Patent Publication Number: US-8539967-B2

Title: Spray pretreatment system and method for pre-treating workpieces by spraying

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a spray pretreatment system comprising a spraying tunnel, in which is provided a treating station with treating installations for the treatment of workpieces by spraying or flooding, the treating installations being supplied with a treating liquid from a tank located below the station, and further comprising a conveyor for transporting workpieces through the spraying tunnel. 
     The invention further relates to a method for the spray pretreatment of workpieces where the workpieces are transported through a spraying tunnel and are treated with liquid from treating installations in at least one treating station and where the workpieces are fed in through an inlet opening. 
     A device and a method of the kind described above are known from DE 43 33 932 A1. 
     Systems of that kind serve for pre-treating workpieces with liquids and chemicals before the workpieces are subjected to a painting treatment or a color powder coating process, for example. A typical pretreatment consists, for example, of a cleaning operation where the workpieces are initially treated with a cleaning liquid before they are rinsed in several stations. In order to permit efficient cleaning, the cleaning liquid is supplied, preferably, at an increased temperature of between 50 and 70° C., for example. As a rule, the workpieces are transported through the spray pretreatment system using a continuously driven conveyor. 
     Given the fact that such spray pretreatment systems mostly have large passage openings, the resulting energy consumption is of course relatively high. As the workpieces are fed into the system through the inlet opening in horizontal direction, and as it is practically impossible, due to the continuously moving conveyor, to close off the inlet opening from ambient air, it is necessary to arrange a correspondingly sized extraction fan in the roof area of the spray pretreatment system. This leads to quite considerable energy demands. 
     SUMMARY OF THE INVENTION 
     In view of this it is a first object of the invention to disclose a spray pre-treatment system which is capable of reducing the energy consumption compared with prior designs known in the art. 
     It is a second object of the invention to disclose a method for the pre-treatment of workpieces by spraying which is capable of reducing the energy consumption compared with prior methods known in the art. 
     These and other objects are achieved in a spray pretreatment system of the kind described above in that the pre-treating station or region is preceded by an entry station or region wherein the workpieces, having been fed in through an inlet opening, are raised by the conveyor to a treating station or region located on a higher level. 
     The object is further achieved by a method for pre-treating workpieces by spraying wherein the workpieces are transported through a spraying tunnel and are treated with a liquid from treating installations in at least one treating station or region, and wherein the workpieces are initially fed in through an inlet opening and are then raised to a higher level in the treating station or region. 
     According to the invention, the spray pretreatment system comprises an inlet opening that is located below the level of the treating system. Due to the vapor pressure resulting from the higher temperature prevailing in the treating station of, for example, 50 to 70° C., the vapor has a considerable tendency to escape through the inlet opening in the case of conventional spray pretreatment systems where the workpieces are fed in at the same level at which they later reach the treating station. 
     This condition is largely remedied by the invention due to the fact that the inlet opening is lowered relative to the level of the spraying tunnel. Formation of vapor at the inlet opening is thereby clearly reduced, and in addition the workpieces are pre-heated in the entry station to the temperature prevailing in the treating station. In addition, the droplets and aerosols forming in the colder entry station lead to an additional cleaning effect in the entry station. 
     This has the result that the treating station or the further treating stations may be reduced a little in overall length or may be operated at a somewhat lower temperature. This also contributes to reducing energy consumption. Especially high energy savings are, however, achieved by the fact that the fan power needed for preventing vapor from escaping through the inlet opening can be clearly reduced or, depending on the particular configuration of the system, that one can do without an extraction system (suction device). 
     Conveniently, a drip pan for liquid is provided in the entry station. 
     According to an advantageous further development of the invention, the inlet opening has an upper edge located at a level below the treating installations at the lowest level. 
     According to another embodiment of the invention, the tank of the treating station is equipped with an admission surface which preferably is inclined toward the tank, the upper edge of the inlet opening being located at a level below the admission surface. 
     These features clearly reduce the formation of vapor at the inlet opening. The more the upper edge of the inlet opening is displaced in downward direction, the greater the energy savings are as a further cooling effect and reduction of the vapor pressure will be obtained. 
     Vapors from the treating station will condense especially on the upside of the entry station, which preferably is formed by an inclined surface, whereby the generation of vapor at the inlet opening is reduced. 
     Additionally, an extraction means may be provided in the area of the inlet opening. 
     Depending on the particular configuration of the spray pretreatment system, that feature may also be fully omitted in some cases. 
     According to a further embodiment of the invention, the conveyor is given a design ensuring that the workpieces are lowered to a lower level at the outlet of the spraying tunnel or in an intermediate zone. 
     The spraying tunnel may have an outlet opening with an upper edge located at a level below the treating installations arranged at the lowest level. 
     Although generally the temperature is lower in the outlet area of the spraying tunnel, because the only liquids used in that area are rinsing liquids, that feature also helps save energy. 
     Additionally, an extraction system (suction device) may be provided in the area of the outlet opening, if desired. 
     According to another embodiment of the invention, a cold trap is provided in the area of the inlet opening. The cold trap may consist, for example, of cooling coils and a coolant flowing through them. The entry station may be extended correspondingly by the length of such a cold trap so that the cold trap will have to be passed as a first step. Alternatively, the cold trap may be provided, for example, above and, if desired, additionally below the inlet opening. 
     Such a cold trap likewise efficiently prevents vapor from escaping through the inlet opening. In this case, one can do without any extraction system. This is highly valuable environmentally, especially when highly alkaline cleaning agents or highly acidic cleaning agents are used. 
