Portable sand blasting device
BACKGROUND OF THE INVENTION 
     Sand blasting devices presently available are generally satisfactory but portability is found lacking. Moreover, a supply of compressed air is required in the operation of such devices and air compressors are not readily available in many instances as for example, in the case of residential use. 
     SUMMARY OF THE PRESENT INVENTION 
     It is the general object of the present invention to provide a portable sand blasting device which is relatively simple in its construction and operation and which yet provides a high degree of dependability and durability in use, and which is adapted further to operate from an electrical power source without the need for a supply of air under pressure. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 of the drawings is an elevational view of the portable sand blasting device of the present invention, portions thereof being broken away for clarity of illustration. 
     FIG. 2 is a top view of an apertured rotatable disc forming a part of the sand blasting device. 
     FIG. 3 is a top view of the sand blasting device of the present invention. 
     FIG. 4 is a top view of an impeller of the present invention, portions thereof being broken away for clarity of illustration. 
     FIG. 5 is a side view of the impeller of FIG. 4 partially in section as indicated by the lines 5--5 in FIG. 4. 
     FIG. 6 is a top view of a cylindrical plate forming a part of the housing of the sand blasting device and partially defining a spiral discharge chamber and discharge opening. 
     FIG. 7 is a sectional view of the disc of FIG. 6 taken generally as indicated by the lines 7--7 in FIG. 6. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring particularly to FIG. 1, it will be observed that a portable sand blasting device is indicated generally by the reference numeral 10. A housing 12 of the sand blasting device is generally cylindrical in form and is adapted to be held and manipulated manually. As illustrated, the housing has oppositely disposed handles 14,14 respectively for the left and right hand of the operator. Disposed within the housing and supported thereby is a conventional electric motor with a rotatable output shaft 16 which projects upwardly within an upper portion of the housing. The electric motor has an associated electrical conductor means in the form of a cord 18 for connecting the same with a source of electrical power. While the invention is not so limited, the housing, handles and motor may take the form of identical units found in conventional portable routers. The working router elements mounted on or attached to the shaft 16 are of course removed in conversion to a portable sand blasting device. 
     An air and sand impeller 20 is mounted on the shaft 16 in accordance with the present invention and while there may be substantial variation in impeller form, an axial inlet-radial flow impeller is presently preferred. That is, the impeller 20 has an inlet opening 22 which introduces air and entrained sand axially to an inlet chamber 24 defined by and within an upper portion of the impeller. The inlet chamber 24 is generally annular in form and communicates with at least one air and sand passageway formed in the impeller. As illustrated, the impeller has a plurality of circumaxially arranged and radially extending passageways, FIGS. 1, 4 and 5. Eight such passageways 26,26 are preferably provided and each passageway may have a generally circular cross section as illustrated. A refinement in passageway construction involves the provision of a generally &#34;V&#34;-shaped trough or groove 28 in the trailing wall of each passageway, the impeller being rotated in a counter-clockwise direction in FIG. 4 as indicated by arrow 30. Each groove 28 extends radially along its passageway wall and, in its progression radially outwardly, becomes somewhat deeper and broader, FIGS. 1, 4 and 5. Sand entrained in air introduced to the impeller at the inlet opening 22 and passing through the inlet chamber 24 and the passageways 26,26 tends to collect in the grooves 28,28 and efficiency in the operation of the device is thus enhanced. 
     A discharge chamber for the impeller is also provided in accordance with the presently preferred practice and takes an arcuate form extending at least partially around and adjacent the periphery of the impeller. As illustrated, a discharge chamber 32 has a spiral configuration, FIGS. 3 and 6, and the chamber cross sectional area increases in counter-clockwise progression toward a discharge opening 34. Further, the discharge chamber 32 is preferably provided with a generally &#34;V&#34;-shaped cross sectional configuration viewed tangientially with the apex of the &#34;V&#34; spaced radially outwardly from the impeller periphery and with the &#34;V&#34; opening toward the impeller. Still further, the &#34;V&#34;-shaped outer wall of the chamber 32 becomes somewhat deeper and thus sharper in progression toward the discharge opening 34. 
     The function served by the &#34;V&#34;-shaped configuration of the discharge chamber 32 is similar to that of the &#34;V&#34;-shaped grooves 28,28 in the impeller passageways 26,26. That is, sand thrown outwardly from the impeller passageways 26,26 tends to collect in the &#34;V&#34; of the &#34;V&#34;-shaped wall and efficiency of operation is thus enhanced. 
     The manner in which the housing is formed in the area adjacent the impeller 20 may vary widely within the scope of the invention. As presently preferred, similar lower and upper flat cylindrical housing plates 36,38 are employed and the said plates are secured in position on the housing proper as by means of a plurality of retaining screws 40,40. Further, a plurality of retaining screws 42,42 may be employed to secure the plates 36,38 in face-to-face relationship. The spiral discharge chamber 32 is formed at inner walls of the plates 36,38 with approximately one half (1/2) of the chamber being formed in each of the plates, FIG. 6. That is, circular central openings 46,48 in the plates 36,38 receive and house the impeller 20 and the discharge chamber 32 is formed in the walls of the openings. Preferably, the impeller 20 and the plates 36,38 are formed of hardened material or, alternatively, hard coatings may be applied in the areas of sand engagement and wear. 
