US3008645A

US3008645A - Electrostatic spraying apparatus

Info

Publication number: US3008645A
Application number: US786120A
Authority: US
Inventors: Morel Roger; Point Marcel
Original assignee: Sames Mach Electrostat
Current assignee: Machines Electrostatiques SA
Priority date: 1958-01-14
Filing date: 1959-01-12
Publication date: 1961-11-14
Anticipated expiration: 1978-11-14
Also published as: FR1216250A; CH348087A; GB851092A

Description

Nov. 14, 1961 Filed Jan. 12, 1959 R. MOREL ET AL ELECTROSTATIC SPRAYING APPARATUS 2 Sheets-Sheet 1 Nov. 14, 1961 R. MOREL ET AL 3,008,645

ELECTROSTATIC SPRAYING APPARATUS Filed Jan. 12, 1959 2 Sheets-Sheet 2 lnvenlord' M K fia ELECTROSTATIC SPRAYING APPARATUS Roger Morel and Marcel Point, Grenoble, France, assignors to Societe Anonyme de Machines Electrostatiques, Grenoble, France, a French body corporate Filed Jan. 12, 1959, Ser. No. 786,120 Claims priority, application France Jan. 14, 1958 8 Claims. (Cl. 239-15) It is possible to atornize or spray a liquid by using various known means. Most of these means use mechanical forces, for example the pressure of a gas or centrifugal force. It is also possible to use electrical forces.

It has also long been known that if an object covered over by a liquid film is subjected to the action of an electric field, said liquid film tends, under the action of the electrostatic pressure, to leave the object, particularly at the places where its surface has points or more or less sharp edges.

It is further well known that it may be advantageous to combine the actions of a mechanical means and of an electrical means for atomizing liquids. Thus advantageous results may be obtained by combining the action of centrifugal force and that of an electric field, for example by rotating discs or cylinders provided with more or less sharp edges, these discs or cylinders being brought to high potentials relative to the masses in the vicinity, and the liquid to be atomized being brought, by any suitable means, on to their surfaces in order to reconstitute the liquid film as atomization proceeds.

Thus it is possible to make an atomizing device, which will be called hereinafter an electrostatic head, and which has the great advantage of not needing to employ com pressed air.

The electric field intended to cause the atomizing tends to precipitate the liquid particles on the objects in the vicinity brought to different potentials, which may be used in order to obtain certain desired effects. It is possible to improve these effects by combining the electric atomizing field with other electric fields created for example by electrodes, the location and potential of which are suitably chosen.

The present invention relates to an equipment which leaves a large measure of freedom to the operator; this result is being obtained by means of a new type of gun for the electrostatic atomizing and spraying, of liquids which does not rely upon any compressed gas in order to disperse the particles to be precipitated. This gun has a low weight and is well balanced in order to reduce to a minimum the effort of the operator.

Moreover, the inventionprovides suitable high potential supply means for this spray gun consisting of an electrostatic generator (preferably one of the types which applicants manufacture and which forms the subject of British Patent No. 637,434, No. 639,635, No. 643,579 or No. 719,687).

Said supply source is provided with a regulating device specially designed for the control of the said electrostatic machines in order to obtain a regulation of the value of the electric field as a function of the working conditions.

In order that the invention may be better understood, reference will now be made to the accompanying drawings which illustrate two embodiments of spray gun particularly intended for the atomization and spraying of paint and in which:

FIGURE 1 is a longitudinal section of one embodiment of spray gun having a central paint delivery.

FIGURE 2 is a longitudinal section of a second embodiment of spray gun having a lateral paint delivery, and

FIGURE 3 is a perspective view of the whole of the spraying equipment, consisting of the gun, the high ponited States Patent 3,008,645 Patented Nov. 14, 1961 tential generator and the connecting cables and pipes.

Referring to FIGURE 1, the spray gun comprises essentially a body 1 constituted by two symmetrical parts made of insulating material, for example made of ethoxyline resins, assembled together by any suitable means, for example by means of screws, welding etc. The screws are preferably made of an insulating material having for example, an amide base. The assembly has generally the shape of a gun, the driving motor 2 for the head being disposed preferably at the rear of the grip 3 in order to balance the assembly about the grip.

