Patent Publication Number: US-2020276604-A1

Title: Colour change system for powder coating

Description:
FIELD OF THE INVENTION 
     The present invention relates to a colour change system for powder coating. More particularly the invention concerns a system for automatic change of a powder coating colour suitable for use with a hand operated or a robot-operated coating applicator. 
     BACKGROUND 
     Powder coating is used extensively for coating components, often metal components, in a wide range of industries such as vehicle manufacturing. A coloured powder is supplied through a suitable conduit from a powder reservoir to an applicator, such as a spray gun. Powder coating is increasingly being carried out in automated production facilities, for example using robotically controlled applicators. When different colours of coating are required, it has traditionally been necessary to use multiple different applicators, one for each different colour, because to change colour using the same applicator and conduit requires a time consuming cleaning operation. Having multiple different applicators and conduits for a robotically operated process adds significantly to the complexity and cost of the coating installation. 
     U.S. Pat. No. 5,928,423 discloses a color-changing powder system for use in powder coating. The powder supply comprises a powder tank and a powder supply apparatus detachably connected to the power tank. 
     The present invention has been conceived in light of the above. 
     SUMMARY 
     In a first aspect the invention provides a colour change system for a powder coating facility, comprising: a plurality of powder containers, each container holding one of a plurality of different coloured coating powders; a conduit for conveying powder from one of the powder containers to a coating applicator; a suction unit connected to the conduit and having an end-piece with an inlet opening into which coating powder is drawn; a cleaning unit; a translation mechanism for moving the end-piece of the conduit; and a controller. Each of the plurality of powder containers has one or more openings in an upper surface into which the end piece of the suction unit can be inserted. The cleaning unit has an opening for receiving the end piece of the suction unit. The controller is configured to effect a change of powder colour by controlling the translation mechanism to extract the end-piece of the conduit from a first powder container, to move the end piece of the conduit to the cleaning unit, and after cleaning to move the end piece to a second, different powder container and insert the end piece into the second container. 
     It is an advantage that the translation mechanism allows for an automated movement and cleaning of the powder spray delivery equipment between changes of colour, which provides a significant reduction in plant operating downtime. 
     The translational mechanism may comprise mechanisms providing a vertical, or y-direction translation of the end piece, a first horizontal, or x-direction translation of the end-piece. The y-direction and x-direction movements may be independently controllable by the controller. The translational mechanism may comprise a third, or second horizontal, or z-direction, of movement of the end-piece, wherein the third direction movement moves the end-piece out of alignment with the openings in the upper surfaces of the powder containers. Each of the y-direction, x-direction and z-direction movements may be independently controllable by the controller. The translation mechanism may comprise at least one pneumatically operated cylinder. 
     The cleaning mechanism may comprise a vertically oriented chamber for receiving the end piece of the suction unit through a top opening, a first air blowing arrangement for cleaning an outer surface of the conduit and a second air blowing arrangement for cleaning the insides of the suction unit and conduit. The first air blowing arrangement may comprise one or more nozzles through which air is blown into the chamber and over the outer surfaces of the suction unit, and an air outlet for removing air and powder removed off the outer surface of the conduit. The one or more nozzles may be located adjacent the top opening and the air outlet is located adjacent a bottom of the chamber. The second air blowing arrangement may comprise an air inlet for blowing air into the inlet opening of the suction unit. The second air blowing arrangement may be sufficiently strong to blow air through to the paint applicators (guns). This allows the paint passages of the paint applicators to be cleaned. The second air blowing arrangement may comprise a spring valve that is configured to be activated by contact from the end piece of the suction unit to open and permit air to be blown into the inlet of the suction unit. A means for providing suction may be connected to the air outlet. 
     The suction unit may comprise an inducer in the end piece adjacent to the inlet opening of the suction unit. The inducer may comprise an air nozzle and a venturi tube section. The inducer may be located at one end of a tube that connects to the conduit and the suction unit further comprises a passage for compressed air to be provided to the inducer nozzle. The inlet of the suction unit may comprise a plurality of inlet channels leading from an exterior of the end piece to the inducer. The suction unit may further comprise an air duct for providing air to fluidise powder in the vicinity of the inlet opening. 
     In a second aspect, the invention provides a method of changing colour in a powder coating facility. The method comprises providing a colour changing apparatus comprising: a plurality of powder containers, each container holding one of a plurality of different coloured coating powders; a conduit for conveying powder from one of the powder containers to a coating applicator; a suction unit connected to the conduit and having an end-piece with an inlet opening into which coating powder is drawn; a cleaning unit; and a translation mechanism for moving the end-piece of the conduit. The method further comprises: extracting the end-piece of the suction unit from a first powder container; moving the suction unit to the cleaning unit; cleaning the suction unit and the conduit; after cleaning moving the suction unit to a second, different powder container, and inserting the end piece of the suction unit into the second container. 
