Abstract:
The invention relates to a spraying tool, in particular as part of a mold-spraying device for spraying at least one section of a wall of a mold with working medium. In at least one embodiment, the spraying tool comprises a plurality of spraying elements for dispensing working medium, and at least one working-medium supply line which supplies working medium to the plurality of spraying elements. In accordance with at least one embodiment, at least some of the spraying elements, the spraying nozzles of which point downwards during operation, are equipped with a separate valve unit which is adjacent to the spraying nozzle and the valve element of which is prestressed elastically into a closed position in which it prevents the dispensing of working medium, but can be transferred under the action of a hydraulic and/or pneumatic pressure into an open position in which it permits the dispensing of working medium.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of PCT application Serial No. PCT/EP2008/005499 filed on Jul. 4, 2008, which claims priority to German application Serial No. 10 2007 031 263.8 filed Jul. 5, 2007 which are hereby incorporated by reference in their entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The invention relates to a spraying tool, in particular as part of a mold spraying device for spraying at least a section of a mold wall of a mold with a working medium, comprising: 
         [0004]    a plurality of spray elements for dispensing a working medium, and 
         [0005]    at least one working medium supply line, which supplies working medium to the plurality of spray elements. 
         [0006]    2. Background Art 
         [0007]    One possible application for using such a spraying tool is as a mold spraying device such as that used after a working cycle to prepare the walls of the mold halves of a drop-forging device for the next working cycle. To do so, the walls of the two mold halves are sprayed with a working medium. Two problems arise here with modern drop-forging devices, namely first the short cycle times of only approximately 1 to 2 seconds per forged molded part, and secondly, the small installation space available for inserting the spraying tool between the mold halves of the drop-forging device. 
         [0008]    To be able to accommodate the aforementioned short cycle times, both mold halves of the drop-forging device must be sprayed with working medium at the same time. To do so, however, it is necessary for the spraying tool to be equipped with a plurality of spray elements on two surfaces facing in opposite directions. This doubling has corresponding consequences for the dimensions of the individual spray elements. Furthermore, the aforementioned short cycle times do not allow the two mold halves of the drop-forging device to move a great distance from one another because this would take too much time. Depending on the size of the molded parts produced in the drop-forging device, an installation space of only approximately 40 mm to approximately 80 mm is available for the height of the spraying tool. 
         [0009]    A spraying tool having spray elements operated according to the internal mixing principle is known in the prior art, where the main body of the spray element comprising the mixing chamber is screwed into a base part of the spraying tool. The working medium is supplied to the plurality of spray elements from a shared switch-off valve via a channel system. It is therefore unavoidable that a residue of working medium remains in the channel system after spraying the mold halves of the drop-forging device. If the spraying tool is then extracted from the space between the two mold halves of the drop-forging device at a high speed, it may happen that due to inertia, a portion of the working medium escapes from the spray element in an unwanted manner without being atomized and then drips into one of the mold halves of the drop-forging device. Since too much working medium is introduced into the drop-forging device in this way, there is the risk of damage to the drop-forging device. 
         [0010]    One of the objects of the invention is therefore to provide a spraying tool of the type defined in the beginning, with which the unwanted escape of working medium during operation is at least reduced in comparison with the prior art, if not being completely prevented. 
       SUMMARY OF THE INVENTION 
       [0011]    This object is achieved according to at least one embodiment of the invention by a spraying tool of the type defined in the beginning, in which at least a portion of the spray elements on which the spray nozzle points downward during operation are equipped with a separate valve unit next to the spray nozzle, its valve element being elastically prestressed into a closed position, in which it stops the dispensing of working medium but can be transferred to an open position, in which position it allows the working medium to be dispensed, under the action of a hydraulic and/or pneumatic pressure. Through this measure, the quantity of working medium capable of passing through the spray nozzle under the influence of inertia in a movement of the spraying tool may at least be significantly reduced. 
         [0012]    Since the valve units arranged next to the spray nozzles are additional components in comparison with the prior art, an additional installation space must also be provided for them. However, since no additional installation space is available because of the circumstances explained above, this installation space must be saved elsewhere. This may be accomplished by a number of measures, which may be implemented individually or in combination with one another in a further embodiment of the invention. 
