Patent Publication Number: US-2015059620-A1

Title: Horizontal mixer for bituminous mixtures

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Application No. 61/975,575 filed Sep. 6, 2012, the entire contents of which are incorporated herein by reference for all purposes. 
    
    
     BACKGROUND 
     The present disclosure is directed to a mixer for bituminous material. The mixer is particularly suited for combining large chunks of solid material with liquid bitumen to provide a uniformly mixed bituminous mixture. 
     Mixtures of bitumen and aggregate, commonly known as asphalt, are used in a wide variety of applications, particularly in the construction and maintenance of roads. The bitumen acts as a binder, coating individual aggregate particles and binding them together in the final composition. Other asphalt binders are used without aggregate to seal or coat surfaces. 
     Asphalt binders generally comprise residue from petroleum refining processes. In addition to the aggregate, many times property-enhancing additives are added to the residue in order to alter the properties of the asphalt binder. 
     SUMMARY 
     The present disclosure describes a mixer suitable for providing a bituminous mixture, the mixture being a combination of asphalt binder, any aggregate, and any additives. This disclosure describes the use of a continuous mixer configured to provide a uniform mixture from large chucks of solid material, asphalt binder and any additives, and any aggregate. The mixer is configured to uniformly disperse aggregate, asphalt binder and additives among the solid material. The mixer is configured to mix, combine, heat, melt, and/or reduce in size the ingredients to produce a uniformly mixed bituminous or asphalt mixture. 
     One particular embodiment of this disclosure is a method of forming a bituminous mixture. The method comprises inputting asphalt shingles to a first inlet of a mixer, inputting liquid asphalt binder to a second inlet of the mixer, passing the asphalt shingles and the asphalt binder through a mixing chamber having a first stage and a second stage, the first stage comprising a helical screw and the second stage comprising a plurality of paddles, and obtaining a uniform mixture comprising asphalt shingle chunks and asphalt binder from the mixer. The second inlet may be the same or different than the first inlet; if different, the second inlet can be downstream of the first inlet. 
     Another particular embodiment of this disclosure is a method of forming a bituminous mixture by inputting large chunks of solid material to a first inlet of a mixer, inputting liquid asphalt binder to a second inlet of the mixer, passing the large chunks of solid material and the asphalt binder through an inclined mixer chamber having a first stage and a second stage, the first stage comprising a helical screw and the second stage comprising a plurality of paddles, and obtaining a uniform mixture comprising small chunks of solid material and asphalt binder from the mixer. The solid material may include asphalt shingles and/or recycled asphalt. The paddles reduce the large chunks of solid material to small chunks of solid material. 
     These and various other features and advantages will be apparent from a reading of the following detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       The invention may be more completely understood in consideration of the following detailed description of various embodiments of the invention in connection with the accompanying drawing, in which: 
         FIG. 1  is a cross-sectional view of a mixer according to the present disclosure. 
         FIG. 2  is a front view of the output end of the mixer of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present disclosure is directed to a continuous mixer and methods of using that mixer to produce a bituminous or asphalt mixture. 
     In the following description, reference is made to the accompanying drawing that forms a part hereof and in which are shown by way of illustration at least one specific embodiment. The following description provides additional specific embodiments. It is to be understood that other embodiments are contemplated and may be made without departing from the scope or spirit of the present invention. The following detailed description, therefore, is not to be taken in a limiting sense. While the present invention is not so limited, an appreciation of various aspects of the invention will be gained through a discussion of the example provided below. 
     Unless otherwise indicated, all numbers expressing feature sizes, amounts, and physical properties are to be understood as being modified by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth are approximations that can vary depending upon the desired properties sought to be obtained by those skilled in the art utilizing the teachings disclosed herein. 
     As used herein, the singular forms “a”, “an”, and “the” encompass embodiments having plural referents, unless the content clearly dictates otherwise. As used in this specification and the appended claims, the term “or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise. 
     As used herein below, “RAZ” means recycled asphalt shingles. These shingles may be completely new (i.e., uninstalled) shingles, shingles rejected from the factory, by a supplier or a consumer for one reason or another (e.g., wrong size, wrong color, bent, broken, etc.), or may be previously installed shingles. 