     In a third aspect, the invention provides a colour change system for a powder coating facility. The system comprises: a plurality of powder containers, each container holding one of a plurality of different coloured coating powders; a conduit for conveying powder from one of the powder containers to a coating applicator; a suction unit connected to the conduit and having an end-piece with an inlet opening into which coating powder is drawn; and a translation mechanism configured to move the end-piece of the conduit from one container to another container. The suction unit comprises an inducer in the end piece adjacent to the inlet opening of the suction unit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an illustration of a powder coating facility employing a colour change system in accordance with embodiments of the invention. 
         FIG. 2  shows more detail of the colour change system of the powder coating facility of  FIG. 1 . 
         FIG. 3  is a plan view of the colour change system of  FIG. 2 . 
         FIG. 4 a    depicts a cleaning unit forming part of the colour change system of  FIG. 2 . 
         FIG. 4 b    shows a sectioned view of the cleaning unit of  FIG. 4   a.    
         FIGS. 5 a  and 5 b    show elevation and cross-sectional views of a conventional powder suction unit. 
         FIG. 6  is a cross-sectional view of a an improved powder suction unit more suitable for use with embodiments of the powder colour change system of the invention. 
         FIGS. 7 a  and 7 b    show elevation and cross-sectional views of the powder suction unit of  FIG. 6  and a receiving piece of a cleaning unit. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , there is shown a powder coating facility with a coating booth  10  inside which is a robotically operated powder spray applicator  12 , for applying a coating to a component  14 , which could, for example, be a body part of a vehicle. Powder is supplied to the applicator  12  from a powder unit  16  by means of a suction unit  18  through a conduit (not shown). Powder unit  16  and suction unit  18  are adapted as a colour change system, which will be described in more detail below with reference to  FIGS. 2 to 4 . As shown in  FIG. 1 , a controller  20  controls operation of the powder coating facility. 
       FIG. 2  shows the powder unit  16  and suction unit  18  forming a colour change system embodiment. A frame  22  supports a number of powder containers  24  in the form of a line of boxes filled with powder, each container  24  containing a different colour of powder (five such containers are shown in  FIG. 2 , but it will be appreciated that any number of such containers may be employed, depending on the number of different colours to be sprayed). The frame  22  is in the form of a steel structure, with the containers  24  mounted on a plate with vibration dampers  38 . A vibrator motor  26  is used to oscillate the boxes to prevent the powder compacting. A separate air supply may be provided to the containers  24  to fluidize the powder in the container that is supplying powder to the applicator  12 . Such containers may be referred to as fluid boxes, as distinct from standard boxes, which are not provided with separate fluidization. Each of the containers  24  has one or more openings  25  for receiving an inlet end of the suction unit  18 . The suction unit  18  connects to a powder delivery conduit  40 . Examples of the suction units are described in more detail below with reference to  FIGS. 5 a , 5 b    and  6 . 
     The suction unit  18  is mounted to a translation mechanism. As shown, the suction unit  18  is attached to a vertical, or Y-Axis linear translator  30  for moving the suction unit  18  up and down in the vertical direction. The suction unit  18  is attached to the conduit  40 , which moves up and down with the suction unit  18 . The inlet end (not shown) of the suction unit  18  can be moved in and out of the containers  24  through the openings  25 . The suction unit  18  has an opening in its end into which powder can be drawn when it is lowered into a container  24 . The conduit  40  extends from the powder unit  16  to the spray applicator  12  in the coating booth  10  by way of flexible hoses (not shown). The Y-axis translator  30 , including the attached suction unit  18  and conduit  40  can be moved horizontally using a horizontal or X-axis translator  28 . The X-axis translator  28  moves the suction unit  18  horizontally along the line of the containers  24 . As shown herein, a third, or Z-axis translator  32  is attached to the Y-axis translator  30  and moves the suction unit  18  in a third direction, out of alignment with the openings  25  on the containers  24 . 
     The Y-axis translator  30  may include a pneumatically operated cylinder for effecting the linear movement in the up and down directions. Alternatively the Y-axis translator may comprise any other suitable type of controllable linear actuator. Similarly, the Z-axis translator  32  may comprise a linear actuator such as a pneumatic cylinder, although it will be appreciated that to move the end of the suction unit  18  as described could be performed with other types of actuators, such as a rotary actuator. The X-axis translator  28  could also employ a pneumatic cylinder for providing linear movement. However, it will be appreciated that the distance of movement required for the X-axis actuator could be much larger, especially if a large number of different colours and associated containers  24  are provided. In that case the X-axis translator could employ a motor driven mechanism, such as a belt or chain. 
