Patent Publication Number: US-2022219186-A1

Title: Wear resistant distributor post

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of the priority date of U.S. Provisional Patent Application Ser. No. 63/137,279, titled WEAR RESISTANT DISTRIBUTOR POST, filed Jan. 14, 2021. 
    
    
     BACKGROUND 
     Field 
     The present disclosure relates to the field of robotic spray painting devices and, more particularly, to a mounting post for a distributor cap used in a rotary bell cup spray painting apparatus, where the mounting post has a flange which is countersunk into the distributor cap and prevents high-velocity paint from undercutting the mounting post into the distributor cap. 
     Discussion of the Related Art 
     The use of industrial robots for spray painting applications is well known. A number of painting and coating devices are known which have been developed for robotic spray painting. These include devices that feed paint or other fluid coating materials through a base unit towards an atomizing bell cup. The bell cup is an assembly that is attached to a hollow shaft and rotates in front of the base. The bell cup spins at high speeds, typically above 30,000 RPM. During painting operation, the coating material is advanced through the hollow shaft and into the bell cup assembly. The coating fluid contacts a distributor cap or plate that is arranged in the bell cup and causes the fluid to be dispersed by centrifugal force along the inner surface of the rotating bell cup. The coating fluid exits an annular area between the distributor cap and the bell cup inner surface and flows along the bell cup to an edge from which it departs the bell cup and travels to the workpiece being painted. 
     In bell cup painting devices of the type described above, it is known to attach the distributor cap to an interior of the base of the bell cup via mounting posts. One known design uses three such mounting posts. The mounting posts are attached to the interior base of the bell cup, such as by screw threads. The distributor cap is then attached to the mounting posts, such as by pressing barbed ends of the posts into holes in the distributor cap. This arrangement allows for straightforward assembly of the distributor cap into the bell cup, and provides a defined stand-off spacing of the distributor cap from the bell cup. The central portion of the mounting posts, which is located between the threaded end in the bell cup and the barbed end in the distributor cap, is typically made a larger diameter than the ends. This is done both to ensure the stand-off spacing mentioned above, and also because high-velocity paint impinges on the central portion of the mounting posts as the paint flows radially outward. The high velocity of the paint can cause abrasive wear of the mounting posts, which makes the larger diameter advantageous. 
     In some circumstances, however, paint can wear into the surface of the distributor cap, creating an undercut which allows the high-velocity paint to impinge on the barbed portion of the posts. This causes abrasive wear of a small diameter barbed portion of the posts, which is undesirable. Other distributor cap mounting arrangements are known, but none allow the simple and convenient assembly of the distributor cap into the bell cup of a barbed mounting post. 
     In light of the situation described above, there is a need for an improved distributor cap mounting post which prevents paint from impinging on and causing abrasive wear to a small diameter portion of the post. 
     SUMMARY 
     In accordance with the teachings of the present disclosure, a wear resistant mounting post for a distributor cap in a rotary bell cup atomizer is described and shown. The mounting post includes a flange separating a thin barbed end from a larger diameter central portion. The flange fits into a countersunk depression in the distributor cap to provide a flange surface which is flush with the distributor cap surface. Paint flowing radially outward across the distributor cap follows the flange surface to the central portion of the post. This design prevents the paint from undercutting the surface of the distributor cap, and ensures that any abrasive wear of the post is limited to the larger diameter portion. 
     Additional features of the presently disclosed devices and methods will become apparent from the following description and appended claims, taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional illustration of a rotary bell cup spray painting apparatus of a type used on painting robots, as known in the art; 
         FIG. 2  is a cross-sectional illustration of the rotary bell cup of  FIG. 1  showing how high-velocity spreads radially on a surface of a distributor cap and impinges on a mounting post; 
         FIG. 3  is an image of a distributor cap of the type shown in  FIGS. 1 and 2 , showing wear patterns in the distributor cap caused by the flow of high-velocity paint as illustrated in  FIG. 2 ; 
         FIG. 4  is a cross-sectional illustration of a rotary bell cup with a distributor cap and mounting post having a flange designed to prevent the flow of high-velocity paint from wearing into the surface of the distributor cap, according to an embodiment of the present disclosure; 
         FIG. 5  is a cross-sectional illustration of the distributor cap and mounting post of  FIG. 4 , according to an embodiment of the present disclosure; 
         FIG. 6  is an isometric view illustration of the mounting post shown in  FIGS. 4 and 5 , where the mounting post flange directs the flow of high-velocity paint in a desired direction, according to an embodiment of the present disclosure; 
         FIG. 7  is a side view illustration of the mounting post of  FIG. 6 , showing details of the flange and other features of the mounting post, according to an embodiment of the present disclosure; and 
         FIG. 8  is a side view illustration of a second design of a distributor cap mounting post having a flange for preventing abrasive wear of the distributor cap and the post, according to another embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     The following discussion of the embodiments of the disclosure directed to a wear resistant mounting post for a distributor cap is merely exemplary in nature, and is in no way intended to limit the disclosed devices and techniques or their applications or uses. 
