Patent Publication Number: US-6341734-B1

Title: Rotary atomizer and bell cup and methods thereof

Description:
BACKGROUND 
     An electrostatic painting device typically uses a rotary atomizer to atomize paint or coating material. A rotary atomizer typically includes a bell shaped body (“bell cup”), which is typically used, but not exclusively, in painting motor vehicles. The bell cup is mounted to one end of a rotatably mounted shaft, which is typically driven by an air motor. The bell cup is generally spun at a relatively high speed, to about 70,000 RPM, to generate sufficient centrifugal force to atomize the coating material exiting the bell cup&#39;s spray edge into a super fine mist. 
     Different bell cups may have different shapes and configuration to offer a variety of flow shapes and rates. Air can be supplied through a shroud that is concentrically positioned over the bell cup, adjacent to where the atomized coating material leaves the bell cup, to direct the atomized coating material to the object to be coated. 
     The bell shaped body can have a cavity defining an inner flow surface that communicates with the coating material source and a spray edge contiguous with the inner flow surface at the front or distal end of the bell shaped body. The bell cup is typically rotated around a stationary nozzle having a passageway or channel for the coating material. 
     One known problem with a bell cup atomizer is that coating material can accumulate on the outer exposed surfaces of the bell cup. During use, the accumulated (old) coating material can dislodge from the bell cup and undesirably mix with the new coating material, especially after changing the paint. Therefore, it is highly desirable to clean the outer surfaces of unwanted material. 
     One solution is to separately feed solvent or jet air to the outer peripheral surfaces to remove or prevent the unwanted material from adhering thereto. See for example, U.S. Pat. Nos. 5,862,988, 5,707,009, and 5,106,025. Another solution, as disclosed for example, in U.S. Pat. No. 5,707,009, uses a stationary nozzle having a plurality of channels that are separate from the coating material channel for delivering solvent to the inner flow surface and the outer surface of the bell cup. Since the solvent channels are independent from the coating material channel, the bell cup can be rinsed with solvent (rinsing or cleaning agent) without having to remove the paint from the paint channel. The feed nozzle, which is coaxially arranged with the bell cup, delivers solvent or coating material from the rear or proximal end of the bell cup through passages formed in the flow control device, e.g., an insert or face cover, of the bell cup. 
     In U.S. Pat. No. 5,707,009, the bell cup has an annular cavity located at the rear section of the bell cup, communicating with the solvent channels. The annular cavity creates a reservoir by which solvent flows via the rearward edge onto the outer periphery of the bell cup. During use, while the bell cup undergoes painting operation, the annular cavity is prone to paint accumulation. Thus, there is a need for a better way of cleaning the outer periphery of the bell cup. The present invention addresses this need. 
     Known bell-cup atomizers are typically monolithically formed (single-piece construction), typically machined from a single block of aluminum. In this vein, a typical bell cup atomizer has a bell cup integrally formed with a flow control device typically comprising a front cover or bell cone covering a portion of the cavity. The front cover or bell cone has a front side having exit passageways. The backside or the proximal end of the bell-cup atomizer has a rather relatively small passage through which the machining or cleaning is accomplished. 
     In practice, the atomized coating material can adhere to the surfaces of the bell cup and impede the flow of the coating material through the exit holes. Consequently, the bell cup must be cleaned frequently. Thorough cleaning of known bell cups entails detaching them from their manifold to access the internal surfaces. Even after detaching it, the narrower or smaller opening at the proximal end of the bell cup makes cleaning difficult. 
     Further, various stages of a coating operation may require different flow configurations of coating materials and, thus, require a different exit hole arrangement. With known bell cups, the entire bell-cup atomizer must be detached from the manifold, and an entire new bell-cup atomizer must be attached. This procedure must be repeated each time the coating operation calls for a change in the flow configuration of the coating material. 
