Patent Abstract:
A powder atomizer comprises a rotatable powder conveying brush operably associated with a powder supply. A powder receptacle has an inlet and an outlet. The powder conveying brush extends along the inlet and supplies powder to the receptacle. A rotatable powder metering brush is operatively associated with the outlet and withdraws powder from the receptacle. A rotatable powder atomizing brush is operatively associated with and receives powder from the metering brush and discharges the powder. A shoe is operatively associated with the atomizing brush, and is pivotable about a pivot axis between a first and a second position.

Full Description:
FIELD OF THE INVENTION 
   The disclosed invention is a modular powder application system for applying powder paint, powder coatings, and like fine powders to moving webs of continuous strip material, such as steel strip. More particularly, the disclosed invention is a powder application system having a powder atomizer module and an electrostatic coating module, with the modules secured together when in an operating condition and adapted to be displaced relative to each other when in a non-operating condition, in order to permit cleaning, service, etc. as may be required. 
   BACKGROUND OF THE INVENTION 
   The application of powder paint, powder coatings, etc to lengths of continuous moving strip material has been achieved through use of electrostatic spray guns and electrostatic application chambers in which powder, in atomized form, is caused to be attracted to the strip through use of charging electrodes positioned. Electrostatic spray guns are limited by the speed at which the strip may move and the rate at which the powder may be applied. Similarly, the electrostatic application chambers are limited by the rate at which powder can be applied to the strip, thus limiting use of these technologies for coating moving strips of material. 
   One drawback to electrostatic application chambers is the service requirements, either on account of routine maintenance or because the powder needs to be changed, as may occur when the type or color of the powder is changed. In those events, the coating line has to be stopped for an excessively long period, and the electrostatic coating apparatus essentially taken apart. This greatly limits the utility of the powder application system, and also increases the cost of the resulting coated product. 
   The electrostatic application of powder paint can be advantageously utilized with different non-metals and metals, such as steel and aluminum, and with strips of different widths. The electrostatic powder application system can be fit into a relatively small footprint, thus eliminating the cost and space of accumulator towers and their sophisticated control assemblies. However, it still is preferred that the tail end of one strip be secured to the lead end of the next to be coated strip, in order to maximize productivity of the coating system. Typically, a stitch is used to connect the tail end to the lead end, but the stitch may extend from one or both strips by such an extent that it may damage the electrostatic coater when it passes through the coating apparatus. 
   Commercially coated strip product must have a uniform coating thickness and a uniform appearance. Rotating auger brushes have in the past been used to move the powder paint from a hopper to a receptacle from which it is drawn and atomized by other rotating brushes. The powder in the receptacle must have a uniform depth, in order to maintain a uniform head assuring uniform removal. Uniform removal is important to uniform deposition, and thus coating thickness or weight and appearance. We have found that auger brushes do not achieve uniform depths of powder in the receptacle, and instead provide more powder proximate the hopper and less powder at the opposite end. Merely increasing the speed of rotation of the auger brush does not solve this problem, and may instead create a different problem due to the sag in the brush which may occur due to its length. Because of brush sag, powder may actually be thrown from the receptacle when the speed of rotation is increased. 
   Typical continuous web powder coating systems utilize a shoe which cooperates with the rotating feeder and atomizing brushes to guide the powder before its is launched into the coating zone. The shoes in the past have been formed from a plurality of individual shoe segments, which were held together by compressive forces. Such a shoe was relatively lightweight, but the compressive forces were generally insufficient to overcome sag of the shoe due to its length and permitted small gaps to be created at abutting sections. The strips to be coated can be up to 108 inches wide, and the shoe must be at least that length. Efforts to shim the shoe segments and otherwise overcome the effect of sag and the formation of gaps were generally unsuccessful. 
   Moreover, because of the tight fit of the shoe to the feeder and atomizing brushes, the shoe made cleaning those brushes and the powder application chamber difficult. The brushes and chamber typically are cleaned with pressurized air, a task made difficult because of the presence and location of the shoe. 
   As noted, the strip material can have a width of up to 108 inches. The brushes, shoe, and other components must therefore have at least a corresponding length. We have found that the atomizing brush, which rotates at a speed sufficiently high to atomize the powder and expel it centrifigally into the electrostatic coating zone, tends to sag at such long lengths. Moreover, when supported by radial bearings, as has typically been done, the brush tended to vibrate excessively due to its natural frequency of vibration. With radial bearings, this was a speed below the operating speed of the brush. The vibrations tended to damage the equipment, and to throw powder from the atomizer in an uncontrolled way. 
   The typical powder atomizing system also utilizes a “wing” in cooperation with the atomizing brush to direct the atomized powder into the coating zone. Once set, the wing was fixed in position, regardless of whether the orientation was optimum for the powder being applied or the strip being coated. 
   Powder application systems can be used to electrostatically apply powder to both surfaces of the strip. Sometimes only one surface is to be coated, however. Although the coaters can be arranged in any orientation, a typical orientation is for the strip to move horizontally. In that event, there is a coater for the upper surface and a coater for the lower surface. The electrostatic coating zone is typically a box-like rectangular assembly. Powder tends to accumulate at corners and on flat surfaces. Once sufficient powder has accumulated, then gravity causes the accumulated clump to fall onto the below moving strip. In that event, a portion of the strip has a non-uniform surface, and is not commercially saleable. 
   The coating thickness is a function of the speed of the strip and the rate at which powder is atomized. Typical coating systems in the past had a single coater, which applied powder to one surface on one pass and to the other on another pass. This was a slow process. Additionally, because the atomizing rate was essentially fixed, then the strip speed was used to regulate coating thickness. 
   SUMMARY OF THE INVENTION 
   The disclosed and claimed invention is an electrostatic powder application system formed from a powder atomizer module and an electrostatic coating module. The modules are adapted to be displaced relative to each other in order to enhance maintenance and cleaning. Each system comprises one of each such module, and there may be a plurality of such systems arrayed along each surface to be coated. The systems are independently operable, in order to permit application of powder as may be desired and as needed to permit sufficient or specified coating weight. 
   Additionally, the atomizer module has a one-piece weldment shoe pivotable between an operating position and a maintenance or cleaning position. Similarly, the wing is adjustable while installed on the atomizer module, to permit maximum regulation of the powder throughput. The atomizing brush is supported by angular contact bearings, which permit a more taut construction, while achieving a natural vibration that is far higher than the operating speed of the atomizing brush. 