     It is well known to use industrial robots for spray painting workpieces such as automobile bodies. Various types of spray painting devices may be used on painting robots to deliver a controlled flow of paint or other coating fluid onto the workpiece in a consistent and well-distributed spray pattern. These devices include air-propelled spray devices and rotary bell cup atomizers, among others. 
       FIG. 1  is a cross-sectional illustration of a rotary bell cup spray painting apparatus  100  of a type used on painting robots, as known in the art. A bell cup  110  is rotatably mounted to a spray atomizer device which is in turn mounted to an outer arm or wrist of a robot. During spray painting operations, the bell cup  110  spins at high speed (typically tens of thousands of RPM) to distribute the paint or other coating fluid (hereinafter simply referred to as paint) in a well-defined spray pattern. The paint is introduced into the bell cup  110  through a central opening  120 . The paint travels as indicated by arrow  122  until reaching a distributor cap  130 , which is fixedly mounted in a position separated from the bell cup  110  by a plurality of mounting posts  140  (discussed later). The distributor cap  130  blocks the axial flow of the paint and causes the paint to spread in a radial direction along a front surface  132  of the distributor cap  130 , as indicated by arrow  124 . The distributor cap  130  is typically constructed of a plastic material such as acetal. An insert  134 , constructed of a high-strength material such as titanium, is provided to block the axial flow of paint without being abrasively worn down by the paint. In some applications, a portion of the paint flows through the insert  134  by design and bleeds out to a rear surface  136  of the distributor cap  130 . 
     All of the paint is flung radially outward from the front surface  132  and the rear surface  136  of the distributor cap  130  due to the high rotational speed of the bell cup apparatus  100 . From the distributor cap  130 , the paint lands on an inner surface  112  of the bell cup  110 . The rotation of the bell cup  110  causes the paint to flow along the inner surface  112  until being expelled from the bell cup  110  as indicated by arrow  150 . The paint leaves the bell cup  110  around its entire circumference as a pattern of finely atomized droplets which are deposited on the workpiece. An electrostatic charge may be applied to improve the deposition of the paint droplets on the workpiece, as known in the art. 
       FIG. 2  is a cross-sectional illustration of the rotary bell cup  110  of  FIG. 1  showing how high-velocity paint spreads radially on a surface of a distributor cap and impinges on a mounting post. In addition to the bell cup  110  (cropped in  FIG. 2 ), the distributor cap  130  having the front surface  132  and the insert  134  are shown in  FIG. 2  as they were in  FIG. 1 . Two of the mounting posts  140  are also shown in  FIG. 2 ; the mounting post  140  at the left is shown in cross-section, as it is positioned at the section plane of  FIG. 2 ; the mounting post  140  at the right is only partially visible, as its two ends are obstructed by the bell cup  110  and the distributor cap  130  in  FIG. 2 . Three of the mounting posts  140  are used to attach the distributor cap  130  to the bell cup  110 , where the third mounting post  140  is not visible in the cross-section of  FIG. 2 . 
     One known design of the mounting posts  140  has a first end  142 , a second end  144  and a central portion  146 . The first end  142  is attached to the interior base of the bell cup  110 , such as by screw threads. The second end  144  has a barbed shape and is pressed into holes in the distributor cap  130 . This arrangement allows for straightforward assembly of the distributor cap  130  to the bell cup  110 , and the larger diameter central portion  146  provides a defined stand-off spacing of the distributor cap  130  from the bell cup  110 . 
     As discussed earlier, paint from the robot flows into the bell cup  110  along the arrow  122 , impinges on the insert  134  and spreads radially outward across the front surface  132  of the distributor cap  130 , as indicated by the arrow  124  (which was shown on the right side of  FIG. 1 ). Most of the paint flowing radially outward across the front surface  132  encounters no obstacles on its way to the peripheral edge of the distributor cap  130  where it is flung outward onto the inner surface  112  of the bell cup  110 . However, a small portion of the paint encounters one of the mounting posts  140  as it flows outward across the front surface  132 . 
