Abstract:
A grit pickup apparatus and method, and a grit pickup member used therewith that avoids the difficulties encountered with conventional devices. In accordance with certain embodiments, the grit pickup member includes an elbow-shaped preferably tubular member, having an aperture or slot formed in a wall thereof that allows communication between grit pickup media and the interior of the grit pickup member. The pickup member is submerged in the media such as granular material (e.g., sand), and as high velocity fluid travels by the aperture, the media is drawn into the interior region of the pickup member through the aperture and becomes entrained in the high velocity air stream, which carries it to the nozzle where it is expelled and directed toward a substrate to be cleaned.

Description:
FIELD OF THE INVENTION 
       [0001]    The embodiments disclosed herein relate to a grit pickup device and method typically used to direct media such as granular material at an object surface to clean the same, or, for example, to strip the same of paint, dirt, grease or other coating, for example. 
       BACKGROUND 
       [0002]    Conventional grit pickup devices are used to clean surfaces for a variety of reasons, including polishing, degreasing, removing coatings such as paint so that the surface can be painted again, for example. These devices typically accomplish this by propelling abrasive media such as particles of sand using a high velocity fluid such as air against the surface to be cleaned, degreased, decoated, etc. For example, an air stream containing the abrasive media is created using pressure, and is directed out of a nozzle towards the substrate of interest. Preferably the abrasive media stream is ejected from the nozzle in a controlled manner, and damage to the underlying substrate is minimal or non-existent. 
         [0003]    Known types of grit pickup devices have several drawbacks. For example, some must be adjusted based on the weight of the media being transferred. Some siphon material off the side of the media pile, causing erratic performance as the media pile erodes and is then replenished. Some cause airflow to change direction abruptly, causing poor air velocity. Most are susceptible to avalanches of media which temporarily reduces or even blocks the airflow, again causing erratic performance. 
         [0004]      FIG. 1  is a rendering of a conventional grit pickup device commonly known as a siphon tube. The tube is submerged into a grit hopper  101  or can be used in a pail. It is constructed by installing a small diameter tube  102  inside an outer larger diameter tube  100 . The inside tube  102  must be smaller than the outside tube to an extent that it allows air to freely flow in the gap created between them. The outside tube  100  is pinched or welded to the inside tube in two or more areas but not around the full circumference so that air is still able to pass between the two tubes freely once they are attached. The inside tube  102  protrudes out the top of the outer tube  100 , creating an area to attach a hose or the like (not shown) to a blast gun or venturi (not shown). The bottom of the inside tube  102  is recessed into the outer tube  100  so that ambient air can pass from the space in between the tubes and convey granular material  105  up the inside tube  102  without being choked off by the bulk of granular material. 
         [0005]    A disadvantage of this design is that the air must completely reverse direction (as shown by the arrows in the exploded insert) between the outer and inside tube which causes a drop in air velocity at exactly the point where it should be the highest. This results in poor performance. 
         [0006]      FIG. 2  shows a conventional style of grit pickup which is attached to the bottom of a grit hopper or blast cabinet. It is constructed by forming or casting an elbow shaped open trough  201 . The open area is to allow the flow of ambient air across the granular material  205  pile and convey the granular material into a blast hose  206  and ultimately to the venturi or blast gun (not shown). On the top side of the elbow there is means to attach to the bottom of a grit hopper or blast cabinet. On the horizontal side of the elbow there is a clamp or other means to attach the hose  206  from the blast gun or venturi. This clamp also allows adjustment of the hose to bring it closer or further away from the granular material pile. This type of grit pickup may have an optional drain plug at its low point to facilitate emptying the hopper. The disadvantages of this design include 1) the granular material has a frequent tendency to erode away and then suddenly avalanche down, momentarily blocking the flow of air. The erosion causes a diminished flow of granular material followed by an avalanche, blocking the flow of air which causes momentary heavy grain flow at diminished velocity. This phenomenon is called “surging” and is undesirable; 2) the performance of this design is affected by the distance from the hose to the grit pile and the height of the grit pile (which is adjustable by mounting closer or further from the material hopper). These adjustments must be made to ensure satisfactory performance when switching between grains of different weight. Because adjustments are infinite and based on trial and error, it is difficult to achieve peak performance; 3) because this design mounts on the bottom of the blast cabinet, it must be mounted externally. A hole must be cut into the blast cabinet for the hose to enter and attach to the blast gun, and the hole usually leaks granular material out of the cabinet onto the floor. 
