Abstract:
The flow of media in shot peening, blast cleaning, and similar equipment is improved by applying a time varying magnetic field to the media to thereby degauss the media, allowing the media to flow through equipment without clogging and clumping due to magnetic attraction between the media.

Description:
[0001]    This application claims domestic priority based upon U.S. Provisional Patent Application Ser. No. 60/461,845, filed Apr. 10, 2003. 
     
    
     
       TECHNICAL FIELD  
         [0002]    This invention relates to improving the flow of media in shot peening, blast cleaning, and similar equipment.  
         BACKGROUND OF THE INVENTION  
         [0003]    Iron or steel granules, also called shot or grit, are used in abrasive blast cleaning, granite cutting, shot peening and other applications. The efficiency of such equipment depends upon media flowing freely through the apparatus and impacting upon the workpiece being treated. However, the flow characteristics of the media vary widely during operation of the equipment. Commonly, the media is directed against the workpiece and then collected and recycled through the equipment.  
         SUMMARY OF THE INVENTION  
         [0004]    Such media materials are subject to magnetic remnance or memory which causes reduced flow capability because of the magnetic remnance or memory which causes reduced flow capability. This invention reduces or eliminates the effect of this magnetic influence and thereby improves the flow characteristics of the media. Media can become “magnetized” by a variety of methods, especially by impact with a surface. As this media is re-cycled through the machine during treatment of a workpiece, its remnace tends to increase and its ability to flow smoothly is reduced, sometimes to the point of complete blockage of the flow-regulating device or passages.  
           [0005]    Other objects are also subject to magnetic remnance, the effect of which can be remedied by subjecting the object to an alternating electro-magnetic field available from, for instance, a coil of wire with multiple turns. Such a coil is commonly referred to as a de-gaussing coil and is used extensively to de-magnetize objects, such as screwdrivers or pliers. Degaussing works on the principle of application of a time-varying magnetic field initially at a sufficient level to cause magnetic dipole alignment. The magnitude of the time-varying magnetic field is reduced until the remnance is at or near zero. In the case of the screwdriver, one would insert the screwdriver into the center of the degaussing coil and slowly extract it. As the screwdriver is extracted, the influence of the de-gaussing coil is diminished, leaving the screwdriver in a de-magnetized state.  
           [0006]    In this invention, the media is briefly submitted to an alternating magnetic field provided by a degaussing coil for a sufficient period of time that the magnetic remnance is reduced to a low (near zero) value. According to the invention, the magnetic field can either be applied to the media in bulk or can be applied to the media by continuously passing the media through the degaussing coil. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    [0007]FIG. 1 is a schematic illustration of a typical shot peening or blast cleaning apparatus to which a degaussing coil of the present invention has been applied;  
         [0008]    [0008]FIG. 2 is an illustration similar to FIG. 1, but illustrating another embodiment of the invention;  
         [0009]    [0009]FIGS. 3 and 4 are microphotographs of media before and after treatment according to the present invention; and  
         [0010]    [0010]FIG. 5 is a view of a coil and a media container within the coil to illustrated bulk degaussing of the media pursuant to another embodiment of the invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0011]    Referring now to FIG. 1, a typical shot peening or blast cleaning apparatus is generally indicated by the numeral  10 . Media is stored in hopper  12  and then directed through a suitable flow path or conduit  14 , which includes a regulating device, for example a fixed orifice  16  in an orifice plate  18 . Typical size of the orifice  16  is, for example, 0.125″ or 0.250″. After the material passes through the orifice  16 , the media enters treatment chamber  20 , which includes, for example, a centrifugal throwing wheel (not shown) or a pneumatic blast nozzle (not shown), both of which are well known to those skilled in the art. The media impacts a target surface for its intended application and is then gathered in and resubmitted to the hopper  12  through return line  22 .  
         [0012]    As has been discussed above, it has been observed that impacts of the media with the target increase the tendency of the material to become “magnetized”. Additional impacts due to recirculation of the media tend to further aggravate this condition. To alleviate this magnetic influence, a de-gaussing coil  24  is placed anywhere within the flow path. A preferred, but not mandatory, location for the location of the de-gaussing coil is immediately above the regulating orifice  18 , as illustrated in FIG. 1. Other locations may be used and even multiple degaussing coils may be used at various locations within a single flow path. An alternating current power supply  25  supplies alternating current to the degaussing coil, thereby causing the degaussing coil to apply a time-varying magnetic field to the media flowing through the flow path  14 , the average value of which is zero. The maximum strength of the magnetic field increases as the media enters the coil to a maximum midway through the coil and then diminishes. Although a degaussing coil has been illustrated, any alternating and diminishing magnetic field will accomplish the de-gaussing. For example, rotation of a small bar magnet could be employed which would present a magnetic field to the passing material and thereby cause the de-gaussing effect.  
         [0013]    Referring now to FIG. 2, elements the same or substantially the same as the preferred embodiment retain the same reference numeral. In FIG. 2, a commercially available magnetic valve  23  replaces the orifice plate  18  and magnet(s)  26  and electromagnetic coils  28 . Valve  23  is disclosed in U.S. Pat. No. 5,362,027, and is a normally-closed device restricting the flow of media caused by the influence of the permanent magnets. Application of an electrical current to electromagnetic coil  28  located within the valve causes a cancellation or neutralization of the permanent magnetic field and thus flow is allowed. The level of this signal determines the amount of net magnetic field and therefore the flow rate. When this level is set to achieve zero, or near zero, net magnetic field flow rate will be maximized. The degaussing coil  24  may be placed in flowpath  14  at either the inlet or outlet (or at both the inlet and outlet) of the magnetic valve and is designed to overcome not only the magnetization of the media by impact and recirculation, but also due to the effect of the permanent magnets within the magnetic valve  23  if a coil is placed at the outlet of the valve  23 .  
         [0014]    The de-gaussing can also be achieve by alteration of the neutral field current signal controlling the electromagnetic coil  26  within the valve  23  in a time-varying fashion. This can be accomplished by applying a complex electrical current to the coil  28 . Accordingly, instead of applying a steady-state field condition, a dynamic time-varying field, is imposed on the steady state magnetic field. The average value of this time-varying portion of the field is zero, and thus the combination of the steady-state signal and the time-varying signal operates similar to just the steady-state signal alone except the presence of the time-varying portion of the signal performs a degaussing function. The steady-state portion of the signal is sufficient to provide the regulation of the flow rate of the media through the valve  23 , while the time-varying portion of the neutral field signal is sufficient to effect the degaussing action desired. This technique has the advantage of not requiring an additional element such as the degaussing coil in order to achieve demagnetization.  
         [0015]    Although continuous degaussing of the media as it flows through the flowpath is preferred, media may also be degaussed in bulk and then added back into the system. Referring to FIG. 5, a container  32  is filled with media into the system. Referring to FIG. 5, a container  32  is filled with media and placed within a coil  34 . Current is applied to the coil to degauss the media in the container. The media is then returned to the hopper  12 .  
         [0016]    Referring now to FIGS. 3 and 4, the effects of degaussing can be seen on the media. FIGS. 3 and 4 are microphotographs of fine steel shot media, before and after degaussing respectively. Magnetized media exhibit “stringing”, which is clearly present in FIG. 3. As shown in FIG. 4, the “strings” are absent from the degaussed media. The effects of degaussing media are also illustrated in Tables 1 and 2. Table 1 sets forth data with respect to a fine powder steel media, and Table 2 sets forth data for an industry standard “cut wire” shot. In both instances, the degaussed media exhibited substantially greater flow rates than either the magnetized media (which had been used in production), and the virgin media which had not been used in production and which was magnetized only to that extent occurring naturally in the manufacture and shipping of the media.  
                                           TABLE 1                           Fine Powder                Magnetic   Flow rate           Condition   pounds/min                        0.250   virgin   2.48       orifice   magnetized   1.43           degaussed   3.15       0.125   virgin   0.47       orifice   magnetized   0.19           degaussed   0.50                  
 
         [0017]    [0017]                                           TABLE 2                           CW20 Shot                Magnetic   Flow rate           Condition   pounds/min                        0.250   virgin   2.70       orifice   magnetized   2.30           degaussed   3.14       0.125   virgin   0.34       orifice   magnetized   0.26           degaussed   0.37