Abstract:
A mixing apparatus for use in conjunction with powder spray paint booths whereby reclaimed powder overspray is automatically mixed with virgin powder in the proper proportions and supplied to the spray gun. Provision is made for quick disconnect and easy change of color of powder.

Description:
PRIOR ART STATEMENT 
     Applicant is not aware of any devices for automatically mixing reclaimed powder with virgin powder in the proper proportions to permit the reclaimed powder to be used and produce a satisfactory, non-grainy coat of paint. To applicant&#39;s knowledge all such mixing is currently performed externally of the source of powder supplied to a spray gun and then poured into the container which supplies the powder to the gun. No novelty search has been conducted. 
     SUMMARY OF THE INVENTION 
     Collection of the oversprayed powder from powder spray paint booths in a common practice. When the collected powder is reused the resulting coat of paint will be grainy. A satisfactory coat of paint may be produced by first mixing the reclaimed powder with virgin powder. The invention comprises an apparatus for automatically mixing the reclaimed powder with the virgin powder and supplying that mixed powder to the paint spray gun. A first chamber is provided for filtering and holding the reclaimed powder in a fluidized state. A second chamber is providing for filtering and holding the virgin powder in a fluidized state. The first and second chambers each communicate with a third chamber through respective variably, controlled apertures. By controlling the size of the variably controlled apertures, the proportion of reclaimed to virgin powder mixed within the third chamber is controlled. The powder mixture in the third chamber is supplied to the powder spray gun. 
     A roll-away reservoir cart is also provided. The cart has two separate chambers, one of which communicates with the above described first chamber of reclaimed powder and the other of which communicates with the above described second chamber of virgin powder. Appropriate valving is provided to permit the contents of the first chamber to be flushed into the one chamber of the cart and to permit the contents of the second chamber to be flushed into the other chamber of the cart. The flushing and use of a roll-away reservoir cart permit easy cleaning of the device and rapid changing of color of the powder paint without contamination of the new color of powder. 
    
    
     DESCRIPTION OF THE FIGURES 
     FIG. 1 is an external front plan view of the mixing device. 
     FIG. 2 is a side plan view of the mixing device. 
     FIG. 3 is a cross-section of the mixing device. 
    
    
     DETAILED DESCRIPTION 
     A common process used to spray paint a wide variety of objects is to spray the objects with a dry powdered paint. Such a process produces a substantial amount of oversprayed powder. It is ecologically and economically desirable to reclaim this oversprayed powder and recycle it for painting other items. In this prior art, if an object is spray painted with 100% of such reclaimed powder, the resulting coat of paint is unacceptably grainy. The grainy quality may be reduced and/or eliminated by mixing the reclaimed powder with a quantity of virgin powder. An acceptable coat of paint is achieved by mixing 1 part reclaimed powder to 2 parts virgin powder. Such mixing may be done at a location remote from the paint spray booth then poured into the powder supply of the spray gun. Utilizing the present invention, this mixing may be accomplished automatically and at a location conveniently near the spray booth. 
     A mixing unit 10 may be suitably affixed for communication with an exhaust hood 12 and an exhaust duct 14 as shown in FIG. 1. Hose 16 which is connected to one side of the mixing unit 10 conveys reclaimed powder to the interior of the mixing unit and a hose 18 which is connected to the side of the mixing unit opposite to hose 16 conveys virgin powder to the interior of the mixing unit 10. Within mixing unit 10, the desired proportions of reclaimed powder and virgin powder are mixed and supplied via a hose 20 to a spray gun 22. 
     Mixing unit 10 communicates with a powder reservoir 24 which, as shown in FIG. 1, is conveniently mounted upon wheels 25. The reservoir 24 can thus be conveniently rolled in and out of the area under the mixing unit 10. Further, because the reservoir 24 is mounted on wheels 25, powder color changes may be easily and quickly effected as explained more fully below. 
     If the level of reclaimed powder within mixing unit 10 rises too high, the excess powder will flow through over flow pipe 26 into the reservoir 24. Likewise, if the level of virgin powder within mixing unit 10 rises too high, the excess powder will flow through overflow pipe 27 into reservoir 24. To effect rapid color changing, the contents of the mixing unit 10 can be rapidly dumped into the reservoir 24 by means of dump lines 28 and 29. The powder within mixing unit 10 is kept in a fluidized state to facilitate flow and mixing, by a fluidizing device which supplies pressurized air through line 30. During normal operation, dump valves 34 and 35 are closed to retain the powder within the mixing unit 10. To change the color of the powder, dump valves 34 and 35 are opened and three way valves 32 and 33 are vented to the atmosphere to urge the fluidized powders to flow through the dump lines 28 and 29 into the reservoir 24. 
