Abstract:
A device for surface treatment, in particular galvanic surface treatment, of workpieces, including at least one reactor housing, having at least one process chamber and being coverable by a cover, and a screen element which is spatially connected to the process chamber, and which has at least one receptacle for a workpiece to be treated, a fixing element having a smaller thermal expansion coefficient being situated between the reactor housing and the screen element, which defines their relationship relative to each other.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a device for surface treatment of workpieces. 
       BACKGROUND INFORMATION 
       [0002]    Among other methods, layers are electrochemically applied for finishing the surface of components. This is accomplished in practice mostly by immersing the components into baths of a galvanic system. In particular in electrochemically applied layers, the component must be completely or partially immersed into the bath. 
         [0003]    If the quality requirements for the layer are strict, the components to be treated are positively inserted into a basket-type or drum-type stand. This stand may be immersed into, or rotated in, the bath, for example. In particular when small components such as injector elements to be chrome-plated are to be precisely coated, these are treated in practice in batches of numerous components, the components being accurately inserted into a receptacle, and their positions are thus defined. 
         [0004]    The problem in this case is, in particular, that thermal expansion occurs due to high temperatures, which cause a change in the dimensions of the component position relative to the screen position in the event of partial coverage of component surfaces not to be coated. 
         [0005]    In the event of increased deposition rate and very strict precision requirements, a robot-operated galvanic machine may be used, which also makes the integrated use of pre-cleaning stages or finishing preservation stages possible. This simplifies the component flow in the plant and the manipulation complexity is minimized. The use of an industrial robot, for example, which moves twelve gripped components through the treatment stations and inserts them into guides using twelve grippers simultaneously, is known from practice. For this purpose, an accurate alignment of the robot, gripper guide rails, and treatment cells is needed, including the parts feed and parts return. 
         [0006]    In the case of aggressive media in the coating process, specially suitable plastics, for example, PVC-C, PVDF, or Teflon may be used, since a metallic base material to be coated with an inert substance is subject to wear and thus to the risk of influencing the process, for example, by leak currents over the base material. 
         [0007]    This plastic is subject to considerable changes in dimensions due to process-related strong temperature fluctuations, in particular during the feed or during idling. Swelling of the plastic when using aqueous media also results in dimensional changes. In addition, there is the problem with plastics that the warping behavior of the mostly amorphous structure of the material cannot be accurately predicted. Asymmetric warping is often observed, in particular in large components. 
         [0008]    In repair or modification work, setting-up is therefore very time-consuming and difficult due to the need to realign the components and tools with respect to each other. After a first temperature cycle, corrections may become necessary, so that the treatment stations must then be realigned. 
         [0009]    Since in the case of a larger number of components to be coated which must be arranged in a row in a screen rail and aligned, a greater change in dimensions of the individual coating positions with respect to the robot gripper system occurs during heating due to the thermal longitudinal expansion than the tolerances of the component guides in the coating positions allow; collisions also more often occur, in particular between a robot and a coating station. 
       SUMMARY OF THE INVENTION 
       [0010]    The exemplary embodiments and/or exemplary methods of the present invention provides a device for galvanic surface treatment of workpieces in particular including at least one reactor housing having at least one process chamber and being coverable by a cover, and a screen element which is spatially connected to the process chamber, and which has at least one receptacle for the workpiece to be treated. A fixing element having a smaller thermal expansion coefficient is situated between the reactor housing and the screen element, defining their arrangement relative to each other. 
         [0011]    The distances between the position of the screen element and the position of the reactor housing relevant for the temperature and media-caused expansion are thus advantageously minimized and optimized, which makes it possible to positively situate the workpiece to be treated. 
         [0012]    Of special advantage is the device according to the exemplary embodiments and/or exemplary methods of the present invention if the screen element and the reactor housing are made of plastic due to the aggressive nature of the medium used and for achieving electrical insulation. 
         [0013]    Due to its amorphous structure, plastic expands in an unpredictable manner and in the event of greater temperature fluctuations it expands considerably, which may cause the otherwise absolute positioning of the component and in particular of an automated gripper device for the component with respect to the screen element and the reactor housing to become lost. 
