Abstract:
An apparatus for applying a thermoplastic powder to internal threads of a fastener includes a vacuum nozzle having an end adapted to engage a first surface of the fastener. A spray tube is sized to be inserted within the bore of the fastener and communicates with a source or sources of thermoplastic powder and pressurized air. A bushing is mounted on the spray tube so that the spray tube is able to slide with respect to the bushing. The bushing is adapted to engage a second surface of the fastener. The spray tube and bushing are movable between clamping positions, where the vacuum nozzle and the bushing engage the first and second surfaces of the fastener, and release positions where the vacuum nozzle and the bushing do not engage the first and second surfaces of the fastener. A fastener holder holds the fastener between the vacuum nozzle and the bushing so that when the vacuum nozzle and the bushing are in the clamping positions, the spray tube enters the bore of the fastener and sprays thermoplastic powder on the internal threads of the fastener with excess thermoplastic powder collected by the vacuum nozzle. The vacuum nozzle and bushing may be machined and to permit either, both or neither of first and second chamfers of the fasteners to also be coated.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates generally to devices, systems and methods for applying thermoplastic powder to fasteners and, in particular, to an apparatus and method for selectively applying powder coatings onto internally threaded fasteners. 
       BACKGROUND 
       [0002]    A number of manufacturing processes attach fasteners having internally threaded bores with open ends, to components by welding. Parts or other components may then be attached to the fasteners using bolts or other externally threaded fasteners in downstream assembly operations. 
         [0003]    Examples of such fasteners are the hexagonal nuts indicated in general at  20  in  FIG. 1 . As illustrated in  FIG. 1 , each nut features an annular chamfer portion  22   a  and internal threads  24  formed within the wall of the bore of the nut. The opposite sides of the nuts  20  not visible in  FIG. 1  each include a second annular chamfer portion. The nuts are provided with weld projections  26 , which are used to weld the nut to a component or part. 
         [0004]    Coatings of thermoplastic material, such as fluoropolymer coatings ( 28  in  FIG. 1 ), are often applied onto the internal threads of the nuts, or other fasteners. As an example only, the thermoplastic material may be TEFLON. The purpose of the fluoropolymer coating is to prevent the build-up of post applied primers, paints and weld spatter on the threads  24  of the fasteners. This prevents fouling of the threads that would otherwise impede downstream assembly operations. The threads are coated up to, and sometimes including, the top ( 22   a ) and bottom chamfers that are at the start and the end of the threads  24 . 
         [0005]    When applying fluoropolymer powders into internally threaded fasteners, such as the nuts of  FIG. 1 , it is sometimes difficult to prevent the fluoropolymer powder from getting onto the external surfaces of the nuts. This is particularly true when the chamfers must be coated with the fluoropolymer material as well. Thermoplastic material on the exterior surfaces of the fasteners causes paint or primer not to stick and could cause other downstream process problems. In addition, it has been noted that if the projections  26  of the weld nuts get contaminated with the fluoropolymer coating, welding failures and welding equipment damage may result. 
         [0006]    Systems and methods for coating the internal threads of fasteners are known. Examples include commonly owned U.S. Pat. No. 5,141,771 to DiMaio et al. and U.S. Pat. No. 5,362,327 to Sessa et al. Each of these patents, however, discloses a nozzle arrangement that uses a fixed vacuum nozzle positioned above a nut opposite a spray nozzle. The fixed vacuum nozzle collects the over-sprayed powder. Such fixed vacuum nozzle designs, however, have limitations with regard to permitting the chamfers to be coating while keeping the outside surfaces of the fastener clean. 
         [0007]    In view of the above, a need exists for a method and apparatus that generally prevents the fluoropolymer powder from escaping from the spray zone and getting on the fastener exterior surfaces. 
