Abstract:
A method and apparatus for reblending sand whereby multiple reblending tanks with a plurality of reblending stations have thin respective outputs joined through a single control system.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    U.S. Pat. No. 6,311,847 discloses a method and means for sand reblending using a single tank for receiving aggregate of various sizes for classification. The tank has a plurality of stations with primary and secondary discharge valves. The tank is then calibrated to determine raw feed analysis, discharge rates and the flow multipliers needed to develop a mathematical model of the tank. Inputting the calibration information data and the desired production specification into a computer allows the tank to be operated and controlled with appropriate adjustments in discharge rates and valve percent settings at each station. The apparatus for this method includes the tank, a pumping device, and a computer interconnected with a PLC and electrohydraulic mechanisms for valves at each tank station such that both the discharge rate from each station and the valve percent settings of the individual valves at each station are variable and controllable.  
           [0002]    It is common in sand reblending to use two or more classification tanks. Currently the available systems for controlling multiple classifying tanks are to use multiple controls. These separate controls blend a specification material and then the two materials are mechanically blended into one presumably specification product. This is a good assumption as long as the material being fed to the tanks is the same. If this material is dissimilar either due to mechanical means or is from different sources then the efficiency of the twin tanks can be severely impaired and it is theoretically possible that a combined product will be out of specification. Finally, control of the fineness modulus (another type of specification designed to make the output of a plant consistent from day to day) is problematic and would require human oversight.  
           [0003]    It is therefore an object of the invention to provide a method and means for sand reblending wherein multiple tanks operate in accordance with the process of U.S. Pat. No. 6,311,847 but are controlled by a single controller so that the tanks act concurrently and in unison as if they were one large tank.  
           [0004]    A further object of the invention is to provide a method and means for sand reblending which improves the efficiency of the tanks and wherein shortages in one tank may be offset by excesses in the other.  
           [0005]    These and other objects will be apparent to those skilled in the art.  
         SUMMARY OF THE INVENTION  
         [0006]    This invention is an improvement of U.S. Pat. No. 6,311,847, which is incorporated herein in its entirety. The essence of the improvement is the controlling of a multi-tank blending system with a single controller rather than separate controllers so that the tanks can operate in unison rather than independently whereby more accuracy and efficiency is achieved in the blending operation.  
           [0007]    The method of reblending aggregate according to this invention includes delivering aggregate of various sizes to classification tanks having a plurality of stations with primary and secondary discharge valves. The tanks are then calibrated to determine raw feed analysis, discharge rates and the flow multipliers needed to develop a mathematical model of the tanks. Inputting the calibration information data and the desired production specification into a computer allow the tanks to be operated and controlled with appropriate adjustments in discharge rates and valve percent settings at each station. The apparatus for this method includes the tanks, a pumping device, and a single computer interconnected with a controller and electrohydraulic mechanism for valves at each tank station such that both the discharge rate from each station and the valve percent settings of the individual valves at each station are variable and controllable. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    [0008]FIG. 1 is a perspective view of the device of this invention;  
         [0009]    [0009]FIG. 2 is a front elevational view thereof;  
         [0010]    [0010]FIG. 3 is an end elevational view thereof as seen from the left-hand end of FIG. 1;  
         [0011]    [0011]FIG. 4 is a top plan view thereof; and  
         [0012]    [0012]FIG. 5 is a schematic diagram showing the control for reblending fine aggregate utilizing the dual tanks shown in the previous figures. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0013]    The hydraulic classification tanks  10  and  10 A shown in FIG. 1 facilitates the use of the control  12  (FIG. 5) and methods of this invention. The controls and methods of this invention utilize a personal computer to track the product discharged, perform the mathematical optimization routines, and determine new valve settings for each station  14 A-J located on each tank  10  and  10 A.  
         [0014]    Referring to FIG. 5, the control  12  includes a controller  18  in communication with each of the stations  14 A-J (one PLC module may share several stations), and the PLC  18  is in communication via cable with and controlled in a closed loop by a personal desktop computer  20 . The tanks  10  and  10 A are operatively connected to the controller  18  by suitable cables  20  and  22 , respectively. Cable  24  connects controller  18  to computer  20 . The control components  18  and  20  simulate the control components of U.S. Pat. No. 6,311,847. Only one set of control components, however, control both tanks  10  and  10 A simultaneously.  
         [0015]    Tanks  10  and  10 A are substantially identical and are supported in an elevated condition by framework  26 . Each tank  10  and  10 A has a discharge flume  28  which receive the discharged material through tank discharge pipes  27  from the stations  14 A- 14 J on each tank. The flumes  28  each discharge into a common trough  30  where they are then conveyed to one or more dewatering devices  32  (shown only in FIG. 2) by conduits  34  and  36 . Again, each tank operates as described in the U.S. Pat. No. 6,311,847 patent, except that the controls  12  treat the two tanks as one.  
         [0016]    The advantages of this arrangement is that separate controls do not have to be made available for both tanks. However, and more importantly, the single control system takes advantage of the possibility for one math model to simulate the two tanks as if they were just one tank. It allows for the coarseness of the material to blend so that if one tank produces a mix toward the lower parameter of the material specifications, and the other tank produces a mix toward the higher parameter of the material specifications, the resulting blended material outputs will provide a resulting coarseness factor (“FM”, or “fineness modulus”) well within the parameters of the material specifications. Without the tanks operating together under one control system, this advantage would not exist.  
         [0017]    More than two tanks could be successfully used for this system. Thus, from the foregoing, it is seen that this invention will achieve at least all of its stated objectives.