US2947281A - Manufacturing apparatus and method of operating the same - Google Patents

Description

Aug. 2, 1960 H. J. REINDL 2,947,281

MANUFACTURING APPARATUS AND METHOD OF OPERATING THE SAME Filed Nov. 25, 1957 2 sheets-sheath mvsmon HAROLD J. BEINDL Hi5 ATTORNEY H. J. REINDL Aug. 2, 1960 MANUFACTURING APPARATUS AND METHOD OF OPERATING THE SAME Filed Nov. 25, 1957 2 Sheets-Sheet 2 INVENTOR. meow J. HEINIJL wurr vUnited States MANUFACTURING APPARATUS AND METHOD OF OPERATING SAME Harold J. Reindl, Dayton, Ohio, assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware FiledNov. 25, 1957, Ser. No. 698,490

1 Claim. 01. 118-632) whereby the article is coated with the coating material in a nonuniform m'anner upon each pass through the spray pattern;

In carrying out the above object, it is another object of the invention to provide a conveyor which conveys articles around a central spray device in a generally rectilinear path, such as a triangular, square or rectangullar path, whereby the articles are at ever changing distances from thecenter of the spray device for providing an ever varying density of deposition of coating ma terial on the articles.-

A further object of the invention is to provide an electrostatic coating apparatus with a conveyor system which permits a greater thickness of coating material to be deposited on the articles conveyed thereon through the spray pattern. This is accomplished by causing the articles to pass the center oct the spray pattern at ever changing distances a plurality of times whereby a nonuniform deposition of coating material is obtained which varies between maximum and minimum figures, whereby the coating material, when it includes a solvent, is partially dried at the points of minimum deposition for reducing or eliminating the tendency to run or tear.

Still another object of the invention is to provide a method for electrostatically coating mticles with a coating material which comprises projecting a spray of liquid coating material particles from a central source and in an expanding, generally-circular pattern and conveying an article to be coated through portions of the pattern at ever changing distances from its center for producing a nonuniform density of deposition of coating particles upon the article while maintaining the article at a particle-attracting potential as it is conveyed through said pattern portions. 7

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

in the drawings: w

Fig. 1 is a diagrammatic view of a portion of a confield of an electrostatic spray apparatus. 7

Fig. Z-is a diagrammatic plan'viewshowingthe general shapeof onetype of conveyor with respect to the electrostatic distributor, heating means being diagrammatically shown at twocomer portions thereof.

veyor for conveying steeringwheels into an electrostatic 2,947,281 Patented Aug. 2, 1960 a path is generally square, and wherein heating means are the paint already applied does not dry. Thus, if any Fig. 3 is a view similar to Fig. 2 wherein the conveyor shown at three corner portions thereof together with shielding means at similar corner portions.

Fig. 4 is a view similar to Fig. 3 showing a conveyor system having a generally square path without heating or shielding means.

Fig. 5 is a view similar to Fig. 3 showing a square conveyor wherein heating devices placed intermediate the corner portions and on three sides of the conveyor.

Fig. 6 is a diagrammatic view of another conveyor system which may include three separate conveyors or one conveyor wherein articles are positioned on four sides of the distributor for spray coating operations in a substantially square pattern and,

Fig. 7 is a diagrammatic view of a system as shown in Fig. 2, showing the distributor, article carrier, etc. in connection with a complete coating apparatus.

In electrostatic paint spray operations, an electrostatic field is used to increase the coverage and decrease the overspray of coating particles. Furthermore, on certain articles, such as steering Wheels for example, it is highly desirable to attract the paint to the wheel so that there is little or no overspray. Obviously, any other openwork article, such as a grill, rack, etc., creates similar problems and is therefore advantageously spray coated electrostatically.

In application Serial No. 687,107, filed September 30, 1957, assigned to the assignee of the present invention, a spray coating apparatus is shown which includes what may be termed a centrifugal distributor. This device embodies a blade-like structure which is whirled at high speed and which is charged oppositely to the article to be coated. The coating material is fed thereto adjacent to the center of rotation and is electrostatically andrcentrifugally distributed and is broken up into fine particles to form a spray. The spray pattern is of generally circular shape taken in a plane normal to the axis of rotation thereof.

