Abstract:
A mixing system with a vessel for supplying a liquid and a device for supplying solid pieces to mix with the liquid. The system has an elongate enclosure with a first end opposing a second end. The enclosure defines a chamber in fluid communication with the vessel to receive the liquid. The chamber also has a inlet and an outlet with the inlet being closer to the first end than the outlet. The chamber receives the pieces from the device through the inlet and issues the pieces through the outlet. A motor driven mixing auger positioned in the chamber between the first and second ends rotates a selected direction about a rotational axis to intermix the liquid and pieces. The auger includes a first helical flight between the inlet and the outlet to convey the pieces from the inlet to the outlet when the shaft is rotated the selected direction. The auger also includes a second helical flight between the first flight and the second end to urge the solid pieces in a direction opposite the first flight. The second flight has a length along the rotational axis of the auger shorter than the first flight. In one variation of this system, the liquid may be a colorant and the solid pieces may include wood chips to be intermixed with the liquid to attain a uniform visual appearance.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present Application is a divisional of U.S. patent application Ser. No. 09/231,691 filed Jan. 14, 1999, which is a continuation-in-part of U.S. patent application Ser. No. 08/650,871 filed May 20, 1996 (now U.S. Pat. No. 5,866,201). 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to mixing solid pieces with a liquid, and more particularly, but not exclusively, relates to coating and coloration of landscaping materials. 
     The problem of landfill crowding has grown steadily. One way to reduce this crowding is to recycle as many materials as possible. One type of material suitable for recycling is wood. Wood may arrive at the landfill from a natural source, such as discarded tree branches, or it may be derived from various discarded products, such as shipping crates and furniture. 
     One way to recycle wood is to reduce the wood to a number of pieces of generally uniform size with a shredder, chipper, or grinder. Such comminuted wood is often suitable for use as a landscaping mulch. However, the varied types of wood typically obtained from a landfill often result in a non-uniform coloration that significantly changes with age and exposure to the elements. To alleviate this problem, recycled wood pieces are sometimes treated with a colorant to provided a more pleasing appearance. U.S. Pat. No. 5,308,653 to Rondy describes one coloring process. 
     One problem often encountered with coloring processes is excessive run-off of liquid colorants used to impart a uniform appearance to the wood pieces. This run-off adversely impacts cost effectiveness. To address this problem, there is a need to optimize the coloration process by determining the minimum amount of liquid colorant needed for a given amount of wood. There also remains a need to provide a more cost effective way to uniformly color landscaping material. 
     Another problem with the coloration process is that mixers used to blend liquid colorant and wood pieces are subject to frequent jamming. Typically, the mixer becomes packed with a mass of wood chips that are stuck together. This mass of chips often prevents discharge of the treated product from the mixer. Equipment down time to unclog the mixer generally increases processing costs and may result in excessive colorant run-off. Thus, there is also a need for a mixing system which resists packing and still economically imparts a uniform color to landscaping materials. 
     SUMMARY OF THE INVENTION 
     One form of the present invention is a system with a mixer defining a chamber that has an opening for inserting solid pieces therein. The chamber is in fluid communication with a conduit. Furthermore, the system has a source of a liquid agent and a metering device to selectively provide the agent from the source to the conduit. A water supply is coupled to the conduit to dilute the agent prior to reaching the pieces in the chamber. A controller is operatively coupled to the metering device to provide a delivery signal. The metering device responds to the delivery signal to adjust delivery of the agent to the conduit from a first non-zero rate to a second non-zero rate. 
     In an alternative form of the present invention, water and a colorant are mixed to produce a colorant liquid mixture during the movement of wood chips within a mixing chamber. Colorant supply to the liquid mixture is metered to control colorant amount or concentration in the mixture. The liquid mixture is put into the chamber to color at least a portion of the chips. The chips are discharged from the chamber. In one variation of this feature, landscaping gravel or rocks may be colored with the mixing process. In another variation, the mixture imparts a clear coating to rocks or another landscaping material to provide a high gloss appearance. 
     Among other alternative forms of the present invention are a mixing system with a vessel for supplying a liquid and a device for supplying solid pieces to mix with the liquid. The system has an elongated enclosure with a first end opposing a second end. The enclosure defines a chamber in fluid communication with the vessel to receive the liquid. The chamber also has an inlet and an outlet with the inlet being closer to the first end than the outlet. The chamber receives the pieces from the device through the inlet and discharges the pieces through the outlet. A motor driven mixing auger positioned in the chamber between the first and second ends rotates about a rotational axis to intermix the liquid and pieces. The auger includes a first helical flight between the inlet and the outlet to convey the pieces from the inlet to the outlet when the auger is rotated. The auger also includes a second helical flight between the first flight and the second end. The second flight has a length along the rotational axis shorter than the first flight. The second flight may have a rotational direction opposite the first flight and be positioned at least partially over the outlet to reduce clogging. In one variation of this system, the liquid may be a colorant and the solid pieces may include wood chips to be intermixed with the liquid to attain a generally uniform color. 
     In yet another alternative form, the first and second flights are mounted about an elongated shaft configured to rotate about the rotational axis and a portion of the first flight does not contact the shaft while turning about the rotational axis for at least three revolutions, defining a space therebetween. This structure enhances intermixing of the wood pieces with the liquid. 
