Abstract:
A spray head for releasing a material made at least of two reactive components includes material supplies for providing two material components and a reciprocating cleaning and control piston Substantially provided in the cleaning and control piston is a mixing chamber which is fluidly connectable to material supplies for receiving and mixing the two material components, when the cleaning and control piston is in a first position. Fluidly connected to the mixing chamber is also a discharge channel for discharging the mixed material components. When the cleaning and control piston is moved to a second position, an air and/or liquid supply is fluidly connected to the mixing chamber so as to allow introduction of purging air or flushing agent to carry out a cleaning process.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS  
       [0001]     This application is a continuation of prior filed copending PCT International application no. PCT/EP2006/061812, filed Apr. 25, 2006, which designated the United States and has been published but not in English as International Publication No. WO 2006/122865 and on which priority is claimed under 35 U.S.C. §120, and which claims the priority of German Patent Application, Serial No. 10 2005 023 233.7, filed May 20, 2005, pursuant to 35 U.S.C. 119(a)-(d), the content(s) of which is/are incorporated herein by reference in its entirety as if fully set forth herein. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     The present invention relates, in general, to a spray head for releasing a material made at least of two reactive components.  
         [0003]     Nothing in the following discussion of the state of the art is to be construed as an admission of prior art.  
         [0004]     Spray heads can be used to mix a polyurethane material from the components polyol and isocyanate and to apply the mixture onto a surface (e.g. the surface of a molding tool). After both reactive components have reacted out, a thin plastic skin forms on the surface and can be peeled off. Such plastic skins can be back-foamed or back injection-molded so that a product can be created with a surface skin of polyurethane material that has a pleasant surface feel.  
         [0005]     International publication no. WO 96/27484, published Sep. 12, 1996, describes a device for mixing miscible components, including a cleaning piston arranged in a mixing chamber. A drawback of this device is the possibility of the reactive mixture in the mixing chamber to settle in the cleaning piston, rendering the mixing device inoperative.  
         [0006]     It would be desirable and advantageous to provide an improved spray head to obviate prior art shortcomings.  
       SUMMARY OF THE INVENTION  
       [0007]     According to one aspect of the present invention, a spray head for releasing a material made at least of two reactive components includes a first material supply for a first component, a second material supply for a second component, a reciprocating cleaning and control piston, a mixing chamber substantially provided in the cleaning and control piston and fluidly connectable to the first and second material supplies for receiving and mixing the first and second components, when the cleaning and control piston is in a first position, a discharge channel fluidly connectable to the mixing chamber for discharging the mixed first and second components, and an air and/or liquid supply which is fluidly connected to the mixing chamber when the cleaning and control piston is in a second position.  
         [0008]     In accordance with the invention, the mixing chamber is arranged substantially in the reciprocating cleaning and control piston. The cleaning and control piston is hereby constructed in such a manner that in cooperation with the material supplies, components can be fed to the mixing chamber and this mixture can then also be discharged in the discharge channel, when the piston is in at least one position, i.e. first position. In at least a second position of the cleaning and control piston, the mixing chamber can be fluidly connected with the air and/or liquid supply to implement the flushing process. As a result, the mixing chamber as well as the discharge channel and all other passages in the cleaning and control piston can be cleaned by being blown out or flushed so as to prevent a hardening or clogging in this region, which would cause a choking of the spray head.  
         [0009]     The discharge channel may be arranged, for example, in a thin and barb-like spray lance by which otherwise inaccessible sites can also be reached. On an outlet side of the discharge channel and in particular on an outlet side end of the spray lance is a spray nozzle by which the mixed material can be applied in the form of a particular spray jet and at a desired spray distribution onto the surface.  
         [0010]     In order to assure a desired and constant product quality, it is oftentimes necessary to circulate the starting materials that have not yet mixed with one another at a moment, when no spraying process is carried out. A return flow channel is hereby provided via which a recirculation can be realized at least temporarily.  
         [0011]     According to another feature of the present invention, a valve may be arranged in each of thee material supplies device controlling the material flow. In particular, the flow path to the mixing chamber can then be cleared, when the return flow in the return flow channel is cut.  
