EP3711864B1 - Method for controlling the supply pressure in a circulation system for a coating device and circulation system - Google Patents

Description

The invention relates to a method for regulating a supply pressure in a circulating system for a coating agent, comprising a pump, a coating device with at least one removal point, a material pressure regulator, a reservoir, a proportional pressure regulator and a control module. The proportional pressure regulator is intended to control the material flow of the coating agent pump by means of the control module in such a way that, with a regulated supply pressure in the circulation system in the coating agent, the volume flow at the material pressure regulator is regulated via a predefined setpoint in the form of a control pressure.

• auf Basis eines im Beschichtungsmittel gemessenen physikalischen Parameters und
• auf Basis von Strömungswiderständen im Umlaufsystem und
• mittels einer Zeitsteuerung abhängig vom eingestellten Versorgungsdruck

variabel einstellbar, so dass im Ringleitungssytem eine kontinuierliche Druckregelung erfolgt.The control pressure is:

• on the basis of a physical parameter measured in the coating agent and
• based on flow resistance in the circulation system and
• by means of a timer depending on the set supply pressure

variably adjustable, so that there is continuous pressure control in the ring line system.

• einen ersten Sollwert mit einem ersten zugehörigen Volumenstrom und einem ersten Steuerdruck und
• wenigstens einen zweiten Sollwert mit einem zweiten zugehörigen Volumenstrom und einem zweiten Steuerdruck.

Pressure control is enabled on:

• a first target value with a first associated volume flow and a first control pressure and
• at least one second setpoint with a second associated volume flow and a second control pressure.

Furthermore, the invention relates to a device/a system which comprises means for carrying out the method according to one of Claims 1 to 6 and a circulating system for applying the coating agent to a surface of a component.

Flowable or fluid media, such as liquids or gases, are distributed in a large number of different applications. These media are either the material to be discharged themselves or are used to transport such a material, for example as an emulsion. For example, a paint or varnish can be applied to a workpiece to be coated by spraying.

Coating with the medium, such as paint, is typically done by spraying through spray nozzles. To supply the medium to the spray nozzle as a consumer, pressurized lines are usually provided, which supply the respective spray nozzles with the medium. In order to enable safe feeding, a pressure circuit fed from a reservoir is usually set up. In this pressure circuit, the medium can be pumped around under pressure in order to be released via the spray nozzles if necessary.

However, as soon as part of the medium is removed from the circuit by one or more of the consumers, ie specifically one or more spray nozzles, the pressure of the medium therein drops. However, this also reduces the exit speed from the nozzle or nozzles. If the system pressure drops below a critical level, maintaining a desired distribution characteristic at the spray nozzles is no longer guaranteed or the removal of the medium or paint is restricted to such an extent that trouble-free operation is no longer possible.

Material pressure regulators can be used to maintain or keep the pressure in the system constant. This is in particular a fixed or adjustable pressure. For this purpose, the material pressure regulator has a pressure chamber whose volume or cross section is variable. In this way, the pressure at the inlet of the pressure chamber can be adjusted. This is achieved by means of a counter-pressure to the pressure of the medium, which is set by applying a pressure medium, such as usually compressed air.

This pressure medium represents a counter-pressure to the pressure of the medium. This allows the cross section of the pressure chamber to be adjusted via movable wall sections as a function of the pressure ratio. If the pressure of the medium at the inlet of the Material pressure regulator compared to the back pressure, the cross section of the pressure chamber is reduced so that the pressure increases again. In this way, the pressure can be kept constant. The volume flow varies.

Due to physical reasons, a volume flow is set at the material pressure regulator, which results not only from the material properties but also from the pre-pressure of the medium and the pressure in the pressure chamber of the material pressure regulator.

The pressure build-up in the ring main is usually carried out by pumps that set a pressure-controlled inlet pressure at the beginning of the ring main. The amount of medium flowing through the material pressure regulator therefore results in a given system during operation from the set inlet pressure at the beginning of the ring line, the withdrawals from the ring line and the set outlet pressure of the material pressure regulator. The setpoint on the material pressure regulator is usually preset for a system.

A minimum volume flow in the ring line is necessary for paints in order to keep them moving and to avoid segregation. For this purpose, manufacturer-specific specifications regarding the minimum volume flows must be observed.

The disadvantage of the method described above is that even when no material is to be removed, material is conveyed through the ring line at high pressure. This results in unnecessary energy consumption, wear of the medium due to shearing and abrasive wear of the components. During longer breaks in painting or at the weekend, the material pressure regulators are therefore often completely deactivated (opened) and the pump switched from pressure control to volume flow control. The disadvantage of this method is that the pressure is no longer regulated and system-related faults or interventions in the system can lead to excess pressure.

In addition, the process only delivers a satisfactory result for one operating point in the painting shop, since different volume flows are set at the material pressure regulator with changing inlet pressures or paints with different viscosities.

