WO2000033971A1

WO2000033971A1 - Powder spray apparatus for spraying exterior can bottoms

Info

Publication number: WO2000033971A1
Application number: PCT/US1999/028042
Authority: WO
Inventors: Douglas C. Mulder; Thomas E. Hollstein; Timothy E. Wilson
Original assignee: Nordson Corporation
Priority date: 1998-12-10
Filing date: 1999-11-24
Publication date: 2000-06-15
Also published as: JP2002531262A; EP1137494A1; AU1832200A

Abstract

Apparatus for spraying powder onto an exterior surface of a can bottom (A) includes a supply of powder (14), a powder spray gun (12) that receives powder from the supply and produces a powder spray directed towards a can bottom, and a control device (40) that shapes the powder spray and collects overspray. A powder collection system (20) is used for recycling substantially all of the powder spray back to the powder supply, thereby increasing the production of fines. In a first embodiment, the control device is realized in the form of an airflow amplifier that draws a vacuum to produce a substantial air movement in the region of the can bottom. This air movement constrains the powder spray to flow within a relatively well-defined envelope. Powder overspray is collected by the amplifier and blown into a powder collection system. In a further embodiment, a deflector sleeve is provided about the gun nozzle to direct secondary powder fines into a well defined more homogenous spray pattern.

Description

POWDER SPRAY APPARATUS FOR SPRAYING EXTERIOR CAN

BOTTOMS RELATED APPLICATIONS

This application is a continuation-in-part of co-pending application serial no. 09/208,678 filed on December 10, 1998 for POWDER SPRAY APPARATUS FOR SPRAYING EXTERIOR CAN BOTTOMS, the entire disclosure of which is fully incorporated herein by reference.

Technical Field of the Invention The present invention relates to powder spraying apparatus and methods. More particularly, the invention relates to powder spraying apparatus and methods featuring a control device that shapes the powder spray pattern to prevent overspray.

Background of the Invention

Powder spraying apparatuses are well known to those skilled in the art. A typical powder spraying apparatus includes a powder source, such as powder stored in a hopper. The powder in the hopper may be fluidized using pressurized air, although not all powder spray systems use fluidized powder. The spraying apparatus also includes a powder spray device such as a spray gun. Many types of spray guns have been developed over the years including electrostatic spray guns. Many powder spraying apparatus also include a powder collection system to collect powder overspray.

Powder spraying apparatuses are used to spray many types of powder onto many types of articles. However, some articles such as the bottoms of cans, have not been powder sprayed in the past because of the difficulty in limiting overspray of the powder. Rather, cans such as a deodorant can, a soda pop can and so forth are sprayed or coated with a liquid. The liquid may be, for example, a sealant or other suitable material to help prevent corrosion. Such corrosion can occur due to moisture collecting around the bottom of the can, for example during shipping or if stored in a humid environment during its useful life, e.g. a deodorant spray can kept in a lavatory. A problem associated with the spraying of liquids is the production of airborne solvents. Powder coating is a solvent free process and therefore desirable in many applications.

Attempting to powder spray can bottoms with known spraying apparatus produces poor results for a number of reasons. First and foremost is that known powder spraying apparatus characteristically produce a large powder spray pattern in an effort to thoroughly coat the article. However, this large spray pattern is a disadvantage when trying to powder spray a limited area of the article, such as the bottom of a can. A large spray pattern produces a substantial amount of powder overspray which can adhere to or collect on the side wall or main cylindrical body of the can. The overspray has a tendency to adhere to the can wall particularly when the powder spray gun is an electrostatic spray gun. In an electrostatic spray gun, an electrostatic charge is applied to the powder. The article typically is electrically grounded, thereby creating an attraction between the powder particles and the article to increase coverage and transfer efficiency and thus to reduce overspray.

The adherence of overspray powder to the can wall, also referred to as feathering, is undesirable because this powder can adversely affect the appearance of the final decoration applied to the can wall. In most consumer can products, the can wall is decorated with an attractive, hopefully eye catching decoration intended to persuade a buyer to purchase the product. These decorations are often applied using rolled on paint. Regardless of the decoration process used, if there is powder adhering to the can wall, the powder may produce bumps and otherwise negatively affect the overall final appearance of the container. Poor appearance of the container may be viewed as a poor sign of quality, and therefore powder overspray onto the can wall must be eliminated as much as possible.

