Spray Apparatus And Method

Abstract

Powder color change is accomplished easily and conveniently by providing a spray device having a channel or groove in its side and traversing its length in combination with one of a plurality of elongated, flexible powder feed tubes. The channel is formed from rigid material. One end of each of the feed tubes is connected to its cooperatively associated powder pump immersed in a powder reservoir. Each feed tube is adapted to be snapped into or out of the channel or groove of the spray device. The feed tube is retained in the channel in such a manner as to prevent harmful movement thereof with respect to the channel and other components of the device during the spraying operation. However, the feed tube is retained in the channel in such a manner as to permit the user to remove the tube from the channel without employing undue force or special tools. The feed tube selected to be snap fitted into the channel of the spray device dictates the color of the powder to be sprayed upon activation of the spray device. The system employing the spray device includes control means for switching from one powder reservoir to another powder reservoir upon removal of one feed tube from the spray device and insertion of another feed tube into the spray device.

Description

The present invention relates to a spray device including means for and method of quickly and conveniently switching the device from ejecting or spraying coating material particles of one color, such as white, to ejecting or spraying coating material particles of another color, such as black, without experiencing harmful contamination of the presently ejected coating material by coating material previously ejected or sprayed from the spray device. Preferably, the coating material is ejected from a spray device employing electrostatic forces; the electrostatic forces assist in depositing particles of coating material on a surface to be coated, the surface being maintained at a coating material attracting potential.

In several of the presently available powder devices, if the user of the spray device desires to switch or change from spraying coating material such as powder of one color to spraying powder of another color, the spray device is disconnected from a powder pump immersed in powder and the passageway of the feed tube from the pump to the spray device and the spray device are purged of residue powder using compressed air, roughage, solvent flush and the like to prevent contamination of a subsequently sprayed powder with a previously sprayed powder. Then the purged spray device is connected to another pump immersed in a reservoir containing powder of the desired color and powder of the newly selected color is sprayed from the spray device. Plastic powder conveyed through a plastic feed tube tends to experience frictional charging during conveyence, due to, it is believed, random collisions with the side wall of the plastic feed tube. Charging of such plastic particles causes particles to cling to the side wall of the feed tube making it difficult to properly clean the tube using, for example, compressed air. It should be appreciated that the steps of disconnecting, purging and connecting the spray device to yet another powder reservoir is a time consuming and expensive method of switching from spraying powder of one color to spraying powder of another color.

Another suggested solution to the color change problem is to use a different spray device for each colored powder to be dispensed. It should be appreciated that such a solution is costly to the user, and requires unusual amounts of space for equipment.

It is, therefore, a desideratum to provide means for and method of easily and conveniently switching from spraying powder of one color to spraying powder of another color without purging the entire body of the spray device and its cooperatively associated powder tube and without experiencing harmful contamination of subsequently sprayed powder with powder previously sprayed from the spray device.

The invention facilitates color change by providing a spray device having a channel or groove in its side and traversing its length in combination with one of a plurality of elongated, flexible feed tubes. The channel is made from a rigid material. One end of each of the feed tubes is connected to its cooperatively associated powder pump immersed in a powder reservoir. Each feed tube is adapted to be snapped into and out of the channel or groove of the spray device. The feed tube is retained in the channel in such a manner as to prevent harmful movement thereof with respect to the channel and other components of the gun during the spraying operation. However, the feed tube is retained in such a manner as to permit the user to remove the feed tube from the channel without employing undue force or special tools. The feed tube selected by the user to be snap fitted into the channel of the spray device dictates the color of the powder to be sprayed upon activation of the spray device.

In the embodiment illustrated in the drawing, the spray device employs swirling gas (air) to assist in effecting a substantially uniform distribution of the powder particles in the spray pattern ejected or sprayed from the device and to assist in providing the powder with sufficient momentum to be propelled to the vicinity of the article to be coated. When employing swirl air, the spray device includes a non-rotating powder distributing means having a sharp edge at which an electrostatic field is concentrated. The field electrically charges the power particles. While in the coating zone, the surface to be coated is maintained at a particle attracting potential. The swirl air can be eliminated by using, at the front end of the spray device, a rotating powder distributing means, a flat-fan type spray nozzle and electrode configuration of the type illustrated in U.S. Pat. No. 3,617,000, and the like.