   Moreover, the auger brush used to supply powder to the receptacle has a varying pitch which maintains relatively uniform depths of powder within the receptacle. The auger brush has a plurality of pitches, with the pitch increasing by a uniform amount along the effective length of the receptacle. 
   A brush for conveying powder in a powder applicator includes an axially extending rotatable shaft. A plurality of deformable members extend radially from and helically along the shaft. A gap is disposed between adjacent turns of the helix, and the gaps define a pitch, with pitch varying along the axis. 
   A powder feeder for conveying powder from a powder supply to a powder discharging device includes a rotatable brush operably associated with the supply for withdrawing powder from the powder supply. The brush includes a shaft and a plurality of deformable members. The deformable members extend axially from and helically along the shaft. A gap is disposed between adjacent turns of the helix and the gaps define a pitch, that varies along the shaft. A powder receptacle for containing the powder withdrawn from the powder supply by said brush has an inlet for receiving the powder and an outlet for discharging the powder. The brush extends along the powder receptacle. 
   A powder delivery device for delivering powder from a powder feeder to a powder atomizer or to a substrate has a rotatable shaft with a plurality of deformable bristles extending therefrom for conveying powder from a first position to a second position. First and second angular contact bearing assemblies are mounted to the shaft at opposite ends thereof and facilitate rotation of the shaft. First and second seal assemblies are disposed about the shaft in cooperation with the bearing assemblies to reduce contamination of powder during rotation of the shaft. 
   A modular powder application system for coating at least one side of a continuous moving substrate with powder from a powder supply includes an atomizer module in operative communication with a powder supply. Actuation of the atomizer module causes powder to be discharged from the atomizer module as a cloud of particulate material. An electrostatic coating module is operatively associated with the atomizer module and selectively displaceable relative to the atomizer module. The electrostatic coating module comprises at least one charging electrode creating an electric field. The electrostatic coating module receives the cloud of particulate material from the atomizer module. Substrate material positioned within the electrostatic coating module will attract and thereby be coated with the particulate material within the cloud. 
   A system for coating at least one side of a continuous moving substrate with powder from a powder supply and for allowing enhanced access to an operator for maintenance of the system includes a powder atomizer in operative communication with a powder supply. Actuation of the powder atomizer causes the powder to be discharged as a cloud of particulate material. At least one charging electrode is operatively associated with and displaceable relative to the powder atomizer and cooperates with the cloud of particulate material, so that particulates from the powder atomizer are electrostatically attracted to a substrate adjacent the charging electrode. 
   A system for electrostatically applying powder to at least one side of a continuous moving substrate with powder from a powder supply includes a powder application system comprising a powder atomizer in operative communication with a powder supply. Actuation of the powder atomizer causes powder to be discharged from the atomizer. An electrostatic coater is operatively associated with the atomizer. The electrostatic coater includes at least one charging electrode creating an electric field, causing the powder to be attracted to the substrate as the substrate travels adjacent to the electrostatic coater. A cover at least partially covers the atomizer and electrostatic coater. The cover defines a gap through which the substrate travels. An actuating assembly is operatively connected to the cover and at least one of the atomizer and the electrostatic coater, and selectively spaces the cover relative to the atomizer and the electrostatic coater between an operating position and a non-operating position. 
   A powder atomizer comprises a rotatable powder conveying brush operably associated with a powder supply. A powder receptacle has an inlet and an outlet, and the powder conveying brush extends along the inlet and supplies powder to the receptacle. A rotatable powder metering brush is operatively associated with the outlet and withdraws powder from the receptacle. A rotatable powder atomizing brush is operatively associated with and receives powder from the metering brush and discharges the powder. A shoe is operatively associated with the atomizing brush, and the shoe is pivotable about a pivot axis between an operating and a non-operating position. 
   A one-piece shoe for a powder atomizing system comprises a laterally extending contoured integral support having an upstream end and a downstream end. The support has a surface including at least first and second arcuate portions extending in spaced relation from the downstream end toward the upstream end. A plurality of reinforcing ribs extends in spaced parallel relation from the support from a surface disposed opposite the first mentioned surface. An outer pair of the ribs include a pivotal mounting, so that the support may be pivoted between an operating position and a non-operating position. 
   A system for coating at least one surface of a substrate moving through a powder application system comprises a powder atomizer in operative communication with a powder supply. Actuation of the powder atomizer causing the powder to be discharged from the atomizer. An electrostatic coater is operably associated with the powder atomizer and comprises at least one charging electrode creating an electric field acting upon the discharged powder and causing the powder to be attracted to a substrate operably positioned within the electrostatic coater. An arcuate guide extends within the electrostatic coater. The guide directs the discharged powder toward and within the electrostatic coater. 
   This invention will now be described with respect to certain embodiments thereof, along with reference to the accompanying illustrations. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a side elevational view with dotted lines illustrating internally located parts of a modular powder application system according to the invention; 
       FIG. 2  is a side elevational view of a second embodiment of a modular powder application system; 
       FIG. 3  is a top plan view of a powder atomizer according to the invention; 
       FIG. 4  is an elevational view of a powder supply auger brush according to the invention; 
       FIG. 5  is a cross-sectional view taken along the line  5 — 5  of FIG.  4  and viewed in the direction of the arrows; 
       FIG. 6  is a fragmentary plan view, with portions shown in section, of a high-speed brush used with the powder atomizer of  FIG. 3 ; 
       FIG. 7  is an enlarged cross-sectional view illustrating a bearing assembly at one end of the high-speed brush of  FIG. 6 ; 
       FIG. 8  is an enlarged cross-sectional view illustrating another bearing assembly used with the high-speed brush of  FIG. 6 ; 
       FIG. 9  is a cross-sectional view partially in elevation of the powder atomizer of  FIG. 3 ; 
       FIG. 10  is a cross-sectional view partially in elevation of the powder atomizer of  FIG. 3  in the operational position; 
       FIG. 11  is a side elevational view of an electrostatic coating module, with the electrodeenclosure in the retracted orientation; 
       FIG. 12  is a fragmentary front elevational view of the powder application system of  FIG. 2 ; 
       FIG. 13  is a top plan view of the powder application system of FIG.  1 . 
