 |
Description  |
|
|
FIELD OF THE INVENTION
The present invention relates to mixing systems, and more particularly, to paint mixing systems for producing relatively small industrial quantities of paint from two or more paint subcomponents.
BACKGROUND OF THE INVENTION
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.
SUMMARY OF THE INVENTION
The present invention in-line mixing system is provided for mixing multiple fluid subcomponents, and particularly, for mixing paints having two or more fluid subcomponents. An in-line mixing system formed in accordance with the present invention
includes multiple subcomponent input lines. Each line includes a valve having open and closed positions for allowing and prohibiting the flow of subcomponent through the input line. The mixing system further includes a reducing manifold including
multiple input passages. One subcomponent input line is connected to each manifold input passage. The multiple input passages converge to form a single output passage. A flow meter is in communication with the manifold output passage and measures the
flow of subcomponent through the output passage. During use, a slugwise line of subcomponents is formed by alternatingly opening and closing the input line valves. Mixing components connect to the output of the flow meter to combine the slugwise
subcomponents into paint.
In accordance with other aspects of this invention, the preferred flow meter is a positive displacement gear-type flow meter. The mixing components preferably include an integrator connected to the output of the flow meter and a static mixer
connected to the output of the integrator. A paint output line is connected between the static mixer and a spray gun. The paint within the output line may be optionally pressurized by an output pressure pump. The mixing system preferably further
includes a control system having a controller in communication with the flow meter and the input line valves. The input line valves are switched between their open and closed positions by the controller. The control system monitors the flow meter,
determines the amount of each subcomponent, and switches the valves accordingly to result in the appropriate subcomponent mix ratio. Where the input line valves are solenoid valves, the controller is capable of electrically switching the solenoid valves
between their open and closed positions. A computer is provided for user interface in operating the control system.
In accordance with further aspects of the invention, one preferred embodiment of the mixing system includes three subcomponent input lines, with each line including a solenoid valve. The reducing manifold includes three input passages. One
subcomponent input line is connected to each input passage, the input passages intersecting to form a single output passage. A flow meter is in communication with the manifold output. The output of the flow meter is connected to an integrator where
partial mixing of the subcomponents occurs. The system further includes a static mixer that is connected to the integrator output. The static mixer more thoroughly mixes the components. The solenoid valves, manifold, flow meter, integrator, and static
mixer are located in a first compartment of a housing.
In accordance with still other aspects of the invention, the first preferred embodiment further includes a check valve connected between each solenoid valve and the manifold. A control system is provided and includes a controller located in a
second compartment of the housing. The second compartment is positively pressurized by an air purge unit. The amount of pressurization is in the range of about 0.6 inches of water to about 4 inches of water.
In accordance with still further aspects of this invention, a unique integrator is provided for use in mixing paint fluid subcomponents. The integrator includes a sealed container having an input port and an output port, an influent tube
positioned within the container and connected to the input port, and an exfluent tube positioned within the container and connected to the output port. Both the influent and exfluent tubes include a series of longitudinal holes and one in the closed end
of each. The sealed container is pressurized according to the supply pump outputs. To accommodate the pressure increase in fluid flowing along the influent tube to its closed end, the influent holes preferably decrease in size in going from the input
port to the influent tube closed end. Likewise, the exfluent holes preferably increase in size in going from the output port to the exfluent tube closed end. Both the influent and exfluent holes decrease and increase nonlinearly in size, respectively.
The integrator is sized to hold about .about.250 cc of fluid.
In accordance with yet other aspects of this invention, a method of mixing paint from multiple paint fluid subcomponents is provided. The method includes forming a line of unmixed subcomponent slugs using a reducing manifold. The manifold
includes multiple input passages that converge to form a single output passage. A single flow meter is in communication with the manifold output passage. A particular quantity of subcomponent is input to the manifold input passages. The quantity is
measured by metering the amount of fluid passing from the output passage using the flow meter. The method further includes mixing the slugwise subcomponents by using an integrator and/or a static mixer. The flow of fluid subcomponent entering the
manifold is accomplished by the opening and closing of solenoid valves that are in communication with each of the manifold input passages. The mix system is capable of mixing one, two, or three or even four subcomponents.
In one embodiment of the method, the integrator includes a sealed container, an influent tube located within the container and having a series of holes, and an exfluent tube located within the container and having a series of holes. The
integrator partially mixes the fluids by passing the subcomponent slugs from the reducing manifold and flow meter to the influent tube and out the influent tube holes into the container. The fluid then passes into the exfluent tube holes and out of the
exfluent tube and integrator. The influent and exfluent holes preferably vary in size to accommodate pressure differences in the tubes.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same becomes better understood by reference to the following detailed description, when taken in conjunction with the
accompanying drawings, wherein:
FIG. 1A is a schematic diagram of an in-line paint mixer formed in accordance with the present invention;
FIG. 1B is a flow diagram of a method of preparing paint formed in accordance with the present invention;
FIGS. 2A is a perspective view of one embodiment of an in-line paint mixer formed in accordance with the present invention;
FIG. 2B is a front view of the mixer of FIG. 2A;
FIG. 3A is a front view of portions of the mixer shown in FIG. 2A;
FIG. 3B is a detail perspective view of the valves shown in FIG. 2A;
FIG. 3C is an exploded detail perspective view of the reducing manifold and flow meter shown in FIG. 2A;
FIG. 3D is a detail view of the reducing manifold of FIG. 2A;
FIGS. 4A and 4B are front and end views of portions of the mixer shown in FIG. 2A;
FIG. 5 is a partial cutaway side view of an integrator formed in accordance with the present invention with interior portions shown in phantom line;
FIG. 6 is an illustration of a Main Menu an instruction system formed in accordance with the present invention;
FIG. 7A and 7B are logic diagrams of the Setup selection listed in FIG. 6;
FIG. 8 is a logic diagram of the Run selection listed in FIG. 6;
FIG. 9 is a logic diagram of the Calibration selection listed in FIG. 6 ; and
FIG. 10 is a logic diagram of the Flush selection listed in FIG. 6.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention is a system of mixing fluid subcomponents, and particularly paint fluid subcomponents for use in industrial paint spraying applications. By mixing paint subcomponents in the manner of this system, relatively small amounts
of paint may be formed. This reduces the amount of materials needed to form the paint and the amount of waste left after a job is complete. The invention is therefore particularly important for those industries in which relatively smaller paint
quantity requirements are the norm, e.g., aircraft manufacturers, auto shops, farm equipment manufacturers, household appliance manufacturers, and others.
Below is a description of the present invention mixing system and method with reference to FIGS. 1A-1B. Following, is a description of one embodiment of a particular mixing system formed in accordance with the present invention. This embodiment
is shown with reference to FIGS. 2A-10. For the reader's convenience, several terms are defined as follows. Cure or catalyst refers to the isocyanate or amine cure component of an enamel and primer formulation, respectively. Base or pigment refers to
the polymerizing component which generally contains the color pigment. (Even though the base contains the true catalyst, for convention's sake it is labeled base herein.) Flow, reducer, or solvent thinner refers to the paint thinner component which
contains a mixture of various solvents.
Referring to FIG. 1A, the present invention mixing system generally includes pressurized subcomponent input lines 20 connected to a reducing manifold 22. The manifold 22 reduces the number of inputs to a single output line 24 that passes through
a flow meter 26. Valves 28 are placed in each input line 20 near the manifold 22. A control system 30 switches the valves 28 on and off in a predetermined manner to create a continuous flow of alternating subcomponent fluid slugs exiting the manifold
22. From the flow meter 26, the slugs pass to an integrator 32 where the slugs are roughly proportioned and partially mixed, and then to a static mixer 34 for more thorough mixing. A static mixer output line 38 connects the output of the static mixer
to a spray gun 40, where the paint is there available for ejection onto an application surface. An optional output pressure pump 36 may be used to provide additional pressurization to the paint in the static mixer output line 38 where desired.
In more detail, referring to the left hand side of FIG. 1A, separate containers 46 supply fluid subcomponents to the present invention in-line mixing system. If possible, it is preferable to use bag containers instead of cans containers in order
to reduce waste. For polyurethane/epoxy type paints, there is one container each of base, flow, and cure subcomponents. The subcomponents are supplied to the mixing system by the separate input lines 20. Movement of the fluid from each container into
the input lines 20 may be initiated by available means, such as gravity, house air pressure, or nitrogen pressure. Once in the input lines 20, the fluid is moved to the mixer via conventional pressure pumps 54 connected to the input lines. The pumps
additionally assure reliable loading of the manifold 22 and flow meter 26. Example pumps include air-operated double diaphragm pumps, piston pumps, pressure pots, etc. Depending on the complexity of the control system 30 and the sophistication of its
sensing devices, it is generally desirable to pressurize the fluids to equivalent levels. Filters (not shown) may also be inserted along the input lines 20 to remove particulate contamination in the subcomponents.
Still referring to FIG. 1A, each input line 20 passes fluid through its own dedicated valve 28 and into the reducing manifold 22. Preferred valves 28 are electronically-controlled two position (on/off) switches biased in the closed position,
such as the direct-acting solenoid valves shown in FIG. 1A. When the valve is opened, the subcomponent is allowed to enter the manifold 22. When the valve is closed, the subcomponent is blocked from entering the manifold 22. Other, more sophisticated
types of valves may be used in lieu of solenoid valves or other on/off switches. However, complicated valves are not required in a mixing system formed in accordance with the present invention. What is important is that the valves be able to open and
close quickly.
The manifold 22 is formed with the appropriate number of inlets, but only one outlet. In preferred embodiments, the manifold is a machined metal block with subcomponent input passages that centrally connect to form a single output passage.
(See, for example, the embodiment shown in FIG. 5A.) The manifold 22 and valve 28 configuration is preferably designed so that the distance from the outlet of each valve to the outlet passage of the manifold is minimized. This lessens the dead volume in
which unwanted difflusion mixing may occur. As such, the outlets of the valves 28 are preferably made to fit directly into the inlets of the manifold. In some designs it may be desirable to include a check valve between each valve 28 and its manifold
inlet to prevent unwanted catalyzed paint from backflowing into the valve 28. (See, for example, check valve 110 in FIG. 3B.)
Only one subcomponent fluid is allowed to enter the manifold output passage at a time. Therefore, one valve 28 will open and close before the next valve is opened and closed. By alternating the opening and closing of the individual valves, the
subcomponents are forced into and out of the manifold 22 in small quantities, or slugs. This produces a line of unmixed subcomponent slugs as indicated in step 56 of FIG. 1B.
The slug size of a particular subcomponent is based on the desired mix ratio. For example, with a 4:3:1 (base:flow:cure) mix ratio, the cure is assigned the smallest slug size of one. The slug sizes of the other components are scaled up
appropriately. The minimum slug volume is determined by a number of factors, including solenoid valve reaction time and the overall paint flow rate. As slug size decreases, the subcomponent valves must react more quickly or the paint flow rate must
decrease in order to maintain accurate slug volumes. Conversely, if the minimum slug size is too large, the integrator will not hold enough slug batches to provide good proportioning. The integrator is preferably sized to hold approximately three
complete micro-batches.
Ideally, the combined volumes of the dead-leg fluid paths (i.e., the lines between the valves and the flow meter) should be less than the minimum slug size for any mix ratio. If the combined dead-leg volume is larger than the minimum slug size,
then errors may occur when mixing paint whose components vary widely in viscosity. The errors are due to preferential flow of less viscous fluid from the dead-legs. To eliminate preferential flow, the combined dead-leg volume must be less than the
minimum slug size and the fluid lines must be sized to minimize pressure drop such that the output pressure pump 36 does not pull a vacuum through the system.
The manifold 22 is not meant to mix the subcomponents, but only to provide an intersection where the subcomponents can meet and flow slug-wise, one behind another, in single-line through the manifold output passage and to a single flow meter. By
making the subcomponent input slugs, however, some degree of crude mixing is accomplished in the sense that there is less mixing required downstream. It is more accurate, however, to characterize the manifold 22 as providing a continuous flow of unmixed
micro-batches.
Referring back to FIG. 1A, the manifold 22 is connected to the integrator 32 through the manifold output line 24. Positioned along this line 24 is the flow meter 26, which measures the volume of fluid flowing from the manifold at any given time. The flow meter then relays this information to the control system 30. In alternative embodiments, the flow meter may be positioned in the system after the static mixer. Preferred embodiments, however, have the flow meter placed immediately following
the reducing manifold. Based on the flow meter information, the control system switches the valves 28 open and closed when the appropriate fluid amount has been metered. Only one valve is open at a time, thus, the use of fast solenoids is important so
that the manifold 22 produces a continuous on-ratio stream of fluid.
The flow meter should be constructed of appropriate material and be able to handle the particulate nature of pigment bases without jamming. Flow meters with few fluid-exposed moving parts and with reduced fluid-trapping interstitial spaces are
best. Positive displacement type flow meters work well, as do mass flow meters with no moving parts (although they are generally more expensive.) The preferred flow meter is a positive displacement gear-type flow meter in which the only moving parts are
two metering gears. There are no moving bearings, the flow meter is less expensive, and the flow path is specifically designed to minimize fluid trapping. As each gear tooth rotates, a Hall-effect sensor produces an electrical impulse that is converted
and sent to the controller via an electrical link. From the accumulation of signals, the controller can calculate volumetric flow. When the rotation count reaches a setpoint value, the valves are switched by the control system 30 to flow the next slug
of material. The flow meter is preferably designed to tight machine tolerances so that changes in material viscosity do not lead to significant flow errors.
As material passes the flow meter, some may become entrained in small spaces and cause problems if the material cures and jams the precision tolerance metering gears. Thus, when possible, the user should avoid running two slugs of base and cure
adjacent to one another. Instead, flow slugs are positioned between base and cure slugs so that mixing and, thus, paint activation do not occur to a significant degree. For three component epoxy-type formulations, the order in which subcomponent slugs
are valved is therefore: flow, base, flow, cure, flow, base, and so forth. Preferably, the base and cure are separated by as much flow as the mix ratio will allow, especially when highly viscous bases and cures are used. The reducer flow acts as a
solvent wash, removing base and cure residue, and preventing unwanted cure reactions in the flow meter.
To ensure proper measurements by the control system 30, the mixing system mechanisms must be accurately calibrated prior to use. This is accomplished by running each subcomponent through the flow meter 26 and siphoning it off to be measured. In
the illustration of FIG. 1A, each subcomponent is siphoned it off through a drain valve 92 connected to the integrator 32. Other arrangements for siphoning fluid may be used, such as an automatic syringe pump. Fluid is dispensed one subcomponent at a
time through the flow meter 26 and out the drain valve 92. The fluid is collected and volumetrically measured in a graduated cylinder. During fluid passage through the flow meter 26, the control system 30 records the volumetric flow as metered by the
flow meter 26. The cylinder measurement is compared to the control system value. If the actual and predicted volumes are within a desired tolerance of each other, the system is calibrated. If the two measurements are not within the tolerance, the
control system 30 and/or flow meter 26 should be updated accordingly.
As stated above, in practice, the flow meter may be located anywhere between the solenoid valves and the output pressure pump. Placing the flow meter after the integrator or static mixer is possible and provides the advantage of requiring only
one calibration on mixed paint instead of the three calibrations required for the individual subcomponents. This system, however, then requires an additional check to verify the mix ratio.
From the flow meter 26, the slug-wise line of subcomponents enters the integrator 32 where the slugs are initially mixed. The integrator preferably includes an enclosed interior space 60 having an inlet, an outlet, and two distributors 62, 64
positioned within the enclosed space. One distributor 62 is connected to the integrator inlet, and one distributor 64 is connected to the outlet. Material flows from the flow meter 26 into the integrator inlet where it is dispersed through the inlet
distributor 62. The material circulates within the integrator 32 and eventually flows into the other distributor 64 and out the integrator outlet. The material flowing out of the integrator 32 is partially mixed.
The integrator 32 is designed to maximize the residence time of material slugs in a minimized volume so that the amount of paint waste is reduced. Therefore, the integrator is always full of fluid. To ensure a proper mix ratio, the integrator
32 is sized to account for the slugs flowing into the integrator at different times behind one another. The integrator is designed according to the flow rate, the approximate subcomponent diffusivity, and the volume the largest complete subcomponent
micro-batch will fill. The integrator 32 is preferably sized about three times the maximum micro-batch size based on the minimum quantity used for a particular ratio. By proportioning the number of slugs of each subcomponent, the proper mix ratio is
attained in the integrator.
Still referring to FIG. 1A, the partially mixed material next passes through an integrator output line 48 to the static mixer 34 which is designed to give thorough mixing according to a paint manufacturer's given specifications. Conventional
stat | | |