     The paint following the arrow  124  will be forced to flow around the central portion  146  when the paint encounters the mounting post  140 . In addition to the paint spreading circumferentially around the central portion  146 , the high-velocity splash will cause some of the paint to deflect axially as indicated by arrows  126  and  128 . The paint following the arrow  126  will soon find its way around the central portion  146  and out to the bell cup  110 . The paint following the arrow  128  has axial energy which must first be deflected by the front surface  132  of the distributor cap  130 . Depending on the flow rate of the paint, the spin rate of the bell cup  110 , the type of paint (e.g., metal-flake) and other factors, over time the paint can abrasively wear the front surface  132  of the distributor cap  130  in the immediate vicinity of the mounting posts  140 . This wear undermines the central portion  146  of the mounting post  140 , and eventually allows high-velocity paint to impinge on the second end  144  where it meets the central portion  146 . The high-velocity flow of paint can then cause abrasive wear to the second end  144  of the mounting post  140 , which is not desirable. 
       FIG. 3  is an image of a distributor cap  300  of the type shown in  FIGS. 1 and 2 , showing wear patterns caused by the flow of high-velocity paint as illustrated in  FIG. 2 . An insert  310  is shown in the center of the distributor cap  300 , as discussed earlier. The distributor cap  300  was installed in a bell cup and the assembly rotated in a direction R indicated by arrow  320 . The high-speed rotation caused paint to flow radially outward along the front surface of the distributor cap  300  as indicated by arrow  330 , and also to take on a tangential component of velocity (relative to the distributor cap  300 ) as indicated by arrow  332 . 
     A portion of three mounting posts  340  are shown in  FIG. 3 . The arrangement of the mounting posts  340  in attaching the distributor cap  300  to the bell cup was discussed earlier. In a vicinity of each of the mounting posts  340 , an undercut area  350  is visible. The undercut area  350  is a crescent-shaped area where the high-velocity paint, particularly the tangential component of the paint flow indicated by the arrow  332 , has abrasively worn the front surface of the distributor cap  300 . It can be seen that the undercut area  350  is concentrated around the mounting post  340  on the side of the mounting post  340  where the tangential flow of paint impinges. On the specimen shown in the image of  FIG. 3 , the undercut areas  350  developed to the point where the high-velocity paint reached the small-diameter barbed end of the mounting posts  340 . The paint then proceeded to cut almost all of the way through the small-diameter barbed ends of the mounting posts  340 . 
     The present disclosure describes a new distributor cap mounting post which is designed to prevent the high-velocity flow of paint from cutting into the surface of the distributor cap and impinging on the small-diameter portion of the post as illustrated in  FIG. 3 . This is discussed in detail below. 
       FIG. 4  is a cross-sectional illustration of a rotary bell cup with a distributor cap and mounting post having a flange designed to prevent the flow of high-velocity paint from wearing into the surface of the distributor cap, according to an embodiment of the present disclosure. A bell cup  410  is equivalent to the bell cup  110  of  FIGS. 1 and 2  discussed earlier. A distributor cap  430  is mounted in the interior of the bell cup  410 . Paint from the robot flows into the bell cup atomizer assembly as indicated by arrow  422  and impinges on an insert  434  in the distributor cap  430 , in the same manner discussed earlier. 
     A plurality of mounting posts  440  are used to fixedly mount the distributor cap  430  in position in the bell cup  410 . Two of the mounting posts  440  are shown in  FIG. 4 ; the mounting post  440  at the left is shown in cross-section, as it is positioned at the section plane of  FIG. 4 ; the mounting post  440  at the right is only partially visible, as its two ends are obstructed by the bell cup  410  and the distributor cap  430  in  FIG. 4 . In this exemplary embodiment, three of the mounting posts  440  are used to attach the distributor cap  430  to the bell cup  410 , where the third mounting post  440  is not visible in  FIG. 4 . 
     Each of the mounting posts  440  has a first end  442 , a second end  444  and a central portion  446 . The first end  442  is attached to the interior base of the bell cup  410 , such as by screw threads. The second end  444  has a barbed shape and is pressed into holes in the distributor cap  430 . The larger diameter central portion  446  provides a defined stand-off spacing of the distributor cap  430  from the bell cup  410 . The mounting post  440  also includes a disc-shaped flange  450  at the junction of the second end  444  and the central portion  446 , as shown. The flange  450  fits into a corresponding countersink recess in the distributor cap  430 , so that an exposed surface  452  of the flange  450  is flush with a front surface  432  of the distributor cap  430 . Because the flange  450  is flush with the front surface  432  or just below it, the flange  450  does not redirect the flow of paint or experience any impingement from the paint. 
     The flange  450  is designed to control the flow of high-velocity paint so that the paint does not undercut the mounting post into the distributor cap  430 . Instead, the high-velocity paint flows along the exposed surface  452  and impinges on the mounting post  440  (radially and tangentially, as discussed above) at the base of the central portion  446 , causing the paint to follow the path indicated by arrow  424 . The paint then quickly flows around the central portion  446  and flies off to the bell cup  410 , as indicated by arrows  426 . 
     The flange  450  ensures that the paint which strikes the mounting post  440  does not deflect (due to the splash effect) into the plastic distributor cap  430 , as with the current design illustrated in  FIG. 2 . Rather, all of the splash energy of the paint striking the mounting post  440  is felt by the mounting post  440  itself, which is a metal component (titanium, stainless steel, or other suitable metal) and is much more resistant to abrasive wear than the plastic distributor cap  430 . In addition, a filet  454  ( FIG. 5 ) at the junction of the central portion  446  and the flange  450  aids in deflecting the flow of paint as indicated by the arrow  424  until the paint flows around the central portion  446  as indicated by the arrows  426 . 
       FIG. 5  is a cross-sectional illustration of the distributor cap  430  and the mounting post  440  of  FIG. 4 , according to an embodiment of the present disclosure.  FIG. 5  simply provides another illustration of these components without the surrounding elements and flow arrows of  FIG. 4 . The mounting post  440  having the flange  450  are shown in  FIG. 5 , as discussed above. The flange  450  fits into a corresponding countersink recess in the distributor cap  430 , so that the exposed surface  452  of the flange  450  is flush with the front surface  432  of the distributor cap  430 , as shown. The filet  454  is also shown in  FIG. 5 . Tolerances may be established such that the exposed surface  452  is slightly “below” the front surface  432  (set into the countersink recess), so that the paint does not impinge on an outer peripheral edge of the flange  450 . 
       FIG. 6  is an isometric view illustration of the mounting post  440  shown in  FIGS. 4 and 5 , including the mounting post flange  450  which directs the flow of high-velocity paint in a desired direction, according to an embodiment of the present disclosure.  FIG. 7  is a side view illustration of the mounting post  440 , showing details of the flange  450  and other features, according to an embodiment of the present disclosure. 
     The first end  442 , the second end  444  and the central portion  446 , discussed earlier, are shown in  FIGS. 6 and 7 . An undercut  448  may be provided at the base of the first end  442 , to avoid stress concentration and to provide for positive seating of the central portion  446  against the bell cup  410 . The flange  450  is also shown in  FIGS. 6 and 7 , with the exposed surface  452  and the filet  454  shown in  FIG. 7 . In addition, a bevel  456  may be provided on the periphery of the flange  450  opposite the exposed surface  452 , in order to improve seating of the flange  450  into the countersink recess in the distributor cap  430 . 
     In one embodiment, the mounting post  440  has reference features and dimensions as follows; the first end  442  is threaded with a male machine screw thread having a diameter of about 1.5 mm; the second end  444  has a barbed cylindrical shape and a diameter of about 1.0 mm; the central portion  446  is cylindrical and has a diameter of about 2.5-3.0 mm; and the flange  450  is disc-shaped with a thickness of less than 1 mm and an outside diameter of about 5 mm. The mounting post  440  is preferably constructed of a single piece of a high strength corrosion resistant material such as titanium or stainless steel. The specifications listed in this paragraph are merely exemplary. Dimensions may be larger or smaller depending on the application and the bell cup and distributor cap sizes. 
       FIG. 8  is a side view illustration of a second design of a distributor cap mounting post  840  having a flange  850  for preventing abrasive wear of the distributor cap and the post, according to another embodiment of the present disclosure. The mounting post  840  is generally the same as the mounting post  440  discussed above, except for a first end  842  which is barbed rather than threaded. The barbed design of the first end  842  allows for the use of the mounting post  840  in applications where a press fit into the base of the bell cup is employed rather than a threaded installation. For example, a hollow cylindrical plastic insert could be placed in a cylindrical hole in the base of the bell cup, and the first end  842  of the mounting post  840  then pressed into the plastic insert. 
     The mounting post  840  has a second end  844  and a central portion  846  which are the same at their equivalent features on the mounting post  440  of  FIGS. 4-7 . Likewise, the flange  850  on the mounting post  840  includes an exposed surface  854  and a filet  854  in the same manner as the equivalent features on the mounting post  440 , where the flange  850  causes the high-velocity paint to flow in the desired manner around the central portion  846  of the mounting post  840 , rather than undercutting the mounting post into the distributor cap. 
     As outlined above, the disclosed embodiments of distributor cap mounting posts provide significant advantages over existing mounting post designs. Specifically, the mounting post flange which is countersunk into a recess in the face of the distributor cap improves the fluid dynamics of paint flow around the mounting post, and solves the problem of abrasive wear of the distributor cap which can lead to wear-through of the barbed end of existing mounting post designs. 
     While a number of exemplary aspects and embodiments of wear resistant mounting posts for a distributor cap in a rotary bell cup atomizer have been discussed above, those of skill in the art will recognize modifications, permutations, additions and sub-combinations thereof. It is therefore intended that the following appended claims and claims hereafter introduced are interpreted to include all such modifications, permutations, additions and sub-combinations as are within their true spirit and scope.