Improvements in and relating to dispensing conductive coating materials

Abstract: An apparatus is provided for transferring electrically conductive coating materials, such as water-based paint, from at least one source (14) to one or more coating dispensers (94a,b,c) for discharge onto a substrate. One voltage block (42) is provided to avoid the creation of an electrical path between one or more sources of coating material and the coating material which is electrostatically charged during a coating operation, and a secondary voltage block is provided between each of a number of individual spray guns (94a,b,c) and the charged coating material so that each spray gun can be electrically isolated from the charged coating material when not in use. The apparatus may comprise a colour changer, and/or a heater which is electrically isolated from the charged coating material and is effective to elevate the temperature of the coating material prior to discharge from the spray guns.

Description: This invention relates to electrostatic spray coating, and, more particularly, to a method and apparatus for dispensing electrically conductive coating materials from one or more dispensers or spray guns, wherein the source of supply of the conductive coating material is electrostatically isolated from the high voltage electrostatic power supply and each of the coating dispensers is electrically isolated from the power supply when not in use. Electrostatic spraying techniques have been used in industry for many years. Typically, the coating material is discharged in atomised form, and an electrostatic charge is imparted to the atomised particles which are then directed toward a substrate maintained at a different potential to establish an electrostatic attraction for the charged atomised particles. In the past, coating materials of the solvent-based variety, such as varnishes, lacquers, enamels, and the like, were the primary materials employed in electrostatic coating applications. The problem with such coating materials is that they create an atmosphere which is both explosive and toxic. The explosive nature of the environment presents a safety hazard should a spark inadvertently be generated, such as by accidentally grounding the nozzle of the spray gun, which can ignite the solvent in the atmosphere causing an explosion. The toxic nature of the workplace atmosphere created by solvent coating materials can be a health hazard should an employee inhale solvent vapours. The use of water-based coatings reduces the problems of explosiveness and toxicity. Unfortunately, the switch from electrostatically spraying solvent-based coatings to water-based coatings has sharply increased the risk of electrical shock, which risk was relatively minor with solvent-based coatings. The risk of electric shock with water-based coatings is due to their extreme electrical conductivity, with resistivities of such water-based coatings often falling within the range of 100 to 10,000 ohm centimetres. This is in contrast to resistivities of 200,000 to 100,000 ohm centimetres for moderately electrically conductive coatings such as metallic paint, and resistivities exceeding 100,000,000 ohm centimetres for solvent-based lacquers, varnishes, enamels and the like. The relative resistivity of the coating material is critical to the potential electrical shock which may arise during an electrostatic coating operation. With coating materials which are either not electrically conductive or only moderately electrically conductive, the coating material extending from the charging electrode at the tip of the coating dispenser through the hose leading back to the supply tank has sufficient electrostatic charging of the material in the supply tank or the tank itself. However, when coating material is highly electrically conductive, as are water-based coatings, the resistance of the coating in the supply hose is very low. As a result, a high voltage charging electrode located in the vicinity of the nozzle of the coating dispenser electrostatically charges not only the coating particles, but the coating material in the hose, the coating material in the supply tank and the supply tank itself. In such circumstances, operating personnel inadvertently coming into contact with an exposed supply tank or a charged hose or any other charged part of the system risk serious electrical shock unless such equipment is grounded to draw off the electricity. If the equipment is indeed grounded at any point, however, the electrostatics will not function because the high voltage charge would be conducted away from the coating dispenser electrode as well. One of the methods for reducing the electrical shock problem is disclosed, for example, in U.S. Patent No. 3971337 which discloses an apparatus for electrostatically isolating the supply tank which is connected to the coating dispenser. While this device is satisfactory for batch operations, it does not readily lend itself to continuous painting lines, wherein an essentially continuous supply of coating material must be provided. This problem has been addressed in apparatus of the type disclosed, for example, in U.S. Patent No. 4313475, in which a "voltage block" system is employed wherein electrically conductive coating material is first transmitted from a primary coating supply into a transfer vessel which is electrically isolated from the spray gun. When filled with coating material, the transfer vessel is first disconnected from the primary coating supply and then connected to an inventory tank, which, in turn, is connected to one or more coating dispensers. The coating material is transmitted from the transfer vessel into the inventory tank to fill the inventory tank with a supply of coating material for subsequent transfer to the coating dispensers. While the inventory tank supplies the coating dispensers with coating material, the transfer vessel is disconnected from the inventory tank and connected back to the primary coating supply to receive another quantity of coating material so that the coating operation can proceed essentially continuously. One feature of apparatus of the type disclosed in US Patent No. 4313475 is that a voltage block or air gap is provided at all times between the primary source of coating material and the electrically charged coating dispensers. One potential operational problem with such apparatus is that separately actuated transfer devices, e.g., pneumatic cylinders or the like, are employed to interconnect the transfer vessel with the primary coating supply, and then to connect the transfer vessel with the inventory tank. Because the two pneumatic cylinders or other transfer devices are actuated independently of one another, it is possible that a malfunction of the controller for such cylinders could result in the connection of the transfer vessel to the primary coating supply at the same time as the inventory tank is connected to the transfer vessel. As discussed above, the lower resistivity of water based coating materials can result in the transfer of a high voltage electrostatic charge from the coating guns, through the coating material to the primary coating supply, thus creating a hazard of electrical shock. This and other problems are addressed in European Patent Application No. 91306401.0 which is owned by the Applicants. European Patent Application No. 91306401.0 discloses an apparatus for transferring electrically conductive coating materials such as water-based paint from a source to an electrostatically charged dispenser which includes first and second shuttle devices and two pumps each having structures for preventing contamination of the coating material and pressure build-up at their piston heads. The first shuttle device is movable between a neutral position wherein it is electrically isolated from the coating material source, and a transfer position wherein coating material is transmitted to one of the pumps through a coupling device. The second shuttle device is movable between a neutral position wherein the second shuttle is electrically isolated from the dispenser, and a transfer position wherein coating material is transmitted from the filled pump, through another coupling device to the second pump for transmission to one or more electrostatic coating dispensers. Movement of the shuttles is controlled to maintain one of the shuttles in the neutral position while the other is at the transfer position. US National Fire Protection Codes require the electrostatics to each manually operated coating dispenser to be shut down when the trigger of the gun is released. One problem with systems of the type disclosed in US 4313475 is that no provision is made to electrically isolate each of the coating dispensers when not in use, i.e., when the operator releases the trigger of the dispenser. As mentioned above, a high voltage electrostatic charge is applied to the coating material discharged from the transfer vessel of US 4313475 upstream from the coating dispensers so that the coating material and, hence, the coating dispensers, all remain charged regardless of whether or not the dispensers are in use. While this system may be satisfactory for automatically operated coating dispensers, the US National Fire Protection Code requirements for manually operated spray guns are not met by the US Patent No. 4313475 system. Another problem with systems of the type disclosed in US 4313475 is that the colour changer associated with such system is located upstream from the inventory tank. In order to change colours, essentially the entire system must be cleaned, i.e., the inventory tank, transfer vessel, coating dispensers, and all the lines interconnecting these elements. This is a time-consuming and cumbersome operation which is unacceptable in applications wherein rapid colour changes are required. A still further problem with systems of the type disclosed in US 4313475 is that they cannot be used with coating materials whose application characteristics are improved when dispensed at elevated temperatures. It is not feasible to use a coating material heater because no provision is made to recirculate the coating material from the coating dispensers back to the source when the coating dispensers