodified HMA in several significant areas. Rubberized asphalt is highly-skid-resistant, quieter than HMA or concrete, and resistant to rutting and cracking. In the process of making rubberized asphalt, used tires are consumed and utilized for a new purpose. A two-inch thick roadway resurfacing project can consume approximately 2000 waste tires per lane per mile. Thus, land-fill can be reduced and environmental concerns associated with the storage of flammable stores of waste tires are alleviated. Research has established that 4″ thick conventional HMA roadway can be replaced with 2″ thick rubberized asphalt, and achieve the same fatigue life. Rubberized asphalt provides excellent long-lasting, color contrast, for road striping and marking. Lastly, rubberized asphalt can generally be applied using conventional road-paving equipment and methods. 
         [0010]    The last mentioned feature of rubberized asphalt has several exceptions, however. Rubberized asphalt is made using smaller and more uniform aggregate, typically on the order of ¼″ to ⅜″, or so, in diameter. This results in a material which is much less susceptible to the segregation problem caused by material transport, characteristic of HMA. But rubberized asphalt cools at a different rate than HMA, and it has a tendency to agglomerate in ways that HMA does not. Between the batch plant where the rubberized asphalt is manufactured and the roadway job site, cooling of the material occurs, especially in areas contingent and adjacent the sidewall and floor of the material hopper. 
         [0011]    When rubberized asphalt has cooled a sufficient amount before it is even deposited into a windrow on the roadway, it may agglomerate into relatively large balls or sheets of material of irregular size and shape known as “clingers”. For example, a sheet of such agglomerated material may be 2″ to 3″ thick, 4″ to 5″ wide, and 12″ to 18″ long. These large pieces of agglomerated material are randomly dispersed through the windrow. 
         [0012]    The present practice is to remove such agglomerated material manually from the windrow, before material pickup and application of the rubberized asphalt to the roadway occurs. This method is labor intensive, and also relies upon the workers finding and removing all of the offending clingers. If not removed, such large chunks of agglomerated material may jam in the paving machine or be deposited into the roadway and remain an unintegrated surface component. 
       SUMMARY OF THE INVENTION  
       [0013]    The present invention comprises an apparatus and a method for fragmenting agglomerated pieces of rubberized asphalt material, and then re-mixing the smaller fragmented pieces with the smaller loose material prior to applying the re-mixture to a road surface. The agglomerated pieces are formed from smaller pieces of rubberized asphalt material which have cooled together to form the agglomerated pieces, during transport to the job site. A random mixture of agglomerated pieces and the rubberized asphalt material is delivered to the job site, forming a windrow along the middle of the roadway. A pickup machine passes over the windrow, and an elevator picks up the mixture. The elevator carries the mixture upwardly, and delivers it to the upper portion of a generally cylindrical housing mounted on the pickup machine. 
         [0014]    In a first embodiment, an auger and tine assembly having a common drive shaft, is mounted for rotation within the housing. The assembly includes first and second auger sections, mounted along the drive shaft in spaced relation. A rotating tine section is mounted on the drive shaft between the auger sections. The auger sections have converging, opposite handedness, effective to transport the agglomerated pieces and the material inwardly toward the rotating tine section. A fixed tine section is mounted in the housing in interdigitized relation with the rotating tine section. 
         [0015]    In a second embodiment, a rotating tine section extending the entire length of the drive shaft, is provided within the housing. A fixed tine section is also provided within the housing, having a length corresponding to that of the rotating tine section. As with the first embodiment, the fixed tine section is arranged in interdigitized relation with the tines of the rotating tine section. 
         [0016]    In both embodiments, the agglomerated pieces and the material are deposited into a fragmenting and re-mixing zone adjacent and around the rotating and fixed tine sections. The spacing between adjacent fixed and rotating tines is such that a pre-determined maximum size is established for agglomerated pieces fragmented by the action of the tines. These smaller fragmented pieces are concurrently re-mixed with the other material resulting in rubberized asphalt having a size and composition appropriate to form a road surface. 