         [0012]     According to another feature of the present invention, the valve may be constructed in the form of a non-return valve. Such a non-return valve opens, when the return flow via the return flow channel is cut, and, as a result, a pressure increase is encountered in the material supply. As soon as a certain pressure causes the non-return valve to open, the respectively reactive material component can then be fed to the mixing chamber. When the return flow channel is cleared again to enable the material component to flow back, pressure drops correspondingly, the non-return valve closes, and a further transport to the mixing chamber is blocked. Other options for the implementation of such a valve are, of course, also possible.  
         [0013]     A spray head according to the present invention is thus compact in structure and easy to clean. 
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0014]     Other features and advantages of the present invention will be more readily apparent upon reading the following description of currently preferred exemplified embodiments of the invention with reference to the accompanying drawing, in which:  
         [0015]      FIG. 1  is a schematic plan view of a first embodiment of a spray head according to the present invention;  
         [0016]      FIG. 2  is a side view of the spray head of  FIG. 1 ;  
         [0017]      FIG. 3  is a sectional view of the spray head of  FIG. 1 , taken along the line A-A in  FIG. 2 ;  
         [0018]      FIG. 4  is an enlarged detailed view of the area encircled in  FIG. 3  and marked “B”;  
         [0019]      FIG. 5  is a schematic sectional view of a second embodiment of a spray head according to the present invention in a first operative position, and  
         [0020]      FIG. 6  is a schematic sectional view of the spray head of  FIG. 5  in a second operative position.  
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0021]     Throughout all the Figures, same or corresponding elements may generally be indicated by same reference numerals. These depicted embodiments are to be understood as illustrative of the invention and not as limiting in any way. It should also be understood that the figures are not necessarily to scale and that the embodiments are sometimes illustrated by graphic symbols, phantom lines, diagrammatic representations and fragmentary views. In certain instances, details which are not necessary for an understanding of the present invention or which render other details difficult to perceive may have been omitted.  
         [0022]     Turning now to the drawing, and in particular to  FIG. 1 , there is shown a schematic plan view of a first embodiment of a spray head according to the present invention, generally designated by reference numeral  10  and typically installed in overall system, which is not shown here in detail for the sake of simplicity, as it does not form part of the invention. The spray head  10  includes a mixing body  12  which connected to a plurality of inlets and outlets for reactive starting materials and other media. A first material component of a reactive material mixture to be produced is fed via a supply line  14  to the mixing body  12 . The first material component can be returned again to a not shown tank via a return line  18 , when no spraying process is carried out. Both supply line  14  and return line  18  may be connected to a high pressure system (not shown) to provide the material components at a desired pressure, when fed from the tank via a pump or returned again to the tank.  
         [0023]     A second material component of the reactive material mixture is fed via a supply line  16  which also ports into the mixing body  12 . Leading back from the mixing body  12  is a return line  20  for feeding back the second material component in the event no spraying takes place and thus nothing is discharged from the spray head.  
         [0024]     As shown in the side view of  FIG. 2 , the spray head  10  has an air and/or flushing agent supply line  22  which is also connected to the mixing body  12  and is provided to feed purging air to the mixing body  12 , as will be described furtherbelow.  
         [0025]     Further provided on the mixing body  12  is a hydraulic piston drive  21  which has a housing secured to the housing of the mixing body  12  and includes a hydraulic piston  30  whose function will be described furtherbelow. The hydraulic piston drive  21  is connected to two hydraulic lines  24 ,  24 ′, namely a hydraulic supply line and a hydraulic return line.  
         [0026]     Arranged to a lower area of the mixing body  12  is a spray lance  26  which terminates in a spray nozzle  28  by which the reactive mixture comprised of the material components can be released and applied onto an unillustrated surface.  
         [0027]     As shown in  FIG. 3 , and in particular in  FIG. 4 , two valve units  34 ,  35  are provided in the mixing body  12  which the two material supply lines  14 ,  16  port into respectively. Both valve units  34 ,  35  are constructed in the form of non-return valves, which accommodate valve needle  36 ,  37 , respectively. The valve needles  36 ,  37  are biased by valve springs  38 ,  39  to normally seek a position against respective valve seats so as to cut a flow communication between the supply lines  14 ,  18 , and a mixing chamber  44 . In this position of the valve needles  36 ,  37 , the supply line  14  is however fluidly connected to the return line  18  and the supply line  16  is fluidly connected to the return line  20  to establish a recirculation of both starting materials, when they are not yet mixed.  
