US3667676A

US3667676A - Apparatus for electrostatically coating powders on a workpiece

Info

Publication number: US3667676A
Application number: US886170A
Authority: US
Inventors: Tamotsu Watanabe; Fumio Onoue
Original assignee: Nippon Kogei Kogyo Co Ltd
Current assignee: Nippon Kogei Kogyo Co Ltd
Priority date: 1969-03-26
Filing date: 1969-12-18
Publication date: 1972-06-06
Anticipated expiration: 1989-06-06
Also published as: DE1962472B2; FR2033960A5; DE1962472A1; GB1255090A

Abstract

Apparatus for electrostatically coating powders on a workpiece from a rotating injection head having a plurality of nozzles disposed outwardly from the axis of the rotating injection head and rotatably mounted on the injection head for dispersing the powders. Each of the nozzles has a curved or bent portion, such that the distance between the nozzle and the axis of the rotating injection head and the angle from which the powders are dispersed are variable. The apparatus is utilized for performing a method of electrostatically coating powders on a workpiece comprising the steps of dispersing the powders in such a manner that the angle at which the powders are dispersed is variable. The apparatus also comprises a mixer connected to a source of compressed air for supplying the powders from a source through a pipe into the injection head with an air stream fed from a compressed air source, a controller for controlling the powder supply from the powder source to the injection head, and a constant powder supplying means for supplying the powders from the powder source to the mixer, whereby the powder supply is controlled by the powder supply means.

Description

United States Patent Watanabe et a1.

[ 1 June 6,1972

[72] Inventors: Tamotsu Watanabe; Fumio Onoue, both of Tokyo, Japan [73] Assignee: Nippon Kogei Kogyo Co., Ltd.

[22] Filed: Dec. 18, 1969 [21] Appl. No.: 886,170

[30] Foreign Application Priority Data Mar. 26, 1969 Japan ..44/22366 June 11, 1969 Japan.... ...44/45364 June 11, 1969 Japan ..44/45365 [52] US. Cl. ..239/15, 239/3 [58] Field of Search ..239/3, 15, 256, 225; 222/70 [56] References Cited UNITED STATES PATENTS 2,998,197 8/1961 Kachergis ..239/256 X 3,498,540 3/1970 Adams ..239/l5 3,144,209 8/1964 Griffiths ..239/l5 3,363,806 1/1968 Blakeslee et a1. ..222/70 FOREIGN PATENTS OR APPLICATIONS 1,486,650 5/1967 France ..239/15 Primary Examiner-M. Henson Wood, Jr. Assistant Examiner-Thomas C. Culp, Jr. Attorney-Oblon, Fisher & Spivak [57] ABSTRACT Apparatus for electrostatically coating powders on a workpiece from a rotating injection head having a plurality of nozzles disposed outwardly from the axis of the rotating injection head and rotatably mounted on the injection head for dispersing the powders. Each of the nozzles has a curved or bent portion, such that the distance between the nozzle and the axis of the rotating injection head and the angle from which the powders are dispersed are variable. The apparatus is utilized for performing a method of electrostatically coating powders on a workpiece comprising the steps of dispersing the powders in such a manner that the angle at which the powders are dispersed is variable. The apparatus also comprises a mixer connected to a source of compressed air for supplying the powders from a source through a pipe into the injection head with an air stream fed from a compressed air source, a controller for controlling the powder supply from the powder source to the injection head, and a constant powder supplying means for supplying the powders from the powder source to the mixer, whereby the powder supply is controlled by the powder supply means.

5 Claims, 11 Drawing Figures 1 PATENTEDJUH 6 m2 SHEET 10F 3 3, 667. 676

I N VEN'IY JRv PATENTED H 61972 SHEET 2 0F 3 IN VENTOR.

