Abstract:
A paint spraying system is proposed with a paint spraying device with a paint spray gun with a fan for dispensing paint via a spray head, which paint spraying device is connected via a paint line to a base station with a connector to a paint reservoir. In order to achieve a low and uniform paint pressure which is required in the paint spray gun, the paint spray gun is equipped with a separate pressure reducing device and the base station is equipped with a pressure monitor, which pressure reducing device and pressure monitor perform a pressure regulation of the paint pressure in the system.

Description:
This application claims the benefit under 35 USC §119(a)-(d) of German Application No. 10 2014 105 016.9 filed Apr. 8, 2014, the entirety of which is incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The invention relates to a paint application system. 
     BACKGROUND OF THE INVENTION 
     A multiplicity of air-powered paint spraying systems exist in the prior art which as a rule comprise an apparatus for air flow generation, for example, a compressor or a fan, and a spray gun. If a relatively small paint supply is used, it is fastened to the spray gun (see, for example, EP 1 602 411 B1). If a relatively large paint supply is provided, it is handled in a separate and stationary manner, for example, in a bucket or container, the operating part with paint spraying lance and spray head representing a transportable part and being connected via a connector hose (see, for example, WO 2011/038712 A1). 
     In what are known as HVLP (high-volume, low-pressure) systems, the paint is atomized in a known way at a low air and paint pressure by means of a large air volume, for example, by a fan. This differs, for example, from what is known as an airless method, in which the paint is atomized by way of very high paint pressure. Here, the fan and the paint pump are either accommodated in the gun unit or, as an alternative, in a base unit. The air and the paint are combined in the spray head and the paint is atomized in a known way. 
     In the case of a multiple-piece paint spraying system with a separate base station, the paint transport takes place via a paint pump which is provided in the base station, sucks in the paint from a paint bucket or another storage container and delivers it to the paint spray gun or a paint roller or the like via a paint hose which is possibly several meters long. Depending on the viscosity of the paint and the length of the paint hose and the relatively small cross section of the paint hose, a considerable paint pressure is necessary on the part of the paint pump in the base station, in order to deliver the paint to the paint application tool, for example, a paint roller, brush or a paint spray gun. In the case of highly viscous paints and a paint hose length of, for example, more than from 5 m to 8 m and a paint hose internal diameter of, for example, only from 6 mm to 8 mm, paint pressures of from 2 bar to 8 bar are necessary, for example, in order to overcome the pressure drop which occurs in the paint hose. Here, the actual spraying operation in the paint spray gun is carried out at a relatively low paint pressure of, for example, only from approximately 0.3 bar to 0.4 bar. 
     The pressure reducing device/pressure regulator which is essential as a constituent part in the present invention is described and claimed in detail in the parallel patent application having the file number DE 10 2014 104 982.9. Reference is made hereby to the disclosure of the patent application and its contents are made the contents of this application by way of reference. 
     As a result of the long hose and the associated elasticity effects, for example, as a result of a partially elastic hose material or the inherent dynamic inertia of the transported liquid (paint), a considerable hysteresis is produced between the pressure which is provided by the paint pump at the base station and the pressure at the transportable element, for example, the paint roller or the paint spray gun. 
     In particular, the spraying operation at the spray head itself should be carried out at an appropriately lower pressure, in order to avoid uncontrolled paint discharge, what is known as “spitting” during opening of a needle valve on the spray head. If this is not realized, an inhomogeneous paint application results on account of fluctuating dispensed quantities of atomizable paint at the paint spray head. In the prior art, this effect is avoided by way of switching the paint delivery on and off in accordance with the paint quantity to be dispensed. However, this necessitates complex and brief switching operations which make the corresponding units complicated, susceptible to disruption and expensive. Paint rollers or paint brushes also have to be supplied continuously with paint, without material pulses of paint being dispensed when a valve is opened. 
     In the context of the invention, a paint inlet line is to be understood to mean a line of the type which is provided for feeding paint to a paint dispensing apparatus, for example, to a spray gun, and is connected upstream of a pressure regulator. In the context of the invention, a paint inlet line can also be understood to mean a paint hose. 
     In the context of the invention, a paint dispensing line is to be understood to mean a line of the type which is connected downstream of a pressure regulator and is provided for feeding paint to the outlet of a paint dispensing apparatus, for example a spray gun. In the context of the invention, the paint dispensing line is arranged within a paint dispensing apparatus, for example a spray gun. 
     SUMMARY OF THE INVENTION 
     The invention is based on the object of proposing a paint application system which makes a regulation of the paint pressure possible both in the base station and in the spray gun, in order to generate a homogeneous paint application on account of an operating pressure which is as constant as possible in the spray gun or the like. 