Another difficulty with can bottoms is that the can bottom is typically a contoured surface, often characterized by a central inverted dome. This dome can be difficult to powder coat without producing the undesired overspray.

It is therefore an objective of the present invention to provide improved powder spraying apparatus and methods that produce a controlled spray pattern with minimal overspray. The invention is intended to be particularly well suited but not limited to powder spraying the bottoms of cans. Summary of the Invention

To the accomplishment of the foregoing objectives, and in accordance with one embodiment of the invention, an apparatus for spraying powder onto an exterior surface of a can bottom includes a supply of powder, a powder spray gun that receives powder from the supply and produces a powder spray directed towards a can bottom, and a control device that shapes the powder spray and collects overspray. In a first embodiment, the control device is realized in the form of an airflow amplifier that draws a vacuum to produce a substantial air movement in the region of the can bottom. This air movement constrains the powder spray to flow within a relatively well-defined envelope. Powder overspray is collected by the amplifier and blown into a powder collection system.

In a further embodiment, a deflector sleeve is provided about the gun nozzle to focus secondary powder fines into a more uniform and defined pattern for spraying can bottoms. As a result, the fines can be advantageously used to produce a smoother powder coating on the can bottom. An apparatus that incorporates the invention tends to recycle about 92-95% of the powder that is sprayed towards a can bottom due to the inherent low transfer efficiency of the spraying process for can bottoms. As a result, the powder is constantly being recycled from the collection system to the powder source, and this recycling tends to increase the production of fines. In accordance with this aspect of the invention, the presence of such fines can be advantageously used to improve the overall smoothness and quality of the powder applied to the can bottom.

The present invention also contemplates the methods embodied in the use of such apparatus, and more generally a method for spraying powder onto an exterior surface of a can bottom, the method including the steps of supplying powder to a powder spray gun, producing a powder spray from a nozzle of the gun and directing the spray towards a can bottom, and shaping the powder spray after the spray exits the gun. These and other aspects and advantages of the present invention will be apparent to those skilled in the art from the following description of the preferred embodiments in view of the accompanying drawings. Brief Description of the Drawings

The invention may take physical form in certain parts and arrangements of parts, preferred embodiments and a method of which will be described in detail in this specification and illustrated in the accompanying drawings which form a part hereof, and wherein:

Fig. 1 is a schematic illustration of a powder spraying system embodying concepts of the present invention;

Fig. 2 is a schematic illustration in plan of a powder spraying system including a powder curing stage; Fig. 3 illustrates additional aspects of the invention as to alignment of the article, powder spray gun and airflow amplifier of Fig. 1; and

Figs. 4A and 4B illustrate a further embodiment of the invention.

Detailed Description of the Preferred Embodiments

With reference to Fig. 1, an embodiment of a powder spraying system 10 in accordance with the present invention is illustrated schematically. While the invention is described herein with specific reference to the powder spraying of metal articles such as can bottoms, anyone skilled in the art will readily appreciate that the invention can be applied to many different powder spraying operations and articles. even powder spraying an entire surface of an article, wherein it is desired to maintain a controlled powder spray pattern or envelope. The invention is not limited to spraying metal articles. The present invention is also not limited to specific components of the apparatus 10 described and shown in the illustrated embodiments herein. For example, the present invention can be realized with many different powder spray guns, not just electrostatic spray guns, many different powder collection systems and so forth. The present invention rather is more directed to the various spray pattern control techniques for powder spraying, which techniques can be applied to a wide variety of powder spraying operations. In accordance with the invention and with reference to Fig. 1 , the apparatus 10 includes a powder spray gun 12. The spray gun 12, in this exemplary embodiment, may be realized in the form of an electrostatic powder spray gun, for example a corona powder gun, such as a Versa-Spray II model spray gun available from Nordson Corporation, Amherst, Ohio. The gun 12 is connected to a powder supply 14 via a powder feed hose 16. The gun 12 also receives a low voltage input from a control unit 18, such as a Versa-Spray II Controller available from Nordson Corporation. This low voltage, which is typically about 16-21 volts DC, is stepped up to about 30-100 kilovolts by a voltage multiplier located in the gun.