     Accordingly, there is a need for a better way of accessing the internal surfaces of the bell-cup atomizer and a more economical way of manufacturing and using the same. In this respect, U.S. Pat. No. 5,707,009 addresses this problem with a detachable flow control device (insert) comprising a front cover and a ring unit. The present invention also addresses this need. 
     Further, a bell-cup atomizer with the integral flow control device or the detachable insert typically has radially or outwardly extending channels through which the paint exits. The bell-cup atomizer or the detachable insert can be formed with a curved or flat wall surface. The present inventor has found that paint can build up on that wall surface even after undergoing a wash cycle. Accordingly, there is a need for a bell-cup atomizer or detachable insert that stays cleaner around the exit side of the channels. The present invention also addresses this need. 
     SUMMARY 
     The present invention relates to a coating device, such as a rotary atomizer, a bell cup thereof, and a detachable flow control device thereof, and methods thereof. The rotary atomizer has a bell cup, i.e., a rotatable body. The bell cup can have a provision for cleaning the outer surface thereof and/or a provision for enabling access to inside, i.e., a cavity thereof, for easier cleaning and/or to alter the flow pattern. 
     The rotatable body can have a cavity defining an inner surface, an outer surface surrounding the cavity, and a spray edge located at a distal end of the rotatable body, where coating material to be atomized leaves the rotatably body. The rotatable body further can have a first axial passage through which a coating material to be atomized or a cleaning agent can be delivered to the cavity. The rotatable body has a plurality of cleaning passages extending from the first axial passage to the outer surface of the rotatable body. The cleaning passages are adapted to deliver cleaning agent to the outer surface. Moreover, the outer surface of the rotary body is deliberately devoid of any fluid accumulating recess or reservoir to enable the cleaning passages to feed the cleaning fluid onto the outer surface without accumulating or storing the cleaning agent or the coating material on the outer surface. 
     The rotatable body can be substantially bell shaped, having an open distal end and a proximal end opposite the distal end, and a hub portion extending axially from the proximal end of the bell shaped body. The outer surface can extend from the hub portion to the distal end. The first axial passage extends concentrically with the hub portion and extends through the proximal end of the bell shaped body to communicate the first axial passage with the cavity. The cleaning passages can extend outwardly and forwardly toward the proximal end of the bell shaped body. 
     The rotary atomizer can further include a rotatable shaft connected to the rotatable body. In this respect, the hub portion can include a first mechanical connector, such as external or male threads, and the rotatable shaft can include a second mechanical connector, such as internal or female threads, that is complementary to the first mechanical connector. 
     A stationary nozzle can be used to deliver the coating material and the cleaning agent. In this respect, the nozzle can have a first passage adapted to deliver the coating material to the cavity, at least one second passage adapted to deliver the cleaning agent to the cavity, and a third passage branching off from the second passage. The nozzle can extend into the first axial passage with a sufficient clearance to permit the rotatable body to freely rotate relative to the stationary nozzle. The distal end of the stationary nozzle can extend into the second axial passage with a sufficient clearance to permit the rotatable body to freely rotate relative to the stationary nozzle. 
     The first passage and the second passage both communicate with the cavity, and the third passage communicates with the cleaning passages to direct the cleaning agent to the outer surface. Because the outer surface is devoid of any fluid accumulating recess or reservoir according to the one aspect of the present invention, the cleaning passages can feed the cleaning fluid onto the outer surface without accumulating the cleaning agent or the coating material on the outer surface. 
     The bell cup can have a flow control device connected or mounted to the rotatable body, which flow control device substantially encloses a portion of the cavity. The flow control device can have a mounting member and a face cover having a front side, a rear side opposite the front side, the rear side facing toward the first axial passage. The mounting member extends from the rear side of the face cover into the first axial passage. The face cover has at least one passageway adjacent its periphery. 
     The mounting member can include a first mechanical connector and the bell shaped body can include a second mechanical connector that is complementary to the first mechanical connector. The first mechanical connector can comprise external threads and the second mechanical connector can comprise complementary internal threads. The flow control device can be attached or detached by rotating the flow control device relative to the bell shaped body. The internal threads can be formed in the first axial passage. 
