Abstract:
With a device for applying a coating agent onto a cyclically moved substrate, a uniform coating thickness may be achieved, although the rate of advance not being constant, in that at least one spray valve ( 6 ) is provided which is permanently supplied with coating agent and the nozzle opening of which being adjustable with regard to the size of its effective discharge area in case of change of the rate of advance of the substrate according to the dependency, for a constant layer thickness of the coating agent, of the discharge rate of the coating agent out of the spray valve ( 6 ) on the rate of advance of the substrate.

Description:
RELATED U.S. APPLICATIONS  
         [0001]    Not applicable.  
         STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
         [0002]    Not applicable.  
         REFERENCE TO MICROFICHE APPENDIX  
         [0003]    Not applicable.  
         FIELD OF THE INVENTION  
         [0004]    The invention refers to a device for applying a coating agent to a cyclically moved substrate, in particular for applying a lubricant to movable sheet metal being supplied to a press in a cycle being adapted to the working cycle of said press.  
         BACKGROUND OF THE INVENTION  
         [0005]    Presses provided with sheet metal manufacture for performing forming processes like deep-drawing processes, work with a certain working cycle. Therefore, the sheet metal must be supplied to such a press in a synchronized cycle. The advance movement of the sheet metal starts with a phase of acceleration and finishes with a phase of deceleration. Inbetween, there may be a period with constant velocity. Therefore, the advance movement is not constant during a step of advance movement.  
           [0006]    With the production of deep-drawing moldings, it is known to coat the sheet metal with a lubricant before the deep-draw process for achieving a high surface quality. Spray valves, e.g. of the kind disclosed in DE 94 08 445 U1 of the applicant have been used hereto up to now. With the known spray valves, the discharge rate of the lubricant is constant during the spray process. Therefore, only with a constant rate of advance a lubricant coating having a constant coating thickness may be achieved. However, during the acceleration and deceleration phases decreasing and increasing coating thicknesses, respectively, are achieved which is undesirable. A too thick layer not only results in an unnecessary consumption of lubricant but may also result in an undesired accumulation of lubricant in the area of the deep-drawing devices.  
           [0007]    With the spray valve disclosed in the above indicated DE 94 08 445 U1, the stroke of the nozzle needle and therewith the outlet diameter effected by it may be adjusted. However, the respective adjustment remains constant during a coating process. The adjustability of the outlet diameter here only serves for the adaption to different viscosities of different lubricants which are used for different applications. Thus, the disadvantages of the above indicated kind have to be feared here too.  
         BRIEF SUMMARY OF THE INVENTION  
         [0008]    Thus, starting herefrom, the problem to be solved by the present invention is to provide a device for the application of a coating agent to a cyclically moved substrate with which also with a non-constant advance movement of the substrate a uniform coating thickness of the coating agent may be achieved.  
           [0009]    This problem is solved by the combination of claim 1. Hereby a combination of the above indicated kind is proposed which is provided with at least one spray valve which is permanently supplied with coating agent and at least the nozzle opening of which is adjustable with regard to the size of its effective discharge area in case of change of the rate of advance of the substrate according to the dependency, existing for a constant layer thickness, of the discharge rate of the coating agent out of the spray valve on the rate of advance of the substrate.  
           [0010]    The area of the nozzle opening belongs to the parameters influencing the discharge rate of the coating agent out of the spray valve, the discharge rate being most influenced by the change of the area of the nozzle opening. Accordingly, the measures according to the invention advantageously result in a dynamic adaption of the discharge rate to the rate of advance of the substrate. By the amendment of the size of the effective discharge area of the nozzle opening according to the invention, the amount of coating agent supplied to the substrate per time unit may be adjusted continuously in such a way that a constant thickness of the coating agent application is achieved. The discharge rate also depends on other parameters, as already indicated, like the viscosity of the coating agent and the pressure of the coating agent at the spray valve. However, the size of the nozzle opening has the largest influence so that advantageously already small changes are sufficient for achieving an adaption of the discharge rate to a varying rate of advance which is advantageous for avoiding undesired standstill times etc. and allows a simple construction. With the inventive measures, with changing rates of advance of the substrate a constant thickness of the coating agent application is achieved for the first time, and therewith the disadvantages mentioned at the beginning are avoided.  