The powder supply 14 is preferably but not necessarily part of a powder collection system 20. The powder is held in a powder hopper 22 that supplies powder to the gun 12 via the feed hose 16.

The gun 12 is positioned and supported on a gun mount (not shown). The mount may be stationary or movable, such as a robot arm, for example. The gun 12 is positioned so as to direct a powder spray 30 towards the bottom A of a can C. The can C includes a side wall or body B, in this case in the form of a hollow cylinder. The can may be supported by a holder device 26. Typically, the can bottom A is contoured, for example having a central dome D. As represented schematically, the can C is electrically grounded so that the charged powder particles of the powder spray 30 will adhere to the can. The apparatus 10 is intended to effectively powder spray the can bottom A with minimal or substantially reduced feathering and powder overspray onto the can wall B. However, conventional spray guns 12 produce a rather wide unconstrained powder spray. Without the present invention, such a spray pattern results in significant and unacceptable overspray of the can wall B.

When spraying the bottoms of cans, for example, only a small portion of the powder spray 30 adheres to the can bottom A. Thus, only a rather small portion of the powder spray is used to coat a can bottom. The rest of the powder spray in effect is overspray, such as indicated by the reference numeral 44. This overspray powder preferably is not only collected and recycled back to the hopper 14, but also in accordance with the invention should not adhere to the can wall B. The nature of spraying only the bottoms of cans necessarily dictates that a large percentage, even as high as 92-95%, of the spray powder, is overspray and is collected and recycled back to the feed hopper 14. In accordance with one aspect of the invention, a spray pattern control device

40 is positioned generally in alignment with the discharge nozzle exit end 24 of the spray gun 12 on an opposite side of the can C. The control device 40 creates a vacuum which causes a substantial movement of air in the region of the powder spray 30 and the can bottom A, as indicated by the air flow arrows 42. Powder particles in the powder spray 30 are called "soft" because they are easily moved by air movement or air currents. By producing a sufficient air movement in the region of the can C, overspray powder particles are entrained in the air flow 42. The control device 40 collects the powder overspray and blows it into the powder collection system 20. In this example, the device 40 blows the overspray powder into a small collection booth 32. The collection system 20 may also include an air filter 34 that evacuates air from the booth 32, with substantially all of the collected powder returning to the supply hopper 14. The collection system 20 may further include a powder level sensor and a bulk powder feed (not shown). The particulars of the collection system 20, available as a cartridge collection system and the control device 40, are well known, such as, for example, as described in United States Patent No. 4,590,884 owned by the assignee of the present invention, the entire disclosure of which is fully incorporated herein by reference. For purposes of this disclosure, the control device 40 is not considered to be part of the collection system 20, even though it is closely mounted with respect thereto so as to force powder overspray into the booth 32. The cartridge type powder collection system 20 available from Nordson Corporation is particularly useful with the present invention because of its small size and high efficiency in collecting and recycling substantially all of the overspray powder back to the feed hopper 14. In contrast, cyclone type collection systems tend to be large systems that not only use a lot of space but tend to separate from the main powder and dump a large amount of powder fines.

The control device 40 thus serves several important functions. First, powder overspray 44 is captured and blown into the collection booth 32 for return to the feed hopper 14. In this manner, powder is not wasted or lost, even though the transfer ratio of sprayed powder to any single can is low. Second, the control device draws the overspray away from the can wall B, thus preventing overspray of the can wall. This is accomplished in this embodiment by using the control device 40 to create an air movement 42 that in effect shapes the powder spray pattern by forcing the powder spray to flow in a constrained well defined envelope as established by the air movement 42 caused by operation of the control device 40, as illustrated schematically in Fig. 1. An inner portion of the overall air movement 42 serves as containment air 43, within which all powder spray is constrained. By constraining the powder spray to a fairly narrow envelope, a well defined boundary edge 46 is produced. When a can bottom A is exposed to the boundary edge 46 of the powder spray 30, powder adheres to the can bottom A with little or no overspray contacting the can wall B. The general method of the present invention thus involves producing a powder spray, directing the spray towards a specific area of an article to be powder coated, and shaping the powder spray pattern to substantially eliminate overspray and feathering on the article outside the desired area. In the preferred embodiment the powder spray is shaped by providing an airflow that constrains the powder spray to a rather well defined envelope. In the preferred embodiments described herein, the control device 40 may be realized in the form of an airflow amplifier, such as transvector model 903 available from ITW Vortec, Cincinnati, Ohio. An air amplifier is a non-electrical device that converts a compressed air flow into a substantial air movement. Compressed air from a supply such as shop air 50 is input to the airflow amplifier 40 via an air line 52 that connects to an air hose fitting on the airflow amplifier. The amplifier 40 design is such that the compressed air causes a vortical flow within the amplifier and draws in air through the throat 48 of the device. The air simply exits through a discharge pipe 54. When positioned generally across from the gun nozzle 24, the amplifier creates the air movement 42 which entrains the powder overspray. The powder overspray is drawn into the amplifier 40 and blown out into the collection booth 32.