are not in use. Absent recirculation, the coating material could not be held at sufficient temperature if the spraying operation were interrupted or discontinued for a period of time. Additionally, any heater utilised would have to be positioned in the loop between the source of coating material and the inventory vessel to isolate the heater from the electrostatic power supply and avoid grounding. At this location, the heater is physically removed from the coating dispensers and could not effectively maintain temperature of the coating material unless the system was always operated continuously. US-A-4017029 discloses an electrostatic spray coating system having two coating supply sub-systems, one of which is electrically grounded the other being connected to a high voltage supply, the two sub-systems being separated from each other by an air space with interlocks which permit transfer of conductive coating material from one supply sub-system to the second supply sub-system only when high voltage is not being applied to the second, high voltage sub-system. Apparatus for dispensing electrically conductive coating material in accordance with the invention comprises a pump for receiving coating material from at least one source and for transmitting the coating material to at least one dispenser and means for applying an electrostatic charge to the coating material, the electrostatic charge being applied to the coating material at the pump, means being provided electrically to isolate the said pump from the or each source of coating material whilst the said pump transmits coating material to the dispenser(s) characterised in that means are provided, connected between the or each dispenser and the electrostatic charging means, for transmitting electrostatically charged coating material to a respective dispenser when the dispenser is open and electrically to isolate a respective dispenser from the charged coating material when the dispenser is closed. A "voltage block", i.e., an air gap may be provided between one or more sources of coating material and electrostatically charged coating material which is directed to the spray guns. This voltage block ensures that there is never an electrical path between the source of water-based paint and the charged coating material during a coating operation. A second voltage block may be provided between each of a number of individual spray guns and the charged coating material so that each spray gun can be electrically isolated from the charged coating material when not in use. Alternative embodiments incorporate colour changers which provide for easy cleaning of the system, and optionally include a heater which is electrically isolated from the charged coating material and is effective to elevate the temperature of the coating material prior to discharge from the spray guns. Such apparatus has a number of advantages including: (1) the fact that a single high voltage electrostatic power supply capable of imparting an electrostatic charge directly to the coating material may be supplied to a number of spray guns; (2) means are provided for isolating the source of one or more coating materials from the high voltage electrostatic power supply; and, (3) means are provided for electrically isolating each of a number of individual coating dispensers or spray guns from the high voltage power supply when not in use. Electric isolation of the source(s) of water-based paint from the high voltage electrostatic power supply may be achieved with a "voltage block" construction which includes a first shuttle device connected to the reservoir of a first piston pump, and a second shuttle device connected to the reservoir of a second piston pump. The first shuttle device is movable with respect to a filling station, which is connected to a source(s) of water-based paint, between a transfer position coupled to the filling station and a neutral position physically spaced or separated by an air gap from the filling station. The second shuttle device is movable with respect to a transfer station, which is connected to the reservoir of the first piston pump, between a transfer position coupled to the discharge station and a neutral position spaced from the discharge station. The second shuttle device is connected to the reservoir of the second piston pump, which, in turn, communicates through a feed line with a number of spray guns. A high voltage power supply may be connected through an electrostatic cable to the metal housing of the second piston pump such that all of the water-based paint directed into the second piston pump from the transfer station, and discharged therefrom, is imparted with an electrostatic charge. This charged water-based paint is then supplied through the feed line to a number of individual spray guns for deposition onto a substrate. In this embodiment of the invention, the electrostatics are not supplied via an electrostatic cable or the like to each spray gun individually, but, instead, the coating material is charged upstream from the spray guns and distributed to each spray gun individually as needed. Movement of the first and second shuttle devices is controlled such that a voltage block or air gap is continuously maintained between one or more sources of water-based paint, and the electrostatic power supply connected to the second piston pump. This voltage block is obtained by ensuring that when the first shuttle device is coupled to the filling station for transfer of coating material from a source into the first piston pump, the second shuttle device is electrically isolated, i.e., placed in the physically spaced, neutral position, with respect to the transfer station which is connected to the second piston pump. A second voltage block is provided during transfer of the water-based paint from the reservoir of the first piston pump into the reservoir of the second piston pump by moving the first shuttle to its neutral position with respect to the filling station so that a physical air gap is obtained between the first piston pump and the source(s) of coating material. When the reservoir of the second piston pump is filled, the shuttles return to their original positions, i.e., the first shuttle couples with the filling station to resume transmission of coating material into the first pump reservoir while the second shuttle moves to its neutral position with respect to the transfer station. With the second shuttle in the neutral position, the source of water-based paint is isolated from the high voltage electrostatic power supply connected to the second piston pump, thus permitting the transfer of charged water-based paint from the second pump to the spray guns without the risk of transmitting an electrostatic charge to the paint source(s). As mentioned above, National Fire Protection Code provisions require that the electrostatics to manually operated spray guns must be disconnected when the trigger of such guns is released. In order to meet this requirement, a separate voltage block structure is provided between the feed line from the second piston pump carrying charged water-based paint, and each of essentially any number of spray guns. Each voltage block structure may include a discharge shuttle connected to one of the spray guns, which is movable to a coupled position in engagement with a discharge station connected to the feed line from the second piston pump carrying charged water-based paint, and a neutral position physically spaced from the discharge station. When it is desired to spray water-based paint from any of the spray guns, depression of the trigger of a gun activates a pneumatically and/or mechanically operated valving system which causes the discharge shuttles to couple with the discharge station thus providing a path for the charged water-based paint directly to such spray gun. When the trigger of a spray gun is released, the valving system is operative to move the discharge shuttle associated with that gun to a neutral position thus creating a voltage block or air gap between the charged coating material at the discharge station and such spray gun. Each spray gun is therefore electrically isolated from the charged water-based paint within the feed line until such time as its trigger is depressed to begin another spraying operation. Such an arrangement has several advantages. First, a voltage block construction is provided to continuously isolate one or more sources of water-based paint from the high voltage power supply which charges the water-based paint transmitted to the spray guns. Additionally, a single high voltage power supply is capable of servicing a number of individual spray guns, thus eliminating the need for separate electrostatic cables to each gun. A further advantage, particularly when operating manual spray guns with this system, is that a voltage block is provided between the feed line carrying charged coating material from the second piston pump and each of the individual spray guns. This ensures that each of the spray guns is electrically isolated when not in use, thus protecting operators against electrical shock hazards. It has been found that the application chacteristics of some types of water-based paints, and other highly conductive coating materials, are improved if they are dispensed at elevated temperatures. As discussed above, the incorporation of paint heaters within systems for dispensing water-based coatings had not been possible in prior art systems. This problem is overcome in this invention by the voltage block configuration incorporated between the coating source and high voltage power supply, as described above, and circulation lines associated with such system to provide for recirculation of the paint when it is not being dispensed from the spray guns. A paint heater, which is grounded, may be incorporated in a loop or line downstream from the source(s) of coating material but upstream from the voltage block. Because the voltage block continuously isolates the source of water-based paint from the high voltage power supply, the heater is never electrically connected to the high voltage power supply and therefore cannot ground the system. The water-based paint discharged from the source passes through the paint