     The face cover can be circular and spaced from a distal end of the first axial passage. The outer periphery of the circular face cover can be spaced from an inner surface to form an annular passageway or can sealingly abut the inner surface to form a plurality of passageways. The rear side and the inner surface define an internal chamber. The mounting member has a second axial passage communicating with the internal chamber and the first axial passage. The second axial passage is adapted to deliver the coating material to the internal chamber. 
     The flow control device can further include a sealing flange positioned between the first mechanical connector and the face cover. The first axial passage includes, at a distal end thereof, a seat for receiving the sealing flange. The flow control device can further include a plurality of substantially radially extending channels that communicate the second axial passage with the internal chamber. The substantially radially extending channels can be positioned between the sealing flange and the face cover. 
     The flow control device can further include a recessed cavity formed between the face cover and the sealing flange. The internal chamber is further defined by the recessed cavity. The recessed cavity can have an annular wall positioned between the face cover and the sealing flange. The radially extending channels open through the annular wall and form exit openings that are kept separated by the annular wall. The exit openings each are radiused to form a sharp longitudinal edge formed on the annular wall between two adjacent channels. 
     The flow control device can further include a center feed outlet at a center of the face cover. The center feed outlet can comprise a center passage communicating the internal chamber with the front side of the face cover and a plurality of substantially radially extending channels communicating with the center passage. The front side can be substantially planar and the substantially radially extending channels can extend substantially parallel to the planar front side. 
     Another aspect of the invention is a flow control device itself, having aforementioned face cover, mounting member, sealing flange, axial passage, plurality of substantially radially extending channels, and annular wall. Specifically, the face cover has a front side and a rear side opposite the front side. The mounting member extends from the rear side of the face cover and has a mechanical connector adapted for attachment to a complementary mechanical connector of a bell cup of the rotary atomizer. The sealing flange is positioned between the mounting member and the face cover. The axial passage extends through the mounting member and the sealing flange. The substantially radially extending channels communicate with the axial passage and are positioned between the sealing flange and the face cover. The annular wall is formed between the face cover and the sealing flange. The radially extending channels open through the annular wall and form exit openings kept separated by the annular wall. The exit openings each are radiused to form a sharp edge formed on the annular wall between two adjacent channels. The radius reduces the wall surface so that the paint exiting the channels has virtually no surface to accumulate. Thus, cleaning the bell becomes much more efficient. 
     According to another aspect of the invention, one method of delivering coating material and cleaning agent to a rotary atomizer comprises: providing the rotatable body having the cavity defining the inner surface, the outer surface surrounding the cavity, and the spray edge at the distal end of the rotatable body, where the coating material to be atomized leaves the rotatably body, with the outer surface that is devoid of any fluid accumulating recess or reservoir; providing the stationary nozzle having the first passage that delivers the coating material to the cavity, the second passage that delivers cleaning agent to the cavity, and the third passage branching off from the second passage; providing a first axial passage in the rotatable body and the cleaning passages in the rotatable body, extending from the first axial passage to the outer surface of the rotatable body; extending the stationary nozzle into the first axial passage with a sufficient clearance to permit the rotatable body to freely rotate relative to the stationary nozzle; feeding coating material through the first passage to deliver coating material to the cavity and thus to the spray edge while rotating the rotatable body or feeding cleaning agent to the cavity through the second passage and to the outer surface through the second and third passages and the cleaning passages while rotating the rotatable body. 
     Because the outer surface is devoid of any fluid accumulating recess or reservoir, the cleaning passages feed the cleaning fluid onto the outer surface without accumulating the cleaning agent or accumulation the coating material on the outer surface. 
