Paint colour change system.

This invention relates to paint colour change systems.

In machine-controlled paint systems as used for spray painting, a limitation on the efficiency of a given machine has been the amount of time required to change from one colour to another, as for example when painting automobiles on a production line. To facilitate the colour change operation it has been proposed to use two paint supply lines to the spray apparatus, each supply line being fed from a separate paint manifold, so that one line can supply paint while the other line is being flushed and refilled with new paint. A disadvantage of that arrangement is the requirement of an extra paint manifold for each spray apparatus.

Another source of inefficiency in painting systems arises from the pressure drop in the . paint supply lines, which is different for paints of different viscosity, and which results-in variations in paint flow rate. Thus a pressure setting at the.paint manifold which is high enough to ensure sufficient paint flow of high- viscosity paint will result in an excessive flow of low-viscosity paint.

In US-A-3,450,092 there is disclosed a paint colour change system including pressure regulation for supplying paint to applicator means from individual fluid sources for paint and cleaning fluid. However, in that system there are separate pressure and paint selection controls disposed at locations remote from the spray head, and the requirements for a fast colour change system are not met.

The present invention is concerned with the provision of a paint colour change system having dual supply lines for rapid colour change, and valved connections to the applicator means (thus, the spray head) which also provide= accurate pressure control at the applicator means.

To this end, a paint colour change system in accordance with the present invention is characterised by: <ul id="ul0001" list-style="none"><li>first and second supply lines;</li><li>manifold means for selectively coupling the individual fluid sources to the supply lines; and</li><li>means for selectively coupling the supply lines to the applicator means, including: <ul id="ul0002" list-style="none"><li>a) a pair of pilot-operated pressure-regulating valves each connected between a respective one of the supply lines and the applicator means and operable in response to pilot pressure to selectively regulate paint flow to the applicator means or disconnect the said one supply line from the applicator means, whereby paint flow rate from the respective supply lines to the applicator means, and paint pressure to the applicator means, are controlled by pilot pressure applied to the respective pressure-regulating valves;</li><li>b) pilot-operated dump means for selectively exhausting the supply lines; and</li><li>c) pilot pressure control means for selectively directing pilot pressure to each of the valves and the dump means so that when one pressure-regulating valve is actuated to connect one supply line to the applicator means the dump means is actuated to exhaust the other supply line;</li></ul></li></ul> whereby when one supply line is flowing paint to the applicator means the other supply line can be flushed with the cleaning fluid.

Thus in a paint colour change system in accordance with the present invention, there is a single paint manifold.means and a valve arrangement for selectively connecting either of the two supply lines to the paint manifold means, and a further valve arrangement for connecting the supply lines to the applicator apparatus and additionally for regulating the pressure at the applicator means.

The dual paint supply lines permit rapid colour change without duplication of paint manifold apparatus.

In the drawings: . <ul id="ul0003" list-style="none"><li>Figure 1 is a block diagram of a paint colour change system in accordance with the present invention; and</li><li>Figures 2A and 2B combined diagrammatically illustrate the paint colour change system in accordance with the present invention.</li></ul>

As is shown in Figure 1, a paint colour change system includes a supply system 10 connected to a spray head 12 comprising a flow regulator 14 ana spray guns 16 by two paint supply lines 18 and 20 and two air pressure pilot lines 22 and 24. An exhaust line 26 is connected from the flow regulator 14 to a sump 28. An air line 30 carries atomizing air pressure to the spray guns. -Each of the lines 18 to 26 and 30 is sufficiently long to allow the spray head 12 to be located remotely from the supply system 10, for example many feet away. As will be seen below, the supply system 10 selects the paint or cleaning fluid to be admitted to the lines 18 and 20, and the flow regulator 14 appropriately connects those lines 18 and 20 to the spray guns 16 or the sump 28. To accomplish both paint feed to the spray guns and flushing of one of the supply lines, the flow regulator 14 accomplishes those functions under the control of the pilot pressure in the lines 22 and 24 and in addition accurately establishes a desired paint pressure at the spray guns as determined by the pilot air pressure.

. Figure 2A depicts the supply system 10 and Figure 2B depicts the spray head 12. In Figure 2A, a plurality of pressurized paint sources 32a, 32b and 32c are connected to respective inlets of a paint manifold 34. The inlets are controlled by normally closed pilot-operated two-way valves 36a, 36b and 36c respectively which selectively connect the paint inlets to a common flow passage 38 that leads to a manifold outlet 40. A cleaning fluid inlet 42 is controlled by a normally closed pilot-operated two-way valve 44 which selectively connects the inlet 42 to the common flow passage 38. A source 46 of solvent under pressure and an-air pressure source 48 are connected through respective pilot-operated two-way valves 50 and 52 to a line 54 which is connected to an inlet port of a four-way pilot-operated valve 56, and the air pressure source 48 is directly connected to another inlet port of the valve 56. The outlet ports of the.valve 56 are connected respectively to the cleaning fluid inlet 42 of the paint manifold 34 and to a bypass line 58. The manifold outlet 40 and the bypass line 58 are connected to respective inlet ports of a four-way pilot- .operated valve 60, and outlet ports of the four-way valve 60 are connected to the paint supply lines 18 and 20 respectively. The air pressure source 48 is connected by way of a downstream-regulated adjustable pressure-regulating valve 62 to the atomizing air line 30. The air pressure source 48 is also connected by way-of a downstream-regulated adjustable regulating valve 64 to produce on a line 66 a pressure establishing the desired paint regulation pressure in the spray head 12. The regulating valves 62 and 64 are solenoid-operated voltage- to-pressure transducers responsive to the voltages on lines 65 and 67 to allow the air pressures to be controlled electrically. Pilot-operated mormally closed two-way valves 68 and 70 selectively connect the line 66 to the pilot lines 22 and 24 respectively.