The appended drawings are intended to illustrate a powder spray device embodying the concepts of the present invention constructed to function in the most advantageous mode presently devised for the practical application of the principles involved in the hereinafter described invention. The powder spray device illustrated in several figures uses electrostatic forces to assist in depositing the powder particles on a surface to be coated. However, it is to be understood that the concepts of the present invention can also be used with non-electrostatic powder spray devices.

In the drawings:

FIG. 1 is a diagrammatic illustration of an electrostatic powder system embodying the concepts of the present invention;

FIG. 2 is a side view of the spray device illustrating an elongated, flexible tube snapped into and retained in position by the spray device;

FIG. 3 is a partial cross sectional view of the front end of the spray device taken across the lines 3--3 of FIG. 2;

FIG. 4 is a rear view of the spray device illustrated in FIG. 1; and

FIG. 5 is a schematic of a control panel for use with the powder spray device illustrated in FIG. 1.

Referring now to FIG. 1 of the drawing, an electrostatic powder spray system is illustrated by the reference numeral 10. The powder spray system 10 includes electrostatic spray device of gun 11, direct current power supply 12 connected to the gun, powder reservoirs 13, and control panel 14.

The structure of spray gun 11, which incorporates the concepts of the invention, is shown in FIG. 2. The spray gun 11 includes barrel 15 and handle 16. Handle 16, including grip portion 17, extends at an angle below barrel 15 to provide the user with means for gripping and manipulating spray gun 11. Barrel 15 is fabricated from a suitable electrically non-conductive material such as nylon, polyethylene and the like. Handle 16 is fabricated from a suitable electrically conductive material such as aluminum, brass and the like.

Channel or groove 18 is formed in and traverses the length of the barrel 15 and handle 16. Bore 19 is formed in and traverses the length of barrel 15 and handle 16. An elongated, flexible feed tube 20 is shown as being snapped fitted into channel 18. Tabs 21 and 22 formed in barrel 15 and handle 16, respectively, cooperate with channel 18 to assist in retaining feed tube 20 therein. The diameter of channel 18 is slightly larger than the outside diameter of tube 20. However, the opening of channel 18 through which feed tube 20 is inserted is slightly less in width than the outside diameter of the feed tube at tabs 21 and 22.

Elongated flexible feed tube 20 defines the passageway for conveying powder particles suspended in gas (air) between powder reservoir 13 and assembly 38 at the forward end of the gun 11. Snap fitting feed tube 20 into channel 18 of the spray gun 11 suitably retains the tube in place with respect to the other components of the spray gun and forms the elongated tube into a gradually curving passageway. The curved passageway of the feed tube is located in that portion of the barrel adjacent the handle. Feed tube 20 is gradually curved in the gun so that abrasive powder articles flowing through the curved portion of the tube have less of an erosion effect on the curve of the passageway than such particles would have if the passageway was abruptly curved. This problem is largely avoided where a feed tube does not curve into the grip portion of the handle but extends rearwardly from the barrel along a straight line and passes out the rear of the gun over the hand of the user. Attaching the feed tube in such a manner is unsatisfactory since the tube imposes a torque-like force on the spray gun which would fatigue the user and restrict the manipulability of the gun. As shown in FIG. 1, a feed tube 20 projects downwardly from the base of handle 16 where it imposes little restriction on the manipulability of the gun.

In the event of failure of feed tube 20 because of erosion of its walls by powder particles or otherwise, the tube can be snapped out of channel 18 and either the failure site removed by severing the tube behind such site and the tube reinserted into channel 18 or another tube can be substituted therefor.

Assembly 38, mounted at the forward end of gun 11, includes bore 42 axially aligned with the forward end 20a of feed tube 20. As shown in FIG. 3, the forward end 20a of feed tube 20 projects into and is retained in place by bore 42 by assembly 38. Powder suspended in air is conveyed through feed tube 20 into assembly 38 of spray device 11. Delivery of the powder particles to spray gun 11 is controlled by the user displacing trigger 43 pivotally carried by gun 11. Depressing trigger 43 actuates switch 28 which activates a solenoid valve (not shown) in power supply 12 causing powder to be withdrawn from powder reservoir 13 by venturi pump 36 and delivered through feed tube 20 to assembly 38. Powder supplied to assembly 38 is formed into a pattern suitable for application to the article to be coated.

