US2975755A - Electrostatic paint spray apparatus - Google Patents

Description

March 21, 1961 H. J. REINDL ELECTROSTATIC PAINT SPRAY APPARATUS 4 Sheets-Sheet 1 REC/PMC1477176 Filed Sept. 30, 1 95? film/r501 Y ure/aura? INVENTOR. Harold J. liei d1 HIS ATTORNEY March 21, 1961 H. J. REINDL ELECTROSTATIC PAINT SPRAY APPARATUS 4 Sheets-Sheet 2 Filed Sept. 30, 1957 INVENTOR. Harold J. Reina! H '5 ATTORNEY March 21, 1961 H. J. REINDL ELECTROSTATIC PAINT SPRAY APPARATUS 4 Sheets-Sheet 3 Filed Sept. 30, 1957 INVENTOR- 0 Harold J. Reindl B 9 H/S ATTORNEY March 1961 H. J. REINDL 75,755

- ELECTROSTATIC PAINT SPRAY APPARATUS Filed Sept. 30, 1957 4 Sheets-Sheet 4 v INVENTOR. m Harold I. lleindl BY HIS ATTORNEY 2,975,755 ELECTROSTATIC PAINT SPRAY APPARATUS Harold J. Reindl, Dayton, Ohio, assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Filed Sept. 30, 1951, Ser. No. 687,107 13 Claims. c1. 118-626) This invention relates to electrostatic painting methods and apparatus and is particularly concerned with electrostatic painting operations wherein the density of paint deposited may be controlled. 7

It is an object of this invention to provide an electrostatic painting apparatus wherein the entire distribution of paint is accomplished by a combination of electrostatic and centrifugal forces.

'In carrying out the above object, it is a further object to provide a method and apparatus for electrostatic painting wherein the deposition pattern of the paint with respect to the density thereof may be controlled within predetermined limits.

Another object of the invention is to provide an electrostatic painting apparatus wherein a rotating member is used as the centrifugal paint distributor which rotating member is of noncircular design and wherein the paint is supplied thereto in a circular pattern whereby the paint thrown from the member by centrifugal force is nonuniform with respect to quantity thereof which phenomena is utilized in the control of density of paint deposition.

Another object of the invention is to utilize a rotating blade as a paint distributing member wherein paint may be supplied thereto adjacent thecenter of the blade and where it may be centrifugally distributed over the blade and broken up and distributed by electrostatic forces in a nonuniform manner so that the control of density of paint distribution is possible.

Another object of the invention is to provide an electrostatic painting apparatus utilizing a centrifugal distributing device for the paint which forms one side of the electrostatic circuit while the object to bepainted is oppositely charged and wherein density of the centrifugally distributed paint undulates between predetermined limits and is electrostatically distributed in a controlled nonuniform manner.

A still further object of the invention is to provide a centrifugal paint distributing mechanism wherein a pump is built into the mechanism which draws paint from a source of supply whereby paint is only present at the distributing surface when the device is rotating at speeds sufficient to cause the pumping action to occur.

Another object of the invention is to provide a centrifugal distributing device for the paint which is noncircular in shape and which has a sharp distributing edge that is undulating in character with respect to the main plane of the device whereby the direction of paint thrown off the edges of the plate is changed in accordance with the slope at the several edge portions of the plate.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings wherein preferred embodiments of the present invention are clearly shown. a

In the drawings:

Figure 1 is a diagrammatic view of an electrostatic paint distributing device together with a carrier having Patented Mar. 21, 1961 automotive steering wheels thereon which are to be painted.

Figure 2 is an enlarged view of the centrifugal distributing device shown in Figure 1 together with a paint spray pattern at the right hand side of the figure showing the nonuniform distribution of paint therefrom, it being understood that the dots on the pattern are indicative of paint density.

Figure 3 is a view taken along line 3-3 of Figure 2.

Figure 4 is a modification'of the device shown in Figure 2 wherein the ends of the distributing device are turned in opposite directions together with a paint distributing pattern for such a device.

Figure 5 is a modification of the distributing device shown in Figure 2 wherein the distributing device is oppositely fluted at the ends thereof together with the paint distribution pattern shown at the right.

Figure 6 is a side view of the device shown in Figure 5 taken in the direction of the arrow marked 6 in Figure 5.

Figure 7 is a plan view of the device shown in Figure 2 wherein the dotted lines around the periphery thereof are indicative of quantity of paint being thrown off during rotation of the device at dilferent portions along the edge thereof.

Figure 8 is an enlarged fragmentary sectional view of a modification of the centrifugal device shown in the aforegoing figures wherein a centrifugal pump is integrally built into the central portion of the distributing device.

Figure 9 is another modification of the central portion of the device wherein paint supplied by an external pump is directed through the shaft at the center of the device whence it flows out of the ports into the central distributing cup.

Figure 10 is a sectional view of the pump taken on line 1010 of Figure 8.

Figure 11 is a plan view of another type of centrifugal device.

Figure 12 is a side view of the device shown in Figure 11 taken in the direction of the arrow marked 12 in Figure 11.

Figure 13 is an end view of the device shown in Figure 11 taken in the direction of the arrow marked 13 in Figure 12.

Figure 14 is a plan view ofsti-ll another modification of the centrifugal device.

Figure 15 is a side view of the device shown in Figure 14 taken in the direction of the arrow in Figure 14.

Figure 16 is an enlarged view of the edge of the several centn'fugal devices showing the bevel thereon and taken at the point encircled in Figure 12 and marked 16.

Electrostatic spray painting is a well-known art and a number of devices have been proposed to accomplish the process. Early eflorts along this line utilized paint atomizing guns wherein the article to be painted was maintained within an electrostatic field. Paint particles emanating from the gun and entering the field became charged and were attracted to the article to be painted. This type of electrostatic spray painting functioned quite well for certain applications where relatively large surfaces required painting. More recently, it has been 7 found that the paint distribution may be accomplished edge of the plate and drops therefrom, it becomes electrostatically charged and is broken up into small particles which are attracted to the article. A device of this 3 character is fully disclosed in copending application, S.N. 549,719, now US. Patent No. 2,911,323, assigned to the assignee of the present invention.

Another type of electrostatic painting apparatus involves the use of a whirling disc or cone which is attached to one pole of the power source while the article to be painted is spaced therefrom and attached to the other pole of the source, face of the disc and is distributed thereover by centrifugal force and, when it reaches the edge of the disc, is centrifugally thrown and simultaneously electrostatically charged and further broken up to form an electrostatically charged paint mist of very minute particles which are attracted to the article to be painted. In this instance, the paint always leaves the edge of the disc in the same plane and in particles of the same size, and, therefore, the pattern of painting is always of equal density if the disc remains immovable with respect to the article. In order to obtain a greater field of painting, it has been past practice to reciprocate the disc while it is whirling in a generally vertical path. In this manner, the disc is moved up and down in the vertical path while it is being rotated and, thus, the field of paint coverage is increased. However, it is apparent that at the top and bottom limits of its reciprocal movement, the amount of paint deposited is twice the amount as that on any other portion of the article to be painted. This is due to the fact that the disc remains in one position twice as long since it is changing direction of vertical movement at these points.

The present invention is directed to a centrifugal type electrostatic painting apparatus which produces a nonuniform pattern of painting and which may be controlled so that any density of paint may be deposited on articles to be painted in accordance with the predetermined desire of the operator. This is accomplished by utilizing nonuniform or noncircular centrifugal distributing members and wherein edge portions ofthe members may be turned at different angles from the major plane thereof to produce a wider field of coverage. Specifically referring to Figure 1, a diagrammatic view of one embodiment of my invention is shown wherein a blade member 20 is the centrifugal distributing device. The member 20 has a centrally depressed cup portion 22 which surrounds the base of a support shaft 24 that is fixedly fastened to the member 20. The shaft 24 extends upwardly to a motor, not shown, which causes rotation of the shaft and the attached member 20. The motor may be carried by a reciprocating apparatus for moving the shaft in a vertical path between predeter mined limits which apparatus forms no part of this invention. Solvent-containing paint is pumped through a stationary supply tube 26, preferably nonmetallic, which opens into the cup 22 whereby paint supplied through the tube 26 is made available to the member 20 from the cup 22.

The shaft 24 and its attached disc 20 is attached to one pole of a power source indicated at 30. The other side of the source is connected to a rack 32 attached to a conveyor mechanism 34. The rack 32 carries, at its lower end, the articles to be painted, in this case, a pair of steering wheels 36.

The rack is preferably coveredwith polyethylene or similar material to prevent paint deposition thereon. This protection forms no part of this invention and is fully disclosed in my copending application, S.N. 677,722, now abandoned, assigned to the assignee of the present invention.

When the device is to be operated, the motor used to drive the shaft is energized and the shaft is rotated at a speed of preferably between 2000 and 3500 r.p.m. This causes the distributing member 20 to rotate at the same speed and paint, which is in the cup 22, is centrifugally distributed over the edge ofthe cup and onto the surface of the member '20. Since the member 20 is noncircular and has a minor axis of considerably less length Paint is supplied to the surthan its major axis, it is apparent that the centrifugally distributed paint will be thrown off the edges 40 and 42 in considerably greater quantities than off the edges 44 and 46 with'the quantity of paint being thrown off the edges 40 and 42 over their entire length diminishing from the center toward the ends thereof. This condition is made use of by turning up the ends 44 and 46 out of the plane of the major portion of the member 20 whereby paint is directed upwardly. This will cause the pattern of painting to approximate that shown on the target at the right hand side of Figure 2 wherein a greater density of paint will be distributed from the edges 40 and 42 than from the edges 44- and 46.

This phenomena can be put to use in the electrostatic painting of articles wherein the distributing member 20 is reciprocated over a substantially vertical path whereby uniform coverage of articles 36 on the conveyor system 34 can be maintained substantially uniform by properly controlling the length of the edges and the angle of the turned up ends 44 and 46 on the member 20. It is understood thatthe rack 32 in the present instance rotates while it is moving along the track of the conveyor 34 so that substantially complete coverage is obtained.

In this connection, it is understood that, as the paint is centrifugally distributed and thrown off the edges of the member 20, it picks up the electrostatic charge which further breaks up these paint droplets as they leave the edge whereby they are attracted in the form of a very fine mist to the articles 36 which have the opposite charge thereon. In this manner, very little paint is dissipated into the atmosphere since the large portion of the paint is attracted and deposited on the articles to be painted in a substantially uniform manner due to the paint pattern predetermined by the shape and angle of the member 20.

In Figure 4, a centrifugal member 50 is shown wherein the end portions of the members 52 and 54 are bent in opposite directions for providing a painting pattern having a density shown on the associated target. In Figure 5, a distributing member 56 is provided wherein the end portions are fluted or grooved at 58, 60 and 62. This produces a pattern of paint distribution similar to that shown on the associated target. It is apparent that many other shapes of distributing devices may be utilized. For example, in Figures 11, 12 and 13, a device 66 is shown which has opposed curved edges 68 and 70 and substantially elevated end edges 72 and 74 which are also curved slightly since, in this instance, the member is made from a cupped disc having the sides cut away. Figure 14 shows still another distributing member wherein the edges 82, 84, 86 and 88 form a scalloped design when viewed from the direction of arrow 15 as shown in Figure 15. Here again, the member provides two relatively long edges and two relatively short edges for nonuniform distribution of the paint.

In all of the embodiments shown here, the distributing member is beveled at 90 at the edge thereof as shown in Figure 16. This bevel or sharp edge improves the electrostatic charge on the paint particles as they leave the blade or member.

Figure 8 shows still another embodiment which may be used in connection with any of the blades heretofore described. In this instance, the central cup 22 houses a pump rotor which is attached to the shaft 24. A stationary plate 102 is carried by a stationary sleeve member 104 and substantially covers the rotor 100. At the top of the rotor 100 is an annular reservoir 106 which connects by means of inclined ducts 108 with an annular clearance between the rotor and the cup 22. The plate 102 covers the reservoir 106 and a paint supply tube 110 passes through the plate and into the reservoir 106. In operation, the device may be primed by pouring paint into the clearance between the rotor and cup and, as the blade is rotated, this paint is centrifugally dispersed over the surface thereof which causes the rotor 100 to act as a centrifugal pump and draw more paint through the tube 110 from a paint supply. In this manner, rotation of the blade produces a pumping action which draws the paint to the blade without any external pumping means. Any type of pump device may be used in this instance.

Another means of supplying paint to the blade or distributing member 20. is shown in Figure 9 whereinthe shaft 24 is drilled axially thereof to provide a longitudinal cavity 120 therein. A paint supply tube 122 which is stationary passes through the shaft 120 and supplies paint at the lower end thereof. The tube 24 is apertured as desired at 124 to permit the paint from the inside cavity thereof to flow into the cup 22. The number and the angle of the orifices 124 can be utilized to aid in distributing the paint over the surfaces of the member in a desired manner. For example, the orifices 124 canbe placed in alignment with only two parallel edges of the distributing member which will cause a controlled uneven distribution of paint as desired, etc.

The uneven centrifugal distribution of paint being thrown from the several edges of the distributing member provides a greater pulsating efifect to the paint. In other words, the paint mist will occur in waves which permits initial deposit of paint which dries sufiiciently before the next Wave of paint mist is applied to prevent drip and run. This permits heavier coatings of paint to be deposited by the instant process and distributing member without tears forming on the part being painted. It has been found that where the distribution of paint is uniform at all times, the density of paint which can be deposited must be reduced in order to prevent the tearing effect whereas, when the paint is deposited in a pulsating manner as disclosed herein, considerably more paint may be supplied and deposited in a satisfactory manner which cuts down the cost of the painting operation and reduces the number of passes required in the conveyor system.

The present system as heretofore described provides a better painting pattern as shown by the paint distribution of the several devices. This condition, which is controllable, permits the use of reciprocating distributing members while likewise permitting the control of paint so that heavier deposits are not apparent at various portions on the articles being painted as is normally the case where a circular plate or cone is being used as the distributing member.

I have found that high speed rotation of the distributing member produces a finer distribution of the particles since centrifugal force enters into the breaking up of the particles to a large extent whereby the electrostatic forces further break up the particles which are quite fine through the high speed rotation of the distributor. Furthermore, the high speed rotation improves the throwing power of the device.

A specific example of spray painting. using the device as shown in Figure 14 in a set-up as noted in Figure 1 is as follows. Steering wheels comprising a metal spider covered with hard rubber are preheated to about 200 F. to increase the conductivity of the rubber and are placed on the conveyor rack 32. The conveyor moves these wheels at about sixteen feet per minute wherein the wheels are rotated about eight times in the field of painting. A conventional enamel type paint, cut with a suitable solvent to about 38% solids, is supplied to the distributing device wherein the electrostatic power pack supplies voltages in the order of 130,000 volts at about .2 of a milliampere. It has been found that wheels are satisfactorily painted passing through this set-up in about one minute wherein less than a pound of cut enamel is being used per minute. In general, the use of a noncircular distributing member, whether it be straight sided, oval or elliptical in shape, provides better control of paint distribution and improves the efficiency of the entire set-up. r

The paint distributing device does not necessarily have to be operated on a vertical axis. This axis may be angled from the vertical as desired to change the paint pattern and, in fact, the axis may be swung about a given point to cause a changing paint pattern as the device is swinging. Furthermore, while the distributing members or blades as described herein are preferably metal such as aluminum, steel or brass, I have found that substantially the same results can be obtained by utilizing nonmetallic members such as Bakelite members. In this instance, the electrical charge is supplied through the shaft and by some phenomena not known to me, the paint particles are charged electrostatically as they leave the knife edge of the distributing member. For obvious reasons, such as strength, ruggedness, etc., metal distributors are preferred although this is not necessarily a limitation in an operative device.

While the foregoing description has been directed to the use of a solvent-containing paint such as an enamel, it is manifest that any covering material may be distributed by the process and device disclosed herein. For example, water solutions of frits for vitreous enamel coat ings may be distributed. Also, metallic paints in solventcontaining carriers may be satisfactorily deposited on articles to be coated with this device. In all cases, where the covering material is conductive in nature, the source of supply of the covering material such as the container therefor must be insulated from ground.

While the embodiments of the invention as herein disclosed constitute preferred forms, it is to be understood that other forms might be adopted.

What is claimed is as follows:

1. In an electrostatic painting apparatus, the combination comprising; a plate-like distributing member of rectilinear shape having at least two pairs of sharp-edged sides wherein the edges of each pair are generally parallel to one another and wherein one pair of edges is of greater length than the other pair of edges, a support associated with the plate adjacent the geometric center thereof and adapted to be attached to means for rotating the support and the plate, and a cup-like supply means surrounding the support and depressed from the surface of the support and adapted to receive paint to be distributed therefrom over the entire surface of the plate-like distributor by centrifugal action and means for impressing an electrostatic charge upon the plate wherein paint distributed therefrom will bear an electrostatic charge.

2. The device claimed in claim 1 wherein each pair of edges is in a different plane.

3. The device as claimed in claim 1 wherein portions of each pair of edges are in difierent planes.

4. The device as claimed in claim 1 wherein a centrifugal pump is associated with the cup-like supply means which pump is operative only upon rotation of the plate to draw paint thereto.

5. The device claimed in claim 1 including means for bodily moving the distributing memberduring rotation thereof.

6. For use in an electrostatic painting apparatus, a plate-like distributing member, comprising in combination; a generally rectangular device having sharp-edged sides wherein respective pairs of sides are generally parallel to one another, means for rotating the member, and means for supplying paint adjacent the center thereof whereby said paint is distributed centrifugally over the entire surface of the member and is discharged nonuniformly from the edges thereof with the greater amount of paint being discharged from the lower edges of the member and means for impressing an electrostatic charge upon the member whereby paint distributed therefrom bears an electrostatic charge.

7. The device as claimed in claim 6 including means for bodily moving the distributing member during rotation thereof. 7

8. The device as claimed in claim 6 wherein only portions of the edges are turned out of the general plane of t the distributor in opposed relation to one another for increasing the depth of the field of the device.

9. The device claimed in claim 6 wherein the edges of the device are scalloped for increasing the depth of the field of paint discharge.

10. The device claimed in claim 9 including means for bodily moving the distributor during rotation thereof.

11. The device claimed in claim 10 wherein said means for bodily moving the distributor reciprocates the distributor in a plane substantially 90 to the plane of rotation thereof.

12. For use in an electrostatic painting apparatus, a distributing member, comprising in combination; a noncircular, plate-like member having a minor axis and a major axis perpendicular thereto, means for supplying paint to said distributor adjacent the geometric center References Cited in the file of this patent UNITED STATES PATENTS 2,220,275 Preston Nov. 5, 1940 2,671,650 Iauch et a1. Mar. 9, 1954 2,784,033 Amberg Mar. 5, 1957 2,808,343 Simmons Oct. 1, 1957 2,899,136 Reindl Aug. 11, 1959

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