         [0008]    A need also exists for a method and apparatus that provides the option to either coat the top chamfer, the bottom chamfer, neither chamfer or both chamfers of the fastener at the same time. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a perspective view of a group of hexagonal nuts having weld projections and where the internal threads and chamfers of the nuts may be coated using embodiments of the apparatus and method of the present invention; 
           [0010]      FIG. 2  is a top plan view of a vacuum nozzle and a spray nozzle assembly and a nut to be coated in an embodiment of the apparatus of the present invention; 
           [0011]      FIG. 3  is a cross-sectional view of the vacuum nozzle, spray nozzle assembly and nut of  FIG. 2  taken along line  3 - 3  of  FIG. 2 ; 
           [0012]      FIGS. 4A-4D  show the vacuum nozzle and the spray nozzle assembly of  FIG. 3  during stages or steps performed to coat the internal threads of the nut in accordance with an embodiment of the method of the present invention; 
           [0013]      FIGS. 5A and 5B  are enlarged views of the nut, bottom end of the vacuum nozzle and top end of the machined bushing of the spray nozzle assembly of  FIG. 3  in alternative embodiments of the apparatus of the present invention; 
           [0014]      FIG. 6  is an enlarged view of the nut, bottom end of the vacuum nozzle, top end of the machined bushing and spray tube and spray diverter of  FIG. 4D ; 
           [0015]      FIG. 7  is a block diagram showing an embodiment of a system incorporating an embodiment of the apparatus of the present invention; 
           [0016]      FIG. 8  is a front perspective view of the spray station of  FIG. 7  and a feeder bowl and supply ramp support bracket; 
           [0017]      FIG. 9  is a rear perspective view of the spray station and feeder bowl and supply ramp support bracket of  FIG. 8 ; 
           [0018]      FIG. 10  is an enlarged top plan view of the spray block of the spray station of  FIGS. 8 and 9  including a block diagram illustrating an embodiment of the control system of the spray station. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0019]    The spray nozzle assembly and vacuum nozzle portion of an embodiment of the apparatus of the present invention is indicated in general at  30  in  FIGS. 2 and 3 . A nut  32  having an internally threaded bore  34  is shown positioned in alignment with a vacuum nozzle  36  and a spray nozzle assembly, indicated in general at  38 . An embodiment of the system for placing the nut in such a position will be described below. While the invention is described below in terms of a nut, it is to be understood that other types of internally threaded fasteners having bores open at each end could be processed by the present invention. 
         [0020]    As illustrated in  FIG. 3 , the spray nozzle assembly  38  includes a powder pump body  42  that is attached to the proximal end of the spray tube and houses a compressed air jet  44  which receives pressurized air through an air supply line or tubing (not shown) that is connected to air inlet connection  46 . A powder inlet connection  48  is connected to a powder feeder via a powder supply line or tubing (not shown). As a result, a thermoplastic powder, such as a fluoropolymer powder, mixes with the air stream from compressed air jet  44  at junction  52  and the resulting powder stream is provided to the spray passage  53  of a spray tube  54 . While the embodiments are described below as using a fluoropolymer powder, it is to be understood that alternative embodiments could use other thermoplastic powders. 
         [0021]    A machined bushing  56  features a central bore and is fitted over the top or distal end portion of the spray tube  54  and a compression spring  58  is positioned between the powder pump body  42  and the machined bushing  56  and urges the machined bushing into the position shown in  FIG. 3 . The central bore  57  of the machined bushing  56  is sized so that the spray tube  54  is free to move through the machined bushing in a telescopic fashion. A stop collar  60  is positioned on the spray tube  54  in a fixed fashion and the bore  57  of the machined bushing features an enlarged diameter upper portion through which the stop collar may travel. The bore of the machined bushing also features a lower portion having a reduced diameter so that an annular shoulder is formed at the intersection with the top portion of the bore. The annular shoulder of the machined bushing bore  57  engages the underside of stop collar  60  of the spray tube  54  so that upward travel of the machined bushing  56  with respect to the spray tube  54  is limited to the position shown in  FIG. 3 . The distal end portion of the spray tube is sized to be inserted into the bore of the nut, as described below. 