Displacing trigger 43 also electrically connects the output terminal of the high voltage power supply 12 to edge 37 of assembly 38 through high voltage cable 23, resistor 24, conductive plug 65 and conductive coating 52 carried by non-rotating cylindrical means 49 of assembly 38. Powder ejected from the assembly 38 is electrically charged by the electrostatic field at edge 37 of assembly 38. Edge 37 is sharp so that the electrical field gradient at the edge is sufficiently high to provide the powder with a high charge-to-mass ratio.

Assembly 38, shown in FIG. 3, includes head 45, outlet passageway 46 terminating in orifice 47, deflector 48 and non-rotating powder distributing means 49. Head 45, deflector 48 and non-rotating means 49 are fabricated from any suitable erosion resistant, dielectric material such as nylon and the like in order to minimize wear sites and electrical charging thereof during operation of the spray gun 11. Preferably, passageway 46 of head 45 has side walls as smooth as are possible in order to minimize sites at which the entrained powder can accumulate.

Powder baffle or deflector 48 is carried by rod 53. Rod 53 is integral with spider-like means 54. The spider-like means 54 includes a plurality of lengthwise apertures through which powder flows from feed tube 20 toward baffle 48. Powder deflector 48 and orifice 47 cooperate so as to provide annular opening 55 through which powder flows. The extent of opening 55 may be varied by moving deflector 48 along rod 53. After selecting the desired location of deflector 48 along the length of rod 53, the deflector is fixed in position by any suitable means such as by frictional engagement of the deflector with the rod. The configuration of the periphery of deflector 48 may be round, ellipsoidal, or the like so as to assist in providing a substantially uniform distribution of powder particles in annular opening 55. The radial extent of deflector 48 should be greater than the radial extent of orifice 47. Orifice 47 is the powder outlet orifice. The forward velocity of the particles of powder ejected from orifice 47 is decreased when the particles strike the rear surface 56 of deflector 48. The powder is deflected about 90.degree. in all directions. Preferably, the axes of orifice 47 and deflector 48 are coincident.

Powder particles are deflected toward interior surface 57 of cylindrical means 49 at a reduced velocity after striking the rear surface 56 of the deflector 48. Jets of air are introduced along surface 57 substantially tangentially to the direction of the flow of powder particles ejected from orifice 47. The jets of air are introduced through a plurality of apertures illustrated, in part, by apertures 58, 59, and 60 formed in the side walls of head 45 to thereby assist in then effecting a substantially uniform distribution of the powder over surface 57 of cylindrical means 49. As many apertures as are necessary to achieve the desired results may be formed in head 45. The jets of air intercept and swirl the powder over surface 57 in a substantially whirling, cyclone-type fashion. The powder moves in a substantially helical fashion outwardly from the surface 57.

The swirl air flowing from apertures 58, 59, and 60 assists in providing the powder particles with the momentum necessary to carry the powder to the article to be coated. Further, the use of swirl air tends to minimize build-up powder particles on surface 57 during the spraying operation. If powder particles build up on surface 57, agglomerations of particles are formed and deposited on the articles. Such agglomerations form a roughness in the coating that are visible after curing. Agglomerations of particles may also result in a multicolor coating.

Air is introduced to the apertures 58, 59, and 60 through bore 66 and air valve 67. Air valve 67 includes a finger actuated head 68, valve stem 69, an annular valve seat 70, and a nut 71 threadably retained on the stem. The user of the gun can regulate the flow of swirl air to assembly 38 by appropriately adjusting nut 71. The user may terminate the flow of swirl air by depressing stem 69.

Assembly 38 can be another configuration when a different spray pattern is desired. For example, a flat-fan spray nozzle including pin-like electrode can be substituted for non-rotating assembly 38. A suitable flat-fan spray nozzle and pin-like electrode combination for powder spraying is shown in U.S. Pat. No. 3,617,000.

Gun 11 includes bore 19 in the handle 16 and curved in barrel 15 to form tubular passageway for electrical circuit means located within the gun. Bore 19 is formed of non-conductive material, has a sufficient wall thickness to withstand high direct current voltages, such as 40,000 up to 100,000 volts, which are applied to the gun. Bore 10 retains one end of high voltage cable 23 and resistor 24 having one end connected to cable 23. Resistor 24 is closely adjacent the forward end of the gun. Resistor 24 is a multi-megohm resistor having a typical valve of about 160 megohms. It is desirable to minimize the quantity of metallic conductive material associated with assembly 38 so as to minimize the effective electrical capacity of the powder spray device. The advantages of minimizing the effective capacity are disclosed in U.S. Pat. No. 3,048,498. The safety features disclosed in that patent are desirably incorporated in the spray gun 11.