APPARATUS FOR ELECTROSTATICALLY COATING POWDERS ON A WORKPIECE BACKGROUND OF THE INVENTION This invention relates to apparatus and method for electrostatically coating powders on a workpiece, and more particularly, to a novel rotating injection head having a plurality of nozzles for electrostatically injecting the powders in such a manner that the angle at which the powders are dispersed from the nozzle is variable.

It has been found that in electrostatically coating materials onto a workpiece, it is preferable to use powdered coating materials as opposed to liquid coating materials because of the dangers involved, such as potential fire hazards, poison and pollution problems created due to the usage of solvents in liquid coating materials. It has further been found advantageous to utilize powdered materials as opposed to liquid materials in that the handling and expense resulting from the necessity to eliminate the above-noted dangers when using liquid materials are eliminated. Moreover, powdered materials need not be handled as carefully as liquid materials, since excess powdered materials which have been scattered may be again collected so as to be reused, resulting in economic and safe electrostatic coating on a workpiece.

In order to maintain the economic advantages of coating with powdered materials, it is required that the powdered materials be uniformly coated onto the workpiece and that the powders be dispersed from a spray gun in a pattern which is consistent to the size and shape of a particular workpiece. To satisfy these requirements, it is preferable to provide an injection head or spraying head for adjustably dispersing the powders through a proper and desirable range with respect to spraying area corresponding to the size and shape of the workpiece being coated so as to avoid the spattering of the powders outside of the workpiece as much as possible, and also to uniformly coat the powders onto the surface of the workpiece. In order to uniformly coat the powders onto the workpiece, the powdered materials must be spattered uniformly onto the workpiece, and in order to achieve uniformity, the powders must be fluidized so as to be dispersed uniformly onto the workpiece.

Heretofore, there has been utilized a method of fluidizing powders consisting of the steps of blowing a compressed air from a source of compressed air through a supply pipe into a tank containing the powders therein and connected through a supply pipe to a powder injection head and at the same time feeding an air-powder mixture by means of the air through the supply pipe to the injection head. Another prior art method of fluidizing powders consisted of the steps of feeding air from a source of compressed air through a supply pipe into the bottom of a fluidizing tank containing the powders therein and connected through a supply pipe to a powder injection head so as to form a fluidizing layer of powders and supplying the powders to the injection head by means of an air blowing pipe provided in the fluidizing layer.

In order to uniformly coat large articles with a high degree of efficiency and with a high quality and uniformity, the entire articles must be uniformly coated by the powder injection heads utilizing an economical method. Furthermore, in order to uniformly coat a multiplicity of articles using mass production techniques, the injection head and supply means for the powdered materials must preferably handle a constant volume per unit time and must control the supply of powders so as to coat a predetermined thickness of the powders onto the workpieces. In order to supply the powders from a limited number of supply means to a number of powder injection heads, the amount of powder supplied should preferably be controlled so as to produce a desired thickness of coating on the articles to be coated with a smooth continuous operation of the coating.

The use of powdered coatings does not require a high speed air stream, since the air stream carries the powders therewith as opposed to liquid coating which requires a high speed atomizing spray for liquid coating materials resulting in a disturbance of the Coulomb's forces for electrostatically coating materials onto a workpiece. Liquid coating also adversely affects the absorbing action by an electrostatic field. In order to obtain a superior electrostatic coating effect with the use of powder coating, relatively large injection patterns should be provided with care being taken not to overcoat or coat too thickly onto the surface.

SUMMARY OF THE INVENTION The present invention contemplates the elimination of the aforementioned disadvantages of conventional apparatus for electrostatically coating powders onto the workpiece and has an object thereof to provide a powder injection head of an electrostatic coating apparatus adapted to uniformly spatter powder onto the workpiece or a plurality of workpieces in response to the size and shape of the workpieces within a proper range and to electrostatically coat the powders onto the workpieces in such a manner that the angle of injection of the powders from a plurality of nozzles which are provided outwardly of the axis of a rotating injection head is variable.