     The operation of the invention will be discussed in relation to the detailed cross sectional view of FIG. 3. Inlet hose 16 communicates with a supply of reclaimed powder from a powder paint spray booth. This supply of reclaimed powder is maintained in a fluidized state to facilitate its flow. Inlet hose 18 communicates with a supply of virgin powder which is also maintained in a fluidized state. These powders are drawn into the mixing unit 10 by the low pressure within the mixing unit 10 which is induced as a result of the low pressure in the exhaust duct 14. The low pressure in the exhaust duct 14 can be provided by a typical exhaust fan or other suitable exhaust device. The low pressure in the hood 12 which may include filter units 13 draws the reclaimed powder through inlet hose 16 and virgin powder through inlet hose 18. 
     The mixing unit 10 is further divided into three chambers. The first chamber, or reclaimed powder chamber 40, is divided into two sections 40a and 40b which are separated by a filter 42. The reclaimed powder travels along hose 16 and enters chamber 40 through an aperture 44 located in section 40a on the first side of filter 42. The reclaimed powder falls to the bottom of section 40a where it is maintained in a fluidized state by a fluidizing means 31. The low pressure in the exhaust duct 14 causes the pressure in section 40b to be lower than the pressure in section 40a. As a result fluidized reclaimed powder is drawn through the filter 42, which removes the large impurities in the powder into section 40b. The fluidized reclaimed powder to seeks the same level in sections 40a and 40b. 
     The second chamber, or virgin powder chamber 46, is similarly divided into two sections 46a and 46b which are separated by a filter 48. The virgin powder travels along hose 18 and enters chamber 46 through an aperture 50 located in section 46a on the first side of filter 48. The virgin powder falls to the bottom of section 46a where it is maintained in a fluidized state by the fluidizing means 31. The low pressure in the exhaust duct 14 causes the pressure in section 46b to be lower than the pressure in section 46a. As a result, the fluidized virgin powder is drawn through the filter 48, which removes impurities, and into section 46b. The fluidized virgin powder will seek the same level in sections 46a and 46b. 
     The third chamber, mixing chamber 52, communicates with section 40b of the first chamber 40 through an aperture 54 and with section 46b of the second chamber 46 through an aperture 56. The size of apertures 54 and 56 are manually adjustable by moving slide gates 58 and 60 back and forth. By adjusting the gates 58 and 60, the ratio of the flow rate of reclaimed powder into mixing chamber 52 to the flow rate of virgin powder into chamber 52 is controlled. As the virgin and reclaimed powder enter mixing chamber 52 they fall to the bottom of chamber 52 where they are maintained in a mixed and fluidized state by the fluidizing means 31. Chamber 52 communicates through the aperture 62 with hose 20 whereby the mixture of reclaimed and virgin powder is supplied to spray gun 22. 
     If the spray gun 22 has not been used for some period of time, or has been operated at low flow rates, the level of fluidized mixed powder in mixing chamber 52 will rise. The level of mixed powder should not be allowed to rise to the level of the apertures 54 or 56 to prevent reverse flow through those apertures. In order to prevent this reverse flow, a sensor 64 is positioned on one of the walls of chamber 52, slightly below apertures 54 and 56. When the level of mixed powder reaches the level of the sensor 64, a control signal closes apertures 54 and 56. The spray gun 22 will resume spraying when it has drawn enough mixed powder out of chamber 52, so that the level of powder will be below the level of sensor 64, and the sensor 64 will cause the apertures 54 and 56 to reopen. 
     During the time that apertures 54 and 56 are closed, or at any time that the powder flowing into reclaimed powder chamber 40 or virgin powder chamber 46, rises to the level of apertures 54 and 56 such that they close, the powders will pass out of chambers 40 and 46 through apertures 66 and 68 respectively into overflow pipes 26 and 27. Assuming that three way valves 32 and 33 are open, the powders will then flow into their respective chambers 70 and 72 in the reservoir cart 24. 
     The reservoir cart 24 comprises a first reservoir 70 which contains the reclaimed powder and a second reservoir 72 which contains the virgin powder. Reservoirs 70 and 72 are attached to the dump lines 28 and 29, respectively, through apertures 78 and 80 provided in the top of reservoir cart 24. Powder from the mixing unit flows through these apertures 78 and 80 into reservoirs 70 and 72 respectively, when the color of the powdered paint is changed to another color. 
     When the color of paint is changed the reservoir cart 24 must be replaced with a new reservoir cart 24 having a supply of reclaimed powder of the new color in reservoir 70 and a supply of virgin powder of the same new color in reservoir 72. 