         [0013]    For example, it is possible to provide for the spray element to atomize the working medium with the help of an auxiliary medium, e.g., air, according to the external mixing principle or without the use of an auxiliary medium. In this way, the installation space required for the internal mixing chamber may be omitted. 
         [0014]    Additionally or alternatively, it is possible to provide for the valve unit to be accommodated in a pot-shaped clearance in a main body of the spraying tool and to be secured therein by a cover plate of the spraying tool. This allows a thread-free design of the valve unit and thus eliminates the installation space required for a thread. 
         [0015]    In a further embodiment of the invention, the cover plate of the spraying tool may also be used independently of the thread-free design of the valve unit to keep the spray nozzle or at least a portion of the spray nozzle having the valve unit in operational connection. Separate connecting elements may be omitted in this way. The spray nozzle or at least a portion of the spray nozzle may be screwed to the cover plate according to one embodiment variant. This embodiment variant has the advantage that it is not necessary to remove the entire cover plate from the spraying tool to gain access to an individual valve unit, so this facilities maintenance of the spraying tool. According to an alternative embodiment variant, the spray nozzle or at least a portion of the spray nozzle may also be inserted loosely into a clearance in the cover plate, preferably from the inside of the cover plate, or held by friction in this clearance, e.g., by being pressed into it. This alternative embodiment variant has the advantage that it is simpler to manufacture due to the omission of a thread on the spray nozzle. 
         [0016]    The valve unit itself may also be designed with a simple design and thus in a manner that saves on installation space in the axial direction in particular. For example, the valve unit may have a working medium inlet channel, which can be brought into connection with the working medium supply line at the inlet end and from whose other end emerges a tapping channel opening into a valve chamber, such that again at least one dispensing channel of this valve chamber leads to an outlet opening of the valve unit, and the valve element is accommodated in the valve chamber. The wall section into which the at least one channel opens forms the valve seating surface for the valve element. 
         [0017]    To be able to easily provide the elastic prestress of the valve element, i.e., in particular without having to provide additional elements, e.g., springs or the like, in a further embodiment of the invention it is proposed that the valve element be formed of rubber material. The inherent elasticity of the rubber material is manifested in particular when the valve seating surface is formed on the outside circumference of the valve unit and is surrounded by a ring-shaped valve element. 
         [0018]    If the cross section of the valve element is designed to be rectangular, whereby preferably at least one of the two lines connecting neighboring corners is designed to be concave, then a sealing guidance of the valve element on the valve unit can easily be ensured in this way, because the corners bordering the concave line act as sealing lips. Such elements are known by the term “quad ring,” for example. Essentially, however, it is also conceivable to use a simple O-ring having a circular cross section. 
         [0019]    However, additionally or alternatively, unwanted leakage of working medium can also be counteracted by providing at least one sealing element on each side of the valve element, as seen in the direction of extent of the working medium supply channel. 
         [0020]    If desired, the effect of the elastic prestress of the valve element can be supported by a control medium, e.g. compressed air, acting on the valve element in the closing direction. 
         [0021]    To simplify the production of the spraying tool, the so-called sandwich design may be used in an essentially known manner. For example, the working medium supply line may be designed in a main body of the spraying tool as a recess provided in a surface of this main body, such that another plate covers the recess to form the working medium supply line. Furthermore, a blasting air supply line may also be formed in the main body of the spraying tool as a recess, which is provided in a surface of this main body opposite the one surface. This recess may be covered by the cover plate to form the blasting air supply line, for example. Finally, it has proven advantageous if two main bodies are provided, preferably separated from one another by a dividing plate, their spray elements dispensing working medium in essentially opposite directions. 
         [0022]    In addition, the spray elements need not necessarily be arranged in straight rows but instead may also be arranged to conform to the geometry of the mold halves. In this way, the contours of the mold halves of the shaping device, in particular the drop-forging device, may be prepared much more effectively for the next working cycle, e.g., cooled more effectively and coated with lubricant. 
         [0023]    It should also be added that through the use of pressure-proportional valves, continuously variable control of the quantity of working medium dispensed can be ensured. 
