US 3086711 A
Description (OCR text may contain errors)
M. A. R. POINT April 23, 1963 A SPRAY GUNS HAVING A FIXED ELETROSTATIC HEAD Filed April 25. leso .E E x Inventor April 23, i963 y M. A. R. PoxNT SPRAY GUNS HAVING A FIXED ELECTROSTATIC HEAD Filed April 25.. 1960 2 Sheets-Sheet 2 @ad venlvor4 '415744' VS2""A ttameyg iinite ttes 3,986,711 SPRAY GUNS HAVING A FIXED ELECTRO- STATIC HEAD Marcel August Roger Point, Grenoble, France, assigner to Societe Anonyme de Machines Elecrostatiques, Grenoble, France, a French body corporate Filed Apr. 25, 1960, Ser. No. 24,582 Claims priority, application France Apr. 27, 1959 11 Claims. (Cl. 239-15) Electrostatic spray guns are known having a rotating head yfor atomizing and spraying tine particles, such as paint, on to an object to be coated.
In certain cases and for certain applications it may be advantageous to have a gun having a iixed, i.e. non-rotatable, electrostatic head.
The present invention consists in a spray gun having a xed electrostatic head for atomizing and spraying tine particles of a materiahfor example paint, wherein said Afixed head comprises a zone provided with several small atomizing orifices through which passes the material to be sprayed and a movable rotating member is in contact with the internal surface of this zone to act as a scraper ensuring a substantially uniform distribution on said internal-surface of the material to be sprayed and preventing the orifices from becoming obstructed or clogged.
In order that the invention may be more fully understood, some embodiments thereof will now be described with reference to the accompanying drawings, in which:
FIGURE 1 lis an axial longitudinal section of a first embodiment according to the present invention;
FIGURE 2 is a partial lsection on a 4larger scale of the electrostatic head of FIGURE 1.
FIGURE 3 is an axial longitudinal section of a second embodiment of the invention.
FIGURE 4 is an end view of the head in FIGURE 3.
FIGURE 5 shows how it is possible to regulate the delivery of the product to be atomized, and
FIGURE 6 is an axial longitudinal section of a third embodiment according to the invention.
FIGURE l shows a gun for electrostatic atom-izing and spraying comprising a metallic hand grip or butt 1 to which is fixed in any appropriate manner an elongated insulating body 2 having a generally cylindrical shape. Through the butt extends a duct 3 for the feeding of the product under pressure to be atomized; an electric low tension cable 4 for feeding a motor 5 whose function will be explained later on; and a high tension cable 6 intended to feed this high tension to the electorstatic head for atomizing and spraying of tine particles of paint or other material. The butt 1 also carries a trigger 7 which may be operated by the user. By means of this trigger it is possible to control as desired through the intermediary of a pivoted rod 8, a switch 9 of any suitable type in order to start or stop the electric motor 5. The trigger 7 also has a further function which will be described below.
The electrostatic head 16 of FIGURE 1 is shown in part-section on a larger scale in FIGURE 2. This head is cylindrical and has thin walls. It is provided towards its end with spraying holes 11, arranged for example in several circular rows and radially directed towards the exterior. These holes have a diameter which may range from one to several tenths of a millimeter and serve for the discharge of the product to be atomized, the latter arriving through the duct 3 from any suitable external source, under a pressure of a few atmospheres for example from 2 to 3 kga/cm?.
In the absence of an electric field, the fine jets of product would be directed radially towards the exterior along the axis of the holes. However, in the presence of an electric field caused by the high ten-sion applied through the cable 6, the action of the electrostatic forces causes these jets of product to divide rise to line particles charged with electricity which the electric ield directs thereafter on the objects to be coated.
In order to avoid the holes 11 becoming obstructed, an internal rotating scraper 12 is provided, which is driven by the motor 5 through an insulating shaft 13. This scraper acts in the manner of an electric'razor, its edges bearing against the internal surface of the head 10 in the zone of the holes 11.
In order to regulate the delivery from the head '10, an external sleeve 14 is provided whose internal surface may slide longitudinally with friction on the external surface of the head 10, in order to obturate a larger or smaller number of holes 11. Thus, in FIGURE 2 the sleeve 143 occupies a position such that only a single row of holes 11 may function. In the example shown the sleeve 14 could also obstruct or uncover the two rows of holes 11, according to the wish of the user.