Another object of the present invention is to provide apparatus for electrostatically coating powders onto a workpiece wherein the apparatus comprises a rotary powder injection head, a powder-air mixer for mixing the powders with compressed air supplied from a source of compressed air, and a constant powder supplying means for supplying the powders in a constant amount in response to the size and shape of the article to be coated in a uniform thickness.

According to a further object of the present invention, there is provided a method of electrostatically coating powders onto a workpiece which comprises the steps of injecting the powders through at least one nozzle having a curved or bent portion and mounted on a rotary head in such a manner that the distance between the axis of the rotary head and the nozzle is variable so as to adjust the angle of injection of the nozzle.

It is a further object of the present invention to provide a method of electrostatically coating powders onto a workpiece in such a manner that the angle of injection of the powders is variable in response to the size and shape of the workpiece.

It is a still further object of the present invention to provide apparatus for electrostatically coating powders onto a workpiece from a rotating injection head having a plurality of nozzles for uniformly coating the workpiece.

It is a still further object of the present invention to provide apparatus for electrostatically coating powders onto a workpiece so as to control the supply amount of the powders to accomplish a desired thickness of coating on the articles to be coated from a limited number of supply means to a number of powder injection heads.

It is a still further object of the present invention to provide apparatus for electrostatically coating powders onto a workpiece which is so constructed as to obtain a superior electrostatic coating efiect such that the relatively large injection pattern may be provided as long as the powders are not too thickly coated onto the surface.

According to one aspect of the present invention, there is provided a rotary powder injection head for electrostatically coating powders onto a workpiece which comprises at least one nozzle having a curved portion and mounted rotatably to a fitting on the injection head such that the distance between the axis of the head and the injection port of the nozzle can be varied so as to vary the angle of injection of the powders from the nozzle.

BRIEF DESCRIPTION OF THE DRAWINGS Other objects, features and advantages of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a side view partially in section of an apparatus for electrostatically coating powders onto a workpiece as constructed in accordance with the present invention;

FIG. 2 is an enlarged side view partially in section of a powder injection head portion of the apparatus shown in FIG.

FIG. 3 is an enlarged end view of the injection head portion of FIG. 2;

FIGS. 4A and 4B are schematic side views of conventional powder supply means;

FIG. 5 is a side view partially in section of powder supply means constructed according to the present invention;

FIG. 6 is a partial plan view of the powder supply means shown in FIG. 5;

FIG. 7 is a sectional view of the powder supply means taken along line VII-,VII of FIG. 6;

FIG. 8 is a front view of the powder supply means shown in FIG. 6;

FIG. 9 is a plan view of the powder supply means shown in FIG. 7; and,

FIG. 10 is a side view of the powder supply means shown in FIG. 7.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIGS. 1 through 3, which illustrates one embodiment of the present invention including apparatus for electrostatically coating powdered materials onto a workpiece and comprising a powder supply device 1 for supplying powdered coating materials by means of an air stream, a flexible supply line 2 connected to the powder supply device 1, a rotary head 5 rotatably mounted to one end of the apparatus and having a plurality of injection nozzles 3 attached thereto by means of fittings 4, a tubular conduit 6 of insulating material with a portion thereof of electroconductive material at one side of the rotary head 5 and connected through a coupling 7 to the flexible supply line 2 for feeding the powdered materials from the powder supply device 1 to the injection nozzles 3. The apparatus further comprises an electric motor 8 for driving the rotary head 5 through the tubular conduit 6 and a ho]- low pulley 80 mounted on the conduit 6 with a belt 8b wound thereon. Bearings 9a and 9b support the tubular conduit 6 at both ends. Supporting means 100 and 1012 are mounted at both ends of the tubular conduit 6 for supporting the bearings 9a and 9b and tubular conduit 6. A tubular support member 11 is mounted coaxially with the tubular conduit 6 between the supporting members 10a and 10 b for isolating a high voltage from the ground. A high voltage power supply 12 is electrically connected through a cable 13 to electroconductive supporting member 100 and bearing 9a and the electroconductive portion of the conduit 6 to the rotary head 5 for producing an electric field between the ground and the article 14 to be coated.