heater where its temperature is elevated, and then the heated paint enters the voltage block for supply to the spray guns. If the spray guns are not operating, a controller may be provided which is effective to temporarily deactivate the high voltage power supply and then couple the first and second shuttles to the filling and transfer stations, respectively, thus providing a path for recirculation of the water-based paint back through the shuttles, and the filling and transfer stations, to the heater and paint source. This recirculation through the heater maintains the paint at the desired temperature, and also aids in preventing settling of the solid content of the paint. A colour changer of essentially any commercially available type may be interposed between a number of sources of coating material of different colour, and the voltage block described above. When a particular colour is required, the colour changer is effective to supply the first piston pump and remaining elements of the voltage block with such colored paint which, in turn, is transmitted from the second piston pump to the individual spray guns. The remaining elements of the system are identical to that described above. Another embodiment of this invention is predicated upon the same concept of providing a continuous voltage block between a source of water-based paint and the high voltage power supply which charges the coating material, but this embodiment is particularly adapted for applications such as automotive paint lines wherein rapid colour changes are required. In this embodiment, a dedicated pump and voltage block construction, including a separate transfer station and shuttle, may be provided for every colour of paint which is to be applied. In this embodiment, a filling station is connected to a source of water-based paint of one colour, and a shuttle is movable with respect to the filling station between a coupled position and a neutral position. The shuttle, in turn, is connected to the reservoir of a piston pump which communicates with a single manually operated spray gun. A dedicated high voltage power supply is connected to the metal body of the piston pump, and through an electrical/pneumatic control system to the spray gun. When the spray gun is not being operated, the shuttle is movable to a coupled position with respect to the transfer station so that water-based paint from the paint source can be transferred into the reservoir of the piston pump. The high voltage power supply is turned off during this filling procedure by the electrical/pneumatic control. In response to depression of the trigger of the gun, the electric/pneumatic control first causes the shuttle to move to a neutral position spaced from the transfer station, and then activates the high voltage power supply to charge the water-based paint within the reservoir of the piston pump. A voltage block is thus created between the source of water-based paint and the high voltage power supply, and, simultaneously, the charged coating material within the pump reservoir is transmitted to the spray gun for deposition on a substrate. Such an apparatus can be adapted for use with multiple colours, each from a separate source, while employing a single source of high voltage electrostatic power. Each of a number of sources of different coloured paint may be connected to a separate, dedicated transfer station, shuttle and piston pump all carried within a grounded, electrically isolated cabinet. The several pumps within the cabinet are electrically connected to one another, e.g., by electrically conductive straps or the like, and the metal pump body of one of the pumps is connected by an electrostatic cable to a high voltage power supply. The reservoir of each piston pump within the cabinet is connected to a colour changer located upstream from a number of manually or automatically operated spray guns. In this system, a voltage block is maintained between the several sources of water-based paint and the high voltage power supply in the same manner described above for a single gun system. In response to actuation of one or more of the spray guns, e.g., by depressing the trigger mechanism thereof, all of the shuttles within the cabinet are moved to a neutral position with respect to their associated transfer stations. This electrically isolates all of the piston pumps within the cabinet, which are electrically connected to the high voltage power supply, from each of the sources of different coloured paint. The colour changer receives the desired colour of paint from one of the piston pumps and, in turn, supplies this colour to one or more spray guns. In addition to the compact construction of this system and the use of a single electrostatic power supply, positioning of the colour changer downstream from the piston pumps requires less flushing of the system and clean up when a colour change is desired. Only the colour changer and the lines interconnecting the colour changer with the spray guns, must be cleaned when a colour change is made. This reduces down time and the difficulty associated with a colour change. In this embodiment, using multiple dedicated shuttles and piston pumps, an electrostatic cable from a high voltage power supply is connected to one of the piston pumps within a grounded cabinet and then straps electrically interconnect the several pumps within this cabinet. This embodiment can be modified to alter the position wherein the coating material is changed by attaching an electrostatic cable from a high voltage power supply to the metal block of the colour change manifold of the colour changer downstream from the shuttles and piston pumps and upstream from one or more spray guns. An electrostatic charge is thus applied to the coating material as it passes through the colour change manifold, instead of within the piston pumps. In either case, one or more spray guns are efficiently supplied with essentially any desired number of different colours, with a voltage block being continuously maintained between the sources of such different coloured paints and the charged coating material. Each spray gun may be electrically isolated from the charged paint when not in use. In this arrangement, a discharge station connected to the feed line carrying charged paint, and a shuttle movable relative to the discharge station, is provided for each individual spray gun. As described above, when the trigger of a gun is depressed, the discharge shuttle is coupled to the discharge station to supply charged paint to the spray gun and the flow of paint is terminated when the trigger is released causing the shuttle to return to a neutral position spaced from the discharge station. Methods and apparatus in accordance with the present invention for dispensing electrically conductive coating materials, such as, for example, water-based paint, protect against the transmission of an electrostatic charge between the high voltage electrostatic power supply and the primary coating supply, enabling a heater to be incorporated without grounding the system and without requiring continuous dispensing of coating material, permit the operation of multiple hand-held or manually operated coating dispensers without the risk of electrical shock from such dispensers when not in use, and incorporate colour changers without requiring time-consuming cleaning between colour changes. Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Fig. 1 is a diagrammatic view of one embodiment of apparatus for dispensing electrically conductive coating material in accordance with the invention; Fig. 1A is an enlarged view in partial cross section of the connection between the electrostatic cable and the pump body shown in Fig. 1; Fig. 2 is a schematic view of a portion of Fig. 1 illustrating the valving system employed to electrically isolate each of the spray guns from the electrostatic power supply; Fig. 3 is a diagrammatic view of the embodiment of Fig. 1 but incorporating a colour change manifold; Fig. 4 is a diagrammatic view of an alternative embodiment of the apparatus in accordance with the invention; Fig. 5 is a schematic view of the apparatus of Fig. 4 adapted for use with a number of different coloured coating materials; Fig. 6 is a plan view taken generally along line 6-6 of Fig. 5; and Fig. 7 is a schematic view similar to Fig. 5 in which the spray guns are electrically isolated from the high voltage electrostatic power supply. Referring now to the Figs., an apparatus 10 is illustrated in Figs. 1-3 and an apparatus 12 is illustrated in Figs. 4-7 which apparatuses are particularly adapted for use with highly electrically conductive coating materials such as water-based paints The apparatus 10 and 12 are constructed to permit the transfer of such coating material from one or more sources, to one or more electrostatic spray guns, without creating an electrical shock hazard or loss of charge at the electrode in the spray gun caused by a ground at any of the equipment that is wetted by the coating material such as pumps, hoses and tanks. As discussed in detail below, the apparatus depicted in Figs. 1-3 is particularly adapted for applications wherein the speed of a colour change operation, i.e., changing from one colour of water-based paint to another, is not a critical consideration. Apparatus 10 uses a relatively modest amount of equipment and is comparatively inexpensive to fabricate and maintain. The apparatus 12 of Figs. 4-7, in the several variations thereof described below, is principally intended for use in applications where rapid colour change is necessary such as in paint spraying lines for automobiles and other vehicles. The apparatus 12 employs additional equipment to achieve this end in comparison to that of apparatus 10. With reference to Fig. 1, the apparatus 10 comprises a source of highly electrically conductive coating material, depicted as paint supply 14, which is grounded at 16 and connected by a line 18 to a pump 20 grounded at 22. Pressurized air is supplied to pump 20 through an air filter and regulator 24 connected to an air supply 26 and a drain 28. A paint heater 30, which is grounded at 32, is connected by a line 34 to the pump 20. This paint heater 30 is optionally included