The corresponding longitudinal displacements of the sleeve are controlled by the trigger 7, which is mechanically connected to said sleeve by an insulating rod 15, which enables the user to control the delivery from the head 10. It is obvious that the adjustment of the longitudinal position of the sleeve does not normal-ly cause the switch 9 to `be operated unless the trigger 7 returns to its rest position as the wish of the user.
Obviously the invention is in no way limited to the number and arrangement of holes shown in FIGURE 2.
It is moreover possible to provide a high tension electrode 16 of metal or high resistivity material in order to avoid the dispersion of the electric eld and direct its lines of force towards the object to ybe coated. Thus the directional action of the eld is reinforced and at the same time the protection of the operator is improved.
Lastly, an electric protection resistor may be provided, which is not shown, and be inserted between the end of the high tension cable 6 and the head 10.
FIGURE 3 shows a longitudinal section of a second embodiment according to theV invention. Elements corresponding to those in FIGURE l have the same reference numbers.
The butt 1 and insulating elongated body 2 are again shown. The high tension cable 6 passes through the butt, as well as the supply duct 3 for the product to be atomized. A trigger 7 enables the operation to be adjusted (as will be described hereunder in more detail) by acting on a hinged rod 8.
In this embodiment the holes 11, as may be clearly seen on FIGURE 4, are disposed on the plane end wall of the head 10 and are arranged in a circle and with suitable spacing from each other.
In order to ensure the rotation of theY internal rotating scraper 12, the arrival under pressure of the product through the duct 3 is utilised, in order to actuate a turbine rotor 1S. This rotor is of helical form and is in electric communication with the high tension cable 6, through an electric protection resistor 17. "Preferably, a damping course be zero.
spring 19 is inserted between the rotor 18 and the scraper 12.
The product under pressure thus rotates the scraper 12 and the excess of product not used for atomizing returns to a tank, not shown, through a duct 20 communicating with the head and passing through the butt 1 of the gun. (FIGURE 3).
In order to adjust the delivery from the head, two valves 21 and 22 have been arranged in the inlet duct 3 and return duct which may be constructed for example in the form of a two-way cock, controlled by the rod 8 pivoted to the trigger 7. The inlet duct 3 is obtained when the return duct 20 is open and vice versa.
By referring to FIGURE 5, it can be seen that the delivery is at a maximum when the duct 3 is open and when the duct 20 is closed. In this case, all the product arriving through the duct 3 is used for atomizing. If the duct 3 is closed and the duct 20 is open the delivery will of In an intermediate position of the rod 8 (and of the trigger 7) the delivery may be adjusted between its maximum and zero values.
Finally, FIGURE 6 shows in section a third embodiment of the invention.
In this embodiment, the scraper is also driven by means of the rotor 18, rotated by the stream of the product to be atomized and the vholes 11 of the head are disposed as in the embodiment of FIGURE 4.
-Also in this third embodiment the high tension cable 6 is connected to the head 10 through an electric protection resistor 17. Moreover, the rotor 18 as well as its housing are made 'of an insulating material. Thus the only metallic elements are the grill or end wall of the head 10, and possibly the scraper 12.
In order to enhance the charge of the particles of paint or other product, it is possible to provide the high tension grill with points or spikes standing on end, not shown, or to provide a disc having a thin discharge edge. This would moreover produce an automatic lowering of the high tension if the operator brings the gun too near to the object to be coated. The spark which might possibly arise under these conditions would be produced at a lower voltage since the energy expended in this spark is proportional to the square of said voltage. This energy would be diminished accordingly and thus also the possible risks of intlammability.
For this dual purpose it would also be possible to provide the end of the gun with an electrode having a thin edge 23, FIGURE 6, made of high resistivity material for example.
The adjustment of the delivery is effected in this third embodiment exactly as in the embodiment of FIGURES 4 and 5.