         [0024]    To illustrate the differences between the external mixing principle and the internal mixing principle, reference shall be made to DE 195 11 272 A1, whose disclosure in this regard is herewith made part of the disclosure content of the present patent application. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]    The invention is explained in greater detail below on the basis of an exemplary embodiment with reference to the accompanying figures, in which 
           [0026]      FIG. 1  shows a roughly schematic diagram of a mold spraying device, in which the inventive spraying tool is used; 
           [0027]      FIG. 2  shows an enlarged diagram of a detail of the inventive spraying tool; 
           [0028]      FIG. 3  shows a top view of the valve unit of the spray element shown in  FIG. 2 , seen here from the direction of the arrow III in  FIG. 2 ; and 
           [0029]      FIG. 4  shows a sectional view of the valve unit along line IV-IV in  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0030]    In a roughly schematic diagram,  FIG. 1  shows a drop-forging device  10  as an example of a device for hot and cold shaping, in which the inventive spraying tool  20  may be used. The drop-forging device  10  comprises a lower press ram  12 , which is fixedly mounted on a building floor U, and an upper press ram  14 , which is movable back and forth by means of devices that are not shown here. In this way, the two mold halves  12   a  and  14   a  of the two press rams  12  and  14  may be brought close to one another to form a press space for shaping a workpiece or may be moved apart from one another to form a sufficient space for insertion of the spraying tool  20 . The latter situation is illustrated in  FIG. 1 . To be able to insert the spraying tool  20  between the two mold halves  12   a  and  14   a , it is mounted on the arm  16   a  of a robot  16 , which is only shown in roughly schematic form in  FIG. 1 . Instead of a robot  16  having a robot arm  16   a  that can only be extended and/or shortened, as shown in  FIG. 1 , a modern multiaxial robot may of course also be used. The robot  16  and a spraying tool  20  together form a mold spraying device  18 . 
         [0031]    Since it is not the design of the device  10  for hot and/or cold shaping or the design of the robot  16 , but rather the design of the spraying tool  20  that is important here, and these parts may also be of a traditional design, a more detailed explanation will not be given here in this regard. 
         [0032]    As also shown in  FIG. 1 , the spraying tool  20  comprises two opposing rows of spray elements  22 , namely a row  24  assigned to the lower mold half  12   a  and a row  26  assigned to the upper mold half  14   a.    
         [0033]    According to  FIG. 2 , the spraying tool  20  is constructed by a sandwich design. It comprises a first main plate  28 , assigned to the lower row  24  of spray elements  22 , a second main plate  30 , assigned to the upper row  26  of spray elements  22 , a dividing plate  32  for separating the two main plates  28  and  30 , a cover plate  34 , assigned to the first main plate  28 , and a cover plate (not shown), assigned to the second main plate  30 . Recesses  28   a  and  30   a  are formed in the two main plates  28  and  30  and are covered by the dividing plate  32 , thus forming supply lines  36  and  38  for working medium. Similarly, additional recesses are formed on the side of the main plates  28  and  30  facing away from the recesses  28   a  and  30   a , only the recess  28   b  of which is shown in  FIG. 2 . This additional recess  28   b  is covered by the cover plate  34 , thus forming a supply line  40  for blasting air, by means of which the working medium dispensed by the spray elements  22  is atomized. The dividing plate  32 , the two main plates  28  and  30  and the two cover plates  34  are held against one another by suitable fastening means, e.g., by screw bolts and nuts. 
         [0034]    In a rapid movement of the spraying tool  20  into or out of the space between the two press halves  12  and  14 , there is the risk that at least for the lower row  24  of spray elements  22 , working medium may escape from the supply line  36  and the lower spray elements  22  under the influence of inertia. To prevent this, according to the invention, a separate valve unit  42  is assigned to each spray element  22 . The valve unit  42  is accommodated in a pot-shaped recess  28   c , the pot bottom of which is connected to the working medium supply line  36  via a passage  28   d.    
         [0035]    With reference to  FIGS. 3 and 4 , the design of the valve unit  42  will now be discussed in greater detail. The valve unit  42  comprises a base body  44 , designed essentially to be cylindrically symmetrical, from whose one end face  44   b  a tapping channel  46  leads away and extends essentially along the cylinder axis Z into the base body  44 . In deviation from the strict cylindrical symmetry, four radial channels  48 , which open into a ring face  50   a  forming the bottom of a ring groove  50 , lead away from the internal end of the tapping channel  46 . Four additional channels  52 , which run obliquely inward with respect to the cylinder axis Z, lead out from this ring groove  50  at locations which are each offset by approximately 45° with respect to the mouth openings of the channels  48  and open into a dispensing recess  54  surrounding the cylinder axis Z, through which the working medium emerges from the valve unit  42  again. 