in apparatus 10 for situations wherein the application characteristics of a coating material such as paint are optimized by dispensing the material at elevated temperatures. As discussed below, the paint heater 30 is incorporated within the apparatus 10 at a location which avoids loss of charge at the coating dispensers or spray guns. The paint is discharged from paint heater 30 through a line 36 into a filter 38 where any particles or other impurities are removed. From the filter 38, the paint travels through line 40 into a voltage block 42 which is collectively formed by the several elements illustrated within the dotted lines in Fig. 1, and which is similar in some respects to the apparatus described in European Patent Application No. 91306401.0. The voltage block 42 comprises a filling station 44 having a male coupling element 46 connected to the line 40 from filter 36, and a spaced, female coupling element 48 connected to a line 50 which forms part of a recirculation loop described in detail below. The filling station 44 mounts a pair of spaced rods 52 along which a first shuttle 54 is axially slidable by operation of a pneumatic cylinder 56. The pneumatic cylinder 56 has a cylinder housing 58 mounted to the opposite sides of rod 52, and a cylinder rod 60 connected to the shuttle 54. In response to operation of cylinder 56, the shuttle 54 is moved along the rods 52 between a coupling or paint transfer position, and a neutral, physically spaced position, with respect to the filling station 44. The shuttle 54 carries a female coupling element 62 and a male coupling element 64 which are engageable with the male and female coupling element 46, 48, respectively, on the filling station 44 with the shuttle 54 in a transfer position. The detailed construction of these coupling elements forms no part of this invention, and is disclosed in European Patent Application No. 91306401.0. The female coupling element 62 of shuttle 54 is connected by a line 66 to the reservoir 68 of a first piston pump 70. The detailed construction of piston pump 70 forms no part of this invention per se and is thus not described herein. The pump reservoir 68 is connected by a line 72 to the male coupling element 74 of a transfer station 76. The transfer station 76 also includes a female coupling element 78 which is interconnected with the male coupling element of shuttle 54 by a circulation line 80. A second shuttle 82 is associated with transfer station 76, and this second shuttle 82 carries a female coupling element 84 and a male coupling element 86 which are matable with the male and female coupling elements 74, 78, respectively, of the transfer station 76 with the second shuttle 82 in a coupling or transfer position with respect to the transfer station 76. The structure for moving the second shuttle 82 with respect to the transfer station 76 is identical to that of first shuttle 54 including rods 52, and a pneumatic cylinder 56 having a cylinder housing 58 and cylinder rod 60. As viewed in Fig. 1, the female coupling element 84 of second shuttle 82 is connected by a line 87 to the reservoir 88 of a second pump 90, and the male coupling element 86 of second shuttle 82 is connected to a recirculation line 91. As described below, paint is discharged from the reservoir 88 of second pump 90 into a gun feed line 92 for supply to one or more spray guns 94. The spray guns 94 are preferably air-type guns wherein atomization of the paint takes place by impacting a stream of paint with one or more jets of air. These types of spray guns are available commercially, and one air-type electrostatic spray gun suitable for use with the apparatus 10 of this invention is a Model No. AN-9 sold by Nordson Corporation of Amherst, Ohio which is the assignee of this invention. Alternatively, the apparatus 10 can be adapted for use with airless-type electrostatic spray guns wherein atomization is obtained hydraulically, and one example of a suitable airless spray gun which can be used with apparatus 10 is found in U.S. Patent No. 4,355,764, owned by the assignee of this invention. A high voltage electrostatic power supply 96 is connected by an electrostatic cable 98 to a monting stud 100 (See Fig. 1A) associated with second pump 90. As depicted in Fig. 1A, the terminal end 102 of cable 98 is held in place against the stud 100 by a nut 104 having an upper flange 106 which engages a ring 108 carried by the cable 98, and a threaded lower portion 110 which engages external threads formed on the exposed end of mounting stud 100. The cable 98 and power supply 96 are effective to impart a high voltage electrostatic charge to the metal body of pump 90, which, in turn, charges the coating material or paint within the pump reservoir 88. As a result, electrostatically charged paint is discharged from paint reservoir 88 into feed line 92 for supply to the spray guns 94. The voltage block 42 is operative to transfer paint from the paint supply 14 to the reservoir 88 of second pump 90, which is electrically connected to the high voltage electrostatic power supply 96, so that a "voltage block" or air space is continuously maintained between the paint supply 14 and a power supply 96, as described in detail in European Patent Application No 91306401.0. Each of the spray guns 94 is electrostatically isolated from the charged paint emitted through line 92 from the reservoir 88 of second pump 90. As shown on the righthand portion of Fig. 1, this line 92 is connected by branch lines 114a,b,c to a separate discharge station 116a,b,c associated with the three spray guns 94a,b,c respectively, depicted in Fig. 1. Each of the discharge stations 116a,b,c, and the structure downstream therefrom to the spray guns 94a, b, c, is identical and therefore only one set of such elements associated with spray gun 94a are described herein, it being understood that the elements associated with guns 94b and c are structurally and functionally identical. Such other structure is given the same reference numbers with the addition of the letters "b" and "c" as illustrated in Fig. 1. With reference to the first discharge station 116a, and its associated spray gun 94a, such discharge station 116a is connected by the branch line 114a to the line 92 from second pump 90. A discharge shuttle 118a is axially movable with respect to the discharge station 116a in the same manner as described above in connection with shuttles 54 and 82, i.e.., the cylinder rod 60 of a pneumatic cylinder 56 is connected to the discharge shuttle 118a to move it along rods 52 which are connected between the discharge station 116a and the cylinder housing 58 of pneumatic cylinder 56. The discharge shuttle 118a has a male coupling element 126 matable with the female coupling element 124 carried by the discharge station 116a, and mating female and male coupling elements 122, 120 are carried by the discharge shuttle 118a and discharge station 116a, respectively. The male coupling element 120a of discharge station 116a is connected to branch line 114a, and the mating, female coupling element 122 carried by discharge shuttle 118a is connected by a discharge line 128a to the spray gun 94a. With the discharge shuttle 118a in the physically spaced, neutral position as depicted in Fig. 1, the spray gun 94a is electrically isolated from the high voltage electrostatic power supply 96, second pump 90 and the line 92 carrying the electrostatically charged paint. On the other hand, the spray gun 94c, for example, is electrically connected to the power supply 96 via the second pump 90 and line 92 by movement of its discharge shuttle 118c to the transfer position with respect to discharge station 116c. In this position, the male and female coupling elements 120, 122 permit the passage of charged paint from the discharge station 116c through the discharge shuttle 118c and discharge line 128c to the spray gun 94c for deposition onto a substrate. With reference to Fig. 2, a control system 130 is provided with the apparatus 10 of this invention which operates the discharge shuttles 118a, b, c and power supply 96 in response to actuation of the spray guns 94a, b, c. This control system is in addition to the pneumatic/mechanical valving arrangement mentioned above in connection with voltage block 42 The control system 130 comprises a separate set of control elements for each of the spray guns 94a, b, c except for a common source of pressurized air 132 and the common power supply 96. The control elements associated with spray gun 94a are described in detail herein, it being understood that the same control elements associated with spray guns 94b and c are structurally and functionally identical, and are given the same reference numbers in Fig. 2 with the addition of the letters "b" and "c". The pressurized air source 132 is connected by a pneumatic trunk line 134 to a flow switch 136a which is connected by line 137a to a pressure regulator 138a. The pressure regulator 138a, in turn, is connected by an air line 139a to spray gun 94a which provides atomizing air to the spray gun 94a. As schematically depicted in Fig. 2, a gauge 141a is located within the air line 139a downstream from pressure regulator 138a. An air line 140a interconnects the trunk line 134 carrying the pressurized air with a solenoid valve 142a. The solenoid valve 142a is electrically connected to the flow switch 136a by a line 143a. In turn, the flow switch 136a is connected by an electric line 144a to a common electric line 145 from the power supply 96. The solenoid valve 142a is connected by an air line 146a to a control or restrictor valve 148a, and by an air line 150a to a pressure switch 152a. The restrictor valve 148a is connected by an air line 154a to the pilot (not shown) of a valve 156a associated with discharge shuttle 118a. See Fig. 1. This valve 156a receives a constant flow of pressurized air through line 158a from the pressurized air source 132. One side of pressure switch 152a is connected by an electric line 160a to a common electric line 161 from the power supply 96. The opposite side of pressure switch 152a is connected by a line 162a to a line 164 which is electrically connected to the other pressure switches 152b, 152c, and to an on/off power switch 166. The opposite