Abstract:
The invention relates to a paint spraying device with a spray head which dispenses a quantity of paint via a needle valve and a paint-dispensing line leading to the spray head, wherein the paint-dispensing line is connected upstream of a pressure reducer/pressure regulator which regulates the paint-dispensing pressure and holds the pressure in the paint-dispensing line to the spray head substantially constant.

Description:
This application claims the benefit under 35 USC §119(a)-(d) of German Application No. 10 2014 104 982.9 filed Apr. 8, 2014, the entirety of which is incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The invention relates to a paint spraying device. 
     BACKGROUND OF THE INVENTION 
     The prior art contains a multiplicity of air-operated paint spraying devices which generally comprise a paint reservoir, a device for generating an air flow, for example, a compressor or a blower and a spray gun. 
     In the case of what are termed HVLP systems (high volume, low pressure), the paint is atomized by means of an air blower through a high volume flow rate of air at a low pressure at a spray head. To that end, the paint is provided at the spray head either by means of a conveying air pressure or otherwise. The quantity of paint dispensed is generally regulated by a needle valve and a trigger mechanism. The air blower and the paint supply are integrated either into the pistol unit or alternatively individually or together in a base station. Such an HVLP atomization is for example mentioned in US 2011/0073677 A1. A transportable spray device with an operating unit, a paint spraying lance and a spray head and separate paint reservoir is described in WO 2011/038712 A1. 
     In order to convey the paint from a paint reservoir which is remote from a paint spraying gun to the paint spraying gun, in particular, in the case of high-viscosity paints, substantial pressures are required. The required conveying pressure is then dictated, in particular, by the length of the line used and the cross section thereof. The spraying process at the spray head itself should, however, take place with an appropriately low pressure in order to avoid an uncontrolled egress of paint, known as “spitting”, upon opening a needle valve on the spray head. If this is not done, the application of paint is uneven on account of variations in the quantity of atomizable paint dispensed at the paint spraying head. In the prior art, this effect is avoided by switching the paint conveying on and off according to the quantity of paint to be dispensed. However, this requires complex and rapid switching processes which make the relevant devices complicated, susceptible to faults and expensive. 
     SUMMARY OF THE INVENTION 
     The present invention is based on the object of proposing a paint spraying device which generates as even an application of paint as possible while having a more economical construction. 
     According to the present invention, the object is achieved in that, on a spray gun or the like, a pressure reducer or a pressure regulator is connected upstream of the paint-dispensing line which supplies a spray head with paint, such that the paint pressure in the paint-dispensing line is held substantially constant. 
     In order to pump the high-viscosity paint through, for example, an approximately 7 m-long supply hose, pump pressures of up to approximately 8 bar are often required. This high pump pressure has to be reduced to a very low value at the spray head, to which end a special pressure reducer is provided. This is in particular critical when the spraying process is interrupted, and thus the high supply pressure builds up in the entire system, since there is no continuous paint removal and associated pressure drop. If the paint pressure acting at the spray head is held as constant as possible at a low value, “spitting” of the gun is reliably prevented. 
     To that end, according to the invention, the pressure reducer is arranged downstream of a paint supply line and upstream of a paint dispensing line. 
     Within the context of the invention, a paint supply line is to be understood as a line which is provided for the supply of paint to the inlet of a paint-dispensing device, for example, to a spray gun or a paint inlet line of such a device. In that context, such a paint supply line can be up to 8 m long. Within the context of the invention, a paint supply line can for example be designed as a paint hose. 
     Within the context of the invention, a paint-dispensing line is to be understood as a line which is provided for supplying paint to the outlet of a paint-dispensing device, for example a spray gun. Within the context of the invention, the paint-dispensing line is arranged within a paint-dispensing device, for example a spray gun. 
     In one preferred embodiment, it is provided that the pressure reducer/pressure regulator comprises a paint inlet line for supplying paint at high pressure and a paint outlet line for supplying paint at an essentially constant lower pressure. The two lines are connected to one another via a pressure reducer housing, wherein the pressure reducer housing has a preferably annular or circular internal space with a diaphragm plate arranged therein. In that context, the diaphragm plate has means which change, in a pressure-dependent manner, the cross section of the paint inlet line or the cross section of the inlet to the preferably annular internal space in the manner of a throttle in the paint inlet line. 