         [0022]    The spray opening or outlet of the spray tube (the open top of the spray tube in the illustrated embodiment) is provided with a spray deflector or diverter  62  so that the powder stream is circumferentially diverted in a generally radial direction. The deflector may take the form of a disk positioned on the top end of a stem, where the bottom end of the stem is positioned within the center of the top end opening of the spray tube  54 . The stem holds the disk in spaced relation with respect to the top end of the spray tube so that the powder stream exiting the spray tube is deflected in a generally radial direction by the disk. 
         [0023]    Operation of the spray nozzle assembly  38  and vacuum nozzle  36  of  FIG. 3  will now be described with respect to  FIGS. 4A-4D .  FIG. 4A  (and  FIG. 3 ) shows the spray nozzle assembly  38 , vacuum nozzle  36  and the nut  32  in alignment so that the nut is in position and ready to have its internal threads (of bore  34  in  FIG. 3 ) and chamfers coated with fluoropolymer powder. As illustrated in  FIGS. 3 and 4A , the bottom end of the vacuum nozzle  36  is positioned above, and in spaced relationship with, the nut, and the top end of the machined bushing  56  of the spray nozzle assembly  38  is positioned below, and in spaced relationship with, the nut so that both have not yet contacted the nut  32  itself. 
         [0024]    During the next step, as illustrated in  FIG. 4B , the vacuum nozzle  36  is lowered onto the top of the nut  32 , as indicated by arrow  64 . As a result, the interior passage  66  and passage opening  67  of the vacuum nozzle  36  is aligned with the bore  34  of the nut. With reference to  FIG. 5A , the bottom end of the vacuum nozzle  36  may be machined to either allow the top chamfer  22   a  of the nut  32  to be coated ( FIG. 5A ) or to keep powder off of the top chamfer ( FIG. 5B ). More specifically, in the embodiment illustrated in  FIG. 5B , the end of the vacuum nozzle  36  has been machined with an angle that matches the angle of top chamfer  22   a . In the positions illustrated in  FIGS. 4B ,  5 A and  5 B, the vacuum nozzle  36  is pressing down on the nut  32  and generally creating a seal or a near-seal. This prevents the powder from escaping and getting on the outside surfaces of the nut during the spray cycle described below with respect to  FIGS. 4D and 6 . 
         [0025]    After the vacuum nozzle  36  is in the position illustrated in  FIG. 4B , as illustrated in  FIG. 4C , the spray nozzle assembly  38  moves upward, as indicated by arrow  68 , and the top end of the machined bushing  56  contacts the underside of the nut  32  (also shown in  FIGS. 5A and 5B ). The machining of the machined bushing  56  may be such that the bottom chamfer  22   b  of the nut is exposed for coating (as shown in  FIGS. 5A and 5B ) or covered to prevent the bottom chamfer from being coated (in the manner illustrated for spray nozzle  36  in  FIG. 5B ). 
         [0026]    As illustrated in  FIG. 5B  by dashed line  71 , the longitudinal center lines of the fastener bore, vacuum nozzle interior passage and bushing central bore are preferably aligned when the fastener is clamped between the vacuum nozzle and the bushing. 
         [0027]    The powder spray or coating cycle is illustrated in  FIGS. 4D and 6 . During the powder spray cycle, the spray tube  54  and powder pump body  42  are moved further upwards so that the top end portion of the spray tube and the spray diverter  62  enter the bore  34  of the nut. As the spray tube and powder pump body move upward, the spring  58  is compressed so that the top end of the machined bushing  56  remains seated or in contact with the bottom side of the nut. 
