Patent Publication Number: US-2022226842-A1

Title: Rotary atomizing coating device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2021-005298 filed on Jan. 15, 2021, the contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a rotary atomizing coating device for performing electrostatic coating by spraying a liquid paint from the distal end of a rotary atomizing head. 
     Description of the Related Art 
     Conventionally, there has been known a rotary atomizing coating device for coating an automobile body or the like. The rotary atomizing coating device rotates a rotary atomizing head while applying a high voltage to the rotary atomizing head. In the rotary atomizing coating device, a conductive paint (liquid paint) is supplied to the rotating rotary atomizing head. After the liquid paint is charged and atomized, the atomized liquid paint is sprayed from the distal end edge of the rotary atomizing head. As a result, electrostatic coating for coating a workpiece such as the body with the liquid paint is performed. 
     For example, a rotary atomizing coating device disclosed in JP 6080127 B2 includes a rotary atomizing head having two head bodies. Each of the head bodies has a bell shape. The two head bodies are coaxially arranged at a predetermined distance from each other in the axial direction. The center of rotation of each of the head bodies is provided with a paint passage forming hole for supplying paint. Each of the head bodies has a plurality of paint passage branch holes. Each of the paint passage branch holes guides the paint from the paint passage forming hole to the surfaces of the two head bodies. 
     In the rotary atomizing coating device, a centrifugal force is generated by rotation of the rotary atomizing head. The paint is supplied from the paint passage forming hole to each of the plurality of paint passage branch holes, and the paint is scattered to the outside in a mist form from the whole periphery of the outer edge portion of each of the head bodies by the centrifugal force. In this way, the paint is discharged from each of the two head bodies. As a result, the thickness of the liquid film of the paint applied to the workpiece can be reduced, and the particles of the paint can be atomized. 
     SUMMARY OF THE INVENTION 
     In the rotary atomizing coating device described above, the paint is supplied through the paint passage branch holes provided in each of the head bodies. This achieves atomization of the paint discharged from the two head bodies. However, when the rotary atomizing head is rotated to discharge the paint, the centrifugal force acting on one of the head bodies that is disposed on the outer side is larger than the centrifugal force acting on the other head body disposed on the inner side. Therefore, a difference is generated between the amount of the paint discharged from one of the head bodies and the amount of the paint discharged from the other head body. As a result, it is difficult to discharge the paint evenly from the two head bodies. 
     In order to solve this problem, in the rotary atomizing coating device, for example, it is conceivable to appropriately design the number, shape (hole diameter), and the like of the paint passage branch holes in the two head bodies. As a result, the discharge amount (discharge ratio) of the paint from one of the head bodies and the discharge amount (discharge ratio) of the paint from the other head body can be arbitrarily distributed. However, the structure of the rotary atomizing coating device becomes complicated, and the design of the rotary atomizing coating device also becomes complicated. 
     An object of the present invention is to solve the above-described problems. 
     According to an aspect of the present invention, provided is a rotary atomizing coating device comprising a rotary atomizing head coupled to a rotary shaft of a rotary drive source and configured to discharge a paint by a centrifugal force caused by rotation thereof, the rotary atomizing coating device coating a workpiece with the discharged paint, wherein the rotary atomizing head includes: a first bell cup including a first paint discharge surface configured to thin the paint by the centrifugal force; a second bell cup fitted to an outer side of the first bell cup and including a second paint discharge surface configured to thin the paint; a paint supply passage which extends in an axial direction of the rotary shaft and through which the paint is supplied; and an inner member disposed inside the first bell cup and communicating with the paint supply passage, and wherein an outer peripheral surface of the inner member includes a paint discharge hole communicating with the paint supply passage, and the first bell cup includes, at a position near the paint discharge hole, a through hole communicating with the second bell cup. 
     According to the present invention, in the rotary atomizing coating device, the paint discharge hole is provided on the outer peripheral surface of the inner member of the rotary atomizing head. The paint discharge hole communicates with the paint supply passage. The inner member is disposed within the first bell cup. The first bell cup includes the through hole at a position near the paint discharge hole. The through hole communicates with the second bell cup. Thus, the paint can be distributed by adjusting the ratio between the amount of the paint supplied to the first bell cup through the paint discharge hole of the inner member and the amount of the paint supplied to the second bell cup through the first bell cup. 
     Therefore, compared with the conventional rotary atomizing coating device, the paint can be distributed by adjusting the supply ratio of the paint to the two first and second bell cups with a simple configuration. As a result, even if the supply amount of the paint discharged from each of the first and second bell cups is increased, the thickness of the liquid film of the paint can be reduced. By reducing the thickness of the liquid film of the paint, the particles of the paint can be atomized. 
