US3155545A - Apparatus for external coating of objects - Google Patents

Description

Nov. 3, 1964 E. H. RocKs ETAL APPARATUS FOR EXTERNAL COATING OF OBJECTS 2 Sheets-Sheet 1 Filed Feb. 27, 1961 n/@Lr AI. KOC/s Mam/w L. Bussy m. wekvwh WMM y rroeA/Eys.

Elmar #5A Nov. 3, 1964 E. H. RocKs ETAL 3,155,545

APPARATUS FOR EXTERNAL COATING OF' OBJECTSl Filed Feb. 27, 1961 2 Sheets-Sheet 2 www Ifo.

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United States Patent O 3,155,545 APPARATUS FR EXTERNAL COATiNG OF OBJECTS Ewalt H. Rocks and Marvin L. Busby, Fullerton, Calif., assignors to Rheem Manufacturing Company, New

York, N .Y., a corporation of California Filed Feb. 27, 1961, Ser. No. 91,839 2 Claims. (Cl. 118--621) This invention relates to a method and apparatus for external coating of objects by the use of an electrostatic charge. lt is adaptable for use in coating of electrically conductive objects having various configurations, and may be utilized to coat said objects with a wide range of materials, such as, by way of example but not by way of limitation, vinyls, polyethylenes, ceramics, epoxy resins, and other matenials capable of being atomized.

Various other methods and apparatus have been devised to apply such coatings to objects but all of such other methods and apparatus are subject yto severe limitations in that they do not accomplish a lirm bond of the coating to the object being coated, they do not attain a substantially even deposit of the coating material, they are not adaptable for coating objects of various metals, they are limited to coating objects of speciiied coniigurations (and many of them are limited to coating flat objects), they are expensive to apply or construct, or they are complicated to operate.

it is therefore an object of the present invention to provide a method and apparatus for applying a wide range of coatings electrostatically to objects of varying coniigurations.

It is ano-ther object of the invention to provide a method and apparatus for eleetrostatically applying coatings to objects so as to form a rm bond between said coatings and said objects.

It is still another object of the invention to provide such a method and apparatus which will rovide a substantially even external coating of improved density on objects, regardless of the contours and configurations of such objects.

lt is a further object of the invention to provide a method and apparatus for applying coatings of various materials to objects of varying metal content.

It is a further object of the invention to provide a simplified method of applying coatings in powder form to objects by use of an apparatus which is easy and iuexpensive to construct and install and which effectively uses a substantially large quantity of the powder introduced into the apparatus.

it is still a further object of the invention to provide such a method and apparatus which is uncomplicated to apply and operate.

With these and other objects in view, the invention consists of the method, and the construction, arrangement and combination of the various parts of the apparatus, whereby the objects contemplated are attained, as hereinafter set forth, defined in the appended claims, and illustrated in the accompanying drawings.

in the drawings:

FXGURE l is a diagrammaticrepresentation of the method and apparatus of the present invention.

FEGURE 2 is a side elevational view, partly in section, of the coating chamber of the present invention` IGURE 3 is a view taken on the line 3 3 of lTlG- URE 2. j v

FEGURE 4 is an enlarged view taken on the line 5 4 of TIGURE 3.

FGURE 5 is a view taken on the line 5--5 of Fl- URE 4.

FiGURE 6 is a perspective view of an alternative form of the coating chamber.