         [0028]    When the spray assembly is in position ready to coat the internal threads of the nut, the compressed air jet attached to the air inlet connection  46  of the powder pump body  42  turns on. At the same time, an aspirated powder stream is delivered from the powder feed system thru the powder inlet connection  48  and the vacuum source connected to the vacuum nozzle  36  remains on, having been turned on previously. Indeed the vacuum source connected to the vacuum nozzle  36  may be run continuously during use of the device or system, or may be sequenced to turn on only during this stage or step of the cycle. The spray nozzle is in continuous motion, moved upward to the top of the nut, and reversing downward while spraying powder at the same time, as illustrated by arrows  72  in  FIG. 4D . As a result, the top end of the spray tube and the spray diverter are moved up and down within the bore throughout the thickness of the nut (indicated at  73  in  FIG. 6 ) while the powder stream circumferentially exits the spray tube so that the powder stream is sprayed onto the threads of the bore. As explained in greater detail below, the nut  32  has been heated prior to the coating cycle so that the powder forms a coating when it contacts the internal treads and exposed chamber(s) (if any). For example, the powder spray stream  74   a  corresponds to the spray tube and spray diverter being in the positions indicated at  54   a  and  62   a  of  FIG. 6 , and the powder spray stream  74   b  corresponds to the spray tube and spray diverter being in the positions indicated at  54   b  and  62   b  of  FIG. 6 . 
         [0029]    As indicated at  76  in  FIG. 6 , as the spray cycle occurs, excess powder is drawn from the process via the vacuum nozzle  36 . 
         [0030]    When the spray nozzle is at the bottom of the nut, and the coating cycle is complete, the powder stream and the air jet are turned off and the spray tube assembly is returned to a location below the nut (illustrated in  FIGS. 4A and 4B ), not in contact with it. In addition, the vacuum nozzle is raised into the position illustrated in  FIGS. 3 and 4A , allowing the nut to be removed from the coating position. The vacuum source in communication with the vacuum nozzle either continues running or is turned off (if sequenced as explained above). 
         [0031]    Because the powder spray is not initiated until after the vacuum nozzle and machined bushing contact the nut, the top surface and the bottom surface of the nut have been “clamped” before the powder spray cycle occurs. This allows for the control of either coating the top chamfer, bottom chamfer, neither chamfer or both chamfers at the same time depending on the machining of the bottom end of the vacuum nozzle  36  and the top end of the machined bushing  56 . 
         [0032]    The vacuum nozzle  36  and spray nozzle assembly  38  of  FIG. 3  and described above are mounted within a spray station, indicated at  80  in the block diagram of  FIG. 7 . Also indicated in  FIG. 7  is a vacuum source  82  that is connected to the vacuum nozzle  36  to collect excess powder from the coating cycle, as described above. The vacuum source may be, as examples only, a central vacuum or suction system of a building or a dedicated vacuum pump for the spray station. A source of pressurized air  84  is connected to the air inlet connection  46  ( FIG. 3 ) of the powder pump body  42 , while a powder feeder  86  is connected to the powder inlet connection  48  ( FIG. 3 ) of the powder pump body  42 . As will be described in greater detail below, the spray station  80  receives and positions nuts or other fasteners and moves the vacuum nozzle and spray assembly during the coating and clamping cycles described above with respect to  FIGS. 4A-4D . 
         [0033]    As illustrated in  FIG. 7 , a vibratory feeder bowl  88  holds a supply of the nuts (or other fasteners) to be coated. The nuts leave the feeder bowl and travel down a supply ramp  90  in a single file or row to the spraying station  80 . As the nuts travel down the ramp  90 , they are heated by coil heater  91  and electrical source  93 . After the internal threads (and possibly chamfer or chamfers) of a nut are coated, the nut exits the spray station  80  via exit ramp  92 . As an example only, ramps  90  and  92  may form an angle of approximately thirty degrees with respect to horizontal. 
         [0034]    Front and back perspective views of the spray station, indicated in general at  80 , are provided in  FIGS. 8 and 9 . In addition, the bracket that supports the vibratory feeder bowl ( 88  of  FIG. 7 ) and the upper end of the supply ramp ( 90  of  FIG. 7 ) is illustrated at  94  in  FIGS. 8 and 9 , while the arm that secures the bracket  94  to the spray station is illustrated at  96 . The vibratory bowl and the supply ramp have been omitted from  FIGS. 8 and 9  for clarity. 