     In still another alternative form, a mixing technique includes moving a number of wood chips through a generally horizontal, elongated passage of a mixer from a top inlet adjacent a first end of the mixer to a bottom outlet adjacent a second end of the mixer. This movement is performed by turning a pair of augers disposed within the passage. The inlet and outlet are spaced apart from one another along a longitudinal axis of the mixer. A liquid colorant and water are mixed to provide a liquid coloring mixture during movement of the wood chips. This mixing is regulated with a controller. The mixture is provided to a spray hood to impart color to the wood chips while moving. The spray hood defines a chamber projecting above the passage and having a plurality of nozzles that deliver the mixture to the chamber under pressure. The chamber intersects the passage to define an area for contacting the wood chips with the mixture. This area is positioned generally opposite the nozzles to extend along the longitudinal axis of the mixture at least about two-thirds of a distance between the inlet and the outlet. Further, this area transversely spans across at least about three-fourths of a top width of the passage occupiable by the wood chips. The wood chips are discharged through the outlet. It has been found that this arrangement facilitates reduction of the amount of water needed to adequately color the wood chips. 
     In a further alternative form, a mixing technique includes moving a number of wood chips within a mixing chamber and blending water and a colorant in a static mixer while the wood chips are moving to produce a generally homogenous liquid colorant mixture for supply to the chamber. The mixer includes a cavity containing one or more internal baffles oriented to mix the water and colorant. The colorant is metered to the mixture with a variable rate pump responsive to a controller while maintaining a generally constant flow rate of the water to the mixture with a flow rate regulator. A coloring property of the wood chips is determined and concentration of the colorant in the mixture is adjusted from a first non-zero amount to a second non-zero amount in accordance with the coloring property. This adjustment includes changing delivery rate of the colorant to the mixture with the controller. At least a portion of the wood chips are colored in the chamber with the mixture. The wood chips are then discharged from the chamber. 
     Accordingly, it is one object of the present invention to provide a system that dispenses a liquid to a mixer for blending with solid pieces therein. 
     It is another object of the present invention to optimize the mixing of a concentrated liquid agent with water to create a liquid mixture for supply to the chamber of a mixer for blending with solid pieces. The agent may include a colorant or clear coat material and the solid pieces may comprise landscaping material such as wood chips or rocks. 
     It is still another object to color wood chips to provide a mulch. Preferably, the coloration technique reduces the amount of water needed to apply a water-based colorant mixture to the chips and the amount of colorant mixture run-off. 
     An additional object of the present invention is to provide a mixer which resists packing of solid pieces being blended with a liquid therein. 
     Further objects, features, aspects, benefits, and advantages of the present invention shall be apparent from the detailed drawings and descriptions provided herein. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic top view of a colorant mixing system of one preferred embodiment of the present invention. 
     FIG. 2 is a diagrammatic view of the colorant dispensing system of the embodiment of FIG.  1 . 
     FIG. 3 is a partial cut-away side view of the mixer of the embodiment of FIG.  1 . 
     FIG. 4 is a side sectional view of the mixer shown in FIG.  3 . 
     FIG. 5 is a top sectional view of the mixer shown in FIG.  3 . 
     FIG. 6 is a partial, cut-away side view of a mixing system of another embodiment of the present invention. 
     FIG. 7 is a partial sectional view of the mixer taken along section line  7 — 7  of FIG.  6 . 
     FIG. 8 is a partial, top view of the manifold shown in FIGS. 6 and 7. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended. Any alterations and further modifications of the described embodiments, and any further applications of the principles of the invention as described herein are contemplated as would normally occur to one skilled in the art to which the invention relates. 
     FIG. 1 depicts a colorant mixing system  10  of the present invention. In system  10 , a number of wood chips  12  are transported by conveyer  14  in a direction along arrow I to mixer  60 . The chips  12  enter chamber  70  of mixer  60  through inlet  72  and are processed therein. This processing includes mixing with a water-based colorant from dispensing system  20 . Processed wood chips  16  exit through outlet  74  of mixer  60  and are carried away by conveyer  18  in a direction along arrow O. 
     Dispensing system  20  combines concentrated colorant from source  22  with water from water supply  24  to provide a liquid mixture for delivery to chamber  70  via conduit  26 . Preferably, source  22  includes a vessel holding an ample supply of the concentrated colorant. Source  22  may include a plurality of vessels or a colorant dispensing sub-system. Water supply  24  is preferably a well water source or city water source of a conventional type. 
     Dispensing system  20  includes control panel  30  with a display  32  indicating the rate colorant is being delivered for mixing. This rate may be continuously adjusted by an operator with rotary control  34 . Control panel  30  also includes a control key pad  33 , a master start switch  36 , and a master stop switch  37 . Switches  36 ,  37  start and stop delivery system  20 , respectively. In addition, control panel  30  has switch  38  corresponding to water supply  24  and switch  39  corresponding to colorant source  22 . Each switch  38 ,  39  has three positions: on, off, and automatic (or “auto”). When each switch  38 ,  39  is in the auto position, delivery system  20  operates normally. The on/off positions are used to separately start and stop water or colorant, respectively, for calibration purposes. 
