Patent Publication Number: US-2005115587-A1

Title: Cleaning device of a powder coating booth

Description:
Detailed Description of the Invention 
     Cross Reference to Related Applications 
      This application is a National Stage of International Application No. PCT/EP02/0834, filed July 25, 2002, which claims the benefit of German Patent Application No. 101 36 453.9, filed July 26, 2001.
Field of the Invention 
      The invention relates to a cleaning device of a powder coating booth as well as to a method for cleaning the powder coating booth . 
Background of the Invention 
      A cleaning device of this type is described in EP 727 258.  The cleaning device has two separate pipes for blowing off the side walls and the top wall of in each case one longitudinal half of the booth.  The two pipes are jointly moved longitudinally through the booth, i.e. in or counter to the workpiece conveying direction.  The bottom is not subject to the action of the blow-off nozzles and is instead freed from powder residues by means of a discharge belt. 
      DE 3516826 discloses a cleaning device for a powder coating booth with a tubular frame system open at the top.  The tubular frame is provided with nozzles, which by means of compressed air blow the coating powder from the surfaces to be cleaned.  The tubular frame is moved along the booth, so that during said movement the powder is blown from the inner surfaces. 
      A similar cleaning device is known from EP 200 681.  This cleaning device, which has a tubular frame open at the top, is also moved longitudinally through the booth.  In the bottom area said booth has a V-shaped construction, the tip of the V issuing into a suction duct for  suctioning off the blown off powder.  In addition to the nozzles, sponges can be fitted to the cleaning device and wet clean the surfaces after blowing off. 
      In all the described cleaning device constructions, the cleaning system is moved longitudinally through the booth.  In order to obtain an optimum blow off action the cleaning system must not be moved too rapidly through the booth.  In the case of longer booths, there is consequently a long cleaning period. 
      The problem of the invention is to provide a method and a device for cleaning a coating booth, which permit rapid cleaning with a good cleaning action, particularly for long booths.
Brief Summary of the Invention 
      This problem is solved by a cleaning device and a method according to the present invention. 
      Unlike in the above-described prior art, a cleaning device according to the invention is not moved longitudinally through the booth, but instead transversely to the workpiece conveying direction.  The cleaning device preferably has two separate pipes, whereof each is associated with one of the two longitudinal halves of the booth.  The pipes are equipped with nozzles.  Each pipe is moved by a drive transversely to the conveying direction initially roughly horizontally and then from top to bottom through the booth.  During this movement the nozzles are supplied with a cleaning fluid, particularly compressed air, so that powder adhering to the inner surfaces can be blown off.  Preferably on the bottom is provided a suction device, which constantly suctions the blown off powder and e.g. supplies it to a recovery or filtering device.  When the two pipes have reached their lower end position, the supply of cleaning fluid is preferably switched off and the pipes are again conveyed into their upper end position.  This upper end position is advantageously located outside the booth, so that the cleaning device is not dirtied during the coating operation. 
      In the case of a cleaning device according to the invention, the cleaning time is essentially dependent on the height and not the length of the booth.  As normally booths are much longer than they are high, there is a much shorter cleaning time than with the known cleaning devices, which are moved longitudinally through the booth.  The cleaning time can be additionally reduced in that pipes are returned at a higher speed than during their downward movement to their upper end position. 
      A further advantage is that the powder is blown in the direction of the suction line and can consequently be more efficiently suctioned off. 
      The invention is described in greater detail hereinafter relative to a preferred embodiment and the attached diagrammatic drawings.
Brief Description of the Drawings 
       Figure 1  is a cross-section through a powder coating booth with a cleaning device according to the invention during the cleaning of the side walls. 
       Figure 2  is a longitudinal section through the booth of  Figure 1  with a side view of a pipe. 
       Figure 3  is a partial longitudinal section corresponding to  Figure 2  of the cleaning pipe with guide, but on a larger scale. 
       Figure 4  is a  partial longitudinal section like  Figure 3  of a modified construction of the guide.
Detailed Description 
      The cross-section according to  fig. 1  reveals a powder coating booth 1 (hereinafter called “booth” for short), where the booth has two longitudinal halves 1a, 1b divided by a median longitudinal plane E, side walls 2, a bottom 3 and a top wall 4, 4 divided by a longitudinal slot 5.  Through the longitudinal slot 5 passes a not shown conveying means for not shown workpieces, which are moved in the longitudinal direction F ( fig. 2 ) through the booth. 
      Within the booth 1 and close to the bottom 3, plates 6 are fitted to the side walls 2 inclined with respect to the bottom 3 and pointing towards one another.  In the two lower corners of the booth, said plates form suction ducts 7, which communicate with a suction line 8 leading out of the booth 1.  The plates 6 are at a distance a from the bottom 3, so that they permit a suction of excess powder deposited on the bottom over the entire length of the booth 1.  At its longitudinal ends, the booth 1 is terminated by front walls 9, which have openings 10 for the passage of workpieces and the conveying means.  The openings 10 are large enough in order to convey the workpieces in unhindered manner into and out of the booth 1.  In addition, it is possible to provide sliding doors, which are not shown, but frequently used in such booths. 
      On the booth inside of each front wall 9 guide grooves 11, 12 or 11’, 12’  are homologously positioned with respect to the median longitudinal plane E of the booth.  The left-hand guide grooves 11, 11’ and the right-hand guide grooves 12, 12&#39;, whereof only the guide grooves 11, 12 are visible in  fig. 1 , precisely face one another and in each case form a left-hand pair of guide grooves 11, 11’ and a right-hand pair of guide grooves 12, 12’. 
