Method and device for mixing at least two liquid components

Abstract

A method for mixing at least two liquid components of a two- or multi-component wet coating system, wherein a feed component under a first hydraulic pressure set at constant is fed discontinuously through a variable passage cross-section to a parent component under a second hydraulic pressure set at constant. An actual feed quantity of the feed component is detected and the feed quantity of the feed component is regulated with respect to a target feed quantity for the feed component in such a way that a timing cycle of the discontinuous feed and the passage cross-section for the feed component are influenced.

Claims

1. A method for mixing at least two liquid components in a multi-component wet coating system, said method comprising: discontinuously feeding a feed component under a first hydraulic pressure set at constant through a variable passage cross-section to a parent component under a second hydraulic pressure set at constant; detecting an actual feed quantity of the feed component; and regulating the actual feed quantity of the feed component with respect to a target feed quantity for the feed component in such a way that a timing cycle of the discontinuous feeding and the variable passage cross-section for the feed component are influenced.

2. The method according to claim 1, wherein the timing cycle comprises a temporal sequence of a feed interval and a feed pause following the feed interval and is influenced in a control-based manner such that: i) in the case of an overshoot of the target feed quantity, a duration of the feed interval is increased and the feed pause is decreased for a following timing cycle, and the passage cross-section is reduced; and ii) in the case of the actual feed quantity remaining within a predetermined target feed quantity tolerance range after a lapse of a control time or of an ascertainment of the actual feed quantity that is smaller than the target feed quantity and falling in a course of time, the variable passage cross-section is increased so that the control-based influencing can be initiated according to step i).

3. The method according to claim 1, wherein the timing cycle begins with a triggering of the feed interval which ends with a triggering of the feed pause when the actual feed quantity reaches or exceeds the target feed quantity.

4. The method according to claim 1, wherein at a start thereof, an oversize is or becomes set for the passage cross-section, so that a ratio of the actual feed quantity to the target feed quantity increasing in the course of time is reached, wherein the feed quantity reaches or exceeds the target feed quantity in less than 5 seconds.

5. The method according to claim 1, wherein an actual feed quantity/target feed quantity ratio is monitored and in the case of the actual feed quantity less than the target feed quantity and/or a reduction of the actual feed quantity/target feed quantity ratio, the passage cross-section is increased in size in such a way that the actual feed quantity/target feed quantity ratio increases during a following feed interval.

6. The method according to claim 1, wherein the variable passage cross-section is changed during the feed pause.

7. The method according to claim 1, wherein the control-based influencing of the variable passage cross-section and of the timing cycle is carried out only if a time-related proportion of the feed interval of a timing cycle is less than 90%.

8. A device for mixing at least two liquid components in a multi-component wet coating system, the device comprising: a line system for the separate feeding of the at least two liquid components under hydraulic pressure, wherein the line system comprises a parent line for a parent component or a parent component mixture and a feed line emerging into the parent line for a feed component; an on/off timing valve for closing or opening the feed line and for the discontinuous feed of the feed component; a throttle device for changing a passage cross-section of the feed line; a flow quantity meter for detecting an actual flow quantity of the feed component; and a control of the actual flow quantity of the feed component comprising an actuator which actuates the throttle device and the control controls both the actuator and the on/off timing valve in such a way that the passage cross-section of the feed line and a timing cycle of the discontinuous feed are influenced for the control-based change of the actual flow quantity.

9. The device according to claim 8, wherein the throttle device is disposed, in a feed direction, upstream or downstream of the on/off timing valve.

10. The device according to claim 8, wherein the on/off timing valve is controlled pneumatically.

11. The method according to claim 1, wherein the variable passage cross-section is changed during the feed interval after further control times when a balanced actual feed quantity/target feed quantity ratio is ascertained.

12. The method according to claim 1, wherein the control-based influencing of the variable passage cross-section and of the timing cycle is carried out only if a time-related proportion of the feed interval of a timing cycle is less than 80%.

13. The device according to claim 8, wherein the throttle device and the on/off timing valve are combined in a common component.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The embodiments disclosed herein are not intended to limit or define the full capabilities of the device or methods. It is assumed that the drawings and depictions constitute exemplary embodiments of the many embodiments of the device and methods.