     The invention relates to a paint application system having a transportable paint roller, paint brush, paint pad, etc., or a transportable paint spraying device or paint spray gun with a fan for dispensing paint via a spray head with a paint nozzle and a needle valve; furthermore, having a base station which is stationary during the work operation for paint application and has a connector to a paint supply, the base station having a paint pump for sucking in paint from the paint supply and delivering paint by means of pressure, and the base station being connected to the paint roller, etc. or the paint spraying device via a paint hose and supplying the paint roller, etc. or the paint spraying device with paint. 
     According to the invention, the paint roller, etc. or the paint spraying device comprises a pressure reducing device/pressure regulator which is connected downstream of the paint hose and regulates the paint pressure in a paint dispensing line to a paint roller, etc. or a paint spray head to a substantially constant paint pressure which is lower than a paint pressure in the paint hose, and the paint pump in the base station is assigned a pressure monitor for monitoring the required paint pressure at the paint pump-side end of the paint hose. 
     The paint application system according to the invention provides the necessary operating pressure of the paint in the paint hose via the paint pump and the pressure monitor which is arranged there. At the same time, it is ensured via the pressure reducing device/pressure regulator at the transportable work implement, for example the paint roller, paint brush, paint pad or a paint spraying device that merely the operating pressure which is necessary for controlled and quality-optimized processing of the paint is available for paint dispensing. 
     This interplay allows it to be possible for a paint delivery pressure in the paint hose to be provided by the paint pump independently of the processing paint pressure. 
     In the following text, the use of a paint spray gun will be described substantially. However, the invention is not restricted hereto; transportable paint rollers which are fed via a paint pump, corresponding paint brushes or paint pads, etc. are also the subject matter of the present invention. 
     It is provided in one expedient development that communications about the paint pressure are performed between the pressure reducing device/pressure regulator and the pressure monitor in such a way that a paint pressure which falls below a first limiting value is detected in the paint hose at the paint pump-side end by the pressure monitor and actuates a switch which switches on the paint pump in order to generate a higher paint pressure in the paint hose, and a paint pressure which rises above a second limiting value at the pressure reducing device/pressure regulator is communicated to the pressure monitor via the paint pressure and actuates a switch which switches off the paint pump. 
     It is provided in this embodiment that the paint pump does not run continuously even during work operation, but rather supplies the system with a paint pressure which lies within certain limiting values, as a result of which the pump wear is reduced and/or pressure-loaded connector regions are protected. 
     It is provided in a further expedient embodiment that a first regulating circuit is provided for regulating the paint pressure at the outlet of the paint pump, and a second regulating circuit is provided for regulating the paint pressure at the paint dispensing line. 
     The aim is to set a substantially constant paint dispensing pressure in a paint dispensing line at a paint dispensing means, for example a paint spray gun, a paint roller or the like. The use of two regulating circuits which firstly, in the first regulating circuit, regulates the paint pressure at the outlet of the paint pump in order to provide a paint pressure in the paint hose as far as the paint dispensing unit, and secondly comprises a second regulating circuit for regulating the paint pressure for the paint dispensing line, allows the behaviour of a long and elastic paint hose between the devices, which behaviour is difficult in terms of regulation technology, to be controllable and to be capable of being used in the application. 
     Moreover, it is provided that the pressure monitor is arranged between the paint pump and the paint hose in the base station. 
     The arrangement of the pressure monitor in the base station upstream of the paint hose makes improved and simple feedback to the paint pump possible, since the complete paint pressure which prevails in the paint hose is available for the pressure monitor. Moreover, the accommodation in a compact module is made possible. 
     It is preferably provided to provide the pressure monitor in a first regulating circuit via a hydraulic control line, as measuring element, with a switch which can be operated via the said hydraulic control line. Here, the switch is set via a corresponding prestressing means in such a way that the required hysteresis during switching on and off of the paint pump is achieved. A regulating loop achieves a situation where the paint pump always provides a necessary minimum pressure in the paint hose, exceeds the said minimum pressure, and switches off at an upper limiting value of the pressure. 
     Here, the hydraulic control line is preferably configured as a flexible line, in particular as a rubber line, in order, via its inherent elastic extensibility, to buffer additional hysteresis effects and/or slight pressure fluctuations in the system, for example pulses of the paint pump. The laying of the line in the housing, in particular at potential-free locations, is also simplified in this way. 
     Moreover, it is provided in a preferred way that a control fluid in the form of oil is arranged in the hydraulic control line. Control fluids of this type afford particularly advantageous properties during the transmission of the pressure to the switch, in particular via a pressure diaphragm. 
