US3527502A

US3527502A - Powder dispensing

Info

Publication number: US3527502A
Application number: US679084A
Authority: US
Inventors: Billy J Graham
Original assignee: Globe Tool and Engineering Co
Current assignee: Globe Tool and Engineering Co
Priority date: 1967-10-30
Filing date: 1967-10-30
Publication date: 1970-09-08
Anticipated expiration: 1987-09-08

Description

p 8, 1970 B. J. GRAHAM 3,527,502

rownnn DISPENSING Filed Oct. so, 1967 64 20 f 4 J15. 3 "o m1 g 5 INVENTOR. 55 1 5 B LL Y .1. GEfll-MM 74 '5 4 H15 arrow/5Y United States Patent Office US. Cl. 302-42 12 Claims ABSTRACT OF THE DISCLOSURE Epoxy powder drawn through feed lines from a fluidized bed by venturi nozzles is sprayed onto a heated workpiece. At the end of a spray operation, sections of each feed line are separated so that air from ambient atmosphere is drawn through the open ends of the sections of the feed lines connected to the spray nozzles. Even spraying of powder is obtained by maintaining a minimum separation between the separate sections of the feed lines. In one embodiment air under pressure blows powder back into the fluidized bed from some sections of the feed lines at the same time as air from atmosphere is drawn through the other sections of the feed lines.

This invention relates to powder dispensing and more particularly to the spraying of a powder coating onto a workpiece.

Epoxy coatings are now commonly applied to electrical components primarily for insulating surface portions thereof. A presently popular method of coating involves the spraying of dry epoxy powder onto metal electrical components which have been pre-heated. The dry powder melts, adheres and cures on the heated metal.

A common procedure for applying the dry powder coating includes the establishment of a fluidized bed of epoxy powder and the withdrawal of a powder-air mixture from the fluidized bed by vacuum suction created at the ends of powder feed lines by venturi nozzles directed onto the heated workpiece. Complete insulating coatings of parts of metal electrical components are obtained by this system within a few seconds. The coated component or workpiece is then removed from the spray area and a heated, but yet uncoated, workpiece is placed in the spray area for a subsequent coating operation. It has been found that the spray coating applied to succeeding heated workpieces is uneven or unequal. Thus, one workpiece may have a thicker or thinner coating than another workpiece. In coating electrical components, the thickness of the coating may be quite critical. Thus, for example, an electric motor armature core may require a minimum insulating coating thickness so that the armature core will remain adequately insulated after coils are wound therein. Too thick a coating may result in armature slots which are too small to receive coils of the desired wire size and number of turns. There is an inherent uncertainty in the amount of powder drawn from a fluidized bed by venturi nozzles because of the nature of fluidized beds. However, this uncertainty or variable normally can be tolerated.

Other factors encountered in the spray operation described above contribute to the uneven or unequal spraying of epoxy coatings. At the end of a spray operation, when the supply of pressure fluid to the venturi nozzles is discontinued, there is an irregular overflow or spillage of powder from the venturi nozzles. Also, powder within the feed lines between the fluidized bed and the nozzles at the end of a spray operation will settle in the feed lines with uncertain results. The powder may accumulate over many spray operations, thereby eflectively reducing the diameter of the feed lines, and some of the settled Patented Sept. 8., 1970 powder may be sucked out of the feed lines in succeeding spray operations which results in an intermittent spurting out of excesive quantities of powder.

An object of this invention is to more accurately control the amount of powder sprayed during any one spray operation. This is accomplished by separating portions of the feed lines prior to the discontinuance of operation of the venturi nozzles, when the portions of the feed lines are separated, the venturi nozzles will draw air from ambient atmosphere through the portions of the feed lines remaining connected thereto. Because of this separation of portions of the feed lines, overflowing or spillage of powder which otherwise occurs is substantially prevented.

Another object of this invention is to provide a method and apparatus for repeated spray coating operations wherein substantially the same amount of powder is sprayed onto workpieces during each of successive spray operations. This object is satisfied by the exposure of the major portions of each of the powder feed lines to ambient atmosphere while vacuum suction at the nozzle end of the spray lines continues, the air taken from ambient atmosphere being drawn through the feed lines to purge them. A still greater repeatability may be obtained by blowing a pressure fluid, such as air, back through the remainder of the feed lines, thereby blowing the powder therein back into the powder supply.