Referring now in particular to FIGS. 2 and 3, which illustrate an enlarged rotary head portion of the apparatus including three injection nozzles 3 mounted on the rotary head 5 by means of fittings 4 such that each injection port 15 of the in jection nozzles 3 is disposed outwardly from the rotating axis of the rotary head 5. The rotary head 5 comprises an inlet port 16 for the powder supplied thereto by powder supply device 1 through a conduit 6. The powder is fed from the inlet port 16 through a passage 17 of the injection nozzle 3 to the injection port 15, at which point it is released to the atmosphere. Since the rotary head 5 is driven to be rotated by a drive motor 8, the powder is uniformly injected from the nozzles 3 of the rotary head 5.

The nozzles 3 mounted on the rotary head 5 may be rotated by loosening the fittings 4 as shown by the broken lines in FIG. 2 such that the injection range of the powder from the nozzles 3 can be adjusted in response to the size and shape of the article 14 being coated. The adjustability in spray area is a result of the ability to twist the nozzles 3, since the distance between the axis of the rotary head 5 and the injection port 15 of the nozzle 3 may be varied and the angle of injection of the powder may also be varied.

It is understood that the number of nozzles may be increased or decreased in response to the amount of powder to be utilized per unit time, and that the curved or bent portion A of the nozzle 3 is provided so as to enable the distance between the axis of the rotary head and the injection port to be varied thus varying the angle of injection of the powdered materials.

It should also be understood that the distance between the axis of the rotary head and the injection port of each noule mounted on the rotary head may be different for each nozzle. thus giving the capability of a large range of spray patterns in response to the size and shape of the particular article to be coated.

In order to avoid the danger of an electric shock caused by the high voltage applied to the rotary head, the nozzle and r0 tary head may be formed of a resistive material such as a semiconductor or may be formed with an insulating material having on the surface thereof a film of resistive material such that the high voltage applied to the nozzle and rotary head may be substantially reduced in response to the resistance of the material.

It is to be understood that the curved portion A of the nozzle attached on the rotary head may be in any configuration, including a bend having a relatively large radius of curvature such that the powder does not undesirably build up in too large of a coating on the surface of the passage of the nozzle.

It is also to be understood from the foregoing description that since the nozzle is adjustable to vary the distance between the axis of the rotary head and the injection port of the nozzle, the powder may be spattered uniformly on the articles to be coated in response to the size and shape of the articles, whereby the coating may be achieved economically and uniformly.

Furthermore, the conduit may not always be mounted coaxially with respect to the insulating member, but may be supported at both ends by the insulating member.

The drive motor may be an air motor in order to lighten the overall weight for use as a relatively portable handy powder injection gun.

In order to clearly understand the apparatus for performing the fluidization of the powdered materials, the conventional powder supplying devices will now be described with respect to FIGS. 4A and 48. One such powder supplying device shown in FIG. 4A comprises a powder injection head l8 connected through a supply line 19 to a tank 20 containing the powders therein, and a source of compressed air 21 connected through a supply line 22 to the tank 20 for blowing the compressed air into the tank 20 so as to fluidize the powders.

In operation of the powder supplying device, the powders accumulated in the tank 20 are fluidized by blowing the compressed air from the source of the compressed air 21 through the line 22 to the tank 20 to feed the powder injection head 18.

Another powder supplying device, as shown in FIG. 4B, comprises a powder injection head 23 connected through a supply line 24 to a fluidizing tank 26 containing the powders therein, a source of air supply 27 connected through a supply line 28 to the bottom of the tank 26 for feeding the air from the source 27, and an air blowing pipe 29 provided in the fluidizing layer of the powder for supplying the fluidized powder through the supply line 24 to the powder injection head 23.