     Delivery system  20  is also operatively coupled to sensor  35 . Sensor  35  provides a stop signal corresponding to the absence of material on conveyer  14 . This stop signal is then used to halt delivery system  20 . Sensor  35  may be a microswitch with an actuation arm positioned above conveyer  14  a selected distance. This arm is configured to either open or close the microswitch when material on conveyor  14  of a selected height no longer contacts it. Opening or closing of this microswitch sends the corresponding stop signal. Other types of sensors as would occur to one skilled in the art are also contemplated. 
     Referring additionally to FIG. 2, further details of delivery system  20  are described. Controller  31  is operatively coupled to display  32 , key pad  33 , rotary control  34 , sensor  35  and switches  36 ,  37 ,  38 , and  39  to coordinate and supervise operation of delivery system  20 . Controller  31  may be an electronic circuit comprised of one or more components. Similarly, controller  31  may be comprised of digital circuitry, analog circuitry, or both. Also, controller  31  may be programmable, an integrated state machine, or a hybrid combination thereof. However, preferably controller  31  is microprocessor with a known construction and has a control program loaded in non-volatile memory. In one embodiment a microcontroller/keyboard combination is supplied as Durant Model No. 5881-5 with part no. 5881-5-400 by Eaton Corporation of Waterloo, Wis., 53094. 
     Controller  31  is also coupled to pump system  40 . Pump system  40  includes positive cavity control pump  41  coupled to source  22  and driven by motor  42 . Controller  31  provides a delivery signal to motor  41  corresponding to a selected rate of delivery of concentrated colorant input to controller  31  with rotary control  34 . In one embodiment, controller  31  responds to a stop signal from sensor  35  to generate a delivery signal which shuts down pump system  40 . This delivery signal may alternatively be characterized as a “shut down” signal. 
     The colorant output by pump  41  encounters valves,  26   a ,  26   b . Under usual operating conditions, valve  26   a  is open and valve  26   b  is closed so that colorant flows through check valve  43 . Check valve  43  generally maintains “one way” flow of colorant away from pump  41 . Colorant from check valve  43  empties into joining conduit  48 . During calibration of pump system  40 , valve  26   a  is closed, and valve  26   b  is open so that colorant flows through calibration outlet  27  for collection and possible reuse. Besides pump system  40 , other metering devices as would occur to one skilled in the art are also contemplated. 
     Controller  31  is also operatively coupled to on/off valve  44  having inlet  44   a  in fluid communication with water supply  24 , and outlet  44   b  for supplying water therefrom. Valve  44  is responsive to a signal from controller  31  to correspondingly start or stop water flow from supply  24 . In one embodiment, controller  31  responds to a stop signal from sensor  35  to shut down water supply  24  by closing valve  44  via a shut down signal. Valve  44  may be a conventional solenoid activated stop valve. 
     Outlet  44   b  of valve  44  is in fluid communication with inlet  46   a  of flow regulator  46 . Flow regulator  46  has outlet  46   b  in fluid communication with check valve  47 . Check valve  47  maintains water flow away from flow regulator  46  to joining conduit  48 . Flow regulator  46  maintains a generally constant flow rate of water despite varying pressures at inlet  46   a  and/or outlet  46   b . Accordingly, flow regulator  46  adjusts to maintain a generally constant pressure differential between inlet  46   a  and outlet  46   b . Flow regulator  46  has an adjustable orifice to correspondingly select the regulated rate of flow from a given range of flow rates. In one embodiment, model no. JB11T-BDM from W.A. Kates, Co., 1450 Jarvis Avenue, Ferndale, Mich. 48220 is used for flow regulator  46  to provide a desired water flow rate selected from between 3 and 80 gallons per minute. In other embodiments, a different flow regulator may be used or a flow regulator may not be used at all. 
     Although water and concentrated colorant may begin mixing in joining conduit  48 , static in-line liquid mixer  50  provides a substantially homogenous liquid mixture of concentrated colorant diluted by water which is not generally provided by a conduit of generally constant internal cross-section. Concentrated colorant and water enter static liquid mixer  50  through inlet  50   a  and exit through outlet  50   b . Static liquid mixer  50  is preferably made from a transparent PVC material so that blending cavity  51  therein may be observed. Within blending cavity  51  are a number of interconnected internal baffles  52 . Baffles  52  are arranged to split the stream of liquid entering through inlet  50   a  and force it to opposite outside walls of mixer  50 . A vortex is created axial to the center line of mixer  50  by the arrangement of baffles  52 . The vortex is sheared and the process re-occurs but with opposite rotation several times along the length of static liquid mixer  50 . This clockwise/counterclockwise motion mixes the liquid to provide a substantially homogenous mixture through outlet  50   b  and into conduit  26 . Notably, static liquid mixer  50  operates without moving internal parts other than the liquid being mixed. This homogenous premixed liquid enhances uniform coloring of wood chips. Cole-Parmer Instrument Company of Niles, Ill. 60714 provides a PVC static liquid mixer model no. H-04669-59 which is preferred for one embodiment of the present invention. 
     In other embodiments, a static mixing cavity arranged to promote mixing without internal baffles may be used. U.S. Pat. No. 4,516,524 to McClellan et al. is cited as a source of additional information concerning a dedicated static mixing cavity of this type. In still other embodiments, premixing of colorant and water prior to entry into chamber  70  is not necessary. 
     By controlling the rate of delivery of colorant with control  34  to static liquid mixer  50  and maintaining a generally constant flow rate of water with flow regulator  46 , a desired concentration of water based colorant mixture may be selected. This concentration, and the rate of flow of the mixture to chamber  70  of mixer  60  may be matched to the rate of transport of wood chips therethrough to optimize colorant system  10  performance. As a result, the minimum amount of water necessary to provide uniform coloration for the wood chips may be determined by taking into account the absorbency of the liquid by the wood chips  12 , the rate of flow of the liquid into chamber  70 , and the rate of passage of wood chips  12  through mixer  60 . Notably, the rate of liquid flow can be adjusted with flow regulator  46  and with rotary control  34 , and the ratio of water to colorant can likewise be adjusted to assure a concentration which will provide uniform coloration. By optimizing these amounts, the amount of liquid runoff can be minimized and this optimal performance can be reliably reproduced. Also, an adjustable flow rate and colorant delivery rate permits re-optimization of the process when various parameters change; including, but not limited to, a different colorant type, different wood chip delivery rate, or different type of wood chips. 
     Besides optimizing colorant mixture delivery to mixer  60 , in other embodiments controller  31  may also be used for a variety of record keeping functions, such as maintaining a record of the amount of colorant dispensed over a given period of time. The amount dispensed may be displayed or otherwise accessed by an operator using keypad  33 . Controller  31  may be configured to provide an operator preferred parameters for flow regulator  46  and metering of colorant with pump system  40  via display  32  and keypad  33 . Also, it may be configured to assist the operator with adjustments relating to different wood chip types, sizes, or delivery rates. In this embodiment, the speed of conveyer  14  may also be sensed with controller  31  to ascertain optimum liquid mixture parameters of delivery system  20 . Also, controller  31  may control speed of conveyer  14  or  18 , or otherwise be coupled to mixer  60  to control various operational aspects thereof. In one alternative embodiment, control panel  30 , controller  31 , display  32 , control  34 , and switches  36 ,  37 ,  38 ,  39  are embodied in a ruggedized personal computer customized with appropriate hardware and software to controllably interface with the other components of delivery system  20  and including a conventional video display and keyboard. 
     In an alternative embodiment, operator control via controller  31  is provided over the rate of water flow to the mixture instead of colorant. In this embodiment, colorant concentration is regulated by adjusting the amount of water with controller  31 , and the colorant flow is kept generally constant. In other embodiments, both water supply  24  and source  22  are operatively coupled to controller  31  to provide dynamic adjustment over the relative flow rate and amount of from each. In still other embodiments, more than two sources of liquid components may be operatively coupled to controller  31  to provide a desired liquid mixture. 
     Delivery system  30  may also be used to control delivery of various other mixtures of liquid agents or mixing components. Also, besides wood chips, other solid pieces may be treated with a given liquid mixture from delivery system  20  in mixer  60 . For example, a high gloss transparent coating on certain types of landscaping rocks or gravel may also be provided with system  10 . Preferably, this clear coat is provided by a mixture of water and an organic-based polymer component. Similarly, other solid pieces and liquid mixtures containing various components may be used with system  10  as would occur to one skilled in the art. 
     Referring next to FIG.  1  and FIGS. 3-5, additional details concerning mixer  60  are next described. Mixer  60  includes enclosure  61  defining chamber  70 . Enclosure  61  is elongated and has end  61   a  opposing end  61   b  along its length. Enclosure  61  has top  62  opposing base  64 . Opposing sides  66  and  68  join top  62  and base  64 . Top  62  defines inlet  72  and grated observation window  76 . Preferably, top  62  is provided by panels which may be removed to gain access to chamber  70  for maintenance purposes. Base  64  defines discharge outlet  74 . 
     In FIG. 3 specifically, internal transverse support members  77   a ,  77   b  are shown in crosssection. Members  77   a ,  77   b  include a square cross-section and are preferably manufactured from carbon steel. Also, support flange  78  is illustrated between ends  61   a  and  61   b  of enclosure  61 . Adjacent end  61   a ,  62   b  is a right angle bearing flange  79   a ,  79   b  which supports mixer  60 . 
     FIGS. 1,  3  and  4  illustrate a spray manifold  80 . Spray manifold  80  is in fluid communication with spray nozzles  82   a ,  82   b ,  82   c  (collectively designated nozzles  82 ). In other embodiments, more or less nozzles may be used. Nozzles  82  are in fluid communication with chamber  70 . Manifold  80  has intake  84  configured to receive liquid through conduit  26  for distribution within manifold  80  to nozzles  82 . Excess liquid within chamber  70  may be drained through drain plugs  88   a ,  88   b , as particularly illustrated in FIGS. 3 and 4. 
     Referring specifically to FIG. 4, a cross-section of chamber  70  is shown. Also, protruding end flange  86   a  is illustrated with a number of attachment sights  87  along its periphery. End flange  86   a  is joined to bearing flange  79   a  using conventional methods. A similar structure at end  61   b  is formed with end flange  86   b  and bearing flange  79   b . At the bottom of chamber  70  is a triangular partition  89 . Preferably, enclosure  61  and manifold  80  are manufactured from a metallic material, such as carbon steel; however, other materials as occur to one skilled in the art are also contemplated. 