Out of U.S. 2006/0177565 A1 a paint circulation system for circulating and dispensing paint is known. The circulation system includes an operating loop (operating loop 14) and an idling loop (idling loop 20). The system also generally includes a pump, a transmitter, a controller, a transducer, and a regulator. In the Low pressure is maintained in the idle loop to maintain circulation and prevent paint settling. In a first embodiment, a circulation system is disclosed in which a pump is provided for both the idling circuit and the working circuit. The pump thus feeds both circuits simultaneously. The pressures and volume flows in both systems are therefore not independent of each other, but influence each other. In a second embodiment, two completely independent systems are provided with their own pumps, controllers, sensors and material containers. The two independent systems are complex overall and can only be switched alternately. Out of U.S. 4,019,653A discloses a paint sprayer for proportioning and mixing two paint components for delivery to a spray gun. The two components are a color component and a catalyst component, which when mixed are highly reactive and have a short pot life. Catalyst and color component are connected to a spray device via a mixing chamber.

Out of DE 10 2017 110 430 A1 a back pressure regulator for regulating the pressure of a liquid is known, in which the walls of the pressure chambers are formed from a plurality of movable sections.

Out of EP 1 789 202 B2 an ink circulation system and method is known in which, in a first mode, which can be referred to as pressure or working mode, the pressure is kept constant by means of a material pressure regulator. In a second mode, which may be referred to as flow, sleep, or pause mode, the fluid pressure regulator is disabled.

• Im Druck- oder Arbeitsmodus der Druck im Farbumlaufsystem konstant auf einem Niveau gehalten, welches auch bei mehreren Verbrauchern, beispielsweise mehreren an das Farbumlaufsystem angeschlossenen Farb-Spritzpistolen, einen gleichbleibenden Farbaustrag gewährleistet. Dieser gleichbleibende Farbaustrag bzw. das für den gleichbleibenden Farbaustrag erforderliche Druckniveau wird auch dann realisiert, wenn eine unterschiedliche Anzahl von Spritzpistolen unterschiedlich stark im Einsatz ist, die pro Zeiteinheit aus dem Farbumlaufsystem abgegebene Farbmenge also variiert.
• Im Durchfluss- oder Energiesparmodus, beispielsweise im arbeitsfreien Wochenendbetrieb, wird bei niedrigem Druck eine konstante Farbmenge durch das Farbumlaufsystem gepumpt um so einen Minimal-Umlauf zu realisieren, der ein Entmischen der Farbe oder sonstige Störungen verhindert.

This achieves that:

• In the pressure or working mode, the pressure in the paint circulation system is kept constant at a level which ensures consistent paint discharge even when there are several consumers, for example several paint spray guns connected to the paint circulation system. This constant paint discharge or the pressure level required for the constant paint discharge is also realized when a different number of spray guns are used to varying degrees, ie the amount of paint delivered from the paint circulation system per unit of time varies.
• In flow or energy-saving mode, for example during non-working weekend operation, a constant quantity of paint is pumped through the paint circulation system at low pressure in order to achieve minimal circulation, which prevents the paint from segregating or other disturbances.

A dosing pump connected upstream of the coating device can—in the activated state of the material pressure regulator—maintain a predetermined medium pressure between said dosing pump and the material pressure regulator. The target value of the medium pressure is therefore set upon activation. In other words, the medium pressure at the material pressure regulator is only switched off to allow the medium to flow freely. The medium pressure is not regulated for this purpose on the material pressure regulator.

This is disadvantageous because the material, such as paint or varnish, can be conveyed through the ring line at unnecessarily high pressure, which can result in energy losses, wear of the medium due to shearing and abrasive wear of all parts of the ring line system, such as the dosing pump, material pressure regulator and seals.

Abrasion can be influenced by a number of factors, such as medium pressure, coefficients of friction, temperature, viscosity of the medium and surface properties of the inner surface of the entire circulating system that is to be in contact with the medium. Due to unfavorable installation of the valve in the circulation system, e.g. B. directly behind bends or branches, there is no uniform flow of the material pressure regulator, which can cause high inaccuracies in the volume flow.

In the fully deactivated, i. H. When the material pressure regulator is open, the dosing pump is also switched from pressure control to volume flow control, so that the medium pressure is no longer controlled. This can result in system-related faults or interventions in the circulating system, which can lead to excess pressure. It is also disadvantageous that different volume flows are set at the material pressure regulator with changing inlet pressures or media of different viscosities.

The object of the present invention is to overcome these disadvantages and to propose a new, improved method for regulating the supply pressure in a circulation system, the volume flow of which should remain constant at the material pressure regulator if there is no paint removal from the ring line, regardless of the media pressure set at the inlet of the ring line. Furthermore, a circulation system is to be proposed with which the new method can be implemented.