     The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings, in which a preferred embodiment of the present invention is shown by way of illustrative example. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an overall cross-sectional view of a rotary atomizing coating device according to a first embodiment of the present invention; 
         FIG. 2  is an exploded perspective view of a rotary atomizing head in the rotary atomizing coating device of  FIG. 1 ; 
         FIG. 3  is an exploded cross-sectional view of the rotary atomizing head in the rotary atomizing coating device of  FIG. 1 ; 
         FIG. 4  is an enlarged cross-sectional view of the vicinity of an inner member in the rotary atomizing head of  FIG. 1 ; 
         FIG. 5  is a cross-sectional view taken along line V-V of  FIG. 1 ; 
         FIG. 6  is an overall cross-sectional view of a rotary atomizing coating device according to a second embodiment of the present invention; 
         FIG. 7  is an exploded perspective view of a rotary atomizing head in the rotary atomizing coating device of  FIG. 6 ; 
         FIG. 8  is an exploded cross-sectional view of the rotary atomizing head in the rotary atomizing coating device of  FIG. 6 ; 
         FIG. 9  is an enlarged cross-sectional view of the vicinity of an inner member in the rotary atomizing head of  FIG. 6 ; and 
         FIG. 10  is a cross-sectional view taken along line X-X of  FIG. 6 . 
     
    
    
     DESCRIPTION OF THE INVENTION 
     As shown in  FIGS. 1 to 5 , a rotary atomizing coating device  10  includes a rotary atomizing head  12 . The rotary atomizing head  12  discharges a paint by utilizing a centrifugal force generated by the rotation of the rotary atomizing head  12 . The rotary atomizing head  12  coats a workpiece (not shown), which is an object to be coated, with the paint discharged from the rotary atomizing head  12 . 
     The rotary atomizing head  12  is coupled to the distal end of a rotary shaft  14  of a rotary drive source such as a motor (not shown). The rotary atomizing head  12  includes an inner member  16  and an outer member  18 . The outer member  18  is fixed to the outer peripheral portion of the inner member  16 . The rotary atomizing head  12  is driven by the rotary drive source (not shown) to rotate. The rotary atomizing head  12  rotates at high speed around the rotary shaft  14  of the rotary drive source. A tube member  22  is disposed inside the rotary shaft  14 . The tube member  22  is connected to a paint supply device (not shown). The tube member  22  includes a paint supply passage  20  through which the paint is supplied. The tube member  22  does not rotate together with the rotary shaft  14 . 
     In the following description, in the rotary atomizing coating device  10 , a direction toward which the paint is discharged is defined as forward (a front end, an arrow A direction). A direction in which the tube member  22  supplied with the paint is connected is defined as rearward (a rear end, an arrow B direction). 
     The inner member  16  has a cup shape having a predetermined length in the front-rear direction (directions of arrows A and B). The cross-sectional shape of the inner member  16  is circular. The front end of the inner member  16  is closed by an end wall  24 . The rear end of the inner member  16  is open. The inner member  16  has a bottomed tubular shape extending from the front end toward the rear end. A paint storage chamber  26  is provided inside the inner member  16 . The paint storage chamber  26  temporarily stores the paint supplied via the tube member  22 . 
     The cross-sectional shape of the paint storage chamber  26  is circular when viewed from the front-rear direction of the inner member  16  (see  FIG. 5 ). An opening  28  is formed at the rear end of the paint storage chamber  26 . The opening  28  is disposed on a single straight line with the distal end (front end) of the tube member  22 . The opening  28  communicates with the tube member  22 . The paint storage chamber  26  gradually increases in diameter from the rear end toward the front end (in the arrow A direction). 
     An outer peripheral wall  30  of the inner member  16  includes a small diameter portion  32 , a large diameter portion  34 , and an enlarged diameter portion  36 . The small diameter portion  32  is positioned closest to the rear end (end portion in the arrow B direction) of the inner member  16 . The large diameter portion  34  is positioned forward (on the arrow A side) of the small diameter portion  32 . The enlarged diameter portion  36  is positioned further forward (on the arrow A side) of the large diameter portion  34 . The enlarged diameter portion  36  is an outer peripheral portion of the end wall  24 . The outer peripheral surface of the enlarged diameter portion  36  gradually increases in diameter toward the front (in the arrow A direction). That is, the outer peripheral surface of the enlarged diameter portion  36  is inclined with respect to the axis of the inner member  16 . 