side of on/off power switch 166 is connected by line 168 to the power supply 96. The purpose of the above-described elements of control system 130 is to control the supply of electrostatics to the spray gun 94a so that it is electrically isolated from the power supply 96 when not in use, i.e., when not spraying coating material or paint. The operation of control system 130 is as follows. Pressurized air from source 132 is continuously present, at system pressure, within the spray gun 94a via a flow path through the flow switch 136a, line 137a, pressure regulator 138a and line 139a. In response to actuation of the spray gun 94a, such as by depressing its trigger 95 depicted schematically in Fig. 1, a flow of atomizing air is obtained through this flow path and out of the spray gun 94a. This movement of air is sensed within flow switch 136a causing it to close the circuit between the power supply 96, flow switch 136a, electric line 143a and solenoid valve 142a which, in turn, closes the solenoid valve 142a. With the solenoid valve 142a closed, pressurized air from air source 132 flows through air line 140a to the restrictor valve 148a and to the pressure switch 152a. The restrictor valve 148a discharges pressurized air to the pilot of valve 156a associated with discharge shuttle 118a, allowing the pressurised air supply to valve 156a through line 158a to actuate the pneumatic cylinder 56 causing cylinder rod 60 to advance the discharge shuttle 118a to the transfer position with respect to the discharge station 116a. As discussed above, this forms a completed flow path for the paint from second pump 90 and feed line 92 to the spray gun 94a. The pressurized air discharged from solenoid valve 142a to the pressure switch 152a causes the pressure switch 152a to close and send an electrical signal to the on/off power switch 166. This power switch 166, in turn, sends an electric signal through line 168 to the power supply 96 which activates the power supply 96 causing a high voltage electrostatic charge to travel through electrostatic cable 98 to the second piston pump 90. Electrostatically charged paint is emitted from the second pump 90 and transferred between the interconnected discharge station 116a and discharge shuttle 118a to the spray gun 94a for deposition onto a substrate. The above-described sequence of operation is individually applicable to each of the spray guns 94a, b and c such that they are connected to the electrostatics of the system only when actuated, and electrically isolated when not in use. Since the pressure switches 152a, b, c associated with the respective spray guns 94a, b, c are each commonly connected to the single power switch 166, actuation of any one of the spray guns 94a, b, c activates the power supply 96 causing an electrostatic charge to be transmitted to the second pump 90. This ensures that even when only one of the spray guns 94a, b, c is operated, charged coating material will be provided to it from the second pump 90. One feature of control system 130 which is advantageous, particularly in using manually operated spray guns 94a, b, c, is the inclusion of the control or restrictor valves 148a, b, c which provide the signal or pilot air to the valves 156a, b, c associated with each discharge shuttle 118a, b, c. The purpose of the restrictor valve 148 is to provide the operator with a brief delay period, i.e., when the trigger is not depressed, before the electrostatics to the spray guns 94a, b or c are cut off. The pressurized air supplied to the restrictor valve 148a from solenoid valve 142a, for example, takes several seconds to bleed off before the pressure lowers to a sufficient extent to cause the pilot associated with valve 156a of discharge shuttle 118a to reverse the direction of air flow through valve 156a and thus force the shuttle 118a to disengage from discharge station 116a and return to a physically separated, neutral position. In making manual spray operations, the operator is thus permitted to shift position or briefly stop the operation of spray gun 94a and then restart the paint flow without interrupting the electrostatics associated with such spray gun 94a. The electrostatics of apparatus 10 are shut down completely when all of the spray guns 94a, b, c are not operated for a period of time, e.g., longer than a few seconds, as follows. With each gun 94a, b, c non-operational, the flow of air through flow switches 136a, b, c is stopped causing such switches 136a, b, c to open. This interrupts the electric signal to solenoid valves 142a, b, c, which, in turn, stop the flow of air to pressure switches 152a, b, c. This opens pressure switches 152a, b, c, thus interrupting the signal to the on/off power switch 166 which shuts down electrostatic power supply 96. As a result, the paint within pump 90, and the elements downstream therefrom, are uncharged. In another aspect of the apparatus 10 of Figs. 1-3, it is recognized that the pigments and other solid content of many highly conductive coating materials such as water-based paint tend to settle if allowed to stagnate over a given period of time. The apparatus 10 is constructed to avoid this problem by providing for recirculation of the coating material between the paint supply 14 and discharge stations 116a, b and c when none of the spray guns 94a, b or c are operating. In order to obtain such recirculation, each of the spray guns 94a, b and c must be non-operational, i.e., with their triggers open, so that each of the discharge shuttles 118a, b and c are moved to the neutral position physically spaced from the discharge stations 116a, b and c, respectively. This shuts down operation of the electrostatic power supply 96, as described above. At the same time, the control system for voltage block 42 moves each of the first and second shuttles 54 and 82 to a transfer position in which the recirculation line 91 is connected through second shuttle 82 to the transfer station 76. The female coupling element 78 of the transfer station 76, in turn, is connected by the line 80 to the first shuttle 54 coupled to the filling station 44. From the filling station 44, the coating material flows through circulation line 50 to a circulation valve 170 located outside of the voltage block 42. This circulation valve 170 is connected to a drain 172, and by a line 174 to the supply line 18 between the paint supply 14 and pump 20. A recirculation flow path is therefore provided from the pump 20, voltage block 42 and the discharge stations 116a, b, c, and then back through the voltage block 42 and circulation valve 170 to the inlet of pump 20. The pump 20 continuously operates to provide for constant movement of the water-based paint while the spray guns 94a, b and c are not operated. As soon as one or more of the spray guns 94a, b and c resume operation, the voltage block 42 and discharge shuttles 118a, b and c are operated as described previously. Another aspect of the embodiment of Figs. 1 and 2 described above is its adaptability for use with a paint heater 30 in situations where the application characteristics of the paint are improved when dispensed at elevated temperatures. Two aspects of the apparatus 10 of Figs. 1 and 2 make it adaptable for use with paint heater 30. In one aspect, all of the elements in the loop upstream from the voltage block 42, including the paint supply 14, pump 20, heater 30, filter 36 and recirculation valve 170 are continuously electrically isolated from the electrostatic power supply 96. As described above, the voltage block 42 is operative to position one of the shuttles 54 and 82 at a neutral or physically spaced position with respect to their associated filling and transfer stations 44, 76, respectively, whenever the electro-static power supply 96 is activated. The heater 30 is therefore continuously electrically isolated from the electrostatic power supply 96 so that it cannot ground the system electrostatics. The second aspect of apparatus 10 which lends itself to use with heater 30 is the provision of a recirculation flow path for the paint as described above. This recirculation flow path not only prevents the solid content of the paint from settling, but permits recirculation of the paint through the heater 30 so that the elevated temperature of the paint can be maintained even when it is not being dispensed from the spray guns 94a, b, c. Without this recirculation capability, all of the paint downstream from heater 30 would cool while the spray guns 94a, b, c were not operating, thus adversely affecting the application characteristics of the paint. Fig. 3 illustrates an apparatus similar to that shown in Fig. 1, but which is adapted for use with multiple colours, the number and types of which are determined by a given application. Referring to Fig. 3, a colour A supply 176 and a colour B supply 178 are schematically depicted, it being understood that essentially any number of different coloured paints could be utilised depending upon the capacity of a particular colour changer. A colour changer 180 is interposed between the supplies 176,178, and the voltage block 42. All of the elements within voltage block 42, and those elements downstream therefrom, are identical in structure and function to those illustrated in Figs. 1 and 2 and described above. The same reference numbers are therefore used in Fig. 3 to identify the same structure shown in Figs. 1 and 2. The colour changer 180 is preferably of the type disclosed in US Patent No. 4,657,047. The detailed structure and operation of colour changer 180 form no part of this invention, and are therefore only briefly mentioned herein. The colour A supply 176 is connected to a pump 182 which, in turn, is connected by a supply line 184 to one of the bypass valves 186 of the colour changer 180. A heater 188 is mounted in the supply line 184 between the pump 182 and colour changer 180. Internal valving (not shown) within the colour changer 180 interconnects the bypass valve 186 with a universal paint supply manifold 192 which is connected by a line 194 to the filling station 44 of voltage block 42. In the event the spray guns 94a, b and c are not operated, provision is made for recirculation of the colour A paint back out of the voltage block 42, in the