This object is achieved by a method having the features of claim 1 and a circulating system having the features of claim 7. The subclaims represent advantageous features of the invention.

Definitions and terms:

• The term "circulation system" is intended to mean a pressure circulation system with associated lines, coating device, pump, material pressure regulator, reservoir for the coating agent and control. In this pressure circuit system, the medium can be circulated under pressure in order to optionally be discharged via the coating device.
• A so-called back pressure regulator (BPR = Back Pressure Regulator) is referred to as a material pressure regulator, with which the medium pressure in the circulation system can be maintained or kept constant. The material pressure regulator is controllable.
• The term "pressure mode", hereinafter referred to as "operating mode" or "regulated operation", refers to a state of the circulating system in which the medium pressure (supply pressure) in the circulating system is maintained or kept constant.
• The term “flow mode”, also called “energy-saving mode” below, refers to a condition of the circulating system with a necessary minimum flow rate of the medium in order to keep it in constant motion and to prevent unwanted segregation.
• The supply pressure is the pressure with which a pump integrated into the paint circulation system delivers the medium to be pumped.
• A supply pressure setpoint is understood to be a pressure that the pump is intended to realize by increasing or reducing its pump capacity. The term "first supply pressure setpoint" is intended to provide a supply pressure that is as constant as possible, e.g. B. 5 bar can be understood throughout the circulation system, which corresponds to the operating mode (regular operation). In contrast, the term "second supply pressure target value" designates a minimum target value (e.g. 0.5 bar) which corresponds to the energy-saving mode.
• A control pressure is understood to mean a pressure that is provided by a pressure regulator as a control variable (fixed control signal) for controlling the material pressure regulator.
• Any pressure regulator suitable for the requirements can be used as the pressure regulator. The use of a proportional pressure regulator is preferred.
• The volume flow, also known as the flow rate, indicates how much volume of a medium, for example paint or varnish, is transported through a predetermined cross-section of the ring main per period of time.
• A programmable logic controller (PLC) is a digital control device that can be used to switch from operating mode to weekend mode using sensors and actuators.
• A coating agent is understood to mean any medium that is suitable for being conveyed through the ring main system and being applied by means of consumers, for example spray guns connected to the ring main system. In particular, paints such as dispersion and latex paints, lacquers, glazes, solvents, water, water with cleaning agents, iron or zinc phosphating agents, wood preservatives, etc. can be provided as coating agents. The paint can be, for example, a base paint, clear paint, effect paint, a mica paint or a metallic paint. The paints can be solvent-based or water-based.

• auf Basis eines im Beschichtungsmittel gemessenen physikalischen Parameters;
• und auf Basis von Strömungswiderständen im Umlaufsystem;
• und mittels einer Zeitsteuerung abhängig vom eingestellten Versorgungsdruck.

The control pressure can be variably adjusted as follows:

• on the basis of a physical parameter measured in the coating agent;
• and based on flow resistances in the circulation system;
• and by means of a time control depending on the set supply pressure.

This enables continuous pressure regulation in the ring line system to at least two setpoint supply pressure values with associated volume flows, the pressure regulation being dependent on the control pressure provided in each case by the pressure regulator.

Thus, the regulation for a first supply pressure target value takes place with a first associated volume flow and a first control pressure. For a second supply pressure setpoint, the regulation takes place with a second associated volume flow and a second control pressure.

Analogous to this, the control is also possible for other setpoints with associated volume flows and control pressures coordinated with them.

Which of the two (or additional) control pressures the material pressure regulator uses depends on one or more boundary conditions, namely the parameters of the coating agent and the flow resistances in the circulating system and a timing control.

Switching from the pressure or work mode to the flow or rest mode can take place automatically via control modules, for example via a PLC (programmable logic controller). The volume flow can be reduced by reducing the supply pressure of the pump. Since the delivery rate drops when the line pressure is reduced, the material pressure regulator is opened further, i. H. the control pressure is reduced to such an extent that the volume flow at the material pressure regulator remains constant. The PLC allows speed control with controlled acceleration or deceleration.

A control algorithm can be used in the programmable logic controller SPS to create a control program with which the control pressure at the material pressure regulator can be called up using various parameters such as pump pressure, volume flow, viscosity, geometric conditions of the entire circulation system, etc.

It is of great advantage that it is no longer necessary to completely deactivate the material pressure regulator and to switch the pump to the disadvantageous volume flow mode. An energy-saving mode can thus be implemented simply by lowering the supply pressure and reducing the control pressure on the material pressure regulator.

The flow resistances always lead to energy losses. The causes for this are in particular the expansion or contraction of the medium, changes in flow cross sections, turbulence due to changes in flow direction and energy losses due to friction in general. The local turbulence occurs, for example, at the deflections, cross-sectional constrictions, shut-off elements, branches, which, together with the length and diameter of the pipeline, the pressure drop between the influence the pump and material pressure regulator. In the case of the pipe sections whose inlet and outlet differ in height position, the difference in medium pressure at both ends also depends on its hydrostatic pressure.

