US3504851A - Electrostatic spray gun - Google Patents

Description

April 7, 1970 .1. DEMETER ELECTROSTATIC SPRAY GUN Filed June 4, 1968 Flig. I

ATTORNEYS United States Patent G 3,504,851 ELECTROSTATiC SPRAY GUN Jenii Demeter, Budapest, Hungary, assignor to Villamos Automatika Intezet, Budapest, Hungary Filed June 4, 1968, Ser. No. 734,452 Claims priority, application l-gungary, June 15, 1967,

Int. Cl.B05b 5/00; B44d 1/08 US. Cl. 239- 3 Claims ABSTRACT OF THE DISCLOSURE A spray gun for the simultaneous atomisation of several different fluid materials having separate channels and passages carrying said fluid and concentrically arranged bells surrounded by a spray head. In the channels grids are arranged and electrically connected to a highvoltage power source to decelerate the flow of the fluid and to produce turbulence in it. In the spray gun there is provided an air space between the internal surface of the spray head and the blades fitted over the outer surface of the outer bell, said air space being connected with an air cushion between the glass sleeve of the outer bell and the outer surface of the outer passage, and said air cushion opening into the inner bell. In said spray head there are bores connected to a compressed air duct. In the mantle of said outer bell air passage openings are located.

The present invention refers to a spray gun which enables the simultaneous atomisation of several different materials and in which the atomisation of the materials begins while passing through air, and terminates on the surface of the objects being coated.

The known apparatus used for the electrostatic deposition of paints have numerous shortcomings, One of these shortcomings is that the ionisation of the material to be sprayed takes place within the spray bell, and on touching the bell an electric shock may occur. Furthermore, when approximating the bell to the subject being coated, a spark may arise and set the material on fire. To avoid such occurrence, low voltages must be applied, which do not cause spark formation. This limitation of the permissible voltage however, means a similar limitation in the materials suitable for electrostatic spraying, because only some of the paints meet the criteria. Further drawback of the known apparatus is that the bells are open behind, with the consequence, that they cannot be used in positions other than horizontal, since the paint introduced into the gun would escape at the open side, in a direction, opposite to the object being coated.

The use of eccentric pipes in the known apparatus for introducing the paint to the spray bell is no advantage either. On the contrary, it is disadvantageous, since it increases the weight and the safety requirements, besides their layout, too, is complicated.

The spray gun developed for the purpose and Which is the subject of present invention has separate channels carrying different fluid materials opening into concentrically arranged bells surrounded by a spray head, each bell having an inner space to store said fluid, a filmproducing surface on its inner surface and an atomising edge for the atomisation of said fluid, said atomising edge being suitable for a relative axial and angular dis- 3,504,851 Patented Apr. 7, 1970 placement, and having in the channels grids electrically connected to a pole of the highvoltage power source for decelerating the flow of fluid and for producing turbulence in it, furthermore, having an air space between the internal surface of the spray head and the blades fitted over the outer surface of the outer bell, said air space being connected with an air cushion between the glass sleeve of the outer bell and the outer surface of the outer passage, and said air cushion opening into the inner bell; furthermore having bores in said spray head connected to a compressed air duct, furthermore having air passage openings in the mantle of said outer bell.

The principal advantage offered by the spray gun according to the invention lies in the arrangement of the grids within the body of the spray gun, separated from one another. This enables the charging-up of the paints with high-voltage current, at a certain distance from the point of atomisation. This solution absolutely precludes the hazard of electric shock on touching any part of the gun, and spark formation. The hidden arrangement of the grids allows the use of higher voltages in charging up the materials to be sprayed, whereby a wide variety of materials becomes suitable for electrostatic spraying. The application of higher voltage, on the other hand, enhances ionisation of the material to be sprayed.

A further advantage offered by the spray gun according to the invention is that, except the grids and the metal inserts, all of its parts are made of insulating materials which not only meet safety criteria to the full, but enable the reduction of the weight and dimensions of the gun to half of the weight and dimensions of its known counterparts.