In operation of the powder supply device as just described, the powder is formed as a fluidized layer in the tank 26 by feeding the air from the source 27 through the supply line 28 into the bottom of the tank 26 and the fluidized powder is then fed through the supply line 24 to the powder injection head 23.

To uniformly coat the large articles to be coated with a high efficiency and high quality, as well as uniformly coating the entire article in an economic manner as well as to uniformly coat a multiplicity of articles with mass production techniques, the injection head in the supplying device for suplying the powders to the injection head should preferably handle a constant volume per unit time and should also control the supply volume of the powders so as to coat a predetermined thickness of the powders onto the workpiece. In order to supply the powders from a limited number of supplying devices to a number of powder injection heads, the supply volume of the powder should preferably be controlled so as to accomplish the desired thickness of coating on the article to be coated with a smooth and continuous operation.

To accomplish the aforementioned advantages and requirements for coating articles, one embodiment of a powder supplying device in accordance with the present invention will now be described in connection with FIGS. 5 through of the drawings. The apparatus for electrostatically coating powders onto a workpiece in accordance with the present invention essentially comprises the injection head portion as heretofore described with respect to FIGS. 1 through 3, a powder-air mixer B and a constant powder supplying device C.

The constant powder supply device C comprises a hopper 30 for containing the powders 29 therein, a trough 31 mounted beneath the hopper 30, a vibrator 33 mounted beneath the trough 31 and connected to a supply controller 32 electrically connected to a source of power (not shown), and a supply controlling member 34 provided beneath the terminal portion of trough 31.

The powder-air mixer B provided beneath the terminal portion of trough 31 of the constant powder supply device C comprises a source of compressed air 35 connected to an air supply pipe 36 which is fed to the powder-air mixer B and a powder-air mixture supply line 37 which is connected from the powder-air mixer B to the powder injection head (not shown). The powder-air mixer B further comprises, as shown in FIG. 8, a powder receiving inlet 38, an air inlet 39, a powder-air mixture supply port 40, an air injection port 41 communicating with the air inlet 39, and an air introducing inlet 42 communicating with the powder-air mixture supply port 40. As shown in FIG. 10, the supply control member 34 is so disposed above a plurality of mixers provided under the end of the trough as to rotate around shaft 43 thereof, as illustrated by arrows E and F in FIG. 7, so as to control the distribution of the powders falling onto the powder mixer by adjusting the position relative to the trough at the uppermost end. As shown in FIG. 9, in order to measure the amount of powder dispensed per unit time onto the mixers, the mixers may be mounted integrally on a shaft 44 at their center such that the mixers are rotatable around the shaft 44 as a unit, as shown by arrow G, and a storage box 45 (FIG. 10) may be mounted for containing the mixers so as to be removable under the end H of the trough when rotated.

In operation of the described embodiments, the powders, such as, for example, polyethylene powders, contained within the hopper, advance on the trough 31 in the direction shown by arrow D by means of the vibration having an amplitude defined by the vibrator which is driven by electric power controlled in accordance with the supply controller so as to supply the mixer at a constant rate. The powder thus supplied to the mixer, is fed through supply line 37 by the air supplied to the nozzle mounted on the rotary head through the insulated rotary supply conduit 6 of the powder injection head portion onto the article to be coated.

The injected powder is charged by a high voltage such that the powders are electrostatically coated onto the article by the attraction created due to a differential potential maintained between the article and the injection head.

The supply control member 34 may be a chute extending from the trough 31 to a number of mixers B, such that the control member 34 will provide material in response to the number of mixers connected to the powder injection head.

The storage box 45 is preferably divided into a number of segments equal to the number of mixers such that in response to the position of the powder supply controller, the distribution of the powder can be easily measured. In such a structure, the supply lines may be of flexible material for supplying the powders and the air.

It is understood from the foregoing description that since this arrangement supplies the powders from the constant supply device to the mixers, regardless of the amount of powders dispensed, a constant amount of powders may be supplied onto the article to be coated so as to coat the article with an even thickness.