         [0007]      FIG. 3  shows yet another style of conventional grit pickup which is generally attached to the bottom of a grit hopper or blast cabinet. It is constructed by attaching one end of an elbow  301  directly to the bottom of the grit hopper or blast cabinet. A tee fitting  308  is attached to the other end of the elbow. The opposite side of the tee fitting is attached to a hose (not shown) which leads to a blast gun or venturi (not shown). The perpendicular side of the tee fitting has an attached valve  309  to limit the flow of ambient air. This type of grit pickup also may optionally have a drain plug at its low point to facilitate emptying the hopper. Disadvantages of this design include 1) the granular material has a frequent tendency to erode away and then suddenly avalanche down, momentarily blocking the flow of air. The erosion causes a diminished flow of granular material followed by an avalanche, blocking the flow of air which causes momentary heavy grain flow at diminished velocity or “surging”; 2) this design must be adjusted to achieve satisfactory performance when switching between grains of different weight. Adjustments are based on are trial and error. 
         [0008]    Accordingly, it is an object of the embodiments disclosed herein to provide an improved apparatus and method for cleaning, finishing or the like surfaces of articles with a pressurized flow of media that reduces or eliminates the problems associated with conventional devices. 
       SUMMARY 
       [0009]    The problems of the prior art have been overcome by the embodiments disclosed herein, which relate to grit pickup apparatus and method, and a grit pickup member used therewith that avoids the difficulties encountered with conventional devices. In accordance with certain embodiments, the grit pickup member includes an elbow-shaped preferably tubular member, having an aperture or slot formed in a wall thereof that allows communication between grit pickup media and the interior of the grit pickup member. Suitable media includes aluminum oxide, silicone carbide, garnet, glass bead, crushed glass, steel shot, sand, chilled iron, steel grit, walnut shells, corn cob, baking soda, plastic beads, polystyrene beads, cut wire shot, sawdust, rice hulls, pumice, slag, resin, or any other material which may abrade, polish or remove dirt or discoloration from a substrate. The particle size should be small enough so that it can pass through the nozzle without particles jamming together and clogging the nozzle. The nozzle is typically double the size of the air jet. The air jet size is determined by the available airflow (or fluid flow where air is not used as the carrying medium) capacity of the compressor or hose (whichever flows less). In use, the pickup member is submerged in the media such as granular material (e.g., sand), and as high velocity fluid travels by the aperture, the media is drawn into the interior region of the pickup member through the aperture and becomes entrained in the high velocity air stream. The air stream carries the granular material to the nozzle where it is expelled and directed toward a substrate to be cleaned. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a cross-sectional diagram of a conventional grit pickup device; 
           [0011]      FIG. 2  is a cross-sectional diagram of another conventional grit pickup device; 
           [0012]      FIG. 3  is cross-sectional diagram of still another conventional grit pickup device; 
           [0013]      FIG. 4  is a perspective view of a slotted grit pickup member in accordance with certain embodiments; 
           [0014]      FIG. 5  is a cross-sectional view of the slotted grit pickup member of  FIG. 4 ; and 
           [0015]      FIG. 6  is a schematic diagram of a grit pickup device including the slotted grit pickup member of  FIG. 4 , in accordance with certain embodiments. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    Turning now to  FIGS. 4 and 5 , there is shown a grit pickup member  10  in accordance with certain embodiments. Preferably the member  10  is made of an abrasive resistant material, such as iron or steel, although other materials including plastic, ceramic, glass (preferably tempered), rubber and the like are suitable. The member  10  is preferably tubular, having first and second open ends  13  and  14 , and a tubular body such that an interior cavity  11  is defined that preferably has a uniform diameter throughout. The member  10  is preferably bent or angled so as to form an elbow. In certain embodiments, the member is U-shaped. The extent of the angle (measured relative to a straight member, see  FIG. 5 ) is not particularly limited, and is preferably between about 30 and about 60°, more preferably about 45° (e.g., θ and θ 1  are each about 45°). Preferably the angle is formed at the center of the member  10 . θ and θ 1  need not be equal. It is important that the angle not be so great that the flow of granular material through the member  10  entrained in the fluid stream is deleteriously inhibited. Although a tubular member is preferred, other shapes of the member  10  are suitable and within the scope of the embodiments disclosed herein. 