     The outer peripheral wall  30  includes an annular groove  38 . The annular groove  38  is disposed between the large diameter portion  34  and the small diameter portion  32 . The annular groove  38  is recessed radially inward relative to the small diameter portion  32 . The annular groove  38  has an annular shape along the circumferential direction of the outer peripheral wall  30 . 
     The large diameter portion  34  includes a plurality of paint discharge holes  40 . The paint discharge holes  40  are disposed adjacent to the rear end of the enlarged diameter portion  36 . The width of the paint discharge hole  40  along the front-rear direction of the inner member  16  (the directions of arrows A and B) is constant along the circumferential direction of the inner member  16 . The paint discharge hole  40  has, for example, a slit shape. The plurality of paint discharge holes  40  are aligned with each other when viewed from a position in the axial direction in the inner member  16 . The paint discharge hole  40  is elongated along the circumferential direction (an arrow C direction in  FIG. 5 ). The paint discharge holes  40  penetrate the large diameter portion  34  in the radial direction. The paint discharge holes  40  allow communication between the outside of the outer peripheral wall  30  and the paint storage chamber  26 . 
     Specifically, as shown in  FIG. 5 , three paint discharge holes  40  are provided. The paint discharge holes  40  penetrate through the paint storage chamber  26  at a position where the diameter of the paint storage chamber  26  is largest. One paint discharge hole  40  and another paint discharge hole  40  are adjacent to each other in the circumferential direction of the inner member  16 . A rib  42  is provided between one paint discharge hole  40  and the other paint discharge hole  40  adjacent to each other. Each of the ribs  42  connects the outer peripheral wall  30  and the end wall  24 . The three paint discharge holes  40  are separated from each other in the circumferential direction (the arrow C direction) by the ribs  42 . Note that the number of the paint discharge holes  40  is not limited to three as described above, as long as the paint discharge holes  40  are arranged at equal intervals in the circumferential direction. 
     The paint is supplied to the opening  28  through the tube member  22  (paint supply passage  20 ). The opening  28  is located at the rear end of the inner member  16 . The paint is supplied to the paint storage chamber  26  through the opening  28  of the inner member  16 . As the rotary atomizing head  12  including the inner member  16  rotates, a centrifugal force acts on the rotary atomizing head  12 . The paint moves radially outward due to the centrifugal force. The paint gradually flows radially outward along the inner peripheral surface of the paint storage chamber  26 . Thereafter, the paint flows from the paint storage chamber  26  to the outside of the outer peripheral wall  30  through the plurality of paint discharge holes  40 . 
     As shown in  FIGS. 1 to 5 , the outer member  18  includes, for example, a first bell cup  44  and a second bell cup  46 . Each of the first and second bell cups  44  and  46  has a circular cup shape. 
     The first bell cup  44  includes a first coupling portion  48  and a first flare portion  52 . The first coupling portion  48  is disposed at the rear end (on the arrow B side) of the first bell cup  44 . The first coupling portion  48  is coupled to the distal end of the rotary shaft  14 . The first flare portion  52  is continuous with the front end of the first coupling portion  48 . The first flare portion  52  gradually expands radially outward toward the front side (in the arrow A direction) relative to the first coupling portion  48 . 
     The second bell cup  46  includes a second coupling portion  50  and a second flare portion  54 . The second coupling portion  50  is disposed at the rear end (on the arrow B side) of the second bell cup  46 . The second coupling portion  50  is coupled to the distal end of the rotary shaft  14  via the first coupling portion  48 . The second flare portion  54  is continuous with the front end of the second coupling portion  50 . The second flare portion  54  gradually expands radially outward toward the front side (in the arrow A direction) relative to the second coupling portion  50 . 
     The front surface of the first bell cup  44  includes a first paint discharge surface  56 . The first paint discharge surface  56  thins the paint supplied to the front surface of the first bell cup  44 . The front surface of the second bell cup  46  includes a second paint discharge surface  58 . The second paint discharge surface  58  thins the paint supplied to the front surface of the second bell cup  46 . 
     Each of the first and second coupling portions  48  and  50  has a cylindrical shape extending in the front-rear direction (the directions of arrows A and B). A connection hole  60  is provided inside the first coupling portion  48 . The rotary shaft  14  of the rotary drive source (not shown) is connected to the connection hole  60 . The first bell cup  44  includes a mounting hole  62 . The mounting hole  62  is located between the first coupling portion  48  and the first flare portion  52 . The inner member  16  is mounted in the mounting hole  62 . 
     The mounting hole  62  has a larger diameter than the connection hole  60 . The inner peripheral surface of the mounting hole  62  includes a first step portion  64 , a second step portion  66 , and an annular protrusion  68 . 