A controller 72 also connected to the air pressure source 48 includes an electric controller operating solenoid valves, not shown, for selectively pressurizing pilot lines denoted by the primed numerals such as 36', 44' and 50' and operatively connected to respective correspondingly numbered valves such as 36, 44 and 50. The electric controller operates the various solenoids in the proper sequence to obtain the desired paint system function. That is, the controller, according to its programming will determine whether paint, and if so of what colour, or cleaning fluid is supplied to the manifold 34, and will also determine the selection of the lines 18 and 20 for paint supply or flushing with cleaning fluid, as well as the control of pilot pressure to the lines 22 and 24. The voltage on the line 65 is selected by the controller 72 to establish the desired atomizing air pressure in the line 30. The voltage on the line 67 is also selected by the controller 72 according to the selected paint, to thereby provide the correct pressure for each paint to obtain the desired flow rate.

The spray head 12 comprises the flow regulator 14 attached to or.immediately adjacent applicator means exemplified by the spray guns 16. The flow regulator 14 comprises part of the paint colour change system, and specifically functions to select which supply line 18 or 20 to connect to the guns 16, to accurately establish a set paint pressure for the desired paint flow rate to the guns 16, to connect the other supply line to the exhaust line for flushing purposes, and to perform some other minor functions to be described below.

The flow regulator 14 has four downstream-regulated pilot-operated regulating valves 74, 76, 78 and 80. These valves may constitute diaphragm-operated poppet valves with pilot air pressure on one side of the diaphragm and downstream fluid pressure acting on the other side of the diaphragm so that the poppet is adjusted to a position effecting pressure balance. If the pilot pressure is set at zero, the poppet valve will be closed. The valve 74 is connected between the ends of line 18 and the exhaust line 26 to control flow of fluid from the supply line 18 to exhaust, thus performing the function of a dump valve. The dump valve 74 operates as an on-off valve,since the exhaust line 26 normally has a back pressure too low for regulation by the-pilot pressure. The valve 76, which is controlled by the pilot line 22,is connected between the end of the supply line 18 and a passage 82 which leads to a common outlet line 84. The valve 78 serves as a dump valve connecting the end of the supply line 20 to the exhaust line 26,and the valve 80,which is operated by the pilot pressure on line 24,connects the end of the supply line 20 to a passage 86 which leads to the common outlet line 84. The line 84 is connected to the spray guns 16 through sharp-edged orifices 88 and 90. The orifices are preferably in the flow regulator 14, but they may optionally be physically located in the spray guns 16 without change of function.

The control of pilot pressure to the pressure-regulating valves 76 and 78 is via lines 22 and 24 as determined by the operation of the valves 68 and 70 respectively. Supply of pilot pressure to the dump valves 74 and 78 is controlled by a pilot-operatec two- position four-way valve 92 which includes a detent 93 for holding the valve in either position. Input ports _ of the valve 92 are connected to the pilot lines 22 and 24, and output ports are connected to lines 94 and 96, which are connected to the pilot port of the dump valves 74 and 78 respectively. in addition a vent 98 is provided an the valve 92. When pilot pressure is applied to line 22 but not line 24,the pressure overcomes the detent and biases the valve to the position shown in the drawings, wherein the line 22 is coupled through the valve to the line 96 and the line 94 is connected to the vent 98. Thus in this condition the regulating valve 76 is open to supply paint from line 18 to the common outlet line 84, the dump valve 78 is open to connect line 20 to exhaust, and the valves 74 and 80 are closed. If pilot pressure is then applied to line 24 while the pressure remains on line 22,the valve 80 also will open; however, the valve 92 will not shift because of the holding action of the detent 93, the pilot pressures being balanced. This allows paint flow from the supply line 18 through the valve 76, the passages 82 and 86,and the valves 80 and 78 to exhaust. That action is useful briefly at the beginning of paint flow through the valve 76 to flush out residual paint of a previous colour from the passage 86 and valve 80. When there is pilot pressure applied to line 24 but not line 22, the valve 92 is shifted to connect the line 24 to line 94 and to connect the line 96 to vent. Then the valve 80 will be open to supply paint to the common output line 84,and the valve 74 will be open to connect the supply line 18 to the exhaust line 26. If pressure is applied also to line 22,the valve 76. will also open,to allow flushing of residual paint from the passage 82.

