US3245828A

US3245828A - Method for electrostatic coating

Info

Publication number: US3245828A
Application number: US232380A
Authority: US
Inventors: Iwata Harukichi
Original assignee: Iwata Tosoki Kogyo KK
Current assignee: Iwata Tosoki Kogyo KK
Priority date: 1962-01-31
Filing date: 1962-10-23
Publication date: 1966-04-12
Anticipated expiration: 1983-04-12

Description

A ril 12, 1966 HARUKICHI IWATA 3,245,328

METHOD FOR ELECTROSTATIC COATING Filed 001;. 23, 1962 FIG] INVENTOR.

BY W/ M 4 M PM,

United States Patent 3,245,828 METHOD FOR ELECTROSTATIC COATING Harukichi Iwata, Tokyo, Japan, assignor to Iwata Tosoki Kogyo Kabushiki Kaisha, Tokyo, Japan Filed Oct. 23, 1962, Ser. No. 232,380 Claims priority, application Japan, Jan. 31, 1962, 37/ 3,208 3 Claims. (Cl. 117-934) This invention relates to a method for coating electrostatically a thing to be coated by using a common spray gun which atomizes a coating material by compressed air.

A system of an electrostatic atomization coating was already proposed in the past in which a coating material was mechanically atomized by a high liquid pressure, a centrifugal force, compressed air, etc.; an atomized coating material was injected into an electrostatic field; and a coating was carried out electr-ostatically by a potential difference provided between a spraying apparatus and a thing to be coated.

In an electrostatical coating, by using a common spray gun, a coating eiliciency is very low because the energy held by an atomized particles group is large and accordingly there is a great defect for practical use.

However, in using a common spray gun, there are many advantageous points such asit is easy to handle in view of its far and wide spread; it is easily possible to inject a coating material only when the thing to be coated appears just in front of a spraying apparatus by using an automatic trigger device of a spray gun; and it is also possible to spray a coating material mechanically which is ditficult to spray by only an electrostatic force.

Generally, the coating power of atomized particles of a coating material under the operation of an electrostatic voltage is very small contrary to our eXpectation, and, even if a speed held by sprayed particles is larger even by a very little, a coating efficiency is effected greatly.

The present invention improves the defects in the past 'by obtaining a composite speed of atomized particles groups of a reduced speed by jetting and causing collision under a relatively low pressure from two spray guns located at symmetrical places at a proper angle which can reduce the speed of sprayed particles as a means of decreasing the energy held by sprayed particles groups to be jetted.

It is understandable that a jetting energy from the two spray guns located at symmetrical places on a straight line is extinguished by the jetting of spray guns holding identical energies given from symmetrical places.

This invention is based on decreasing speed of injection from said symmetrical places, and the energy held by a sprayed particles group after collision caused by injection from the spray guns located at symmetrical places on a straight line is the smallest, but a mist to be shaped cannot actually be advantageous for practical use.

Under the present invention, an oval-shape mist is obtained 'by giving spray guns which are located at symmetrical places, a proper angle by which the speed of sprayed'particles groups can be decreased.

This invention is characterized by decreasing the speed of sprayed particles groups, and the injected atomized particles groups are further subdivided on the occasion they are made to collide with each other, and, as a result, fixing efliciency of a coating material is increased. As mentioned above, the speed of the mists which collide with each other after being injected from spray guns located at symmetrical places on a straight line becomes almost to be zero, and, from this fact, if the nearer the angles of injection of these two spray guns which make the mists collide with each other are made to approach 3,245,828 Patented Apr. 12, 1966 'ice to a straight line, the slower the speed of these mists becomes, and to the contrary, if the greater these angles are separated, the faster the speed of these mists becomes; and if the angle of injection becomes smaller than 120, the speed of mists becomes larger than that in the case of one spray gun. Therefore, the angle of injection should not be made smaller than 120.

The principal efficacy by this invention is, by using two common automatic spray guns, in coating very efficiently even dented faces, caved-in faces, etc. by having injected particles groups cross and collide with each other and by preparing an oval spray particles group of a slow speed.

Now the electrostatic coating method according to the present invention will be described with reference to the illustrated embodiments in the accompanying drawing wherein,

FIG. 1 shows an electrostatic coating system which uses one embodiment of subject invention, and

FIG. 2 is a perspective View of a spraying apparatus excluding a thing to be coated.

In FIG. 1 and FIG. 2, the atomized particles groups injected from automatic spray guns 1 and 1 located at symmetrical places and supported by stay 4 cross and are caused to collide with each other at cross angle 2 which can reduce the speed of the sprays, the speed of the atomized particles group is reduced and they become an oval particles group and is coated on thing 5 to be coated. Cross angle 2 can be changed by adjusting

butterfiy nuts

10 and 10, and better results can be obtained by adjusting said cross angle 2 to a smaller one in the case the shape of the thing to be coated is complicated, and in the case the shape of the thing to be coated is a relative-1y simple one, to a larger one.

Automatic spray guns 1 and 1' are ones commonly used, and compressed air enters from compressed air source 7 through air hoses 12 and 12' into compressed

air introduction holes

8 and 8; the opening and closing of a needle valve of a spray gun is carried out and the starting and closing of injection can be carried out speedily by a cam device or an electromagnetic device (not shown in the drawings). At the same time, compressed air is used for atomization of a paint; it is led from compressed

air introduction holes

8 and 8 to

air caps

13 and 13 at the end portion of said automatic spray guns and is injected from central portions 11 and 11' and thereby the paint is atomized.