     The first step portion  64  is located most rearward (on the arrow B side) in the mounting hole  62 . The small diameter portion  32  of the inner member  16  is engaged with the first step portion  64 . The second step portion  66  is disposed forward (on the arrow A side) of the first step portion  64 . The large diameter portion  34  is engaged with the second step portion  66 . The second step portion  66  has a larger diameter than the first step portion  64 . The annular protrusion  68  is disposed between the first step portion  64  and the second step portion  66 . The annular protrusion  68  protrudes radially inward from the first step portion  64  and the second step portion  66 . 
     The inner member  16  is inserted into the mounting hole  62  of the first bell cup  44  from the front side. The small diameter portion  32  of the inner member  16  is engaged with the first step portion  64 . The large diameter portion  34  of the inner member  16  is engaged with the second step portion  66 . The annular protrusion  68  of the inner member  16  is engaged with the annular groove  38 . As a result, the inner member  16  and the first bell cup  44  are positioned relative to each other in the front-rear direction (the directions of arrows A and B). 
     The inner member  16  and the first bell cup  44  are arranged coaxially. The annular protrusion  68  of the first bell cup  44  is engaged with the annular groove  38  of the inner member  16 . Accordingly, the first bell cup  44  and the inner member  16  do not move relative to each other in the front-rear direction (the directions of arrows A and B). As a result, the inner member  16  is fixed inside the first bell cup  44 . At this time, the enlarged diameter portion  36  of the inner member  16  is disposed inside the first flare portion  52 . 
     The first paint discharge surface  56  of the first flare portion  52  is inclined forward toward the radially outer side. When the first bell cup  44  is viewed from the front-rear direction, the first paint discharge surface  56  is an annular surface. Due to the centrifugal force generated by the rotation of the first bell cup  44 , the paint moves radially outward from the paint storage chamber  26  of the inner member  16  along the first paint discharge surface  56 . At this time, the paint is thinned. 
     The mounting hole  62  is disposed at the rear end of the first flare portion  52 . The mounting hole  62  is disposed radially inward of the first flare portion  52 . The enlarged diameter portion  36  of the inner member  16  is housed in the rear end of the first flare portion  52 . The enlarged diameter portion  36  is disposed at a position adjacent to the front end of the mounting hole  62 . A first clearance S 1  is provided between the first paint discharge surface  56  of the first flare portion  52  and the outer peripheral surface of the enlarged diameter portion  36 . The first clearance S 1  has an annular shape. 
     The first paint discharge surface  56  of the first flare portion  52  includes a plurality of through holes  70 . The plurality of through holes  70  are disposed radially outward of the enlarged diameter portion  36  of the inner member  16 . The plurality of through holes  70  are arranged along the circumferential direction of the first flare portion  52 . Each of the through holes  70  has, for example, a rectangular cross-sectional shape elongated in the circumferential direction. The plurality of through holes  70  are aligned with each other when viewed from a position in the front-rear direction of the first flare portion  52  (the directions of arrows A and B). The plurality of through holes  70  are arranged at equal intervals along the circumferential direction of the first flare portion  52 . Each through hole  70  penetrates the first flare portion  52  in the radial direction. 
     The total opening area obtained by adding the opening areas of the plurality of through holes  70  is ½ of the projected area of the first paint discharge surface  56  on which the through holes  70  are projected. That is, the size (cross-sectional shape) of each through hole  70  and the number of the through holes  70  are set such that the total opening area thereof is ½ of the circumferential area of the second paint discharge surface  58  along the circumferential direction on the outer circumferential side of the through holes  70 . 
     The paint is supplied from the paint discharge hole  40  of the inner member  16  toward the first flare portion  52 . Half (½) of the supply amount of the paint is supplied to the first paint discharge surface  56  of the first flare portion  52 . The remaining half (½) of the paint flows radially outward of the first bell cup  44  through the through holes  70 . The remaining half of the paint is supplied to the second bell cup  46 . 
     On the other hand, the second paint discharge surface  58  of the second flare portion  54  is inclined forward toward the radially outer side. When viewed from the front-rear direction of the second bell cup  46 , the second paint discharge surface  58  is an annular surface. Due to the centrifugal force generated by the rotation of the second bell cup  46 , the paint moves radially outward from the paint storage chamber  26  of the inner member  16  along the second paint discharge surface  58 . At this time, the paint is thinned. 