The paint to be sprayed is fed through a channel 4 to a needle valve 16, regulated by a knurled wheel 6. The paint is then fed through a channel 7 which is not completely shown on the sectional drawing, up to a cavity 8 provided in a metallic body 9 inside which rotates the support 10 for the head, 10a. This support is provided with a longitudinal channel and small transverse channels enabling the paint to pass from the cavity 8 to this longitudinal channel in order to proceed towards the head. The latter may be of any known type and, preferably, the support 10 is formed so that interchangeable heads may be secured to it.

The support 10 is rotated by the motor 2 positioned at the rear of the gun by means of a coupling shaft 11 made of an insulating material and of suflicient length to ensure that the motor is not influenced by the parts of the head brought to a high potential.

On the other hand a shielded cable 5 for supplying the high potential is provided, which passes through the gun along the whole of its length in order to arrive at a point 12 on the metallic body 9, so as to bring the assembly of the head, its support 10 and the body 9 to the necessary high potential.

The control system of the gun is thus constituted by the wheel 6 for regulating the supply of paint, as already described, and by the trigger 13 having multiple triggering. Pressure on the trigger will control in succession through mechanical linkages (not shown): 1) The starting of the motor through switch 13a, (2) The application of the high potential through switch 13b, (3) The admission of paint through valve 130, and the inverse operat-ions on stopping.

The safety device is constituted by a guard ring 14, earthed by means of an earthing wire to the supply 15 for the motor 2.

The gun shown in FIGURE 2 essentially comprises a metallic grip 21 and an insulating barrel 22. 'The metallic grip 21, preferably a light alloy, consists of two symmetrical parts assembled together by any suitable means, for example by screws. The insulating barrel 22 is made of a mouldable material having a strong electrical resistivity and capable of resisting solvents generally used with paints. Applicants have obtained good results with filled or non-filled epoxy resins.

The barrel contains a paint supply channel 23, which ends in a metallic tip 24, Resistances 25 for high potentiels, having a value of several tens of megohms are placed in series with the high potential input between the high potential generator and the atomizing head 27. The barrel also contains a channel 26 for the passage of the insulating driving shaft 28 for the head 27, as well as a channel 29 for the passage of the high potential cable 30.

There is therefore no packingebox or sealing means, the paint being directly supplied through the tip 24 to the inside of the head 27.

The trigger 31 is provided with a return spring 32. Manual operation of this trigger initiates through linkage 43 the successive release of the following operations: (1) The operation of the small switch 33, controlling the starting of the motor 34 driving the head 27 by means of the insulating shaft 28, as well as the appearance of the high potential by excitation of the electrostatic generator 34 (see FIGURE 3). This excitation is obtained by polarising a grid of an electronic tube of the high frequency excitation generator. (2) The admission of'paint. The valve 35 having an adjustable flow control opens, the adjustment of the flow being obtained by acting on the adjusting screw 36.

The metallic grip 21 is earthed, on the one hand by the conductive sheath 37 of the high potential cable 30 and on the other hand by the earth wire 38 of the supply 39 of the motor 34.

A small metal clip 40 ensures an electrical connection between the metal end 41 of the insulating shaft 28, the metal tip 24 of the paint channel 23 and the high potential input 42, at the output of the resistances 25. This electrical connection is useful so as to avoid sparks at the end of the barrel.

The number and the nature of the operations controlled by the triggers of the two above-described guns may be modified without departing from the scope of this invention. A switch for starting the high potential generator may be added if desired.

On the other hand, it is possible if necessary to control a paint inlet pump, in the case when the paint supply system from the store to the guns is not provided. It is also possible to provide on the guns a system of high potential adjustment so as to alter the shape of the lines of force of the field in the vicinity of the heads. It is also possible, Without going beyond the scope of the invention, to dispose a paint reservoir on the guns themselves, and possibly to let the

motors

2 or 34 drive the paint pumping system which would have the advantage of proportioning the paint flow to the speed of rotation of the head.

Lastly one may provide for the use of a screen, either insulated or placed at the high potential which will be disposed in the vicinity of the head, in order that the field lines will be directed towards the object which must receive the spray.