     Any further flow of the virgin powder through hose 18 is stopped by closing a valve (not shown) in hose 18. Also, the apertures 54 and 56 are closed to prevent further entry of the powder into chamber 52. Chamber 52 is emptied by spraying the mixed powder back into the spray booth through spray gun 22 for reclaimation. The reclaimed powder passes through hose 16 into chamber 40a. After chamber 52 has been emptied (which can be observed by an operator through a plexiglass window 82 located on the front of mixing unit 10) and the flow of reclaimed powder into chamber 40a has essentially stopped, the exhaust fans in duct 14 are turned off. Three way valves 32 and 33 are vented to the atmosphere utilizing the high pressure air until flowing through line 30 from the fluidizing means to vent chambers 40 and 46 and reservoirs 70 and 72 until the pressure in the mixing unit and reservoirs are at atmospheric pressure. Valves 34 and 35 are then opened. The high pressure air from line 30 pushes the fluidized powders through dump lines 28 and 29 into their respective reservoirs 70 and 72. The dumping of the powders continues until both of the mixing chambers 40 and 46 are empty. At this point all of the powders, are in roll away reservoir cart 24. Another method for voiding the mixing chamber 52 is providing chamber 52 with its own three way valve and dump line communicating with reservoir 70, like those of chamber 40 such that when the three-way valve is open the powders will immediately fall into their respective reservoirs. 
     When chambers 40, 46 and 52 have been emptied into the appropriate reservoir 70 or 72, all lines, pipes and other connections between mixing unit 10 and reservoir cart 24 are disconnected at a quick disconnect means (not shown). Cart 24 is rolled away and a new cart 24 having a supply of the new reclaimed powder in reservoir 70 and a supply of the new virgin powder in reservoir 72 is rolled under mixing unit 10. All pipes lines and hoses between the reservoir cart and the mixing unit are appropriately connected. Inlet hose 18 is connected to the new source of virgin powder, and the valve (not shown) in line 18 is opened. 
     Before the spray gun 22 can spray the new colored powder, the empty mixing unit 10 is filled with powder in chambers 40, 46 and 52. To fill these chambers, dump valves 34 and 35 are closed and overflow valves 32 and 33 open to cause the top of reservoirs 70 and 72 to achieve atmospheric pressure. Apertures 54 and 56 are then reset to their open position. The fans in exhaust duct 14 are turned on which produces a low pressure within chambers 40, 46 and 52. The pressure differential between chamber 40 and reservoir 70 causes the new reclaimed powder to flow out of reservoir 70 through charging tube 84 into chamber 40 where it is fluidized. Similarly, the pressure differential between in chamber 46 reservoir 72 causes the virgin powder of the new color out of reservoir 72 through charging tube 86 into chamber 46 where it is fluidized. High pressure air injection nozzles 85 and 87 are provided at the bottom of the charging tubes to direct the high pressure air and powder up the tubes. The powders rise in chambers 40 and 46 to the level of the now open apertures 54 and 56 and powder flows into chamber 52 automatically in the proper proportions. As the powders in chamber 52 are fluidized, the level of mixed powder will rise. When the levels of powder in chambers 40, 46 and 52 have risen to an acceptable working level, (which may be determined by viewing through plexiglass window 82) the three way valves 32 and 33 are opened to reset the overflow pipes 26 and 27 for proper functioning. The injection nozzles 85 and 87 are turned off and powder ceases to travel up charging tubes 84 and 86. The apparatus is now ready to begin spray painting with a new color of powder. 
     On occasion, it may be desirable to give chambers 40 and 46, especially the bottoms of the chambers, a thorough cleansing. To facilitate such cleansing access ports, 88 and 90 respectively, are provided near the bottom of the chambers. 
     When spray painting with a mixture of reclaimed and virgin powder, the critical limitation is selecting the correct concentration of reclaimed powder in the mixture. In the preferred embodiment, the reclaimed powder is about 331/3% of the total mixture. When the powder contained in the mixing chamber 52 is voided into the reservoir 70 of reclaimed powder there will be some virgin powder emptied into the reclaimed reservoir powder. This effectively reduces the concentration of reclaimed powder in reservoir 70 and is not critical. Such contamination only improves the quality of the resulting coat of paint. 
     While the invention has been described above with reference to FIGS. 1 through 3, those figures and the description are for purposes of illustration only and should not be interpreted as limiting the invention disclosed herein. It should be appreciated that various changes in structure and material, and modifications of function can be readily implemented by one of ordinary skill in the art without departing from the spirit and scope of the present invention as defined in the appended claims.