     In the outer member  18 , the first bell cup  44  is housed inside the second bell cup  46 . The first coupling portion  48  is fitted into the second coupling portion  50  in the outer member  18 . Thus, the first bell cup  44  and the second bell cup  46  are coaxially coupled to each other. A second clearance S 2  is provided between the rear surface of the first flare portion  52  and the front surface (second paint discharge surface  58 ) of the second flare portion  54 . The second clearance S 2  has an annular shape and extends along the first and second flare portions  52  and  54 . The second clearance S 2  has a substantially constant width in the radial direction. 
     As shown in  FIG. 1 , the front end (large-diameter-side opening) of the first flare portion  52  has a maximum diameter in the first bell cup  44 . The front end (large-diameter-side opening) of the second flare portion  54  has a maximum diameter in the second bell cup  46 . A maximum outer diameter D 1  of the first flare portion  52  is identical to a maximum outer diameter D 2  of the second flare portion  54  (D 1 =D 2 ). 
     Next, the operation and effects of the rotary atomizing coating device  10  will be described. 
     When coating a workpiece (not shown), first, the rotary drive source (not shown) is driven. The rotary shaft  14  of the rotary drive source rotates, and the rotary atomizing head  12  rotates at high speed with the rotation of the rotary shaft  14 . Paint is supplied from the paint supply source (not shown) to the paint supply passage  20  of the tube member  22 . 
     The paint is supplied to the paint storage chamber  26  of the rotary atomizing head  12  through the paint supply passage  20 . In the paint storage chamber  26  shown in  FIG. 4 , the paint moves radially outward due to the centrifugal force generated by the rotation of the inner member  16 . The paint moves toward the front end along the inner peripheral surface of the paint storage chamber  26 . 
     The paint is discharged radially outward from the paint storage chamber  26  through the plurality of paint discharge holes  40 . At this time, as shown in  FIG. 5 , the plurality of paint discharge holes  40  are opened substantially uniformly along the circumferential direction of the inner member  16  (the arrow C direction). Therefore, the paint is discharged substantially uniformly in the circumferential direction of the inner member  16  through the plurality of paint discharge holes  40 . 
     As shown in  FIG. 4 , after the paint has passed through the paint discharge holes  40 , the paint flows out to the first paint discharge surface  56  of the first bell cup  44 . The paint flows toward the front end of the first bell cup  44  through the first clearance S 1  between the enlarged diameter portion  36  of the inner member  16  and the first paint discharge surface  56 . A portion of the paint flows out toward the second bell cup  46  through the plurality of through holes  70  opened on the first paint discharge surface  56 . 
     At this time, the total opening area obtained by adding the opening areas of the plurality of through holes  70  is ½ of the circumferential area of the first paint discharge surface  56 . Therefore, half (½) of the paint supplied from the inner member  16  toward the first bell cup  44  flows to the first paint discharge surface  56  of the first flare portion  52 . The remaining half (½) of the paint flows to the second paint discharge surface  58  of the second flare portion  54  through the plurality of through holes  70 . 
     That is, the amount of the paint supplied from the inner member  16  toward the outer member  18  is evenly distributed to the first bell cup  44  and the second bell cup  46  by the plurality of through holes  70 . In other words, in the rotary atomizing coating device  10 , the flow of the paint is divided on the outer periphery of the inner member  16  into flow of the paint supplied to the first bell cup  44  and flow of the paint supplied to the second bell cup  46 . 
     In this manner, the paint is evenly supplied to the first paint discharge surface  56  and the second paint discharge surface  58 . Due to the centrifugal force generated by the rotation of the first and second bell cups  44  and  46 , the paint flows radially outward along the first and second paint discharge surfaces  56  and  58  and is thinned. Thereafter, the paint is discharged from the outer edge portions that are the front ends of the first and second flare portions  52  and  54 . The paint is atomized as paint particles. 
     At this time, in the rotary atomizing coating device  10 , a high voltage is applied between the rotary atomizing head  12  and a workpiece which is an object to be coated. Therefore, after the paint particles are atomized and charged in the rotary atomizing head  12 , the paint particles fly toward the workpiece and are applied thereto. 
     As described above, in the first embodiment, the rotary atomizing head  12  of the rotary atomizing coating device  10  includes the first bell cup  44 , the second bell cup  46 , the paint supply passage  20  (the tube member  22 ), and the inner member  16 . 
     The first bell cup  44  has the first paint discharge surface  56  for thinning the paint by the centrifugal force. The second bell cup  46  is fitted to the outer side of the first bell cup  44 . The second bell cup  46  has the second paint discharge surface  58  for thinning the paint. The paint supply passage  20  extends inside the rotary shaft  14  and the paint is supplied through the paint supply passage  20 . The inner member  16  is disposed inside the first bell cup  44  and communicates with the paint supply passage  20 . The outer peripheral wall  30  of the inner member  16  is provided with the paint discharge holes  40 . The paint discharge holes  40  and the paint supply passage  20  communicate with each other. The first bell cup  44  includes the through holes  70 . The through holes  70  are disposed near the paint discharge holes  40  and communicate with the second bell cup  46 . 
     The conventional rotary atomizing coating device is provided with paint passage branch holes for discharging paint to two head bodies. In the present invention, the first bell cup  44  includes the plurality of through holes  70  for supplying paint toward the second bell cup  46 . By appropriately setting the shape and the number of the through holes  70 , it is possible to adjust, at a desired ratio, the amount of the paint supplied to the first bell cup  44  and the amount of the paint supplied to the second bell cup  46  through the paint discharge holes  40  of the inner member  16 . 
     As a result, with a simple configuration including the two first and second bell cups  44  and  46 , the rotary atomizing coating device  10  can distribute the paint by adjusting the discharge ratio between the paint discharged to the first bell cup  44  and the paint discharged to the second bell cup  46 . Therefore, even when the amount of the paint supplied to the rotary atomizing head  12  is increased, the thickness of the liquid film of the paint on the workpiece can be thinned and the paint can be atomized. 
     The outer member  18  has a two-layer structure including the first and second bell cups  44  and  46 . Therefore, the liquid film per layer can be made thinner without increasing the rotational speed of the rotary atomizing head  12  as compared with a rotary atomizing coating device having a single-layer structure. As a result, the paint particles can be atomized. 
     In other words, compared with the rotary atomizing coating device having the single-layer structure, even when the rotary atomizing head  12  is rotated at a lower rotational speed, the paint particles can be atomized to the same degree as the paint particles obtained by the rotary atomizing coating device having the single-layer structure. 
     The plurality of through holes  70  are arranged on the same circumference in the first flare portion  52  of the first bell cup  44 . The plurality of through holes  70  are disposed to be spaced apart from each other by the length of the through holes  70  in the circumferential direction. The total opening area obtained by adding the opening areas of the plurality of through holes  70  is set to be ½ of the circumferential area of the first flare portion  52 . 
     As a result, half of the paint supplied from the inner member  16  to the first bell cup  44  can be supplied to the second bell cup  46  through the plurality of through holes  70 . Thus, by setting the total opening area (projected area) of the plurality of through holes  70  to ½ of the circumferential area, it is possible to evenly distribute the paint to the first bell cup  44  and the second bell cup  46 . 
     The paint discharge holes  40  of the inner member  16  and the through holes  70  of the first bell cup  44  are substantially aligned with each other when viewed from a position in the axial direction of the rotary shaft  14 , that is, in the front-rear direction of the rotary atomizing head  12  (the directions of arrows A and B). The through hole  70  penetrates in a radial direction orthogonal to the front-rear direction of the first bell cup  44 . 
     When the rotary atomizing head  12  rotates and the centrifugal force acts on the paint, no component force is generated in the paint and only a centrifugal force in the radial direction is uniformly applied to the paint. Thus, it is possible to evenly distribute the paint from the paint storage chamber  26  to each of the through holes  70  by using the centrifugal force. 
     The maximum outer diameter D 1  of the first bell cup  44  is identical to the maximum outer diameter D 2  of the second bell cup  46  (D 1 =D 2  in  FIG. 1 ). As a result, the amount of the paint discharged radially outward from the first bell cup  44  and the amount of the paint discharged radially outward from the second bell cup  46  can be made even. 
     The size of the paint particles discharged radially outward from the first bell cup  44  and the size of the paint particles discharged radially outward from the second bell cup  46  can be made even. 
     Next, a rotary atomizing coating device  80  according to a second embodiment is shown in  FIGS. 6 to 10 . The same components as those of the rotary atomizing coating device  10  according to the first embodiment described above are denoted by the same reference numerals, and detailed description thereof is omitted. 
     The rotary atomizing coating device  80  includes a plurality of paint discharge holes  86 . The plurality of paint discharge holes  86  are disposed in the outer peripheral wall  30  of an inner member  84  constituting a rotary atomizing head  82 . The plurality of paint discharge holes  86  penetrate the outer peripheral wall  30  in the radial direction. A first bell cup  88  includes a plurality of through holes  90 . The plurality of through holes  90  are disposed on the first paint discharge surface  56  that is on the outer peripheral side of the paint discharge holes  86 . The number of the through holes  90  is half the number of the paint discharge holes  86 . 
     The rotary atomizing coating device  80  includes the plurality of paint discharge holes  86  and the plurality of through holes  90 . In this respect, the rotary atomizing coating device  80  is different from the rotary atomizing coating device  10  according to the first embodiment. 
     The outer peripheral wall  30  of the inner member  84  in the rotary atomizing head  82  is provided with the plurality of paint discharge holes  86 . The plurality of paint discharge holes  86  are disposed adjacent to the rear end of the enlarged diameter portion  36 . The cross-sectional shape of the paint discharge hole  86  is circular. Each of the paint discharge holes  86  penetrates the outer peripheral wall  30  in the radial direction. Each of the paint discharge holes  86  allows communication between the outside of the outer peripheral wall  30  and the paint storage chamber  26 . The plurality of paint discharge holes  86  are aligned with each other when viewed from a position in the front-rear direction of the inner member  84  (the directions of arrows A and B). The plurality of paint discharge holes  86  are arranged along the circumferential direction in the outer peripheral wall  30 . The plurality of paint discharge holes  86  are arranged at equal intervals in the circumferential direction of the inner member  84 . 
     The paint discharge holes  86  include first hole portions  92  and second hole portions  94 . The first hole portion  92  and the second hole portion  94  have the same shape. The number of the first hole portions  92  is the same as the number of the second hole portions  94 . The first hole portions  92  and the second hole portions  94  are alternately arranged adjacent to each other along the circumferential direction of the outer peripheral wall  30 . That is, the paint discharge holes  86  are configured such that the number of the first hole portions  92  and the number of the second hole portions  94  are equal. 
     The first bell cup  88  of the outer member  18  includes the first paint discharge surface  56  of the first flare portion  52 . The first paint discharge surface  56  is disposed outside the enlarged diameter portion  36 . The first paint discharge surface  56  includes the plurality of through holes  90 . The plurality of through holes  90  are arranged along the circumferential direction of the first flare portion  52 . 
     Each of the through holes  90  has, for example, the same diameter as the paint discharge hole  86  and has a circular cross-sectional shape. The plurality of through holes  90  are aligned with each other when viewed from a position in the front-rear direction of the first bell cup  88  (the directions of arrows A and B). That is, the plurality of through holes  90  are arranged on a single imaginary circle in the first bell cup  88 . 
     As shown in  FIG. 10 , the plurality of through holes  90  are arranged at equal intervals along the circumferential direction of the first bell cup  88 . Each of the through holes  90  is disposed radially outward of the second hole portion  94  of the paint discharge hole  86 . The through hole  90  and the second hole portion  94  adjacent to each other in the radial direction are arranged on a straight line in the radial direction. The through hole  90  and the second hole portion  94  adjacent to each other in the radial direction communicate with each other. 
     That is, the number of the through holes  90  is the same as the number of the second hole portions  94 . In the circumferential direction of the first bell cup  88 , the plurality of through holes  90  are disposed at positions shifted from the plurality of first hole portions  92 . In other words, the through holes  90  communicate with half (½) of the paint discharge holes  86 . 
     Next, the operation and effects of the rotary atomizing coating device  80  will be described. 
     First, a rotary drive source (not shown) is driven. As the rotary shaft  14  of the rotary drive source rotates, the rotary atomizing head  82  rotates at high speed. As shown in  FIG. 9 , the paint supplied to the paint storage chamber  26  of the inner member  84  moves radially outward in the paint storage chamber  26  by a centrifugal force. 
     The paint moves forward (in the arrow A direction) along the inner peripheral surface of the paint storage chamber  26 . The paint is discharged to the radially outer side of the inner member  84  through the plurality of paint discharge holes  86 . 
     The plurality of paint discharge holes  86  are opened at equal intervals along the circumferential direction of the inner member  16 . Therefore, the paint is discharged substantially evenly along the circumferential direction of the inner member  84  through the first and second hole portions  92  and  94  of the paint discharge holes  86 . In other words, the paint is discharged radially and substantially evenly over the entire circumference of the inner member  84 . 
     The paint discharged from the plurality of first hole portions  92  is supplied to the first clearance S 1  between the first paint discharge surface  56  and the inner member  16 . Thereafter, the paint flows toward the front end of the first bell cup  88  through the first clearance S 1 . 
     On the other hand, the paint discharged from the second hole portions  94  of the paint discharge holes  86  passes through the through holes  90  and flows out toward the second bell cup  46 . That is, a portion of the paint passes through the through holes  90 , the number of which is half the number of the paint discharge holes  86 . As a result, the amount of the paint that passes through the first hole portions  92  and is supplied to the first bell cup  88  and the amount of the paint that passes through the second hole portions  94  and the through holes  90  and is supplied to the second bell cup  46  are equalized. 
     In this way, the paint is evenly supplied to the first paint discharge surface  56  of the first bell cup  88  and the second paint discharge surface  58  of the second bell cup  46 . Due to the centrifugal force generated by the rotation of the first and second bell cups  88  and  46 , the paint flows radially outward along the first and second paint discharge surfaces  56  and  58 , and is thinned. Thereafter, the paint is discharged from the outer edge portions that are the front ends of the first and second flare portions  52  and  54 . The paint is atomized as paint particles and discharged. After the paint particles are discharged from the first and second bell cups  88  and  46 , the paint particles fly toward the workpiece and are applied thereto. 
     In other words, in the rotary atomizing coating device  80 , the paint is passed through the plurality of paint discharge holes  86  in the inner member  84 . Thus, the paint supplied to the inner member  84  is divided into paint supplied toward the first bell cup  88  and paint supplied toward the second bell cup  46 . As a result, compared to the rotary atomizing coating device  10  according to the first embodiment, the rotary atomizing coating device  80  is capable of dividing the flow of the paint on the further upstream side in the flow path of the paint. 
     As described above, in the second embodiment, the rotary atomizing head  82  of the rotary atomizing coating device  80  includes the first bell cup  88 , the second bell cup  46 , the paint supply passage  20 , and the inner member  84 . The first bell cup  88  has the first paint discharge surface  56  for thinning the paint by the centrifugal force. The second bell cup  46  is fitted to the outer side of the first bell cup  88 . The second bell cup  46  has the second paint discharge surface  58  for thinning the paint. 
     The paint supply passage  20  extends inside the rotary shaft  14  and the paint is supplied through the paint supply passage  20 . The inner member  84  is disposed inside the first bell cup  88  and communicates with the paint supply passage  20 . The outer peripheral wall  30  of the inner member  84  includes the plurality of paint discharge holes  86 . The plurality of paint discharge holes  86  communicate with the paint supply passage  20 . The first bell cup  88  includes the plurality of through holes  90 . The plurality of through holes  90  penetrate toward the second bell cup  46 . The second hole portions  94  of the paint discharge holes  86  and the through holes  90  are aligned with each other when viewed from a position in the circumferential direction, and the second hole portions  94  and the through holes  90  communicate with each other. 
     The conventional rotary atomizing coating device is provided with paint passage branch holes for discharging paint to two head bodies respectively. In the present invention, the paint can be distributed by adjusting the amount of the paint supplied to the first bell cup  88  and the amount of the paint supplied to the second bell cup  46  at a desired ratio by appropriately setting the number of the through holes  90  in the first bell cup  88 . 
     As a result, in the rotary atomizing coating device  80 , by providing the two first and second bell cups  88  and  46 , it is possible to reduce the thickness of the liquid film of the paint and atomize the paint. In the rotary atomizing coating device  80 , with a simple configuration, the paint can be distributed by appropriately adjusting the discharge ratio between the paint discharged from the first bell cup  88  and the paint discharged from the second bell cup  46 . 
     The paint is passed through the plurality of paint discharge holes  86  in the inner member  84 . As a result, the flow of the paint can be reliably and easily divided into the flow of the paint supplied to the first bell cup  88  and the flow of the paint supplied to the second bell cup  46 . Therefore, compared with the rotary atomizing coating device  10  according to the first embodiment, the paint can be distributed on the further upstream side. As a result, in the rotary atomizing coating device  80 , it is possible to more reliably distribute the paint evenly along the circumferential direction. 
     The paint discharge holes  86  and the through holes  90  are substantially aligned with each other when viewed from a position in the front-rear direction of the rotary atomizing head  82  (the directions of arrows A and B). The paint discharge holes  86  and the through holes  90  penetrate in a radial direction orthogonal to the front-rear direction. Therefore, when the rotary atomizing head  82  rotates and the centrifugal force acts on the paint, no component force is generated in the paint and only a centrifugal force in the radial direction is uniformly applied to the paint. As a result, it is possible to evenly distribute the paint from the paint storage chamber  26  to each of the through holes  90 . 
     The maximum outer diameter D 1  of the first bell cup  88  is identical to the maximum outer diameter D 2  of the second bell cup  46  (D 1 =D 2  in  FIG. 6 ). As a result, the amount of the paint discharged radially outward from the first bell cup  88  and the amount of the paint discharged radially outward from the second bell cup  46  can be made even. The size of the paint particles discharged radially outward from the first bell cup  88  and the size of the paint particles discharged radially outward from the second bell cup  46  can be made even. 
     Note that the present invention is not limited to the embodiments described above, and various configurations can be adopted therein without departing from the gist of the present invention.