         [0014]    In particular in a system having a plurality of reactor housings in rows or fields, in the case of reactor housings made of plastic considerable problems arise regarding the dimensional stability with respect to the screen element and a gripper device for the workpiece to be treated. 
         [0015]    With the device according to the exemplary embodiments and/or exemplary methods of the present invention very narrow tolerances between the workpiece to be treated and the screen element are possible even in the case of a larger number of reactor housing and workpieces to be treated arranged in parallel or in fields. 
         [0016]    The fixing element is advantageously fixedly mounted, while the reactor housing and the screen element are mounted on the fixing element. The fixing element may be a simple metallic element such as a steel support which is screw-mounted or pin-mounted on a machine stand. 
         [0017]    Any number of reactors in any arrangement may be built into a machine on such a fixing element without problems arising due to thermal effects. 
         [0018]    Due to the modular design and the possibility of situating a plurality of small reactors on the fixing element, the manufacturing costs may also be advantageously reduced, since such a device of modular design may be manufactured much less expensively than, for example, a reactor on which a plurality of treatment cells is formed by machining. 
         [0019]    In the process chamber of the device, both galvanic processes, in which case an anode cooperating with the workpiece acting as a cathode is situated in the process chamber, as well as purely chemical processes such as chemical nickel-plating, may be performed. 
         [0020]    Furthermore, different treatment stages may be implemented in the process chamber, such as pre-treatment, coating, preservation, or drying of the workpiece to be treated. 
         [0021]    Due to the modular design of the device according to the exemplary embodiments and/or exemplary methods of the present invention, a treatment cell may be modified inexpensively for new workpiece types or adapted to a modified process. 
         [0022]    In an advantageous embodiment of the present invention, not only a fixing element is provided between the screen element and the reactor housing, but also a cover holder, fixing the position of the cover of the reactor housing with respect to the reactor housing, having a smaller thermal expansion coefficient than the cover. A cover made of plastic, which is exposed to strong thermal fluctuations, may thus also be situated with small deviations regarding its positioning with respect to the screen element and the reactor housing. A cover holder of this type may be designed as the fixing element regarding its construction. 
         [0023]    Further advantages and advantageous embodiments of the subject matter of the present invention are presented in the description, the drawings, and as further described herein. 
         [0024]    An exemplary embodiment of the device for galvanic surface treatment of workpieces according to the present invention is schematically depicted in the drawings and elucidated in greater detail in the description that follows. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]      FIG. 1  shows a depiction in principle of a device for galvanic surface treatment of a workpiece in a longitudinal section. 
           [0026]      FIG. 2  shows a section through the device according to  FIG. 1  along line I-I. 
           [0027]      FIG. 3  shows a simplified longitudinal section through a constructive embodiment of the device of  FIG. 1 . 
           [0028]      FIG. 4  shows a perspective bottom view of the device of  FIG. 3 . 
           [0029]      FIG. 5  shows a perspective top view onto the device of  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION 
       [0030]      FIGS. 1 and 2  are highly abstracted depictions of a device  1  for galvanic surface treatment of a workpiece  2 , a reactor housing  3  being provided with a process chamber  4 , which is connected to a screen element  5  accommodating workpiece  2 . 
         [0031]    Reactor housing  3  and screen element  5 , which may be made of any resistant material and in the present case is made of plastic, are attached to each other via a fixing element  6  for preserving their positional accuracy in the event of process-related temperature fluctuations. Fixing element  6  is made of a material having a smaller thermal expansion coefficient than the material of reactor housing  3  and screen element  5  and in this case represents a U-shaped steel support, which accommodates both reactor housing  3  and screen element  5 . 
         [0032]    Reactor housing  3  is accommodated by fixing element  6  in such a way that fixing element  6  includes an end face  3 A facing screen element  5  and a peripheral area  3 B, adjacent thereto, of reactor housing  3 . Screen element  5  is inserted in the direction of reactor housing  3  defined in the peripheral direction through an opening  6 C, which is round in the present case, and rests on the side of fixing element  6  facing away from end face  3 A of reactor housing  3 . 
         [0033]    Unlike the embodiment shown, the fixing element may also have an H-shaped cross section. Ribs may also be provided on the fixing element for reducing the bending line. 
         [0034]    To close reactor housing  3  and screen element  5  while workpiece  2  is exposed to a process bath, a cover  7  is provided, whose position with respect to reactor housing  3  and screen element  5  is fixed with the aid of a cover holder  8 , which in the present case is made of steel and thus has a smaller thermal expansion coefficient than cover  7  made of plastic. 
         [0035]    Cover holder  8  includes an end face  7 A facing screen element  5  and a peripheral area  7 B of cover  7 , adjacent thereto, cover holder  8  having a round recess  8 A into which cover  7  is placed positively in the peripheral direction. 
         [0036]    In the depicted embodiment, cover holder  8  and fixing element  7  are designed as a commercially available U-steel whose dimensions are reworked in the simplest possible way. 
         [0037]    Fixing element  7  and cover holder  8  are fixedly situated on a machine stand in a way not shown in greater detail, and are pinned, for example, to an adjustable base, so that the position may be reliably found again even after modifications or service work. A receptacle  9  for a centering pin for fixing element  6  on a machine stand is depicted in  FIG. 2 , the centering pin or passing pin may be placed flush with opening  6 C of fixing element  6 . 
         [0038]    Cover holder  8  may be connected to a cover actuating mechanism; in a modular design of the device having a plurality of reactor housings and accordingly a plurality of associated covers, these may be mounted on a single cover holder and operated by a single cover actuating mechanism. After a one-time adjustment, the particular cover, even in the case of a plurality of covers, remains in the correct position both in the case of a treatment station bottom-heated by process baths and in the case of an open cell and raised cover in cold exhaust air current and may be easily set in place again without clamping. 
         [0039]    Similarly, a plurality of reactor housings  3  may also be held by fixing element  6 ; the reactors may then have small dimensions due to the simple-to-align and dimensionally stable attachment of reactor housing  3  on fixing element  6  despite unfavorable process parameters as occurring in particular in galvanic processes, and may be automated, for example, using a robot gripper. 
         [0040]    In one embodiment of cover holder  8  and cover  7  as the upper receptacle and fixing element  6  together with screen element  5  and reactor housing  3  as the lower receptacle, it is possible that the upper receptacle moves automatedly relative to the lower receptacle and thus a tight seal of the treatment cell is achieved. The principle according to the exemplary embodiments and/or exemplary methods of the present invention of the holder of cover  7  and of the alignment of screen element  5  with respect to reactor housing  3  may also be applied to manually operated machines. 
         [0041]    The upper receptacle made up of cover holder  8  and cover  7  may also be designed as a goods support, workpiece  2  remaining stationary during treatment by process chamber  4 . 
         [0042]    In addition to the holder of cover  7 , screen element  5 , and reactor housing  3 , other intermediary elements, possibly to be operated automatically, may also be similarly positioned. 
         [0043]    Making reference to the constructive design according to  FIGS. 3 through 5 , it is apparent that workpiece  2  to be treated is inserted into a holder  11  on screen element  5  with the aid of an automated gripper device  10 , which has gripper jaws  10 A,  10 B for gripping workpiece  2 , screen element  5  having a through opening  12  for contacting workpiece  2  with an electrolyte for electrolytical coating of workpiece  2 . 
         [0044]    Screen element  5  may be inserted into opening  6 C of steel fixing element  6  using tight tolerances and is sealed against reactor housing  3  also situated on fixing element  6  using a gasket  13 . 
         [0045]    For electrochemical coating of workpiece  2 , which is connected for this purpose as the cathode, an anode  14 , whose ends facing workpiece  2  are suitably designed, is situated in process chamber  4 . 
         [0046]    For performing the process, an electrolyte is filled into process chamber  4  via an inlet  15 , process chamber  4  being subdivided into a first, approximately cylindrical chamber  4 A of a small diameter and a second chamber  4 B of a larger diameter, adjacent to workpiece  2 . The process bath may be drained again after contact with workpiece  2  via second chamber  4 B, and removed from reactor housing  3  via a return line  17 . 
         [0047]    In addition to the depicted application of device  1  for galvanic coating of a workpiece  2 , which may represent for example a component of a motor vehicle injection system, device  1  may also be used for purely chemical processes, where any number of reactors in any arrangement may be provided, in which positioning problems due to thermal effects may be avoided due to the design according to the exemplary embodiments and/or exemplary methods of the present invention of the device.