         [0028]     However, the return flow can be cut. This can be realized by respective—here not shown—valves. Thus, when the material return flow is barred, pressure increases in the supply lines  14 ,  18 . When the pressure reaches a certain level above the preset spring tension, the valve needles  36 ,  37  are pushed back in opposition to the resistance of the corresponding springs  38 ,  39 . As a consequence, the respective material component is able to reach a first nozzle and a second nozzle  40  or  41 , respectively, via a hollow valve space and a channel arranged in the mixing body housing. Further bores extend from the nozzles  40 ,  41  to a central bore  50  which accommodates a reciprocating cleaning and control piston  32 .  
         [0029]     The internal structure of the mixing body  12  is shown in greater detail in  FIG. 3  and in particular in  FIG. 4 . The cleaning and control piston  32  which is able to move back and forth in the central bore  50  of the mixing body  12  is connected at its upper end with the hydraulic piston  30  which, when suitably acted upon, moves back and forth in a hydraulic cylinder of the hydraulic piston drive  21 . The cleaning and control piston  32  is operated by routing hydraulic oil via the hydraulic lines  24 ,  24 ′ to one or the other side of the hydraulic piston  30  to displace the hydraulic piston  30  and thereby the cleaning and control piston  32 .  
         [0030]     The cleaning and control piston  32  has a lower region formed with a coaxial bore which extends downwardly and has a widening open end and which serves as a mixing chamber  44 . Near an upper end of the mixing chamber  44  are two diametrically opposing small passageways  46 ,  48  to provide a flow communication between the mixing chamber  44  and the outer side of the cleaning and control piston  32 .  
         [0031]     Immediately adjacent to the lower end of the mixing body  12  is a spray lance  26  which accommodates a discharge channel  27 . The spray lance  26  is attached to the mixing body  12 , with the discharge channel  27  forming a prolongation of the bore  50  in coaxial manner and porting on an outlet side of the spray lance  26  in a spray nozzle  28  which is so configured as to produce a spray jet in a desired manner.  
         [0032]     As can be seen more clearly in  FIG. 4 , which shows in greater detail the area marked “B” in  FIG. 3 , the cleaning and control piston  32  is able to move back and forth in the bore  50  within a certain stroke range (up and down). In an upper position, as depicted in  FIG. 4 , the passageways  46 ,  48  are in alignment with associated bores in the mixing body  12  so that both material components can be introduced into the mixing space  44  of the cleaning and control piston  32  via the valves  34 ,  35  and the nozzles  40 ,  41  as well as via the passageways  46 ,  48 .  
         [0033]     When the hydraulic piston  30  is acted upon to move the cleaning and control piston  32  downwards, the passageways  46 ,  48  shift also downwards, causing the outlets of both nozzles  40 ,  41  to be blocked by the cleaning and control piston  32 . When the cleaning and control piston  32  has moved far enough downwards to a lower position, limited by a shoulder  51  of the spray lance  26 , both passageways  46 ,  48  come into fluid communication with a chamber  52  which is connected to the air and/or flushing agent supply line  22 . Purging fluid, such as air or a flushing agent, from a suitable fluid source can thus be conducted via the supply line  22  and the chamber  52  through the passageways  46 ,  48 , the mixing chamber  44 , the bore  50  and the discharge channel  27 , and these hollow spaces can be liberated from reactive mixture.  
         [0034]     The mode of operation of the spray head  10  is as follows. When switching a valve (not shown) in each of the return channels  18 ,  20  to allow passage, the material components recirculate from the supply lines  14 ,  16  without any substantial pressure buildup to the corresponding return lines  18 ,  20 . When closing the valves in the return lines  18 ,  20 , pressure increases in the supply lines  14 ,  17  and acts in opposition to the valve needles  36 ,  37  which are pressed by the preset tension of the springs  38 ,  39  against their valve seats. When the pressure buildup reaches a predetermined level, the valve needles  36 ,  37  are lifted off their valve seats to allow a throughflow of the material components through the valve space toward the respective nozzles  40 ,  41 .  
         [0035]     When the cleaning and control piston  32  is moved by the hydraulic piston  30  to the retracted (upper) position, as shown in  FIG. 4 , the material components from the supply lines  14 ,  16  can flow via the confronting passageways  46 ,  48  into the mixing chamber  44 . As the passageways  46 ,  48  are placed in opposition to one another, the incoming component jets impact each another, thereby attaining an intimate mixing process to form a reactive material. The thus produced reactive material flows downwards in the mixing chamber  44 , through the clear part of the bore  50  and enters the discharge channel  27 . After flowing through the discharge channel  27 , the mixed reactive material is released via the spray nozzle  28 .  