The rear face 50 and outer surface 51 of means 49 are provided with a substantially continuous conductive coating 52 having a high resistivity. A suitable material for coating 52 is described in U.S. Pat. No. 3,021,077. Conductive plug 65 and coating 52 connect resistor 24 to edge 37 of assembly 38. Assembly 38 also includes electrically insulative washer 25.

Powder spray gun 11, as illustrated in FIG. 1, ejects electrically charged particles of powder toward articles 30 moved or displaced in the direction of arrow 31 by conveyor 32. For the purpose of illustration, but not for the purpose of limitation, articles 30 are panels. While being coated with charged particles of powder, the articles 30 are maintained at a powder particle attracting potential, such as ground potential, by electrical connection to earth or ground 33 through electrically conductive hangers 34 of conveyor 32. Electrically charged particles of powder are propelled to the vicinity of articles 30 in coating zone 35 and are guided to the surface of the articles 30 by electrostatic forces present in the coating zone. Coating zone 35 is the zone in which the powdered particles are deposited on the article(s) being coated.

High voltage direct current power supply 12, capable of supplying a no-load voltage of from about 40,000 up to 100,000 volts or more, is connected in series with the spray gun 11 through electrical cable 23. The polarity of direct current voltage as supplied to gun 11 may be either negative or positive, depending upon, among other things, the type of powder sprayed. Some powder particles are more advantageously charged by a negative voltage than by a positive voltage and vice versa.

The powder reservoirs 13, as shown in FIG. 1, each contain a powder of a different color or type. The reservoirs 13 may number as few as two or as many as ten or more. Each reservoir includes means (not shown) for fluidizing the powder by passing flowing gas such as air through a foraminous sheet (not shown) located near the bottom of each reservoir. Gas flows through the foraminous sheet and is directed upwardly through the powder causing the powder to expand in volume and become "fluidized." Powder of a suitable color or type is withdrawn from reservoir 13 by means of a venturi pump 36 immersed in the powder and delivered to gun 11 through an elongated flexible tube 20. Each reservoir includes a venturi pump 36.

Referring now to FIG. 5, one means of several possible means is shown to select and control the flow of powder in the feed tube connected to the spray gun. One side of manually operated 3-way air valve 71, located in control panel 14, is connected to a compressed air source (not shown) via hose 72. The other side of valve 71 is connected to air manifold 73 through hose 72a. When valve 71 is manually operated to an "on" position (depressed), compressed air flows from valve 71 through manifold 73 through hose 72b to spring biased pressure regulator 74. The pressure of the compressed air exiting regulator 74 is regulated by that regulator. The output of regulator 74 is connected to pressure gauge 75 through hose 72c. Gauge 75 is used to display the air pressure of the air delivered to the nozzle of the venturi pump. Compressed air also flows from the output of regulator 74 through hose 72d to air piloted, spring return 3-way valve 76. Activating valve 76 "on" causes compressed air to flow from the regulator 74 through valve 76 and hose 72e to a group 77 of selector valves. Each of the selector valves of group 77 is an air piloted spring return, 3-way valve. Air flowing through the activated valve of group 77 flows to a venturi pump.

Compressed air flowing through valve 76 also supplies air through hose 72f for piloting reversing relay valve 78.

Compressed air from the compressed air source flow from air manifold 73 through hose 72g to power supply 12 where such air flow is biased either "on" or "off" by an electrical solenoid (not shown) internal of power supply 12. The electrical solenoid is biased "on" by depressing trigger 43 causing activation of switch 28 which in turn causes the solenoid to be biased "on" and hence allowing compressed air to flow therethrough. Returning trigger 43 to its normal position biases switch 28 "off" as well as biasing "off" the solenoid (not shown) connected thereto. Biasing the solenoid in the power supply "on," allows compressed air to pass therethrough and return to control panel 14 through hose 72h. Hose 72h is connected to double air piloted 3-way valve 80. Biasing the solenoid of the power supply to "off" causes air to be exhausted to the atmosphere through valve 80. However, biasing the solenoid "on" causes air from the compressed air source to flow through valve 80 and hose 72i to selector valve group 81 composed of air piloted, spring return 3-way valves. Group 81 of 3-way valves is used to activate the pump valve cylinder associated with each of the venturi pumps.