According to the invention it is provided that when there is no or reduced discharge of coating material from the at least one removal point, the supply pressure is regulated down to a low pressure and the control pressure is set to the second control pressure by means of the material pressure regulator. The second control pressure and the supply pressure are selected in such a way that a constant volume flow is achieved in the circulating system.

To put it simply, a lack of or reduced material removal at the point of use causes the proportional pressure regulator to switch to the second control pressure. The second control pressure is then used as a basis for setting the pump performance of the pump to the second supply pressure target value, for example 0.5 bar. The pump then starts to work in flow or energy saving mode. In order to avoid the control pressures in the proportional pressure regulator switching back and forth, it can be provided that a time offset is provided as an additional condition for switching. Switching from the second to the first control pressure, and thus indirectly also switching from the working mode to the idle mode, takes place when, on the one hand, no more coating material emerges from a delivery point and, on the other hand, a predefined time interval, for example 10 minutes, has expired.

Depending on the properties of the coating agent to be conveyed, the volume flow is selected in such a way that a minimum volume flow is conveyed that is required to avoid disturbances in the circulation system. The minimum volume flow required depends in particular on the properties of the coating material and the circulation system. Paints and varnishes tend to separate and stick more than water or cleaning agents. The minimum volume flow for paint is therefore generally higher than the minimum volume flow for water or cleaning agent with the same circulation system. Since the properties of the system and coating agent are already known, corresponding default values with regard to the minimum volume flow can be predefined and then implemented when the control switches from "working mode" to "sleep mode". The automatic tracking of the target value on the material pressure regulator ensures that a process-related, necessary, minimum flow rate is set, energy is saved and component wear is reduced of the entire circulation system is reduced. The pressure control is also maintained at a lower level.

It is of particular advantage that the continuous pressure control in the ring main system enables a flexible change to both operating states, namely pressure mode and flow mode. Depending on which mode (pressure mode or flow mode) is currently activated, the regulation of the pressure only causes a change in the currently activated circuit. Contrasted with the out US 2006/0177565 A known system, in which an adjustment of the controller causes systemic pressure changes in both circuits, there is no mutual influence of the circuits in the system according to the invention. Undesirable pressure and flow fluctuations, which have an impact on the aging of the paint, are thus avoided and the paint in the circulation system is protected.

The control pressure at the material pressure regulator is preferably set to the first control pressure when the coating medium emerges from the at least one removal point. The control thus reacts to the start of a coating process, ie the emergence of coating material from the point of delivery, in that the first control pressure is set on the material pressure regulator. This first control pressure is provided by the proportional pressure regulator and acts on the membrane of the material pressure regulator. It is selected in such a way that it enables the coating device to be operated in a controlled manner with the supply pressure being as constant as possible in the entire supply line. On the basis of the first control pressure, the first supply pressure target value is specified, ie the specification for the pump with regard to the quantity to be delivered. The pump is thus prompted by means of the first control pressure to implement a first supply pressure target value, for example 5 bar, and thus to work in the pressure or working mode.

Furthermore, a bypass routed around the material pressure regulator can be arranged on the ring line, which bypass comprises a valve, for example a ball valve, with which said bypass can be activated. The valve can also be actuated automatically--if there is no material discharge from the at least one removal point--by it being controlled by the control module (PLC). The activated bypass remains in place until the pick-up point, for example a paint outlet nozzle arranged on a robot arm, is actuated by remote control and releases the outlet of coating material. If removal of the coating agent is detected, the system can automatically switch to a higher pressure and the bypass can be deactivated.

If no coating agent is required for a certain period of time, e.g. 30 minutes, or at predefined idle times, e.g. at night or at the weekend, the ball valve can be opened by the control signal coming from the control module (PLC) and at the same time the supply pressure can be reduced to the second, minimum setpoint ( e.g. 0.5 bar) can be set. The material pressure regulator can remain in operation.

Provision can be made for the ball valve to remain closed when the coating device is in the operating mode. The control module (PLC) controls the pump speed accordingly so that the supply pressure (e.g. 5 bar) is maintained in the circulation system.

In addition, the ball valve can allow overpressure relief if the supply pressure at the outlet of the coating material pump increases unexpectedly (e.g. as a result of a technical error). If an increase in pressure is detected, the ball valve can then be controlled accordingly by a control signal (from the PLC control module).