An advantage of the air amplifier 40 is that it creates an envelope of large air movement that draws overspray powder away from the can C side wall B and forces the powder spray to be constrained within a well defined envelope. This is a significant improvement over the use, for example, of air jets which are commonly used in powder spraying apparatus to blow away overspray powder in a fairly random manner into a collection system, for example.

In accordance with another aspect of the invention, the spray gun 12 as noted can be, for example, a Versa-Spray II gun. However, the standard Versa-Spray II gun is intended to produce a rather wide spray pattern. Therefore, to help improve the overall performance of the spraying apparatus 10 of the present invention, a different spray nozzle may be used to produce a narrower spray pattern from the gun nozzle. For example, nozzle part no. CG2756 available from Nordson Corporation can be used with the Versa-Spray II gun to produce such a spray pattern. The narrower spray pattern from the gun 12, in combination with the airflow amplifier 40, produces a well-defined powder spray that greatly eliminates powder overspray when spraying can bottoms. However, other conventional spray guns and nozzles may be used as required. Fig. 2 illustrates a further embodiment of the invention to include a powder curing operation. It is contemplated that to maximize throughput of the spraying operation, cans to be sprayed will be mounted on a moving conveyor system that will pass the can bottoms over the powder spray from a series of stationary guns. The view of Fig. 2 is taken from the top of the system.

In the arrangement of Fig. 2, a series of cans 100 are held on a moving conveyor 102, such as a conventional belt. The conveyor belt 102 includes a series of spaced can holders (not shown) to hold the cans for accurate presentation alignment to the spraying powder apparatus. In this exemplary embodiment, the cans are vertically mounted with the can bottoms pointed downward. However, other arrangements may be used. The conveyor carries the cans 100 into a spray booth 104 which may be conventional in design. In order to assure thorough coating of the can bottoms, in this embodiment several spray guns 106a-d are used. The first set of guns 106a and 106b spray the cans 100 from a first side, while the second set of guns 106c and 106d spray the cans from a second or, in this example, opposite side. The number and position of guns 106 used may vary and will be determined based on a number of factors including the amount of powder each gun 106 is able to apply to a can during one pass, the speed at which the cans are moving past the gun, the material of the powder and so forth. As shown in Fig. 2, for each gun 106 there is a respective facing powder spray control device 108a-d. As in the embodiment of Fig. 1, the control devices 108a-d are generally disposed across from the gun nozzle on an opposite side of the cans, so as to shape and capture the powder overspray.

The control devices 108a-d may each be, for example, an airflow amplifier as described herein before with respect to Fig. 1. Each airflow amplifier 108 blows the powder spray into a collection booth 1 10, there being a separate booth 110a for the first two guns 108a,b and a booth 110b for the guns 108c,d. Depending on the specific design parameters for a particular application, a single collection booth may be used for all the guns. Each airflow amplifier 108a-d receives a compressed air input (not shown in Fig. 2) as described herein before. As the conveyor moves the cans 100 past the guns 106, the can bottoms pass through the powder spray boundary edge of each of the spray guns to coat the can bottoms with powder. The conveyor 102 further transports the coated cans to a powder curing system 120. As is known by those skilled in the art, powder coatings are typically cured by exposing the sprayed article to heat. In some applications the cans 100 may be heated before the powder is applied, so that the powder cures upon contact with the can. In the embodiment of Fig. 2, the powder is cured after the powder spray operation. In this embodiment, the conveyor 102 transports the cans with the can bottoms in close proximity to a series of induction heaters 122. The induction heaters heat the can bottom by producing an electromagnetic field that interacts with the can to heat the metal. The induction heaters include a heater control system 124 as is known. A suitable induction heating system is model ISC-2A available from Mountain Gate. Other curing systems may be used, including but not limited to electric and gas ovens for flash heating. The cured cans are then taken by the conveyor 102 to a suitable staging area (not shown). In general, the alignment of the spray gun nozzle with respect to the can bottom A and the throat of the control device airflow amplifier, will affect the characteristics of the powder spray applied to the can bottom and the nature of any overspray adhering to the can wall. Fig. 3 illustrates these various geometric relationships for the example of a vertically mounted bottom down can C. The air amplifier 40 has a centerline axis 60 and the spray gun 12 has a nozzle centerline axis 62. The can vertical axis is labeled 64 and the can travels horizontally in direction transverse its vertical axis 64 (an axis perpendicular to the drawing sheet as illustrated in Fig. 3). In this embodiment, the spray gun 12 has been rotated so as to form an

angle α between the nozzle centerline 62 and the horizontal axis of travel of the can past the nozzle. In this manner the gun nozzle sprays powder across and towards the

can bottom. The angle α will be selected based on the overall design of the powder

spraying system 10, but we have found that an angle of about 8.5° is useful in many

applications. Fig. 3 also illustrates various distances that should be considered by the designer, including the distance XI from the throat of the amplifier 40 to the can near side 63; the distance X2 from the nozzle tip 24 to the can near side 66; the distance Yl from the bottom 68 of the amplifier throat 48 to the can bottom A; and the distance Y2 from the centerline (horizontal axis) 60 of the amplifier to the bottom of the can A. It is also contemplated that the airflow amplifier 40 may be aligned at an angle with respect to horizontal. Again, these and other topology considerations will be determined for each particular system design. In many cases, it is contemplated that the gun nozzle will be positioned within one foot or so of the can bottom with the airflow amplifier 40 being positioned within six inches or so of the can bottom. With reference to Figs. 4A and 4B we have observed that when fine grain powders (for example, with a mean particle size less than 30 microns or so) are used or produced within the powder spray pattern 30, a secondary spray pattern may be observed even with the use of the airflow amplifier 40. Fig. 4A illustrates this phenomenon in a simplified manner. The main spray pattern 70 contains most of the powder particles, particularly the heavier particles on the order of 30 microns or larger. However, a secondary spray pattern 72 may occur that has the appearance of a fine haze outside the main spray pattern 70. This secondary spray pattern 72 is made up of powder fines, which are separated from the larger, heavier particles of the main spray pattern 70 at the nozzle exit 24. These fines typically are less than 30 microns in size, very light and can cause a light dusting of the can wall B, possibly causing appearance problems in the final decorated can. In conventional powder spraying apparatus, the presence of fines and feathering are considered to be at least a nuisance if not undesirable. This is because the small light fines tend to disperse at the nozzle outlet into a poorly defined non- homogenous spray pattern outside the main spray pattern. Additionally, the fines are so small that their electrostatic charge is significantly weaker than that of larger particles. Accordingly, it is common practice in conventional powder overspray collection systems to separate the fines from the main powder and dump the fines out of the main powder supply. A common apparatus for accomplishing this separation is a cyclone separator. In a conventional cyclone separator based collection system, the powder overspray is fed into a cyclone that induces a vortex flow of the powder stream. The heavier particles fall to the bottom of the cyclone where they are collected and recycled back to the powder feed hopper. The lighter fines are blown up and out of the cyclone with the exhaust air and typically dumped as waste. Fines, however, tend to produce a better finish and powder coating on the article being sprayed. The velocity of the larger particles is much higher than the velocity of the smaller particles or fines. The fines zone 72 or outer region of the powder spray which is principally fines, is created by factors of particle mass (weight) and electrical fields that influence the smaller particles into the fines zone.

The particle velocities and air flow in the fines zone 72 are much slower (i.e. the particles tend to "linger") than the particle velocities and air flow in the large particles zone 70. With the present invention, the lower velocities of the particles in the fines zone are better suited for transferring the powder particles onto the can bottom. It is generally known that high velocities of powder particles along with the high velocities of air flow are not desirable for deposition of powder onto a substrate.

The air amplifier 40 is used to establish a controlled air flow and particle velocities within the fines zone. The amplifier 40 establishes a desired particle velocity and air flow for effective transfer of powder to a substrate, in this example, a can bottom. The air amplifier 40 also establishes a controlled air flow outside the fines zone 72. This outside air flow region (e.g. the inner lines labeled 42 in Fig. 1 substantially prevents powder particle fines from migrating outside the controlled fines zone, thereby improving control over undesired overspray powder.

The apparatus described herein for spraying can bottoms necessarily produces a large amount of oversprayed powder that is not transferred directly onto the can bottom. As a result, the oversprayed powder is constantly being recycled through the collection system and back to the feed hopper. From the feed hopper the powder is pumped back to the gun and sprayed towards the can again. All of this repeated movement and turbulence of the powder tends to produce more fines. The continual recycling of the powder therefore continues to replenish the fines that are transferred onto the can. The repeated cycling of the powder from the collector to the feed hopper to the gun produces particle fracturing which breaks the larger particles into the smaller and sub-micron sizes that replenish the fines which are being applied to the can. Thus, we have found that this constant production of fines can be put to advantageous use for better powder spraying of the can bottoms, rather than having to be viewed as producing fines that need to be separated and dumped which is typical in other types of powder coating applications. It should be understood, however, that not only fine powder particles are applied to the cans. Midsize and larger particles are applied as well. But a part of the powder applied to the cans is comprised of the fine particles and these are replenished by the system described herein.

In accordance then with another feature of the invention as illustrated in Fig. 4B, a close fitting cylindrical sleeve 74 is placed around the nozzle 76. In this embodiment, the sleeve 74 is slipped over the nozzle body 76 with a snug fit to hold the sleeve 74 in place during spraying. The sleeve 74 functions to direct and focus the fines 72 into a more uniform, well-defined and homogenous pattern that is part of but not necessarily blended into the main spray pattern 70 (although the drawing indicates that the fines are blended, such is just one possible result; alternatively, for example, the fines may be formed into a better defined pattern so that the fines are principally used to coat the can bottoms). By producing a better defined spray pattern for the fines, the fines can be used to spray the can bottoms and need not be viewed as a nuisance. Moreover, the apparatus 10 as described hereinabove uses a closed cartridge type dry filter collection system 20 that for all practical purposes collects and recycles all of the overspray. This is in distinct contrast to other collection systems, such as cyclone based systems, that separate and dump a significant amount of the powder overspray that enters the powder collection system as fines. The use of the cartridge type powder collection system 20 disclosed herein tends to increase the production of fines due to the inherent low transfer, high overspray characteristic of the process for spraying can bottoms followed by recycling of the overspray back to the feed hopper. With 90% or more of the powder spray 30 being recycled, the powder tends to breakdown over time into finer and finer particle sizes. The invention thus not only compensates for the presence of fines in the spray pattern, but additionally functions to actually produce more fines because the collection system 20 recaptures and recycles all of the powder overspray.

The axial position of the sleeve 74 with respect to the nozzle exit 24 is important. The sleeve is positioned forward enough to direct the fines, but not so far forward as to interfere with the main spray pattern 70. It is contemplated that the sleeve 74 be adjustable in axial position to accommodate for variations in fine formation from nozzle to nozzle. In the embodiment of Fig. 4B the sleeve 74 can be moved by simply sliding it to the best position on the nozzle body 76.

An alternate method for directing the fines back into the main pattern 70 would be to provide powder shaping air from a device that creates an outer flow of compressed air around the main spray pattern 70.

By re-directing the fines into a better defined and focused spray pattern, the fines can be advantageously used to produce a more uniform and better powder coating on the can bottoms. In this way, the low transfer efficiency spraying apparatus in combination with the powder collection system 20 that collects and recycles all of the powder overspray, advantageously produces these fines that are used to spray the can bottoms.

The invention has been described with reference to the preferred embodiment. Obviously, modifications and alterations will occur to others upon a reading and understanding of this specification. It is intended to include all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.

Claims

CLAIMSHaving thus described the invention, it is claimed:

1. Apparatus for spraying powder onto an exterior surface of a can bottom, comprising: a supply of powder; a powder spray gun that receives powder from said supply and produces a powder spray to be directed towards a can bottom; and a control device that shapes said powder spray and receives powder overspray.

2. The apparatus of claim 1 wherein said control device operates to substantially prevent powder overspray from contacting said can side wall.

3. The apparatus of claim 1 wherein said control device operates to shape said powder spray into a spray pattern with a reduced width.

4. The apparatus of claim 1 wherein said control device produces an air vacuum that shapes said powder spray by drawing a part of said powder spray into said control device.

5. The apparatus of claim 1 wherein said control device comprises an air amplifier that produces a vacuum near enough to a nozzle of said spray gun to capture powder spray that does not adhere to the can bottom.

6. The apparatus of claim 5 comprising a holder for positioning a can bottom within an edge spray region of said powder spray.

7. The apparatus of claim 6 wherein said holder moves the can past said spray gun.

8. The apparatus of claim 7 wherein said holder moves the can past a heater after powder is applied to the can bottom.

9. The apparatus of claim 6 wherein said holder holds a plurality of cans.

10. The apparatus of claim 6 wherein said holder positions a can bottom between said spray gun nozzle and said control device.

1 1. The apparatus of claim 1 further comprising a powder collection system; said collection system receiving powder from said control device and returning said powder to said powder supply.

12. The apparatus of claim 1 wherein said spray gun comprises an electrostatic powder spray gun.

13. The apparatus of claim 1 wherein said control device collects substantially all of said powder spray that does not adhere to the bottom of a can.

14. The apparatus of claim 1 wherein said control device produces a vacuum near said spray gun to restrict said powder spray to a relatively narrow envelope pattern.

15. The apparatus of claim 14 wherein said control device comprises an air amplifier.

16. The apparatus of claim 1 comprising a second control device for shaping said powder spray, said second control device being disposed proximate a spray nozzle of said spray gun.

17. The apparatus of claim 16 wherein said second control device comprises a sleeve disposed about said spray nozzle for deflecting powder spray particles from an outer region of the spray back towards a central region of said spray.

18. The apparatus of claim 17 wherein said sleeve can be adjustably positioned along a longitudinal axis of said nozzle.

19. The apparatus of claim 1 wherein said spray gun nozzle ejects powder generally along a first longitudinal axis, said control device collects powder spray along a second longitudinal axis, and wherein said first and second axes are other than colinear.

20. The apparatus of claim 4 wherein said can bottom is located between said spray gun and said control device.

21. The apparatus of claim 20 comprising a second control device for shaping said powder spray, said second control device being disposed proximate a spray nozzle of said spray gun.

22. The apparatus of claim 21 wherein said second control device comprises a sleeve disposed about said spray nozzle for deflecting powder spray particles from an outer region of the spray back towards a central region of said spray.

23. A method for spraying powder onto an exterior surface of a can bottom, comprising the steps of: supplying powder to a powder spray gun; producing a powder spray from a nozzle of the gun and directing said spray towards a can bottom; and shaping the powder spray after the spray exits the gun.

24. The method of claim 23 wherein the step of shaping the powder spray comprises the step of producing a vacuum near enough to a nozzle of the spray gun to capture powder spray that does not adhere to the can bottom.

25. The method of claim 23 wherein the step of shaping the powder spray comprises the step of producing a vacuum that maintains the powder spray within a relatively tight envelope.

26. The method of claim 25 wherein said powder spray envelope includes a well-defined edge region to which the can bottom is exposed to coat the can bottom with substantially reduced powder spray adhering to the can wall.

27. Apparatus for spraying powder onto an exterior surface of a can bottom, comprising: a supply of powder; a powder spray gun that receives powder from said supply and produces a powder spray to be directed towards a can bottom; a control device that shapes said powder spray and collects powder overspray; and a powder overspray collection device that receives said powder overspray and recycles said powder overspray to said supply of powder.

28. The apparatus of claim 27 wherein said collection system recycles substantially all of said powder overspray back to said powder supply.

29. The apparatus of claim 27 comprises a spray pattern control device that shapes the powder spray into a pattern; said pattern control device directing fines into a well defined pattern to spray the can bottoms.

30. A method for spraying powder onto an exterior surface of a can bottom, comprising the steps of: supplying powder to a powder spray gun; producing a powder spray from a nozzle of the gun and directing said spray towards a can bottom; shaping the powder spray after the powder spray exits the gun; and recycling substantially all of the powder overspray back to the spray gun to increase the production of fines.