Air flowing from valve 80 through hose 72j is used to pilot air piloted, spring return 3-way valve 76. Air also flows from valve 80 through hose 72k and restrictor valve 89 to the pilot of air piloted spring return 3-way valve 82. Valve 89 allows air to free flow in one direction and by appropriate adjustment of valve 89 restricts the air flow in the reverse direction. Piloting 3-way valve 82 causes that valve to open. Opening valve 82 causes compressed air from manifold 73 to flow through hose 72L and 72m to reversing relay valve 78. Valve 78 is a reversing relay which provides an output pressure that is the difference between a manually set, spring loaded pressure and a variable pneumatic signal. Reversing relay valve 78 controls the flow of air through it dependent upon the air pressure supplied to its pilot by 3-way valve 76 through hose 72f. As the pressure of the pilot air supplied to reversing relay valve 78 increases, the relay valve is activated so as to decrease the air flow allowed to pass through valve 78 from line 72m. Compressed air flowing through reversing relay valve 78 and hose 72n is supplied to selector group 82 consisting of air piloted spring return 3-way valves. Air flowing through the activated valve of group 84 flows to the air injector of a venturi pump.

Compressed air from manifold 73 flows through hose 72o to selector group 85 consisting of air piloted spring return 3-way valves. Air flowing through the activated valve of the group 85 flows to the fluidizing chamber of the powder reservoir. There is one selector valve in each group 77, 81, 84 and 85 for each reservoir. Two selector valves are shown in each group since, for clarity, two powder reservoirs have been shown in the drawing. If ten powder reservoirs are incorporated into the system, then ten selector valves are included within each of the groups of selector valves.

As shown in FIG. 5 there are four air lines 72p, 72q, 72r, and 72s connected to each reservoir. The flow of air in these four lines is controlled by the four groups of valves 77, 81, 84 and 85; one group of valves for each line and each group contains one valve for each powder reservoir. The valves of groups 77, 81 and 84 are supplied air from the compressed air source when the solenoid in the power supply is activated "on" by switch 28. The valves of group 85, which control the flow of air to the fluidizing section of the reservoirs, received air from the compressed air source through manifold 73 when valve 71 is activated.

When using the circuit of FIG. 5, the selection of powder to be sprayed from gun 11 is accomplished by manually activating either spring return 4-way valve 87 or 87a each cooperatively associated with one valve in each of the selector valve groups 77, 81, 84 and 85. The number of 4-way spring return valves 87 and 87a is dictated by the number of different powders to be sprayed from gun 11. For convenience only two valves 87 and 87a are shown in FIG. 5. Valve 87 is connected to manifold 73 through hose 72t; valve 87a is serially connected to 4-way valve 87 through hose 72v. All other 4-way valves likewise are serially connected to valve 87. It is seen that each 4-way valve obtains its supply air from the preceding serially connected 4-way valve. The 4-way valve 87 includes a suitable activating device 88 designed to hold a feed tube 20. The feed tube 20 is connected to the outlet of a venturi pump. When the tube is retained by device 88, the 4-way valve 87 or 87a associated therewith is biased "off." When the tube is removed from activating device 88 and inserted into channel 18 of the gun 11, 4-way valve 87 or 87a cooperatively associated therewith is activated, thereby activating one valve in each of the four groups 77, 81, 84 and 85 cooperatively associated therewith. The selected powder is withdrawn from the reservoir and supplied to gun 11. The powder feed begins when trigger 26 is depressed. It should be understood other means for selecting the powder to be sprayed from gun 11 can be substituted for the means illustrated in FIG. 5.

Swirl air for assembly 38 is supplied from manifold 13 through hose 72u to gun 11.

In operation, the user depresses trigger 43. As the trigger is depressed, portion 27 of the trigger actuates switch 28 contained within the gun 11. Conductors (not shown) from electrical switch 28 run through the grip portion of the handle and are connected to the solenoid valve (not shown) internal of the power supply 12 in such a manner as to turn "on" the voltage supply and withdraw powder from the desired power reservoir. Air flowing through venturi pump 36 thus entrains the solid particles of coating material and directs the entrained powder into feed tube 20. Since the entire passageway of the feed tube 20 from the venturi pump 36 into the assembly 38 has a uniform cross-section and curves gradually in the barrel, the coating material particles flow to assembly 38 in a substantially stable suspension. The operator may easily change the color of the powder being ejected by removing one feed tube and inserting another feed tube by snapping it into channel 18.