manner described above, and then through a line 196 to the universal paint return manifold 198 of colour changer 180. The recirculating colour A paint is transmitted through the colour changer 180 by internal valving (not shown) where it is discharged from a colour module 200 into a return line 202 connected to the pump 182. As described in US-A-4,657,047, the colour A supply may also be provided with a return loop comprising a line 203 connected to the supply line 184 upstream from colour changer 180, which line 203 is connected through a bypass valve 205 and line 207 to the return line 202. This return loop is utilized to recirculate colour A paint when another coloured paint is being dispensed, and a similar return loop is provided for each different coloured paint supply. After a paint operation has been completed with the colour A paint, solvent is introduced into a bypass valve 209 of the colour changer 180, in the manner described in detail in US-A-4,657,047, and then flows through the line 194 through the remainder of the apparatus 10 described in connection with Figs. 1 and 2 and depicted on the righthand portion of Fig. 3. The solvent also flows through the line 196 and universal paint return manifold 198 to a dump container 211 which ensures that the colour changer 180, and the entire system downstream therefrom, are cleaned of the colour A paint. Painting can then proceed with the colour B paint, or any other colour paint, in the same manner as described above in connection with paint colour A. The colour B supply 178 is connected to a pump 204 which feeds colour B paint through a supply line 206 to a second bypass valve 208 in the colour changer 180. A heater 188 is included in supply line 206. Paint colour B passes through the colour changer 180 and is discharged from the universal paint supply manifold 192 through line 194 to the voltage block 42 as described above. During recirculation of paint colour B, the line 196 transmits such colour B paint into the universal paint return manifold 198 for passage through the colour changer 182, a second colour module 210 and then a return line 212 to the pump 204. The apparatus 10 as depicted in Fig. 3 is therefore capable of dispensing essentially any number of different coloured paints using a single electrostatic power supply 96, while providing an effective voltage block between the power supply 96 and each of the paint sources 176, 178 as well as between the power supply 96 and each of the individual spray guns 94a, b and c. With reference to Figs. 407, apparatus 12 is depicted which is particularly adapted for more rapid colour changes than permitted with the apparatus 10 discussed above in connection with Figs. 1-3. Apparatus 12 is particularly useful in applications such as the painting of automotive or other types of vehicle bodies wherein the painting line moves rapidly and a colour change must be accomplished in a short period of time in order to maintain line speed. As described in detail below, this is achieved in apparatus 12 by providing a dedicated shuttle and pump for each of a number of sources of different coloured paints which are selectively transmitted to a colour changer for distribution to one or more spray guns. Only the colour changer, the lines downstream therefrom and the spray guns must be cleaned with solvent in between colour changes, and this can be done efficiently and quickly to accommodate the time constraints of applications such as vehicle painting lines. With reference to Fig. 4, the apparatus 12 comprises a source of highly conductive coating material depicted as paint source 214 which is grounded at 216 and connected by a line 218 to a pump 220 grounded at 222 and by a line 223 to a dump container 225. The pump 220 is connected by a feed line 224, having a filter 226 mounted therein, to a male coupling element 230 carried by a filling station 228 which also mounts female coupling element 232. A shuttle 234 is movable along a pair of rods 236, 237 relative to the filling station 228 by operation of a pneumatic cylinder 238. The rods 236, 237 extend between the filling station 228 and the cylinder housing 240 of the pneumatic cylinder 238, and this cylinder housing 240 carries a cylinder rod 242 mounted to shuttle 234. The shuttle 234 has male and female coupling elements 244, 246 which mate with the coupling elements 232 and 230, respectively, of the filling station 228. These coupling elements are the same type mentioned above in connection with a discussion of Figs. 1-3, are preferably of the type disclosed in European Patent Application No. 91306401.0 and form no part of the present invention per se. The pneumatic cylinder 238 is effective to extend and retract its cylinder rod 242 to move the shuttle 234 between a transfer position in which the coupling elements 244, 246 of shuttle 234 mate with the coupling elements 232, 230 of the filling station 228, and a neutral position in which the shuttle 234 is physically spaced from the filling station 228. The female coupling element 246 of shuttle 234 is connected by a line 248 to the reservoir 250 of a piston pump 252 which carries a piston 251 shown in dashed lines in Fig. 4. As illustrated schematically in Fig. 4, the filling station 228 is grounded at 229 and is housed along with the shuttle 234 and piston pump 252 within a container 253 preferably formed of a dielectric material such as plastic. A supply line 254 extends from the pump reservoir 250, outwardly from container 253, to an electrostatic coating dispenser or spray gun 256 which is preferably of the same type as spray gun 94 discussed above in connection with Figs. 1-3. A return line 258 is connected to the supply line 254 between the piston pump 252 and spray gun 256, and this return line is connected to the male coupling element 244 of shuttle 234 within the container 253. The female coupling element 232 of filling station 228, which mates with the male coupling element 244 of shuttle 234, is connected by a line 260 to a recirculation valve 262 which, in turn, is connected by a line 264 to the line 218 interconnecting the paint source 214 and pump 220. The return line 258, line 260, recirculation valve 262 and line 264 form a recirculation path for the water-based paint when the spray gun 256 is not operating, as discussed in more detail below. With reference to the lefthand portion of Fig. 4, a control system is provided for imparting an electrostatic charge to the water-based paint flowing from the piston pump 252 to the spray gun 256, while ensuring that a voltage block or air gap is continuously maintained between the charged paint and the paint source 214. This control system includes a high voltage electrostatic power supply 266 which is connected by an electrostatic cable 268 to the piston pump 252 in the identical manner depicted in Fig. 1A and described above. When activated, as described below, the power supply 266 is effective to impart an electrostatic charge to the water-based paint within the pump reservoir 250 through the metal elements of pump 252 so that charged water-based paint is supplied to the spray gun 256. The remaining elements of the control system of this embodiment are similar to that depicted in Fig. 2 above. A source of pressurized air 270 is connected by a line 272 to a flow switch 274, and by a line 276 to a solenoid valve 278. The pressurized air from source 270 passes through flow switch 274 and into a line 280 connected to a pressure regulator 282. From the pressure regulator 282, the pressurized air is transmitted by a line 284, having a pressure gauge 285, to the spray gun 256. A branch line 286 is connected to line 284 and extends to the piston pump 252. The pressurized air from pressure regulator 282 and line 284 comprises the atomizing air for spray gun 256. The air from line 286 is required at the piston pump 252 to axially move its internal piston 251 within the reservoir 250 in order to discharge paint therefrom. The electrostatic power supply 266 is connected by an electric line 288 to the flow switch 274 which, in turn, is connected by an electric line 290 to the solenoid valve 278. An air line 292 from the solenoid valve 278 is connected to a control valve 294, and a branch line 296 extends from the air line 292 to a pressure switch 298. This pressure switch 298 is connected by an electric line 300 to an on/off switch 302, and by an electric line 304 to the electrostatic power supply 266. The on/off switch is connected by a line 306 to the power supply 266. In response to actuation of the spray gun 256, such as by depressing its trigger 257, the atomizing air supplied to the spray gun 256 from air source 270, and through flow switch 274 and pressure regulator 282, is permitted to move through the spray gun 256. This movement of air is sensed within the flow switch 274, which is connected to the pressure regulator 282, causing the flow switch 274 to close thus completing an electric circuit between the power supply 266, flow switch 274 and solenoid valve 278. The solenoid valve 278 is closed upon receipt of the signal from flow switch 274, which permits the passage of pressurized air from air source 270 and line 276 through the solenoid valve 278 to the control valve 294 and pressure switch 298. The control valve 294 is connected by a line 308 to the pilot 310 of a valve 312 associated with the pneumatic cylinder 238 which controls the motion of shuttle 234. This valve 312 is constantly supplied with pressurized air from air source 270 through a line 314. When the spray gun 256 is not activated, the air flow through valve 312 causes the shuttle 234 to move to a transfer position coupled to the filling station 228 as shown in Fig. 4. In response to the supply of pilot air from control valve 294 to the pilot 310 of valve 312, i.e., when the spray gun 256 is activated as described above, the direction of air flow through valve 312 is reversed causing the pneumatic cylinder 238 to move the shuttle 234 to a physically spaced, neutral position with respect to the filling station 228. This creates an air gap between the paint source 214, and the piston pump 252 which is connected to the power supply 266. As the shuttle 234 is being moved to the neutral position, the