     Cross section changes to a pressurized paint inlet line have the effect of reducing the pressure, according to known physical principles (force per unit area, hydrostatic paradox). The preparation of corresponding means for changing the cross section of a paint inlet line at a pressure reducer housing by means of a diaphragm plate arranged in that housing has the advantage that, using simple mechanical means, the pressure acting inside the housing is fed back to the inlet cross section of the paint inlet line, and thus no additional control loops are required. 
     In a further preferred embodiment, it is provided that a spring or the like, whose preload is preferably adjustable, presses on the rear side of the diaphragm plate with an annular pressure diaphragm, on its side oriented away from the paint supply line. 
     The fact that a pressure acts on the diaphragm plate on its side oriented away from the paint sets with precision the setpoint internal space pressure and makes it possible, in the event that the preload is also designed to be adjustable, to select the internal space pressure according to the required parameters. 
     In a further expedient embodiment, it is provided that a front side of the diaphragm plate, upon which the pressure of paint to be supplied acts, is connected via a piston rod to a closure element, in particular a cross slide for the cross section of the paint inlet line, wherein the closure element changes, or reduces to a lower pressure, the cross section of the paint inlet line according to a deformation of the diaphragm and an associated movement of the diaphragm plate. 
     The direct coupling of the diaphragm plate via a piston rod with a closure element regulates, depending on the internal pressure of the internal space, the cross section of the paint inlet lines and thus has the result, according to the known physical principles, that only a proportion—corresponding to the open cross section area—of the pressure in the paint inlet line is transmitted into the internal space. 
     A development which is expedient in this regard provides that the position of the closure element relative to the piston rod can be adjusted, and in particular can be set by means of a thread. Depending on the viscosity properties of the paint, it can be expedient to change the ratio of the internal pressure to the open cross section of the paint inlet line, which is brought about by changing the relative position of the closure element to the piston rod. It is thus possible, for example, to bring about an increased internal pressure and thus an increased pressure on the paint outlet line at the pressure reducer/pressure regulator. 
     It is moreover expedient that the diaphragm plate is formed as an umbrella-shaped element with a moulded-on piston rod and consists of a rigid material and at least partially receives a diaphragm which is flexible in comparison with the rigid material or a diaphragm is attached to the diaphragm plate, wherein the diaphragm forms, in the outer region of the diaphragm plate, a flexible section for sealing the in particular annular internal space with respect to a housing cover. 
     The diaphragm plate, which together with the diaphragm acts as a pressure receiver for the pressure in the internal space of the housing, is held in its rim region by the corresponding diaphragm such that it can move, without a substantial influence on or change to the pressure-force ratios in the internal space being necessary for moving the diaphragm unit consisting of the diaphragm plate and the diaphragm. 
     In an expedient development it is provided to form the closure element with at least one, preferably two, seal elements. The seal elements can in this context be arranged in a recess, in particular as O-rings. 
     A further expedient development provides that a structure which stands proud from a face is arranged in the region of the internal space, wherein the structure, as a flow deflector or flow collar or the like, at least partially surrounds a paint inlet opening and generates a flow for continuously circulating the paint in the interior when the paint spraying device is in operation or is being cleaned. This avoids paint lingering in the region of the pressure reducer/pressure regulator and possibly drying, or the formation of quiescent regions which are not exposed to the paint flow. 
     It is further provided that a flexible diaphragm is circumferentially attached, in particular clamped or welded, between a housing lower part of the pressure reducer and a housing cover of the pressure reducer. 
     The flexible diaphragm, which is clamped between two housing constituents of the pressure reducer housing or is held in a similar manner, serves as an attachment for the diaphragm plate which in turn operates the means for changing the cross section of the paint inlet line. It is thus possible to simply separate the paint region from a rear-side region which for example comprises a spring for providing a counter-force. 
     It is moreover expediently provided that the closure element is formed as a slide or valve element with an internal duct. 
     In this embodiment, the closure element permits either a cross section change by direct effect on the duct cross section of the paint inlet line, or a cross section change by means of a relative displacement of two ducts with respect to one another, as is, for example, effected in conventional ball valves or the like. 