         [0017]    Although air is the preferred fluid used to pick up, carry and expel the grit, other fluids, including water, also may be suitable. Although air is used as an example of a suitable fluid below, the embodiments disclosed herein are not limited to air as the fluid. 
         [0018]    The member  10  includes an aperture  12 . The aperture  12  extends through the thickness of a wall of the member  10 , leads to the internal cavity  11 , and is preferably oval-shaped, although other shapes are suitable and within the scope of the embodiments disclosed herein. In accordance with certain embodiments, the aperture is formed at the vertex of the angle of the member  10 , and preferably the center of the aperture is formed there. In certain embodiments, the aperture is about ¾″ long at its longest dimension “L”, and ½″ wide at its widest dimension “W”. In certain embodiments, the aperture is symmetrically located with respect to the ends  13 ,  14 . The aperture  12  can be formed by any suitable means, such as by drilling, or, for example, the member  10  can be molded with the aperture  12  formed during the molding process. 
         [0019]    The inside diameter of the member  10  is sized based upon available airflow (e.g., the compressor size, air hose size, air et size, nozzle size, and blast hose size), and the particular diameter chosen is within the skill  1 n the art. In general, the component sizes will either be determined by the available air flow or the grit size required to carry out the job effectively. 
         [0020]    For example, a compressor capable of delivering 45 CFM @90 PSI, ⅜″ I.D. air hose, a 7/32″ I.D. airjet, a 7/16″ I.D. nozzle, a ½″ I.D. blast hose and a grit pickup member  10 ) with an I.D. of ½″ is a suitable combination. The size of the aperture can vary considerably with little or no effect on performance, because the lower pressure inside of the grit pickup is what determines how much grit can be conveyed to the blast gun. The lower pressure area will pick up grit until the weight of the grit in suspension exceeds the available lift. At that point, the air speed will start to slow and subsequently the lower pressure will start to moderate. The lack of strong low pressure will cause less grit to be picked up, until the airspeed recovers or the low pressure recovers, at which point full grit pickup will resume. One suitable aperture is ⅔ as wide and equal in length to the internal diameter of the tubular elbow. The size of every component can be determined by how much airflow is available and how much of that airflow is to be used. For example, an air jet that flows at 45 cfm cannot be used effectively with a compressor or air hose that can only deliver 30 cfm as air pressure will drop off instantly. However, an air jet that flows at 45 cfm (or less) can be used with a compressor/hose combination that that is capable of delivering 500 cfm. The air jet should have the lowest flow rate of all components in the system. In certain embodiments, the nozzle internal diameter is twice the internal diameter of the air jet. It will be appreciated by those skilled in the art that although in the embodiment shown the member  10  is tubular and the internal diameter is of circular cross-section, other shapes are within the scope of the present invention, and the term “diameter” as used herein is not limited to circular shapes. An internal diameter of ½ inch has been found to be suitable (for the typical application). A very large compressor could use a ¾″ I.D. or even 1″ I.D. or larger grit pickup for increased productivity. A small compressor should use a ⅜″ I.D. or ¼″ I.D. grit pickup due to low air flow capacity. 