     According to another aspect of the invention, a method of manufacturing a bell cup comprises: providing the bell shaped body having the cavity defining the inner surface, the outer surface surrounding the cavity, and the spray edge at a distal end of the rotatable body, where the coating material to be atomized leaves the rotatably body; providing the first axial passage in the rotatable body that communicates with the cavity; providing the flow control device comprising the face cover and the mounting member, the face cover having the front side, the rear side opposite the front side, the rear side facing toward the first axial passage, and wherein the mounting member extends from the rear side of the face cover into the first axial passage, and the face cover having a plurality of passageways adjacent its periphery; providing the first mechanical connector on the mounting member and the second mechanical connector that is complementary to the first mechanical connector on the first axial passage; and connecting the first and second mechanical connector. 
     Because the first and second mechanical connectors can be detachably connected, using, for example, threads or any suitable conventional mechanical connectors, the flow control device can be removed to fully expose the cavity and to readily replace the same for different flow control or spray pattern. 
     The present invention encompasses the above-described aspect or combination of the aspects described above, or other features described below. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other features, aspects, and advantages of the present invention will become more apparent from the following description, appended claims, and accompanying exemplary embodiments shown in the drawings, which are briefly described below. 
     FIG. 1 illustrates a cross-sectional view of a bell-cup atomizer according to one embodiment of the present invention. 
     FIG. 2 is an enlarged view of section II of FIG.  1 . 
     FIG. 3 is an enlarged view of section III of FIG.  1 . 
     FIG. 4 is an exploded view of the bell-cup atomizer of FIG.  1 . 
     FIG. 5 illustrates an alternative embodiment of a detachable insert illustrated in FIG.  1 . 
     FIG. 6 is a cross-sectional view taken along line VI—VI of FIG. 5 (cross-sectional view of the detachable insert illustrated in FIG. 1 being identical). 
     FIG. 7 is an enlarged cross-sectional view of section VII of FIG.  5 . 
     FIG. 8 is an enlarged view of section VIII of FIG.  6 . 
     FIG. 9 illustrates a cross-sectional view similar to FIG. 6 for purposes of illustrating an external wall surface that can accumulate paint. 
     FIG. 10 is an enlarged cross-sectional view of section X of FIG.  9 . 
    
    
     DETAILED DESCRIPTION 
     Same or corresponding elements of different embodiments are labeled with the same reference numerals. Any reference made below to directions in describing the structure is relative to the drawings (as normally viewed) for convenience. The directions are not intended to be taken literally or limit the present invention in any form. 
     FIGS. 1-5 illustrate an embodiment of a rotary atomizer according to the present invention. The rotary atomizer can be used for spraying a coating material, such as water-soluble or other pigmented paint. The rotary atomizer has a bell cup  10  that can be coupled to a rotatable shaft  110 . The rotatable shaft  110  can be hollow with a sufficient clearance from a stationary injector or nozzle  90  so that it can spin relative to the stationary nozzle  90 . A mounting shroud  100  has a through hole  102  for accommodating the rotatable shaft  110 , which can be driven by a conventional motor, such as an air or pneumatic motor. 
     The bell cup  10  comprises a rotatable body  12  with a cavity C. The cavity C is defined by the rotatable body&#39;s inner surface  14  terminating at a spray edge E generally located at a distal end D of the rotatable body  12 , where atomized coating material leaves the rotatably body  12 . The rotatable body  12  also has an outer surface  16  surrounding the inner surface  14 . The rotatable body  12  has a first axial passage  20  (see FIG. 4) through which a coating material to be atomized or a cleaning agent is delivered to the cavity C. The rotatable body  12  further has a plurality of cleaning channels or passages  22  extending from the first axial passage  20  to the outer surface  16  of the rotatable body  12 . The illustrated embodiment includes eight such passages  22 . But any desirable number of these passages  22  can be included, from a minimum of one, to as many as needed, depending on the desirable flow rate. The cleaning passages  22  are adapted to deliver cleaning agent to the outer surface  16  of the rotatable body  12 . 
