US2297497A - Spraying process and apparatus - Google Patents

Description

Patented Sept. 29, 1942 Mintscho Popofl', Berlin, Germany; vested in the, Alien Property Custodian Application November 25, 1940, Serial No. 367,091

- In Germany December 9, 1939 7 Claims. (Cl. 299-140) This invention relates to a method and apparatus for spraying fluids such as paints and varnishes onto surfaces, wherein the fluid is atomized by means of a gas, such as air.

In my copending patent application Serial No.

' 273,535, filed May 13, 1939, I have described a method and apparatus for spraying paints and varnishes onto surfaces, using separate air currents of difierent velocity for the atomizing process and for increasing the kinetic energy of the atomizing jet, and a spraying device consisting of two concentric nozzles, i. e., aninner atomizing nozzle and an outer depositing nozzle. This renders it possible ,to effect a very uniform atomization while avoiding the formation of too flne liquid particles or drops. Moreover, the jet of liquid is subsequently imparted a greater kinetic energy, for increasing its penetrative or depositing force.

I have now found by further investigations and from the practical use of this novel apparatus, that in such spraying apparatus acertain portion of the liquid 'passes to the inner wall of the atomizing nozzle, where it adheres, being slowly entrained by the flowing air towards the orifice. Moreover, I have found that the liquid thus carried to the orifice creeps radially outwards on the front face of the atomizing nozzle, owing to the. suction effect produced by the higher velocity depositing jet. This creeping liquid when coming into contact with the high velocitydepositing air current passing from the depositing nozzle, owing to ;the too high relainconnection with the accompanying drawing, showing by way of example two embodiments of the invention and in which:

Fig. 1 is a longitudinal cross-sectional view through a paint spray pistol with the spraying head' screwed thereon, having the invention applied thereto.

Fig. 2 is a longitudinal section through a modi-' fled construction of spraying head which can be screwed on the Pistol shown in Fig. 1.

Fig. 3 is a detail of Fig-1.

Similar charactersof reference denote similar parts in the figures.

In the drawing,,A designates generally the pistol body and B the spraying headattached thereon. The compressed air serving for the atomization passes through the bore 21 in the handle 28. The quantity of air is regulated by the spring-actuated valve 25 which is actuated by the trigger 26. The air-passes behind the valve through the bores 24 and 23 into the annular chamber IS.

The air passes from annular chamber l9 through a plurality of bores 1 into another annular chamber l2. The air jets subdivide therein and pass partly into the inner nozzle I, which is formed by the central members l3 and I4 and the surrounding members I5 and 39, and partly into the outer nozzle 2, which is formed by the tive velocity of the depositing air current to liquid, undergoes a too fine atomization, where- :by undesirable paint mist is formed.

. It is an important object of the present in-" vention to preclude the above mentioned drawback of the known spraying apparatus. To this end, an additional annular nozzle which will be hereinafter referred to as the blowing nozzle" is arranged at the front face of the spraying apparatus, between the atomizing nozzle and the depositing nozzle, for discharge of an air jet having a velocity which, is 'at. least approximately equal to the exit velocity of the atomizing air current. In this manner the nonatomized paint liquid creeping outwards on the front face between the two concentric nozzles is prevented from coming into contact with the high velocity depositing air current, so that the undesirable formation of mist is precluded and the losses of paint or varnish involved with such mist formation are also avoided. The leakage means of the rectifier 5, which consists of fine The air serving for atomization passes first through the bores III, the passages of which may 22'attached to the annular slide and which engages in a helical groove 35 of the housingl6.

As a result of throttling the air by means of slide valve II a lower air, velocity prevails in nozzle l than in the outer nozzle.2. The airis uniformly distributed over the nozzle chamber by wire screening. Air meets the liquid at the liquid discharge opening 4. Atomization begins at this point. I

The air passing into the outer nozzle 2 is not throttled but merely distributed uniformly over the nozzle chamber by the rectifier 6. The liquid to be atomized is passed from a pressure container through the passages into the spray head B. Delivery to the liquid discharge point 4 takes place through the bore 8. The quantity of paint is regulated by the paint needle valve 3, which is opened forwardly by the trigger 26 ,through the plunger -29 and the lever 30. The latter acts against a housingel which is attached on the spindle 36 of the needle velvet and is slidable in a guide 31 of the shank A. A spiral spring 32, the other end of which surrounding member i5 and the outer housing is applied against a housing 33 screwed in the shank A, acts against the housing 3|. For centering the needle valve 3, the bore 8 is provided with a guide member I8 provided with bores or passages 38 for the passage of the paint.

The'liquid discharging at the point 4 comes uniformly in contact with the air passing over the periphery of the discharge cleft and is ato mized thereby as a result of the prevailing relative velocity. Atomization takes place within the inner nozzle I, in'which a controlled air velocity is present. By suitable regulation of the air velocity thru the annular slide .valve II the fineness of the fluid drops is controlled so that drops of minimum size which, as'a result of insuflicient penetrative force, are tending to form a mist, are almost entirely prevented from forming. k

The outer nozzle 2, from which the air discharges at a greater velocity than from inner nozzle I, encompasses the latter nozzle. My novel spray head now is distinguished from the spray head already described in my above men tioned copending patent application Serial No. 273,535, by the fact that an additional blast of air is produced which discharges between the atomizing nozzle and the depositing nozzle. To this end, according to Fig. 1, a conical or nozzleshaped sleeve 39 is concentrically disposed within the nozzle body I 5, and detachably secured therein by means of spring-actuated balls 4| engaging recesses 42 and held in sleeves 43 under action of springs 44, as best seen in Fig. 3.

In operation of my novel spraying apparatus,'

shown in Fig. 1, a portion of the air or other compressed gas passing through the bores I0 enters into the annular space 40 betweensleeve 39 and nozzle body I5 constituting the blowing nozzle. The paint which during the atomizing process is deposited on the inner walls of the sleeve '39, is gradually creeping forwards under action of the atomizinggas current, towards the front face of the sleeve 39, meeting there the air blast from the blowing nozzle 40 and being atomized thereby. Since the velocity of this air blast is substantially the same as that of the atomizing jet I, the creeping paint is atomized in about the same manner as in the region of the atomizing nozzle, without the formation of fine mist. Any

\ direct contact of the creeping paint with the depositing jet from the nozzle 2, which may occur in adevice having no sleeve 39, causing the formation of fine mist owing to the higher speed of the depositing jet, is preventedin this-manner.

Fig. 2 shows a different construction of the spray head B. In contrast to the case described relative to Fig. 1, here the atomizing air for the inner nozzle I is taken from another source than that of the outer nozzle 2 intended for depositing the spray jet.

As in Fig. l, theatomizing air passes thru the pistol shank into the annular chamber I9, from which it passes through the bores 1 into the other annular chamber" I2 and from there directly through the bores III and the rectifier 5 into the inner nozzle I. This is again formed by the central members I3 and I4 and the encompassing member I5.

In this modificationno controllable slide valve is provided.

The outer nozzle 2 is formed by the surrounding member IS and the outer housing I6. The .passages for the paint 8 and 2| are constructed in the same manner-as in the modification shown in s-I It will be noted that in both figures the discharge outlet of the atomizing nozzle is located relative to the direction of flow in front of the discharge outlet of the blowing nozzle, which in turn is located in front of the dischargeoutlet of the depositing nozzle. Moreover, in both cases the blowing nozzle is screened from the fluid to be sprayed.

The method and apparatus of the present invention have been described in detail with reference to specific embodiments. It is to be understood, however, that the invention is not limited by such specific reference but is broader in scope and capable of other embodiments than those specifically described and illustrated in the drawing.

I claim:

1. A spraying apparatus, comprising an atomizing nozzle, a depositing nozzle associated with said atomizing nozzle, and concentrically positioned about said atomizing nozzle, means for passing agas current through said atomizing nozzle, means for passing a gas current of higher speed through said depositing nozzle. an additional annular blowingnozzle concentrically positioned between said atomizing and depositing nozzles, and means for supplying a gas jet discharging from said blowing nozzle with a velocity which is substantially equal to the velocity of the jet discharging from the atomizing nozzle.

2. A method of coating surfaces with liquids, particularly paints and laquers comprising forming a liquid jet, an atomizing jet atomizing said liquid jet, a further driving jet concentric with' said atomizing jet accelerating said atomizing jet mixed with the atomized liquid whereby the discharge velocity of the driving jet is considerably greater than the velocity of the atomizing jet at the point where the atomizing jet meets the liquid jet, 2. further blowing jet also concentric with said atomizing jet and being located between said driving jet and said atomizing jet adapted to prevent atomizing action of the driving jet upon creeping liquid at the discharge outlet, whereby the discharge velocity of that blowing jet is substantially equal to the discharge velocity of the atomizing jet.

3. A spray gun for coating surfaces with liquids, particularly paints and lacquers comprising a chamber means provided with an opening constituting an atomizing nozzle, 'a liquid outlet means located within said chamber and spaced from said opening whereby the atomizing nozzle provides an atomizing jet,a blowing nozzle surrounding said atomizing nozzle and formed by the outer wall of that chamber and a further wall spaced from said outer wall, a driving nozzle surrounding said blowing nozzle and formed by the outer wall of the housing of the blowing nozzle anda further wall spaced from said housing, a compressed air conduit communicating with said drivingnozzle to form a driving jet, communicationmeans between said driving noz- 1 ale and said ,atomizing nozzle and throttling ishing the velocity of the compressed air in said atomizing nozzle so that the velocity of the unthrottled driving jet discharging from said driving nozzle is greater said atomizing jet at said liquid outlet means, a communication between said atomizing nozzle and said blowing nozzle for supplying compressed gas from said atomizing nozzle to said blowing nozzle, so that the discharge velocity of said blowing jet is substantially equal to the discharge velocity of the atomizing jet said blowing jet adapted to prevent atomizing action of the driving jet upon creeping liquid at the discharge outlet of the atomizing nozzle.

4. A spray gun for coating surfaces with liquids, particularly paints and lacquers comprising a chamber means provided with an opening constituting an atomizing nozzle, a liquid outlet means located within said chamber and spaced from said opening whereby the atomizing nozzle provides an atomizing jet, a blowing nozzle surrounding said atomizing nozzle and formed by the outer wall of that chamber and a further wall spaced from said outer wall, a

driving nozzle surrounding said blowing nozzle and formed by the outer wall of thehousing of the blowing nozzle and a further wall spaced fromsaid housing, a compressed air conduit than the velocity of wall of said sleeve and communicating with said driving nozzle to form a driving jet, communication means between said driving nozzle and said atomizing nozzle and throttling means in said communication means for diminishing the. velocity of the compressed air in said atomizing nozzle so that the velocity of the unthrottled driving jet dischargmg from said driving nozzle is greater than the velocity of said atomizing jet at said liquid outlet means a communication means between said driving nozzle and said blowing nozzle, throttling means in said communication means for supplying compressed gas of reduced pressure from said driving nozzle to said blowing nozzle, so that the discharge velocity of said blowing jet is substantially equal to the discharge velocity of the atomizing jet said blowing jet adapted to prevent atomizing action of. the driving jet upon creeping liquid at the discharge outlet of the atomizing nozzle.

5. A spray gun for prising a chamber means provided with an openso that the discharge velocity of the unthrottled driving jet discharging-from said driving nozzle is considerably greater than the velocity of said atomizing jet at said liquid outlet means, and constituting ablowing jetj between the outerthe wall of said chamber means, so that the-discharge velocity of said blowing jetyis substantially equal to the discharge velocity of said atomizing jet, said blowing jet adapted to prevent atomizing action of the driving jet upon creeping liquid at the discharge outlet of the atomizing nozzle.

6. A spray gun for coating surfaces with liquids, particularly paints and lacquers comprising a chamber means provided with an open- .ing, a liquid outlet means located within said chamber means and spaced from said opening, a detachable sleeve concentrically positioned in said chamber and spaced from the wall of said chamber. the inner part of said detachable sleeve constituting an atomizing nozzle surrounding sai liquid outlet means providing an atomizing jet, the outer part of said detachable sleeve constituting a blowing "nozzle formed by the wall of said detachable sleeve and the wall of said chamber, a driving nozzlesurrounding said blowing nozzle and formed by the outer wall of the housing of said chamber and a further wall spaced from said outer wall, a compressed air conduit communicating with driving .nozzle to form a driving jet, communication means between said driving nozzle and said chamber means, throttling means in that communication means to diminish the velocity of the air in said chamber means constituting anatomizing jet in the inner part of said detachable sleeve so that the discharge velocity of the unthrottled driving jet discharging from said driving nozzle is considerably greater than the velocity of said atomizng jet at said liquid outlet means, and constituting a blowing jet between the outer wall of said detachable sleeve and the-wall ,of said coating surfaces with liquids, particularly paints and lacquers coming, a liquid outlet means located within said chamber means and spaced from said opening, a sleeve concentrically positioned in said chamber and spaced fromthe wall of said chamber,

the inner part of said sleeve constituting an atomizing nozzle surrounding said liquid outlet means providing an atomizing jet, the outer part of said sleeve constituting a blowing nozzle formed by the wall of said sleeve and the wall of said chamber, a driving nozzle surrounding said blowing nozzle and formed by the outer wall of the housing of said chamber and a further wall spaced from said outer wall, a compressed air. conduit communicating with said driving nozzle to form a driving jet, communication means between said driving nozzle-and said chamber means, throttling means in that communication means to diminish the velocity of the air insaid chamber means constituting an.

atomizing jet in the inner part of said sleeve chamber means so that the discharge velocity of said blowing jet is substantially equal to the discharge velocity of said atomizing jet, said blowing jet adapted to prevent atomizing action of the driving jet upon creeping liquid at the discharge outlet of the atomizing nozzle.

'7. A method of coating surfaces with liquids, particularly paints and lacquers comprising forming a liquid jet, an atomizing'jet atomizing said liquid jet, a further driving jet concentric with said atomizing jet accelerating said atomizing jet mixed with the atomized liquid whereby the discharge velocity of the driving jet is considerably greater than the'velocity of the atomizing jet at the point where the atomizing jet meets the liquid jet, a. further blowing jet also concentric with said atomizing jet adapted to prevent atomizing action of the driving jet upon creeping liquid at the discharge outlet whereby the discharge velocity of said blowing jet is substantially equal to the discharge velocity of the atomizing jet, the discharge outlet of said driving jet being located relative to the direction of the flow in front of the discharged outlet of the blowing jet, and the discharge outlet of said blowing jet being located relative to the direction 01 the flow in front of the discharge outlet of said atomizing jet.

MINTSCHO POPOF'L

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