       FIG. 14  is a top plan view of the powder application system of  FIG. 1  with the atomizer module and the electrostatic coating module in spaced position; 
       FIG. 15  is a side elevational view of the powder application system of  FIG. 2  in a spaced orientation; 
       FIG. 16  is a side elevational view of the powder application system of  FIG. 15  in the coating orientation; 
       FIG. 17  is a side elevational view of the electrostatic coating module of  FIG. 11  in the closed or operational position; 
       FIG. 18  is a side elevational view of the powder application system of  FIG. 1  in the lowered orientation; 
       FIG. 19  is an exploded assembly drawing view of the one-piece weldment shoe of the invention; 
       FIG. 19A  is a side elevational view of the shoe of  FIG. 19 ; 
       FIG. 20  is an elevational view, partially in section, illustrating the wing adjustment mechanism; 
       FIG. 21  is a fragmentary cross-sectional view of the electrostatic coating module illustrating the powder recycle mechanism; 
       FIG. 22  is a fragmentary cross-sectional view of the powder application system of  FIG. 2 ; 
       FIG. 23  is a fragmentary front elevational view of the lower frame of the powder application system of  FIG. 1 ; 
       FIG. 24  is a fragmentary elevational view of the upper frame of the powder application system of  FIG. 2 ; 
       FIG. 25  is a side elevational view of  FIG. 11  with portions removed in order to illustrate internal details; 
       FIG. 26  is an enlarged fragmentary assembly drawing of the slider mechanism used for translating the electrostatic coating module between the positions of  FIGS. 11 and 17 ; 
       FIG. 27  is a front elevational view of the electrostatic coating module; and 
       FIG. 28  is an elevational view of a coating line having the powder application systems of the invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Powder application system PC of  FIG. 1  includes a powder atomizer module A and an adjacently disposed and cooperating electrostatic coating module E. The powder application system PC of  FIG. 1  is particularly adapted for electrostatically applying a fine powder, such as powder paint, to a first or lower surface of continuously moving substrate, such as steel sheet. Powder application system PC 1  of  FIG. 2  likewise has a corresponding powder atomizer module A 1  and an adjacently disposed and cooperating electrostatic coating module E 1 . Powder application system PC 1  is particularly adapted for electrostatically applying fine powder, such as powder paint, to continuously moving substrate, such as steel sheet. The powder application systems PC and PC 1  are preferably disposed on opposite sides of the moving substrate, and preferably are spaced along the longitudinal or direction of movement of the substrate. Although the powder application systems PC and PC 1  are illustrated as applying powder to a horizontally disposed strip, the powder application systems PC and PC 1  may be positioned in any convenient orientation. 
   Powder atomizer module A of  FIG. 1  includes a lower frame  10  having rollers  12  and  14  permitting the lower frame  10  and thereby the powder atomizer module A to be translated relative to the electrostatic coating module E, as best shown in  FIG. 14 , when the modules A and E are not secured together. The modules A and E may be translated or moved relative to one another transverse to the movement direction of the substrate material, in order to permit access to either module for cleaning and maintenance purposes. When the modules A and E are in the operational position of  FIG. 13 , then substrate material S moving in the direction  16  may be coated with the electrostatically applied powder paint. The modules A 1  and E 1  of the powder application system PC 1  are not movable relative to each other, however. 
   Atomizer module A has an upper frame  18  to which a powder feed and atomizing system is attached in order to communicate powder from hopper  20 . Pneumatic cylinder  22  and its piston  30  interconnect lower frame  10  to upper frame  18 . Preferably, support  24  upwardly extends from upper frame  10  and cooperates with the rollers  26  secured to support  28  depending from upper frame  18 . In this way, operation of cylinder  22  and extension of piston  30  permits guided vertical movement of upper frame  18  relative to lower frame  10 . Additionally, we provide a screw jack assembly  32  comprising a rotatable jack  33  and extensible screw  35 . The jack  33  is driven by variable speed motor  37 . There is a screw jack assembly  32  and a corresponding cylinder  22  and piston  30  at each corner of the powder coating system PC. Electrostatic coating module E likewise has a lower frame  34  carrying rollers  36  and  38  in order to permit vertical translation of electrostatic coating module E relative to atomizer module A. As with atomizer module A, electrostatic coating module E includes an upper frame  40  from which V-rollers  42  depend for engagement with support  44  extending from lower frame  34 . Similar cylinders  22  and piston assemblies  30  and screw jacks  32  extend between upper frame  40  and lower frame  34 . Actuation of the cylinder  22  causes extension and retraction of piston  30  and thereby displacement of the upper frame  40 . The screw jacks  32  permit precise control over the position of atomizer module A and electrostatic coating module E, in order to accommodate differences in the position of the strip S due to its thickness, tension, etc. The pneumatic cylinder  22  thus provides a rough positioning, with operation of the screw jack assembly  32  permitting fine control, which may permit pitch and yaw to be given to the powder application system PC. 
   Support  46  extends from upper frame  40  and has a C-shaped bracket  48  opening toward atomizer module A, as best shown in  FIGS. 1 and 11 . A support  50  extends from upper frame  18  adjacent support frame  46 . A cylinder and piston assembly  52  is secured to bracket  54 , so that locking element or disk  56  may be selectively positioned within bracket  48 . Actuation of cylinder and piston assembly  52  causes the locking element  56  to engage bracket  48 , thus securing atomizer module A to electrostatic coating module E. Correspondingly, extension of the piston will cause the locking element  56  to be moved out of engagement with bracket  48 , thereby releasing the modules A and E. A similar C-shaped bracket  48  is secured to lower frame  34 , such as by brace  58 , so that it may receive a corresponding locking element  56  of adjacent cylinder and piston assembly  52  secured to brace  60 . Preferably there are like locking mechanisms on both lateral sides of modules A and E. 
   Extending from the bracket  48  carried by brace  58  is a plate  61  that confronts sensor  62 . The sensor  62  is in electrical communication with a control module. The control module determines whether the modules A and E are secured together in the operational position. The control module, in response to the signal from sensor  62 , permits operation of the powder application system PC when the atomizer module A is secured to the electrostatic coating module E through actuation of the cylinder and piston assemblies  52 . If the modules A and E are not secured together in the operational position, then the powder application system PC is not permitted to operate. 
   The powder atomizing system of atomizer module A includes a first rotatable auger brush  64 , as best shown in  FIGS. 1 and 3 , disposed below the outlet of hopper  20  for receiving powder, and for communicating the powder across the powder receptacle  66 . A feeder or metering brush  68  withdraws the powder from receptacle  66  through an outlet  67  extending along the lower portion thereof, as best shown in  FIGS. 1 and 9 . See also U.S. Pat. No. 6,109,481, the assignee of which is the assignee hereof, and the disclosure of which is incorporated herein by reference. High speed atomizing brush  70  interacts with feeder brush  68  in order to receive the powder, and to atomize the powder so that it may be dispersed as a cloud and enter electrostatic coating module E. Preferably, a wing  72  is adjacent and cooperates with high-speed brush  70 , in order to more accurately direct the cloud of powder particulate material into the interior of the electrostatic coating module E. See also U.S. Pat. No. 5,996,855, the assignee of which is the assignee hereof, and the disclosure of which is incorporated herein by reference. 
   As best shown in  FIG. 3 , auger brush  64  has a first portion that extends through the opening  74  of hopper  20 . The brush  64  extends laterally across atomizer module A, between spaced sidewalls  76  and  78 , along the open top of receptacle  66 . Tubes  80  and  82  circumscribe brush  64  and are mounted for extension and retraction from walls  76  and  78 , respectively, in order to permit adjustment of the effective width of receptacle  66 . In this way, movement of the tubes  80  and  82  and the depending sidewalls extending into receptacle  66  permits adjustment of the effective width of atomizer module A, thus permitting substrate of different widths to be coated. 
   The walls  76  and  78  are displaced by rotation of shafts  330  and  332  in response to rotation of servomotors  334  and  336 , respectively. Operation of the motors  334  and  336  thus permits the walls  76  and  78 , and thereby their attached tubes  80  and  82 , to be selectively positioned within receptacle  66  in order to set the effective width of receptacle  66 . The walls  76  and  78  are secure cy clamps  338  and  340 , respectively, to nuts  342  and  344 , respectively, which are driven by the shafts  330  and  332 . 
   The receptacle  66 , as best shown in  FIG. 10 , is triangular in cross section with an open top and a bottom outlet  67  proximate feeder brush  68 . Rotation of feeder brush  68  causes essentially uniform removal of powder from the receptacle  66  over its length. We have found that the pitch of the bristles  84 , as best shown in  FIGS. 4 and 5 , should be varied in order to assure an essentially uniform level of powder within receptacle  66 . For a brush of constant pitch, there may not be sufficient powder in the receptacle  66  towards end wall  68 . This is because uniform removal across the length of receptacle  66  by feeder brush  68  requires uniform replacement of powder by auger brush  64 . We have surprisingly found that uniformly decreasing the pitch from one flight of bristles to the next has the effect of assuring sufficient powder over the entire length of the receptacle  66 . We have found that decreasing the pitch by approximately {fraction (1/16)} of an inch per flight assures sufficient powder for a receptacle having a width of 108 inches. 
   As best shown in  FIG. 4 , brush  64  has the bristles  84  helically arrayed about shaft  86  between its opposed ends, and are secured to the shaft  84  by steel banding or the like. The helix creates a series of gaps  88 , in which the powder is received and transported by rotation of shaft  86  by a suitable motor. The gaps  88  have bristles  84  at opposite ends thereof, with the spacing between the bristles  84  as defined by the gaps  88 , thus defining a pitch. We have found that the brush  64  should have a first pitch  90  in the area underlying the opening  74  in hopper  20 , a second pitch  92  extending through tube  80 , and a constantly decreasing pitch portion  94 . A fourth pitch portion  96  is provided for tube  82 , with a final pitch  98  for transporting any powder not deposited into the receptacle  66  into a recycle line. The bristles  84  preferably are 6,6 nylon. 
   The variable pitch cross-feed auger  64  is used to uniformly convey powder paint from the hopper discharge opening  74  across the length of the receptacle  66 . The receptacle  66  is used to supply powder to the metering brush  68 . The receptacle  66  is open at the bottom. The metering brush  68  protrudes slightly into the opening. The opening  67  in the bottom of the receptacle allows powder to fill the bristles of the brush  68  by gravity. The powder is removed from the receptacle  66  at a steady rate along the entire exposed or effective length of the auger brush  64  by the underlying feeder brush  68 . Each end of the auger brush  64  is partially blocked by the edge-guide tubes  80  and  82 . The amount of blockage provided by tubes  80  and  82  varies, depending on the width adjustments made for coating various strip widths. 
   A benefit of the variable pitch auger brush  64  is the ability to keep a relatively uniform level of powder throughout the entire operating length of the receptacle  66 . Keeping a uniform level of powder prevents starvation from occurring. Starvation occurs when the metering brush  68  does not receive an adequate supply of powder from the receptacle  66 . Starvation of the metering brush  68  results in a thin coating of powder on the strip. 
   The powder in the receptacle  66  is being uniformly extracted while at the same time the auger brush  64  is advancing additional powder from the hopper  20 . A unit volume of powder being advanced across the receptacle  66  is continuously subjected to the extraction of powder by the metering brush  68 . The unit volume of powder will be greatly diminished or totally consumed if it is advanced at a uniform rate. The varying pitch in the flights of the auger brush  64  gradually slow the advancement of the powder as it moves across the receptacle  66 . 
   The auger brush  64  flights start at a 3″ pitch and incrementally get tighter by {fraction (1/16)}″ each flight until a final pitch of 1½″ is achieved. The greater pitch at the start advances the powder relatively rapidly. The advancement of powder gradually slows down with each successive pitch. The rapid advancement of powder at the start does not allow the metering brush  68  to extract significant volume, resulting in more powder collecting at the far end of the receptacle  66 . In effect, the advancing powder is gradually stalled along the length of the auger brush  64 . 
   The flights at the end of the auger brush  64  are designed to allow some overflow out of the receptacle  66 . The overflow amount will vary as a function of the auger speed and metering brush speed. These speeds are set by the coating requirements for various strip widths, coating thicknesses and line speeds. Overflow prevents the powder from packing at the tighter flight pitches. Overflow also allows the auger brush  64  to work well for a range of powder volume requirements. 