     According to one aspect of the invention, the outer surface  16  is deliberately devoid of any fluid accumulating recess or reservoir to enable the cleaning passages  22  to feed the cleaning fluid onto the outer surface  16  without accumulating the cleaning agent or the coating material on the outer surface  16 . 
     The rotatable body  12  can be bell shaped, having an open distal end D and a proximal end P opposite the distal end D, and a hub portion H extending axially away from the proximal end P thereof. In this respect, the bell-shaped body  12  can have a substantially conical configuration, with the inner and outer surfaces  14 ,  16  being substantially conical as shown in FIGS. 1 and 4. The outer surface  16  of the bell shaped body  12  can be defined as extending from about the exit opening of the cleaning passages  22  to the distal end D or the spray edge E. 
     The first axial passage  20  extends concentrically with and through the hub portion H and extends through the proximal end P of the bell shaped body  12  to communicate the first axial passage  20  with the cavity C. The cleaning passages  22  extend outwardly and forwardly from the first axial passage  20 , from the hub portion H, and terminate adjacent to the proximal end P (i.e., the distal end of the hub portion H) of the bell shaped body  12 . The cleaning passages  22  extend at an acute angle relative to the first axial passage  20 , and can be equally distributed around the hub portion H. 
     Referring to FIG. 4, the stationary nozzle  90  comprises a cylindrical body  90   a  with a first passage  91  adapted to deliver the coating material, at least one second passage  92  adapted to deliver cleaning agent, and a third passage  93  branching off from the second passage  92 . The first passage  91  extends axially, but can be slightly offset from the rotation axis R. The second passage  92  also extends axially, but offset from the rotation axis R and the first passage  91 . 
     Referring to FIG. 3, the second passage  92 , at its distal end portion, has an inwardly angled entry pathway  92   a,  followed by an axially extending discharge pathway  92   b,  which extends parallel with the first passage  91 . The nozzle  90  also has a tapered or conical distal head portion  95  (FIG. 4) at which the first and second passages  91 ,  92  extend parallel. 
     Although, the embodiment illustrated here shows a single second passage  92 , additional second passages  92  can be added if desired. In that case, the first passage  91  can be coaxial with the rotation axis R and the second passages  92  can be distributed around the first passage  91 . 
     The distal end portion of the stationary nozzle  90  extends into the first axial passage  20  with a sufficient clearance to permit the rotatable body to freely rotate relative to the stationary nozzle  90 . The third passage  93  communicates with the second passage  92  and terminates axially adjacent to the entry of the cleaning passages  22 . The distal end portion of the stationary nozzle  90  is inserted into the first axial passage  20  so that the third passage  93  ends near or close to where the cleaning passages  22  open into the first axial passage  20 . 
     The first passage  91  and the second passage  92  both communicate with the cavity C. The third passage  93  communicates with the cleaning passages  22  to direct the cleaning agent to the outer surface  16 , via a clearance space  94  formed between the flow control device  60 ,  60 A (FIGS. 4 and 5) and the stationary nozzle  90 . The first axial passage  20  includes a distal portion  20 A that has a larger dimension to provide the clearance space  94 . The cleaning passages  22  extend from the distal portion  20 A to the outer surface  16  of the rotatable body. Moreover, the nozzle  90  includes an annular recess  96  to provide additional clearance space. Because the outer surface  16  is devoid of any fluid accumulating recess or reservoir, the cleaning passages  22  can feed the cleaning fluid directly onto the outer surface  16 . 
     The bell cup  10  includes a detachable flow control device  60 ,  60 A concentrically disposed inside the bell shaped body  12  to substantially enclose or block a portion of the cavity C, forming an internal chamber IC (FIG.  1 ). The flow control device  60 ,  60 A comprises a face cover  62  and a mounting member  80 . The face cover  62  has a front side  62   a,  a rear side  62   b  opposite to the front side  62   a,  the rear side  62   b  facing the first axial passage  20 . The mounting member  80  extends from the rear side  62   b  of the face cover  62  into the first axial passage  20 . 
