Nozzle

Abstract

A spray nozzle for an apparatus which hydraulically atomizes and sprays coating material. The spray nozzle includes a body and a passageway in the body. A forward portion of the passageway has converging side walls. An opening, formed in the body, communicates with the passageway to provide an orifice for the coating material. A step is provided in the passageway. The passageway, the opening and the step in the passageway of the nozzle cooperate to provide a pattern of deposited coating material having feathered edges.

Description

The present invention relates to an apparatus which atomizes and sprays coating material. More particularly, the present invention relates to a nozzle for either a non-electrostatic or electrostatic hydraulic or airless spraying apparatus. The nozzle of the apparatus assists in hydraulically atomizing coating material and provides a deposited pattern of coating material particles having a relatively wide central portion within which the distribution of coating material particles is reasonably uniform. The opposite extremities or margins of the pattern have a progressively decreasing number of particles per unit of width.

A hydraulic or airless spraying apparatus causes the coating material to emerge from the orifice of its nozzle under high pressure. When the coating material emerges from the orifice of the nozzle, it is atomized into a fine spray. The airless apparatus has advantages over several other techniques of depositing the coating material such as reducing the amount of coating material sprayed in order to obtain a suitable film thickness of coating material upon the article thereby resulting in a coating material savings. Another advantage of the airless apparatus is that it is capable of projecting the coating material into the recesses of articles.

A problem generally associated with several known spray nozzles used with an airless spraying apparatus is the apparent inability of such nozzles to atomize the coating material in a manner as to provide a pattern having a relatively wide central portion within which the distribution of coating material particles is reasonably uniform and opposite extremities or margins thereof having a progressively decreasing number of particles per unit of width. The relatively heavy number of paint particles at the opposite extremities of the pattern are sometime referred to as "pig-tails" or simply "tails". The apparent inability of such nozzles to reduce the number of coating material particles at the margins or extremities of the pattern in relation to the number of particles in the central portion of the pattern, that is to feather the pattern, renders it difficult to properly blend together adjacent patterns in such a manner as to provide a suitably uniform film of coating material upon the article.

Therefore, it would be desideratum to provide a means and/or a method whereby a deposited pattern of coating material has a wide central portion having a substantially uniform distribution of material particles with opposite extremities feathered by a decreased number of material particles in relation to the number of particles in the wide central portion of the pattern. The apparent inability of several of the known nozzles to provide a pattern of coating material which substantially eliminates "tails" may be due, in part, to either the physical properties of the coating material such as viscosity, surface tension, density and the like or to the construction of the nozzle or both. Attempts have been made to improve the atomization properties of the coating material by improving properties of material such as viscosity, surface tension, density and the like and by altering the construction of the nozzle.

An attempt to improve the atomization properties of coating material includes heating the material prior to atomization. While heating of the material tends to improve properties such as viscosity, surface tension and the like, other properties of the material remain substantially uneffected resulting in a pattern which does not appear to be particularly advantageous for high quality finishes.

Another attempt to improve the atomization properties of coating material includes thinning of material such as paint so as to reduce its viscosity and subjecting the thinned paint to high pumping pressure so as to provide the paint with a high velocity as it emerges from the nozzle. The thinning of the paint and pumping the thinned paint at a high pressure of about 80 to 100 Kg/cm.sup.2 or higher, which when converted to pounds per square inch is approximately 1,100 to 1,450 p.s.i., may result in excessive paint flow through the orifice of the nozzle thereby resulting in an undesirable finish on the article. Furthermore, subjecting the apparatus to high internal pressures may result in undesirable wear of components such as paint seals and the like of the apparatus.

It is, therefore, an object of the present invention to provide a spray nozzle with means for substantially reducing the number of coating material particles at the opposite extremities of a deposited pattern in relation to the number of material particles found in the wide central portion of the pattern. A further object of the present invention is to provide a spray nozzle having an annular step at about the junction between the cylindrical and the converging wall portions of a passageway in the body of the spray nozzle. The annular step assists in substantially eliminating the "tails" from the pattern of coating material deposited upon the article. Yet another object of the present invention is to provide a spray nozzle structure including a substantially V-shaped orifice opening or groove in the body of the nozzle. The base or root of the "V" of the opening projects to about or beyond the annular step at the junction between the cylindrical and the converging wall portions of the passageway.

Generally speaking, the present invention relates to a spray nozzle which significantly reduces the number of coating material particles at opposite extremities of a deposited coating material pattern when compared to number of material particles found in the wide central portion of the pattern. The spray nozzle includes a body and a passageway in the body. The passageway formed in the body includes a converging wall portion formed at one end thereof. An opening, formed in the body, communicates with the passageway to provide an orifice through which the pressurized coating material emerges. The other end of the passageway is adapted to be connected to a source of coating material. A step is provided in the passageway at about the junction between the converging wall and the cylindrical portions of the passageway. The passageway, the opening and the step in the passageway cooperate so as to substantially eliminate "tails" from the pattern of coating material deposited upon the article.

In the drawing:

FIG. 1 is a perspective view of a spray apparatus incorporating the nozzle of the present invention in operation and the surface of an article being coated by coating material emerging from the nozzle of the spray apparatus;

FIG. 2a is a diagrammatic illustration of a spray pattern obtained employing the nozzle of the present invention with the spray apparatus shown in FIG. 1;

FIG. 2b is a diagrammatic illustration of a spray pattern generally obtained using a conventional nozzle with the spray apparatus shown in FIG. 1;

FIG. 3 is a cross sectional view of a conventional nozzle which provides the spray pattern illustrated in FIG. 2b;

FIG. 4 is a cross sectional view of the conventional nozzle taken across the line 4--4 of FIG. 3;

FIG. 5 is a cross sectional view of an embodiment of the nozzle according to the present invention;

FIG. 6 is a cross sectional view of the nozzle illustrated in FIG. 5;

FIG. 7 is a cross sectional view taken along line 7--7 of FIG. 6;

FIG. 8 is a cross sectional side view of another embodiment of the nozzle of the present invention;

FIG. 9 is a cross sectional plane view taken along line 9--9 of FIG. 8;

FIG. 10 is a cross sectional side view of yet another embodiment of the nozzle of the present invention;

FIG. 11 is a cross sectional plane view taken along line 11--11 of FIG. 10;

FIG. 12 is a cross sectional side view of yet still another embodiment of the nozzle of the present invention;

FIG. 13 is a cross sectional plane view taken along line 13--13 of FIG. 12; and

FIG. 14 is a schematic of an airless electrostatic apparatus using a nozzle of the present invention.

Referring now to FIG. 1 of the drawing, an apparatus including an airless non-electrostatic spray gun 10, coupled to a suitable source (not shown) of coating material under pressure, is predeterminately spaced from the surface article 11. Maintaining the spray gun 10 spaced from the surface of article 11 by about 20 to 30 cm (approximately 8 to 12 inches) results in an instantaneous spray pattern 12 being deposited upon the surface of article 11. Moving the spray gun 10 across the article 11 or displacing the article 11 in relation to the spray gun 10 results in a continuous spray pattern 13 being deposited upon the surface of article.

As shown in FIGS. 1 and 2a, an advantageous instantaneous pattern of an airless spray gun is the oval-like or barshaped pattern 12. The strip-shaped pattern 13, illustrated in FIG. 2a, results from a substantially continuous application of coating material from the gun 10 across the article 11. The absence of "tails" at the opposite extremities of each of the deposited patterns should be noted.

A conventional nozzle 20, as exemplified in FIGS. 3 and 4, includes a nozzle body 21 in which is formed a passageway 22 opened at its rear end 23 so as to communicate with a source of coating material (not shown) under pressure. The passageway 22 includes a substantially hemispherical concavity or dome-shaped portion 24 at the front thereof. The radius of the cylinder portion of the passageway 22 is substantially equal to the radius of the concavity portion 24 of the passage way. An elongated, substantially V-shaped notch 25 is in the front of the nozzle body 21. The notch 25 opens forwardly and the base or root portion thereof projects rather shallowly into the concavity portion 24 of the passageway 22. The interface between the notch 25 and the concavity portion 24 of the passageway 22 provides a relatively small orifice through which the coating material under pressure emerges.

Generally, coating material is fed into the passageway 22 under pressure of about 100 Kg/cm.sup.2 or higher, (about 1,450 p.s.i.) and emerges forwardly from the orifice formed by the concavity portion 24 of the passageway and the V-shaped notch 25. The pressurized coating material emerging from the orifice of nozzle 20 breaks into a very fine spray of coating material particles. However, when employing conventional nozzle 20 with airless spray gun 10, its instantaneous spray coating pattern 14 tends to include at its margins or extremities "tail-like" deposits 15 and 16 as shown in FIG. 2b. The "tail-like" deposits 15 and 16 of coating material at the extremities of the pattern make feathering of adjacent patterns difficult at best. The continuous pattern 17 provided by conventional nozzle 20 is shown in FIG. 2b. Note that the continuous pattern 17 is accompanied by strip-like marks 18 and 19 at the opposite extremities thereof.

A conventional nozzle 20, which provides either an instantaneous pattern 14 or a continuous pattern 17 with "tail-like" extremities 15 and 16 or 18 and 19, respectively, is suitable for non-finish coating but is not entirely satisfactory for high quality finish coating. Further, since some coating material used for high quality finish coating has more of a tendency to produce such "tail-like" marks than other types of coating material, airless coating methods have not been as widely accepted for finish work as is desired.

A nozzle 27 embodying concepts of the present invention is illustrated in FIGS. 5-9. It has been found that if the base or root of a coating material opening or groove 26 in body 34 of nozzle 27, such as an elongated V-shaped notch, projects into passageway 28 to such an extent so as to substantially adjacent with or project beyond the boundary or junction 29 between the converging wall or concavity portion 30 and the cylindrical portion 31 of the passageway, as shown in FIGS. 5-9, the "tail-like" marks in the deposited pattern are not as pronounced as are found when using a conventional nozzle 20. The base or root of the "V" of the V-shaped notch 25 of the conventional nozzle 20, shown in FIGS. 3 and 4, does not project to about the boundary or junction between the converging wall portion and the cylindrical portion of the passageway.

Also, it was found that it is possible to further reduce pronouncedness of such tail-like marks in the deposited pattern of coating material by forming an annular corner section or step 32 in body 34 of nozzle 27' as shown in FIGS. 10-13, at about the boundary or junction 29 between the converging wall portion 30 and the cylindrical portion 31 of the passageway 28. The "tail-like" marks of the deposited spray pattern are substantially completely eliminated by the combination of a V-shaped groove 26 formed in the body 34 of the nozzle 27' such that the base or the root of the "V" of the notch is substantially adjacent with or projects beyond the annular corner section 32 at the boundary or junction 29 between the converging wall portion 30 and the cylindrical portion 31.

The substantially complete elimination of the tails from the deposited pattern may be realized by selecting the diameter of the cylinder portion 31 of the passageway 28 so as to be slightly larger than the diameter of the converging wall portion 30 of the passageway thereby forming the annular corner section or step 32 at the boundary or junction 29 between the converging wall portion 30 and the cylindrical portion 31. It is preferred that step 32 be formed in such a manner as minimize the possibility of a formation of step having a "rounded" or fillet area at junction 29. A nozzle 27' including step 32 at junction 29 is shown in FIGS. 10-13.

A theoretical explanation of the factors acting to inhibit or substantially eliminate the appearance of such tails in the pattern by using nozzles 27 or 27' of the present invention is not presently clearly understood.

Nozzle 27' including an annular corner section or step 32 of substantially a right angle at the boundary or junction 29 between the converging wall portion 30 and the cylindrical portion 31 of the passageway 22 and a V-shaped groove 26 projecting into the passageway in such a manner that the base of the "V" of the groove is substantially adjacent with or projects beyond the boundary or junction 29 is the preferred embodiment of the present invention.

In the foregoing embodiments of the nozzles 27 and 27' illustrated in FIGS. 5-13, inclusive, the converging wall portion 30 may be shaped in the form of a hemisphere, or shaped in a shallow saucer-like form having a depth less than that of a hemisphere or shaped in a cup-like form having a depth greater than that of a hemisphere. The embodiments illustrated in FIGS. 5-13 show the converging wall portion 30 having either a saucer-like form having a depth less than that of a hemisphere or a cup-like form having a depth greater than that of a hemisphere. It is to be understood that the converging wall portion 30 may be in the form of a hemisphere.

The passageway 28 of the nozzles 27 and 27' is open at its rear end 33 so as to communicate with a source of suitable coating material (not shown) under pressure. The interface between groove 26 and the converging wall portion 30 provides a relatively small orifice through which coating material emerges.

As disclosed above, the present invention substantially prevents the appearance of the "tail-like" marks in the deposited pattern which have been associated with several of the coating patterns provided by conventional nozzles. Also, it was found that a melamine resin coating material, which tends to produce the "tail-like" marks when sprayed from an airless spray device using a conventional nozzle of the type shown in FIGS. 3 and 4, can be effectively used with the nozzles of the present invention without producing such marks in the deposited pattern.

Furthermore, the spraying distance, which has conventionally been set at more than 30 cm (about 12 inches) for fear of producing a non-uniform coating film can be reduced to 20 cm (about 8 inches) or less without the undesirable "tail-like" marks appearing in the deposited pattern. The airless device may be effectively used with coating material pressures of about 70 Kg/cm.sup.2 (about 980 p.s.i.) or less as compared with the conventional devices which pressurize the coating material to about 1,450 p.s.i. or higher.

The nozzles of the present invention as illustrated in the drawing and described above may have the following dimensions:

The diameter of the cylindrical portion 31 of the passageway 28 may be about 0.25 to 1.3 of a millimeter (approximately 0.010 to 0.051 of an inch) or more with the preferred diameter of the cylindrical portion being about 0.45 to 0.8 of a millimeter (approximately 0.017 to 0.032 of an inch).

A suitable thickness for the annular corner section or step 32 may be about 0.01 of a millimeter (approximately 0.0004 of an inch) to about 0.03 of a millimeter (approximately 0.0012 of an inch) or more. It is to be understood that the dimensions of the annular corner section or step 32 are merely illustrative and are not to be construed as limiting with regard to the step dimensions which cooperate to assist in substantially eliminating "tail-like" marks from the spray pattern.

A suitable radius for the converging wall portion 30 of the passageway at the junction 29 only may be about 0.115 to 0.64 of a millimeter (approximately 0.0045 to 0.025 of an inch). It is to be understood that the axial radius of the converging wall portion 30 may either be equal to, greater than or less than that of a hemisphere.

A suitable location of the root of the V-shaped groove is to extend to a location adjacent the junction or boundary 29. For example, the root of the V-shaped groove may extend to within about 0.01 of a millimeter (approximately 0.0004 of an inch) of the junction or boundary, coincide with the junction or boundary or extend beyond the junction or boundary by about 0.01 of a millimeter or more.

The angle of groove 26 depends on the desired pattern size. A suitable angle for the groove 26 is about 30.degree.-90.degree. with the preferred angle being about 55.degree..

The ratio of the length of the cylindrical portion 31 of the nozzle to the diameter of the cylindrical portion of the nozzle may be from about 2 to 1 to 6 to 1 or greater.

Coating material, as used herein, includes but is not limited to a fluid or semi-fluid material which may be applied to the surface of an article in relatively thin layers and which changes to a solid coating with the passage of time. The change of the material to a solid may or may not be reversible and may occur by evaporation of solvent, by chemical reaction, or by the combination of the two. A suitable coating material is paint.

The nozzles 27 and 27' of the present invention may be used with any suitable non-electrostatic airless spray apparatus 10 or electrostatic airless spray apparatus 40. Referring to FIG. 14 of the drawing, an airless electrostatic spray gun is designated by the reference numeral 40. The airless electrostatic spray gun 40 includes a barrel 41 and a handle 42. Conduit 43 connects the gun, and hence the nozzle 27', to a source 44 of coating material under pressure to be sprayed. A voltage lead 45 extends into the handle 42 from an ungrounded terminal of a voltage source 46, the other terminal of which is grounded as indicated at 47. A trigger 48 carried by the gun controls the supply of coating material under pressure and voltage in any convenient manner to the gun. Exterior portions of the gun 40, including the handle 42 and trigger 48 may be grounded as through a conductive sheave surrounding, but insulated from, the voltage lead 45. FIG. 14 also shows a grounded article 49 in position to receive the spray from the gun. An electrostatic spray gun is described in detail in U.S. Pat. No. 3,169,883.

The nozzle 27 or 27' should be fabricated from any suitable wear resistant material such as tungsten carbide, ceramic, sapphire, stainless steel, titanium carbide and the like. A preferred material from which either nozzle 27 or nozzle 27' may be fabricated is tungsten carbide.

Claims

I claim:

1. A nozzle for an airless coating apparatus for hydraulically atomizing and spraying coating material, the nozzle comprising

a unitary, one-piece body,

a passageway in the body,

a converging wall portion at one end of the passageway, the other end of the passageway adapted to be connected to a source of coating material,

an opening in the body, the opening communicating with the converging wall portion of the passageway to provide a coating material discharge orifice, and,

a step in the passageway at about the junction between the converging wall portion of the passageway and a main portion of the passageway, the step and the passageway and the opening cooperating to provide a spray pattern of deposited coating material having feathered opposite extremities.

2. A nozzle for an airless coating apparatus as claimed in claim 1, wherein the opening is a substantially V-shaped groove.

3. A nozzle for an airless coating apparatus as claimed in claim 1, wherein the step in the passageway is at the junction between the converging wall portion of the passageway and the main portion of the passageway.

4. A nozzle for an airless coating apparatus as claimed in claim 3, wherein the opening is a groove having a base extending to a location adjacent the junction between the converging wall portion of the passageway and the main portion of the passageway.

5. A nozzle for an airless coating apparatus as claimed in claim 3, wherein the converging wall portion of the passageway is a concavity.

6. A nozzle for an airless coating apparatus comprising

a body,

a passageway in the body,

a converging wall portion at one end of the passageway, another end of the passageway adapted to be connected to a source of coating material,

a substantially V-shaped groove in the body, the groove communicating with the converging wall portion of the passageway and adapted to provide a coating material discharge orifice, and

a step displaced from the other end of the passageway and in the passageway at about the junction between the converging wall portion of the passageway and the main portion of the passageway, the base of the "V" of the V-shaped groove being at about the junction between the converging wall portion and the main portion of the passageway, the step and the passageway and the groove cooperating to provide a spray pattern of deposited coating material having feathered opposite extremities.

7. A nozzle for an airless coating apparatus as claimed in claim 6 wherein the converging wall portion of the passageway is a concavity.

8. A nozzle for an airless coating apparatus as claimed in claim 6, wherein the step in the passageway is an annular step.

9. A nozzle for an airless coating apparatus as claimed in claim 8, wherein the step is at about a right angle with the main portion of the passageway.

10. In combination an electrostatic airless spray gun and a nozzle for the electrostatic spray gun comprising

a body,

a passageway in the body,

a converging wall portion provided at one end of the passageway, another end of the passageway adapted to be connected to a source of coating material

a substantially V-shaped groove in the body, the groove communicating with the converging wall portion of the passageway adapted to provide a coating material discharge orifice, and

an annular step displaced from the other end of the passageway and in the passageway at about the junction between the converging wall portion of the passageway and the main portion of the passageway, the base of the "V" of the V-shaped groove being adjacent the junction between the converging wall portion and the main portion of the passageway, the step and the passageway and the groove cooperating to provide a spray pattern of deposited coating material having feathered opposite extremities.

11. In combination, an electrostatic airless spray gun and a nozzle for the gun as claimed in claim 10, wherein the converging wall portion of the passageway is a concavity.

12. A nozzle for airless coating apparatus characterized in that the nozzle body has formed therein a dome-shaped cavity which is opened to the outside at its rear end, said nozzle body also having formed at its front a V-shaped groove arranged to cross the foremost end portion of said cavity, said dome-shaped cavity being defined by a saucer-shaped or deep cut-shaped concavity and a cylinder having a diameter equal to or slightly larger than the diameter of said concavity, and an annular corner section is formed at the boundary between said concavity and cylinder, said V-shaped groove being formed such that its root is adjacent said boundary, the corner section and the cavity and the groove cooperating to provide a spray pattern of deposited coating material having feathered opposite extremities.

13. A nozzle comprising a unitary, one-piece body, a passageway in the body, a concavity at one end of the passageway, a substantially V-shaped groove in the body, the groove communicating with the concavity providing a discharge orifice for material, and a step in the passageway at the junction between the concavity of the passageway and a main portion of the passageway, the step being annular and at about a right angle with the main portion of the passageway, the base of the "V" of the V-shaped groove projecting to or beyond the junction between the concavity and the main portion of the passageway, the step and the passageway and the groove cooperating to provide a spray pattern of deposited material having feathered opposite extremities.

14. The nozzle of claim 13 wherein the main portion of the passageway is cylindrical in shape and has a diameter slightly larger than the largest dimension of the concavity.

15. A nozzle providing a spray pattern of deposited material having feathered opposite extremities, the nozzle comprising a unitary, one-piece body, a passageway including a rear end in the body, a concavity at an end of the passageway opposite the rear end, an opening in the body, the opening communicating with the concavity providing a discharge orifice for material, and a substantially annular step in the passageway at about the junction between the concavity of the passageway and a main portion of the passageway and displaced from the rear end of the passageway, the step and the passageway and the opening cooperating to provide the spray pattern of deposited material having feathered opposite extremities.