     Furthermore, it is expedient that coupling means between the pressure monitor and the paint line are configured as a pressure diaphragm, the said coupling means being integrated substantially without edges and dead spaces into a paint duct on the pressure side of the paint pump. Stagnation points or constrictions in the region of the pressure monitor in the paint duct are disadvantageous and should be avoided, since they falsify the corresponding detected pressure. The arrangement of the coupling means as a pressure diaphragm is therefore to be carried out at the paint pump, in particular in the region of a wall of the paint dispensing means. 
     It is expedient to configure the paint pump as a peristaltic pump. Pumps of this type are established and can provide corresponding paint pressure ranges. 
     It is provided in a further preferred embodiment that, in a second regulating circuit, the pressure reducing device/pressure regulator functions as a measuring element via a hydraulic force sensor. The method of operation of the pressure reducing device/pressure regulator is explained in detail in the parallel German patent application DE 10 2014 104 982.9 which was indicated at the outset. Reference is herewith made thereto and its contents are made the disclosure and the subject matter of this application, in particular the use of the said pressure reducing device/pressure regulator in the second regulating circuit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the following text, the invention is to be explained in greater detail using a diagrammatic exemplary embodiment. 
         FIG. 1  shows an arrangement of a paint application system with a paint supply, a base station and a paint spray pistol; and 
         FIG. 2  shows a detailed illustration of the base station with paint pump and pressure monitor, and of the paint spray gun with pressure reducing device/pressure regulator. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In detail,  FIG. 1  shows a paint application system  1  which comprises a base station  2  and a paint spray gun  3  and a paint supply in the form of a paint bucket  4 . Here, the base station  2  is attached to the paint bucket  4  via a paint intake line  5  which is held in a hose guide  6 . Starting from the base station  2 , a paint pressure line  10  leads to a connector  11  on the pressure reducing device/pressure regulator  12  on the paint spray gun  3 . The pressure reducing device/pressure regulator  12  is arranged below a spray head  13 , at which the paint is atomized and dispensed in a known way by way of an air flow from a fan  14 . In order to control the dispensing of paint and/or the fan  14 , a trigger  15  is provided in the region of a handle  16 , which trigger  15  preferably operates a needle valve. If the trigger  15  is then released when paint is provided in the paint pressure line  10 , no paint is dispensed from the spray head  13 . A back-pressure of paint builds up in the pressure reducing device/pressure regulator  12  via the connector  11  and the paint pressure line  10  as far as the base station  2 . The paint pump is arranged in the base station  2 , which paint pump is then deactivated via the pressure monitor when a predefined maximum pressure is reached. 
     The technical interaction of the individual components is to be explained in greater detail in the following text using  FIG. 2 . 
       FIG. 2  shows the open housing of the base station  2  and a diagrammatically shown paint bucket  4  which is connected to the base station  2  via a paint intake line  5 . Furthermore,  FIG. 2  diagrammatically shows the paint pressure line  10  which leads from the base station  2  to a front part of a paint spray gun  3 , what is known as a front end  17 . 
     In the following exemplary embodiment, the arrangement according to the invention exhibits two regulating circuits which are coupled via the paint pressure line  10 . 
     A peristaltic pump  20  with a pump motor  21  is arranged in the base station  2 . The paint intake line  5  is guided via the pump inlet  22  to the peristaltic pump  20 , and the peristaltic pump  20  produces a paint pressure at the pump outlet  23 , which paint pressure is provided in accordance with the pump performance of the said peristaltic pump  20 . A paint pressure of 8 bar±2 bar is advantageously set as a controlled variable at this location, namely at the pump outlet  23 . Other paint pressures which are appropriate depending on the application are likewise conceivable. 
     A constituent part of the pressure monitor  30  is situated connected to the pump outlet  23 , which pressure monitor  30  records the paint pressure at the pump outlet as a measured variable via a membrane coupling  31  in a volume, through which flow passes. The paint pressure at the pump outlet  23  is transmitted via the membrane coupling  31  to a hydraulic control line  32  which leads as a flexible line which can be laid in the housing to a membrane switch  33 . An advantage of the flexible hydraulic control line  32  is that it can be routed in the housing in virtually any desired, but kink-free paths, and no potential guiding of an electric switching operation has to take place in the region of the pump outlet  23  and the paint pressure region. The hydraulic control line  32  opens onto the membrane switch  33  which has a membrane  34  on the top side. The membrane  34  is moved by way of the paint pressure which is transmitted by means of the hydraulic control line  32 , preferably is raised up, and therefore likewise lifts a spring lever  40  which is fastened to a switch  41 . The spring lever  40  can be preloaded with a spring prestress, in order to cover the necessary hysteresis range of the controlled variable. If it is raised up sufficiently, the spring lever  40  operates a button  42  on the switch  41  which then performs a switching operation on the peristaltic pump  20 , in particular on the motor  21  or its controller. The setpoint value setting of the regulating circuit can take place via the spring lever  40 , since the latter has a direct influence on the controlled variable. If the pressure in the paint at the pump outlet  23  drops again, the pressure in the hydraulic control line  22  will also drop across the membrane coupling  31 , and the membrane  34  is lowered on the membrane switch  33  in such a way that the spring lever  40  relieves the button  42  and operates the switch  41  correspondingly. 