(2) FIG. 1 shows a schematic diagram of a mixing device according to one embodiment;

(3) FIG. 2 shows a schematic diagram of a mixing device according to an alternative embodiment;

(4) FIG. 3 shows a schematic diagram of a mixing device according to an alternative embodiment;

(5) FIG. 4a shows a time/flow quantity diagram relating to an initial operational state of an example mixing device used with an example method;

(6) FIG. 4b shows a time/timing cycle diagram in the initial operational state;

(7) FIG. 4c shows a diagram relating to the time-related course of the ratio of the actual feed quantity to the target feed quantity in the initial operational state;

(8) FIG. 4d shows a diagram of the time-related course of the passage cross-section at the throttle device of the example mixing device;

(9) FIG. 5a shows a flow quantity/time diagram in an operational state of the example mixing device;

(10) FIG. 5b shows a timing cycle/time diagram in the operational state of the example mixing device;

(11) FIG. 5c shows a diagram relating to the time-related course of the ratio of the actual feed quantity to the target feed quantity in the initial operational state in a controlled operational state of the example mixing device;

(12) FIG. 5d shows a diagram of the time-related course of the passage cross-section at the throttle device of the example mixing device in a controlled operational state of the example mixing device;

(13) FIG. 6a shows a flow quantity/time diagram in a particular operational state of the example mixing device;

(14) FIG. 6b shows a time/timing cycle diagram in the initial operational state in a particular operational state of the example mixing device;

(15) FIG. 6c shows a diagram relating to the time-related course of the ratio of the actual feed quantity to the target feed quantity in the initial operational state in a particular operational state of the example mixing device; and

(16) FIG. 6d shows a diagram of the time-related course of the passage cross-section at the throttle device of the example mixing device in a particular operational state of the example mixing device.

DETAILED DESCRIPTION

(17) FIGS. 1 to 3 show in general, with reference number 1, three different embodiments of an example mixing device similar to one another in structure. To improve the readability of the description of the figures, the same reference numbers relating to the same or similar components are used for the three different embodiments.

(18) In the represented embodiments, mixing device 1 is used for a two-component mixing system, wherein a parent component A and a feed component B are processed. In one embodiment, parent component A is a parent lacquer, and feed component B is a hardener.

(19) An individual holding reservoir 3, 5 is stored both for parent component A and for feed component B. A piston pump 11 for parent component A and a piston pump 13 for feed component B draw respective components A, B out of reservoir 3, 5 and generate a hydraulic pressure in components A, B, wherein a pressure difference between the hydraulic pressures of 20 bar is intended to be generated. The parent component can, for example, have a hydraulic pressure of 160 bar, while the feed component has a hydraulic pressure of 180 bar. The pressure generation, which is produced by a piston pump 11, 13 in the embodiments shown in FIGS. 1-3, is designed, in certain embodiments, to provide constant hydraulic pressure conditions both for component A and also for component B during the entire operation of mixing device 1. Control-based influencing of the hydraulic pressure during the mixing method of mixing device 1 is not necessary, and in certain embodiments even ruled out. Provision can certainly be made to make the hydraulic pressure adjustable, for example, depending on a type of component A, B, with respect to physical operating conditions, such as temperature, pressure, etc., but the hydraulic pressure remains a constant as a control variable for the feed component quantity control, which is explained below.

(20) A feed line 15, 17, in which components A, B put under hydraulic pressure set at constant are located, runs in each case from respective piston pumps 11, 13 for parent component A and for feed component B. Both feed lines 15, 17 emerge into a line junction 21, in which feed component B is added discontinuously to parent component A.

(21) A measuring cell 23 for detecting the flow quantity for parent component A and a valve 25 are disposed in feed line 15 for parent component A, with valve 25 being set pneumatically. Measuring cell 23 for parent component A is connected to a control and regulating device 27 for the signal communication. Control and regulating device 27 receives flow quantity signals from measuring cell 23, processes the signals as appropriate according to the mixing method and emits control signals to valve 25 as appropriate in order to interrupt, as required, a control-based continuous flow of parent component A in feed line 15 to line junction 21. The continuity of the flow of parent component A is to be understood in such a way that, for the mixing method according to certain embodiments described herein, valve 25 is not actuated in order to set the mixing quantity ratio between component A and component B. Valve 25 does not represent throttling of the continuous flow, i.e., when the main mixing flow leaving mixing device 1 is released at a coating gun, parent component A flows unhindered under the influence of its hydraulic pressure of 160 bar towards line junction 21.

(22) Located upstream of line junction 21 in each respective feed line 15, 17 is a non-return valve 51, 52, which is intended to prevent the respective other component from getting into feed line 15, 17.

(23) Disposed in feed line 17 for feed component B is a flow quantity meter 31, which transmits an actual flow quantity signal to control and regulating device 27. A throttle valve 33 and a timing valve 35 are also disposed in feed line 17, both valves 33, 35 receiving control signals s, t from control and regulating device 27. Throttle valve 33 has an actuator, by means of which the passage cross-section (S, see FIGS. 4d to 6d) of feed line 17 can be increased or reduced in size in a control-based manner. Timing valve 35 is actuated pneumatically and, according to the embodiments shown in FIGS. 1 and 2, serves (solely) to completely open or completely close feed line 17, in order to produce the discontinuous feed of feed component B to line junction 21.