     Also shown in  FIG. 2  is a cleaning unit  34  that provides for cleaning of the suction unit  18  and conduit  40  between colour changes. The cleaning unit may also be used to clean the paint passages of the one or more applicator guns. More details of the cleaning unit and its operation are described below with reference to  FIGS. 4 a    and  4   b.    
       FIG. 3  is a plan view showing the principal components of the powder unit  16 , and where equivalent components have the same reference numerals as shown in  FIG. 2 . In  FIG. 3  each of the containers  24  has been assigned a unique reference number— 24   a  to  24   e . As shown in  FIG. 3  the suction unit  18 , Y-axis translator  30  and Z-axis translator  32  are shown in two different X-axis positions, one position is shown with solid lines and the other with broken lines. In the position with solid lines, the Y-axis translator is positioned with the suction unit directly in line with an opening  25  on the top of the container  24   d . In this position the end of the suction unit has entered the opening  25  by being vertically lowered into the container  24  by the Y-axis translator. In the broken line position the Y-axis translator is positioned in between openings  25  on containers  24   d  and  24   e . In this position the Z-axis translator has moved the end of the suction unit  18  so that it extends beyond the openings  25  in the tops of the containers  24 . 
       FIGS. 4 a  and 4 b    depict the cleaning unit  34 , which includes a vertical duct  50  with an open top  52 . The open top  52  may be provided with a gasket. The gasket is configured to contain overspray of powder that may otherwise occur due to the application of air. A first compressed air inlet  54  is provided close to the top  52 . An extraction duct  56  is attached along a lower part of one side of the duct  50  for connection to a suction device and filter (not shown). A conduit receiving piece  58  is attached to the bottom end of the duct  50  and is shaped to receive the end of the conduit  40  described above with reference to  FIGS. 2 and 3 . The conduit receiving piece  58  is connected to second compressed air inlet  60 . 
       FIGS. 5 a  and 5 b    show a conventional suction unit  70 , which is used in a generally vertical orientation as shown, and lowered into a container of coating powder. The suction unit  70  includes a central vertical tube  71 , which is surrounded by an annular air passage  72 . Air from a compressed air source is supplied to three connections  73   a ,  73   b  and  73   c . The air supplied to connection  73   a  is fed to a nozzle  74  of an inducer  75 . The air supplied to the nozzle  74  enters the throat of a venturi section  76  and this creates a suction in the central vertical tube  71  to draw powder up the tube. The venturi section  76  has an outlet end  77  which feeds into a conduit (not shown) along which the powder is to be conveyed. Air supplied to the connection  73   b  is also fed into the conduit as an additional flow for conveying the powder. Air supplied to the third connection  73   c  passes down the annular passage  72  to an end plug  78  where the air exits. This air fluidizes the surrounding powder in the container into which the suction unit  70  has been lowered. The end plug  78  surrounds inlets  79   a ,  79   b ,  79   c  distributed around the bottom end of the suction unit  70  and through which the powder is drawn up into the central tube  71 . 
     The conventional suction unit  70  could be used in conjunction with the colour change system described above with reference to  FIGS. 1 to 5 . However, there are certain drawbacks with this design of suction unit. Firstly, the inducer  75  has to provide enough suction to lift powder up the entire height of the unit, which requires a large amount of energy in the compressed air leading to poor efficiency. Also, the suction unit  70  employs additional fluidisation air to assist the drawing in of powder around the inlets  79   a/b/c  because the amount of suction at the inlets  79   a/b/c  is limited by the capacity of the inducer. 
       FIG. 6  shows a cross-sectional elevation of an improved suction unit  80 , which is particularly suitable for use with the colour change system described above with reference to  FIGS. 1 to 5 . The suction unit  80  includes a central vertical tube  81 , which is surrounded by a narrow air passage  82  and a further air duct  83 . Air from a compressed air source is supplied to two connections  84   a  and  84   b . The air supplied to connection  84   a  is fed via the air duct  83  to a nozzle  85  of an inducer  86 , which is located close to the bottom end of the suction unit  80 . The air supplied to the nozzle  85  enters the throat of a venturi section  87 . The inducer  86  creates a suction, for drawing powder into the venturi section and blowing it on up the central tube  81 . The powder is drawn in through openings  88  formed around a bottom section  89  of the suction unit  80 . Powder drawn into the suction unit  80  is blown up the central tube  81  to an outlet end  90  which feeds into a conduit (not shown) along which the powder is to be conveyed. Air supplied to the connection  84   b  is also fed into the conduit as an additional flow for conveying the powder. Also shown in  FIG. 6  is a screw  84   c  that is provided to hold the central vertical tube  81  in place. 