pressurised air supplied from solenoid valve 278 to the pressure switch 298 closes the pressure switch 298 which sends an electric signal to the on/off switch 302. This signal closes the on/off switch 302 to complete a circuit activating the power supply 266 which provides a high voltage electrostatic charge through cable 268 to the piston pump 252. The water-based paint within the pump reservoir 250 therefore becomes charged due to contact with the metal housing of the piston pump 252 and is forced from the pump reservoir 250 through supply line 254 to the spray gun 256. The control valve 294 of the control system described above is essentially the same as control valve 148 described above in connection with Figs. 1-3. Should the operator release the trigger 257 of spray gun 256 for a few seconds, the electrostatics to the gun 256 are not disconnected because the control valve 294 allows the pressurized air supplied by line 308 to pilot 310 to bleed off slowly, therefore maintaining the direction of air flow through valve 312 which retains shuttle 234 in its neutral position spaced from the filling station 228. When operation of the spray gun 256 ceases for a longer period than a few seconds, the above-described operation of the control system reverses. Flow of atomizing air through the spray gun 256 stops which causes the flow switch 274 to open, thus disconnecting the circuit to solenoid valve 278. In turn, solenoid valve 278 opens which stops the flow of pressurized air to pressure switch 298 thus breaking the circuit to on/off switch 302. As a result, the power supply 266 is deactivated so that no electrostatic voltage is supplied to the piston pump 252. Closure of the solenoid valve 278 also stops the flow of pressurised air to the control valve 294 which, in turn, stops the flow of pressurized air to the pilot 310 of valve 312. The flow of air through valve 312 is therefore reversed, allowing the pressurised air from line 314 to cause pneumatic cylinder 238 to move the shuttle 234 to a transfer position with respect to the filling station 228. As depicted in Fig. 4, with the shuttle 234 in a transfer position, the water-based paint flows through filling station 228 and shuttle 234 to refill the pump reservoir 250. When the pump reservoir 250 is filled, the paint exits the reservoir 250 through supply line 254 and then flows back through the return line 258 to the shuttle 234 and filling station 228. From the filling station 228, the coating material passes through line 260 and through recirculation valve 262 and line 264 back to the pump 220. A recirculation flow path is therefore provided in the apparatus 12 of Fig. 4 which is operative when the spray gin 256 is deactivated and aids in preventing settling of the solid content of the paint within the system. Additionally, such recirculation capability enables a paint heater 315 to be included in line 224, upstream from the filling station 228 as depicted in Fig. 4, to maintain the paint at an elevated temperature if desired. The construction of apparatus 12 depicted in Fig. 4 includes a single paint source 214 and a single spray gun 256. This same construction can be duplicated for a number of individual paint sources, each having a different colour, to provide a system for supplying a variety of different coloured paints to essentially any number of spray guns with minimum down time between colour changes. The systems depicted in Figs. 5-7 each provide for rapid colour change from a number of individual sources, but each employ the same control system and voltage block depicted in Fig. 4 and described in detail above. With reference to Figs. 5 and 6, an apparatus 316 is illustrated comprising a housing 318, preferably formed of a dielectric material such as plastic, which carries a dedicated piston pump, shuttle and filling station for each of a number of water-based paint sources of different colours. The piston pump, shuttle and filling station associated with each paint source is identical to that described in connection with Fig. 4, and, for purposes of the present discussion, the same reference numbers used in Fig. 4 are applied to the same structure appearing in Figs. 5 and 6 with the addition of the letters "A", "B", etc., corresponding to different coloured paints. The apparatus 316 is adapted for use with essentially any number of paint sources. For purposes of discussion, a colour A paint source 320a and a colour B paint source 320b are shown in Fig. 5, both of which are connected to a dedicated piston pump, shuttle and filling station. A total of six sets (Fig. 6) of dedicated piston pumps, shuttles and filling stations are depicted in Fig. 6, which is a view from the top of housing 318, to illustrate one manner of charging the different coloured paints prior to transmission to the spray guns. It should be understood that the following discussion of the paint flow path of colours A and B is the same for any of the other colours to be dispensed from apparatus 316. The "colour A" paint source 320a is grounded at 324 and is connected to a pump 322 which is grounded at 325. The pump 322 is connected by a supply line 326 to a filling station 228a which is adapted to couple with a shuttle 234a using the same male and female coupling elements as described above in connection with Fig. 4. The filling stations 228a is grounded at 327. A line 328 from shuttle 234a is connected to piston pump 252a having a reservoir 250a for receiving colour A paint. The pump reservoir 250a is connected by a line 330 to a paint supply valve 332 of a colour changer 334. This colour changer 334 is preferably of the type disclosed in US Patent No. 4,830,055. The details of the structure and operation of colour changer 334 form no part of this invention and are therefore not discussed herein. Internal valving within the colour changer 334 transmits the colour A paint from paint supply valve 332 through a paint supply manifold 336 to a common feed line 337 which is connected by branch lines 339a,b,c to a number of spray guns 256a,b,c, respectively, of the type discussed in connection with Fig. 4. While three spray guns 256a, b, c are shown, it should be understood that essentially any number of spray guns 256 could be utilized. The identical construction is employed to supply a paint colour B to spray guns 256a, b, c. As schematically depicted in Fig. 5, a colour B paint source 320b is connected through a pump 342 and a supply line 344 to the filling station 228b which is grounded to the housing 318 at 343. The colour B paint source is grounded at 340 and the pump 342 is grounded at 345. In the identical manner described above, the colour B paint is introduced into the reservoir 250b of piston pump 252b, and flows therefrom through a line 346 into a second paint supply valve 348 associated with colour changer 334. The colour B paint is discharged through the paint supply manifold 336 of colour changer 334 and supplied by feed line 337 and branch lines 339a, b, c to spray guns 256a, b, c. The apparatus 316 of Figs. 5 and 6 also employs the same recirculation feature as that of apparatus 12 depicted in Fig. 4. As viewed in Fig. 5, the line 330 which interconnects the pump reservoir 250a to colour changer 334 is connected by a branch line 350 to one side of the shuttle 234b. With the shuttle 234b coupled to the filling station 228b, as depicted in Fig. 5, colour A paint from line 330 enters the branch line 350 and passes through the shuttle 234a and filling station 228a for recirculation back to the pump 322 via a return line 352, connected to filling station 228a. The identical construction is provided with respect to the supply of colour B paint, wherein a branch line 354 is connected between the line 346 from piston pump 252b to colour changer 334 and one side of the shuttle 234b. The colour B paint flows through shuttle 234b and the filling station 228b back to pump 342 through a return line 356. In this manner, the paint associated with each of the individual sources 320a and b, or any other number of sources, is continuously recirculated when not being supplied to the colour changer 334 for discharge to the spray guns 256. The apparatus 316 of Figs. 5 and 6 therefore comprises essentially a number of individual apparatus 12 described above and shown in Fig. 4, wherein a dedicated apparatus 12 is provided for each different coloured paint. Accordingly, a control system having the identical control elements shown in Fig. 4 and described in detail above is employed to operate each of the dedicated shuttles 234a, b and their associated cylinders 238a, b. Such control system also operates a single electrostatic power supply 266 which is utilized to impart a high voltage electrostatic charge to each of the several different colours of paint. One addition to such control system is a common electric line (not shown) interconnecting the pressure switch 298 of each set of control elements with the common on/off switch 302. This common electric line functions in the same manner as line 164 described above in connection with the control system 130 of the embodiment of Figs. 1-3. As shown in solid lines in Fig. 5 and in Fig. 6, an electrostatic cable 358 from power supply 266 is connected to one of the piston pumps, e.g., piston pump 252b, in the identical manner shown in Fig. 1A and described above. A total of six piston pumps 252a-f are in shown in Fig. 6 within housing 318 for purposes of illustrating the concept of this invention. These six piston pumps 252a-f are interconnected by electrically conductive straps 360, and a cross-over strap 361, so that the electrostatic charge from power supply 266 is transmitted to each of the piston pumps 252a-f. In an alternative embodiment shown in phantom in Fig. 5, an electrostatic cable 359 is connected to the metal body of colour changer 334. In this embodiment, the paint is electrostatically charged in the course of passage through the colour changer 334 instead of at the piston pumps 252a-f. In either embodiment, charged paint is emitted from colour changer 334 to the spray guns 256a, b, c. The operation of apparatus 316 proceeds in the same manner as described above for apparatus 12. When one or more spray guns 256a, b, c are