         [0035]    As illustrated in  FIGS. 8 and 9 , the spray station  80  features a spray block  102  that features a machined fastener channel  104 . The spray block is mounted to the framework of the spray station so that the bottom surface of the fastener channel  104  forms an angle of around thirty degrees with horizontal. Of course, alternative angles may be used. A top view of the spray block  102  and the machined fastener channel  104  are provided in  FIG. 10 . As illustrated in  FIG. 10 , the fastener channel is sized so that the heated nuts, indicated in phantom at  32   a - 32   d  may be held and travel through in a single file or row. As a result, and as explained in greater detail below, the fastener channel serves as a fastener holder for the coating process. Of course alternative holding arrangements and devices may be used as the fastener holder in alternative embodiments. 
         [0036]    Returning to  FIGS. 8 and 9 , the spray station features a support plate  106  upon which the components of the spray station are mounted. The support plate  106  features a window  108  which receives the lower end of the supply ramp ( 90  of  FIG. 7 ) and through which the nuts travel to the spray block  102 . 
         [0037]    A pneumatic upper slider mechanism, indicated in general at  110  in  FIGS. 8 and 9 , features an upper slider plate  112  that moves up and down, as indicated by arrows  114 . As an example only, the slider mechanism may be an MXS series slider available from SMC Corporation of America of Noblesville, Ind. 
         [0038]    A vacuum nozzle holder  116  is mounted to the slider plate  112  and features a passage sized to receive the vacuum nozzle  36  in a sliding fashion. The open top end of the vacuum nozzle is connected to the vacuum source ( 82  of  FIG. 7 ) via a vacuum line or tubing. The vacuum nozzle  36  is provided with upper and lower collars  122   a  and  122   b , respectively. A compression coil spring  124  is positioned between the bottom of the vacuum nozzle holder  116  and the lower collar  122   b  so that the vacuum nozzle is urged into the position shown in  FIGS. 8 and 9 . The upper collar  122   a  limits downward travel of the spray nozzle  36  with respect to the vacuum nozzle holder  116 . 
         [0039]    An L-shaped bracket  126  ( FIG. 8 ) is also secured to the slider plate  112  and supports a fastener stop or gate  128  positioned at the exit of the machined fastener channel  104  of the spray block  102 . Due to the attachment with the slider plate  112 , the fastener gate  128  may be moved between the release position illustrated in  FIGS. 8 and 9 , and the raised or stop position illustrated in  FIG. 10  and indicated in phantom at  128   a  in  FIG. 8 . As a result, the fastener gate  128  and fastener channel  104  of the spray block form an escapement mechanism for handling the fasteners during the coating process. 
         [0040]    A pneumatic lower slider mechanism is indicated in general at  130  in  FIG. 8  and features a lower slider plate  132  that moves up and down as indicated by arrows  134 . A spray nozzle assembly holder  136  is secured to the slider plate  132 . As illustrated in  FIGS. 8 and 9 , the powder pump body  42  is mounted to the spray nozzle assembly holder  136 . 
         [0041]    In operation, when the vacuum nozzle  36  and the spray nozzle assembly  38  are in the positions illustrated in  FIG. 4A , the fastener gate  128  is in the position raised position illustrated in  FIG. 10  and in phantom (at  128   a ) in  FIG. 8 . The nuts travel from the vibratory bowl ( 88  of  FIG. 7 ) down the supply ramp  90 , where they are heated by coil  91 , and into the machined fastener channel  104  of the spray block  102  into the positions illustrated at  32   a - 32   b  in  FIG. 10 . As illustrated in  FIG. 10 , nut  32   a  abuts the raised fastener gate  128  so that the gate serves as a stop. 
         [0042]    The nut  32   b  of  FIG. 10  is in the coating position illustrated in  FIGS. 4A-4D . In other words, the nut  32  of  FIGS. 4A-4D  is in the position of nut  32   b  of  FIG. 10 . 