         [0017]    The first embodiment of the invention can also be used advantageously with HMA paving material, to alleviate the material segregation. In other words, without making any modifications or changes to its structure or operation, the same apparatus which fragments and re-mixes rubberized asphalt material will also re-mix size and weight segregated HMA into a homogeneous material ready for instant use by a paving machine. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0018]      FIG. 1  is a perspective view, showing a road paving machine incorporating the apparatus for fragmenting and re-mixing agglomerated pieces of rubberized asphalt material of the present invention; 
           [0019]      FIG. 2  is a fragmentary top plan view of the road paving machine, with portions of the cover and the housing broken away to show the windrow elevator, the auger sections, and the tine section; 
           [0020]      FIG. 3  is a fragmentary cross-sectional view, taken through the longitudinal axis of the windrow elevator of  FIG. 2 , showing the delivery of rubberized asphalt material into the auger and tine housing; 
           [0021]      FIG. 4  is a fragmentary perspective view showing the upper end of the elevator and the auger and tine housing of the first embodiment; 
           [0022]      FIG. 5  is a view as in  FIG. 4 , but with a portion of the housing broken away to show the arrangement of the auger sections and the tine sections; 
           [0023]      FIG. 6  is a side elevational view of the auger and tine housing, showing discharge of the fragmented and re-mixed rubberized asphalt material; 
           [0024]      FIG. 7  is a fragmentary perspective view showing the upper end of the elevator and the tine housing of the second embodiment; 
           [0025]      FIG. 8  is a view as in  FIG. 7 , but with a portion of the housing broken away to show the tine section; and, 
           [0026]      FIG. 9  is a front elevational view of the tine housing, showing discharge of the fragmented and re-mixed rubberized asphalt material. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0027]    Turning now to  FIG. 1 , the fragmenting and re-mixing apparatus  11  of the present invention is shown in combination with a windrow elevator  12  and a paving machine  13 . At the job site depicted in  FIG. 1 , the paving machine  13  is re-paving a roadway surface  14  with a mat  15  of rubberized asphalt  16 . 
         [0028]    At an off-site batch plant, the rubberized asphalt material  16  is manufactured from first combining a hot and liquid asphalt cement binder with particles of rubber. Generally, the amount of rubber in the mixture will vary from approximately 15% to 25%, or so, by weight. The rubber is preferably in the form of recycled “crumb rubber”, made from used automobile and small truck tires which have been shredded to a crumb-like size and consistency. At the plant, this crumb rubber has been heated to a sufficient amount that it physically swells, enabling it to combine and integrate with the asphalt cement. Next, this asphaltic combination is mixed with aggregate, such as crushed rock. The aggregate used in making rubberized asphalt is fairly small and uniform in size, ranging from ¼″ to ⅜″, or so, in diameter. This hot mixture is then loaded into a belly dump trailer, and the trip to the job site begins. 
         [0029]    The best case scenario for transporting rubberized asphalt is a short trip during the hottest part of the day during the summer season. Deviations from those circumstances during transport will cause varying amounts of greater cooling to the rubberized asphalt mixture. The most critical areas for cooling tend to be around the floor and sidewalls of the trailer, where the mass of the metal plates and the trailer frame can absorb heat from the mixture. In contrast to HMA, rubberized asphalt cools and agglomerates more quickly. With more paving and re-paving jobs occurring during evening hours to avoid traffic delays, the problem with material agglomeration has become worse for rubberized asphalt jobs. 
         [0030]    Upon arrival at the job site, the belly dump trailer deposits its load of rubberized asphalt material  16  in a windrow  17 . Under circumstances where the material had sufficiently cooled during transport, agglomerated pieces  18  in various shapes and sizes known as “clingers” have formed. As shown in  FIG. 1 , these pieces may be globular or sheet-like in configuration. Reports indicate that the sheet pieces appear to peel off the floors and sidewalls of the trailer, and these pieces may be 2″ to  3 ” thick, 4″ to 5″ thick, and 12″ to 18″ in size. The agglomerated pieces are randomly dispersed throughout the windrow, with some pieces exposed and others located within the body of the windrow out of sight. Heretofore, these pieces have been manually removed from the windrow, by workers who pick through the windrow before the paving machine  13  reaches the freshly dumped rubberized asphalt material. 