     FIGS. 1,  3 , and  5  depict various features of drive mechanism  90 . Drive mechanism  90  includes motor  92  mounted to enclosure  61  by support  94 . Also drive mechanism  90  includes drive box  100  and gear box  110 . Preferably, motor  92  is electrically powered, but other types of motors may also be employed, such as a gasoline-fueled internal combustion engine. A shaft from motor  92  extends into drive box  100  and is connected to sprocket  102  therein. Sprocket  102  is operatively coupled to sprocket  104  by drive chain  106 . 
     Sprocket  104  is attached to auger  120  by coupling shaft  129   b  at the end of auger  120  closest to end  61   b  of enclosure  61 . An opposing end of auger  120  is attached to coupling shaft  129   a  which extends into gear box  110 . Within gear box  110 , gear wheel  112  is coupled to coupling shaft  129   a  and intermeshes with gear wheel  114  coupled to coupling shaft  149   a . Shaft  149   a  is coupled to auger  140  at the end of auger  140  closest to end  61   a  of enclosure  61 . At the opposing end of auger  140 , coupling shaft  149   b  is coupled thereto. Coupling shafts  129   a ,  149   a  are rigidly attached to shafts  122 ,  142 , respectively, and are journaled to enclosure  61  at end  61   a  by appropriate bearings. Coupling shafts  129   b ,  149   b  are rigidly attached to shafts  122 ,  142  and are journaled to enclosure  61  at end  61   b  by appropriate bearings. 
     Referring specifically to FIGS. 3-5, auger  120 ,  140  are further described. Auger  120  includes a shaft  122  generally oriented along the length of enclosure  61 . Attached to auger  120  is helical or spiral flight  124 . Flight  124  is configured to turn about shaft  122  in a counterclockwise direction as it advances from end  61   a  toward end  61   b . Preferably, flight  124  makes at least three revolutions about shaft  122 . More preferably, flight  124  makes at least five revolutions about shaft  122 . Most preferably, flight  124  makes at least nine revolutions about shaft  122 . 
     Preferably, the pitch angle of flight  124  is at least 45°. More preferably, the pitch angle of flight  124  is in the range of 65° to 80°. Most preferably, the pitch angle of flight  124  is about 75°. As used herein, “pitch angle” means the angle formed between a tangent to an edge of the helical flight and the rotational axis of the flight. FIG. 3 illustrates a pitch angle of flight  124  as angle A. In one embodiment, the pitch angle of flight  124  varies, with a portion closest to end  61   a  having a different pitch angle than the rest of flight  124 . In other embodiments, the pitch angle varies in a different fashion or is generally constant. 
     Referring specifically to FIG. 3, auger  120  includes mixing paddles  125  interposed along flight  124 . Each mixing paddle  125  is attached to shaft  122  by fastener  127 . Each fastener  127  has bolt  127   a  extending through shaft  122  and secured thereto by nut  127   b . By loosening nut  127   b , the pitch of mixing paddle  125  relative to flight  124  may be adjusted. Nut  127   b  is then re-tightened to secure the newly selected paddle pitch. Preferably, mixing paddles  125  do not extend as far from shaft  122  as flight  124 . It is also preferred that auger  140  include mixing paddles distributed along shaft  142  which are interposed with flight  144  (not shown). 
     In one embodiment, about twelve mixing paddles  125  are distributed along shaft  122 , being spaced along the segment of axis R 1  corresponding to flight  124  at approximately equal intervals. From one to the next, mixing paddles  125  of this embodiment are positioned about axis R 1  approximately 75 degrees apart. In addition, each mixing paddle has a portion extending from shaft  122  that has a generally planar sector shape. This sector shape sweeps about a 40 degree angle between radii extending from axis R 1 . Preferably, auger  140  is similarly configured for this embodiment. 
     Referring again to FIGS. 3-5, auger  120  also has a reverse spiral flight  128  spaced apart from flight  124  by gap  126  along shaft  122 . Preferably, flight  128  turns around axis R 1  at least 180 degrees. More preferably, flight  128  turns about axis R 1  at least 330 degrees. Most preferably, flight  128  turns about axis R 1  approximately 360 degrees or makes about one revolution around shaft  122  (including axis R 1 ) between flight  124  and end  61   b . Flight  128  advances in a direction from end  61   a  to  61   b  with a clockwise spiral rotation. Thus, the rotational direction of flight  128  is opposite the rotational direction of flight  124 . 
     Generally, shaft  122  along gap  126  is flightless. The length of gap  126  along shaft  122  is preferably about the length of flight  124  along shaft  122  corresponding to one revolution about shaft  122 . Gap  126  and flight  128  both partially overlap or overhang outlet  74  so that at least a portion of flight  128  is positioned over outlet  74 . 
     Auger  140  is configured similar to auger  128  except the rotational orientation of the flighting is reversed. Specifically, helical flight  144  of auger  140  turns about shaft  142  in a clockwise direction as it advances from end  61   a  to end  61   b . Flight  148  turns about shaft  142  in a counterclockwise direction as it advances in a direction from end  61   a  toward end  61   b . Augers  120  and  140  preferably intermesh a slight amount as most clearly depicted in FIG.  4 . This intermeshing is accomplished by slightly offsetting the maximum extension point of the flights relative to each other. 