activated, all of the shuttles 234a-f are moved to a physically spaced, neutral position with respect to their respective filling stations 228a-f. As soon as this voltage block is created, the power supply 266 is activated, as discussed above, which charges the water-based paint within each of the piston pumps 252a-f via electrostatic cable 358 and the interconnecting straps 360, 361, or within the colour changer 334 via electrostatic cable 359. Depending upon which colour is required, one of the piston pumps 252a-f is operated to discharge a water-based paint of desired colour to the colour changer 334 which discharges such colour to the spray guns 256a, b, c through the paint supply manifold 336 and line 337. When a coating operation is completed for this particular colour, the spray guns 256 are deactivated which, in turn, deactivates the power supply 266 and causes the shuttles 234a-f to return to a coupled, transfer station with respect to their associated filling stations 228a-f. In this transfer position, the pump reservoir 250 carrying the particular colour which had just been sprayed is replenished with paint, while the paint within the other pump reservoirs 250 is recirculated as described above to avoid settling of their solid content. One advantage of the apparatus 316, whether the electrostatic charge is applied at the piston pumps 252a-f or at the colour changer 334, is that rapid colour change can be obtained. This is attributable to two features of apparatus 316. First, a dedicated filling station 228, shuttle 234 and piston pump 252 is employed for each colour, and these element carry the same colour throughout operation of the system. Additionally, the colour changer 334 (Fig. 5) has a paint supply valve 332 for each of the separate colours supplied from a dedicated piston pump 252. Accordingly, when a colour change is required, the only elements which must be cleaned are the universal internal passages of the colour changer 334, as discussed in US Patent No. 4,830,055, the lines 337 and 339a,b,c downstream from the colour changer 334 and the individual spray guns 256. The remainder of the apparatus 316, upstream from colour changer 334 need not be cleaned. As a result, the cleaning operation can be performed rapidly with minimum down time. The apparatus 316 depicted in Figs. 5 and 6 is primarily intended for use with automatically actuated spray guns 256 wherein no manual intervention is required or contemplated. As depicted in Fig. 5, a single supply line 337 extends from the paint supply manifold 336 of colour changer 334 to the branch lines 339a,b,c connected to spray guns 256a,b,c, respectively. As a result, all of the spray guns 256 are continuously charged by the charged paint regardless of whether or not they are operating. Only when the electrostatics of the entire system is shut down, i.e., by deactivating power supply 266, will the electrostatics to each of the spray guns 256 be deactivated. In order to adapt the apparatus 316 for use with manual spray guns, to comply with the requirements of the US National Fire Protection Code, the individual shuttle system of the apparatus 10 depicted in Figs. 1 and 2, is employed and interposed between the colour changer 334 and the spray guns 256. As shown in Fig. 7, a separate discharge station 116a,b and c, and an associated discharge shuttle 118a,b and c, is provided for each of the spray guns 256a,b and c. The operation of the discharge station 116a,b,c and discharge shuttle 118,b,c, and the control system associated therewith, is identical to that described in detail above in connection with Figs. 1 and 2 and is not repeated herein. As described above, such system provides a voltage block between the electrostatically charged coating material and each of the spray guns 256a,b and c so that such spray guns 256a,b and c are deactivated when they are not in use. The structure and operation of the apparatus of this embodiment is otherwise identical to apparatus 316, with the electrostatic power supply 266 being connected either to colour changer 334 as shown in Fig. 7 or to one of the piston pumps 250 within housing 318 as shown in Figs. 5 and 6.

Claims: Apparatus for dispensing electrically conductive coating material comprising a pump (90,252) for receiving coating material from at least one source (14,214) and for transmitting the coating material to at least one dispenser (94,256) and means (96,266) for applying an electrostatic charge to the coating material, the electrostatic charge being applied to the coating material at the pump (90,252), means being provided electrically to isolate the said pump (90,252) from the or each source (14,214) of coating material whilst the said pump (90,252) transmits coating material to the dispenser(s) (94,256) characterised in that means (56,238) are provided, connected between the or each dispenser (94,256) and the electrostatic charging means (96,266) for transmitting electrostatically charged coating material to a respective dispenser (94,256) when the dispenser (94,256) is open and electrically to isolate a respective dispenser (94,256) from the charged coating material when the dispenser (94,256) is closed. Apparatus according to Claim 1 characterised in that the isolating/transmitting means comprises a first pump (70) for receiving coating material from the source (14), the said pump (90) for receiving coating material from the first pump (70) and for transmitting the coating material to the dispenser(s) (94), means (58) for electrically isolating the first pump (70) from the source (14) while transmitting coating material from the first pump (70) to the said pump (90) and means (56) for electrically isolating the first pump (70) from the said pump (90) while transmitting coating material from the said pump (90) to the dispenser(s) (94). Apparatus according to Claim 1 or 2, comprising a number of sources (176,178) of coating material, each source (176,178) containing a coating material of a different colour, characterised in that a colour changer (180) is provided between the sources (176,178) of coating material and the said pump (90) for selectively supplying a coating material of a desired colour to the said pump (90). Apparatus according to Claim 1 or 2, comprising a number of sources (320a,320b) of coating material, each source (320a,320b) containing a coating material of a different colour, and a said pump (252a,252b) associated with each source (320a,320b) for receiving coating material therefrom, characterised in that a colour changer (334) is provided between the said pumps (252a,252b) and the dispenser(s) (256) for selectively supplying a coating material of a desired colour to the dispenser(s) (256). Apparatus according to Claim 4, characterised in that means (238a,238b) are provided electrically to isolate each of the said pumps (252a,252b) from its associated source (320a,320b) of coating material while charged coating material is transmitted from the colour changer (334) to the dispenser(s) (256). Apparatus according to any preceding claim characterised in that means (30,188,315) for heating the coating material is provided between the or each source (14,176,178,225) of coating material and the said pump(s) (90,252), the or each source (14,176,178,225) and the or each heating means (30,188,315) being electrically grounded. Apparatus according to any one of Claims 2 to 6, characterised in that control means (130) are provided, which means (130) are operative in response to the opening of a coating dispenser (94) to actuate an isolation means (56) to isolate a respective first pump (70) from the electrostatic charging means (96) to activate the electrostatic charging means (96) so as to electrostatically charge the coating material and to transmit coating material of a desired colour from the said pump (90) to the coating dispenser(s) (94). A method of dispensing electrically conductive coating material, comprising supplying coating material from a source (14,214) to a transfer device (90,252), electrostatically charging the coating material supplied to the transfer device (90,252) in the course of transmitting the coating material from the transfer device (90,252) to at least one dispenser (94,256), electrically isolating the transfer device (90,252) from the source (14,214) whilst transmitting the charged coating material from the transfer device (90,252) to the dispenser(s) (94,256), and operating the dispenser(s) (94,256) to dispense charged coating material characterised in that the method comprises electrically isolating a dispenser (94,256) from the charged coating material when the dispenser is not operating. A method according to Claim 8, comprising selectively supplying coating material of a desired colour from one of a number of sources (176,178,320a,320b) to a colour changer (180,334) and transmitting the coating material from the colour changer (180,334) to the transfer device (90,252). A method of dispensing electrically conductive coating material comprising supplying coating material from each of a number of sources (176,178,320a,320b) of coating material of different colours to a number of associated transfer devices (90,252a,252b), selectively transmitting the coating material of a desired colour from one of the transfer devices (90,252a,252b) to a colour changer (180,334) which supplies the coating material to at least one dispenser (94,256), electrostatically charging the coating material supplied from the transfer device (90,252a,252b) through the colour changer (180,334) to the dispenser(s) (94,256), electrically isolating each of the transfer devices (90,252a,252b) from the sources (176,178,320a,320b) while transmitting the charged coating material to the colour changer (180,334) and the dispenser(s) (94,256), operating the dispenser(s) (94,256) to dispense charged coating material and electrically isolating a dispenser (94,256) from the charged coating material when the dispenser (94,256) is not operating.

Inventors: COELING KENNETH J, HILLS BRUCE C, KONIECZYNSKI RONALD D, COELING, KENNETH J., HILLS, BRUCE C., KONIECZYNSKI, RONALD D.
Applicants: NORDSON CORP, NORDSON CORPORATION
Application year: 1992
Main classification: B05B5
IPC codes: B05B5, B05B12, B05B7