Whilst particular embodiments have been described, it will be understood that various modifications may be made without departing from the scope of this invention.
l. A spray gun for an electrostatic spray coating process comprising a gun body having a hand grip, a hollow sprayer head attached to and insulated from said body, means for applying a high direct voltage to said head, conduit means for delivering sprayable fluid into said head, a plurality of spray discharge orices in said head each having a transverse dimension not greater than about one half a millimeter whereby said uid will issue from said orices as a spray of discrete, electrically charged particles, a scraper member mounted for rotation within said head and engaging the inner surface thereof in the oriticed area, means for driving the scraper in rotation, a finger operable trigger control on said grip and means operated by said iinger operable trigger control for controlling the rotation of said scraper member.
2. A spray gun for an electrostatic spray coating process comprising a gun body having grip means for holding said gun, a hollow spraying head attached to and insulated from said body, means for applying a high direct voltage to said head, conduit means for delivering iiuid to be sprayed into the hollow spraying head, a plurality of spray discharge orices in said head each having a transverse dimension such that said tuid will issue from said oriiices as a spray of discrete, electrically charged particles, a scraper member mounted for rotation within said head and engaging the inner surface thereof within the region of said orices, an electric motor mounted on said gun body adjacent said grip and having an insulated motor shaft connected with said scraper member for driving said member in rotation, a finger operable trigger control on said grip and switch means operated by said iinger operable trigger control for controlling the energization of said motor.
3. A spray gun as claimed in claim l, wherein said means for driving the scraper member comprises a rotor member rotatably mounted in said body in the path of said iluid for rotation thereby and connected to said scraper member to rotate said member.
4. A spray gun as claimed in claim 1, wherein said means for driving 'the scraper member comprises a bladed rotor made of insulating material and rotatably mounted in said body in the path of said liuid delivered to the head for rotation by said tiuid, and said scraper member is connected to a front end of said insulating rotor member.
5. A spray gun as claimed in claim 1, comprising means on said spray head providing an electrode having a thin discharge edge.
6. A spray gun as claimed in claim l, including a sleeve slidable over a surface of the spraying head so as to uncover a variable number of said orifices, and means connecting the sleeve for displacement by said finger operable trigger control.
7. A spray gun according to claim l, wherein the internal surface of the spraying head in the zone of said orifices is shaped as a body of revolution, the atomizing orilices having their axes directed radially of the spraying head and being arranged in circular rows situated in planes perpendicular tothe longitudinal axis of the spraying head.
8. A spray gun according to claim 3, wherein a return duct for unused spraying material communicates with the spraying head in order to evacuate the excess material.
9. A spray gun according to claim 8, wherein said ymeans operated by said iinger operable trigger control second valves such that as one of said valves opens the other valve closes and vice versa in order to adjust the delivery of said iiuid from said gun.
10. A spray gun for an electrostatic spray coating process'comprising a gun body having grip means for holding said gun, a hollow spraying head attached to and insulated from said body, means for applying a high direct voltage to said head, conduit means for delivering iiuid to be sprayed into the hollow spraying head, a plurality of spray discharge orices in said head dimensioned so that said fluid will issue from said orifices as a spray of discrete, electrically charged particles, a scraper member mounted for rotation within said head and engaging the inner surface thereof within the region of said oria'ices, means on said gun for driving the scraper member in rotation, a nger operable trigger control on said grip means operated by said finger operable trigger control for controlling the rotation of said scraper member, and a high tension electrode disposed in the immediate vicinity of said spraying head to decrease dispersion of the electric field.
11. A spray gun for an electrostatic spray coating process comprising a gun body having grip means for holding said gun, a hollow spraying head attached to and insulated from said body, means for applying a high direct voltage to said head, conduit means for delivering uid to be sprayed into the hollow spraying head, a plurality of spray discharge orifices formed through a generally cylinmoving said member to vary the number of said orifices drical coaxial wall of said head and dimensioned so that that are uncovered for the discharge of said uid.
said uid will issue from said orifices as a s ray of discrete, electrically charged particles, a scraper iember en- References cned m the me of this patent gaging the inner surface of the head within the region 5 UNITED STATES PATENTS of the orifices and means for driving the scraper mem- 636,273 Mine,- Nov' 7, 1899 ber in rotation, a longitudinally movable member fitted 1,454,280 Hem-ikson May g, 1923 around said cylindrical wall of the head, a nger oper- 1,493,359 Mauery May 6', 1924 able trigger control on said grip and means operated by 1,608,030 Miller Nov 23, 1926 said iinger operable trigger control for longitudinally 10 2,558,376 Opp June 26, 1951