US2766064A - Paint gun - Google Patents

Description

@ct 9, E95@ PAINT GUN Filed Aug. 22, 1955 lo I2 92 5| 2l 75 2 35 20\\7o 65 90 45 7' i e3 L y 6l lk' u y Y 42 40 4| f 5 1 l V /v H l i \\36 O\ 34 23 INVENTOR. HOWARD SCHWEITZER (am QQVOQM) ATTORNEYS PAINT GUN Howard V. Schweitzer, Fort Lauderdale, Fla. Application August 22, 1955i Serial No. 529,728 Claims. (Cl. 299-1) The present invention relates 4t0 coating operations involving paint atomization, and more particularly to an atomizing head or paint gun. This application is, in part, a continuation of my application Serial No. 282,858, for

tiled April 17, 1952, now abandoned.

Solvent loss is one of the greatest single cost factors in coating operations involving paintatomization. To be able to eiectively atomize and disperse solvent paints, it is necessary to reduce paint viscosity by increasing solvent content. After the coating operation is completed, the coating dries and the solvent volatilizes and yis thereby either lost to the atmosphere or recovered from the environmental drying air by elaborate solvent recovery arrangements. In either case, the corollary of high solvent content is the high cost of solvent loss or the somewhat lesser cost of solvent recovery procedures.

In hot melt coating operations, the requirement of maintaining a suiciently low viscosity for atomization is met by heating the liquid coating composition at elevated temperatures. To maintain these elevated temperatures on a continuous basis is expensive. Moreover, the necessary high `temperature of the coating composition precludes its use in processes in which the permissible temperature of the coating operation is restricted by the temperature tolerance of the object to be coated or by other limitations.

The necessity of constantly provid-ing a continuously exhausted supply of high pressure air is another important cost factor in coating operations involving paint atomization. The considerable energy represented by the continuous supply of high pressure air is. required in conventional atomizing heads to do the work of overcoming coating cohesion and surface tension in order to transform the liquid coating composition into a finely divided discontinuous mist.

lt is the object of my invention to atomize a coating co-mposition which may be held at substantially environmental temperature and in which the solvent content is eliminated or is far below that required in previous paint spraying operations.

It is a further object of my invention to obviate the necessity of providing a continuously depleted supply of high pressure air to effect atomization.

Still another object of my invention is to employ my atomizing means in conjunction with electrostatic coating means to achieve an unusually effective electrostatic spraying device. I have discovered that the pointed vibrating needle provided in accordance with the general teaching of the aforementioned parent application lends itself ideally to the technique of deposition of an electrostatic charge upon a coating fluid which is undergoing atomization, such technique broadly having been heretofore employed. That is, I have improved upon conventional electrostatic spraying means by providing a new and improved means to atomize and charge the coating fluid.

`Other objects and advantages of my invention will become apparent from a study of the following specification and the accompanying drawings in which:

Figure l is a cross-section of a spray head embodying my invention, the relative positions of the parts being those of the inoperative or oil condition.

nited States Patent tive positions' of the parts when the spray head is in the operative or on condition.

As illustrated in the drawings, a body receives the threaded plug 11 which, in its installed position, seats in sealing relationship on the plug seat 12. The bore 13 of the plug 11, together with the stepped bore 14 of the body 1i), defines an elongated chamber having open end l5. A cap 16 lits over the plug 11 and is threaded to the body 10 to define an air manifold chamber 17. Extending rearwardly of the bore 14 is a narrow bore 20 and counterbore 21. The bore Ztl opens into a rear chamber 22 which is closed by a suitable cap 23.

Slidably received in the narrow position 25 of the bore i4 is a sleeve 36, preferably fabricated from Bakelite, catalin, lead or other material of very small ultrasonic transmission. The sleeve in turn receives a press-fitted ultrasonic transducer 3l, preferably a barium titanate transducer having silver plated front and rear faces 32 and 33 and which may be hexagonal in cross-s'ecton. The rear face 33 engages the small annular shoulder 34 formed on the sleeve 30 and faces an air gap chamber 35 which minimizes rearward energy loss and damping. The central portion of the sleeve bore may also be relieved as at 36 to further minimize damping.