     The face cover  62  is circular and spaced from a distal end of the first axial passage  20 . In the embodiment illustrated in FIGS. 1 and 4, the face cover  62  has a plurality of evenly spaced notches or serrations that form a plurality of passageways  65  with the inner surface  14 . The circular periphery  62   p  of the face cover  62  in this embodiment can have sharp peripheral edges that sealingly abut the inner surface  14 . The rear side  62   b  and a portion of the inner surface  14  confined by the face cover  62  define the internal chamber IC. In the embodiment illustrated in FIGS. 5 and 7, the face cover  62  has a rounded edge R that is spaced away from the inner surface  14  to provide an annular passageway (i.e., predetermined gap) therebetween instead of a plurality of passageways  65 . 
     The mounting member  80  includes a first mechanical connector  82 . The bell shaped body  12  has a second mechanical connector  50  that is complementary to the first mechanical connector  82 . The first mechanical connector  82  can comprise external threads and the second mechanical connector  50  can comprise complementary internal threads formed on the first axial passage  20 . The flow control device  60 ,  60 A is attached or detached by rotating the flow control device  60 ,  60 A relative to the bell shaped body  12 . 
     The flow control device  60 ,  60 A can be detachably mounted via threads, as shown in FIG.  5 . The first and second mechanical connectors  82 ,  50 , however, can be other conventional means of removably attaching or coupling two bodies, such as a bayonet mount, keyed or splined coupling, snap-fit, interference fit, etc. This enables replacement of the flow control device  60 ,  60 A after usage, such as during an overhaul, and eases maintenance and manufacturability of the bell cup  10 . 
     The flow control device  60 ,  60 A can further include a sealing flange  70  positioned between the first mechanical connector  82  and the face cover  62 . The sealing flange  70  is cylindrical and can be dimensioned the same as or wider than the first mechanical connector  82 . The flange  70  has a groove  72  for receiving and seating an O-ring O or the like. At a distal end of the first axial passage  20 , the bell shaped body  12  includes a seat  24 . The seat  24  comprises a cylindrical recess that extends collinearly and concentrically with the first axial passage  20  at its distal end. The cylindrical recess  24  is dimensioned to seat the sealing flange  70 . The O-ring O is designed to seal the flange  70  against the seat  24 , and prevent coating material from leaking. 
     The flow control device  60 ,  60 A has a second axial passage  61  (center channel) that communicates with the internal chamber IC and the first axial passage  20 . The second axial passage  61  extends axially through the first mechanical connector  82  and the sealing flange  70  and delivers the coating material/cleaning agent to the internal chamber IC. The second axial passage  61  extends to the backside  62   b  of the faceplate  62 . The entry or proximal end  61 T of the center channel  61  is tapered  61 T and configured complementary with the tapered distal head portion  95  of the nozzle  90 . A sufficient clearance is provided between the head portion  95  and the center channel  61  to allow the bell cup  10  to rotate relative to the nozzle  90  without contacting any portion of the nozzle  90 . The nozzle  90  remains stationary while the bell cup  10  rotates. 
     The flow control device  60 ,  60 A further includes a plurality of substantially radially or outwardly extending channels  63  that communicate the second axial passage  61  with the internal chamber IC. The outwardly extending channels  63  can be positioned between the sealing flange  70  and the face cover  62 . 
     The flow control device  60  has a plurality of outlet passageways  65  distributed around adjacent its outer periphery, which passageways  65  communicate with the cavity C. In this embodiment, cleaning agent or coating material discharges to the exposed cavity C through the channels  63  and passageways  65 . In the second embodiment (FIG.  5 ), the flow control device  60 A forms a continuous annular gap between the peripheral edge  62   p  and the inner surface  14  of the bell cup  10  to form a passageway. In the second embodiment, cleaning agent or coating material discharges to the exposed cavity C through the channels  63  and the annular gap. 