3,l55,54l5 Patented Nov. 3, 1964 ice As illustrated, a furnace l0, preferably a radiant furnace, is provided. f an elongate workpiece i5, such as steel pipe, is to be coated, a roller conveyor table 20 may be placed adjacent to furnace 10 to aid in convenient handling of said workpiece 15, and in introducing said workpiece 15 into furnace lil. Furnace l@ is equipped to receive, heat, and discharge said workpiece 15. Workpiece 15 will either be a metallic workpiece or a nonmetallic workpiece coated with metal lrn or otherwise treated to make it electrically conductive.

lt has been found advantageous to clean the workpiece l5 thoroughly before introducing it into furnace 10, and to maintain it in clean condition on discharge from furnace it?, in order to provide a clean surface to be coated and thus aid in attaining a rm bond of the coating to the workpiece i5. Furthermore, -it has been determined that in coating with epoxy resins, a temperature range of 400 F. to 450 F. in workpiece l5 produces good results, but the temperature range varies substantially with the coating material being used, satisfactory results having been attained generally with lower temperature ranges for vinyls and polyethylenes, but no limitation on temperature ranges is intended or contemplated.

A coating chamber 3b, having au entry end 39a and a discharge end Silla, is located adjacent furnace 1li, and a metal roller conveyor table 31, or other suitable means of electrically grounding workpiece 15 while it is passing through chamber 39, is provided and disposed between furnace lll and the entry end 3tlg of chamber 3d. Chamber Sii is equipped to receive, treat, and discharge said workpiece 1S.

To assure that said workpiece 15 will remain constantly electrically grounded while it is passing through chamber 3d, a second metal roller conveyor table 32, or other suitable means of electrically grounding said workpiece 15, is provided adjacent the discharge end 30h of chamber 30, so that as workpiece 15 passes beyond metallic roller conveyor 3i or other ground means adjacent the entry end Sila of chamber 3i), it is in Contact with metall-ic roller conveyor 32'; or other ground means adjacent the discharge end .St-'1b of chamber 30.

Disposed longitudinally and axially in said coating chamber 3d so as to surround, but be spaced apart from, workpiece 15, is an electric grid ell, suitably connected to a source of electric power (not shown). Said grid du comprises end members 41 and ft2., spaced apart from each other, and grid wires 43 spaced apart from and in parallel relationship to each other, are mounted on said end members il and 42, and stretched between said end members dl and 52.

Said grid wires 43 are preferably of small gauge. Furthermore, it has been found preferable to space said grid wires apart from each other a suflicient distance to prevent an electric current flow therebetween and thus attain a greater degree of ionization. In the normal operation of the device it has been ascertained that grid 4l? performs satisfactorily if said grid Wires 43 are spaced apart from each other twice the distance of a spark gap, and normally a distance of approximately six inches is satisfactory.

Also, workpiece l5 should be spaced apart from the grid Y wires i3 at least that same distance.

Again it has been found advantageous to utilize a current volt range of from 50,000 to 150,000 volts for normal operation, but greater or lesser voltage may be found desirable, depending on the coating material used, the heat of workpiece 15, and other factors.

Mounted in said coating chamber Elli, preferably on or adjacent to discharge end Slb of said chamber 30, isa spray nozzle manifold Sil. It has been found desirable to form said manifold Silas a ring, and to dispose it so that it will surround, but be spaced apart from, workpiece i5. A plurality of spray nozzles 5l, spaced apart Y from each other, are mounted on manifoid 50, and said nozzles 51 protrude and point into coating chamber 30. Said spray nozzles 51 are preferably directed toward workpiece 15, and although any angular mounting of said nozzles 51 on manifold 50 may be used, it has been found that a 15 angular mounting produces satisfactory results. However, if it is desired to let the powder or dust hereinafter mentioned, fall on workpiece 15 by gravity, said nozzles 15 may be directed about grid 40 so that said powder or dust may pass downwardly through said grid wires 43. Furthermore, although any number of spray nozzles 51 may be used, eight (8) nozzles 51 are preferred.

Spray nozzles 51 may be equipped with hoods 52 to direct the powder or dust being discharged from said spray nozzles 51 (in the manner hereinafter described) toward workpiece 15.

Attached to manifold t) is a pipe or hose 53. Said pipe or hose 53 is also connected to a feeder member 60, and pipe or hose 53 provides a passage for the powder or dust from feeder member 60 to manifold 50, and hence to nozzles 51.

Also mounted on feeder member 6i) is an air supply line 61, leading from a suitable supply of air Linder pressure (not shown) to said feeder member 6i), said air supply line 61 being disposedso that air under pressure will be mixed with the powder or dust in pipe or hose 53 and will aid in discharging said powder or dust from manifold 50 and nozzles 51 into coating chamber 3) in evenly distributed atomized form, and, if desired, at a velocity to maintain said powder or dust in suspension in such atomized form. To aid in establishing and maintaining the proper amount and Velocity of air to accomplish said purposes, a regulator valve 62 may be interposed on air line 61.

A powder or dust hopper 79, containing a quantity of powder or dust 71, is disposed adjacent to feeder member 60, and in order to insure proper atomization of powder or dust 71, a vibrator 72 is mounted on said hopper 70 and disposed so as to disperse said powder or dust 71 as it flows from said hopper 70. A passage line 73 is mounted on said vibrator 72 and leads from vibrator 72 to feeder member 60.

A dust remover bin S0 is disposed adjacent to coating chamber 30, and a passage line 81 leads from the interior of chamber 30 to said bin S0.

If it is desired to cool workpiece 15, after it has passed out of coating chamber 30, a cooling chamber 90 may be disposed adjacent to conveyor 32 so as to be available to receive, cool and discharge said workpiece 15. In actual operation it has been found that a quenching device performs satisfactorily as a cooling chamber, but any other form of cooling chamber, such as an air-cooled chamber, will accomplish satisfactory results, no claim being made to a cooling chamber, or any specific form of cooling, as a necessary element of the invention.

In the alternative form of the invention illustrated in FIGURE 6 of the drawings, in order to coat workpieces other than elongate workpieces, and to keep said workpieces properly grounded while they are passing through coating chamber 3), a different form of grid and manifold is provided, and a new grounding arrangement is introduced.

In said alternative form, a workpiece is suspended on a conductor cable 101, which in turn is suspended from a trolley 102 mounted on a longitudinally disposed and suitably grounded conductor cable 163 (the ground means not being illustrated in said FIGURE 6). In lieu of grid 40, which surrounds workpiece 15, in the alternative form of the invention a U-shaped grid 11@ is provided, and said grid 110 is suitably connected to a source of electric power (not shown). Said grid 110 has an entry end 111 and a discharge end 112, and also has vertical side members 113 and 11d. Vertically disposed on Said side members 113 and 114 are grid wires 115, spaced apart from and in parallel relationship to each other. Clear passage of workpiece 190 and cable 191 between side members 113 and 114 is provided. The disposition of grid wires 115 relative to each other and to workpiece is substantially similar to the disposition of grid wires 43 relative to each other and to workpiece 15 in the preferred form of the invention.

1n said alternative form, a spray nozzle manifold 120, also U-shaped, is mounted on or adjacent to discharge end 112 of grid 110, and a plurality of spray nozzles 121, spaced part from each other, are mounted on manifold 12d protruding from and pointing into the center of coating chamber 30 in which grid 11i) is mounted. Said spray nozzles 121 are directed toward workpiece 100.

In operation, an e.ectrically conductive workpiece 15, or 100 as the case may be, is heated in furnace 10 to a desired degree. Said workpiece 15, or 100, is then removed from the furnace and conducted into the coating chamber 39. During its entire time in coating chamber 30, workpiece 15, or 109, is constantly electrically grounded as hereinabove described.

The workpiece is disposed in coating chamber 30 in spaced relationship to grid 4G and grid wires 43, or grid 119 and grid wires 115 in the alternative form of the device. An electric current is introduced into said grid wires 43, or said grid wires 115.

Simultaneously the powder of dust which is to be used to coat workpiece 15, or workpiece 100, is atomized and introduced in suspended form into coating chamber 30 by way of manifold 5?, or 120, and spray nozzles 51, or 121, and said powder or dust may be maintained in suspension in said chamber 30 by means of the introduction of air, under pressure, through air supply line 61, if desired.