The control pressure (back pressure) can be controlled via the preferably electronically controlled, pneumatic proportional pressure regulator arranged on a pressure line (control line). The proportional pressure regulator is used to adjust the pneumatic control pressure proportionally to a specified setpoint. The input variable is continuously compared with the output pressure. If a control difference occurs, the proportional pressure controller adjusts. With regard to its working accuracy, a proportional pressure regulator designed for a maximum pressure of 5 or 6 bar is preferably selected. A pressure sensor can be arranged in front of the dynamic pressure regulator. In this case, the material pressure controller located at one end of the ring line acts as a dynamic pressure controller, which compares a "dynamic pressure signal" with a setpoint and outputs a corresponding control signal for controlling the proportional pressure controller. As a result, better control behavior can be generated.

The first and the second control pressure can be calculated using a control algorithm, which can be created using the physical parameters of the coating agent and the flow resistances in the circulating system and the set supply pressure.

The control algorithm can be combined by creating a formula or in tabular form. For example, a simple formula for both operating and energy saving modes can be given by specifying the two specified supply pressures, the Volume flows and pump speed or the time can be created and programmed. The stored data can be continuously read by the computerized control module (PLC).

Furthermore, the control pressure on the material pressure regulator can be called up via a graphic characteristic field or via a simple flow measurement.

In the method according to the invention, the first control pressure and/or the second control pressure and/or the pressure (P) is preselected via a time and/or a calendar time setting. In the case of exclusive control by means of a timer, provision can be made, for example, for the control pressure to be set every day at 6:00 a.m. to a value which subsequently sets the supply pressure setpoint at the pump to 5 bar (working mode). As a further time setting, it can be provided that the control pressure is set to a value every day at 5 p.m.

In addition to time control, the control pressure can be selected on the basis of characteristic curves, a pressure measured at the pump or in the ring line system, the geometric conditions of the ring line system, the viscosity of the medium or other parameters.

• eine Beschichtungsmittelpumpe,
• eine Beschichtungseinrichtung mit wenigstens einer Abnahmestelle,
• einen Materialdruckregler,
• einen Vorratsbehälter für das Beschichtungsmittel,
• einen Proportionaldruckregler und
• ein Steuerungsmodul.

To carry out the method, a circulation system for the application of a coating agent, such as body paint, can be installed, which at least includes the system parts listed below:

• a coating agent pump,
• a coating device with at least one removal point,
• a material pressure regulator,
• a reservoir for the coating agent,
• a proportional pressure regulator and
• a control module.

The coating medium pump is preferably an electrically operated double-piston pump, which can be equipped with a pressure sensor.

The coating device can consist of a number of pick-up points, for example a number of spray devices, which each comprise a spray gun or a robot arm with a spray nozzle.

The material pressure regulator is used to regulate the dynamic pressure at the end of the coating agent flowing in the line system. With a pneumatic material pressure regulator, the medium pressure can be controlled remotely, e.g. for medium pressures dependent on speed or volume flow. The material pressure regulator can be regulated via an electropneumatic converter or preferably via a direct control line (for example with compressed air). An advantage over manual control is that the pressure level can be lowered even if no coating material is removed.

The proportional pressure regulator is preferably a pneumatic type pressure regulator which regulates the output signal in proportion to an electrical input signal. In particular, piezo-controlled proportional pressure regulators are used with different pressure conditions, since piezo technology enables very precise and rapid regulation to the desired pressure.

The control module (PLC) is preferably a digital, programmable logic device for controlling and/or regulating the circulation system. If the system (circulation system) works with explosive or combustible substances, such as paint with solvents, the control module is preferably placed in a control room outside the hazardous area.

The control pressure (pneumatic back pressure) is preferably adjustable via a pressure regulator, for example via an above-mentioned electronically controlled, pneumatic proportional pressure regulator located on a pressure line (control line) or purely mechanically, for example via a spring that can be tensioned by a motor.

A pressure reducer, which is connected upstream of the proportional pressure regulator, can also be arranged on the pneumatic control line. With the help of the pressure reducer, the outlet pressure of the compressed air can be regulated and possibly reduced if the outlet pressure exceeds its setpoint.

Pressure sensors, pressure regulators and microcontrollers, possibly additionally a viscosity measurement and/or a volume flow measurement, can also be used to set the pneumatic control pressure.

The control pressure can also be regulated via a flow measurement, in that a flow meter records a volume flow in a unit of time.

At least one flow meter can be arranged on the ring line of the circulating system, with which a flow rate, ie a volume flow (for example liters per minute) can be recorded. The flow meter can be equipped with an analog or digital interface.

The flow meter can, for example, work according to the toothed wheel or oval wheel principle and can be installed in the ring line and connected to the control module.

"Non-invasive" flow meters, such as ultrasonic flow sensors, can also be used.

The flow meter is preferably placed between the coating device and the material pressure regulator.

With the programmable logic control module (PLC) built into the circulation system, the coating agent pump and the proportional pressure regulator can be controlled wirelessly or via lines using the data from the flow sensor and pressure sensor.