           [0011]    Advantageous embodiments and practical modifications of the generic measures are indicated in the claims. Thus, with the use of spray valves having a valve needle cooperating with an associated seat and being lifted from the seat against the force of a closing spring by means of a control medium and being contacting a stop, said stop may practically being formed as a rotatable cam which is at least drivable during changing rates of advance of the substrate and comprises a contour being derived from the dependency, existing for a constant thickness of the coating agent layer, of the discharge rate of the coating agent out of the spray valve on the rate of advance of the substrate. The formation of the stop, associated with the valve needle, as a rotatable cam advantageously enables a very simple and cheap construction of a needle stroke adjustment dynamically adapted to the changing rate of advance and therewith to a discharge rate adapted accordingly. The rotational movement of the cam may simply be achieved and controlled.  
           [0012]    If several spray valves arranged side by side in line are necessary, the cams associated with them may advantageously be held on a camshaft traversing above all spray valves, said cam shaft being drivable by means of a drive unit controllable by means of a control device. Hereby it is ensured that only one cam drive unit is necessary for all spray valves of one line.  
           [0013]    If several spray valves and spray valve lines, respectively, facing each other are necessary which are associated with drive units, said drive units may be controllable by means of the same control device. By this measure the constructional effort may also be reduced and the accuracy increased.  
           [0014]    The control device associated with the cam drive unit is practically formed in such a way that at least for one layer thickness information associated with the connection between rate of advance of the substrate and of the cam may be stored in it. The dependency between the rate of advance and the angle position of the cam may thereby simply be stored in the control device in form of a table. The same applies to the course of the advance movement. This facilitates the data collection and supply.  
           [0015]    Further advantageous embodiments and practical modifications of the generic measures are indicated in the remaining claims and may be taken from the following description of examples on the basis of the drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0016]    [0016]FIG. 1 is a diagrammatic view of the application device according to the invention.  
         [0017]    [0017]FIG. 2 is the velocity diagram of the advancing device of the arrangement according to FIG. 1 and  
         [0018]    [0018]FIG. 3 is a sectional view of a spray valve of the arrangement according to FIG. 1. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0019]    The principal field of use of the present invention is the deep-drawing forming of sheet metals. Thereby, they are supplied in form of successive plate-like cuttings or in form of an endless strip to a not shown deep-drawing press. The example illustrated in FIG. 1 is based on processing of sheet metal plates.  
         [0020]    The sheet metal plates  1  are successively accommodated uniformly spaced from each other on an advancing device  2  which is here formed as a conveyor belt and associated with the not shown deep-drawing press, said advancing device being drivable by means of an associated driving unit  3 . With each working cycle of the deep-drawing press one sheet metal plate  1  is formed. The sheet metal plates  1  must therefore be supplied to the deep-drawing press with a cycle which is harmonized with its working cycle. The same applies of course to the advance movement of an endless strip during processing of it.  
         [0021]    The driving unit  3  associated with the advancing device  2  is therefore activated and deactivated, respectively, in the desired cycle, the advancing device  2  being first accelerated from standstill to a maximum rate of advance and then again decelerated until standstill. The rate of the advancing movement during a step of advance is accordingly not constant but proceeds over the time according to the diagram shown in FIG. 2 comprising an acceleration phase a, a constant phase b and a deceleration phase c. Between two steps of advance with such a rate of advance a standstill phase d may be provided.  
         [0022]    The material to be subjected to a deep-drawing process is usually coated on the opposed surfaces with a lubricant forming a coating  4  shown in FIG. 1 by broken lines. For simplification of the illustration in the shown example only the top surface of the sheet metal plates  1  is provided with a lubricant coating  4 . In practice, the plates are usually coated on both surfaces.  
         [0023]    The coating forming the lubricant application  4  is sprayed by means of an application device  5 . The application device  5  comprises at least one spray valve  6 . Since with one spray valve  6  generally not the total width of the sheet metal may be coated, usually several spray valves  6  are provided arranged in form of a line traversing the width of the sheet metal, in FIG. 1 only the front valve of said spray valves may be seen. The spray valves  6  arranged side by side are held on a cross bar  7  of a machine framework, not shown, traversing the width of the advancing device  2 .  
         [0024]    The spray valves  6  comprise, as may best be seen from FIG. 3, a chamber  9  which may be charged via a supply line  8  with pressurized lubricant, said chamber  9  having an outlet formed as a conical valve seat  10 . A valve needle  11  is associated with the valve seat  10  which may be pressed to the associated seat surface for closing the outlet and which may be lifted from it for opening the outlet. The lubricant supplied to the chamber  9  is constantly pressurized in said chamber  9 . As soon as the valve needle  11  is lifted from the associated seat and a nozzle opening with a certain discharge area is accordingly exposed, a lubricant jet ejecting from the chamber  9  is generated. Said jet is atomized by air jets  12  so that a spray jet  13  results being formed by fine lubricant particles. For achieving said atomization a ring chamber  14  is provided surrounding said chamber  9  chargeable with lubricant, said ring chamber  14  being supplied with compressed air via a supply line  15  and comprising several, here obliquely downwardly directed, discharge nozzles  16  for the generation of air jets  12 .  
         [0025]    The valve needle  11  is pressed by an associated closing spring  17  to the associated valve seat  10 . For lifting the valve needle  11  from the associated valve seat  10 , the valve needle  11  is provided with a piston  19  arranged within a cylinder  18 , said piston separating the interior space of the cylinder  18  into two chambers  20 ,  21 . The closing spring  17  is arranged in the chamber  20  opposite to the valve seat  10  and is supported on the one hand at the piston  19  and on the other hand at the cylinder front wall opposed to it. The chamber  21  near to the valve seat forms a working room which may be supplied with a controlling pressure means, preferably compressed air, via a supply line  22 . As soon as said controlling pressure means is provided in the chamber  21 , the valve needle  11  is lifted from the valve seat  10  by the force generated hereby and acting upon the piston  19  against the force of the closing spring  17 , thereby forming a nozzle opening the discharge area of which corresponds to the area of the ring chamber between the valve seat  10  and the valve needle  11 . The above mentioned supply lines  8  and  15  and  22 , respectively, may advantageously branch from the associated main lines laid in the cross bar  7  which are provided with appropriate connections.  
         [0026]    For limiting the stroke of the valve needle  11  a stroke limiting device  23  is provided. Hereto, the valve needle  11  is provided with a rearward pin  24  surrounded by the closing spring  17 , the end of which projecting out of the cylinder  18  being enclosed by a stop and may be contacted with it by the force acting upon the piston  19 . For formation of said stop a rotatable cam  25  is provided, the driving unit of which being connected with the driving unit of the advancing device  2  in a certain manner, said cam having a certain contour which is described below in more detail. The cam  25  enables a continuous adjustment of the stroke during operation.  
         [0027]    The cams  25  of the spray valves  6  arranged side by side in the form of a line are hold on a cam shaft  26  traversing the width of the advancing device  2 . Said cam shaft may rest, as may be seen from FIG. 1, onto supports  27  projecting from cross bar  7 , resulting in a compact construction. The cam shaft  26  is derivable, as may further be seen from FIG. 1, by means of an associated driving unit  28  which may be controlled by an associated control device  29 . The driving unit  28  may be formed as a servo motor with a subsequent gear, preferably a planet gear, having no or less clearance. The control device  29  may be formed as a freely programmable control device comprising a computer and associated memories.  
         [0028]    If the substrate formed here by the sheet metal plates  1  is coated as mentioned above from above and below, an upper and a lower application device  5  is provided, the upper and lower cam shaft may be associated with own driving units  28 . They are practically controlled by means of a common control device  29 . The driving unit  3  associated with the advancing device  2  is practically also controlled by the control device  29 . The control device  29  may hereto comprise a control circuit associated with the driving unit  3 , the velocity target values may be available as a table. The cyclization is generated by an actuating signal provided by the not shown deep-drawing press, as is indicated by an associated signal input  30  of the control device  29 . Of course, it would also be possible to provide the driving unit  3  with an own control device.  
         [0029]    The thickness of the coating  4  produced by means of the application device  5  depends on the rate of advance of the advancing device  2  and of the discharge rate of the lubricant out of the spray valve  6 , i.e. the lubricant throughput per time unit through the opened nozzle opening. The discharge rate in turn depends on the viscosity of the lubricant, the pressure of the lubricant in the chamber  9 , and from the size of the discharge area of the nozzle opening which may be adjusted continuously by the stroke limiting device  23 . The pressure and the viscosity shall be constant in the illustrated example. Only the size of the discharge area is changed. Depending on the position of the cam  25  a bigger or smaller discharge area of the nozzle opening results.  
         [0030]    The coating  4  shall have a uniform thickness all over. For ensuring this also in the areas of the sheet metal plates  1  passing below the application device  5  during the acceleration phase a and the deceleration phase c, the contour of the cam  25  is formed in such a way that during the acceleration phase a an increase of the effective discharge area of the nozzle opening corresponding to the increase of the velocity and during the deceleration phase c a decrease of the effective discharge area, of the nozzle opening corresponding to the decrease of the velocity results. With the increase and decrease, respectively, of the effective discharge area the discharge rate is accordingly increased and decreased, respectively. Thus, a dynamic adjustment of the discharge rate to the rate of advance results in such a way that the outlet rate during the acceleration phase a increases according to the increase of the velocity and decreases during the deceleration phase c according to the decrease of the velocity so that a coating  4  having a constant thickness is achieved. Thus, the driving velocity of the cam  25  is harmonized in such a way with the contour of the cam that at any time the desired circumferential area of the cam  25  cooperates with the pin  24  of the valve needle  11 .  
         [0031]    The cam radius associated with the basic position of the cam  25  during the standstill phases d is such that the valve needle  11  is pressed against the associated valve seat  10 , and therewith the outlet of the chamber  9  being kept closed. As soon as the driving unit  3  associated with the advancing device  2  is started, the driving unit  28  associated with the cam  25  is also started, the cam  25  being rotated in such a way that the discharge area of the nozzle opening increases. When reaching the maximum rate of advance, i.e. during the constant phase b, the driving unit  28  may be stopped. As soon as the deceleration phase c begins, the driving unit  28  is activated in an opposite direction so that the cam  25  is rotated in such a way that the size of the effective discharge area of the nozzle opening decreases with the rate of advance. At the end of the deceleration phase d, i.e. at the end of the advance movement, the initial position of the cam  25  is again reached with which the spray valve  6  is closed.  
         [0032]    The necessary increase and decrease, respectively, of the cam is practically distributed over a circumference of 90°-210°. Thereby, it is ensured that on the one hand the cam increase is not too steep, and on the other hand not too weak, thereby on the one hand undesired accelerations of the valve needle  11  and on the other hand an undesired high driving velocity of the cam  25  may be avoided as well as a smooth continuous adjustment of the needle stroke and therewith a high accuracy may be achieved. The cam standstill during the constant phase ensures that no cam circumference is needed for it and thus, the contour associated with the acceleration and deceleration phase, respectively, may be arranged on a comparably big circumferential area.  
         [0033]    The dependency between the rate of advance following from FIG. 2 and the related angle position of the cam, i.e. the dependency between rate of advance and discharge rate may be stored in form of a table in the control device  29  as is indicated in FIG. 1 by an appropriate input  31 . In the same way, the velocity diagram of the advance movement may simply be stored in the control device  29  and may be used for calculation of the desired angle position of the cam  25 . This may be applied if the advance movement always takes the same course. However, for achieving an especially high accuracy, it is advantageous to detect the actual value of the advance rate, as is indicated by an appropriate actual value input  32  of the control device  29 , and to determine from said actual value of the velocity by means of a stored table of angles the associated position of the cam.  
         [0034]    Further aggregates contributing to the coating process, preferably the compressed air supply of the ring chamber  14  supplying the air jets  12 , may also be controlled by the control device in addition to the driving units  28  and  3 . For reducing the consumption of compressed air the supply of compressed air to the ring chamber  14  during the standstill phases d may be turned off. The supply of controlling pressure means of the working chamber  21  associated with the piston  19  may also be turned of during the standstill phases d. These measures are advantageously used if the standstill phase d is longer than a certain minimum value. For achieving a high degree of accuracy, the supply of the working chamber  21  and of the ring chamber  14 , respectively, must again be activated in advance, preferably 100 milliseconds in advance, before the beginning of the next advance movement. The control device  29  accordingly comprises appropriate memories for the reception of the necessary information and connections.  
         [0035]    In the illustrated embodiment only the size of the effective discharge area of the nozzle opening is continuously changed dynamically adapted to the rate of advance. It would also be possible to change one or several of the further parameters influencing the discharge rate dynamically adapted to the rate of advance. However, the largest influence has a change of the size of the effective discharge area of the nozzle opening so that with a device of the kind described above good results may be achieved in a simple manner.