In place of a noncircular distributor, a circular distributor may be used to coat the articles, although the coating operation will be carried out in'a difierent manner since the distribution of coating particles will be more uniform and it will be more diflicult to provide a heavy coating free from runs and tears. In either case, however, the spray pattern is of generally circular shape, and a somewhat similar pattern will be present if the distributor is cone-like, although in this case, the depth of pattern will be greater but will be generally circular In all of these centrifugal-type distributors, there is a distinct problem in setting up the conveyor system for conveying articles to be coated into and away from the field of the spray. It has been proposed to convey the articles in a path of equal distance from the center of the paint distributor. In this type of conveyor system, uniform deposition of coating particles is obtained and, in fact, such a condition is the optimum objective of such a conveyor system.

7 I have found that when coating articles with a solvent containing paint that the coating of such articles at a uniform rate limits the film thickness of paint which may be deposited on the articles. This is explained by the fact that paint particles constantly being applied simultaneously supply additional solvent to the article whereby substantial thickness of paintis applied to the article, the

paint will run and tear which will present an undesirable.

appearance on the coated article. For this reason, in

conveyor systems used in electrostatic painting opera:

tions wherein the articles pass the electrostatic paintzdistributor in a generally uniform manner through the spray pattern, it is necessary to use two or more distributors in order to obtain a substantial thickness of paint coating which is freefrom runs and tears on the article.

The present invention is directed to an apparatus and method wherein articles may be conveyed into the electrostatic coating field of an electrostatic distributor, and due to a nonuniform deposition of paint, it is possible to coat the article with more paint on one pass around the conveyor whereby the articles have a paint film of adequate thickness that is free from runs and tears. This is accomplished by using a rectilinear conveyor path in conjunction With a circular spray pattern.

Referring specifically to Fig. 1, a portion of one type of conveyor is shown which includes a track 21, a plurality of hangers 22 suspended therefrom and connected by a chain 24. Each hanger has a horizontal cross bar 26 thereon which supports a steering wheel 28, for example, at opposite ends thereof. The hangers 22 rotate through suitable means such as a rack and gear arrangement 30 as the chain causes the hanger to move along the track 21.

In order to coat the wheels with a paint, an electrostatic spray head is used which comprises a blade, disk or cone 34 that is appended to or supported on a shaft 36 that is driven by a motor (not shown) at speeds of from 1,000 to 3,000 rpm. The shaft and distributor 32 may be reciprocated vertically within limits to enlarge the field of application, if desired. A solvent containing paint is applied to the distributor 32 from a supply tube 38, which provides paint adjacent the center of the distributor 32. The distributor 32 is connected to one pole of a high-voltage D.C. power source 40 while the conveyor and steering wheels are connected to the other pole of said power source. It is understood that the conveyor'and the hangers 22 are metal as is the core of the steering wheels 28. The core of the steering wheels 28 is generally covered with hard rubber which is the material to be coated. In this manner paint particles from the distributor 32 carry a charge opposite to the charge on the wheels 28, and are thereby attracted to the wheels 28 for deposition thereon.

The conveyor 20 follows a path, as shown in Figs. 2 through 6 for example, whereby the wheels are maintained at constantly ever-changing distances from the center of the distributor. In this instance, each carrier 22 is identified as a circle while the conveyor path is shown as a solid line. In Fig. 2 the conveyor takes the form of a triangle wherein the wheels are at ever-changing distances from the center of the distributor 32. The corners of the triangle are substantially outside of the normal spray pattern which is indicated by a dash line 42. Since the articles on the carriers 22 each carry a charge opposite to the charge on the paint particles, there is a tendency for the spray pattern of the distributor to distort and to assume a form shown in dotted lines and designated at 44, thus there is very little tendency toward over-spray at the corner portions of the triangle.

It will be noted that as the articles enter the spray pattern, they are at the extreme edge thereof where very little paint is being deposited, and as they progress they move into a greater density of paint distribution and then move toward a zone of low paint density, finally coming to acorner portion Where there is substantially no deposition of coating material. This path of movement obviously permits the solvents in the paint to evaporate partially prior to the time that the articles again enter a second phase of the painting operation. This sequence of events is again repeated prior to the articles passing through the third phase. In this manner more paint can be deposited on the articles which is free from runs and is an acceleration of drying at the corner portions whereby heavy application of paint may be accomplished between the heaters.