     It is further provided, in an expedient embodiment of the paint spraying device according to the invention, to form the pressure reducer as an exchangeable subassembly, in particular as a subassembly with a screw connection and/or a quick-action fastener to the paint inlet line and/or the paint outlet line. The pressure reducer, which can attract dirt or dried-on paint on account of its moving parts and the possibly narrow cross sections, can be formed as an exchangeable subassembly, in particular as a single-use part, in order not to reduce the lifespan of the entire paint spraying device. 
     It is moreover advantageously provided that the diaphragm plate and/or the diaphragm is formed as a one-piece component, in particular as an injection-moulded component, wherein in particular rigid constituents are formed with thick walls and flexible constituents are formed with thin walls and/or the diaphragm has, in its outer rim region, a bead or a clamping rim. 
     The diaphragm plate and the diaphragm can be produced in one piece (especially from plastic) e.g. by means of a plastic injection moulding method. In that context, elastic parts are created with thin walls, rigid parts are created with thick walls, and are thus respectively given the desired property and elasticity. Threads can also be moulded thereon. Preferably, the outermost diaphragm circumference is made thicker in order to stabilize the attachment/clamping in the housing. Moreover, an undulation, which establishes in a defined manner what will later be the deformation region, can be imparted to the cross section of the diaphragm. 
     In addition to spraying paint, also known is a paint applying device for applying paint to a substrate, for example a paint roller, a paintbrush, a paint pad or the like, wherein the paint applying device is supplied with paint via a paint reservoir by means of a paint pump. According to the invention, it is also possible in this case to provide that a pressure reducer/pressure regulator is arranged according to that set out in the preceding description of the invention. 
     For the purpose of a more detailed explanation of the embodiment according to the invention, and of the expedient developments, exemplary embodiments are presented below. 
     For the purpose of the desired paint application, an essentially constant paint pressure, in particular conventionally a reduced pressure at approximately 0.3 to 0.4 bar, is to be striven for in order to generate an even spray pattern. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a fully understanding of the nature and objects of the invention, reference should be made to the following detailed description of a preferred mode of practicing the invention, read in connection with the accompanying drawings. 
         FIG. 1  shows, in section, a paint spraying device with a spray head and a spray nozzle, along with the associated pressure reducer/pressure regulator; 
         FIGS. 2 a  to 2 c    show a pressure reducer according to the invention in various closing positions of the paint inlet line; 
         FIG. 3  shows a view of part of the pressure reducer housing, in various views; and 
         FIG. 4  shows a paint spraying device with a pressure reducer/pressure regulator having a modular construction as a subassembly. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a paint spraying device  1  as what is termed the front end  2  of a paint spray gun. Such constructions are known from a multiplicity of appliances produced by the applicant. In that context, what is termed the front end, as a subassembly which contains the paint-conveying constituents, is releasably connected to a further subassembly which for example bears the blower or comprises the air supply line, thus generating degrees of flexibility by means of exchangeable front ends. The paint spraying device comprises a spray head  3  with a front paint nozzle  4  which is actuated by means of a needle valve  5  via a trigger  6 . The spray head  3  then forms, by means of an air cap  7  and an air gate  8 , an atomizing nozzle which can be opened or closed by means of the needle head  9  of the needle  10  of the needle valve  5 . The system of the spray head  3  is fixed and held on the body  12  by the union nut  11 . The needle  10  is drawn back by the trigger  6  via a bolt  13  against a spring  14  and can then dispense paint through the spray head  3 , in the manner of a paint spray gun. 
     If the needle valve  5  remains closed, a certain internal pressure builds up inside the paint-conveying constituents of the paint spraying device  1 , that is to say in the volume around the needle  10 , in the paint-dispensing line  20  and in the paint-dispensing space  21 , which pressure, in addition to the atomizing effect of the air atomization, allows the paint to issue forth from the needle valve  5  when the needle valve  5  is re-opened. If this internal pressure is too high, the paint spraying device spits out the first paint drops, which leads to undesired results. 
     Below the spray head  3  there is provided a connection housing  30  for the supply of paint and for receiving a pressure reducer/pressure regulator  40  (in the following just pressure reducer). 
     The pressure reducer  40  comprises a paint inlet line  41  to which the paint supply line  42  is connected via a connection hose. The cross section  43  of the paint inlet line  41  narrows at the pressure reducer, with a closure element  44  being arranged at this point. 
     An internal space  50  of the pressure reducer  40  is connected to the narrowed cross section location  43 , in which space there is in turn arranged a diaphragm plate  51  which acts on the closure element  44  via a piston rod  59 . The diaphragm plate  51  is suspended laterally circumferentially on a diaphragm  52  and its rear side  53  is supported by a spring  54 . 
     Thus, via the diaphragm plate  51  and the diaphragm front side  55 , a paint pressure prevailing in the internal space  50  will move the diaphragm plate  51 , and thus the closure element  44  via the piston rod  59 , in the direction of the spring  54  until the pressure force of the paint from the internal space  50  is compensated for by the spring force of the spring  54 . At the same time, the closure element  44  closes the cross section  43  and thus reduces the transfer of pressure from the paint supply line  42  via the paint inlet line  41  into the internal space  50 . By means of this interaction, the pressure in the internal space  50  remains essentially constant. 
     The paint-dispensing line  20  opens into the paint outlet line  56  which connects to the internal space  50 , via which paint-dispensing line the paint is then transferred to the paint-dispensing space  21  at a constant, reduced pressure with respect to the inlet side. 
       FIGS. 2 a  to 2 c    show the pressure reducer  40  in an isolated sectional representation. In that context,  FIG. 2 a    shows the open state,  FIG. 2 b    shows the state in the intermediate regulated operation and  FIG. 2 c    shows the closed state. The constituents are provided with the same reference signs as were introduced in the description relating to  FIG. 1 . 
     The pressure reducer housing  60  represented in  FIGS. 2 a  to 2 c    comprises a housing lower part  61  and a housing cover  62 . The paint supply line  42  (not shown) is attached by means of a screw-thread connection  63  according to the representation in  FIG. 1 . The upper side of the pressure reducer  40  is connected, at its paint outlet line  56 , to the paint-dispensing line  20  in the paint spraying device  1  by means of a quick-action fastener  64 , in the present case in the form of a form-fitting latching connection. 
     The pressure reducer housing  60  represented in  FIGS. 2 a  to 2 c    comprises a pressure regulating device by means of a diaphragm  52  control. To that end, a diaphragm plate  51 , which comprises an annular pressure diaphragm  52 , is arranged in a lateral housing projection  65  with a pot-shaped housing cover  62 . The annular pressure diaphragm  52  is attached by means of a clamping  66  between the housing projection  65  and the pot-shaped housing cover  62 . The diaphragm plate  51  with the annular pressure diaphragm  52  thus delimits an annular internal space  50  through which flows the paint to be conveyed. 
     The diaphragm plate  51  comprises, on its front side  55  oriented towards the internal space  50 , a piston rod  59  which extends transversely to the paint throughflow direction  70 . The piston rod  59  is connected in a receiving bore  71 , on its side oriented away from the diaphragm plate  51 , to a closure element  44 . The closure element  44  is formed as a type of cross slide and is mounted within the pressure reducer housing  60  perpendicular to the throughflow direction  70 . Mounting and sealing in the transverse direction is achieved by means of two O-rings  72 ,  73  which surround the cylindrical part of the closure element  44 . By means of the receiving bore  71 , with the threaded rod  75  of the piston rod  59  therein, it is possible to change the starting position of the closure element  44  with respect to the piston rod  59 . This changes the separation between the diaphragm plate  51  and the closure element  44  having the effect of changing a throttling of the paint flow. 
     The cylindrical body of the closure element  44  serves to change the inlet cross section  43  of the paint inlet line  41  to the annular internal space  50  of the housing projection  65  of the pressure reducer housing  60 . 
     The movement of the piston rod  59 , represented in  FIGS. 2 a  to 2 c   , opens and closes the cross section  43 .  FIG. 2 a    shows one type of open position,  FIG. 2 b    shows a position of the closure element  44  at the beginning of the closed position and  FIG. 2 c    shows the closed position of the cross section  43 . In this position, the O-rings  72 ,  73  completely seal off the internal space  50  from the paint inlet line  41  by means of the closure element  44 . 
     The transverse movement of the piston rod  59  moves the diaphragm plate  51  from the open position in  FIG. 2 a    to the closed position of the cross section  43  in  FIG. 2 c   . In order to generate a counter-pressure, and hence to carry out the reverse movement, the pot-shaped housing cover  62  has a coil spring  54  which presses the diaphragm plate  51  and thus the annular diaphragm  52  in the opposite direction, that is to say in the direction of the closure element  44 . In that context, the coil spring can be made to have an adjustable preload. 