         [0021]    As seen in  FIG. 6 , in accordance with certain embodiments the member  10  is adapted to be attached at one end to an elongated member such as a pipe, hose or the like  20  (hereinafter “pipe”) of sufficient length such that when the member  10  is embedded in the granular material, the open end  21  of pipe  20  extends out of the granular material and is in fluid communication with ambient air; e.g., the flow ambient air into the pipe  20  is uninhibited by granular material in the material hopper. The other end of the member  10  is adapted to be attached to an elongated pipe, hose or the like  25  (hereinafter “hose”), which is preferably flexible, and also extends out of the granular material, leading to a nozzle, sandblast gun, venturi or the like  30 . The pipe  20  and hose  25  can be attached to the member  10  by any suitable means. For example, the member can include interior threads  18  at each end ( FIG. 5 ) that mate with corresponding exterior threads on the pipe  20  and hose  25 . Alternatively, clamps or the like can be used to secure the pipe and hose to the member  10 . 
         [0022]    In accordance with certain embodiments, the member  10  could be integral with the pipe  20  and/or the hose  25 ; e.g., formed with one or both as a single unitary unit, thereby eliminating any necessity for attachments. 
         [0023]    In operation, the member  10  with pipe  20  and hose  25  are positioned in a material hopper  1 , preferably in an orientation such that the aperture  12  in the member  10  is facing downward toward the bottom of the hopper  1 , as shown in  FIG. 6 . Granular material such as abrasive particles (e.g. sand) is introduced into the material hopper  1  in at least an amount sufficient to submerge the member  10 , while leaving the open end of pipe  20  exposed to ambient air. The hose  25  is connected to a nozzle  30 , such as a venturi, and a source of high pressure gas such as compressed air is supplied to the nozzle  30 . Suitable pressures range from about 60 to about 80 psig for most typical blast jobs, although much higher and lower pressures can be used (the upper limit of pressure is ultimately determined by the tolerable amount of damage to the substrate or rapid breakdown of the grit. As a practical matter, the upper pressure may be determined by the pressure output of the air compressor. The lower limit is that at which the system cannot generate sufficient velocity to pick up and expel the grit). This creates a region of low pressure in the hose  25 , member  10  and pipe  20 , such that ambient air enters the open end of the pipe at high velocity. As this high velocity air passes the aperture  12  in member  10 , granular material surrounding the aperture  12  enters the high velocity air stream in the cavity  11  of the member  10  through the aperture  12  and becomes entrained in the stream. The entrained granular material is then carried in the high velocity air stream towards the nozzle, where it is expelled out of the nozzle and directed to the substrate surface to be cleaned, degreased, etc. 
         [0024]    The velocity should be sufficient to propel grit from the gun and reach the substrate. 
         [0025]    In certain embodiments, a screen or sieve  35  may be placed over the source of granular material to allow grit to pass through but not allow clumps through. This would be helpful in keeping foreign objects from clogging the grit pickup or nozzle. The size of the screen or sieve openings  36  is within the skill in the art. The screen  35  is preferably removable to enable service or to replace it with a different size screen. Because the nozzle is always smaller than the blast hose or the aperture, the screen or sieve size must be small enough to allow only particles to pass which will not jam or clog the nozzle. 
         [0026]    Preferably the screen  35  is high enough in the material hopper  1  so that all or at least most of the grit is screened as soon as it is introduced into the hopper  1 . This allows the user to see and remove clumps or foreign items before blasting is commenced. In the embodiments where the material hopper  1  is shaped like an inverted cone or pyramid, the higher the screen is (i.e., the closer it is to the top or inlet of the hopper), the more surface area it will have, which aids in unobstructed flow. In certain embodiments, the screen can be positioned from just over the grit pickup to several feet above the grit pickup. An example of the screen being feet above the pickup would be in a large blast cabinet. The screen could act as the floor which supports the parts to be blasted. As blast proceeds, the screen filters out coating or rust particles which are too big to pass through but allows the grit to fall through to the hopper where it can be picked up and used again. The advantage of this design is foreign matter can be easily cleaned out through the cabinet door with a brush and dustpan. The downside is if it is a fine screen the grit will erode it and it will require frequent replacement.