With the material pressure regulator, the medium pressure in the circulation system can be maintained or kept constant. This can in particular be a fixed or adjustable medium pressure. For this purpose, the material pressure regulator has a pressure chamber whose volume or cross section is variable. In this way, the pressure at the inlet of the pressure chamber can be adjusted. This is achieved by means of a counter-pressure to the pressure of the medium, which is set by applying a pressure medium, such as usually compressed air. This pressure medium represents a counter-pressure to the pressure of the medium. This allows the cross section of the pressure chamber to be adjusted via movable wall sections as a function of the pressure ratio. If the pressure of the medium at the inlet of the material pressure regulator falls compared to the back pressure, the cross section of the pressure chamber is reduced so that the pressure rises again. In this way, the pressure can be kept constant. The volume flow varies. For physical reasons, a volume flow is set at the material pressure regulator, which results from the pre-pressure of the medium and the pressure in the pressure chamber of the material pressure regulator as well as from the material properties (parameters of the medium).

At least one coating medium pump, such as a piston, eccentric worm or gear pump, can be provided for the material transport. An electrically driven double-piston pump is preferably provided, which reduces the pulsation that negatively influences the spray pattern. The pump automatically reduces its speed when a specified pressure is reached and automatically increases it when the medium pressure drops below the specified setpoint.

An electronic volume flow sensor, for example a volume flow transmitter based on the differential pressure, Coriolis, ultrasound, turbine principle or the variable area measuring principle, which can also include additional connections for pressure and/or temperature transmitters, can be used to record the volume flow.

The viscosity of the medium can be automatically detected, for example, using a viscometer with moving measuring bodies that is known per se.

Overall, a process and circulation system was created in which the material pressure regulator (BPR) continuously regulates the back pressure at the end of the supply line. The pressure is not regulated at a single defined pressure level, but at different pressure levels that can be adapted to different requirements. For example, in pressure mode, a high pressure can be maintained to enable a uniform supply of coating agent. At another time, a minimum circulation of the coating agent can be implemented analogously to this in the energy-saving mode at a reduced pressure level. This effectively avoids the initially explained disadvantages of deactivating the material pressure regulator.

Fig. 1

Schema eines Umlaufsystems in einer ersten Ausführung, mit Steuerung;

Fig. 2

das Umlaufsystem gemäß Fig. 1, in einer zweiten Ausführung, mit eingebautem analogen Durchflussmesser, ebenso schematisch;

Fig. 3

das Umlaufsystem gemäß Fig. 1, in einer dritten Ausführung, mit eingebautem digitalen Durchflussmesser und

Fig. 4

das Umlaufsystem gemäß Fig. 1, in einer vierten Ausführung, mit eingebautem Bypass.

The invention is explained in more detail in some exemplary embodiments with reference to the drawing. The figures show:

1

Schematic of a circulation system in a first embodiment, with control;

2

the circulation system according to 1 , in a second version, with built-in analog flow meter, also schematic;

3

the circulation system according to 1 , in a third version, with built-in digital flow meter and

4

the circulation system according to 1 , in a fourth version, with built-in bypass.

The 1 schematically shows a circulation system 100, comprising a ring line 12, a reservoir 16 with an agitator (not shown) for homogenizing a medium, such as paint (e.g. car paint), a coating medium pump 18, a coating device 10 and a material pressure regulator 15.

In order to avoid deposits of pigments in the ring line 12, the minimum flow rate of the medium in the ring line 12 should exceed the value 0.35 m/s. The amount of medium in circulation, such as paint or varnish, should also be significantly higher than the purchase amount.

The coating device 10 includes several, in the present case four removal points 11 (spray applicators) for coating work parts with the car paint. The coating device 10 (spray booth) is part of a painting system for painting bodywork components.

The material pressure regulator 15 comprises a schematically indicated pressure chamber 29 with a variable volume. The medium pressure is applied to an inlet 28 of the pressure chamber 29 via a pressure line 25 with a control medium (compressed air), with which a counter-pressure (control pressure PS) to the supply pressure P is exerted. The compressed air is guided from a pressure container 17 via a pressure reducer 21 and a proportional pressure regulator 22 downstream of the pressure reducer 21 to the lateral pressure piston of the material pressure regulator 15 (not shown here). The two in one symmetrically arranged pressure pistons exert pressure on the wall of the pressure chamber 29 perpendicular to the direction of flow of the coating agent (paint, varnish), whereby the cross section of the pressure chamber 29 can be adjusted via movable wall sections depending on the pressure ratio.

The task of the pressure reducer 21 is to regulate or reduce the different pressure influences on its input side, so that the output pressure (of compressed air) does not exceed a predetermined value. The pressure reducer 21 is controlled without auxiliary power. The control medium of the pressure reducer 21 is the compressed air itself. Its valve closes when the pressure behind the valve increases.