The installation shown in FIGURE 3 comprises an assembly (high potential generator and supply of materials to be sprayed) 51 and a gun 52 effecting the spraying or atomization. By way of example it is assumed that this apparatus is intended for paint spraying. The essentially mobile assembly is mounted on wheels or on runners, or any other device enabling easy handling and movement of the apparatus.

The body of this assembly contains an electrostatic generator 53, an exciter 54, a system for the adjustment and regulation of thepotential 5S, and a paint tank 56. The generator 53, for example of the type forming the subject of British Patent No. 719,687 is constituted by a hermetically sealed enclosure containing an electrostatic generator having an insulating cylindrical conveyor, driven by a motor and immersed in compressed hydrogen.

The regulation system 55 gives to the electrostatic generator 53 a load characteristic which may thus be defined.

If the value of the current required from the generator is lower than that of the maximum current which it may supply (i.e. for example 250 microamps), the potential remains practically constant, whatever the value of the current required.

If on the other hand the value of the current reaches the maximum current, the potential decreases rapidly. It is known that for an electrostatic machine, the value of the short circuit current hardly exceeds the value of the maximum utilisation current. This characteristic is particularly suited to the use envisaged.

On the one hand it. ensures the stability of the high potential, in spite of the variations of current caused by the relative movements of the head of the spray gun and of the objects to be painted and on the other hand, if the head gets abnormally near to an object, the increased current drawn immediately causes a reduction of the high potential.

The button 57 enables an adjustment of the high potential to the desired value. The body 51 is provided with a socket 60 having a special plug for earthing. The device 56 for feeding paint to the gun 52 comprises a small tank and a system enabling paint to circulate up to the gun, a system which may be either a small paint pump, or a small air pump, constituted by a cylinder and a piston which may be operated externally by means of the handle 58, and which enables a slight over pressure of air to be applied on the free surface of the paint in the tank, said over pressure being sufficient in order to cause the paint to rise up to the gun.

The assembly 51 is connected to the gun 52 by one or several flexible tubes 63 containing the shielded high potential supply cable to the gun, the supply wires to the small motor 59 for driving the head, and the paint supply tube.

The use of an electrostatic generator affords a high potential source which does not take up much space, is light and completely harmless, and which easily supplies the necessary potential, for example kv. The characteristics of this generator give to the apparatus described in the invention a degree of freedom which could not be obtained by means of a conventional high potential source.

It will be understood that although the invention has been particularly described as applied to paint spraying devices it may be employed for the spraying or precipitation of any thin or thick liquid, or paste or a pulverulent product.

We claim:

1. A portable device adapted to be held in the hand for the atomising and spraying of a fluid by electrostatic means, said device comprising a body of insulating material, a rotatable shaft extending through said body, an electric motor mounted on said body for rotating said shaft, means for mounting an atomising head on said shaft, a passage through said body for feeding the fluid to be sprayed to said atomising head, a high tension conductor extending through said body for applying a high voltage to said atomising head and trigger means mounted in said body and arranged so that operation of said trigger means initially controls the starting of the motor and the application of high voltage to said atomising head and subsequently the flow of fluid through the passage.

2. A portable device adapted to be held in the hand for the atomising and spraying of a fluid by electrostatic means, said device comprising a hand grip portion and a body portion of insulating material attached to said hand grip portion, a rotatable insulated shaft extending through said barrel portion, an electric motor mounted on said body portion for rotating said shaft, means for mounting an atomising head at one end of said shaft, a passage through said hand grip portion and said body portion for feeding the fluid to be sprayed to said atomising head, and a high tension conductor extending through said hand grip portion and said body portion for applying a high voltage to said atomising head, a supply conductor to said electric motor extending through said hand grip portion, trigger means mounted in said hand grip portion and arranged so that operation of said trigger means initially controls the starting of the motor and the application of the high tension supply to said atomising head and subsequently the flow of fluid through the passage and adjustable valve means for adjusting independently of said trigger means the rate of flow of fluid through the passage.

3. Apparatus for the atomising and spraying of fluid by electrostatic means comprising a spray device adapted 'to be held in the hand and including a body portion, an electric motor carried by said body portion, an atomising head driven by said motor, a passage in said body portion for feeding the fluid to be sprayed to said atomising head, a high tension conductor extending through said body portion for feeding a high voltage to said atomising head, a hand operable trigger control mounted on said body portion and controlling the supply of fluid through said passage, a separate casing containing a high tension voltage generator, control means for said generator and a tank for the fluid to be sprayed, and a flexible tubular connection between said spray device and said casing, said tubular connection including the high tension conductor for feeding the output of said generator to said atomising head and a pipe for feeding the fluid to be sprayed from said tank to said atomising head and adjustable valve means mounted on said spray device for adjusting independently of said trigger the rate of flow of fluid through said passage.