     As used herein below, “RAP” means recycled asphalt. The asphalt is composed of asphalt binder and aggregate. Typically, the material is solid rather than liquid or semi-liquid. The asphalt may be reclaimed, for example from a roadbed or other application, or may be waste material that for one reason or another was not installed. 
     The mixer of this disclosure is designed to mix liquid asphalt with any other ingredient that needs to be mixed, heated, melted, reduced in size, or any combination of the above. The mixer is a continuous-type mixer, having a separate inlet and outlet. The interior chamber of the mixer includes a helical screw and paddles and/or breaker bars. The screw pushes material through the interior chamber, much like a pump. The paddles mix the materials together and the breaker bars can reduce the physical size of the material. 
     Referring to  FIG. 1 , a mixer  10  is illustrated. Mixer  10  has an elongate, cylindrical body  12  extending from a first end  14  to a second opposite end  16  along axis line A. Present within body  12  is an elongate, cylindrical interior chamber  18  through which material being processed passes. First end  14  can be referred to as the inlet end, end  14  having at least one inlet into interior chamber  18  proximate thereto. In the illustrated embodiment, mixer  10  has a first inlet  20 , a second inlet  22  and a third inlet  23 , each in fluid communication with and operably connected to interior chamber  18 . First inlet  20  is configured as a solids inlet  20 , second inlet  22  is configured as a liquid inlet  22 , and third inlet  23  is also configured as a liquid inlet  23 . Solids inlet  20  and liquid inlet  22  are located on an inlet stack  24 , positioned above body  12 . A high level safety switch may be present on stack  24 . First end  14  also includes a drain  26  operably connected to interior chamber  18 . Any materials exiting via drain  26  passes to a pump or drum mixer (not shown) via piping  38 . 
     In some embodiments, mixer  10  may be referred to as a horizontal mixer, with interior chamber  18  configured to move material present therein in a generally longitudinal direction, one having a horizontal component. Although referred to as a “horizontal” mixer, mixer  10  is angled, sloped or inclined, with the output end, second end  16 , positioned higher than the input end, first end  14 . In some embodiments, second end  16  is vertically adjustable, to modify the incline of mixer  10 . The desired incline is dependent on the input material and the desired output material. 
     Present within interior chamber  18  is a mixing element  28  having a first stage and a second stage, the first stage being closer to the input end, first end  14 , than the second stage. In other words, the second stage is downstream of the first stage. In the illustrated embodiment, the first stage occupies approximately the upstream-most 20-30% of the length of interior chamber  18 , and the second stage occupies approximately the downstream-most 70-80% of the length of chamber  18 . It is understood that the relativity of the first stage and the second stage can be modified, depending on the specific mixing element  28  and materials to be processed. 
     The first stage of mixing element  28  includes a helical screw  32  extending around and out from a central shaft  30 . Helical screw  32  may be one continuous flight or may be formed by a plurality of smaller flights. Screw  32  may be a single helix or a double helix. The second stage of mixing element  28  includes a plurality of paddles or bars  34  extending around and out from central shaft  30 . Paddles/bars  34  are downstream from helical screw  32 . Screw  32  pushes material from inlet end  14  through interior chamber  18  to paddles/bars  34 , which mix the materials together and optionally reduce the size of the solid material. Mixing element  28  can be powered by a gearbox and electric motor (not shown). Mixing element  28  may have a single set speed (e.g., 200 rpm), multiple set speeds (e.g., 100 rpm, 200 rpm and 300 rpm), or may have variable speeds. 
     As illustrated in  FIG. 2 , at second end  16 , body  12  includes an outlet  36  in fluid communication with and operably connected to interior chamber  18 . From outlet  36 , material from interior chamber  18  passes to a pump or drum mixer (not shown) via piping  38 . In some embodiments, a pump may be present at outlet  36  or in piping (not shown) to assist in pushing material exiting outlet  36  to the drum mixer. 
     Referring back to  FIG. 1 , mixer  10  is preferably insulated and optionally heated to maintain a low viscosity of the material within interior chamber  18 . For example, body  12  may be insulated with a 1 inch R rated insulation. Chamber  18  may be heated via hot oil external to body  12 , via electric heating elements within body  12 , or via plug heaters or the like extending into chamber  18 . Body  12  may be jacketed with a metal jacket over the insulation and/or over any heating mechanism. Various temperature probes and high temperature alarms may be present. 
