WO2008150790A1 - High density powder coating pump and nozzle for producing a narrow, dense spray pattern - Google Patents

Abstract

A nozzle (5) for use with a spray gun (1) of a dense phase powder application system includes a closed end (100,130) cap with a number of powder flow passages (7) that result in a narrow dense powder spray pattern. The flow passages (7) may have any cross-sectional shape with cylindrical passages being one example. A typical nozzle (5) may have one or more such passages (7) with the exemplary nozzle (5). using ten.

Description

HIGH DENSITY POWDER COATING PUMP AND NOZZLE FOR PRODUCING A NARROW, DENSE SPRAY PATTERN

RELATED APPLICATIONS

[0001] This application claims the benefit of pending United States provisional patent application serial number 60/932,136 filed on May 29, 2007, for POWDER COATING SYSTEM WITH HIGH DENSITY PUMP AND SPRAY GUN NOZZLE PRODUCING A NARROW, DENSE SPRAY PATTERN, the entire disclosure of which is fully incorporated herein by reference.

FIELD OF THE INVENTION

[0002] The inventions involve a powder coating system having a high-density pump which provides a relatively dense stream of powder coating material to a spray gun that is designed to spray a narrow dense phase powder spray pattern useful for coating recesses and corners of products such as the inside of file cabinets, for example.

BACKGROUND

[0003] In order to appreciate the inventions, it is useful to first discuss the prior art.

US Patent Nos. 6,840,463 and 6,622,937 are hereby incorporated by reference in their entirety. With reference to Fig. 31 of the '463 Patent a prior art pump is shown that supplies powder to a spray gun such as, for example, the gun shown Fig. 2 from US Patent 6,622,937. The pump is commonly known as a venturi type pump. In a venturi type pump, compressed air is supplied to the pump which creates a low-pressure condition in the pump to pull powder from a power supply hopper into the pump and then push the powder through a hose to the spray gun. One problem with this type of pump and gun in a powder coating system is that it is difficult, and realistically not possible, to spray a narrow dense spray pattern from the spray gun. That is because a relatively large amount of transport air is required to transport the powder, also referred to as dilute phase, from the venturi pump, to the hose, to the spray gun. Since there is a relatively large volume of transport air, compared to the powder being transported to the gun, there is a great deal of transport air issuing from the powder spray nozzle and thus the powder cloud sprayed is not a dense powder cloud, with a high ratio of powder to air, but instead is a relatively dilute powder cloud, with a relatively high ratio of air to powder.

[0004] Pending United States patent application serial number 10/711,434 (the "434 application") published as US patent application publication number 2005/0126476 on June 16, 2005, is also fully incorporated herein by reference. With reference Fig. 1 from the published patent application, the system shown therein includes a dense phase pump 402a that supplies a relatively dense stream of powder coating material through a relatively small diameter hose 406a to a spray gun 20a. The pump is shown in detail in Fig. 1OB from the published patent application. The pump has pinch valves 480, 481 that supply powder to powder transfer chambers 438, 440. Focusing on chamber 438, for example, suction is applied to the chamber to pull powder into the chamber from a powder supply through a pinch valve at the inlet to the chamber. That pinch valve is then closed. Next, positive pressure is applied to the powder transfer chamber 438 while a pinch valve at the outlet of the chamber is opened to allow powder to be pushed out of the chamber through the hose 406a towards the spray gun 20a. Two chambers 438, 440 are used in combination so that while one chamber is drawing powder in, the other chamber is pushing powder out, and vice versa, to provide a relatively constant supply of dense phase powder through the hose to the spray gun 20a.

[0005] The pump shown in Fig. 1OB of the published application is akin to a positive displacement pump meaning that once powder is pushed out of the chamber, it can only go in the direction through the hose to the spray gun. The reason is that when the powder is pushed out of the chamber 438 (or 440) only the pinch valve that controls the flow from the chamber 438 to the gun is open. The pinch valve that controls the flow of powder from the powder supply to the chamber 438 is closed. Consequently, powder cannot be pushed from the chamber 438 back towards the powder supply. Hence, it is not possible for the pump to "reverse direction" like is possible with a Venturi pump as described above.

SUMMARY OF THE INVENTIONS

[0006] The inventions provide nozzle design concepts that may be use to produce a narrow dense phase powder spray pattern, hi one embodiment, a nozzle for a spray gun used with a dense phase powder pump includes at least one flow passage that has at least a portion that is cylindrical. In an alternative embodiment, a plurality of such flow passages may be used. In an alternative embodiment, the flow passage has an inlet and an outlet that have the same cross-sectional area, hi an alternative embodiment, the combined cross-sectional area of a plurality of flow passages is equal to or greater than the cross-sectional area of a hose that supplies powder to the nozzle, hi an alternative embodiment, each flow passage has a cross-sectional area that is small relative to the cross-sectional area of a hose that supplies powder to the nozzle, with one embodiment thereof being flow passages that each have a cross-sectional area no greater than twenty-five percent of the hose cross-sectional area. The inventions further contemplate use of such nozzles with a spray gun in a dense phase powder coating system. These and other embodiments, features and aspects of the inventions are described in detail below, in view of the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Fig. 1 is an exemplary spray gun suitable for use with the present inventions including one embodiment thereof, shown in longitudinal partial cross-section; [0008] Fig. 2 is a front perspective of the spray gun of Fig. 1;

[0009] Fig. 3 is an enlarged illustration of the nozzle end of the spray gun of Fig. 1 ; and

[0010] Figs. 4, 4A and 4B are sectional views of the spray nozzle of Figs. 1-3.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0011] While the inventions are described and illustrated in the context of specific examples of system, pump and spray gun designs and configurations, such examples are intended to be exemplary in nature and not limiting as to the use and application of the inventions. The nozzle concepts set forth herein may be alternatively used with many different spray gun configurations, dense phase pump designs and system designs. Further, while the inventions are useful with robot mounted spray guns, such use is not required. [0012] While various inventive aspects, concepts and features of the inventions may be described and illustrated herein as embodied in combination in the exemplary embodiments, these various aspects, concepts and features may be used in many alternative embodiments, either individually or in various combinations and sub-combinations thereof. Unless expressly excluded herein all such combinations and sub-combinations are intended to be within the scope of the present inventions. Still further, while various alternative embodiments as to the various aspects, concepts and features of the inventions—such as alternative materials, structures, configurations, methods, circuits, devices and components, software, hardware, control logic, alternatives as to form, fit and function, and so on—may be described herein, such descriptions are not intended to be a complete or exhaustive list of available alternative embodiments, whether presently known or later developed. Those skilled in the art may readily adopt one or more of the inventive aspects, concepts or features into additional embodiments and uses within the scope of the present inventions even if such embodiments are not expressly disclosed herein. Additionally, even though some features, concepts or aspects of the inventions may be described herein as being a preferred arrangement or method, such description is not intended to suggest that such feature is required or necessary unless expressly so stated. Still further, exemplary or representative values and ranges may be included to assist in understanding the present disclosure; however, such values and ranges are not to be construed in a limiting sense and are intended to be critical values or ranges only if so expressly stated. Moreover, while various aspects, features and concepts may be expressly identified herein as being inventive or forming part of an invention, such identification is not intended to be exclusive, but rather there may be inventive aspects, concepts and features that are fully described herein without being expressly identified as such or as part of a specific invention, the scope of the inventions instead being set forth in the appended claims or the claims of related or continuing applications. Descriptions of exemplary methods or processes are not limited to inclusion of all steps as being required in all cases, nor is the order that the steps are presented to be construed as required or necessary unless expressly so stated.

[0013] With reference to Fig. 1, powder coating material is supplied from a powder pump and supply arrangement 50 through a powder feed hose 3 to the spray gun 1. The hose 3 typically will be a small diameter hose compare to a hose such as would typically be used to connect a Venturi pump with the spray gun because a low density or dilute phase powder hose is primarily filled with transport air as described above, whereas a dense phase hose 3 is primarily filled with powder. A dilute phase powder hose is typically a 0.500 inch diameter hose, whereas the dense phase hose 3 is typically a 0.236 inch diameter hose or about less than half the diameter. As a further non-limiting example, a dense phase hose typically will have a diameter not greater than about 0.3 inches. The density of the powder in a dilute phase system or hose is typically 0.0018g/cc, whereas the density of the powder in hose 3 for a dense phase system is typically O.OO33g/cc at a powder delivery rate of 225 g/min. In a venturi pump type system, typically 2 - 4 cubic feet per minute (CFM) of air are sprayed from the spray nozzle of a gun in order to transport the powder through the nozzle, whereas in a typical system utilized with the present invention, .7 - .9 CFM of air are typically sprayed through the nozzle in order to transport the powder through the nozzle.

[0014] With continued reference to Fig. 1, the powder supply and pump arrangement

50 controls powder flow from a powder supply 52 to the gun 1 by the use of pneumatically actuated pinch valves 54, such as for example, bladder type pinch valves that open and close in response to external pressurized air. The powder is pumped to the gun 1 via one or more powder pump or transfer chambers 56. The chamber 56 receives positive and negative pressure 58, 60 in a controlled sequence whereby under negative pressure powder is pulled into the chamber 56 and under positive pressure powder is pushed out of the chamber 56 into the hose 3 to the spray gun 1. The pinch valves 54 selectively operate to seal the chamber 56 from the supply 52 when the chamber is under positive pressure so that powder is only able to flow to the spray gun 1. The pinch valves 54 also selectively operate to seal the chamber 56 from the gun when the chamber is under negative pressure so that powder is only able to flow into the chamber from the supply. Accordingly, the dense phase system operates with a positive displacement pump that in this embodiment comprises the pinch valves 54, the chamber(s) 56 and the pneumatic sources 58, 60.

[0015] An electrical power and control system 62 may be used to control operation of the gun 1, as well as the supply and pump system 50. hi the exemplary system of Fig. 1, the spray gun may be an electrostatic spray gun, although the inventions herein are not limited to electrostatic spray technologies. The spray gun 1 may thus include a multiplier 64 which receives a low input voltage and produces a high output voltage to an electrode 66 having an electrode tip 9 that is preferably but not necessarily disposed in the center of the output spray pattern 70 produced by the gun 1. Actuation and control of the spray gun and a coating operation may be effected by one or more trigger mechanisms 72 on the gun. Automatically triggered guns may alternatively be used, such as may be typically mounted on a robotic arm (not shown). Further details of a complete dense phase system including the gun 1, the supply and pump arrangement 50 and the power and control system 62 are provided in the above referenced '434 publication. Other systems may alternatively be used as needed.

[0016] Figs. 4, 4 A and 4B, which will be described in more detail below, illustrate a spray nozzle 5 in an embodiment of a closed end cap 100 having a number of powder flow passages 7 extending through the cap 100. If this type of spray nozzle 5 were put on a dilute phase spray gun, for example, a great deal of back pressure would be created in the hose extending from the Venturi pump to the spray gun. The result would be that very little or no powder would be sprayed from the nozzle. It is likely that so much back pressure would be created, that more flow resistance would be created between the pump and the gun than between the pump and the powder supply hopper. The result would be that compressed air supplied to the pump would find it easier to flow from the pump into the hopper than from the pump to the spray gun, and consequently, the compressed air would reverse its normal direction and flow backward into the powder supply hopper, with the result that no powder would be sprayed from the gun. [0017] If, on the other hand, a nozzle 5 such as that shown in Figs. 2 and 4 were to be utilized with the gun and dense phase system shown in Fig. 1 for example, a narrow dense powder spray pattern 70 will issue from the nozzle. This is stylistically represented in Fig. 4 for two of the streams to illustrate that the nozzle 5 produces separate and distinct narrow powder streams that are rich in powder (dense phase). These streams may form like small diameter ropes of dense powder flow from the passages 7, with one stream for each passage 7. Depending on the design objectives for the nozzle 5, these streams may recombine a distance from the outlet ends 8 of the passages 7, such as for example, one inch. This distance is not critical and may be achieved by controlling the angle of the passages 7 relative to a centerline X of the nozzle, as well as the cone angle as will be described herein below. The streams may recombine along or near the cenlerline X of the nozzle but this is optional. The tight narrow stream pattern of dense powder helps to make the spray pattern less susceptible to air flow and movement of the nozzle, such as for example when the nozzle is on a gun that is moved by a robotic arm. This is also the case for a recombined stream. [0018] Thus, even when a nozzle such as the nozzle 5, which can generate a large amount of back pressure in the hose between the gun and the pump, is placed on the spray gun 1, powder will still be pushed out of the nozzle from the dense phase pump chamber 56 because the powder has no other place to go than from the pump through the hose to the gun and out the nozzle.

[0019] The external configuration of the exemplary spray nozzle 5 is illustrated in

Fig. 2. The nozzle 5 may have a number of powder flow passages 7 with outlet ends 8 surrounding the charging electrode tip 9. Although ten passages are shown in Fig. 2, the number of passages may be selected based on the overall spray pattern shape desired. A single stream pattern using one passage 7 may even be used. The nozzle 5 may be provided with an optional flat 102 on its forward end to facilitate positioning the electrode tip 9, but alternatively the forward end of the nozzle 5 may have any desired profile. A portion 104 of the nozzle face may be provided to run the electrode 9 through the nozzle body interior (see Fig. 3), but alternatively the electrode may be routed through a rib along the outer surface of the nozzle 5, for example.

[0020] Turning next to Fig. 3, the forward end of the exemplary spray gun 1 is illustrated. The nozzle 5 may include an interior passage 106 that receives the electrode 66 which extends forward to the electrode tip 9. The electrode 66 may include a spring like contact 108 that contacts an electrically conductive ring 110 that makes an electrical connection to a contact 112 from the power supply (not shown). [0021] The nozzle 5 may be retained on the spray gun by any suitable means, in this example a threaded ring 114 that pulls the nozzle up snug against the gun body when the ring 114 is tightened. A nozzle insert 116 mates with a forward end of a hose connector 118 that slips into the back end of the insert 116. The hose connector 118 may include a barbed extension 120 that the powder hose 3 is pushed onto. An optional retaining ring 122 cooperates with the hose connector 118 to keep the powder flow path tight and sealed. The hose connector 118 may include a throat having a reduced diameter portion 111 as illustrated. This reduced diameter will tend to create turbulence and re-direct powder towards the center of the connector 118 before the powder is introduced into the main flow volume of the nozzle. This helps to direct the dense tight powder flow towards the tip of the cone (128) for better diffusion and distribution of powder to all the flow passages 7.

[0022] The nozzle insert 116 also retains an optional air permeable filter 124 in the shape of a truncated cone. This filter allows air to be added to the powder stream inside the nozzle to facilitate dispersion and atomizing/fluidizing the powder, and also to direct the powder flow generally along the axis X. Air is provided through air passages 126 in the insert 116 which communicate with a flow of pressurized air in the gun body (not shown). [0023] The nozzle 5 may include an optional conical projection 128 that extends rearward from the closed end cap 130 of the nozzle. By closed end cap is meant that the only outlet for powder or air through the nozzle is through the small powder flow passages 7. The optional conical projection 128 may have a different profile, including but not limited to a frusto-conical shape, a rounded tip and so on. The conical projection 128 may be used to help shape the spray pattern 70 produced by the nozzle, particularly the width of the pattern. The cone angle a (referenced to the centerline X of the nozzle) may be selected to minimize impact fusion while at the same time directing a more uniformly dispersed powder flow outward toward the powder flow passages 7. The powder stream that exits the connector 118, along with the assist of air from the optional filter 124, tends to be a cylinder shape of dense phase powder, so that the cone 128 helps to disperse and diffuse that flow pattern more uniformly towards the passages 7.

[0024] In forming the projection 128 such as by machining for example, an optional annular recess or groove 132 may be formed (Fig. 3). The powder flow passages 7 may then be machined from the recess 132, through the closed end cap 130 to the outlet ends or orifices 8. As best illustrated in Fig. 4, each passage 7 (in the Fig. 4 view, only two passages 7a and 7b are visible) may be formed as simple round through holes of uniform diameter from an inlet end 10 to the outlet end 8. However, the selected geometry, shape and configuration of the passages 7 are not limited to cylinder shapes, but may be any shape including but not limited to square, triangular, octagonal, oval and so on. For a balanced spray pattern 70, the passages 7 will all typically have the same size (e.g. diameter), shape and length and even spacing around the electrode tip 9 (for electrostatic guns) but such is not always required such as for example applications that may use an unbalanced spray pattern. [0025] Still referring to Fig. 4, each passage 7 may be formed at an angle β (also relative to the centerline X of the nozzle). This angle may be selected based on the size of the desired spray pattern 70 (for example, the width of the overall spray pattern 70 produced from the nozzle 5), the amount of dispersion of the pattern desired, the location that the streams recombine, if at all, and so on. In many cases, the angle β may equal the angle a, which avoids the presence of a lip or radius at the juncture between the groove 132 and the inlet 10 of each passage, hi the illustrated embodiments, however, the angle a is slightly greater than the angle β, so that a small radius 134 is present. The inlets of the passages 7, as well as the angle β, may be selected as needed to reduce impact fusion effects of this radius, hi the Fig. 4 embodiment the angle β is positive meaning that the powder streams from the nozzle will be diverging to some extent, even though the overall design may have them recombining a distance from the nozzle. The angle β may alternatively be negative (again with reference to the centerline X as drawn in Fig. 4) so that a converging set of streams flow from the nozzle initially. This may be useful, for example, to produce a single tight pencil like stream a short or other selected distance from the nozzle. Still further, β may be about or equal to zero meaning that the passages 7 would be generally parallel to the centerline X. [0026] The cross-sectional area of each passage 7 is preferably but not necessarily kept uniform from inlet to outlet in order to maintain a consistent velocity of powder through each passage and for all the passages. If all the passages also preferably though not necessarily have the same shape and cross-sectional area, then the overall spray pattern will tend to be uniform with a consistent powder distribution in all the streams. It is also desirable, although again not required, in many applications that the total combined cross- sectional areas of the passages 7 (based on the inside diameter of each passage wall) be equal to or greater than the cross-sectional area of the hose 3 (based on the hose inside diameter). If the passages had a total cross-sectional area smaller than the hose area, there could be undesired acceleration of the powder. As a non-limiting example, for a typical hose having an internal diameter of about .244 inches, the cross-sectional area is about .0467 in² so that if there are ten circular passages 7 each passage would have a cross-sectional area of at least .00467 in and a diameter of about .09 inches for the passages 7 to have about the same or somewhat greater cross-sectional combined area as the hose 3. If the combined cross- sectional area of the passages 7 is somewhat greater than the hose cross-sectional area, then the powder flow will decelerate as it passes through the nozzle. Whether such deceleration is needed will depend on overall system design and spray pattern criteria. A typical nozzle for a dense phase powder coating system using ten passages 7 will have passage diameters in the range of about .08 inches to about 0.1 inches.

[0027] As noted above, because the hose 3 and passages 7 are transporting dense phase powder, their diameters are going to be significantly smaller than would be used for a dilute phase powder system. As a result, each passage 7 will typically have a length that is substantially longer than the diameter, for example a length to width ratio of about 3:1 or more. A typical length for a passage 7 is about 0.29 inches. This can help assure a uniform narrow flow of dense phase powder from the passage. When ten passages 7 are used, each passage will have a cross-sectional area of about ten percent of the cross-sectional area of the hose 3. While the percentage for each passage will be determined by the size and number of passages 7 used, it may typically be that each passage will be no more than about ten to twenty-five percent, and preferably about fifteen percent, of the hose cross-sectional area for narrow dense phase powder streams 70. All of the above exemplary numbers, dimensions, ratios and so on are intended to be exemplary and non-limiting as the actual values will depend on overall system, nozzle and gun design criteria. But, these example demonstrate the overall concept of using one or more narrow passages through a closed end cap nozzle to produce narrow well-defined and stable dense phase spray patterns.

[0028] In addition to being forced to flow out of the nozzle 5, since the powder is transported with much less transport air than was the case with systems utilizing a venturi type pump, much less air is forced to through spray nozzle with the powder. The result is a dense narrow spray pattern that is very effective for coating interior corners and recesses, for example, of a product which is being powder coated. Moreover, in that there was so much transfer air with the venturi type pump powder coating systems of the prior art, the transport air caused the powder to be sprayed from the nozzle at a much higher velocity than is the case in the present invention. The result with the prior art systems was that once the powder was sprayed from the nozzle, the powder cloud tended to expand. In that the powder is sprayed through the nozzle of the present invention with less transport air, the powder is sprayed from the nozzle at a much lower velocity and thus the powder spray pattern does not expand like spray patterns of the prior art. Therefore, the spray pattern remains somewhat tubular and constant in diameter as compared to the conical expanding spray patterns of prior art spray guns.

[0029] Since the cloud of powder coating material sprayed from the gun 1 of Figure 1 is so dense with powder, the spray gun can be mounted on a robot, for example, and moved at a higher speed relative to the product while still achieving good quality powder coating than was possible with prior art spray systems. This improves the production efficiency.

[0030] Note that although the longitudinal axis of each of the passages 7a, 7b in Fig.

4 are shown as angled outwardly relative to the longitudinal centerline of the nozzle, the axis of each of the flow passages could be parallel to the longitudinal centerline of the nozzle, or angled inwardly relative to the longitudinal centerline of the nozzle, or any combination thereof, to create an even a narrower spray pattern or another desired spray pattern.

Claims

We claim:

1. A powder coating system comprising: a pump, a hose, a spray gun and a nozzle on the spray gun, the pump comprising a powder transfer chamber, a source of negative pressure and a source of positive pressure, powder being pulled into the chamber under negative pressure from a powder supply and then being sealable from the powder supply, powder being pushed out of the chamber under positive pressure through a hose to the spray gun, the chamber also being sealable from the spray gun, the nozzle comprising a closed end cap having at least one powder flow passage through the closed end cap, said at least one flow passage having at least a portion thereof that is circular in cross-section.

2. The powder coating system of claim 1 further comprising an electrode extending through the closed end cap, the electrode being connected to an electrical power supply.

3. The powder coating system of claim 2 further comprising a plurality of powder flow passages surrounding the electrode.

4. The powder coating system of claim 1 wherein the entire powder flow passage is circular in cross-section.

5. The powder coating system of claim 4 wherein a plurality of powder flow passages, each circular in cross-section, is formed through the closed end cap.

6. The powder coating system of claim 5 wherein the spray nozzle has a longitudinal centerline and each of the powder flow passages has a longitudinal centerline and the centerline of the powder flow passages is angled outwardly relative to the centerline of the spray nozzle.

7. The powder coating system of claim 1 further comprising a small diameter powder supply tube connected between the pump and the spray gun.

8. The powder coating system of claim 7 wherein the internal diameter of the powder supply hose is no more than about 0.3 inches.

9. The powder coating system of claim 1 wherein said at least one flow passage has a diameter between .08 inches and 0.1 inches.

10. The powder coating system of claim 1 comprising a plurality of powder flow passages through the closed end cap, wherein the combined cross-sectional area of said plurality of passages is about equal to or greater than the cross-sectional area of a powder tube for the nozzle.

11. The powder coating system of claim 1 wherein said at least one powder flow passage is cylindrical along its entire length.

12. The powder coating system of claim 10 wherein each said powder flow passage is cylindrical along its entire length.

13. Powder coating apparatus, comprising: a dense phase powder pump, a hose, a spray gun and a nozzle on the spray gun, the hose comprising a first end for flow of powder from said pump and a second end at the nozzle, said nozzle comprising a closed end cap and a plurality of powder flow passages through said closed end cap, each said powder flow passage having a length that is substantially greater than its width.

14. The apparatus of claim 13 comprising at least five powder flow passages in said nozzle.

15. The apparatus of claim 13 wherein each powder flow passage is circular in cross- section.

16. The apparatus of claim 13 wherein said plurality of flow passages surround an electrode tip.

17. The apparatus of claim 13 wherein said nozzle comprises an internal conical projection between the inlets of said powder flow passages, and an annular groove about the base of said conical projection, said powder flow passages inlets being formed at said groove.

18. Powder coating apparatus, comprising: a dense phase powder pump, a hose, a spray gun and a nozzle on the spray gun, the hose providing powder to the nozzle during a coating operation, said nozzle comprising a plurality of powder flow passages, each powder flow passage producing a separate dense phase powder stream, each powder flow passage comprising a cross-sectional area that is no more than about twenty-five percent of the cross- sectional area of said hose.

19. The apparatus of claim 18 wherein each passage has a cross-sectional area of no more than about fifteen percent of the cross-sectional area of said hose.

20. The apparatus of claim 18 wherein said separate dense phase powder streams recombine near a centerline of the nozzle.

21. The apparatus of claim 18 wherein each flow passage has an inlet and an outlet with said inlet and outlet having the same cross-sectional area.

22. A nozzle for a dense phase powder coating system, comprising: a hollow body, said body comprising a closed end cap with at least one powder flow passage through the closed end cap, said at least one powder flow passage having at least a portion thereof that is circular in cross-section.

23. The nozzle of claim 22 wherein said passage is cylindrical along its entire length.

24. The nozzle of claim 22 comprising a plurality of said powder flow passages with each passage comprising a cross-sectional area that is no more than about twenty-five percent of the cross-sectional area of said hose.