4. Apparatus for the atomising and spraying of a fluid by electrostatic means comprising a spray device adapted to be held in the hand and including a body portion, an electric motor carried by said body portion, a rotatable shaft driven by said motor and extending through said body portion, an atomising head adapted to be detachably secured to said rotatable shaft, a passage through said body portion for feeding the fluid to be sprayed to said atomising head, a high tension conductor extending through said body portion for feeding a high voltage to said atomising head, a supply conductor to said electric motor, a hand operable trigger means mounted on said body portion and arranged so that its operation initially controls the energisation of said motor and the application of high tension to the atomising head and subsequently the supply of fluid through said passage, valve means for adjusting independently of said trigger means the rate of flow of fluid through said passage, a separate casing containing an electrostatic generator of low internal capacity, driving and control means for said electrostatic generator and a tank for the fluid to be sprayed, and a flexible tubular connection between said spray device and said casing, said tubular connection including the supply conductor for said motor, the high tension conductor for feeding the output of said electrostatic generator to said atomising head and a pipe for feeding the fluid to be sprayed from said tank to the passage in said body portion.

5. Apparatus as claimed in claim 4, in which the shaft includes a portion made of insulating material and a portion adjacent the atomising head made of metal to which the high tension is applied, and a bore through said metal portion by means of which fluid is fed from said passage to said atomising head.

6. Apparatus as claimed in claim 4, in which the shaft includes a portion made of insulating material and a portion adjacent the atomising head made of metal, a metal nozzle for feeding the fluid to be sprayed to said atomising head eccentric of its axis of rotation, means for applying the high tension to said metal nozzle and a conducting connection between said metal nozzle and said metal portion of said shaft,

7. A portable device adapted to be held in the hand for the atomising and spraying of a fluid by electrostatic means, said device comprising a hand grip portion and a body portion of insulating material attached to said hand grip portion, a rotatable shaft extending through said body portion, an electric motor mounted on said body portion for rotating said shaft, means for mounting an atomising head at one end of said shaft, a passage through said hand grip portion and said body portion for feeding the fluid to be sprayed to said atomising head, a high tension conductor extending through said hand grip portion and said body portion for applying a high voltage to said atomising head, said shaft including a portion made of insulating material and a portion adjacent the atomising head made of metal to which the high tension is applied, and a bore through said metal portion by means of which fluid is fed from said passage to said atomising head, a supply conductor to said electric motor extending through said hand grip portion, a trigger mounted in said hand grip portion and controlling the starting of the motor and the flow of fluid through the passage, and means for adjusting the rate of flow of fluid through the passage.

8. A portable device adapted to be held in the hand for the atomising and spraying of a fluid by electrostatic means, said device comprising a hand grip portion and a body portion of insulating material attached to said hand grip portion, a rotatable shaft extending through said body portion, an electric motor mounted on said body portion for rotating said shaft, means for mounting an atomising head at one end of said shaft, said shaft including a portion made of insulating material and a portion adjacent the atomising head made of metal, a metal nozzle provided for feeding the fluid to be sprayed to said atomising head eccentric of its axis of rotation, a conducting connection between said metal nozzle and said metal portion of said shaft, a passage through said hand grip portion and said body portion for feeding the fluid to be sprayed to said metal nozzle, and a high tension conductor extending through said hand grip portion and said body portion for applying a high voltage to said metal nozzle, a supply conductor to said electric motor extending through said hand grip portion, a trigger means mounted in said hand grip portion and arranged so that when operated it initially controls the starting of the motor, and the application of the high tension supply and subsequently controls the flow of fluid through the passage.

References Cited in the file of this patent UNITED STATES PATENTS 2,728,607 Smart Dec. 27, 1955 2,926,106 Gauthier Feb. 23, 1960 FOREIGN PATENTS 1,004,558 Germany Mar. 14, 1957