The pressure of the compressed air used for subject apparatus is not limited under present invention, but tests show that it is within the scope of 0.5-1.5 kg./cm. and the quantity of the compressed air used is around 1./min.

Automatic spray guns 1 and 1' are supported by stay 4; stay 4 is fixed to stand 9 and the fixing place of stay 4 can be changed up and down and the height of injection can be adjusted freely. Of course, it is possible to fix two or three sets of automatic spray guns to stand 9.

The paint which is divided into two directions from paint container 3, is led to said two spray guns 1 and 1 through paint hoses 14 and 14' and is injected from the spray guns 1 and 1 in the same quantity and it collides with each other; but even in case the paint is led from only one hose, it is possible to practice the purpose of this invention. However, in this case, the quantity of paint to be injected is reduced in comparison with the quantity of air to be injected, and preferable results cannot 'be obtained, resulting in a drop of an atomization efficiency. Therefore, the paint should be injected in the same quantities from the two spray guns 1 and 1'.

According to the shape of the thing to be coated, it is necessary to adjust the quantity of the paint to be injected and a pattern form of mist, and the quantity of 3 paint to be injected can be adjusted simply by turning paint adjusting knobs 15 and 15'.

A pattern shape can be changed by changing a cross angle or spray air pressure, or by exchanging an injection nozzle.

A pole of stand 9 is made of an insulating material, and electricity which is generated from high voltage generator 6 is transmitted to stay 4 which is made of an electricity conducting material and automatic spray guns 1 and 1', and atomized particles are injected in an electrostatic field formed between a spraying mechanism and thing to be coated 5 which is grounded, and coated electrostatically on thing to be coated 5 by the operation of an electrical field.

Under the present invention, it is possible to carry out an electrostatic coating of good coating efliciency in which dented faces and caved-in faces are well coated, by preparing an electrostatic coating apparatus which can be practically used rather simply by employing two automatic spray guns which are commonly used.

What is claimed is:

1. A method of electrostatically coating an object by means of a stream of compressed gas atomized coating material directed generally toward an object to be coated, comprising directing two separate substantially equal streams of compressed gas atomized coating material toward and against each other from two spaced locations symmetrically disposed on opposite sides of a plane extending from the object to be coated and between said spaced locations, said separate streams being at equal angles to said plane and being at an angle to each other which is from 180 to as measured on the sides of the streams remote from the object to be coated, and while directing said streams, maintaining an electrostatic field between the object and the said spaced locations, whereby the colliding separate streams are combined into said stream directed generally toward the object and said stream moves toward the object with a velocity from a velocity equal to the velocity of the separate streams to a velocity imposed solely by the electrostatic field.

2. A method as claimed in claim 1 in which automatic spray guns are used as the sources of the separate streams of atomized coating material, and the step of maintaining the electrostatic field comprises insulating the spray guns from support means therefor charging a high voltage on said spray guns, and grounding the object to be coated.

3. A method as claimed in claim 2 in which the automatic spray guns are adjustably mounted on the supports therefor, whereby the angle between the separate streams can be varied.

References Cited by the Examiner UNITED STATES PATENTS 2,428,991 10/ 1947 Ransburg 11793.4

JOSEPH B. SPENCER, Primary Examiner.

RICHARD D. NEVIUS, Examiner.

Claims

1. A METHOD OF ELECTROSTATICALLY COATING AN OBJECT BY MEANS OF A STREAM OF COMPRESSED GAS ATOMIZED COATING MATERIAL DIRECTED GENERALLY TOWARD AN OBJECT TO BE COATED, COMPRISING DIRECTING TWO SEPARATE SUBSTANTIALLY EQUAL STREAM OF COMPRESSED GAS ATOMIZED COATING MATERIAL TOWARD AND AGAINST EACH OTHER FROM TWO SPACED LOCATIONS SYMMETRICALLY DISPOSED ON OPPOSITE SIDES OF A PLANE EXTENDING FROM THE OBJECT TO BE COATED AND BETWEEN SAID SPACED LOCATIONS, SAID SEPARATE STREAMS BEING AT EQUAL ANGLES TO SAID PLANE AND BEING AT AN ANGLE TO EACH OTHER WHICH IS FROM 180* TO 120* AS MEASURED ON THE SIDES OF THE STREAMS REMOTE FROM THE OBJECT TO BE COATED, AND WHILE DIRECTING SAID STREAMS, MAINTAINING AN ELECTROSTATIC FIELD BETWEEN THE OBJECT AND THE SAID SPACED LOCATIONS, WHEREBY THE COLLIDING SEPARATE STREAMS ARE COMBINED INTO SAID STREAM DIRECTED GENERALLY TOWARD THE OBJECT AND SAID STREAM DIRECTED GENERALLY TOWARD THE OBJECT AND SAID STREAM MOVES TOWARD THE OBJECT WITH A VELOCITY FROM A VELOCITY EQUAL TO THE VELOCITY OF THE SEPARATE STREAMS TO A VELOCITY IMPOSED SOLELY BY THE ELECTROSTATIC FIELD.