       FIGS. 7 a  and 7 b    show elevation and cross-sectional views of the powder suction unit  80  of  FIG. 6  and a receiving piece  100  of a cleaning unit, such as the receiving piece  58  of the cleaning unit  34  of  FIGS. 4 a  and 4 b   . The receiving piece  100  includes a connection  101  for a cleaning fluid such as compressed air and an internal valve member  102 . The valve member  102  is biased by a spring  103  so as to urge the valve member  102  into a closed position by virtue of a valve seat  104 . The receiving piece  100  also includes a top opening  105  into a bore  106  for receiving the bottom end of the suction unit  80 . The valve member  102  has an end  107  that extends upwardly into the bore  106  when the valve member  102  is in the closed position. When the suction unit  80  is inserted into the bore  106  through the opening  105  (e.g. by being lowered into the cleaning unit by the translation mechanism of the colour change system as described above), the bottom end of the suction unit  80  contacts the end  107  of the valve member  102  and pushes it down against the action of the spring  103  to open the valve and allow the cleaning fluid to be blown through the valve and into the suction unit  80  through the openings  88 . In this way the inner surfaces of the suction unit  80  and ducting leading on to a powder spray applicator can be cleaned. 
     In use, when the powder coating applicator  12  (see  FIG. 1 ) is applying a colour of coating, the bottom end of the conduit  40  is lowered into the correct colour container  24 , such as container  24   d  as shown in the solid line position of the conduit  40 , Y-axis translator  30  and Z-axis translator  32  in  FIG. 3 . The containers  24  are vibrated by the vibrator  26 . In addition, embodiments may provide that air is supplied to the container  24   d  to fluidize the powder therein. The suction unit  18  (see  FIG. 2 ) draws powder into the conduit  40 , through its open end and this is conveyed along the conduit  40  to the applicator  12 . 
     When it is required to change the colour of the coating at the applicator  12 , the suction unit  18 , vibrator  26  and fluidization air supplied to the container  24   d  are switched off. The Y-axis translator  30  is activated to raise the conduit  40  out of the container  24   d . The Z-axis translator is activated to move the end of the conduit  40  out of alignment with the openings  25  in the tops of the containers  24 . The X-axis translator then moves the conduit  40 , together with Y-axis translator  30  and Z-axis translator  32 , along to the cleaning unit  34 . Note that during this movement the end of the conduit is moved across and above the container  24   e , but because the end of the conduit  40  has been moved by the Z-axis translator it is not above the openings  25  and any powder that drops off or out of the conduit  40  will not fall into the different colour container  24   e  through its opening  25 . 
     When the conduit  40  has been moved to the cleaning unit  34 , the Y-axis translator lowers the conduit into the cleaning unit  34  through the open top  52 , and down until the end of the conduit  40  is positioned in the receiving piece  58 . Suction is provided to the extraction duct  56  and compressed air provided to the first compressed air inlet  54  for cleaning the outer surfaces of the conduit  40 . This air is drawn down and out through the extraction duct  56 . Compressed air is also provided to the second compressed air inlet  60  into the conduit receiving piece  58 , which is shaped to direct the compressed air into the inside of the conduit  40 . This air is blown along the entire length of the conduit  40  and out through the applicator  12 , cleaning both the inside surfaces of the conduit  40  and the applicator  12 . 
     Once cleaning has been completed, the air supplied to the first and second compressed air inlets is switched off, the Y-axis translator raises the conduit  40  out of the cleaning unit  34 , the Z-axis translator moves the end of the conduit out of alignment with the openings  25  and the X-axis translator moves the conduit (with the Y-axis translator, and Z-axis translator) to the position of the container  24  of the next colour to be used (for example container  24   b ). During this movement the end of the conduit is moved across and above the containers  24   e ,  24   d  and  22   c , but because the end of the conduit  40  has been moved by the Z-axis translator it is not above the openings  25  and any powder that drops off or out of the conduit  40  will not fall into the different colour containers through their openings  25 . The Z-axis translator then moves the conduit  40  so that the end is directly above the opening  25  on the container  24   b  and the Y-axis translator lowers the conduit  40  into the container  24  through the opening  25 . The vibrator  26  then restarts to vibrate the containers  24  and fluidising air is provided to the container  24   b . Spray coating of the powder can then commence by activating the suction unit  18  to deliver powder to the applicator  12 . 
     The examples above describe a system and method with a single end piece to be inserted into an opening of a powder container. It will be appreciated that the system may comprise any number of suction units, eg one, two or more suction units. For instance, a multiple gun system may comprise two or more suction units. Each powder container of a selected colour may comprise a corresponding number of openings, to allow each suction unit of a multiple gun system to be refilled at the same time.