         [0036]     As soon as the valves in the return channels  18 ,  20  open again, pressure drops in the supply lines  14 ,  16  so that the non-return valves  34 ,  35  close again, when the pressure drops below the predetermined level and the springs  38 ,  39  force the valve needles  36 ,  37  against their valve seats. This concludes the spraying process.  
         [0037]     Prior to the conclusion of the material supply, or simultaneously, or also subsequently, the cleaning and control piston  32  is moved downwards to the lower position by suitably acting upon the hydraulic cylinder  30  so that the flow connection between both nozzles  40 ,  41  and the passageways  46 ,  48  in the cleaning and control piston  32  is cut. As the cleaning and control piston  32  moves downwards, reactive material in the piston bore  50  is pushed out downwards as well. When the cleaning and control piston  32  reaches the lower position, the passageways  46 ,  48  are fluidly connected to the chamber  52  so that purging air or flushing agent from the supply line  22  is able to flow through the passageways  46 ,  48 , the mixing chamber  44 , and the discharge channel  27  to liberate all passages and spaces from residual reactive material mixture.  
         [0038]     To initiate a next spraying process, the cleaning and control piston  32  is moved back to the upper position by the hydraulic piston  30  and the valves in the return lines  18 ,  20  are closed again, causing a pressure buildup in the supply lines  14 ,  16  to ultimately open the non-return valves  34 ,  35  to repeat the cycle, as described above.  
         [0039]     Turning now to  FIG. 5 , there is shown a schematic sectional view of a second embodiment of a spray head according to the present invention, generally designated by reference numeral  100 . In describing the embodiment of  FIG. 5 , like parts of the spray head  100  corresponding with those of the spray head  10  in  FIGS. 1-4  will be identified by corresponding reference numerals, followed by the distinguishing character “a” in case corresponding but modified elements are involved. The description below will center on the differences between the embodiments. In this embodiment, provision is made for a mixing body  12   a  having a different configuration as far as the air and/or flushing agent supply is involved. In this embodiment, the air and/or flushing agent supply in the housing of the mixing body  12   a  is positioned above the material supply. As a result of such construction of the mixing body  12   a , reactive material mixture can be removed not only from the mixing chamber  44  and the discharge channel  27  but also the space between the cleaning and control piston  32  and the spray lance  26  can be cleaned.  
         [0040]     As shown in  FIG. 5 , the mixing body  12   a  is configured in the absence of any substantial space between the mixing chamber  44  and the spray lance  26  during the mixing and discharge (spraying) process. This operational state in which the starting materials are introduced via the non-return valves  34 ,  35 , the nozzles  40 ,  41  and the passageways  46 ,  48  is shown in  FIG. 5 .  
         [0041]     When the mixing and discharge process should be stopped or interrupted, the material supply is stopped in a same manner as described with reference to the spray head  10 , with the exception that the cleaning and control piston  32  now moves up instead of down. The upper position is shown in  FIG. 6 . As the cleaning and control piston  32  moves up from the lower position, shown in  FIG. 5 , a space  50   a  is formed between the cleaning and control piston  32  and the spray lance  26 . Although material, e.g. from the discharge channel  27 , may accumulate there, no new or additional material can reach the space  50   a.    
         [0042]     When the cleaning and control piston  32  reaches the upper position, a flow communication is established between the passageways  46 ,  48  and an annular groove  52   a  which is fluidly connected to the air and/or flushing agent supply line  22  and arranged above the passageways  46 ,  48  and thus the incoming material supply. As result, purging fluid, e.g. air or flushing agent, from a not shown supply source and entering the mixing body  12   a  via the annular groove  52   a  is able to flush the passageways  46 ,  48 ′, the mixing chamber  44 , the space  50  downstream of the mixing chamber  44  and the discharge channel  27  in the spray lance  26 .  
         [0043]     The spray head  100  requires thus flushing of slightly less material than the spray head  10 .  
         [0044]     While the invention has been illustrated and described in connection with currently preferred embodiments shown and described in detail, it is not intended to be limited to the details shown since various modifications and structural changes may be made without departing in any way from the spirit of the present invention. The embodiments were chosen and described in order to best explain the principles of the invention and practical application to thereby enable a person skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated.  
         [0045]     What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims and includes equivalents of the elements recited therein: