Electrostatic compressed air paint spray gun

• US 5,188,290 A
• Filed: 02/12/1991
• Issued: 02/23/1993
• Est. Priority Date: 02/16/1990
• Status: Expired due to Fees

• Current Assignee: J. Wagner GmbH
• Original Assignee: J. Wagner GmbH
• Inventors: Gruber, Johann, Gebauer, Gerhard
• Primary Examiner(s): Kashnikow, Andres
• Assistant Examiner(s): YOUNG, KAREN MERRITT
• Application Number:
  US07/654,342
• Time in Patent Office: 742 Days
• Field of Search: 239/3, 239/690, 239/696, 239/704, 239/706, 239/707, 239/708, 239/132-132.5
• US Class Current: 239/3
• CPC Class Codes: B05B 5/03 characterised by the use of gas , e.g. electrostatically assisted pneumatic spraying B05B5/04, B05B5/043, B05B5/047 take precedence

Abstract

In an electrostatic compressed air paint spray gun, the overall exit area of the compressed air discharge opening as well as the pressure and the quantity of the supplied compressed air are dimensioned such and matched such to one another that, first, the ratio (V_L) of the air pressure (P₁) prevailing immediately upstream of the compressed air discharge opening to the air pressure (P₂) prevailing downstream of the compressed air discharge opening is less than 2:1 and, second, quantity and flow rate of the compressed air emerging from the compressed air discharge opening and magnitude of the applied high-voltage guarantee an adequate atomization of the paint as well as a conveying of the atomized paint particles to the workpiece with a given paint throughput and given paint viscosity. A high precipitation efficiency and a good paint compass are thus achieved.

Claims

1. In an electrostatic compressed air paint spray gun having a spray head which receives paint and compressed air, said spray head having a liquid paint discharge nozzle connected to a paint delivery conduit, a compressed air discharge opening arranged concentrically surrounding the liquid paint discharge nozzle and connected to a compressed air delivery conduit, said compressed air discharge opening capable of discharging a continuous quantity of compressed air adjacent to the liquid paint discharge nozzle for atomizing and transporting said paint during spraying, said spray head also having an electrode arrangement connected to a high voltage supply, and arranged adjacent to the liquid paint discharge opening, the improvement comprising the overall discharge area of the compressed air discharge opening being dimensioned to pass said continuous quantity of compressed air from the compressed air delivery conduit to the outside atmosphere wherein the ratio of the absolute air pressure prevailing immediately upstream of the compressed air discharge opening to the absolute air pressure prevailing downstream of the compressed air discharge opening is less than 2:

1, and wherein said liquid paint discharge nozzle and said air discharge opening open directly to the atmosphere in front of said spray head.

2. The improvement of claim 1, wherein the ratio of the absolute air pressure prevailing immediately upstream of the compressed air discharge opening to the absolute air pressure prevailing downstream of the compressed air discharge opening is between 1.3:

1 and 2;

1.

3. The improvement of claim 1, wherein the ratio of the absolute air pressure prevailing immediately upstream of the compressed air discharge opening to the absolute air pressure prevailing downstream of the compressed air discharge opening is between 1.8:

1 and 2;

1.

4. The improvement of claim 1, wherein the electrode arrangement comprises a plurality of electrode needles arranged adjacent to the liquid paint discharge opening.

5. In an electrostatic compressed air paint spray gun having a spray head which receives paint and compressed air, said spray head having a paint discharge nozzle connected to a paint delivery conduit, a compressed air discharge opening arranged concentrically surrounding the paint discharge nozzle and connected to a compressed air delivery conduit, said compressed air discharge opening capable of discharging a continuous quantity of compressed air adjacent to the paint discharge nozzle for atomizing and transporting said paint during spraying, said spray head also having an electrode arrangement, connected to a high voltage supply, and arranged adjacent to the paint discharge opening, the improvement comprising the overall discharge area of the compressed air discharge opening being dimensioned to pass said continuous quantity of compressed air from the compressed air delivery conduit to the outside atmosphere wherein the ratio of the absolute air pressure prevailing immediately upstream of the compressed air discharge opening to the absolute air pressure prevailing downstream of the compressed air discharge opening is less than 2:

1; and

wherein the compressed air delivered to the spray gun has a temperature above room temperature, and the spray gun further comprises a cooling means for cooling the compressed air before discharge of the compressed air through the compressed air discharge opening, to a temperature at least as low as room temperature.

6. An electrostatic compressed air material spray gun receiving a supply of liquid material to be sprayed which is capable of providing a desired flow rate of material therefrom, and receiving a supply of compressed air at a first pressure which is capable of providing a select continuous quantity of pressurized air therefrom, comprising:

a liquid material discharge nozzle mounted at a terminal spraying end of said gun and opening directly to the atmosphere in front of said terminal spraying end;

a liquid material delivery conduit, connected for flow to said liquid material discharge nozzle, receiving said flow rate from said supply of liquid material, for delivering liquid material to be sprayed to said liquid material discharge nozzle;

a compressed air delivery conduit receiving said select continuous quantity of pressurized air and having a discharge opening at said terminal spraying end of said gun opening directly to the atmosphere in front of said terminal spraying end, said opening surrounding said liquid material discharge nozzle;

means for delivering said select continuous quantity of pressurized air through said compressed air discharge opening from said compressed air delivery conduit and for controlling the ratio of the absolute air pressure prevailing immediately upstream of the compressed air discharge opening to the absolute air pressure prevailing downstream of the compressed air discharge opening to less than 2;

1, said select continuous quantity of pressurized air sufficient to atomize and transport said desired flow rate of material to be sprayed.

7. An electrostatic compressed air material spray gun according to claim 6, wherein said means for delivering and controlling comprises the compressed air discharge opening being selectively dimensioned to pass the select continuous quantity of pressurized air with a restriction orifice-type pressure drop across said compressed air discharge opening equivalent to the air pressure prevailing immediately upstream of the compressed air discharge opening minus the air pressure prevailing downstream of the compressed air discharge opening;

and

said means for delivering and controlling comprises means for dropping said first pressure of said pressurized air delivered into said compressed air delivery conduit to a pressure equal to the air pressure prevailing immediately upstream of the compressed air discharge opening.

8. An electrostatic compressed air material spray gun according to claim 7, wherein said means for delivering and controlling controls the ratio of the absolute air pressure prevailing immediately upstream of the compressed air discharge opening to the absolute air pressure prevailing downstream of the compressed air discharge opening to between 1.3:

1 and 2;

1.

9. An electrostatic compressed air material spray gun according to claim 8, wherein said means for delivering and controlling controls the ratio of the absolute air pressure prevailing immediately upstream of the compressed air discharge opening to the absolute air pressure prevailing downstream of the compressed air discharge opening to between 1.8:

1 and 2;

1.

10. An electrostatic compressed air material spray gun according to claim 7, wherein said means for dropping comprises at least one valve in flow communication with said compressed air delivery conduit.

11. An electrostatic compressed air material spray gun according to claim 6, wherein said absolute air pressure prevailing immediately upstream of the compressed air discharge opening is substantially equivalent to said first pressure of said supply of compressed air.

12. An electrostatic compressed air material spray gun according to claim 11, wherein said means for delivering and controlling controls the ratio of the absolute air pressure prevailing immediately upstream of the compressed air discharge opening to the absolute air pressure prevailing downstream of the compressed air discharge opening to between 1.3:

1 and 2;

1.

13. An electrostatic compressed air material spray gun according to claim 11, wherein said means for delivering and controlling controls the ratio of the absolute air pressure prevailing immediately upstream of the compressed air discharge opening to the absolute air pressure prevailing downstream of the compressed air discharge opening to between 1.8:

1 and 2;

1.

14. An electrostatic compressed air material spray gun receiving a supply of liquid material to be sprayed which is capable of providing a desired flow rate of material therefrom, and receiving a supply of compressed air at a first pressure which is capable of providing a select continuous quantity of pressurized air therefrom, comprising:

a material discharge nozzle mounted at a spraying end of said gun;

a material delivery conduit, connected for flow to said material discharge nozzle, receiving said flow rate from said supply of liquid material, for delivering material to be sprayed to said material discharge nozzle;

a compressed air delivery conduit receiving said select continuous quantity of pressurized air and having a discharge opening surrounding said material discharge nozzle;

means for delivering said select continuous quantity of pressurized air through said compressed air discharge opening from said compressed air delivery conduit and for controlling the ratio of the absolute air pressure prevailing immediately upstream of the compressed air discharge opening to the absolute air pressure prevailing downstream of the compressed air discharge opening to less than 2;

1, said select continuous quantity of pressurized air sufficient to atomize and transport said desired flow rate of material to be sprayed;

wherein said means for delivering and controlling comprises the compressed air discharge opening being selectively dimensioned to pass the select continuous quantity of pressurized air with a restriction orifice-type pressure drop across said compressed air discharge opening equivalent to the air pressure prevailing immediately upstream of the compressed air discharge opening minus the air pressure prevailing downstream of the compressed air discharge opening;

said means for delivering and controlling comprises means for dropping said first pressure of said pressurized air delivered into said compressed air delivery conduit to a pressure equal to the air pressure prevailing immediately upstream of the compressed air discharge opening; and

wherein the compressed air delivered into said compressed air delivery conduit has a temperature above room temperature, and said spray gun further comprises a cooling means for cooling the compressed air before discharge of the compressed air from the compressed air discharge opening, to a temperature at least as low as room temperature.

15. An electrostatic compressed air material spray gun receiving a supply of liquid material to be sprayed which is capable of providing a desired flow rate of material therefrom, and receiving a supply of compressed air at a first pressure which is capable of providing a select continuous quantity of pressurized air therefrom, comprising:

a material discharge nozzle mounted at a spraying end of said gun;

a material delivery conduit, connected for flow to said material discharge nozzle, receiving said flow rate from said supply of liquid material, for delivering material to be sprayed to said material discharge nozzle;

a compressed air delivery conduit receiving said select continuous quantity of pressurized air and having a discharge opening surrounding said material discharge nozzle;

means for delivering said select continuous quantity of pressurized air through said compressed air discharge opening from said compressed air delivery conduit and for controlling the ratio of the absolute air pressure prevailing immediately upstream of the compressed air discharge opening to the absolute air pressure prevailing downstream of the compressed air discharge opening to less than 2;

1, said select continuous quantity of pressurized air sufficient to atomize and transport said desired flow rate of material to be sprayed;

wherein said absolute air pressure prevailing immediately upstream of the compressed air discharge opening is substantially equivalent to said first pressure of said supply of compressed air; and

wherein the compressed air delivered into said compressed air delivery conduit has a temperature above room temperature, and said spray gun further comprises a cooling means for cooling the compressed air before discharge of the compressed air from the compressed air discharge opening, to a temperature at least as low as room temperature.

16. A method for using an electrostatic compressed air material spray gun having a spray head which receives material and compressed air, said spray head having a liquid material discharge nozzle connected to a liquid material delivery conduit, a compressed air discharge opening arranged concentrically surrounding the liquid material discharge nozzle and connected to a compressed air delivery conduit, said compressed air discharge opening capable of discharging a sufficient continuous quantity of compressed air adjacent to the liquid material discharge nozzle for atomizing and transporting said liquid material during spraying, said spray head also having an electrode arrangement, connected to a high voltage supply, and arranged adjacent to the liquid material discharge opening, the method comprising the steps of:

delivering said liquid material directly to the atmosphere in front of said spray head;

delivering said compressed air directly to the atmosphere in front of said spray head to atomize said liquid material in front of said spray head;

during spraying, maintaining the ratio of the absolute air pressure prevailing immediately upstream of the compressed air discharge opening to the absolute air pressure prevailing downstream of the compressed air discharge opening to less than 2;

1;

maintaining a flow rate of said sufficient continuous quantity of compressed air through said compressed air discharge opening; and

maintaining said electrode arrangement at a sufficient voltage to adequately charge said liquid material to be sprayed.

17. A method according to claim 16 comprising the further step of, during spraying, maintaining the ratio of the absolute air pressure prevailing immediately upstream of the compressed air discharge opening to the absolute air pressure prevailing downstream of the compressed air discharge opening between 1.3:

1 and 2;

1.

18. A method according to claim 16 comprising the further step of, during spraying, maintaining the ratio of the absolute air pressure prevailing immediately upstream of the compressed air discharge opening to the absolute air pressure prevailing downstream of the compressed air discharge opening between 1.8:

1 and 2;

1.

19. A method for using an electrostatic compressed air material spray gun having a spray head which received material and compressed air, said spray head having a material discharge nozzle connected to a material delivery conduit, a compressed air discharge opening arranged concentrically surrounding the material discharge nozzle and connected to a compressed air delivery conduit, said compressed air discharge opening capable of discharging a sufficient continuous quantity of compressed air adjacent to the material discharge nozzle for atomizing and transporting said material during spraying, said spray head also having an electrode arrangement, connected to a high voltage supply, and arranged adjacent to the material discharge opening, the method comprising the steps of:

during spraying, maintaining the ratio of the absolute air pressure prevailing immediately upstream of the compressed air discharge opening to the absolute air pressure prevailing downstream of the compressed air discharge opening to less than 2;

1;

maintaining a flow rate of said sufficient continuous quantity of compressed air through said compressed air discharge opening; and

maintaining said electrode arrangement at a sufficient voltage to adequately charge said material to be sprayed; and

cooling said select continuous quantity of compressed air before said select quantity passes through said compressed air discharge opening.