The subject matter disclosed herein relates to a method and a device for mixing at least two liquid components. In particular, the subject matter disclosed herein relates to a method and a device for mixing at least two liquid components of a two- or multi-component wet coating system and a two- or multi-component mixer of a two- or multi-component wet coating system. Such a method is used for example in a two-component lacquering system in the wet area, wherein hydraulic conditions with a delivery pressure of the liquid components of, for example, 50 bar to 530 bar, and, in one embodiment, 160 bar to 180 bar, are built up. At least two liquid components are brought together in a common flow and then mixed in a mixing block, in order that the component mixture can then be atomized at a nozzle, for example, of a spray gun. Such a system is used to coat large-area components, such as steel girders, or small-area components, such as plastic components, for example, in automotive engineering. In one embodiment, the coating is formed by a mixture of the components which is as homogeneous as possible.
In the area of the wet lacquering technique, two liquid components separated from one another are united at a feed point, whereby a feed component, such as a hardener, a thinner or a colorant, is added to a parent component, such as a lacquer component A. The two components are conveyed, for example, with a piston pump. For a discontinuous feed of the feed component, an inlet valve is disposed in the conveying line thereof for opening and closing the feed line. Such a mixing device is known from German Patent Reference No. DE 33 05 890 A1, wherein the parent component is also fed discontinuously to the feed point for the formation of the main flow of the mixture, which is then passed on to the mixing block. After the discontinuous component feeds have been brought together, the main flow of the mixture represents an alternating sequence of component packets of high, if not pure, concentration. The mixing block and the mixing line to the delivery nozzle serve to mix the packet sequence and to distribute the component concentration of the main flow as uniformly as possible. A control system monitors the discontinuous conveying of the individual components and sets or resets the inlet valves accordingly. Different mixture metering ratios can be set with the known device. A flow quantity meter is provided in each case for the components for the purpose of monitoring. With the known mixing device, however, a problem arose in that, even with very efficient mixing blocks and mixing tubes, a sufficiently homogeneous mixing concentration can not be achieved or can only be achieved with a very high outlay on a suitable control and design. To this extent, the known mixing device is used only where the concentration ratio is permitted in a relatively high tolerance range, in particular, in the case of large-area coatings. The known mixing device is, however, less suitable for metering rapidly reacting components with a high required metering accuracy because sufficiently homogeneous mixing cannot be achieved.
In order to achieve a higher metering accuracy, it is conceivable to consider a continuous feed of the feed component, i.e., without a preliminary packet formation in the main flow. It has been possible to create a continuous delivery by means of control-based adjustable pressure controllers and control technology. Such a continuous, electronically controlled pressure control is known from German Patent Reference No. DE 43 32 125 A1. According to the known mixing method, electronically actuated pressure controllers are used both for the parent component and for the feed component. It has emerged that such continuous feeding methods are not suitable in the case of frequently fluctuating hydraulic conditions of the system. Particularly in the area of the wet coating method with delivery pressures between 50 bar and 530 bar, a non-linear hose expansion always has to be taken into account. When use is made of piston pumps, the unavoidable reversal point leads to a non-constant delivery quantity and delivery pressure. A constant consumption quantity is also prevented by frequent activation and deactivation of spray guns. As a result of the hydraulic conditions of high pressure and the unavoidable inertia of mechanical and pneumatic components of the control circuit, a mixing method according to German Patent Reference No. DE 43 32 125 A1 is used only in the case of sustained continuous component flows. On account of very high feed pressures for the components, a stable, non-oscillatory control with short response times can in particular scarcely be achieved when disturbance variables, such as the constant switching-on and switching-off of the spray guns, use of further spray guns and the change in the pump direction of piston pumps, frequently occur. A change in the mixing concentration, such as a readjustment due, for example, to changes in the temperature and the viscosity of the feed component, can be achieved in the case of the known method only by means of correspondingly expensive preliminary adjustments.
It is one object of the disclosed embodiments to overcome the drawbacks of the prior art, in order to make available a method and a device for mixing at least two liquid components in an economically favorable manner, wherein a feed component is fed discontinuously to a parent component to achieve a more homogeneous metering concentration and/or to enable a higher variability in the adjustment of the mixing ratio without high design and ergonomic outlay.