     Referring to FIG. 2, the flow control device  60 ,  60 A can further include a center feed outlet  84  at a center of the faceplate  62 . The center feed outlet  84  comprises a center passage  86  communicating the internal chamber IC with the front side  62   a  of the face cover  62  and a plurality of channels or passages  88  communicating with the center passage  86 , which communicates with a plurality of feeding passages  63   a  formed through the faceplate  62 . The channels  63  communicate with the center passage  86  through the plurality of entry openings of the feeding passages  63   a.  The feeding passages  63   a  are angled so that they converge into the center passage  86 . The front side  62   a  can be substantially planar and the channels  88  can extend substantially parallel to the planar front side  62   a.  The center feed outlet  84  can discharge cleaning agent to clean the front face  62   a  of the faceplate  62 . In this respect, the radially extending passages  88  direct cleaning agent parallel to the front face  62   a.  This is achieved by having the passages  88  aligned parallel to the front face  62   a  and radially outwardly directed. Cleaning agent can be thus delivered through the passages  88  to clean the front face  62   a,  and through the channels  63  to clean the internal chamber IC and the inner surface  14  of the bell shaped body  12 . 
     Referring to FIGS. 1 and 4, the bell cup  10  is adapted to be connected to a hollow rotatable shaft  110 , which has a passage  112 . In this respect, the hub portion H can include a mechanical connector  40 , such as external or male threads, and the rotatable shaft  110  can include a mechanical connector  120 , such as internal or female threads, that is complementary to the mechanical connector  40 , similar to the first and second mechanical connectors  82 ,  50  of the flow control device  60 ,  60 A and the rotatable body  12 . These mechanical connectors  40 ,  120  also can be other conventional complementary means of attaching or coupling two bodies, such as a bayonet mount, keyed or splined coupling, etc. 
     The mounting shroud  100  comprises a substantially cylindrical member  101  with a central through hole  102  dimensioned to pass the hollow rotatable shaft  110  with a sufficient clearance. The rotatable shaft  110  extends coaxially with the cylindrical member  101  and can be rotatably journaled relative to the cylindrical member  101 . The rotatable shaft  110  can be directly driven, which can be driven by an air or pneumatic motor (not shown), or connected to another driven hollow shaft, so that rotatable shaft  110  spins the bell cup  10 , while the stationary nozzle  90  and the cylindrical member  101  are maintained stationary. 
     The distal end portion  110 D of the rotatable shaft  110  can protrude beyond the distal end  101 D of the cylindrical member  101 , toward the hub portion H. The fastener  120  comprises a first recess  122 . The first recess  122  is substantially cylindrical and can extend toward the distal end portion  110 D of the rotatable shaft  110 , extending beyond the cylindrical member  101 . The first recess  122  can be concentric with the passage  112  and can have internal threads that are complementary with the external threads on the hub portion H. As explained before, the mechanical fastener can be any other suitable conventional means, such as the ones identified previously. 
     The rotatable shaft  110  further has a second recess  130 , concentric with the passage  112 , extending collinearly from the first recess  122 . The second recess  130  is substantially cylindrical, with a conical section  132  that tapers out to form a wider mouth at the distal end portion of the passage  112 . The conical section  132  is complementary to a tapered section HT of the hub portion H so that when the bell cup  10  is mounted to the rotatable shaft  110 , the tapered section HT and the conical section  132  abut each other. The distal end of the rotatable shaft  110  ends before the exit openings of the cleaning passages  22 . 
     The cylindrical member  101  also includes a plurality of axially extending passages  104  distributed about its periphery. The passages  104  can direct compressed air jets to the outer surface  16  of the bell cup  10  to direct coating material away from the outer surface  16  and prevent the coating material from sticking thereto, and/or to shape the atomized coating material. 
