Known aircraft paint mixing methods include the batch method and the in-line method. In the batch method, containers of cure (catalyst), flow (reducer), and base (resin) are prepared separately and then poured into a large container where they are manually stirred. After an induction waiting period, required for some paint systems, the paint is transported to the point-of-use where it is sprayed using hand-held pressurized spray guns. The containers are rinsed with solvent, left to dry, and then disposed of as waste.
In the in-line method, mixing is limited to two subcomponents. Separate lines of base and cure are fed into a small mixing container. Prior to reaching the mixing container, each paint subcomponent passes through an adjustable valve (e.g., a needle valve or a pneumatic valve) its own flow meter. A control system tracks the flow and adjusts the valves as needed to ensure the proper mix ratio. The mixing container mixes the subcomponents by passing the fluid through a static baffling or other torturous path. After the subcomponents are mixed in the container, the paint travels along an output line to a spray gun, as in the batch method.
In the aircraft industry, both current batch and in-line mixing methods have disadvantages. In the batch method, any unused material must be properly disposed of according to government regulations. The waste therefore adds unnecessary expense to the cost of producing a painted plane and to the environment. In the current in-line method, the flow meter and adjustable valves must be both extremely accurate and responsive in order to ensure a proper mix ratio of the fluid components. Such equipment tends to be mechanically complex and expensive. The extra mechanisms required for each component line also make the current in-line systems expensive. Extra solvent is needed to flush the additional parts during cleanup, which further increases the system's total waste. In addition, current in-line systems are generally designed to mix only two components. Popular polyurethane/epoxy aircraft formulations, however, often consist of three components (base, flow, and cure). Thus, it is necessary to batch mix two of the three components (i.e., the flow and cure), and then add the third component (base) in-line--a system that therefore suffers the disadvantages of both methods.
Thus, a need exists for an improved system of mixing two, three and even four fluid subcomponents (in particular, paint subcomponents) which is capable of producing a paint of a proper ratio on demand and without having to overmix the amount for a particular job. The ideal system would preferably consistently yield a product with less than about .+-.2% error in mix ratio error, and would be capable of mixing two or more subcomponents in-line without the need for batch mixing. Such an ideal system would receive the benefit of reduced costs of material supplies, reduced waste to the environment, and reduced need for cleanup solvent. The present invention is directed to such an ideal system.