In Fig. 3 another form of conveyor is shown which follows a square path. In this instance three heaters 50 are used and in order to more definitely establish the spray pattern shielding means 52 are positioned between the articles on the conveyor and the distributor 32 adjacent the corner portions of the conveyor. These shielding means 52 may be screens, rods or plates which carry a charge similar to the charge on the distributor 32. Thus the shields 52 have a charge similar to the charge carried on the paint particles whereby the shields 52 actually repel the paint particles and thereby change the paint pattern to cause deposition on articles carried by the conveyor between the shields. This expedient improves the nonuniforrnity of deposition and, when used in conjunction with heating means, permits very heavy coatings to be applied that are free from runs and tears.

Fig. 4 shows the same type of square conveyor without heating means or shields wherein the deformed pattern is shown in dotted lines 44 as occasioned by the attraction of spray particles toward the charged articles.

Fig. 5 shows another type of conveyor which is generally square in design and which includes heating means 60 at central portions at straight sides of the square. In this instance, the conveyor loops outwardly from the square and carries the articles beyond the spray pattern and preferably into a heating area.

Fig. 6 shows still another modification. In this instance three separate conveyors 62, 64 and 66 are used or theseconveyors may all be joined at positions remote from the distributor 32. In this case, the coating on the articles has ample opportunity to dry when the conveyor is outside the spray pattern.

Fig. 7 is a'diagrammatic view of a complete setup used to spray paint a plurality of articles each supported upon a carrier 82 wherein the articles 80 are small cylindrical objects such as metal sleeves. The conveyor 84 in this instance is generally triangular shaped and includes a slotted track'86 having a chain 88 passing therethrough which includes spaced plates upon which the supports 82 are carried. The chain 88 is driven by suitable sprocket by motor 89 to cause the plates 90 and supports 82 to move at a substantially constant rate around the conveyor track 86. A distributor 32, similar to that shown in Fig. 1, is positioned within the conveyor 84 substantially at the intersection of the imaginary perpendiculars drawn from the midpoints of each side of the conveyor. The distributor is driven by a motor through a gear box 102 and is preferably rotated at speeds of about 2,000r.p.m. Paint is supplied to the distributor through tube 104 by a pump 106 which draws paint from a container 108. The distributor 32 is connected to one pole of a high voltage DC. power source 110 while the other pole of said source is connected, as shown, to the conveyor. The power source supplies voltages in the the order of from 90,000 to 120,000 volts at about .2 of a milliampere. At one corner of the device heating means 112 are shown, which include a plurality of infrared lamps 114 therein that are used to supply heat to the articles 80 as they pass the heating means 112 to at least partially evaporate the solvent in the paint covering the articles 80, this modification being optional as determined by the operation being performed. Also, shielding devices as shown at may be used at one or more of the corners, if desired. The shields 120, if used, are connected to the same pole of the power source .as the distributor 32.

It willbe seen from Fig. 7 that articles '80 pass at everchanging distances to the center of the distributor and similarly pass-through the spray pattern of the distributor so as to accept the paint in a nonuniform mannerwhcrein very little paint is distributed thereon as the articles enter the field which deposition increases to the midpoint of While the embodiments of the present invention as herein disclosed constitute preferred forms, it is to be understood that other forms might be adopted.

What is claimed is as follows:

Electrostatic spraying apparatus comprising in combination; a rotating centrifugal spraying device adapted to dissipate paint particles in a generally circular pattern, a conveyor means capable of transporting a plurality of articles to be coated, said conveyor means having an entrance to and an adjacent exit from said circular pattern and otherwise substantially surrounding said spraying device, said spraying device being located at the geometrical center of said surrounding conveyor means, said conveyor having at least two portions which extend beyond and return to said circular spray pattern in addition to the original entrance and the final exit, heating means positioned adjacent said extended portions of said conveyor to dry the coatings, plate-type electrostatic deflectors positioned adjacent said conveyor and between said conveyor and said spraying device at said extended portions to prevent paint from depositing on the articles adjacent the heater, and means for placing an electrical charge of one polarity on said deflector and said spraying device and a charge of the opposite polarity on said articles whereby a heavy coating of electrodeposited paint particles may be obtained on said conveyed articles.

Lamrn Dec. 11, 1956 Juvinall Feb. 5, 1957

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