         [0043]    The vacuum nozzle  36  is moved into the position illustrated in  FIG. 4B  by lowering the upper slide plate  112  (of  FIGS. 8 and 9 ), and thus the vacuum nozzle holder  116 . The coil compression spring  124  causes the bottom end of the vacuum nozzle  126  to gently push down and clamp the top side of the nut with the passage of the vacuum nozzle in alignment with the bore of the nut. While the upper slider plate  112  and vacuum nozzle  116  have been lowered, at this point, the fastener gate  128  is still in the raised position illustrated in  FIG. 10  and in phantom at  128   a  in  FIG. 8 . 
         [0044]    Next, the bottom slider plate  132  is raised so that the spray nozzle assembly  38  is moved into the position illustrated in  FIG. 4C . As illustrated in  FIGS. 8-10 , the bottom of the fastener channel  104  of the spray block is provided with an opening  140  through which the machined bushing  56  ( FIGS. 4C and 4D ) passes to contact the bottom side of the nut. The bottom slider plate  132  continues to rise and then drops so that the spray tube  54  ( FIGS. 3 and 6 ) passes through the opening  140  of the fastener channel  104  and throughout the thickness of the nut ( FIGS. 4D and 6 ) during the coating cycle as described above. 
         [0045]    Once the coating cycle is completed, the upper slide plate  112  travels further downward and the fastener gate  128  is lowered into the position illustrated in  FIGS. 8 and 9 . As a result, the nut  32   a  of  FIG. 10  travels off of the spray block  102  and down the exit ramp  92  ( FIG. 7 ) to be collected. The nut  32   b  remains clamped in place by the vacuum nozzle and the machined bushing. 
         [0046]    Next, the upper and lower slider plates  112  and  132  are raised and lowered, respectively, so that the vacuum nozzle  36  and spray nozzle assembly  38  return to the positions illustrated in  FIG. 4A , and the fastener gate  128  returns to the raised position illustrated in  FIG. 10  and in phantom at  128   a  in  FIG. 8 . As a result, the nut  32   b  moves into the position formerly occupied by nut  32   a  and the nut  32   c  moves into the position formerly occupied by nut  32   b , etc. The above process is repeated. 
         [0047]    As illustrated in  FIGS. 8-10 , the spray block  102  may be provided with apertures  142  and  144  through which a fiber optic beam, indicated in phantom at  150  in  FIG. 10 , from sensors  152  and  154  may pass to detect when a nut is present in the position occupied by nut  32   a . The sensors communicate with the system controller  156  ( FIG. 10 ) that controls the upper and lower slider mechanisms  110  and  130 . As a result, the sequencing of the movement of the vacuum nozzle, fastener gate and spray nozzle assembly may be coordinated with the movement of the nuts through the fastener channel  104  of the spray block. For example, when the beam of light  150  passing across the fastener channel  104  is unbroken, the controller  156  knows that the nut in position  32   a  ( FIG. 10 ) has traveled off of the spray block and the vacuum nozzle and fastener gate are ready to be raised and the spray nozzle assembly is ready to be lowered. When the beam of light  150  is broken, the system knows that a nut has moved into the position of nut  32   a  (of  FIG. 10 ), and thus that a nut has moved into the position of nut  32   b  so that the vacuum nozzle may be lowered and the spray nozzle assembly may be raised for the coating cycle. Similar sensors may be used to activate the supply of powder and pressurized air flow to the spray nozzle assembly and to activate the vacuum source for the vacuum nozzle based on the positions of the machined bushing  56  of the spray nozzle assembly and the vacuum nozzle. 
         [0048]    Additional details regarding control of the system, and alternative embodiments, are provided in commonly owned U.S. Pat. No. 5,141,771 to DiMaio et al., the contents of which are hereby incorporated by reference. 
         [0049]    While the preferred embodiments of the invention have been shown and described, it will be apparent to those skilled in the art that changes and modifications may be made therein without departing from the spirit of the invention, the scope of which is defined by the following claims.