The air cushion between the inner surface of the sleeve of the outer bell and the outer surface of the outer passage leading one of the paints, has a twofold role. It renders lubrication between the two surfaces unnecessary and minimises friction enabling higher revolution speed of the bells without increasing power consumption on the one hand, and prevents paint from getting between the two surfaces, dispensing with packing problems, on the other,

By the application of the air cushion and a sliding bearing in the second bell, the revolution speed of the bells can be increased from 5000 to 8000 r.p.m. with a simultaneous reduction of power consumption of the drive by 40 percent, as compared to the known counterparts and atomising the same quantity of material, i.e. that of paint. By higher revolution speed, the amount of paint sprayed per unit of time can be increased, the efficiency of coating enhanced, and its quality improved.

The invention will be further described, by Way of example with reference to the accompanying drawings, in which FIG. 1 is the horizontal cross sectional view of the spray gun according to the invention.

FIG. 2 is a section on line 22 of FIGURE 1.

FIGURE 1 of the drawings shows a preferred form of the spray gun according to the present invention which results in a round spray pattern. The portions of the spray gun which are common with the parts of the usual well known spray guns functioning with compressed air, so as the body of the gun with the handle, and the compressed air producing means are deleted from the drawing and the description to make the essence of the invention clearer. The usual guns have internal passages in the hand portion through which the fluid material enters the gun. To this passage are connected the channels 1 and 2 represented in FIG. 1.

One of the paints used for spraying enters through channel 1, and the other paint used for spraying enters through channel 2. To channel 1insert 4 is connected in whichgrid 35 is removably located. To channel 2insert 3 is connected in whichgrid 36 is removably located.Grids 35 and 36 are located ininserts 3 and 4, perpendicularly to the axis of the flow of the fluid.Insert 3 is concentrically arranged ininsert 4. Inserts 3 and 4 as well asgrids 35 and 36 are made of any suitable conductive metal.

The mesh size and the dimensions of the grids are dependent on the viscosity and density of the fluid material flowing through them. Both mesh size and dimensions are adjustable.Inserts 3 and 4 are electrically connected withgrids 35 and 36 and coupled to the negative pole of a high-voltage power source 5, by means of acable 6. The positive pole of the high-voltage power source 5 is grounded.

One end of apassage 7 is connected toinsert 4. To the other end of saidpassage 7 the end of smaller crosssection of a taperingouter bell 11 is connected. One end of apassage 8 is connected toinsert 3. At the other end of saidpassage 8holes 21 are arranged. Passage 8 is concentrically located inpassage 7 and supports at its end perforated with saidholes 21 the end of smaller crosssection of a taperinginner bell 17. In the disc-shaped part 28 of saidinner bell 17 which connects said latter with theinner bell 11openings 23 are arranged. Bell 17 withinbell 11 is either rigidly fixed, for instance by welding or by friction, in such a way that the two tapering surfaces rub over each other. The hub ofbell 11 is fitted with a sliding bearing 10 made of glass, the hub ofbell 17 is fitted with a sliding bearing 22.

Bothbells 11 and 17, are surrounded by aspray head 9 in whichbores 13 are arranged. To bores 13 a compressed-air duct 26 fitted with acontrol valve 25 is connected, through which duct compressedair 27 is delivered in known manner from a container (not shown in the figure) to the spray gun.

Theouter bell 11 has a film-producingsurface 24 on its inner surface and anatomising edge 15; also theinner bell 17 has a film-producingsurface 19 on its inner surface and anatomising edge 18. In addition, over the mantle of theouter bell 11,blades 12 are fitted. In the mantle ofbell 11openings 16 are arranged, close toedge 15.Bells 11 and 17 are fixed to the end ofchannel 8 by means of a threadedring 20. Bell 11 revolves at the end ofchannel 7 which latter, at the same time, forms the shaft ofbell 11.

Part of thecompressed air 27 entering throughbores 13 in thespray head 9 and reaching the clearance between the external surface ofshaft 7 and the internal surface of the slidingbearing 10, forms anair cushion 14 between said two surfaces. In such manner, thebell 11 revolves free from friction.

With the exception ofinserts 3 and 4 and thegrids 35 and 36, all components of the spray gun are made of an insulating material.

The spray gun according to the invention function as follows:

The first fluid, i.e. paint entering channel 1, passes throughinsert 4 and thegrid 35. The other fluid, i.e. paint entering channel 2 passes throughinsert 3 and thegrid 36. The fluids flowing throughinserts 3 and 4 andgrids 35 and 36, are charged up to high voltage from the highvoltage power source 5 through thecable 6 whilst themetal grids 35 and 36 decelerate the flow of the fluid and disturb the cross section of the fluid column. This turbulence enhances the charge-up of the fluid particles with negative ions. Subsequently, one of the charged-up fluids passes to the internal space ofbell 11 throughpassage 7 and thence, through opening 23 to the film-producingsurface 24 ofhell 11, and finally, to the atomisingedge 15, there to be atomised. The other fluid passes to the internal space ofbell 17 throughpassage 8 and holes 21 and is atomised on theedge 18 while travelling over thefilm producing surface 19.

Compressed air entering thespray head 9 throughbores 13 and passing through opening 16 of thebell 11 reach the air space situated betweenbells 11 and 17. Thiscompressed air 27 partly draws together the fluid particles atomised at the atomisingedge 18 ofbell 17 diverging in direction 29, and partly pushes the fluid 30 atomised at the atomisingedge 15 of thebell 11 towards the subject to be coated. This operation brings about a spray pattern uniformly distributed over the surface of the subject to be coated, without sprayless area in its centre.

Thebores 13 in thespray head 9 are developed in such a way that they should open in the space between theblades 12 near to the end of small cross section ofbell 11.

Passing simultaneously a black fluid through channel 1 andpassage 7 intobell 11 to its atomisingedge 15 and a white fluid through channel 2 andpassage 8 intobell 17 to its atomisingedge 18 and atomising both fluids on saidedges 15 and 18 due to compressedair 27 arriving fromduct 26, such a spray pattern can be achieved in which the free area within the black ring is filled out with white paint, provided that the atomisingedge 18 extends further than the atomisingedge 15. In such manner, a third colour can be produced from the two colours, the shade of which depends on the ratio of the two starting colours fed into the gun. The shade, viz. the superposition of the two colours can be adjusted partly by relatively displacing thebells 11 and 17 in axial direction and partly by rotating thebells 11 and 17 relatively to each other.

In the spray gun according to the invention, the ratio and conditions of the flow of the fluids in the passages can be regulated in several ways. For instance, by varying the pressure in the passages, or by varying the passage cross sections. In the spray gun according to the invention more than two channels and passages can be located, consequently it can be provided with more than two inserts, grids, bells respectively, for atomising simultaneously more than two sorts of materials.

While there has been shown and described a particular embodiment of the invention, it will be obvious to those skilled in the art that changes and modifications may be made in the invention.

What I claim is:

1. Spray gun for the simultaneous electrostatic atomisation of several different fluid materials, in which are separate channels carrying said fluids and opening into concentrically arranged bells, the outermost bell having blades fitted into outer surface thereon, surrounded by a spray head, each bell having an inner space to store said fluid, a film-producing surface on its inner surface and an atomising edge for the atomisation of said fluid, said atomising edge being suitable for a relative axial and angular displacement, and having in the channels grids electrically connected to a pole of the high-voltage power source, for decelerating the flow of the fluid and for producing turbulence in it, furthermore having an air space between the internal surface of the spray head and the blades fitted over the outer surface of the outer bell, said air space being connected with an air cushion between a glass sleeve carried by the outer bell and the outer surface of the outer passage, and said air cushion opening into the inner bell; furthermore having bores in said spray head connected to a compressed air duct, furthermore having air passage openings in the mantle of said outer bell.

2. Spray gun according to claim 1 wherein the dimensions and the mesh size of the grids are variable depending on the viscosity and density of said fluid material flowing through them.

3. Spray gun according to claim 1 wherein said grids and said inserts are made of metal and all the other parts of the spray gun are made of insulating material.

(References on following page) References Cited UNITED FOREIGN PATENTS STATES PATENTS 251,232 9/1960 Australia.

K t t 1. 239- 1s fg i l 239 15 EVERETT W. KIRBY, Pnmary Examlner Point 239-15 3 Oesterle 239-3 U'S' CL X'R' Wirth 239 15 239 224

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