     It is understood that the features of the invention mentioned above and those yet to be explained below can be used not only in the respective combination indicated, but also in other combinations or in isolation, without leaving the scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further features and advantages of the invention will become apparent from the description that follows of a preferred embodiment of the invention, with reference to the drawing. In the drawings: 
         FIG. 1  shows a first embodiment of a spray pretreatment system according to the invention; 
         FIG. 2  shows an alternative embodiment of a spray pretreatment system according to the invention comprising two spray treating stations; 
         FIG. 3  shows a partial view of another embodiment of a spray pre-treatment system according to the invention, illustrating the area of the entry station; and 
         FIG. 4  shows a partial view of another embodiment of a spray pre-treatment system according to the invention, illustrating the area of the entry station: 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In  FIG. 1 , a first embodiment of a spray pretreatment system according to the invention is shown in part and is indicated by reference numeral  10 . 
     The spray pretreatment system  10  comprises a spraying tunnel  12  through which workpieces  16  are conveyed using a conveyor  14 . 
     The spraying tunnel  12  comprises an entry station  32  that has an inlet opening  34  with an upper edge  36 . The upside of the entry station is formed by an upwardly inclined surface  48 . The entry station  32  is followed by a treating station  18 , which may be followed by further stations not shown in detail in the drawing. The bottom of the entry station is formed by an inclined admission surface that extends from the inlet opening  34  to a drip pan  38 . The drip pan  38  is followed by a section that extends in vertically upward direction and that terminates in a tank  22  placed on the bottom of the treating station  18 , via an inclined admission surface  28 . Above the tank  22 , there are provided treating installations  20  for the spray pretreatment of workpieces  16  at a higher temperature of, for example, 50 to 70° C. The treating installations  20  may consist, for example, of spray registers from which the workpieces are spayed by nozzles. The spray registers are supplied with cleaning liquid from the tank  22  via a pump  24  and a line  26 , for spraying the workpieces  16 . 
     Any condensate forming in the entry station  32  is collected in the drip pan  38  and is likewise recirculated to the tank  22  of the treating station  18 , via a pump  42  and a line  44 . 
     Now, the arrangement is such that the upper edge  36  of the inlet opening  34  of the entry station  32  is located at a level below the upper end of the admission surface  28  and below the treating installations  20  located at the lowest level. 
     Though vapors arising in operation in the treating station  18  will reach the entry station  32  via the connection area of the spraying tunnel in the region of the inclined admission surface  28 , they will for the greatest part condense on the inclined surface  48  and the cold workpieces  16 , and will then drop down and be carried back into the drip pan  38  via the inclined admission surface  40 . 
     The workpieces  16  pass the inlet opening  34  and enter the entry station  32  where they are transported in an obliquely upward direction until they reach the level at which they will be conveyed through the treating station  18 . On their way, they are additionally cleaned by droplets and aerosols in the area of the entry station  32 . This results for example in a preliminary degreasing effect. In addition the workpieces, as well as the atmosphere in the entry station  32 , are preheated gradually on the way to the treating station  18 . 
     As a result of the considerable condensation effect in the area of the entry station  32  and of the low arrangement of the upper edge  36  of the inlet opening  34 , the extraction system in the area of the roof  46  of the spraying tunnel  12 , which is required in the systems of the prior art, may be fully omitted. If desired, an extraction system  50  may be installed additionally in the area of the inlet opening  34 , in which case a relatively low exhaust capacity will be required only. All in all, that arrangement leads to considerable energy savings compared with known spray pretreatment systems. 
       FIG. 2  shows another embodiment of a spray pretreatment system according to the invention, indicated generally be reference numeral  10   a . Identical parts are identified in this drawing by the same reference numerals. 
     The design of the first part of the spray pretreatment system  10   a  is identical to that of the system discussed with reference to  FIG. 1 . In the present case, however, a second treating station  18   a , following the first treating station  18 , is shown by way of example. While the first treating station  18  may serve for example for cleaning the workpieces, the second cleaning station  18   a  may be designed as a rinsing station that operates at clearly lower temperatures of, for example, approximately 30° C. For the rest, the two treating stations  18 ,  18   a  may be identical in design, to the extent this is suitable for the particular application (for example preliminary degreasing and degreasing). 
     The outlet end of the spraying tunnel  12   a  may again be provided with a corresponding inclined surface  48   a  that extends in downward direction to the upper edge  36   a  of an outlet opening  34   a . And again, a drip pan  38   a  may be provided on the bottom, from which the collected liquid can be recirculated into the tank  22   a  of the treating station  18   a . Similarly, an extraction system  50   a  may be provided in the area of the outlet opening  34   a , to the extent such a system is required for the particular application. 
     It is understood that such a spray pretreatment system may of course comprise significantly more treating stations than have been illustrated in  FIGS. 1 and 2  by way of example. For example, several treating stations may be followed by several rinsing stations. 
       FIGS. 3 and 4  show the area of the entry station of certain modified designs of the spray pretreatment system according to the invention, indicated by reference numerals  10   b  or  10   c , respectively. As before, identical elements are again identified by the same reference numerals. 
     In both embodiments shown, a cold trap  52  is provided in the area of the inlet opening  34  of the entry station. The cold trap  52  comprises a plurality of pipes  54  with a cooling liquid flowing through the pipes. 
     In the case of the embodiment shown in  FIG. 3 , the entry station  32  is extended to the front by the cold trap  54  so that workpieces  16  fed into the station will have to pass the cold trap  54  first. 
     In the case of the embodiment illustrated in  FIG. 4 , the cold trap  54  is arranged above the inlet opening  34 . 
     In both cases, no extraction system is needed in the area of the inlet opening. This is especially valuable environmentally when highly alkaline or highly acidic cleaning agents are used in the cleaning station. 
     All in all, the structure according to the invention leads to clear energy savings compared with conventional spray pretreatment systems.