     FIG. 4 illustrates additional characteristics of flight  124 ,  144 . Shaft  122  has a maximum cross-sectional dimension (M) perpendicular to the plane of view of FIG. 4, and flight  124  has a distance D extending from shaft  122  along this plane. Preferably, the extension ratio (ER), of D to M is greater than 1; where ER×D÷M. More preferably, ER is at least 1.5, and most preferably ER is at least 2.0. The quantity M is determined as the maximum cross-sectional dimension of the shaft for its given shape along a cross-sectional plane perpendicular to its rotational axis. Similarly, D is determined as the distance the flight extends from the shaft along an axis perpendicular to the rotational axis of the shaft. Preferably, shafts  122 ,  144  each have a generally right cylindrical shape, presenting an approximate circular cross-section perpendicular to rotational axes R 1 , R 2 ; and flights  124 ,  128 ,  144 ,  148  present a generally circular cross-section along a plane perpendicular to the rotational axes R 1 , R 2  of the shafts  122 ,  142 , respectively. 
     Generally referring to FIGS. 1-5, selected operational features of mixer  60  are next discussed. Chips  12  enter inlet  72  of enclosure  61  via conveyer  14 . When activated, motor  92  turns sprocket  102  which rotates sprocket  104  via chain  106 . Rotation of sprocket  104  turns auger  120  about rotational axis R 1  in the direction RD 1 , driving auger  120  in a counterclockwise or “left hand” direction. Rotational axes R 1 , R 2  are shown in FIG. 4 as cross-hair points generally concentric with the cross-section of shafts  122 ,  142 , respectively. Notably, these axes are generally parallel to each other and are parallel to the longitudinal axis of augers  120 ,  140 , and enclosure  61 . 
     The rotation of auger  120  turns gear wheel  112  contained in gear box  110 . Gear wheel  112  rotates gear wheel  114  in response in the opposite direction. Correspondingly, auger  140  rotates along with gear wheel  114  in a clockwise or “right hand” direction indicated by arrow RD 2 . 
     Rotation of flights  124 ,  144  of auger  120 ,  140  about axes R 1 , R 2  provides an “archimedes screw” type of conveyer which transports wood chips  12  entering inlet  72  along the direction indicated by arrow F, from end  61   a  toward end  61   b . At the same time that flights  124 ,  144  move material along arrow F, flights  124 ,  144  also tumble and intermix the solid pieces with a liquid colorant mixture sprayed into chamber  70  via nozzles  82 . The liquid mixture is supplied by dispensing system  20  to manifold  80 . The mixing of the liquid and solid pieces continues as it travels past manifold  80  and by window  76  along arrow F. Mixing paddles  125  assist intermixing by agitating the mixture of solid pieces and liquid. Preferably, mixing paddles  125  are pitched to oppose the flow of material along arrow F; and thereby enhance mixing. By adjusting the pitch of mixing paddles  125  relative to flight  124 , the average dwell time in chamber  70  of a given material may be changed. This feature further assists in controlling absorption of the liquid mixture by the wood chips to minimize run-off. 
     As gap  126  is encountered by material moving through chamber  70 , processed wood chips  16  begin to exit through outlet  74  to be carried away by conveyer  18  in a direction indicated by arrow O. 
     Unfortunately, the wet mass of material at gap  126  has a tendency to stick together—despite gravity urging it to fall through outlet  74 . As a result, material may occasionally bridge gap  126  and encounter either or both of flights  128  and  148 . Because flights  128 ,  148  oppose the rotational orientation of flights  124 ,  144 , respectively; flights  128 ,  148  both tend to move material opposite the direction of arrow F—that is in a direction away from end  61   b . The opposing configurations of flights  124 ,  144  with respect to flights  128 ,  148  tend to break up a mass of material bridging gap  126  to thereby facilitate discharge through outlet  74 . Consequently, the auger configuration of mixer  60  tends to reduce the incidence of material packing in outlet  74  and so reduces the number of mixing interruptions due to jamming or clogging. 
     Mixer  60  may be used with a variety of liquid mixture types for coating or adhering a desired substance to wood chips. Likewise, various solid pieces other than wood chips may be processed in this manner. Preferably, mixer  60  is used so that the direction of the flow along arrow F is generally horizontal. However, in other embodiments, mixer  60  may be inclined in varying amounts as would occur to one skilled in the art. 
     FIGS. 6 and 7 depict mixing system  210  of another embodiment of the present invention; where certain reference numerals are the same as those used in connection with system  10  and are intended to represent like features. System  210  includes dispensing system  20 , spray hood  250 , and mixer  260 . Dispensing system  20  delivers a liquid mixture to spray hood  50  via conduit  26  that is dispersed within chamber  252  of spray hood  250  and then contacts solid pieces passing through mixer  260 . As previously described, system  20  is controller-based and regulates the blending of a mixture of an agent from source  22  with water from supply  24 . Likewise, as described in connection with mixing system  10 , the regulation and control processes implemented with dispensing system  20  also apply to system  210 . 