"Powder," as that term is used herein, means and includes thermoplastic dry powders such as polyester, polyvinyl chloride, polypropylene, polyethylene, nylon, cellulose acetate butyrate; thermosetting resins such as epoxies, polyesters, acrylics; other powder such as starch, talc, vitreous enamel; and the like. Preferably, the individual powder particles are receptive to acquiring and retaining an electric charge for a predetermined length of time or are capable of being suitably treated so as to accept and retain an electric charge for a predetermined length of time. The powder particle shape and size should be such as to permit proper distribution on the surface to be coated so that the fused coating is of good structural strength and appearance. The melt viscosity and surface tension of the particles of powder should be such as to provide a film that adheres to the surface to protect and decorate that surface.

Generally, powders suitable for spraying are prepared by grinding bulk material, usually at a low temperature. Powder having a particle size in the order of about 20 to about 250 microns is preferred for electrostatic powder spraying, however, the powder may be coarser or finer, depending on the particular material and application thereof.

While we have shown and described the preferred embodiment of our invention, it is to be understood that it is capable of many modifications. Changes, therefore, in the construction and arrangement may be made without departing from the spirit and scope of the invention as disclosed in the following claims.

Claims

We claim:

1. A powder spray device for easily and conveniently accomplishing switching from spraying one type of coating material to spraying coating material of another type without harmfully contaminating the subsequently sprayed coating material with previously sprayed coating material, the spray device including means forming a barrel, and a handle and carrying a spray forming nozzle, a channel provided in the side of the barrel traversing the length of the barrel and communicating with the spray-forming nozzle, and an elongated feed tube adapted to have one end connected to a powder reservoir and to fit in the channel, the means being shaped to retain the feed tube in the channel and in sealed engagement with the spray-forming nozzle so as to deliver powder to the nozzle and to prevent harmful movement thereof during the spraying operation.

2. The spray device of claim 1, wherein the channel is curved within the barrel and handle of the spray device.

3. The spray device of claim 2, wherein the forward end of the feed tube is retained at the forward end of the spray device by the spray-forming nozzle and at the handle by means of the elongated feed tube adapted to cooperate with the handle.

4. The spray device of claim 1 in combination with means for selecting one coating material reservoir from several coating reservoirs from which coating material is withdrawn and supplied to the feed tube.

5. The combination of claim 4, wherein the means for selecting the coating material includes a plurality of feed tubes, a different feed tube cooperatively associated with each reservoir and means for retaining unused feed tubes to deactivate the coating material reservoirs cooperatively associated with the unused feed tubes, removing the feed tube from the retaining means activating the coating material reservoir cooperatively associated therewith so that coating material can be withdrawn from that reservoir and delivered to the gun.

6. A powder spray gun for easily and conveniently accomplishing switching from spraying powder of one color to spraying powder of another color without harmfully contaminating the subsequently sprayed powder with previously spray powder, the spray gun comprising a barrel and a handle projecting at an angle from the barrel, a channel provided in the side of the barrel and handle and traversing the length of each, a spray-forming nozzle carried at the front of the barrel and an elongated feed tube adapted to have one end connected to a powder reservoir, the feed tube capable of being inserted into the channel and retained in the channel at the front of the gun by the spraying nozzle and at the rear of the gun by means on the tube cooperating with the handle so as to prevent harmful movement thereof, the elongated tube being in communication with the spray-forming nozzle when retained in the channel.

7. The spray gun of claim 8, wherein the gun includes tab means in the barrel and the handle for retaining the tube in the channel.

8. The spray device of claim 6, in combination with means for selecting one powder from several powders and for supplying the selected powder to the feed tube in the channel of the spray gun.

9. The combination of claim 8, wherein the means for selecting the powder includes at least two feed tubes and two powder reservoirs, and means for retaining the unused feed tube to deactivate the reservoir connected to the unused feed tube, removing a feed tube from the retaining means activating the reservoir connected thereto so that powder can be withdrawn from that reservoir and delivered to the gun.

10. In a method for easily and conveniently accomplishing switching from spraying powder of one type to powder of another type without harmfully contaminating the subsequently sprayed powder with previously sprayed powder, the steps including providing a spray device having a barrel, carrying spray-forming nozzle, and including a channel traversing the length of the barrel and communicating with a spray-forming nozzle, inserting and removing feed tubes having one end connected to powder reservoirs into the channel and in sealed communication with the spray-forming nozzle with a snap-like action, and spraying coating material withdrawn from the reservoir from the spray-forming nozzle of the device.