     Mixer  10  is particularly useful for mixing together bituminous materials, including bitumen (asphalt binder), any binder additives such as surfactants, emulsifiers, etc., and aggregate. Because of the particular configuration of mixing element  28 , mixer  10  is particularly suited for receiving physically large materials and reducing the material down to a suitable size. Recycled asphalt shingles (RAZ) are one example of a solid material that can be provided to mixer  10  to be combined with bitumen (asphalt binder) to provide a useable bituminous material. Recycled asphalt (RAP) is another example of a material that can be provided to mixer  10 , either as a solid, semi-solid or a liquid, to be combined with bitumen (asphalt binder) to provide a useable bituminous material. Other materials, such as binder additives, aggregate, polymer, warm mix additive, and crumb rubber, could also be added. 
     Sizes for body  12  of mixer may be as small as 20 inch diameter up to about 26 inches diameter, and as short as 78 inches and as long as 14 feet. Typically, the diameter of body  12  does not increase proportionately with the length of body  12 . Of course, larger and smaller mixers (in either or both length and diameter) may be useful for certain applications. Inlets  20 ,  22 ,  23 , particularly solids inlet  20  and any other inlet through which solid material (e.g., RAZ, RAP, aggregate, etc.), are sized and shaped to allow large chunks of material to be fed to interior chamber  18 . Typical mixing rates for mixer  10  are from 7.5 tons/hour of material up to 35 tons/hour at about 70% by weight of solids (depending on density). Of course, lower levels of solids, such as 50%, 55%, 60%, 65%, and everything therebetween could be run through mixer  10 . Depending on the input material (particularly, the size, composition, etc. of the RAZ and/or RAP) the amount of solids could be as high as 75% by weight. 
     The RAZ material is provided to mixer  10  via solids inlet  20 . Because of the configuration of mixing element  28 , the inputted RAZ material may be any size, as long as it fits in inlet  20 . Additionally or alternately, solid RAP material is provided to mixer  10  via solids inlet  20 . Because of the configuration of mixing element  28 , the inputted RAP material may be any size, as long as it fits in inlet  20 . Asphalt binder is added via either or both liquid inlet  22  and inlet  23 . In some embodiments, the binder may be added through inlet  23  and additives such as surfactant, emulsifier, polymer, etc. are added through inlet  22 . Other solids, such as aggregate and crumb rubber may also be added via solids inlet  20 . 
     From the various inlets  20 ,  22 ,  23 , the material is carried by helical screw  32  up through interior chamber  18 . Typically helical screw  32  merely lifts or pushes the material, although some larger pieces or chunks of solid material (e.g., RAZ) may be reduced in size. From helical screw  32 , the material progresses to paddles/bars  34 , which beat the material and breaks the solid material into suitable size. It is mixing element  28 , having both helical screw  32  and paddles/bars  34 , which provides for large chunks of RAZ to be processed and mixed into bituminous material. 
     After passing through interior chamber  18 , the mixed material now comprises small chunks or pieces of RAZ and/or RAP homogeneously mixed with the asphalt binder and other ingredients. The incline of body  12  may be increased or decreased as needed, to adjust the residence time of the material within interior chamber  18 . The percentage of solid materials (i.e., RAZ, RAP, etc.) will affect the desired incline of body  12 . 
     The previous described embodiments of the horizontal mixer are not limiting, and variations on the mixer are within the scope of this disclosure. For example, in some embodiments, inlet stack  24  may be longer or shorter; depending on the volume of material (e.g., solid material) desired to be retained. As another variant example, more or less inlets may be present in inlet stack  24 ; in some embodiments, only a solids inlet such as first inlet  20  is located on stack  24 , whereas in other embodiments, three or more inlets may be located on stack  24 . As a further variant example, inlet stack  24  may be longitudinally removed from first end  14  a predetermined distance towards second end  16 , so that material from inlet stack  24  is delivered not at an end of helical screw  32 . 
     Thus, embodiments of the HORIZONTAL MIXER FOR BITUMINOUS MIXTURES are disclosed. The implementations described above and other implementations are within the scope of the following claims. One skilled in the art will appreciate that the present invention can be practiced with embodiments other than those disclosed. The disclosed embodiments are presented for purposes of illustration and not limitation, and the present invention is limited only by the claims that follow.