Because of the pressure regulation by the valves 76 and 8D,paint flow therethrough from the respective supply line will be regulated so that the paint pressure in the common line 84 will be the same as the air pressure set by the adjustable air regulating valve 64. This permits accurate paint pressure regulation at -the spray guns 16 even though pressure drops through the supply lines 18 and 20 are large as well as variable due to differences in paint viscosity. By maintaining a desired paint pressure at the spray guns, the flow rate of the paint through the guns is also well regulated, to give good control of the paint coating thickness on the part being sprayed. If the primary metering orifice in the system is a conventional spray gun nozzle,then the flow rate will be slightly dependent on the paint viscosity,even if a constant paint pressure is maintained to the gun. Substantial freedom from paint viscosity effects is obtained by using the sharp-edged orifice 88 or 90 in each paint flow passage to the gun,and maintaining a constant paint pressure upstream of the orifice. A sharp-edged orifice has a length which is less than five times its diarneter. In practice, it has been found that a hole drilled through a plate, of a diameter nearly equal to the plate thickness and having a square edge at the upstream terminus of the orifice,gives good xesults. Paint flow rate through such an orifice depends primarily on the orifice pressure drop. Thus the controlled pressure determines flow rate. The variations in paint viscosity have substantially no effect on the flow rate for the range of viscosity normally encountered in automotive paints. On the other hand, paint flow through the sharp-edged orifice will vary with paint density. Since different paints have different densities,the paint pressure is selected for each paint to compensate for density effects. This is accomplished by programming the controller 72 to provide the proper pressure-controlling voltage on line 67.

Each paint spray gun 16 is depicted schematically as a spray nozzle 100 coupled to the line 30 which furnishes atomizing air, and coupled to the common paint line 84 via a gun paint-passage 102, and a respective two-way pilot operated valve 104 which is normally closed but is piloted by the atomizing air on line 30. Thus when atomizing air pressure is applied on line 30 by the operation of the valve 62,the valve 104 in each spray gun is opened to admit paint to the atomizing nozzle.

In operation,assume that the pilot line 22 is pressurized,so that the valve 76 permits flow from line 18 to the spray guns, and the dump valve 78 is open to allow flow from supply line 20 to the sump 28. Further assume that the valve 60 is in the position shown in the drawings,and the valve 36a is open to supply a first colour of paint from the source 32a through the flow passage 38 of the manifold 34 to the supply line 18 and to the spray guns. To remove any residual paint from the supply line 20,the valve 56 is actuated to connect the cleaning fluid passage 54 to the bypass line 58,which in turn is connected through the valve 60 to the line 20, and cleaning fluid is supplied through those lines by opening the valves 50 and 52 alternately to provide-pulses of solvent and air which flow through the lines 54, 58 and 20 and through the dump valve 78 and the exhaust line 26 to the sump 28, thereby ensuring that the supply line 20 is free of all paint. Then when the part being painted is nearly completed, such that there is sufficient paint remaining in the supply line 18 to finish the part,the valve 36a is closed, the valve 56 is returned to its normal position shown in the drawings to supply air through the bypass line 58,and the valve 60 is shifted to connect the bypass line 58 to the supply line 18, thereby supplying air to the supply line 18 to push out the paint in the supply line to complete the painting of the part. In the meantime the valve 44 is opened to admit cleaning fluid from line 54 to the manifold.flow passage 38 for cleaning out the first colour paint from the passage and exhausting it through the valve 60 and supply line 20 and valve 78 to the exhaust line26. Then another manifold inlet valve, say valve 36b,is opened to connect a second colour paint from the source 32b to the passage 18, and to fill the line 20 with the second colour paint while the first colour paint is still being depleted from the supply line 18. At the completion of painting of the part,the atomizing air is removed from line 30 to shut off the spray guns 16. The pilot pressure is removed from line 22 by closing valve 68,and pilot pressure is admitted to line 24 by opening valve 70. Then the regulating valve 76 is closed, the valve 80 is opened, and the valve 92 is shifted,causing the dump valve 78 to close and the dump valve 74 to open. Valve 68 is opened momentarily to apply a pulse of pressure on pilot line 22 to open the regulator valve 76,thus allowing the second colour of paint to flow from the supply line 20 through the valves 80 and 76 and dump valve 74 to clean out any first colour paint in the passage 82 and the valve 76, to avoid any contamination of the second colour paint during spraying of another part. The pressure in line 22 is removed to close the valve 76,and the atomizing air is applied on line 30 to cause operation of the guns and flow of the second paint colour through the guns to clean out residue of the first colour. Then painting commences on the new part,and the supply line 18 is purged with cleaning fluid in the same manner as for the previous cleaning of the line 20.

It will be seen that the system is very efficient due to the short time that the spray guns are out of service for colour change operation,and that by using only one paint manifold in the system the expense of the system is minimized,even though all the advantages of dual supply lines are maintained. Moreover, by incorporating paint pressure regulation as a function of the colour change valving immediately adjacent the spray guns,accurate paint flow control is attained even though large pressure changes may occur in the paint supply lines.