     In operation, when the coating material is changed, or to wash the bell cup  10 , cleaning agent, is directed through the passage  92  instead of feeding the coating material through the passage  91 . Cleaning agent is discharged through the first and second solvent passages  92 ,  93  when the bell cup needs rinsing (without paint change) to eliminate the need to use the coating material passage  91  and reduce paint loss. The axial pathway  92   b  feeds cleaning agent to the flow control device  60 ,  60 A, which delivers cleaning agent through the passageways  86 ,  88  to clean the flow control device front face  62   a,  and through the channels  63  to clean the internal chamber IC, and the inner surface  14 . Some cleaning agent also branches into the third passage  93  from the second passage  92 . Cleaning agent then enters the clearance space  94 . Some cleaning agent flows through the cleaning passages  22 , which communicate with the outer surface  16 , and some cleaning agent can bleed or seep into the second axial passage  61 , which communicates with the internal chamber IC, through the clearance space between the tapered nozzle head portion  95  and the tapered entry  61 T. Cleaning agent is delivered through the cleaning passages  22  to the distal end of the hub portion H, to access the entire backside of the outer surface  16 . Because there is no recess, cavity, reservoir, or equivalent of any kind at the backside of the outer surface that would accumulate solvent (or coating material for that matter), the solvent channels  22  communicate directly with the outer surface  16 . And because the backside does not have any place to harbor coating material, the bell cup  10  will require less maintenance, and will be easier to manufacture. 
     Typically, a bell cup  10  is machined from an aluminum alloy, and is integrally formed with the flow control device, bell cone, or face cover, which makes machining more difficult and complicated. By providing a removable flow control device  60 ,  60 A, which can be made from plastics or aluminum alloy, or any other durable and light material, the inner surface  14  of the bell cup  10  becomes accessible for machining and cleaning. During the bell-cup cleaning operation, the flow control device  60 ,  60 A may be removed, if needed, by unthreading, cleaned with a bristle brush, and then reinserted back into the same bell cup  10 , or simply replaced. When the flow control device  60 ,  60 A is removed, the inner surface  14  of the bell cup  10  becomes completely exposed for easy cleaning. 
     Referring to FIGS. 1 and 5, the internal chamber IC is defined by a portion of the inner surface  14  and a recessed cavity  67  formed between the front cover  62  and the sealing flange  70 . An annular wall  67   a  is formed between the front cover  62  and the sealing flange  70  and defines the inner chamber IC along with the front cover  62 , the sealing flange  70 , and the inner surface  14 . The channels  63  extend through the annular wall  67   a  and form exit openings at the periphery of the annular wall  67 . The wall  67   a  separates the exit openings of the adjacent channels  63 , as illustrated in FIG.  6 . 
     Referring to FIGS. 9 and 10, the present inventor discovered that the outer wall surface  67   s  of the wall  67   a  can accumulate paint. The accumulated paint will remain there even after a bell wash cycle. The present inventor discovered a solution to this problem. 
     Referring to FIGS. 5,  6 , and  8 , the present inventor contemplates solving this problem by beveling or removing portions  67   p  (see FIG. 10) of the wall  67   a  at the exit openings of the channels  63 . For example, in the embodiment shown in FIG. 8, a radius  67   r  has been added to each exit opening of the channel  63  so that a sharp edge  67   e  is formed on the wall  67   a  between the two adjacent channels  63 . The radius  67   r  reduces the wall surface  67   s  to an edge  67   e.  With this configuration, the paint exiting the channels  63  has virtually no surface to accumulate. Thus, the bell wash cleaning becomes more effective. 
     The removable flow control device  60 ,  60 A adds the benefit of interchangeability, according to particular coating requirements. A different spray pattern or flow rate may be achieved by simply replacing one flow control device  60 ,  60 A with another, rather than replacing the entire bell cup  10 . 
     Given the disclosure of the present invention, one versed in the art would appreciate that there may be other embodiments and modifications within the scope and spirit of the present invention. Accordingly, all modifications attainable by one versed in the art from the present disclosure within the scope and spirit of the present invention are to be included as further embodiments of the present invention. The scope of the present invention accordingly is to be defined as set forth in the appended claims.