     Referring again to FIGS. 3 and 6, it will be observed that the discharge opening 36 takes a generally cylindrical cross sectional shape and is arranged along a centerline which extends substantially tangentially with respect to the impeller 20. A nozzle means of nozzle 50 is adapted to enter and fit the discharge opening 34 and thus to receive and discharge air and entrained sand in a high speed stream for a blasting operation. A set screw 52 may be provided to secure the nozzle 50 in position. 
     With the particular arrangement illustrated, it will be observed that the high speed discharge of a sand spray results at least in part from entrainment of the sand in a high speed stream of air. Further, it is to be observed that the sand is physically thrown or ejected from the passageways 26,26 as the individual passageways approach and pass the discharge opening 34. A component of movement of each sand particle, collected in a passageway 26 and groove 28, is at least approximately tangential as the sand leaves the discharge end of the groove. Such component of movement causes the sand to be thrown or ejected outwardly through the discharge opening 34 and nozzle 50 or in the alternative, the sand may engage the outer wall of the discharge chamber 32 of the discharge opening 34 and thus be deflected outwardly through the nozzle. The formation of the outer wall of the discharge chamber 32 and the discharge opening 34 at their area or zone of junction is such that a smooth blending contour is achieved. 
     From the foregoing, it will be apparent that a relatively high speed operation of the impeller 20 is to be desired. The electric motor in the router unit presently employed operates in a speed range of 19,000 to 20,000 RPM and excellent results have been achieved with impeller speeds in this range. 
     Still further, it has been found that an additional supply of ambient air to the impeller substantially enhances the efficiency of operation of the device. Accordingly, at least one additional ambient air inlet opening is provided for the impeller independently of the aforementioned air and sand inlet opening 22. Such additional opening may take various forms but in the presently preferred form, air flow adjustment is provided for and an apertured disc 54 is mounted atop the plate 38 by means of a thin annular retainer member 56. The member 56 is in turn secured in position by a plurality of screws 58,58 threadably entered in suitable openings in the plate 38. The disc 54 has an annular series of small openings 60,60 (7 shown) and each communicating with the impeller inlet chamber 24 and exposed upwardly for the entry of surrounding air. Mounted atop the disc 54 is a smaller diameter rotatable disc 62 similarly provided with an annular series of small openings 64,64 (5 shown), FIG. 2. The disc 62 is secured in position by means of a thin flat annular retainer 66 which may be welded or otherwise secured in position atop the disc 54. 
     As will be apparent, the openings 60,60 and the openings 64,64 provide through openings for the introduction of ambient air to the impeller inlet chamber 24. With the disc 62 rotated to a position of exact alignment of the openings 60,60 and 64,64 a maximum flow of ambient air is provided for. On rotation of the disc misaligning the openings in varying degree adjustment of the flow of ambient air can be readily achieved. 
     A supply of air and entrained sand to the aforementioned inlet opening 22 may be conveniently provided from a receptacle 68 in the form of a sand pouch adapted to be carried on the body of the operator of the sand blasting device. Sand disposed in the pouch at 70 surrounds an inlet end of a conduit means 72 in the form of an elongated flexible tube. The tube 72 extends from the sand to a fitting 74 at its discharge end adjacent the impeller inlet opening 22. Preferably, a sand screen 74 is provided about the inlet end of the sand supply tube 72 and a short length of similar tubing 76 serves as an air inlet conduit means. That is, the tube 76 has an upper end portion 78 which is exposed to ambient air and a lower end portion 80 is disposed in the sand adjacent the inlet end of the tube 72. On operation of the sand blasting device, the sand in the pouch adjacent the lower ends of the tubes 72,76 is sufficiently disturbed and intermixed with the air flowing downwardly through the tube 76 so as to cause the entrainment of sand particles in the air stream flowing within the tube 72 to the impeller inlet. A substantial suction is achieved with the high speed impeller operation as mentioned above. 
     The sand blasting device of the present invention is highly efficient in operation and, while operation is not understood to the point of certainty, it is believed that a jet pump effect may be achieved in the inlet chamber 24 adjacent the air and sand inlet opening 22. That is, the air flowing into the chamber 24 from the ambient air inlet openings 60,60 and 64,64 passes the inlet opening 22 at a high rate of speed in its progress to the inlet ends of the impeller passageways 26,26. A lowered pressure may thus be provided at the inlet 22 and throughout the length of the flexible supply tube 72 to the sand in the pouch 68. 
     From the foregoing, it will be apparent that a relatively simple construction has been provided for a portable sand blasting device. Operation of the device is convenient to the user as he may simply grasp the handles 14,14 and direct or aim the device and its nozzle 50 bodily toward the workpiece to be blasted. Control over nozzle direction and the blasting stream is thus readily achieved. There is no need for a supply of compressed air and instead, a radially available electrical power source may be employed. Finally, portability is enhanced in the provision of the pouch 68 which can be carried on the body of the operator and readily moved about as the blasting device is manipulated to difficult and otherwise inaccessible areas.