An electric ow will thus be established between grid wires 43, or grid wires 115, to the particles of said powder or dust in suspension in said chamber 30, and the particles of dust or powder, so electrically charged, will be attracted to the grounded workpiece 15, or 100, and will form a fused coating completely surrounding the outside surface of said workpiece 15, or 100.

When workpiece 15, or 160, has been in coating chamber 3G a sutlicent time to be coated to a desired density, workpiece 15, or 10i), is removed from chamber 30, after which, if desired, it may be cooled in cooling chamber itt). Excess powder or dust in coating chamber 30 may then be drawn out of coating chamber 30 through passage line 81, into bin 30, by suction or vacuum means (not shown).

Although the invention has been herein shown and described in what is conceived to be the most practical and preferred embodiment, it is recognized that departures may be made therefrom within the scope of the invention, which is not to be limited to the details disclosed herein but is to be accorded the full scope of the claims so as to embrace any and all equivalent structures and devices.

What is claimed is:

1. An apparatus for externally coating objects, which comprises: a furnace for preheating an electrically conductive workpiece; means for conveying said preheated workpiece from said furnace and electrically grounding said preheated workpiece; a chamber separate from said furnace, adapted to receive said preheated, grounded workpiece in axially aligned, suspended position in said chamber; an electric grid for producing an electrostatic charge, said grid being mounted in said chamber so as to substantially surround said preheated, grounded workpiece in spaced relationship to said workpiece; a plurality of powder spray nozzles mounted in said chamber and disposed so as to introduce atomized powder between said grid and said workpiece and subject the particles of said powder to electrostatic charge from said grid prior to deposit of said electrostatically charged particles externally on said workpiece, said nozzles being positioned so as to direct said powder in one direction only; hoods on said nozzles disposed so as to direct said powder toward the exterior of said workpiece; and an air supply line connected to said nozzles and disposed so as to introduce air under pressure into said nozzles and blow said powder in said chamber and toward said workpiece.

2. Apparatus as dened in claim 1, wherein the means for conveying and electrically grounding said preheated workpiece is a plurality of grounded metallic rollers disposed adjacent said coating chamber so as to be in contact with said workpiece while said workpiece is disposed in said coating chamber.

References Cited in the 111e of this patent UNITED STATES PATENTS Barord Sept. 27, Barord Sept. 4, Ransburg Oct. 14, Kearsley Mar. 30, Gustin et al. Jan. 16, Ferverda Mar. 19, Gemmer July 22, Davis Jan. 19, Paton Oct. 16,

Claims (1)

1. AN APPARATUS FOR EXTERNALLY COATING OBJECTS, WHICH COMPRISES: A FURNACE FOR PREHEATING AN ELECTRICALLY CONDUCTIVE WORKPIECE; MEANS FOR CONVEYING SAID PREHEATED WORKPIECE FROM SAID FURNACE AND ELECTRICALLY GROUNDING SAID PREHEATED WORKPIECE; A CHAMBER SEPARATE FROM SAID FURNACE, ADAPTED TO RECEIVE SAID PREHEATED, GROUNDED WORKPIECE IN AXIALLY ALIGNED, SUSPENDED POSITION IN SAID CHAMBER; AN ELECTRIC GRID FOR PRODUCING AN ELECTROSTATIC CHARGE, SAID GRID BEING MOUNTED IN SAID CHAMBER SO AS TO SUBSTANTIALLY SURROUND SAID PREHEATED, GROUNDED WORKPIECE IN SPACED RELATIONSHIP TO SAID WORKPIECE; A PLURALITY OF POWDER SPRAY NOZZLES MOUNTED IN SAID CHAMBER AND DISPOSED SO AS TO INTRODUCE ATOMIZED POWDER BETWEEN SAID GRID AND SAID WORKPIECE AND SUBJECT THE PARTICLES

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