Method and system for evaluating local compactness of a granular material

Abstract

An evaluation method in which a capacitive sensor is placed in a region of a container, into which a granular material is fed so as to contact the sensor, and the variation in the impedance of the sensor caused by feeding in the material is evaluated. The method is particularly useful for evaluating the compactness of sand in a formwork for making metal castings. The evaluation system includes a sensor defined by plates sensitive to the variation in the dielectric; and a conditioning and control circuit for indicating the variation in the capacitance of the plates, or more generally the total impedance of the system, when the granular material is fed into the container. In one embodiment, the plates of the sensor are defined by two combs made of conducting material, having two numbers of interlacing segments, and located on a rigid or flexible support.

1 . A method of evaluating local compactness of a granular material inside a container, characterized by comprising the steps of: 
 setting up a compactness evaluation system ( 1 ) comprising a capacitive sensor ( 5 ), and a conditioning and control circuit ( 6 ) for conditioning and controlling said sensor ( 5 ) and capable of evaluating the variation in impedance of the sensor;    placing said sensor ( 5 ) inside a region of said container ( 3 ) in which the compactness of said granular material ( 2 ) is to be evaluated;    feeding said granular material ( 2 ) into said container ( 3 ) and into contact with or close proximity to said sensor ( 5 ); and    directly evaluating, by means of said conditioning and control circuit ( 6 ), the local compactness of the granular material ( 2 ) contacting or in close proximity to said sensor ( 5 ), on the basis of the variation in the impedance of said sensor ( 5 ), and in particular in the capacitive component of said impedance.    
   
   
       2 . A method as claimed in  claim 1 , characterized in that said conditioning and control circuit ( 6 ) may also measure the resistive and inductive impedance components of said sensor ( 5 ) to identify any spurious effects or undesired synergies between such spurious effects and the compactness of the granular material.  
   
   
       3 . A method as claimed in  claim 1 , characterized in that said sensor ( 5 ) comprises a capacitor ( 8 ) having two or more plates ( 9 ,  10 ;  19 ,  20 ) for generating an electromagnetic field ( 14 ) close to said plates ( 9 ,  10 ;  19 ,  20 ).  
   
   
       4 . A method as claimed in  claim 1 , characterized in that said conditioning and control circuit ( 6 ) indicates said compactness continuously.  
   
   
       5 . A method as claimed in  claim 1 , characterized in that said granular material ( 2 ) is defined by sand, or by sand mixed with additives and/or binders; said container ( 3 ) being defined by a formwork or by a metal casting pattern.  
   
   
       6 . A method as claimed in  claim 1 , characterized in that said granular material is defined by sand, or by sand mixed with additives and/or binders; said container ( 3 ) being defined by a foundry core mold.  
   
   
       7 . A method as claimed in  claim 1 , characterized in that said granular material ( 2 ) is defined by sand; said container ( 3 ) being defined by a formwork containing a cluster of polymer foam for Lost Foam Casting.  
   
   
       8 . A method as claimed in  claim 1 , characterized in that said granular material ( 2 ) is a polymer in pellets or powdered or granular ceramic; said container ( 3 ) forming part of a conveyor and/or loading line.  
   
   
       9 . A method as claimed in  claim 1 , characterized in that said granular material ( 2 ) is defined by building sand and/or gravel; said container ( 3 ) being defined by a store, or by an industrial vehicle, or by a mixer.  
   
   
       10 . A system for evaluating local compactness of a granular material ( 2 ) inside a container ( 3 ), and comprising a capacitive sensor ( 5 ) defined by a capacitor ( 8 ) in turn comprising two or more plates ( 9 ,  10 ;  19 ,  20 ); and a conditioning and control circuit ( 6 ) for conditioning and controlling said sensor ( 5 ); said capacitor ( 8 ) having a given no-load capacitance; and the system being characterized in that said sensor ( 5 ) comprises an outer surface ( 15 ) so shaped as to be positioned, in use, contacting or in close proximity to said granular material ( 2 ); said circuit ( 6 ) receiving from said sensor ( 5 ) a signal indicating the variation in the impedance of said sensor ( 5 ) , when said surface ( 15 ) contacts or is in close proximity to said granular material ( 2 ), and accordingly indicating the local compactness of said granular material ( 2 ).  
   
   
       11 . A system as claimed in  claim 10 , characterized in that said circuit ( 6 ) may also measure the resistive and inductive impedance components of said sensor ( 5 ), to identify any spurious effects or undesired synergies between such spurious effects and the compactness of the granular material.  
   
   
       12 . A system as claimed in  claim 10 , characterized in that the plates ( 9 ,  10 ;  19 ,  20 ) of said capacitor ( 8 ) are located on a support ( 16 ) which is fitted to or incorporated in said container ( 3 ).  
   
   
       13 . A system as claimed in  claim 12 , characterized in that said plates ( 9 ,  10 ) are defined by thin, rigid or flexible plates.  
   
   
       14 . A system as claimed in  claim 13 , characterized in that said plates ( 9 ,  10 ) are defined by a thick or  5  thin conductive film.  
   
   
       15 . A system as claimed in  claim 14 , characterized in that said support ( 16 ) is defined by a thin adhesive film which is applied to said container ( 3 ).  
   
   
       16 . A system as claimed in  claim 14 , characterized in that said container ( 3 ) is defined by a formwork containing a cluster of polymer foam for Lost Foam Casting; said thin film being deposited directly on a surface of said cluster.  
   
   
       17 . A system as claimed in  claim 10 , characterized in that said plates ( 9 ,  10 ) comprise two or more numbers of straight interlacing segments ( 12 ,  13 ).  
   
   
       18 . A system as claimed in  claim 10 , characterized in that said plates ( 9 ,  10 ) are defined by two or more coplanar concentric spirals defined by circular ( 17 ) or  20  straight ( 18 ) portions.  
   
   
       19 . A system as claimed in  claim 12 , characterized in that said plates are in the form of two or more concentric cylinders ( 19 ,  20 ) of given length.  
   
   
       20 . A system as claimed in  claim 10 , characterized in that said plates ( 9 ,  10 ;  19 ,  20 ) have a protective coating.  
   
   
       21 . A system as claimed in  claim 10 , characterized in that said plates ( 9 ,  10 ;  19 ,  20 ) are structured to generate, by means of edge effects, an electromagnetic field ( 14 ) close to the surface ( 15 ) of said sensor ( 5 ).