It is also to be understood that by adjustment of the supply control member, the amount of powder supplied to the powder injection head is controlled such that even if only one powder supply device is utilized, the injected amount of powder from multiple powder injection heads is controlled in response to the size and shape of the article.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

l. A rotary powder injection head for apparatus for electrostatically coating powdered materials onto a workpiece comprising at least one noule having a bent portion and rotatably mounted by means of a fitting on said injection head such that the distance between the axis of rotation of said head and the injection port of said nozzle is variable whereby the injection angle of said powder material is variable, powder supply means for supplying powder coating materials by means of an air stream, a flexible supply line connected to said powder supply means, a plurality of injection nozzles attached to said rotary head, a tubular conduit of insulating material having the end portion thereof of electroconductive material, and connected through a coupling to said flexible supply line for feeding said powder from said powder supply means to said injection nozzles, a drive motor for driving said rotary head through said tubular conduit, a hollow pulley mounted on said conduit and having a belt wound thereon, bearings for supporting said tubular conduit at both ends, supporting means mounted at both ends of said tubular conduit for supporting said bearings and said tubular conduit, a tubular supporting member mounted on said tubular conduit between said supporting members for isolating high voltage from ground, a high voltage power supply electrically connected through a cable, and means for producing an electric field between the ground and the article to be coated.

2. A rotary powder injection head as set forth in claim 1, wherein said rotary head comprises an inlet port for receiving said powders from said powder supply means through said conduit and a passage in said injection nozzle to said injection port.

3. Apparatus for electrostatically coating powdered materials onto a workpiece comprising a rotary powder injection head, a powder-air mixer for mixing said powders with compressed air supplied from a source of compressed air and a constant powder means for supplying said powders at a constant rate in response to the size and shape of the article to be coated so as to provide an even coating of said powdered materials onto said article, wherein said constant powder supply means comprises a hopper for containing the powders therein, a trough mounted beneath said hopper, a vibrator mounted beneath said trough and connected to a supply rate controller electrically connected to a source of power, said supply rate controlling member provided beneath the terminal portion of said trough for receiving powder materials falling therefrom.

4. Apparatus as set forth in claim 3, wherein said powder-air mixer comprises a source of compressed air connected through an air supply pipe to said powder-air mixer and a powder mixture supply line connected from said powder-air mixer to said powder injection head, a powder receiving inlet, an air inlet, and a powder-air mixture supply port, an air injection port communicating with said air inlet, and an air introducing inlet communicating with said powder-air mixture supply port.

5. Apparatus as set forth in claim 4, wherein said supply rate controlling member is so disposed above a plurality of mixers provided beneath the terminal end of said trough as to rotate about a shaft to control the distribution of powder falling on said mixer by adjusting the position relative to said trough at the upper end thereof.

k 0 III k

Claims

1. A rotary powder injection head for apparatus for electrostatically coating powdered materials onto a workpiece comprising at least one nozzle having a bent portion and rotatably mounted by means of a fitting on said injection head such that the distance between the axis of rotation of said head and the injection port of said nozzle is variable whereby the injection angle of said powder material is variable, powder supply means for supplying powder coating materials by means of an air stream, a flexible supply line connected to said powder supply means, a plurality of injection nozzles attached to said rotary head, a tubular conduit of insulating material having the end portion thereof of electroconductive material, and connected through a coupling to said flexible supply line for feeding said powder from said powder supply means to said injection nozzles, a drive motor for driving said rotary head through said tubular conduit, a hollow pulley mounted on said conduit and having a belt wound thereon, bearings for supporting said tubular conduit at both ends, supporting means mounted at both ends of said tubular conduit for supporting said beArings and said tubular conduit, a tubular supporting member mounted on said tubular conduit between said supporting members for isolating high voltage from ground, a high voltage power supply electrically connected through a cable, and means for producing an electric field between the ground and the article to be coated.