      In its upper area, each guide groove has a section with two approximately horizontally directed legs 14, 15, the leg 14 being positioned within the booth and the leg 15 outside the booth on the front wall 9.  The two legs 14, 15 are linked by means of a crosspiece section 16 of the guide groove passing through the slot 5. 
      With each of the two legs 14, 15 is associated a booth-inner support 17 and a booth-outer support 18 for guide rollers 19. 
      Each pair of guide grooves 11, 11’ and 12, 12’ guides a pipe 20, which extend parallel to one another and horizontally over the length of the booth 1 and specifically by means of in each case one suspension 21, fixed to each pipe end, with associated guide roller 19 and roller chain 22 which, according to  fig. 3 , is guided in the particular guide groove 11, 11’, 12, 12.  In each case one chain wheel 23 deflecting the roller chain 22 by 90° is used for driving the said roller chain.  The chain wheels 23 of each roller chain pair associated with a longitudinal half 1a or 1b are driven by aligned shafts 24, which are rotated in the same direction and synchronously by a common drive motor 25 with a downstream gear 26 for each longitudinal half.  Thus, for each pipe 20 there is an independent drive with drive motor 25 and gear 26. 
      Thus, each pipe, through the rotation of the chain wheel pair 23, 23 in one direction y can be drawn upwards and by an opposite rotation of the chain wheel pair in the other direction x can be slid downwards, the sliding movement being assisted by the weight of the pipes 20.  The two pipes can be moved in the same direction and synchronously by synchronizing the two drives with the chains 22, chain wheels 23, shafts 24 and drive motors 25 with gears 26. 
      The two pipes 20 associated with each booth wall are mutually heightwise offset according to  fig. 1 .  The reason for this is that the central longitudinal slot 5 in top wall 4, 4 of booth 1 must be kept as narrow as possible, which can only take place if the two pipes 20 can successively and not simultaneously pass through said slot 5.  A narrower slot 5 has a favourable influence on the flow conditions in the booth 1. 
      Each end of a pipe 20 is engaged by means of a suspension 21 and supported by means of a guide roller 19 on supports 17, 18 alongside the horizontal, inner and outer sections (“cross-pieces”) 14, 15 of the guide in order to prevent tilting of the roller chain 22 in said sections.  The outermost end of each roller chain 22 is bound by means of a suspension 21 on the associated pipe end and is slidingly guided in the guide groove 11 or 11. 
      Each pipe 20 is equipped with a series of nozzles 28 arranged with a clearly defined, uniform spacing b in the longitudinal direction of the pipe.  The spacing b of the nozzles in the longitudinal direction can be between 50 and 150 mm.  Trials have revealed that a spacing of 100  mm is particularly advantageous. 
      The distance c between the nozzles and the inner and top walls 2, 4 respectively is also defined by the guide grooves 11, 11’, 12, 12’.  Said distance c can be in a range between 30 and 100 mm and is preferably approximately 50 mm. 
      Finally, it is appropriate to downwardly adjust the nozzles 28 with respect to the normal booth wall direction by an angle which is between 10° and 30° and is preferably approximately 18°.  Thus, the cleaning fluid is always blown downwards in the direction of the suction ducts 7, 7’. 
      Besides the row of nozzles 28, the ends of the pipes also have nozzles 28’ directed onto the guide grooves in order to also ensure the cleaning of the latter. 
      In operation, the roller chains are moved by the drive 25, 26, via the chain wheels 23 in the direction of the continuous arrows x, the pipes 20 in the booth being entrained downwards along the guide grooves (cf. fig. 1).  During this movement assisted by the weight of the pipes 20, compressed air is fed via connections 29 ( fig. 2 ) into the pipes and blown through the nozzles 28 against the booth walls 2, 4.  The pipes reach their lower end position at the end of guide sections  13 of the guide grooves 11,12 bent inwards corresponding to the inclined plates 6. 
      Powder which has been deposited on the bottom is sucked out of the booth 1 by means of the suction duct 7 and suction line 8. 
      When blowing off is at an end, the drives 25, 26 are switched into the opposite direction, so that the chain wheels 23 rotate in the broken line arrow direction y and the roller chains 22 draw the pipes 20 within the booth in the broken line arrow direction y upwards into their initial position outside the booth into the vicinity of the upper leg 15 of the guide grooves 11, 11’, 12, 12’. 
      Whereas in the construction according to  fig. 3  the guides with the guide grooves 11 and 11 for the pipe 20 in longitudinal half 1a and guide grooves 12, 12’ for pipe 20 in longitudinal half 1b are located within the booth, with the exception of the sections of crosspieces 16 and leg 15 located above the top wall 4, in the subsequently described construction according to  fig. 4  the guides are entirely located outside the booth.  For this purpose the end walls are constructed in sandwich-like manner with an inner wall 9a and an outer wall 9b linked by crosspieces 9c.  A spigot 20a forming the pipe end and which is coaxial to the pipe 20 traverses a slot 30 in the inner wall 9a and is connected to the roller chain 22, which is in this case guided in a guide groove 11” in a guide strip 32.  On both sides said guide strip 32 is flanked by slots 33, 34 through which, in operation, ambient air is sucked in the arrow direction into the interior of the booth. 
      The construction according to  fig. 4  has the important advantage that the guides are not exposed to dirtying by the powder and also maintenance thereto is easily possible from the outside. 
      It is clear that the blowing off time is exclusively dependent on the length of the path covered by the pipes 20 within the booth, i.e. starting with the entry into the booth, initially horizontally (for blowing off the inner surfaces of the top wall 4) and then vertically downwards over the booth height.  This path length is much smaller than in an arrangement where pipes positioned vertically in the booth are moved in the longitudinal direction of said booth. 
      The features disclosed in the above description, drawings and claims can be individually and in random combination important for the implementation of the present invention.