The front face 32 of the transducer 31 is cemented to the shank portion 41 of the needle 40. The needle tapers downwardly from its shank portion to a narrow tip 42 which may extend beyond the nozzle opening 15. The upper portion 43 of the needle is adapted to mate with the seat 45 of the plug 11.

A hollow stem Si) is threadedly received in a boss 51 for-ined on the rear of the sleeve 36. The stem extends through the narrow bore 20 into the chamber 22. A piston assembly 52 including an air-seal ring 53 is mounted on the rearward end of the stem 50. Extending through the hollow center of the stem 50 is a cable 61, the inner end of which is stripped to expose the lead 62 which is soldered to the silvered rear face 33 of the transducer 31. The cable 61 extends beyond the hollow stem Si) and through the hollow boss 63 formed on the cap member 23.

A coil spring 65 is compressed between the cap member 23 and the piston assembly 52 to constantly urge moving parts of the needle assembly to the left or closed or off position. A plug 76 surrounds the stern 56 and is received in the body portion l0. The plug is adapted to be tightened against the packing 71 to prevent leakage in either direction 'along the stem 50. Another plug '75 is received in the bore portion 14 of the body 10. The plug '75 is in sliding contact with the forward silver plating 32.

The atomizing assembly includes a trio of inlet connections 86, 8l and 82. The inlet 80 communicates with the air manifold 17 which, in turn, communicates with the plug bore portion 13 through the plug passages 84. The inlet 3l communicates with the body bore portion 14. The inlet 62 communicatesthrough passage S6 with the chamber 22.

A source of high electric potential or power pack is connected to the needle 40 through a lead 91 which is suciently exible to move with the needle 40 through slight translation-al movement. Leakage of coating composition from the body bore portion 14 through the passage in which extends the cable containing the lead 91 is prevented by suitable removable sealing grommets 92, which, when in position, easily withstand the relatively low pressure of coating composition within the body bore portion 14.

Operation The atomizing head is initially actuated by high presair valve (not shown) controlling admission of air at this inlet is coupled to an electricswitch (not shown) in any conventional manner so that high frequency current is supplied to the cable 61 upon actuation of the piston 52. As will be apparent to those familiar with high-frequency vibrator drives, the power to vibrate the transducer 31 may be produced by any suitable high-frequency osc-illator. Circuit potential is applied at the rear face 33 of the transducer through the lead 62. Ground return from the opposite face 32 of the transducer is accomplished through -the sliding contact of the periphery of the face 32 and the needle shank portion 41 against the bore of the plug 75.

When the piston 52 is moved rearwardly by air pressure, it carries with it the needle mounting assembly including the stem 50, the sleeve 30, the transducer 3i and the needle 40. This movement stops when the boss l is seated against the rear shoulder of the counterbore 2i. The needle 40 is thereby lifted olf the plug seat 45 allowing liquid coating composition, admitted through the inlet connection 81, to pass down along the tapered sides of the needle. The now ultrasonically vibrating needle lowers the viscosity of the coating composition and breaks the coating composition up into a fine air-borne colloidal dispersion. The dispersed coating composition then passes out through the opening 15, this movement being preferably aided by low pressure air admitted through the passages 84. Exhaustion of the atomized coating composition may also be augmented by the aspirating action of air expelled through the ports 90 which may be in communication with 'the air manifold chamber 17.

The air-emulsification and exhaustion of the coating composition is a continuous process. No high pressure air is required to do the work of atomization. Exhaustion of the coating composition may be augmented by very small air pressure differentials, and the function of any air which may be continuously admitted through the inlet connection is merely to aid in such exhaustion. Thus, the air requirements of my spray head are minimal.

It will be apparent that the gun is turned off by releasing pressure at the inlet 82 allowing the needle mounting assembly to be shifted to the left by the spring 65 so that the needle seats .against the seat 4S. Upon this release of pressure the electric switch which is coupled to the on-ofi air valve is opened so that the transducer 40 is no longer driven by the oscillator circuit as the needle seats.