         [0036]    A valve ring  56  made of rubber material and having an essentially square or rectangular cross section is arranged in the ring groove  50 . The diameter of the valve ring  56  is such that in the unloaded state, free of external forces, it is in contact with the bottom  50   a  of the ring groove  50 , a predetermined prestress being provided, if desired. Due to the fact that the surface  56   a  of the valve ring  56  on the inside radially is designed to be concave, the corners  56   b  of the valve ring  56  are compressed slightly in this case, so they can act as sealing lips especially effectively and can prevent unwanted escape of working medium. If the working medium coming from the tapping channel  46  is in contact with the bordering surface  56   a  of the valve ring  56  with pressure, then it widens the valve ring  56  when this pressure exceeds a predetermined value. This state is illustrated in  FIG. 4 . Based on the displacement of the valve ring  56 , the working medium can flow starting from the tapping channel  46  through the channels  48 , the ring groove  50  and the additional channels  52  to the dispensing recess  54 . As soon as the pressure of the working medium subsides, the valve ring  56  contracts again due to its inherent elasticity and prevents the working medium from leaking out of the channels  48  into the other channels  52 . 
         [0037]    The valve function provided by the valve ring  56  reliably prevents working medium from leaking out of the spray elements  22  due just to inertia with a rapid movement of the spraying tool  20 . If the inherent elasticity of the rubber material of the valve ring  56  is insufficient to provide the valve function, it is possible to consider additionally prestressing the valve ring  56  from its outside, e.g., by means of compressed air or suitable spring elements. Indeed, in this case one might even consider completely omitting the inherent elasticity. The additional prestress could also be utilized to control the flow rate of working medium through the valve unit  42 . 
         [0038]      FIG. 4  also shows two sealing elements  58  and  60  designed as traditional O-rings, serving to seal the valve unit  42  in the receptacle recess  28   c  of the main plate  28 . 
         [0039]    In the exemplary embodiment shown in  FIG. 2 , the dispensing nozzle  62  is designed in two parts. In particular, it comprises a nozzle mouthpiece  64 , which engages with the dispensing recess  54  of the valve unit  42  and serves to eject working medium, and an air-guiding nozzle  66 , which serves to eject blasting air that is used to atomize the working medium according to the external mixing principle. The air-guiding nozzle  66  passes through an opening  34   a  in the cover plate  34 . 
         [0040]    Furthermore,  FIG. 2  shows that neither the valve unit  42  nor the air-guiding nozzle  66  is designed with a thread. Instead, the valve unit  42  is simply inserted into the recess  28   c  in the main plate  28  and is held there by the air-guiding nozzle  66  by the fact that the latter is in contact at its inner end face  66   a  with the outer end face  44   a  of the base body  44  of the valve unit  42 . The air-guiding nozzle  66  in turn has a ring shoulder  66   b  with which it is in contact with the section of the inner bordering surface of the cover plate  34  surrounding the opening  34   a . Essentially, however, it is also conceivable to omit the ring shoulder  66   b  and to screw the air-guiding nozzle  66  into the opening  34   a , as indicated at  66   c . In the latter case, it is possible to replace the valve unit  42  without therefore having to remove the entire cover plate  34  from the spraying tool  20 . 
         [0041]    It is of course also conceivable to design the dispensing nozzle  62  as a one-piece design. Furthermore, the spray angle of the dispensing nozzle  62  may be selected through its corresponding design. Regardless of that, however, the same valve unit  42  may always be used. 
         [0042]    It should also be added that the recesses  28   a  and  28   b  may be created in the main plate  28  by milling, for example. Additionally or alternatively, however, it is also possible to provide these recesses in the main plate already during their shaping. For example, a plurality of recesses that are not interconnected but which are then connected by removing individual partitions, e.g., by milling, to form a channel system of the desired course, might be provided in molding. 
         [0043]    It should also be pointed out that a dispersion of graphite and water, for example, may be used as the working medium. 
         [0044]    While embodiments of the invention have been illustrated and described, it is not intended that these embodiments illustrate and describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention.