Abstract:
Method for applying powder to objects, such as electric motor stators and permeable substrates. The apparatus includes a first chamber having upper and lower portions. A powder fluidizing bed is disposed at the lower portion and receives and fluidizes a bed of powder to form a powder cloud within the first chamber. An opening is disposed at the upper portion of the first chamber and directs at least one stream of the powder from the powder cloud out of the first chamber. An object holder is disposed above the opening and is configured to hold at least one of the objects at a position for intersecting the stream of powder.

Description:
This application is a divisional of application Ser. No. 09/578,171, filed May 24, 2002 U.S. Pat. No. 6,458,210, the disclosure of which is fully incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention generally relates to apparatus and methods for applying powder to objects. More specifically, the invention relates to electrostatic and other powder application apparatus and methods. 
     BACKGROUND OF THE INVENTION 
     Powder coating technology has generally evolved over several years into several different coating techniques performed with various types of coating systems. Generally, a powder, such as a resinous polymer or paint, is initially adhered to an electrically conductive object. This initial coating process typically involves electrically grounding the object and electrostatically charging the powder particles such that the electrostatic attraction causes the powder to adhere to the object ideally, in most applications, with a uniform coating thickness. This initial powder coating is then cured using heat or other techniques, such as infrared or ultraviolet light. This fully adheres the coating to the object. 
     Applying powder to internal portions of certain objects presents unique problems. For example, electric motor stators are often shaped cylindrically with inwardly facing slots configured to receive copper windings. There must be an electrically insulating layer between the copper windings and the metal defining the slots of the stator. Therefore, when powder coating techniques are used to provide a layer of insulation on these metal surfaces, the powder must penetrate into the slots of the stator, preferably without saturating the end faces of the stator with powder. Especially when faced with stators having deep slots, it has been difficult to fully penetrate into these slots and provide uniform coatings on the internal stator surfaces. Powder spray guns have been attempted in these situations, but generally impart too much powder velocity and, therefore, blow too much powder out from the slots. On the other hand, parts have been placed in the powder cloud formed by electrostatic fluidized beds. However, this may not provide a uniform coating to internal portions of a part for opposite reasons. That is, in conventional forms electrostatic fluidized bed coaters form a powder cloud within a chamber, but this powder cloud generally moves with very low velocity. For this reason, the powder deposits at the end faces of the stators, but does not penetrate fully into the slots. 
     For the reasons stated above, as well as other reasons, it would be desirable to provide powder application techniques and apparatus which can more uniformly and effectively coat internal portions of an object, such as a motor stator or other object requiring internal penetration of an object with a more uniform application of powder than provided with past apparatus and techniques. 
     SUMMARY OF THE INVENTION 
     The present invention generally provides apparatus for applying powder to objects including a first chamber having first and second portions. A powder fluidizing bed is disposed at the first portion of the first chamber and fluidizes a bed of powder to form a powder cloud in the first chamber and moving generally toward the second portion. An opening is disposed at the second portion of the first chamber and directs at least one stream of the powder from the powder cloud out of the first chamber. An object holder is disposed outside the chamber and is configured to hold at least one of the objects at a position for intersecting the stream of powder. In general, the apparatus provides a flow of powder from the chamber which is directed at a greater velocity than the typical velocity of powder within a fluidized bed coating chamber, but less than the velocity from a typical powder spray gun. This allows internal portions of an object, such as a motor stator, to be coated uniformly by forcing the powder through the slots of the stator, or other internal portions of an object, without forcing the powder at such a speed that it will not adhere to the object surfaces due, for example, to electrostatic attraction between the powder and the object. 
     The apparatus more specifically includes a porous member disposed at a lower portion of the first chamber below the bed of powder. The opening is disposed at an upper portion of the first chamber and having an upper side facing the bed of powder and an opposite lower side. An electrostatic charging device is positioned in an air flow path leading to the lower side of the porous member. A pressurized air inlet directs pressurized air into the air flow path such that the air is charged by the electrostatic charging device and then passes respectively through the lower and upper sides of the porous member and into the bed of powder. The apparatus includes a second chamber having an object inlet and an object outlet. The object holder is positioned in the second chamber and is movable to deliver the object from the object inlet to the object outlet. The object holder preferably includes an arm which rotates to move the object from the object inlet to the object outlet. More preferably, and especially in the case of coating motor stators, the arm extends into the second chamber along an axis and the arm further rotates about that axis to rotate the object within the stream of powder and expose multiple sides of the object to the stream of powder. This can facilitate more uniform penetration of powder into the object, such as into the slots of a motor stator. 
     As another feature of the preferred apparatus, the opening is adjustable in size to vary physical characteristics of the stream of powder. For example, the velocity and/or the amount of powder in the powder stream may be varied by reducing or increasing the size of the opening in the upper portion of the first chamber. The opening is formed generally at the narrowest region of a converging area inside the first chamber. This, for example, may be accomplished by using a plurality of converging plates which have upper ends generally forming an apex and the opening. At least one of the converging plates is movable with respect to the other to adjust the size of the opening. A height adjustment mechanism may also be coupled with either the first chamber or the object holder, or both, for adjusting the distance between the opening and the object holder. This feature can be helpful to adjust the amount of powder penetration into the object and to adjust for smaller or larger objects being coated or otherwise applied with powder using the same apparatus. As another alternative feature, the opening may further comprise a plurality of separate channels for directing a plurality of separate streams of powder out of the first chamber to thereby increase the velocity of the powder prior to contacting the object. This has been found especially useful when impregnating objects, such as nonwoven substrates, with a powder for various reasons. 
     A method performed in accordance with the inventive principles generally involves forming a powder cloud within a chamber having first portion with a constricted opening and a second portion; moving the powder cloud generally toward the constricted opening within the chamber; directing a stream of the powder through the constricted opening; and holding the object adjacent the opening and in contact with the stream of powder. As generally discussed in connection with the apparatus described above, the powder cloud is preferably formed and moved by introducing pressurized air through a bed of powder at the lower portion of the chamber and the powder is preferably electrostatically charged, while the object is charged in an opposite manner, such as by electrically grounding the object. In accordance with the preferred method, the object is a motor stator having internal and external portions and the method involves directing the stream of powder through the internal portion and over the external portion of the motor stator to coat the internal and external portions thereof with powder. In accordance with another illustrative example, the object may be a permeable object such as a nonwoven substrate, and the object may be impregnated with powder while holding the object in contact with the stream of powder. 
     These and other features, objects and advantages of the invention will become more readily apparent to those of ordinary skill in the art upon review of the following detailed description of the preferred embodiments, taken in conjunction with the accompanying drawings. 
    
    
     DETAILED DESCRIPTION OF DRAWINGS 
     FIG. 1 is a partially fragmented top view illustrating a preferred coating apparatus constructed in accordance with the invention. 
     FIG. 1A is a fragmentary cross section view of the indexing mechanism. 
     FIG. 2 is a cross sectional view generally taken along line  2 — 2  of FIG.  1 . 
     FIG. 3 is a cross sectional view generally taken along line  3 — 3  of FIG.  1 . 
     FIG. 4 is a cross sectional view of a coating apparatus similar to FIG. 3, but illustrating an alternative opening for forming a stream of powder. 
     FIG. 5 is a fragmented perspective view showing the upper portion of the apparatus illustrated in FIG.  4 . 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring first to FIGS. 1-3, a preferred embodiment of the invention is shown in the form of a coating apparatus  10 . Coating apparatus  10  includes a stationary frame structure  12  for supporting first and second coating structures  14 ,  16 . Although two coating structures  14 ,  16  are shown herein, and are of identical construction, only one coating structure may be necessary for certain applications, or more coating structures may be necessary for other applications. Only the details of coating structure  14  are shown and described herein with the understanding that the details of coating structure  16  are the same. A rotatable indexing mechanism  18  is provided having a plurality of arms  20   a,    20   b,    20   c,    20   d  extending radially therefrom. Apparatus  10  preferably includes six arms, however, more or less arms may be provided as necessitated by the application. Each arm includes a part holder  22   a-d  at an outer end thereof for holding respective parts, shown as motor stators  24   a,    24   b,    24   c  in FIGS. 1-3. Part holders  22   a-c  include a v-notch  26  for receiving the parts, as shown with respect to part  24   b.  Part holders  22   a-d  preferably include permanent magnets (not shown) which hold the ferrous metal stators  24   a-c  in place during a powder coating operation. Indexing mechanism  18  rotates about an axis  28  in the direction of arrow  30  such that arms and part holders  20   a-d,    22   a-c  rotate through inlet  14   a  of coating structure  14  out the outlet  14   b,  into inlet  16   a  and, finally, out the outlet  16   b  of coating structure  16 . Indexing mechanism preferably stops each part  24   a-c  within each coating structure  14 ,  16  at the positions shown to allow coating to take place as described below. In this embodiment, parts  24   a-c  stop for 20-30 seconds within each coating structure  14 ,  16 . Simultaneously, arms  20   a-d  each rotate about their own respective longitudinal axis in the direction of arrow  32  (FIG. 2) for purposes to be described below. Referring to FIG. 1A, rotation of arm  20   a,  as well as the other arms, is accomplished with an electric motor  18   a  and sprocket assembly  18   b.  Arm  20   a  is supported for rotation by one or more bearings  18   c,  as necessary. Arm  20   a  preferably rotates about its axis continuously during the coating process, but rotation may be stopped and started as necessary instead. 
     Respective powder feeders  34 ,  36  are coupled to coating structures  14 ,  16  and include motors  38 ,  40  and feed chutes  42 ,  44 . Motors  38 ,  40  drive conventional screw augers for conveying powder into the respective feed chutes  42 ,  44 . Flexible boots  46  (one shown in FIG. 2) allow for vertical movement of coating structures  14 ,  16  for purposes to be described below. Each feed chute  42 ,  44  leads into a respective first chamber  48 , as shown in FIG. 2 with respect to coating structure  14 . A second chamber  50  has at least a portion thereof disposed above first chamber  48 . First chamber  48  includes a bed of powder  52  at a lower portion thereof which is supported on top of a porous plate  54 . An upper portion of first chamber  48  includes a pair of angled plates  56 ,  58  which converge in an upward direction to define an opening  59  therebetween. Plates  56 ,  58  each are movable in a pivoting manner due to respective living hinges  60 ,  62  disposed at lower ends thereof. Each plate  56 ,  58  is generally movable in the direction of arrows  64 ,  66 , respectively, or in opposite directions. This allows opening  59  to be varied in size and, more specifically, in width along its length. At lower ends, plates  56 ,  58  are securely fastened to support members  68 ,  70  by fasteners  72 ,  74 . Slots  76 ,  78  are provided at upper ends of plates  56 ,  58  and allow for selective locking of plates  56 ,  58  at desired angular positions relative to one another by tightening fasteners  80 ,  82 . Side walls  84 ,  86  disposed perpendicular to plates  56 ,  58  define the other two sides of first chamber  48 . 
     A vibrator unit  90  is coupled with coating structure  14 , as shown in FIG. 3, to assist in maintaining the fluidized state of powder bed  52 . The main fluidization occurs due to a conventional pressurized air system including a pressurized air inlet  92  which directs pressurized air into a third chamber  93  disposed below first chamber  48  and including an electrostatic charging device  94 . A high voltage line  96  (FIG. 2) is coupled to electrostatic charging device  94 , which also may be of conventional design. Air traveling in the direction of arrows  98  carries the electrostatic charge through porous plate  54  and into powder bed  52  thereby electrostatically charging the powder particles forming powder cloud  100  emanating from bed  52 . A stream of electrostatically charged powder  102  exits chamber  48  through opening  59  and internally and externally coats part  24   a  as shown in FIG.  3 . During at least the time that part  24   a  is stopped at the position shown, part  24   a  is rotated in the manner shown by arrows  32  to expose multiple sides of part  24   a  to powder stream  102 . As further shown in FIG. 2, a conduit  104  is coupled to a vacuum source  106  to suction excess powder out of second chamber  50 . Any additional excess powder in second chamber  50  falls through powder collection outlets  108 ,  110 . 
     As further shown in FIG. 2, a height adjustment mechanism  120  is coupled to coating structure  14  and includes a hand wheel  122  coupled with a rotatable rod  124  having a pivoting coupling  126  and coupled with a gear box  128 . Gear box  128  converts rotational movement of rod  124  to vertical translational movement of member  129 , which may be a drive screw. Other suitable supports (not shown) may be used to support the weight of coating structure  14 . Drive screw  129  is coupled with a horizontal support  130  and horizontal support  130  is coupled with vertical supports  132  received by bushings  134 . It will be appreciated that when hand wheel  122  is turned, coating structure  14  will be adjusted in height relative to part  24   a  which extends into second chamber  50  through a slot  136 . A sensor  140  is provided with a sensor tip  142  disposed in an appropriate location to sense the amount of powder in bed  52  and, as needed, instruct a suitable control (not shown) to activate motor  38  to feed additional powder into first chamber  48 . 
     Referring to FIGS. 4 and 5, an alternative coating apparatus  150  is shown and includes a first chamber  152  defined by side walls  154 , a top wall  156  including converging portions  158 ,  160 . Converging portions  158 ,  160  converge upwardly to an opening  162  defined by a plurality of channels  164 . A bed of powder  166  resting on a porous plate  168  defines the bottom of first chamber  152 . The other components necessary to create a powder cloud within chamber  152  and, if necessary, electrostatically charge the powder, may be the same as described above with regard to the first embodiment. Other structure associated with apparatus  150  may be the same as apparatus  10  or may be modified in accordance with the needs of a particular powder application needs of the object to which the powder is to be applied. A stream of powder  170  exits channels  164  and impinges upon a substrate  172 . Channels  164  are contained in an elongate section  174  and preferably are of constant dimension along their length, in a vertical direction, as shown in FIG.  4 . This significantly increases the velocity of stream  170 . In this embodiment, substrate  172  may, for example, be a nonwoven substrate, such as a high loft fiberglass batt between about {fraction (1/16)} inch thick and 3 inch thick. In one example, section  174  was 6 inches in length and 4 inches in height and achieved approximately ½ inch penetration of powder into a high loft fiberglass batt. It will be appreciated that other dimensional and geometric variations will achieve other powder flow velocities and penetrations and that air pressure within first chamber  152  can also effect the physical characteristics of powder stream  170 . In general, channels  164  prevent powder stream  170  from significantly fanning out and instead cause the powder to culminate for better penetration into a part, such as permeable substrate  172 . It may also be possible to compress various thicker substrates during the powder application so that better penetration is achieved and more uniform impregnation results upon decompression of the substrate. 
     While the present invention has been illustrated by a description of various preferred embodiments and while these embodiments has been described in some detail, it is not the intention of the Applicants to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. The various features of the invention may be used alone or in numerous combinations depending on the needs and preferences of the user. This has been a description of the present invention, along with the preferred methods of practicing the present invention as currently known. However, the invention itself should only be defined by the appended claims.