(24) Disposed downstream of line junction 21 is a mixer, such as a static mixer 37, which performs final thorough mixing of components A, B, before main mixing flow M leaves static mixer 37 and is delivered atomized to a delivery nozzle, such as a spray gun (not represented) for the purpose of coating, which is intended to be represented by arrow 41.

(25) When the delivery nozzle, such as the spray gun, is actuated, parent component A flows, as explained above, continuously past the line junction 21 into static mixer 37. The feed component B is fed discontinuously to parent component A on account of the closing and opening procedure of timing valve 35. When timing valve 35 opens, feed component B is injected into the continuous flow of parent component A on account of the hydraulic pressure difference between components A and B, as a result of which parent component B overtakes or displaces a partial region of the parent component flow, as a result of which a first mixing process takes place during the feed of feed component B.

(26) When timing valve 35 is closed, there arises in main mixing flow M, before it passes into static mixer 37, a flow section which includes solely parent component A. This inhomogeneity of the main mixing flow is partially compensated for by means of static mixer 37 and in the course of the line following the latter.

(27) Flow quantity meter 31 for feed component B constantly detects the actual feed quantity that leaves reservoir 5 of feed component B. On account of the constant flow of parent component A or on account of the measurement result of measuring cell 23 for parent component A being taken into account, a mixing quantity ratio between components A and B can be determined.

(28) At the start of the example mixing method, the passage cross-section defined by the throttle valve 35 actuated by the pneumatic actuator is set in such a way that a target feed quantity value for feed component B stored in control and regulating device 27 is reached in a short time. When this target feed quantity value is exceeded, control and regulating device 27 causes the closing of timing valve 35 in a control-based manner, wherein the actual mixing quantity ratio between components A and B does not fall abruptly, but does so only gradually on account of inertia effects, until the components present in the lines are consumed. If the actual feed quantity correspondingly falls below the target feed quantity value, control and regulating device 27 opens timing valve 35 again, in order to inject feed component B into parent component A with at all times constant pressure conditions.

(29) In order to increase the duration of the opening of timing valve 35 in accordance with the example mixing method, the passage cross-section of throttle valve 33 is reduced upon reception of a corresponding control signal s while the timing valve is closed, as a result of which the volume flow or the mass flow of feed component B is reduced with a constant hydraulic pressure. Consequently, the target feed quantity is reached only after a longer opening phase than was the case with the preceding timing cycle of timing valve 35. Once the target flow quantity value has been reached after a longer opening phase of timing valve 35, timing valve 35 is again closed, wherein the closing phase to the next opening is also shortened on account of the smaller volume flow, consequently on account of the reduction in the size of the passage cross-section. The effect of this is that the feed interval of timing valve 35 is markedly lengthened with a discontinuous feed of component B, whereas the feed pause of the timing valve is reduced. Flow sections with a pure parent component concentration are thus markedly reduced in size.

(30) The embodiments according to FIGS. 1, 2 and 3 differ only in the positioning and/or implementation of throttle valve 33 and timing valve 35. In the case of the embodiment of the mixing device according to FIG. 2, timing valve 35 is disposed upstream of throttle valve 33, whereas in the mixing device according to FIG. 3 the throttle valve function as well as the timing function are constituted in a common valve component, which both leaves the passage cross-section variable and also implements a pure opening and closing movement.

(31) The example mixing method and specific method states can be explained with the aid of the diagrams in respective FIGS. 4a to 4d and FIGS. 5a to 5d.

(32) Four diagrams are represented in each case in FIGS. 4a to 4d and FIGS. 5a to 5d, wherein the flow quantity, the timing cycle, the ratio of the actual flow quantity to the target flow quantity and the passage cross-section setting of throttle valve 33 are illustrated over time.

(33) FIG. 4a represents the flow quantity situation of parent component A and of feed component B at the start of the example mixing method during four cycles. Timing valve 35 is opened at time t.sub.1, the closing being carried out at time t.sub.2. The closed feed pause lasts until the next opening at t.sub.1. A timing cycle of the timing valve is defined by t.sub.1-t.sub.1. A duration of t.sub.1-t.sub.2 represents the feed interval, while the feed pause is defined by interval t.sub.2-t.sub.1.

(34) As can be seen in FIG. 4a, no flow for feed component B prevails before the actuation of timing valve t.sub.1, but a maximum flow quantity for parent component A. After the opening of the timing valve, the flow for feed component B abruptly increases and, more precisely, at the expense of the flow for parent component A.

(35) Considering FIG. 4c, the ratio of the actual feed quantity to the target feed quantity increases gradually with the opening of timing valve 35.

(36) If flow quantity meter 31 for the control senses that the actual flow quantity exceeds the target flow quantity, timing valve 35 is switched and closed (t.sub.2) in a control-based manner, as is shown by FIG. 4b. At this time, the flow for feed component B diminishes sharply in favor of the increase in the flow for parent component A. This timing cycle is repeated unchanged four times without changing the passage cross-section of throttle valve 33, which is indicated in FIG. 4d.