If the methods mentioned immediately above are followed, the amount of powder sprayed during each successive coating operation may be easily and inexpensively, yet accurately, controlled. However, during each spray operation there is some spurting or irregular flow of powder from the spray nozzles. A further object of this invention is to reduce the uneven spraying during a spray operation. For reasons not fully understood, this. is accomplished in accordance with this invention by providing a small air gap between portions of the feed lines so that air from ambient atmosphere is continuously drawn into the feed lines while powder is being drawn from the powder source. For convenience, a small air gap for this purpose may be maintained between the sections of feed lines which are separated by a greater gap just prior to the end of the spray operation for reasons mentioned above.

Other objects and advantages will become more apparent from the following description.

Referring to the drawing:

FIG. 1 is a perspective "view, with parts broken away and in cross section, of a portion of a powder spray apparatus made in accordance with this invention along with a workpiece positioned to be coated by the spray apparatus.

FIG. 2 is a plan and partly cross sectional view of a portion of the apparatus of FIG. 1 as viewed in the direction of arrow 22 thereof.

FIG. 3 is a perspective view of a portion of a presently preferred embodiment of this invention.

FIG. 4 is a cross sectional view of the apparatus of FIG. 3 as viewed in the direction of arrows 44 thereof.

Referring to the drawing in greater detail, a spray coating apparatus generally designated 10 is illustrated in FIG. 1 arranged to spray a coating of epoxy powder onto a workpiece 12 which is illustrated as an electric motor armature and which is mounted in the spraying region by a hollow support shaft 14. It will be understood that the powder spraying would normally take place within an enclosure for the workpiece 12 and a portion of the spray apparatus to be described hereafter. The bottom of the enclosure will usually have a collection bin or trough for collecting powder which does not fall onto the workpiece 12. Also, it will be understood that the workpiece 12 will either be preheated before being inserted into the spray area or else heater means of some sort will be located within the enclosure. The illustration of the armature and the hollow support shaft 14 are merely representative of a wide variety of workpieces which could be coated with the apparatus disclosed herein and of suitable supports or mountings therefor.

Four aspirator or venturi spray nozzles 16 are shown directed toward the workpiece 12. Such spray nozzles 16 may be supported within the spray enclosure in any conventional fashion. Connected to each of the spray nozzles 16 is a fluid pressure conduit 18, each of which is connected to a source (not shown) of compressed air. Vacuum suction created in the spray nozzles 16 when air under pressure is supplied by the pressure conduits 18 draws a powder-air mixture from a fluidized bed housing 20 through feed lines or tubes generally designated 22. The powder-air mixture drawn from the housing 20 mixes with the air supplied through the pressure conduits 18 and passes out of the spray nozzles 16 onto the workpiece 12.

The fluidized bed housing 20 forms no part of this invention and may be of any conventional design. As well known, a fluidized bed may be formed in an upper housing chamber 20a by air under pressure introduced in a lower housing chamber 20b and passing through a porous ceramic plate 200 which divides the housing into the two chambers 20a and 20b.

As will become apparent, powder sources or supplies other than fluidized beds may be useable with the invention described herein. The apparatus as described thus far may be entirely conventional and, for example, the nature of the powder being sprayed, the construction of the spray nozzles 16, and the number of such nozzles 16 are all matters of choice and depend upon the particular spraying operation to be accomplished. Also, a fluid other than air may, in some circumstances, be used as the pressure fluid which is passed through the conduits 18 to create the vacuum suction in the nozzles 16.

Referring now to both FIGS. 1 and 2, each powder feed line or tube 22 comprises a nozzle intake tube 24 forming part of the spray nozzle 16, an elongate, flexible feed tube or hose 26, a short straight tube 28 connected by a hexagonal hose connector 30 to the end of the flexible feed tube or hose 26, and a short outlet tube 32 which projects through a wall of the fluidized bed housing 20 into the fluidized bed in the upper housing chamber 20a. The four outlet tubes 32, for convenience, are mounted in parallel relation on the same wall of the housing 20 by flanges 34.

In accordance with this invention, each of the feed lines 22 has separable sections or portions and to this result, the open ends of the straight tubes 28 are fixedly received within apertures in a movable valve plate 36 which is movable toward and away from a fixed valve plate 38 having apertures fixedly receiving the open ends of the outlet tubes 32. The movable valve plate 36 is mounted upon the fixed valve plate 38 by a pair of guide rods 40 aflixed to the movable valve plate 36 in any suitable fashion and slidable within apertures in the fixed valve plate 38. The fixed valve plate 38 may derive its support from the outlet tubes 32 or may be attached to the housing 20 by brackets or the like (not shown). Movement of the movable valve plate 36 relative to the fixed valve plate 38 is accomplished by a compound air cylinder 42 mounted on the movable valve plate 36 and having a pair of air pressure connections 44 communicating with a source of compressed air (not shown). The air cylinder 42 drives a piston rod 46 associated therewith having a threaded outer end receiving a nut 48 and having a reduced portion passing through still another aperture in the fixed valve plate 38 such that the fixed valve plate 38 is sandwiched between the nut 48 and an enlarged shoulder portion of the piston rod 46.

In the embodiment illustrated in FIGS. 1 and 2, the movable valve plate 36 can be horizontally moved relative to the fixed valve plate 38 along the axes of alignment of the

tubes

28 and 32 to vary the separation between the confronting ends of the

tubes

28 and 32. The short tubes 28 may terminate in the bases of vertical recesses 50 in the rear face, designated 52, of the movable valve plate 36. The outlet tubes 32 project slightly beyond the forward face, designated 54, of the fixed valve plate 38 in alignment with the tubes 28. The minimum separation between the two

valve plates

36 and 38 is determined by an adjustable abutment or stop which may, as illustrated, comprise a threaded stop screw 56 adapted to engage the forward face 54 of the plate 38. The stop screw 56 extends through a threaded aperture within the movable valve plate 36 and receives a lock nut 58 for maintaining any adjusted position thereof.

The mechanism described above is intended to operate as follows. A heated workpiece 12 is placed in the spray area and a spraying operation is initiated by passing air under pressure through the conduits 18 as is conventional. At the time the spray operation begins, the movable valve plate 36 is positioned as near to the fixed valve plate 38 as permitted by the position of the stop screw 56. In this position the confronting ends of the

tubes

28 and 32 are in mutual engagement or preferably, as will be discussed below, almost in mutual engagement. The vacuum suction created at the spray nozzle 16 accordingly draws a powder-air mixture from the fluidized bed housing 20. This powder-air mixture is mixed with the compressed air flowing through the conduit 18 in the spray nozzle 16 and ejected onto the workpiece 12. Just prior to the shutting ofl of the flow of compressed air through the conduits 18, the air cylinder 42 is actuated to move the movable valve plate 36 and, hence, the short tubes 28, away from the fixed valve plate 38 and the outlet tubes 32 along the axis of alignment of the contiguous open ends thereof by a distance sufficient that only air from ambient atmosphere is drawn through the open ends of the short tubes 28. Thus, the gap created in the feed lines 22 is sufficient that the spray nozzles 16 are ineffective to draw powder from the fluidized bed housing 20 and the pressure at the free ends of the outlet tubing 32 is at atmospheric pressure so that no more powder is drawn into even the outlet tubes 32. During the interval in which ambient atmosphere only is being drawn through the open ends of the short tubes 28, the portions of the feed lines 22 comprising the short tubes 28, the flexible hoses 26, and the nozzle intake tubes 24 are purged of all of the powder therein which powder is ejected by the spray nozzles 16 onto the workpiece 12. The coating of the workpiece 12 being completed, it is removed from the spray area and another workpiece positioned in the spray area for a subsequent coating operation. Using this system, powder cannot accumulate in the spray lines 22 to either clog the spray lines 22 or spurt out in subsequent spray operations.

For reasons not fully understood, a more even spray is obtaned if a minimum air gap is maintained between the contiguous, confronting ends of the

tubes

28 and 32 during the entire spray operation. I have found that an air gap of approximately .005 inch between the

tubes

28 and 32 maintained during the spray interval in which powder is being drawn from the fluidized bed 20 results in a more even spray than is possible if the

tubes

28 and 32 are brought fully together. When the

tubes

28 and 32 are brought fully together larger quantities of powder occasionally spurt out of the spray nozzle 16 at intervals during each spray operation. This phenomenon does not occur, or is minimized, when the minimum separation or airgap mentioned above is maintained. Of course, this minimum separation or air gap is much smaller than the separation or air gap required to discontinue the drawing of powder from the fluidized bed housing 20 for the purposes mentioned above.

The duration of the spray coating operation must, as a practical matter, be determined empirically and depends upon several variables, such as the nature of the coating powder being used, the area of the workpiece 12 to be covered, the air pressure within the conduit 18, and the desired coating thickness. The system described above has been successfully used with air pressures in the conduits 18 of three to six pounds and a spray operation of about six seconds with the separation between the contiguous open ends of the

tubing sections

28 and 32 increased from the minimum separation of approximately .005 inch to .025 inch about one second before discontinuing the supply of air under pressure to the conduits 18.

The method and apparatus described above results in a more even spraying of powder from the spray nozzle 16 and an accurate control over the amount of powder drawn from the fluidized bed housing during each spray operation. A problem still exists, however, in that powder may accumulate or settle in the outlet tubes 32, because, of course, air from ambient atmosphere is not drawn through the tubes 32 as it is through the other portions of the feed lines 22. It should be noted that the outlet tubes 32 may be quite short. As an alternative to the structure illustrated in FIGS. 1 and 2, the fixed valve plate 38 could be mounted directly on the fluidized bed housing 20 and the outlet tubes 32, accordingly, would be even shorter than illustrated.

For spray applications in which the settling or accumulation of powder within the sections of outlet tubes 32 is a problem, this problem can be overcome by passing air under pressure through the exposed ends of the outlet tubes 32 so as to blow the residual powder therein back into the fluidized bed housing 20 substantially simultaneously with the exposure of the open ends of the tubes 28 to atmosphere alone. FIGS. 3 and 4 illustrate apparatus operable in accordance with this method. In FIGS. 3 and 4 parts which may be identical to the parts already described in relation to FIGS. 1 and .2 are given the same reference characters. Thus, the apparatus includes a fluidized bed housing 20 from which powder is drawn through powder feed lines 22 including flexible tubes or hoses 26, straight tubes 28 connected thereto by hose connections 30 and outlet tubes 32 mounted by flanges 34 on the fluidized bed housing 20.

For exposing the open ends of the straight tubes 28 to atmosphere and substantially simultaneously exposing the open outer ends of the outlet tubes 32 to air under pressure, a valve assembly, generally designated in FIGS. 3 and 4, is provided which includes a fixed valve plate 62 apertured to fixedly receive the outlet tubes 32 and a movable valve plate 64 apertured to fixedly receive the tubes 28. The valve assembly 60 can be supported on the housing 20 by the outlet tubes 32 or by brackets or the like (not shown). The movable valve plate 64 is guided for movement by and between the fixed valve plate '62 and a vertical guide plate 66 having spaced notches 68 which receive and guide mating surface portions formed on the forward face of the movable valve plate 64. Both the fixed valve plate 62 and the vertical guide plate 66 are shown mounted upon a support plate 70 which also serves as a fixed stop for the lowermost position of the movable valve plate 64. An air cylinder 72 fed by a pair of air lines 74 is attached to the support plate 70 and has a piston rod 76 connected to the movable valve plate 64 for raising and lowering the same relative to the fixed valve plate 62. With special reference to FIG. 4, the passageway receiving one of the outlet tubes 32 in the fixed valve plate 62 is designated 78 whereas the passageway receiving the confronting tube 28 is designated 80. The

passageways

78 and 80 are aligned, as illustrated in FIG. 4, when the movable valve plate 64 is in its lowermost position. In this position, vacuum suction created by spray nozzles, which are not shown in FIGS. 3 and 4, at the outer ends of the feed lines 22 would cause powder to be drawn from the fluidized bed housing 20*.

In accordance with this invention, the air cylinder 72 would be actuated, as in the case of the air cylinder 42 discussed in connection with FIGS. 1 and 2, shortly before discontinuing the vacuum suction at the free ends of the feed lines 22. In the embodiment of FIGS. 3 and 4, however, the movable valve plate 64 is moved vertically upwardly or transversely to the axes of alignment of the open ends of the

tubes

28 and 32 thereby to expose the passageway and the open ends of the tubes 28 to ambient atmosphere as illustrated by the dotted

lines

28a and 80a in FIG. 4, thereby purging most portions of the feed lines 22 of powder. At the same time, four passageways or ports 82 communicating with a manifold chamber 84 in the movable valve plate 64 are positioned in alignment with the open ends of the passageways 78 and a pressure fluid, such as air under pressure, is supplied to the chamber 84 by a pressure line 86 (FIG. 3) connected to a suitable source of compressed air or other pressure fluid (not shown). Accordingly, powder trapped within the passageway formed by the outlet tubes 32 and the passageways 78 is blown back into the fluidized bed housing 20. The pressure fluid need be supplied to the pressure line 86 and the manifold chamber 84 for only a moment. Thus, the entire length of each feed line 22 can be purged at the end of each spray operation.

Again I have found it desirable to maintain a minimum gap in each of the feed lines 22 illustrated in FIGS. 3 and 4 for more even spraying of powder. This gap is conveniently between the movable valve plate 64 and the fixed valve plate 62. Because this gap is so small, on the order of .005 inch, it is not illustrated in FIGS. 3 and 4.

It will be understood by those skilled in the art that the operation of the embodiment of FIGS. 3 and 4 is the same as that of FIGS. 1 and 2 but for the addition of the supply of compressed air back through the outlet tubes 32 at the end of each spray operation. As apparent, the relative positions of parts could be changed without effecting the method of operation or the results accomplished thereby. Thus, the valve assembly 60 could be mounted upside down from the position shown in FIGS. 3 and 4 or the outlet tubes 32 and the valve 60 could be so designed that the movable valve element 64 would move horizontally rather than vertically. Generally these same comments would apply to the embodiment of FIGS. 1 and 2'.

The materials used in forming parts described herein and the manner of connection of various parts connected together are not shown or described in detail since such are matters of choice. The various portions of the feed line 22, for example, could be made from plastic or partially from plastic and partially from metal. Also, it will be appreciated that conventional controls could be used for timing the operations of the various air cylinders with the operation of the spray nozzles 16 and the introduction of air under pressure into the manifold chamber 84.

Having thus described my invention, I claim:

1. In powder spray apparatus of the type wherein powder from a powder supply is drawn through a feed line by vacuum suction created at a spray nozzle mounted on one end of the feed line, the improvement wherein said feed line has two sections with adjacent ends which are aligned as powder is drawn therethrough, said spray nozzl being connected to one of said sections, and the improvement further comprising means for separating said ends of said sections of said feed line by a distance sufficient to render said spray nozzle ineffective to draw powder from said powder supply and to open said end of said one of said sections to atmosphere only.

2. The apparatus of claim 1 wherein said sections are supported with a small air gap therebetween as powder is being drawn from said supply.

3. In powder spray apparatus of the type wherein powder from a powder supply is drawn through a feed line by vacuum suction created at a spray nozzle mounted on one end of the feed line, the improvement comprising means for separating sections of said feed line by a distance sufiicient to render said spray nozzle ineffective to draw powder from said powder supply and to expose an end of one of said sections to atmosphere, and means supplying a pressure fluid to the other of said sections at the same time as said end of said one of said sections is exposed to atmosphere to blow powder in the other of said sections back to said powder supply.

4. In a powder spray apparatus of the type wherein powder from a powder supply is drawn through a feed line by vacuum suction created at a spray nozzle mounted on one end of the feed line, the improvement comprising means for separating sections of said feed line by a distance sufficient to render said spray nozzle ineffective to draw powder from said powder supply and to expose an end of one of said sections to atmosphere, said means for separating sections of said feed line including a first valve plate connected to an open end of said one of said sections, a second valve plate connected to an open end of the other of said sections, said valve plates being mounted with said open ends aligned along an axis and contiguous one to the other, and means connected to one of said valve plates for moving said one of said valve plates relative to the other of said valve plates thereby to separate said sections.

5. The improvement of claim 4 further including means mounting said one of said valve plates for movement along said axis toward and away from the other of said valve plates, and wherein said means moving said one of said valve plates relative to the other of said valve plates moves said one of said valve plates along said axis.

6. The improvement of claim 4 further including means mounting said one of said valve plates for movement in a direction transverse to said axis, and wherein said means moving said one of said valve plates relative to the other of said valve plates moves said one of said valve plates in said transverse direction.

7. In a powder spray apparatus of the type wherein powder from a powder supply is drawn through a feed line by vacuum suction created at a spray nozzle mounted on one end of the feed line, the improvement comprising: means for separating sections of said feed line by a distance suflicient to render said spray nozzle ineffective to draw powder from said powder supply and to expose an end of one of said sections to atmosphere, said means for separating sections of said feed line including a first valve plate connected to an open end of said one of said sections, a second valve plate connected to an open end of the other of said sections, said valve plates being mounted with said open ends aligned along an axis and contiguous one to the other, and means moving one of said valve plates relative to the other of said valve plates thereby to separate said sections; and means supplying a presure fluid to the other of said sections at the same time as said end of said one of said sections is exposed to atmosphere to blow powder in the other of said sections back to said powder supply.

8. The improvement of claim 7 wherein said means supplying a pressure fluid to the other of said sections includes a chamber in said first valve plate having a port communicating with said open end of the other of said sections when said sections are separated.

9. In powder spray apparatus of the type wherein powder from a powder supply is drawn through a feed line by vacuum suction created at a spray nozzle, the

improvement wherein said feed line comprises at least two sections, said spray nozzle being connected to one of said sections, and means are provided to open said one of said sections of said feed line to ambient atmosphere only, whereby air from ambient atmosphere is drawn by vacuum suction through said one of said sections to remove the powder therein.

10. In powder spray apparatus of the type wherein powder from a fluidized bed of powder and air is drawn through a feed line by vacuum suction created at a spray nozzle, the improvement wherein said feed line comprises two sections separated by a gap which is sufiiciently small that air from ambient atmosphere is drawn into one of said two sections while powder is being drawn from said fluidized bed, and means are provided for increasing the gap between said two sections whereby said spray nozzle is ineffective to draw powder from said fluidized bed but continues to draw air from ambient atmosphere into said one of said two sections.

11. In powder spray apparatus of the type wherein powder from a fluidized bed of powder and air is drawn through a feed line by vacuum suction created at a spray nozzle, the improvement wherein said feed line comprises two sections separated by a gap which is sufficiently small that air from ambient atmosphere is drawn into one of said two sections while powder is being drawn from said fluidized bed, means are provided for increasing the gap between said two sections whereby said spray nozzle is ineflective to draw powder from said fluidized bed but continues to draw air from ambient atmosphere into said one of said two sections, and means are provided for introducing air under pressure into the other of said two sections at the same time as said gap is increased.

12. In powder spray apparatus of the type wherein powder from a powder supply is drawn through a feed line by vacuum suction created at a spray nozzle, the improvement wherein said feed line comprises two sections separated by a gap which is sufliciently small that air from ambient atmosphere is drawn into one of said two sections while powder is being drawn from said powder supply, wherein means are provided to increase said gap whereby said spray nozzle is ineflective to draw powder from said powder supply but continues to draw air from ambient atmosphere into said one of said two sections, and said improvement including means introducing air under pressure into the other of said two sections at the same time as said gap is increased.

References Cited UNITED STATES PATENTS 2,667,384 1/1954 Phipps 239-434 3,032,929 5/1962 Glesener 51-8 3,251,550 5/1966 Lippert et al. 239-336 X 3,136,584 6/1964 Whitlock 302-52 3,316,028 4/ 1967 Lloyd 302--52 3,345,111 10/1967 Bies 302-52 ANDRES H. NIELSEN, Primary Examiner US. Cl. X.R. 30258