         [0031]    A paving machine  13  fitted with the fragmenting and re-mixing apparatus  11  of the present invention does not need additional workers to remove clingers or agglomerated pieces  18  from the windrow  17 . Instead, the apparatus  11  aboard the paving machine  13  is capable of processing the agglomerated pieces in such a way that it can be intermixed with the remainder of the material and incorporated directly into the mat  15 . To that end, as the paving machine  13  advances over the windrow  17 , the windrow elevator  12  picks up the rubberized asphalt material  16  including the agglomerated pieces  18  in the usual way and delivers it to an upper discharge end  19  of the windrow elevator  12 . 
         [0032]    As shown in the various Figures, the apparatus  11  is located at the discharge end  19 , and comprises an auger and tine assembly  21  having a first helical auger section  22  and a second helical auger section  23 . First auger section  22  has a top portion  24  and an inner portion  26 . Second auger section  23  has a top portion  27  and an inner portion  28  opposing inner portion  26 . As shown most clearly in  FIG. 5 , auger section  22  and auger section  23  are mounted in spaced relation over respective ends of a rotatable drive shaft  29 . 
         [0033]    A rotating tine section  30  having a top portion  32  is mounted on drive shaft  29  between inner portions  26  and  28 . The rotating tine section  30  is comprised of a plurality of tines  31 , arranged in a plurality of rows, extending perpendicularly from drive shaft  29 . Each of the rotating tines comprises an inner shank portion and an enlarged outer head portion, especially adapted for fragmenting agglomerated pieces  18 . It should be noted that the first and second auger sections are of converging, opposite handedness, so as to advance rubberized asphalt material  16  and the agglomerated pieces  18  inwardly toward the rotating tine section  30 . 
         [0034]    Apparatus  11  further comprises an auger and tine housing  33  having an upper portion with a material inlet  34  and a lower portion with a material discharge  36 . Housing  33  also includes a first endwall  37  and a second endwall  38 . Auger and tine assembly  21  is mounted for rotation within the lower portion of housing  33  between said first endwall  37  and second endwall  38 . A fixed tine section  39  is mounted in housing  33  in interdigitized relation with rotating tine section  30 . Tine section  39  is comprised of a plurality of fixed tines  41 , welded to a plate bolted to auger and tine housing  33 . Fixed tines  41  are arranged in a row, extending in perpendicular fashion from the axis of drive shaft  29 . Preferably, material discharge  36  is located just below tine section  39 . 
         [0035]    The spacing between fixed tines  41  and an adjacent rotatable tine  31  is approximately 1″ to 1½″, or so, thereby establishing a maximum transverse dimension for agglomerated pieces as they are forced between the two structures. This dimension can be changed as the circumstances demand. For example, smaller fragmented pieces may be achieved by reducing the spacing between the rotating and stationary tines. This will provide the paving machine with an even more homogeneous mixture, as the fragmenting process will produce smaller pieces. The downside of such a modification, is that the material “throughput” of the apparatus  11  will be reduced. This will necessarily reduce the speed of the paving machine  13 . 
         [0036]    Material inlet  34  in housing  33  allows rubberized asphalt  16  and agglomerated pieces  18  to be delivered into the top portions of the first and second auger sections and the rotating tine section. The remainder of auger and tine housing  33  substantially surrounds the first auger section  22 , the second auger section  23 , the rotating tine section  30 , and the fixed tine sections  39 . The first auger section and the second auger section acting in conjunction with the housing  33 , transport and direct asphalt  16  and agglomerated pieces  18  to the rotating tine section  30 . Housing  33  further defines a fragmenting and re-mixing zone  42  adjacent and around rotating and fixed tine sections  30  and  39 . 
         [0037]    Drive means  43 , preferably a hydraulic motor, is provided for rotating drive shaft  29  and auger and tine assembly  21  at the desired speed. If more aggressive fragmenting and re-mixing is desired or necessary, the speed of drive means  43  may be increased. This might be appropriate, for example, where more than the usual number of agglomerated pieces  18  are found in a particular load. A hydraulic motor  44  is included on drive shaft  46  of windrow elevator  12 , to provide a continuous stream of rubberized asphalt material  16  and agglomerated pieces  18  into the material inlet  34 . In operation, agglomerated pieces and material entering the material inlet are advanced inwardly toward the center of housing  33 , and deposited onto the rotating tine section and the fixed tine section in the fragmenting and re-mixing zone  42 . In this manner, the agglomerated pieces are fragmented and re-mixed with the asphalt material before passing through the material discharge  36 . 
         [0038]    The fragmented pieces  47  and the rubberized material  16  are deposited as a substantially homogeneous mixture into a hopper  48 , in readiness to be utilized by the paving machine  13 . The size and physical shape of the pieces  47  is such that when the mat  15  is laid by the paving machine  13  and subsequently compressed by a street roller, all of the rubberized asphalt forms a uniform and structurally integrated surface that is durable and long-lasting. 
         [0039]    Apparatus  49 , comprising a second embodiment of the invention, is shown in  FIGS. 7-9 . For the sake of clarity, the same element numbers will be used in describing this embodiment, where the structure and operation of those elements are identical to those in the first embodiment, set forth above. It should also be noted that this second embodiment is also an apparatus for fragmenting and re-mixing rubberized asphalt material containing agglomerated pieces, and may be used interchangeably in the same application as the apparatus of the first embodiment. Therefore, since the structure and operation of the upstream and downstream components, such as the windrow elevator, hopper, and paver devices have already been described, this discussion will not be repeated. 
         [0040]    Apparatus  49  includes a rotating tine section  50 , mounted on a rotatable drive shaft  51 . Rotating tine section  50  comprises of a plurality of tines  31 , arranged in a plurality of rows, extending radially from drive shaft  51 . For ease of construction, tine section  50  may be welded to a pipe or tube (not shown) which fits over and is bolted to drive shaft  51 . Alternatively, the tines may be welded directly to shaft  51 . Tine section  50  also includes a top portion  52 , into which incoming rubberized asphalt  16  and agglomerated pieces  18  are deposited. 
         [0041]    Apparatus  49  also includes a fixed tine section  53 . As is shown most clearly in  FIG. 9 , fixed tine section  53  is substantially coextensive in length with rotating tine section  50 . Fixed tine section  53  is comprised of a plurality of tines  41 , arranged in a row and extending perpendicularly from drive shaft  51 . Each of the rotating and fixed tines comprises an inner shank portion and an enlarged outer head portion, especially adapted for fragmenting agglomerated pieces  18 . It should also be noted that the enlarged outer head portions of the rotating and fixed tines are arranged in opposing relation, to enhance the fragmentation and re-mixing process. 
         [0042]    Apparatus  49  also includes a tine housing  54 , having an upper portion with a material inlet  56  and a lower portion with a material discharge  57 . Tine housing  54  further has a first endwall  58  and a second endwall  59 . Rotating tine section  50  is mounted for rotation within the lower portion of housing  54 , between the first and second endwalls.  FIG. 9  shows that fixed tine section  53  is mounted in tine housing  54 , in interdigitized relation with rotating tine section  50 . The spacing between adjacent rotating and fixed tines is selected to ensure a maximum acceptable size for the fragmented pieces discharged from the apparatus  49 . 
         [0043]    Tine housing  54  substantially surrounds rotating tine section  50  and fixed tine section  53 , but leaves the top portion  52  of the rotating tine section exposed to material inlet  56 . Rubberized asphalt and agglomerated pieces of asphalt are thereby delivered into the rotating tine section. Tine housing  54  further defines a fragmenting and re-mixing zone  61  adjacent and around the rotating tine section  50  and the fixed tine section  53 . 
         [0044]    Drive means  43  is also provided, for rotating tine section  50  at an appropriate speed. Preferably, a hydraulic motor is used for drive means  43 , as the speed of the rotating tines can easily be changed by the operator independently either from the forward speed of the paving machine  13  or from the speed of the windrow elevator  12 . 
         [0045]    In operation, rubberized asphalt material  16  and agglomerated pieces  18  entering the material inlet  56  are deposited onto the rotating tine section  50  and the fixed tine section  53  in the fragmenting and mixing zone  61 . The agglomerated pieces which are larger than the space between the rotating tines and the fixed tines are fragmented and re-mixed with the asphalt material  16  before the homogeneous mixture passes through the material discharge  57 . In all other respects, the operation and general function of the second embodiment, represented by the apparatus  49  is identical to that of the first embodiment, represented by the apparatus  11 .