     Mixer  260  is coupled to spray hood  250  and includes a mixing trough  261  extending along its longitudinal axis L with opposing ends  261   a ,  261   b . Trough  261  is partially covered by top  262 . Top  262  is opposite base  264 . Trough  261  is bounded by opposing side walls  266 ,  268  and defines a mixing passage  270 . Trough  261  has inlet  272  defined through top  262  adjacent end  261   a  and outlet  274  defined through base  264  adjacent end  261   b . Inlet  272  and outlet  274  intersect passage  270 . Inlet  272  and outlet  274  are separated from each other along axis L by distance LD 1 . 
     Disposed within passage  270  are augers  120 ,  140 . Augers  120 ,  140  extend from inlet  272  to outlet  274  and are turned by drive mechanism  90  via drive box  100  and gear box  110  as described in connection with mixer  60  of system  10 . Augers  120 ,  140  have shafts is  122 ,  142  and helical flights  124 ,  144 , respectively, as previously described. As shown in FIG. 6, a space  223  is defined between flight  124  and shaft  122  except at the ends  225 ,  227  which are connected to shaft  122 . Space  223  corresponds to a cross-section along axis L having a generally circular outer and inner contour bounded by flight  124  and shaft  122 , respectively. A like space is preferably defined between flight  144  and shaft  142  of auger  140 . To accommodate mixing, it is also preferred that space  223  extend between shaft  122  and flight  124  for a distance corresponding to at least three revolutions of flight  124  about shaft  122 . More preferably, this distance corresponds to at least six revolutions of flight  124  about shaft  122 . Most preferably, flight  124  is separated from shaft  122  and does not make contact therewith, defining space  223  therebetween, except where connected at ends  225  and  227 . 
     Further, FIG. 6 depicts flight  128  overlapping outlet  274  with an opposite rotational direction relative to flight  124 . Flight  124  is separated from flight  128  by a flightless gap  126  along shaft  122 . Preferably, auger  140  has a second flight sized and positioned like flight  128  with a rotational direction opposite flight  144  as described in connection with system  10 . The second flights  128 ,  148  for each auger  120 ,  140 , respectively, have been found to reduce clogging at outlet  274 . Also as described in connection with system  10 , augers  120 ,  140  preferably include adjustable mixing paddles  125 . Paddles  125  may be utilized to adjust dwell time of products being mixed in trough  261 . 
     Spray hood  250  defines chamber  252  and has a hinged access door  254  to facilitate maintenance as is best depicted in FIG.  7 . Manifold  280  is connected to the top of hood  250  and includes a number of spray nozzles  282  for delivering the liquid from system  20  to chamber  252  via supply conduit  284 . Conduit  284  receives and distributes the liquid from system  20  via conduit  26  coupled thereto. Several brackets  283  support conduit  284  along hood  250  above nozzles  282 . Conduit  284  terminates in end cap  284   a.    
     Referring to FIG. 7, it is preferred that each nozzle  282  have a spray pattern SP that subtends an angle A. Preferably, angle A is at least 60 degrees. More preferably, angle A is at least 80 degrees. One preferred nozzle  282  is model no. USS8060 provided by Spraying Systems Company having a business address of P.O. Box 7900, Wheaton, Ill. 60189-7900. This model is of the VEEJET line and sprays about 6 gallons per minute when supplied liquid at a pressure of about 40 lbs. per square inch (psi). Preferably, at least 8 nozzles are utilized. More preferably, at least 12 nozzles are utilized as depicted in FIG.  6 . 
     Referring additionally to FIG. 8, conduit  284  of manifold  280  includes a four-way conduit junction  286  for every four nozzles  282 . Each junction  286  is in fluid communication with two valves  287  on opposite sides thereof. Each valve  287  is in fluid communication with a “T” junction coupling  288 . A hose  289  is coupled to each opposite end of coupling  288  to a corresponding valve  290  in fluid communication with one of nozzles  282 . Thus, for the configuration depicted in FIG. 6, three junctions  286 , six valves  287 , and six “T” junction couplings  288  are utilized. Further, there are twelve hoses  289  and twelve valves  290  each corresponding to one of nozzles  282 . 
     In one preferred embodiment of hood  250 , chamber  252  is defined by a metal enclosure and door  254  is similarly formed from metal. For this embodiment, conduit  284  of manifold  280  is preferably formed from a two-inch diameter PVC pipe and junctions  286  are each provided as a four-way two-inch PVC connector. Valves  287  and  290  are of a half-inch variety and may be adjusted by hand. For this embodiment, transition members/reducers are used between values  287  and corresponding junctions  286 . Couplings  288  are likewise formed from PVC and hoses  289  are of a standard reinforced rubber type for this embodiment. 
     At the intersection of chamber  252  with passage  270  an area for contacting pieces in trough  261  is defined. This area is designated as contact area CA in FIGS. 6 and 7. Area CA has a length LD 2  along the distance LD 1  as shown in FIG.  6 . Preferably, distance LD 2  is at least about half of distance LD 1 . More preferably, distance LD 2  is at least two-thirds of distance LD 1 . Augers  120 ,  140  occupy a maximum width across passage  270  below spray hood  250  represented as width W 1  in FIG.  7 . W 1  is the maximum transverse distance across axis L collectively occupied by augers  120 ,  140 . Area CA preferably has a width that is at least one-half the width W 1 . More preferably, the width of area CA is at least about three-fourths of the width W 1 . Most preferably, the width of area CA is substantially all of width W 1  as shown FIG.  7 . 
     In correspondence with area CA, nozzles  282  are spaced at intervals along axis L to provide a collective spray pattern along distance LD 2 . Preferably, the spray pattern has a length of at least about one-half of distance LD 1  and a width at least about one-half of width W 1 . More preferably, the length of the spray pattern along axis L is at least about two-thirds the distance LD 1  and a maximum width of at least about three-fourths of width W 1 . Most preferably, the spray pattern has a length generally the same as distance LD 2  that is greater than or equal to about two-thirds of the distance LD 1  and a width that is substantially all of the width W 1  at a number of intervals along the distance LD 2 . As depicted in FIG. 7, it is also preferred that nozzles  282  be separated from augers  120 ,  140  by a height of at least one-half W 1  to facilitate dispersal of the liquid from system  20  in chamber  252  before contacting solid pieces being carried through passage  270 . 
     In operation, mixer  260  is configured to accept solid pieces through inlet  272  which are then advanced along passage  270  towards outlet  274  in the direction indicated by arrow F by turning augers  120 ,  140  with drive mechanism  90 . As the pieces are advanced with augers  120 ,  140 , they are tumbled and intermixed facilitating coating, coloring, or another mixing process with a liquid introduced through spray hood  250 . The pieces passing through mixer  260  may be, for example, wood chips of a suitable size and consistency for use as a mulch and the liquid delivered with system  20  may be a mixture of a liquid colorant and water to impart a desired color to the wood chips. 
     Collectively, the valves  287 ,  290  may be adjusted to provide a desired spray pattern within chamber  252  with nozzles  282 . For example, each valve  290  may be adjusted to selectively reduce or shut-off the spray from the nozzle  282  coupled thereto. Valves  287  may each be used to shut-off or adjust flow to each respective pair of nozzles  282  coupled thereto via a corresponding coupling  288 , pair of hoses  289 , and pair of valves  290 . In one mode of operation, valves  287  are used to make coarse adjustments and valves  290  are used to make fine adjustments. By selectively adjusting valves  287 ,  290  and parameters of system  20  previously described, greater control over the mixing process may be obtained. In one alternative embodiment, these nozzles are electronically controlled by a controller to establish various predetermined patterns (not shown). 
     Moreover, it has been found that the expansive spray pattern of system  210  facilitates a reduction in water usage needed in order to color wood chips to provide a suitable mulch with a generally uniform color. It is believed this reduction in water consumption results because the amount of chip surface area contacted by the color-imparting spray is greater than with existing systems, so that the amount of color-imparting liquid that needs to freely flow in trough  261  to properly color the wood chips is comparatively less. However, it should be understood that it is not intended that the claimed invention be limited to any stated mechanism or theory. 
     Several experiments were performed using equipment arranged as described for system  210 . A number of different types of wood based products were colored in a manner suitable to serve as a mulch. The tested products may be as much as 40% by volume saw dust with the balance being wood pieces having a maximum dimension in a range of about ½ inch to about 2 inches. Also, the tested product has a widely varying moisture content. Coloration was performed by contacting the wood product with a liquid coloring mixture obtained by mixing a concentrated liquid colorant with water. Water consumption of 10 gallons or less per cubic yard of wood product colored was observed under these conditions. This result indicates at least a 20% reduction in water consumption compared to other coloration systems. 
     In one preferred embodiment, system  210  is used to color wood chips provided in a consistency suitable for application as a mulch; however, in another embodiment, a scent is additionally supplied in order to simulate a known type of mulch such as eucalyptus, cedar, or pine. For this embodiment, scent may be dispensed in a liquid form from a separate system comparable to system  20  and may be introduced into chamber  252  through one or more nozzles  282  instead of the colorant mixture. Alternatively, the scent may be homogeneously mixed with colorant and water before being dispensed to hood  250 , or a single vessel containing concentrated liquid colorant and scent that has been premixed may be mixed with water in dispensing system  20  and subsequently supplied to hood  250 . 
     In still other embodiments, system  210  may be used with a variety of liquid mixture types for coating or adhering a desired substance to solid pieces. Indeed, solid pieces other than wood chips may be processed in this manner, such as rocks, cardboard, synthetic resin pieces, and the like. Moreover, while it is preferred that mixer  260  generally be maintained in a horizontal position, in other embodiments, trough  261  may be inclined in varying amounts as would occur to one skilled in the art. In addition, it is envisioned that various components and operations described in connection with systems  10  and  210  may be interchanged, deleted, substituted, combined, modified, divided or reordered as would occur to one skilled in the art without departing from the spirit of the invention. 
     All publications and patent applications cited in this specification are herein incorporated by reference as if each individual publication or patent application were specifically and individually indicated to be incorporated by reference, including, but not limited to, commonly owned U.S. patent application Ser. No. 08/650,871, filed May 20, 1996. 
     While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiments have been shown and described and that all changes, modifications, and equivalents that come within the spirit of the invention as defined by the following claims are desired to be protected.