(37) It can be seen with this timing rhythm that timing valve 35 is closed during a 75% proportion of the timing cycle and is opened only during a 25% proportion of the timing cycle, which is indicated in FIG. 4b.

(38) The embodiments of the example mixing method disclosed herein extend the feed interval (t.sub.1-t.sub.2) at the expense of the feed pause (t.sub.2-t.sub.1). According to certain embodiments, this is achieved by the fact that the passage cross-section of throttle valve 33 is reduced by means of the actuator (FIG. 5d). The maximum through-flow of feed component B is thus reduced, as can be seen in FIG. 5a.

(39) If the actual flow quantity value falls below the target flow quantity value, control and regulating device 27 switches timing valve 35 into the open state (t.sub.1), which can be seen in FIG. 5b. The reduction in the flow quantity for parent component A becomes markedly smaller, because the maximum flow quantity for feed component B is reduced. At the same time, the target flow quantity is reached at a later time, which can be seen from the increased duration of the feed interval (t.sub.1-t.sub.2). After the target flow quantity value has been exceeded, control and regulating device 27 switches timing valve 35 into the closed state, as a result of which the feed pause (t.sub.2-t.sub.1) is initiated. On account of the smaller flow quantity for feed component B, the overshoot of the ratio between the actual and the target flow quantity value (FIGS. 4c and 5c) is markedly diminished, for which reason the feed pause (t.sub.2-t.sub.1) is reduced. When there is a drop below the target flow quantity value, the timing valve is opened again. The reduction in the cross-section is accompanied by an influence on the timing cycle such that the feed interval is extended to 75% of the entire timing cycle and the feed pause is reduced to 25% of the timing cycle.

(40) A special case of a specific operational situation is represented in FIGS. 6a to 6d, such that the main mixing flow is intended to serve a second delivery nozzle, as a result of which the requirement for the parent component and the feed component increases markedly. As shown in FIG. 6b, timing valve 35 is switched into the open position, during which feed component B is added to parent component A. Immediately after t.sub.1, the feed quantity for feed component B increases correspondingly at the expense of the feed quantity of parent component A. At time t.sub.x, a second consumer, such as a second spray gun, is actuated, as result of which the parent component quantity and the feed component quantity increase abruptly, as can be seen in FIG. 6a. However, FIG. 6c clearly shows that the ratio of the actual flow quantity value to the target flow quantity value drops markedly after time t.sub.x, because feed quantity B, which is permitted by throttle valve 33, is no longer sufficient to cover the total requirement of feed component B. To this extent, timing valve 35 always remains open, but the mixing quantity ratio is not reached. In this regard, the extended mixing method according to certain embodiments makes provision, after a control time tk.sub.1 of, for example, 1.5 seconds (sec.), to permit a change in the passage cross-section, i.e., an increase, for throttle valve 33 itself in the opened state of the timing valve. The stepwise increase is reached after control time t.sub.k in FIG. 6d. When the trend in the ratio of the actual to the target feed quantity value is examined according to FIG. 6c, it can be ascertained by control and regulating device 27 that the flow for feed component B is still not sufficient, for which reason a further increase in the size of the passage cross-section of throttle valve 33 is carried out after tk.sub.2. Only when the target flow quantity value is exceeded is timing valve 35 actuated again and closed in order correspondingly to initiate the example mixing method.

(41) It is thus ensured that, in the case of an excessively small feed of feed component B, an excessively small mixing ratio is compensated for.

(42) The system and the method as described herein can be designed in such a way that, once a mixing ratio has adjusted itself and scarcely any further disturbance variables occur, it is possible to dispense with the use of a timing valve. The control then takes place exclusively with the aid of throttle valve 33. It is also conceivable for the control to be extended with the aid of an additional hydraulic pressure control in certain embodiments. Both the hydraulic pressure of the feed component and also of the parent component can thereby be adjusted in a control-based manner. Moreover, in certain embodiments, an additional timing valve is provided in the parent line in order to feed the parent component in a metered manner.

(43) The features disclosed in the above description, the figures and the claims may be of importance both individually and also in any combination for the implementation of the various embodiments. The foregoing description of embodiments and examples has been presented for purposes of illustration and description. It is not intended to be exhaustive or limiting to the forms described. Numerous modifications are possible in light of the above teachings. Some of those modifications have been discussed and others will be understood by those skilled in the art. The embodiments were chosen and described for illustration of various embodiments. The scope is, of course, not limited to the examples or embodiments set forth herein, but can be employed in any number of applications and equivalent devices by those of ordinary skill in the art. Rather, it is hereby intended the scope be defined by the claims appended hereto. Additionally, the features of various implementing embodiments may be combined to form further embodiments.