   Brush  70  rotates rapidly in order to atomize the powder and permit it to be communicated into electrostatic coating module E in cooperation with wing  72 . The powder deposition rate onto the substrate is a function of the speed at which the substrate moves through the electrostatic coating module E and the rate at which powder is communicated into the electrostatic coating module for being electrostatically applied onto the substrate. Because the brush  70  can have a length in excess of 108 inches, then high-speed rotation, which is a speed sufficient to atomize the powder and cause the particles to be centrifugally thrown from the bristles, may cause vibration of the brush  70 . The brush  70 , as best shown in  FIG. 6 , also has 6,6 nylon bristles  100  extending outwardly from shaft  102 . We have found that radial support bearings permit the shaft  102  to vibrate excessively at or below the operational speed of rotation of the brush  70 . The excessive vibration can damage the atomizer module A, delay operation of the powder application system PC, and disrupt the smooth transfer and communication of powder between hopper  20  and the electrostatic coating module E. We have found that providing angular contact bearings at the spaced opposite ends of shaft  102  avoids the vibration problems and permits deflection of the shaft  102 , as sometimes occurs, to be easily accommodated without damage to the equipment. Angular contact bearings are considered both thrust and radial bearings. They preferably are arranged in a dual back-to-back orientation. 
   As best shown in  FIG. 7 , end  104  of shaft  102  extends through opening  106  in sidewall  108  of atomizer module A. We provide a resilient seal  110  within opening  106  to minimize powder that might otherwise flow through the gap created between shaft  102  and opening  106 . A retaining ring  112  is positioned adjacent spacer  114  having another resilient seal  116 . A first angular contact bearing  118  and a second angular contact bearing  120  are mounted about reduced diameter portion of end  104  for facilitating free rotation of shaft  102  by a suitable motor. A lock washer  122  secures the bearings  118  and  120  about the shaft  102 . We provide a cap  124  for sealing the bearing housing  126 , and thus assure that powder will not be withdrawn. The seals  110  and  116  provide double protection against powder flowing inwardly or contaminating the bearings. 
   End  128  of shaft  102 , as best shown in  FIG. 8 , is operably connected to a suitable motor or the like for causing rotation of shaft  102 . As with end  104 , we provide seals  130  and  132  on either side of spacer  134  in order to prevent powder and/or contaminant flow. Angular contact bearing assemblies  136  and  138  are mounted to reduced diameter portion of end  128  adjacent lock washer  140 . Yet another seal  142  is provided adjacent lock nut  144 . The angular contact bearing assemblies  136  and  138  and  118  and  120  permit the brush  70  to be rotated at a very high speed, while avoiding vibration and permitting shaft deflection as might occur. 
   The atomizing brush  70  assembly and metering brush  68  assembly have the same bearing and seal arrangement. The atomizing brush  70  is a fast rotating 6¼″ diameter brush and the metering brush  68  is a relatively slow rotating 4½″ diameter brush. The atomizing brush  70  and its bearing system avoid resonant vibration. Resonant vibration occurs when the rotating speed of the brush matches the critical speed. The critical speed is the same as the natural frequency or the speed at which the rotating assembly will naturally vibrate. The critical speed of a rotating assembly is dependent on the span, stiffness, mass, and the rigidity of the end (bearing assembly) constraints. 
   Prior art powder application systems had a 4¼″ diameter atomizing brush which had a carbon fiber wound core. The increased stiffness and reduced weight of the carbon core tended to reduce the actual critical speed. The actual critical speed occurred at about 2,500 rpm, which was less than the typical operating speed of 3,500 rpm. The rotating atomizing brush had to pass through the critical speed each time the coater was started for production. The entire powder-coating machine shook from the vibration. The bearing arrangement at each end of the shaft was a single-row radial ball bearing. The small diameter carbon fiber core of the brush and the non-rigid bearing design contributed to reducing the critical speed. 
   The brush  70  diameter preferably is 6¼″. The carbon fiber core diameter of the atomizing brush  70  preferably is 4″, resulting in a stiffer brush core. The bearing design has dual “back-to-back” mounting of angular contact bearings. The “back-to-back” mounting provides more rigid constraints at each end of the shaft, and results in less radial deflection. The actual critical speed is about 7,500 rpm. The atomizing brush  70  has an operating speed range of 2,000 to 2,400 rpm. The critical speed is thus higher than the operating speed by a factor of three. The atomizing brush  70  cannot reach the critical speed and therefore does not experience the detrimental effects of resonant vibration. 
   The “back-to-back” mounting configuration of the angular contact bearing assemblies is the same at each end of both the atomizing brush  70  and metering brush  68 . The inner races are locked against a shoulder on the shaft and are held securely in place with a bearing lock-washer and nut. The width of the inner race is ground slightly thinner on each bearing to create a pre-load when configured in the “back-to-back” arrangement. This results in stiffer bearing constraints. 
   Each angular contact bearing set is protected from paint powder with either a totally enclosed cover or dual-lip contact seals. The outer angular contact bearings of the non-driven ends are protected with enclosed covers. The outer angular contact bearings of the driven ends are protected with single dual-lip contact seals mounted in covers. Both inside angular contact bearings, non-driven end and driven end, are protected with double dual-lip contact seals. The inner dual-lip contact seals are pressed into the bores of ground steel spacer rings. The outer dual-lip contact seals are mounted in covers. The angular contact bearing assembly on the driven end of each shaft is held rigidly to the bearing housing. The angular contact bearing assembly on the non-driven end of each shaft is allowed to float {fraction (1/16)}″ in each direction with respect to the bearing housing. The {fraction (1/16)}″ float in either direction allows for growth or shrinkage in shaft length due to thermal changes. 
   Brushes  70  and  68  extend between sidewalls  146  and  108 , as best shown in  FIGS. 6 and 9 . Shoe  148  likewise extends between sidewalls  146  and  108  and cooperates with brushes  68  and  70  for causing the powder to be communicated from the receptacle  66 . The shoe  148  has a linear wall  149  that receives one wall of receptacle  66 , as best shown in FIG.  10 . The shoe  148  has a first arcuate portion  150  and a second arcuate portion  152  depending therefrom, as best shown in FIG.  9 . The arcuate portion  150  has a radius of curvature less than the radius of curvature of portion  152 . The portions  150  and  152  extend along parallel, offset axes. Arcuate portion  150  conforms to the periphery of brush  68 , in order to cause powder to be transported by rotation of the bristles of brush  68 . Similarly, arcuate portion  152  has a contour conforming to the periphery of the bristles  84  of brush  70 , for likewise causing the powder contained between the bristles to be transported by rotation of the bristles. Shoe  148  preferably has a plasma coating that allows powder to slide freely from metering brush  68  to atomizing brush  70 . 