     The paint pressure line  10  is arranged so as to start from the threaded flange  50  of the base station  2 . As a disturbance variable at the threaded flange  50  there, the pressure change Δp1 is propagated via the pressure line  10  as far as the paint inlet line  141  at the pressure reducing device/pressure regulator  12  at the front end  17 . 
     The pressure fluctuation Δp2 will prevail as a disturbance variable at the paint inlet line  141  in the pressure reducing device/pressure regulator  12 , depending on which paint pressure the paint pump of the base station  2  provides and how the pressure conditions have been set in the paint hose. Here, both hydrostatic and hydrodynamic effects play a considerable role. The pressure is propagated from the paint inlet line to the measuring element in the form of the hydraulic force sensor  160  which is configured in the present case as a diaphragm plate  151 . The diaphragm plate is understood to be a measuring element which is defined by the setpoint value setting of a prestressed spring  154 . The controlled variable is to be set in the form of from 0.3 bar to 0.4 bar in the paint outlet line  156 . To this end, the hydraulic force sensor  160  or diaphragm plate  151  is moved in the direction of the spring  154  by the disturbance variables Δp2 at the paint inlet line  141 , a slide  144  which is coupled to the diaphragm plate  151  narrowing or even closing the passage of the paint inlet line  141  to the diaphragm plate  151 . The controlled variable of from 0.3 bar to 0.4 bar which is provided in this way at the paint outlet line  156  is subject to the disturbance variable of the dispensed paint volume and the associated pressure drop which depends on whether the needle  110  at the needle valve  105  of the spray head  13  is pulled, that is to say is open or closed. If the needle valve  105  is closed, no paint discharge takes place, with the result that the pressure which is built up in the front end  17  between the paint pressure in the paint line  10  at the paint inlet line  141  and the controlled variable in the paint outlet line  156  is adjusted. As soon as a corresponding system pressure is reached, the pressure monitor  30  will likewise switch off the paint pump via the above-described embodiment and will hold the system under static pressure. If the needle  110  is then withdrawn via the trigger  15  and paint is dispensed as a result via the needle valve  105  at the spray head  13 , a volumetric flow is produced and the regulation at the second regulating circuit in the front end  17  of the paint spray gun  3  adjusts the desired paint pressure in the paint outlet line. 
     It goes without saying that, in addition to the paint spray gun  3  which is shown, other apparatuses for dispensing paint are also conceivable, for example paint rollers or paint brushes or the like which have a corresponding trigger or a paint dispensing valve and are supplied with paint via a paint pump by way of a paint hose. 
     Moreover, it is possible to operate a plurality of “paint consumers” on one paint pump, since the necessary system pressure in the paint hose or in a plurality of paint hoses downstream of a diverter at the base station with a paint pump is provided in the entire system via the pressure monitor. 
     Moreover, it is provided in one preferred embodiment to also make it possible to set the prestress of the spring lever  40  or a corresponding means, in order to influence the switching point. 
     The invention is not restricted to the embodiment which is shown; rather, it includes those refinements which make use of the concept which is essential to the invention, as indicated in the patent claims. 
     LIST OF REFERENCE NUMERALS 
     
         
           1  Paint application system 
           2  Base station 
           3  Paint spray gun 
           4  Paint bucket 
           5  Paint intake line 
           6  Hose guide 
           10  Paint pressure line 
           11  Connector 
           12  Pressure reducing device/pressure regulator 
           13  Spray head 
           14  Handle, fan 
           15  Trigger 
           16  Handle 
           17  Front end 
           20  Peristaltic pump 
           21  Motor 
           22  Pump inlet 
           23  Pump outlet 
           30  Pressure monitor 
           31  Membrane coupling 
           32  Hydraulic control line 
           33  Membrane switch 
           34  Membrane 
           40  Spring lever 
           41  Switch 
           42  Button 
           50  Threaded flange 
           105  Needle valve 
           110  Needle 
           141  Paint inlet line 
           144  Slide 
           151  Diaphragm plate 
           154  Spring 
           156  Paint outlet line 
           160  Hydraulic force sensor