When electrostatic coating is being carried out, high potential is supplied through the lead 91 to cause a corona discharge to occur from the pointed tip 42 of the needle, as will be apparent to those familiar with the art of electrostatic coating. The projection of electrostatically charged particles of coating material is greatly enhanced by accomplishing atomization of the paint with a vibrating needle as disclosed above, rather than bythe use of conventional means for mechanically feeding or atomizing from a charged spray-head member a liquid to be used in electrostatic coating processes.

There are many self-suggestive alterations which may be made in the particular embodiment of my invention which I have disclosed, and the scope of my invention is therefore not to be limited to this specific embodiment but is to be defined solely by the following claims.

What is claimed is:

1. A coating composition atomizing head comprising a body assembly having formed therein an elongated chamber open at one end, a needle tapering from a relatively wide shank to a relatively narrow pointing end, said needle being received within said chamber and pointed lthrough said one open end, means to position said needle Within said chamber in a rst position in which said needle is supported solely at the base of said shank,

, of said needle whereby said liquid coating composition transducer means associated with said needle to vibrate said needle ultrasonically in said rst position, and means to introduce liquid coating composition onto the surface will be atomized at the surface of said needle.

2. A coating composition atomizing head comprising a body assembly having formed therein a chamber open at one end, a needle tapering from a relatively Wide shank to a relatively narrow pointingend, said needle being received within said chamber and pointed to said one open end, means to position said needle within said chamber -in a iirst position in which said needle is supported solely at the base of said shank, transducer means associated with said needle to vibrate said needle ultrasonically in said first position, means to introduce liquid coating composition onto the surface of said needle whereby said liquid coating composition will be atomized within said chamber and means to introduce air into said chamber to aid in expulsion of atomized coating cornposition out said one open end.

3. A coating composition atomizing head comprising a body assembly having formed therein an elongated spray chamber open at one end and communicating through a port at its opposite end with a liquid chamber, a needle tapering from a relatively wide shank to a relatively narrow pointing end, said needle extending from within said liquid chamber through said portv and through said spray chamber to point through said one open end, said needle being movable within said body and in mating relationship with said port whereby said needle may be shifted between port-closed and-port-open positions, said needle being supported solely at the base of said shank when in said port-open position, transducer means associated with said needle `to vibrate said needle ultrasonically in said iirst position, and `means to supply liquid coating composition to said liquid chamber whereby when said port is open and said transducer is actuated, said liquid coating composition will pass down along said .tapered sides of said needle and be atomized within said spray chamber.

4. A coating composition atomizing head comprising means defining an elongated chamber open at one end, said means including a needle tapering from a relatively wide shank to a relatively narrow pointing end and detining at least in part the interior volume of said chamber, said needle being supported in a iirst position on said atomizing head solely at the base of said shank, trans'- ducer means associated with said needle to vibrate it ultrasonically in said first posi 'on, means to ow liquid coating composition to said needle and contact it with said needle whereby said liquid coating composition will be atomized off said needle, and a source of high electrical potential connected to said needle whereby corona discharge will occur from said pointed end to impart a static charge to coat-ing composition atomized by said needle.

5. A coating composition atomizing head comprising a body assembly having formed therein a chamber open at one end, a needle tapering from a relatively wide shank to a relatively narrow pointing end, said needle being received within said chamber and pointed to said one open end, means to position said needle Within said chamber in a first position in which Said needle is supported solely at the base of said shank, transducer means associated with said needle to vibrate said needle ultrasonically in said lirst position, means to introduce liquid coating composition onto .the surface of said needle whereby said liquid coating composition will be atomized from the surface of said needle, and a source of high electrical potential connected to said needle whereby corona discharge will occur from said pointed end to impart a static charge to coating composition a-tomized by said needle.

References Cited in the tile of this patent l y Y LNITED STATES PATENTS 1,323,778 Kemp Dec. 2, 1919 2,453,595 Rosenthal Nov. 9, 1942 2,577,853 Kurata Dec. 1l, i951

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