   In the event that the type of powder being atomized changes, such as because the material or its color is changed, then the brushes  68  and  70  and the shoe  148  need to be cleaned in order to prevent contamination by subsequent operation of atomizer module A. We therefore provide shafts  154  upon which the shoe  148  is pivotally mounted. The shoe  148  may therefore be pivoted from the operational position of  FIG. 10  to the cleaning or maintenance portion of FIG.  9 . The shoe  148 , as best shown in  FIGS. 9 ,  10 , and  19 , is preferably a one-piece welded member in order to provide a structurally rigid integral assembly. The shoe  148  is formed from a series of appropriately contoured plates  156 ,  158 ,  160 ,  162 ,  164 , and  166 , as best shown in FIG.  19 . Extending from each of the plates  156 - 166  is a centrally located rib  168  that provides rigidity to the plates  156 - 166 . The ribs  168  may have one or more apertures  170 , in order to minimize weight. The end plates  156  and  16  have bushings  167  for receiving shafts  154  extending from the sidewalls of atomizer module A. 
   The shoe  148  facilitates transport of the powder for ultimate communication to electrostatic coating module E. We have found that a non-conductive tip  172  is preferably positioned at the end or discharge portion of arcuate portion  152 . The non-conductive tip  172  minimizes agglomeration of powder as might otherwise occur. 
   The one-piece weldment shoe  148  is designed to allow an operator to clean the double brushes in the atomizing modules A and A 1  with ease. Prior art designs required an operator to remove each brush from the atomizing zone for cleaning. The constant removal of the brushes during each cleaning required the same equal man-hours to clean the brushes pneumatically. The one-piece weldment shoe, that pivots away from the double brushes  68  and  70 , reduces cleaning man-hours. 
   Prior art shoe designs were comprised of segmented pieces held tightly together with contracted tie rods. The multiple pieces resulted in small steps or uneven surfaces between adjacent segments. The small steps caused uneven coating film thickness and difficulties with cleaning. The one-piece weldment shoe  148  has a continuous smooth plasma-coated surface throughout the entire brush contact area. The shoe  148  can pivot down away from the brushes  68  and  70 . The pivoting feature allows the operator to have easy access to the brushes  68  and  70  for inspection or cleaning. The shoe pivoting action is accomplished with a pair of air-operated rotary actuators. The shoe  148  can be rotated back into the coating position by means of accurate mechanical stops. The shoe  148  increases the overall quality and functionality of the powder application systems PC and PC 1 . 
   In order to pivot shoe  148  from the orientation of  FIG. 9  to the orientation of  FIG. 10 , then the sidewalls  76  and  78  need to be disengaged from nuts  342  and  344 . This is because pivoting of shoe  148  would otherwise engage the sidewalls  76  and  78 . It can be seen in  FIG. 10  that the shoe surface  149  forms one wall of receptacle  66 . The other or opposed wall is provided by plate  350  that is adjustably carried by bracket  352 .we can adjust plate  350  in order to adjust opening  67 , thereby providing more precise control over the discharge of powder from receptacle  66 . Because the sidewall  76  and  76  and the plate  350  are made of aluminum, then we provide brushes  352  and  354 at each of the endwalls  76  and  78  to prevent metal-to-metal contact between the endwalls  76  and  78  and shoe  148  and plate  350 . 
   As noted, wing  72  is provided adjacent brush  70  for assisting in directing the atomized powder particulates toward electrostatic coating module E. We have found that it may sometimes be necessary or desirable to adjust the orientation of wing  72 . For this reason, we provide a bracket  174 , as best shown in  FIGS. 9-10  and  20 , to which the wing  72  is mounted through bosses  176 . There is a bracket  174  at either sidewall of atomizer module A. Each of the brackets  174  has an arcuate slot  178  through which the bosses extend. Additionally, the bracket  174  may be pivoted about shaft  180 . Pivoting of the bracket  174  and movement of the bosses  176  within slot  178  permits the orientation of wing  72  to be selectively adjusted. Additionally, wing  72  may pivot about shaft  181 . 
   Electrostatic coating module E, as best shown in  FIGS. 1 and 12 , is rectangular in plan and elevation and has a frame  182  extending along the spaced lateral sides thereof. The frame  182  is secured to slider  184  that carries V-notch rollers  300 , as best shown in FIG.  26 . The rollers  300  contact hardened rods  302  and  304  extending along block  306 . A similar block  306  having hardened rods  302  and  304  extends below and preferably is integral with the first mentioned or upper block  306 . Slider  308 , having like V-notch rollers  300  is secured to frame  40 . The rollers  302  and sliders  184  and  308  permit the enclosure  310  of electrostatic coating module E to be shifted between the  FIG. 11  position and that of FIG.  17 . 
   The electrostatic coating module E of the powder application system PCo telescopes independently because of rollers  300 . The telescopic electrostatic coating module E allows quick access by an operator to the electrostatic coating module E or the atomizer module A. The design allows the operator to avoid damage to the electrodes within the electrostatic coating module E during an operational adjustment to the atomizer module A. 
   The electrostatic enclosure  310  slides out 24″ in the direction of strip travel by virtue of the rollers  300  and blocks  306 . The enclosure  310  is mounted on the top rail of a three-rail telescopic slide provided by sliders  184  and  308  and integral blocks  306 . The bottom rail is mounted to the rigid electrostatic zone base frame  40 . There is a three-rail telescopic slide on each lateral side of the enclosure  310 . The sliders use a v-shaped track rollers  300  that ride on hardened round rods  302  and  304 . The v-shaped rollers  300  and rods  302  and  304  work well with powder coating machinery. The very high contact forces between the v-shaped rollers or wheels  300  and round rods  302  and  304  allow the sliders to remain free of packed powder. Prior art powder application systems allowed the atomizing zone to be removed in a traverse manner from the entire powder application system. This setup was complicated and cumbersome, due to the need to remove the atomizing zone from the actual powder application system. The configuration required an independent cart to be connected directly to the powder application system. The atomizing zone was removed from the powder application system and onto the cart. These additional steps added more work time for the operator to clean and maintain the entire powder application system. It did not allow quick or easy access to the electrostatic or atomizing zone. 
   As best shown in  FIG. 21 , we provide an avalanche  192  angularly disposed along the bottom of electrostatic coating module E. It can be seen from  FIG. 1  that the avalanche  192  extends into atomizer module A. Rotating brush  194  is positioned at one end of avalanche  192  and causes powder falling on avalanche  192  to be transported to a recycle system (not shown). Brush  194  is rotated by motor  193 , as best shown in  FIG. 25 , and is displaceable with enclosure  310 . In this way, when the powder application system PC is in the operating position of  FIG. 1 , any powder discharged from atomizer module A into electrostatic coating module E that does not become electrostatically attached to substrate will ultimately fall onto avalanche  192  and be recycled through rotation of brush  194 . 
   As best shown in  FIGS. 1 and 18 , a cover  196  extends above the open top of atomizer module A and electrostatic coating module E when the modules are in the secured together position. The cover  196  is rectangular in plan, and has resilient seals  198  extending along its spaced laterally extending lower edges. The seals  198  engage the upper surfaces  200  and  202  of atomizer module A and electrostatic coating module E, in order to form a seal therewith. The cover  196  and the transversely extending surfaces  204  and  206  form a gap  208 , as best shown in  FIG. 12 , through which the substrate material, such as steel strip, is translated for coating. In the operating mode of  FIGS. 1 and 12 , the gap  208  is relatively small, in order to minimize leakage of powder, air entrainment, and the like which would reduce the efficiency of powder application. 
   Continuous movement of substrate through powder application system PC achieves maximum productivity of powder application system PC. When coating strip materials, such as steel strip, there occurs a need to join a tail end of one strip with the lead end of the next strip to be coated. In order to avoid the need and expense for accumulator towers and the like, as may be provided in steel mills and liquid coil coating lines, and in order to permit coating of strips of differing widths, then the tail end of one strip is typically stitched to the lead end of the next strip. Formation of the stitch causes a protrusion of sometimes as much as one inch from the joined strips. The gap  208  preferably is less than one inch, with the result that the presence of a stitch might damage the powder application system PC should it contact the cover  196  or the edge  206 . 
   The powder application system PC allows the entry and exit openings to expand, permitting a moving strip stitch to pass through without damaging the chamber frame and structure. The powder application system PC retracts from a coating position to a stationary position automatically, without operator assistance. The purpose of automatic retraction is to allow a mechanical stitch, which joins the head and the tail of a continuous moving metal strip, to pass through the powder application system. A mechanical stitch can damage a powder application system severely because sections are fabricated from polycarbonate. When the powder application system retracts, a proximity switch located near the atomizer module A detects when the powder application system PC is in the open position. The proximity switch then sends a signal to a control module to shut down the electric current being supplied to the electrostatic coating module E. 
   Each module A and E is divided into upper and lower sections. The upper section or cover  196  retracts away from the lower section when a stitch passes. The lower section retracts away from the upper section when a stitch passes. Each section retracts a calculated distance, in order to allow the stitch  218  to pass, as best shown in FIG.  18 . The distance is calculated in relationship to the catenary, the sag of the metal strip between two supports. 
   Prior art powder application systems required the operator to track the location of the stitch prior to its arrival. The operator then manually opened the powder application system to prevent the stitch from hitting the entrance opening, exit opening, and internal structure of the powder application system. The operator was also required to manually shut off the electrostatic zone electric current. 
   In order to prevent damage by the presence of a stitch, we provide pneumatic cylinder and piston assemblies  210  and  212 , which are secured to the frames  18  and  40  respectively, and to the cover  196 , on each lateral side thereof. The cylinder and piston assemblies  210  and  212  each have a cooperating piston which, when extended, cause the cover  196  to be lifted from the atomizer module A and the electrostatic coating module E, as best shown in FIG.  18 . Because the stitch  218 , as best shown in  FIG. 18 , extending from tail end  220  and lead end  222 , may extend above and/or below the respective ends, then we also utilize the cylinder and piston assemblies  22  and  32  in order to lower the atomizer module A and electrostatic coating module E an amount sufficient to preclude the stitch  218  from engaging the surface  206 . We have found that lifting the cover  196  a distance of 6 inches and lowering the modules A and E a distance of 4 inches results in a gap of 2 inches, which is sufficient to accommodate the stitch  218  without causing damage to the powder application system PC. After the stitch  218  has passed beyond the powder application system PC, then the cover  196  is lowered and the atomizer module A and electrostatic coating module E raised into the operating position of FIG.  1 . 
   The powder application system PC of  FIG. 1  is adapted for coating one surface of the substrate. As illustrated in  FIG. 1 , the powder application system PC is intended for coating the lower surface of the strip because it is a floor mounted assembly. The powder application system PC 1  of  FIG. 2  is similar to the powder application system PC and has an atomizer module A 1  and an electrostatic coating module E 1 . Unlike the powder application system PC of  FIG. 1 , however, powder application system PC 1  is intended to be mounted to the roof or similar horizontal support of the coating line. In this regard, supports  224  and  226  are secured to the horizontal support  228 . The rollers  230  receive corresponding angles  232  which extend transversely to the movement direction of the strip. Unlike the powder application system PC of  FIG. 1 , the V-rollers  230  permit movement of the powder application system PC 1  and not the individual modules thereof. The supports  224  and  226  thus fix the position of the angles  232 . 
   Disposed below the atomizer module A 1  and the electrostatic coating module E 1  is a recycle cart  234  that has an open top. Recycle cart  234  is moveable on rollers  236 . An avalanche  238  is positioned within recycle cart  234  and communicates with rotating brush  240  in order to recycle powder which may fall into cart  234  from electrostatic coating module EC 1 . Cylinder and piston assemblies  242  extend between frame  244  and the hopper  246  of recycle cart  234 . Actuation of the cylinder and piston assemblies  242  therefore permits the height of upper surface  248  of hopper  246  to be adjusted relative to strip  220 , as best shown in FIG.  15 . 