       FIG. 2 a    shows, inside the housing projection  65 , a first endstop  80  against which the diaphragm plate  51  presses sideways in one of its end positions, and a second endstop  81  in  FIG. 2 c    on the pot-shaped housing cover  62 . 
     The housing lower part  61  with the housing projection  65  is again represented separately in  FIG. 3 .  FIG. 3  shows the housing projection  65  without the diaphragm plate. Particularly visible is a U-shaped web in the form of a flow collar  90 , which partially surrounds the inlet opening  91  of the paint inlet line  41 , the closure element  44  being movably arranged in the inlet opening. When the paint enters from the paint inlet line  41  into the annular internal space  50  through the inlet opening  91 , the paint is deflected by the U-shaped flow collar  90  and flows from the annular internal space  50  into the opening  93  for the paint outlet line  56 . The U shape of the flow collar  90  within the pressure reducer  40  also serves to generate turbulence during cleaning (for example with water), such that the entire pressure reducer is flushed through; at the same time, this also avoids, during operation with paint, fluidic dead spaces in which for example crumbs of paint could be deposited. 
       FIG. 4  shows, by way of example, the construction of the pressure reducer  40  as a subassembly  96  which can be located on a front end  2 . In this manner, the pressure reducer can be exchanged and can be adapted to the physical properties of the paint to be processed, or can be easily exchanged in the event of fouling. 
     On the Mode of Operation of the Pressure Reducer: 
     The paint spraying device is operated with a reduced pressure of approximately 0.3 to 0.4 bar. The paint is supplied via a supply hose or connection hose of the paint spraying device, which hose is for example approximately 7 m long. A high pump pressure of for example 8 bar is required at the paint reservoir (not shown) in order to pump the high-viscosity paint through this long supply hose  98 . 
     The pressure reducer according to the invention now serves to reduce the high pressure of up to 8 bar prevailing in the paint supply line  42  to a lower pressure of approximately 0.3 to 0.4 bar required in the paint-dispensing line  20 . This is in particular necessary in the event of an interruption of the paint dispensing, for example in the case of a work break, in order to ensure the quality of the paint application. 
     In comparison with arrangements which, in addition to the pressure reduction or pressure regulation, comprise a paint return line into a paint reservoir in order to regulate a dynamic pressure by means of circulating paint, the present invention achieves this in particular with just one paint supply line and just one paint-dispensing line. 
     Within the context of the invention, a needle valve is to be understood as any type of needle valve, including those with a needle head which deviates from a rotationally symmetric head shape, as are known from the applicant&#39;s inventions. 
     Within the context of the invention, an annular or circular internal space is to be understood as that internal space which is formed in a substantially annular fashion about a paint inlet. In that context, it is immaterial whether what is in fact formed is a ring with a centrally located interruption of the space, or whether there is a circular cavity with an inlet duct located in the centre without an interruption. 
     The invention is not restricted to the represented and described exemplary embodiment. Rather, it also encompasses all variants within the scope of the patent claims. 
     LIST OF REFERENCE SIGNS 
     
         
           1  Paint spraying device 
           2  Front end 
           3  Spray head 
           4  Paint nozzle 
           5  Needle valve 
           6  Trigger 
           7  Air cap 
           8  Air gate 
           9  Needle head 
           10  Needle 
           11  Union nut 
           12  Body 
           13  Bolt 
           20  Paint-dispensing line 
           21  Paint-dispensing space 
           30  Connection housing 
           40  Pressure reducer/pressure regulator 
           41  Paint inlet line 
           42  Paint supply line 
           43  Cross section 
           44  Closure element 
           50  Internal space 
           51  Diaphragm plate 
           52  Diaphragm 
           53  Rear side 
           54  Spring 
           55  Front side 
           56  Paint outlet line 
           59  Piston rod 
           60  Housing 
           61  Housing lower part 
           62  Housing cover 
           63  Thread-screw connection 
           64  Quick-action fastener 
           65  Housing projection 
           66  Clamping 
           70  Throughflow direction 
           71  Receiving bore with internal thread 
           72  O-ring 
           73  O-ring 
           75  Threaded rod 
           80  Endstop 
           90  Flow collar 
           91  Inlet opening 
           93  Opening 
           96  Subassembly