The electronically controlled proportional pressure controller 22 is used to set the pneumatic control pressure PS proportional to a specified setpoint. The pressure at the working connection is recorded by means of a pressure sensor (not shown) and compared with the target value. A first control pressure PS1 corresponds to the regular operation of the coating device 10 with a supply pressure P1 that is as constant as possible. A second control pressure PS2 is defined to represent the minimum supply pressure P2 (power saving mode). Any deviations of the pressure P1 or P2 from the respective desired value are corrected by means of the proportional pressure controller 22, so that the pressure P1 or P2 is brought back to the desired value.

The coating medium pump 18 is equipped with an external pressure sensor 20 and with digital inputs and outputs (not shown).

Furthermore, the 1 a programmable logic control module 19 (PLC) can be seen, with which the proportional pressure regulator 22 and the coating agent pump 18 (at the inlet and outlet of the pump) are controlled via lines 27 or wirelessly.

The 2 shows the same circulation system 100 with the difference that a flow meter 26 with analog interface is placed on the ring line 12 between the coating device 10 and the material pressure regulator 15, which is also controlled by the control module 19 (PLC). The flow meter 26 records the flow rate, ie a volume flow.

On the ring line 12 between the coating device 10 and the material pressure regulator 15 is according to 3 a flow meter 26 arranged with a digital interface and a user-friendly, large display.

Finally is in 4 a circulation system 200 is shown, which consists of the same parts as in 1 are shown, there is a bypass 23 guided around the material pressure regulator 15 being arranged on the ring line 12 . A ball valve 24 is mounted on the bypass 23, with which the bypass 34 can either be blocked or released.

How it works (in connection with Figures 1 to 3):

A first pressure regulation of the liquid medium, here: car paint, is carried out at a beginning 13, ie at the pressure sensor 20 of the coating agent pump 18, and a second pressure regulation at an end 14 of the circulating system 100. The setpoint at the material pressure regulator 15 is set to a first supply pressure setpoint P1 adapted to the pressure mode of the coating device 10 and to a second, significantly lower supply pressure P2 (second supply pressure setpoint P2) corresponding to weekend operation. In a preferred exemplary embodiment, the first setpoint supply pressure value P1 is 5 bar and the second setpoint supply pressure value P2 is 0.5 bar. In this case, the values P1 and P2 are matched to one another in such a way that the minimum flow rate of the medium in the ring line 12 is maintained at 0.35 m/s. Depending on the individual requirements of the circulating system, other setpoint supply pressure values P1, P2 or minimum flow rates can also be predefined.

The material pressure regulator 15 is thus activated in both states, namely in regular operation and in weekend operation. There is no deactivation of the material pressure regulator 15 (BPR). With the minimum medium pressure P2=0.5 bar, the medium located in the ring line 12 can circulate without losing its material properties.

If there is no material discharge, the control pressure at the material pressure regulator 15 is regulated by means of the programmable logic control module (PLC) in such a way that a constant volume flow is set regardless of the set supply pressure.

How it works (in connection with Figure 4):

The ball valve 24 which is arranged on the bypass 23 is closed when the coating device 10 comprising a plurality of delivery points 11 is in regular operation and requests the paint. The paint (coating agent 30) is shown schematically in Figures 1 to 4 shown as a spray jet. The control module 19 (PLC) controls the speed of the coating agent pump 18 in such a way that the supply pressure P1 (5 bar) in the circulation system is kept constant.

If no more coating agent is requested, the ball valve 24 opens automatically by a control signal coming from the control module 19 (PLC) and at the same time the first setpoint supply pressure value P1 is switched to the second setpoint value P2. The circulation system is thus in the energy-saving mode with the minimum flow rate. The minimum flow rate of the medium in the ring line 12 should be at least 0.35 m/s for some paints, for example.

The bypass 23 with the ball valve 24 is used in a timing control. The ball valve 24 remains open, for example, on weekends or holidays to maintain the minimum supply pressure in the circulating system.

Reference List

10

coating device

11

delivery point

12

loop line

13

Beginning

14

End

15

material pressure regulator

16

reservoir

17

pressure vessel

18

pump

19

Control module SPS (PLC)

20

pressure sensor

21

pressure reducer

22

pressure regulator

23

bypass

24

ball valve

25

Pressure line (compressed air)

26

flow meter

27

Lead (of 19)

28

Entrance (of 29)

29

Hyperbaric Chamber (of 15)

30

coating agent

100

circulation system

200

circulation system

P

supply pressure

P1

first supply pressure setpoint

p2

second supply pressure setpoint

hp

control pressure

PS1

first control pressure

PS2

second control pressure

Claims (14)

1. A method for controlling a supply pressure (P) in a circulation system (100; 200) for a coating agent (30), comprising:

   - a pump (18),

   - a coating device (10) with at least one delivery point (11),

   - a material pressure regulator (15),

   - a supply tank (16),

   - a pressure regulator (22) and

   - a control module (19),

   wherein the pressure regulator (22) is provided for controlling the material flow of the coating medium pump (18) by means of the control module (19) in such a way that, in the case of a supply pressure (P) regulated in the circulation system (100, 200) in the coating medium (30), the volume flow at the material pressure regulator (15) is regulated by means of a predefined setpoint in the form of a control pressure (PS),

   wherein the control pressure (PS) can be variably adjusted on the basis of a physical parameter measured in the coating medium

   as a function of the set supply pressure (P), so that a continuous pressure control is achieved in the circulation system (100, 200) based on:

   - a first setpoint (P1) with a first associated flow rate and a first control pressure (PS1) and

   - at least a second setpoint (P2) with a second associated flow rate and a second control pressure (PS2),

   and wherein, in the absence of or reduced discharge of coating agent (30) from the at least one delivery point (11), the supply pressure (P) is regulated down to a low pressure and the control pressure (PS) is set to the second control pressure (PS2) by means of the material pressure regulator (15), with the second control pressure (PS2) and the supply pressure (P2) being selected in such a way to achieve a preset volume flow (Vk) in the circulation system (100, 200) and wherein the constant volume flow (Vk) is selected as a function of the properties of the coating agent (30) to be conveyed in such a way that a minimum volume flow (Vmin) required to avoid disturbances in the circulation system (100, 200) is conveyed,

   characterized in that the control pressure (PS) is set

   - on the basis of flow resistances in the circulation system (100, 200);

   - and by means of a time control as a function of the set supply pressure (P).
2. The method as claimed in claim 1, characterized in that, when coating agent (30) is discharged from the at least one delivery point (11), the control pressure (PS) is set to the first control pressure (PS1) by means of the material pressure regulator (15), wherein the first control pressure (PS1) is selected in such a way that it enables a control operation of the coating device (10) with a supply pressure (P1) that is as constant as possible in the entire supply line.
3. The method as claimed in claim 1 or 2, characterized in that, in that, in the absence of material outflow from the at least one delivery point (11), a bypass (18) is activated around the material pressure regulator (15) and is maintained until the at least one delivery point (11) is activated and coating medium (30) is discharged from the delivery point (11).
4. The method as claimed in claims 1 to 3, characterized in that the control pressure (PS) is controlled via the, preferably pneumatic, pressure regulator (22) arranged on a pressure line (25), and the material pressure regulator (15) acts as a back-pressure regulator at the end of the line.
5. The method as claimed in claims 1 to 4, characterized in that the first and second control pressures (PS1, PS2) are calculated via an algorithm generated on the basis of the physical parameters of the coating agent (30) and the flow resistances in the circulation system (100; 200) and the set pressure (P) and/or are retrieved via a characteristic curve field or via a flow measurement.
6. The method as claimed in claims 1 to 5, characterized in that the first control pressure (PS1) and/or the second control pressure (PS2) and/or the pressure (P) is preselected via a time and/or a calendar time setting.
7. A data processing apparatus/system comprising

   - means for carrying out the method according to any one of claims 1 to 6 and

   - a regulation of the supply pressure (P) in a circulation system (100; 200) comprising a material pressure regulator (15), a pressure regulator (22) and a control module (19).
8. A circulation system (100; 200) comprising

   - a coating agent pump (18),

   - a coating device (10) with at least one delivery point (11),

   - a material pressure regulator (15),

   - a supply tank (16),

   - a pressure regulator (22),

   - a control module (19) and

   - a data processing apparatus/system as claimed in claim 7.
9. The circulation system (100; 200) as claimed in claim 8, characterized in that the control pressure (PS) can be controlled via the, preferably pneumatic, pressure regulator (22) located on the pressure line (25).
10. The circulation system (100; 200) as claimed in claim 8 or 9, characterized in that at least one analogue or digital flow meter (26) is provided on the loop line (12) and is preferably positioned between the coating device (10) and the material pressure regulator (15).
11. The circulation system (100; 200) as claimed in any one of claims 8 to 10, characterized in that a programmable logic controller module (19) is installed in the circulation system (100) and is connected via lines (27) at least to the coating agent pump (18), the pressure sensor (20) and the pressure regulator (22).
12. The circulation system (100; 200) as claimed in any one of claims 8 to 11, characterized in that the coating agent pump (18) and/or the pressure sensor (20) and/or the pressure regulator (22) and/or the flow meter (26) are connected wirelessly by the control module (19)
13. The circulation system (100; 200) as claimed in any one of claims 8 to 12, characterized in that a bypass (23) guided around the material pressure regulator (15) is arranged on the loop line (12) and that the bypass (23) can be activated by actuating a valve (24).
14. The circulation system (100; 200) as claimed in any one of claims 8 to 13, characterized in that the material pressure regulator (15) is preferably a back-pressure regulator with a variable pressure chamber (29) having at least one flexible wall, so that the volume of the pressure chamber (29) can be varied.

Images