   Atomizer module A 1  and electrostatic coating module E 1  are secured to horizontally disposed frame  250 , as best shown in  FIGS. 2 ,  15  and  16 . Upper frame  252  depends from supports  224  and  226  through braces  254 . Thus, the position of upper frame  252  is fixed. Cylinder and piston assemblies  256  have the cylinders  258  thereof secured to upper frame  252  and the pistons  260  thereof operably secured to frame  250 . Actuation of the cylinder and piston assemblies  256  causes displacement of the pistons  260 , and thus movement of the frame  250  and hence of the atomizer module A 1  and the electrostatic coating module E 1 . As with the powder application system PC, operation of the powder application system PC 1  needs to take into account the presence of a stitch  218 . For this reason, when a stitch is closely adjacent powder application system PC 1 , we retract the pistons  260  in order to raise the frame  250 , as best shown in FIG.  15 . Similarly, we retract the pistons of the cylinder and piston assemblies  242  in order to lower recycle cart  234 . After the stitch  218  has passed, then the pistons  260  extend and lower the frame  250  and thus the atomizer module A 1  and the electrostatic coating module E 1 . Correspondingly, the pistons of the cylinder and piston assemblies  242  extend and cause the recycle cart  234  to move to the operative position of FIG.  16 . We also provide cylinder and piston assemblies  320 , as best shown in  FIG. 24 , to permit the frame  250 , and thus the modules A 1  and E 1 , to be lowered to a service position, as shown in the dashed lines. 
   Preferably, a resilient seal extends along the laterally disposed upper surfaces  248  of the recycle cart  234  in order to provide sealing engagement with the atomizer module A 1  and the electrostatic coating module E 1  to eliminate air entrainment while the strip is being translated at speeds of up to 600 feet per minute. 
   The atomizer module A 1  is similar in construction to the atomizer module A. Similarly, electrostatic coating module E 1  is similar to the electrostatic coating module E. Thus, as best shown in  FIG. 22 , like parts are identified by like reference numerals. Comparing  FIGS. 22 and 9 , it can be noted that the orientation of the wing  72  is different. This is because in the orientation of  FIG. 9 , the particulates are being upwardly directed in order to coat the lower side of the strip, whereas in the orientation of  FIG. 22 , the particulates are being directed downwardly to coat the strip. 
   The electrostatic coating module E 1 , as best shown in  FIG. 2 , is rectangular in elevation. Because of the rectangular contour of the interior of the electrostatic coating module E 1 , then we provide an arcuate roof  262 , as best shown in FIG.  22 . The roof  262  extends from the wing  72  to the terminal edge  264 . The roof  262  preferably is formed of Lexan® or other non-conductive material. The roof  262  directs the flow of the particulates from the brush  70 , preventing agglomeration of particulates in corners and horizontal and vertical surfaces within the interior of the electrostatic coating module E 1 . The powder application system PC 1  is intended to provide a high quality surface on the strip. Agglomeration of powder may mar that surface when the agglomeration eventually falls. The roof  262 , by providing a gentle arcuate flow path, minimizes any tendency to agglomerate. 
   The powder application system PC 1  applies a powder coating to the topside of a metal coil. This side of the metal coil is not considered a prime coating side. A prime coating side is defined as a visually defect free coating surface. The powder application systems PC and PC 1  apply a powder coating by using two zones: the atomizing and electrostatic zones. The powder is distributed from the atomizing module A or A 1  using a double brush system. The double brush system is comprised of a metering brush  68  and an atomizing brush  70 . The metering brush  68  controls the amount of powder coating applied/deposited to the metal coil. The atomizing brush  70  controls the velocity and distribution of the powder to the metal coil. The atomizing brush  70  directs the powder coating from the atomizing module A or A 1  to the electrostatic coating module E or E 1 . The powder particles then pass between a series of four (4) electrode wires  188  located in a parallel plane. The powder particles receive a positive or negative electrostatic charge from the ionized air around the electrode wires  188 . The charged powder particles then naturally adhere to the moving strip, due to the grounding effect of the strip. The shape of the upper electrostatic coating module E 1  is typically rectangular. The enclosure is rectangular also. The enclosures  310  of electrostatic coating modules E and E 1  are constructed of non-metallic material, e.g. poly-carbonate. The use of non-metallic material prevents potential electrostatic discharge from the four (4) electrode wires  188 . The rectangular shape facilitates construction of the electrostatic coating module E 1  with polycarbonate material. 
   During normal operation of the powder application system PC 1 , powder particles are generated from the atomizing module A 1  to the electrostatic coating module E 1 . The majority of the powder particles pass through the electrostatic zone and land on the moving strip S. The powder particles that do not land on the strip circulate inside the rectangular chamber. Some charged powder particles can adhere to the top or side of the rectangular chamber. The charged powder particles that do not land on the strip can accumulate on the top and side surfaces due to the charged attraction forces. Over time, the accumulated charged powder particles&#39; weight, or gravitational force, becomes greater than the charged attraction force. The accumulated charged powder particles then fall on to the moving strip called “clumping”. This “clumping” is considered a visual surface defect on the coating surface. 
   As best shown in  FIG. 28 , a coating line C preferably has two powder application systems PC and one powder application system PC 1  spaced along strip S. The two powder application systems PC are preferred in order to assure adequate powder application to the lower side of strip S. Gravity tends to pull the atomized particulates downwardly away from strip S, so two powder application systems PC permits more precise control over the coating weight or thickness along that lower side. The powder application systems PC are preferably independently operable, and thus may be used as needed and controlled as desired. Each of the powder application systems PC, for example, can apply a different coating weight onto the strip S. Gravity assists powder application system PC 1 , and only one such system is required. It also is operated independent of powder application systems PC, because sometimes only one side is coated or the coating weight on one side of strip S differs from the coating weight on the other side. 
   While this invention has been described as having a preferred embodiment, it is understood that the invention is not limited to the illustrated and described features. To the contrary, the invention is capable of further modifications, uses, and/or adaptations following the general principles of the invention and therefore includes such departures from the present disclosure as come within the known or customary practice in the art to which the invention pertains, and as may be applied to the central features set forth above, and which fall within the scope of the appended claims.

Technology Classification (CPC): 1