MXPA95004021A - Device and method of recirculation for automat dosing device - Google Patents

Abstract

A recirculation device associated with an automatic dosing apparatus uses pressurized supply tanks for fluid materials to be dosed and a recirculation circuit that allows the fluid material to be recirculated through the dosing head and returned to the pressurized supply tank. The recirculation device includes a buffer vessel in fluid communication with the dosing head and with the pressurized supply tank. In the course of an operating mode of recirculation, the fluid material supplied to the dosing head will be forced to recirculate through channels defined in the dosing head and will then be directed to the buffer vessel. The recirculated paint will accumulate in the cushion container until the recirculation operating mode has been completed. At that time, an operational transfer mode will be started, in order to make the buffer vessel pressurized with a pressure higher than that existing in the tank containing the product. This greater pressure in the cushioning container will be used to forcibly transfer the accumulated recirculated paint inside to feed the tank.

Description

DEVICE AND RECIRCULATION METHOD FOR AUTOMATIC DOSING APPARATUS Field of the invention The present invention relates to the field of automatic dosing apparatuses, in general. More specifically, the present invention relates to a device and methods of recirculation useful for automatic dosing apparatuses that expend very exact quantities (doses) of fluid components that must be mixed. BACKGROUND AND SUMMARY OF THE INVENTION Car painters typically maintain a relatively small inventory of paint colors that can be selectively blended according to established recipes to obtain an exact color match for virtually any model and year of an automobile brand. Hence, automotive paint finishing can make considerable cost savings from inventory keeping a relatively small inventory of paint colors that can be batch mixed when necessary and that match a particular original color. Indeed, the costs would be prohibitive if a complete inventory of pre-mixed paint colors was maintained that matched the original colors of all manufactured automobiles, since the formulations of the car paint colors of a model can change - and change - one year to the next. In the conventional practice of automotive paint finishing, the paint colors are mixed manually. That is, when a specific paint color needs to be matched for a make and model / year of cars, the painter will cast each individual color component of the inventory until achieving the desired weight dose (which is determined by means of a recipe). to match the color).

? In this way a batch of the matching paint color can be obtained by combining these doses of each paint color component manually poured. However, by manually pouring the individual components of paint colors it is not always possible to exactly duplicate the color formulations. For example, the accuracy in the weight of the doses of the paint components is limited. In addition, the doses of heavy paint components are characteristically cast in sequences in a single mixing vessel to minimize inaccuracies that would increase if the individual doses were poured into containers. * weighing separated and then individual doses will be combined. There is also the possibility that human errors increase the amount of a paint color in the batch of previously spilled paint components, which results in rendering the entire batch unusable. The equipment for automatic dosing is known and is used in a number of final applications in cases where it is desirable to mix very precise quantities (doses) according to established recipes. For example, some commercial paint mixing devices are known, which present a balance «And a computerized correction function. In such known devices, when an overdose of a certain component occurs, the other component (s) is added in smaller amounts under computerized control, in order to compensate for the overdosed component. However, the addition of additional amounts of components to compensate for the overdose component may produce new dosing errors and is therefore not a completely satisfactory solution. Also known is an automatic dosing apparatus of European Patent Application No. 0353197 (hereinafter referred to as "EP '197") with which individual fluid components can be collected and mixed in precise amounts.

Specifically, Figure 2 of EP '197 discloses a device that includes a multi-outlet diverter valve (eg, 3-way) by means of which an individual component flowing from a pressurized supply vessel can be directed, either to a dosing head or recirculated to your supply tank. However, since the supply tank is pressurized, a downstream pump is needed to overcome the pressure in the supply tank during recirculation and cause the individual component to return to the supply tank through the recirculation line. While the automatic dosing equipment of the type disclosed in EP '197 can be used to pour very precise doses of paint colors for individual cars (rendering obsolete conventional manual dosing techniques for car painters) several technical disadvantages will still exist real and nothing trivial. For example, since automotive finishing paint is characteristically a mixture of solid pigments in a suitable carrier (eg resin and solvent) there is a possibility that the pigment will settle and / or that the carrier will float (called here). hereinafter "separation of the paint") in the dosing equipment, particularly in the pipes that feed paint to the dispensing head from the paint supply container, during periods when the equipment is inactive. The separation of the paint can result in serious inaccuracies and produce color variations and therefore, color mismatches. The recirculation of the paint through the automatic dosing equipment is part of the equipment intended for the start-up procedures and / or prior to any dosing operation can remedy paint separation problems. However, as briefly mentioned above, in the pressure paint supply device disclosed in EP 197, the paint will only recirculate through the diverter valve and not through the metering head (ie, when the valve diverter is upstream of the dosing head). Therefore, any paint that rests on the pipe that connects fluid from the diverter valve to the dosing head would still be subject to separation of the paint. Hence, it would be highly desirable for automotive paint finishing applications to provide a recirculation device and techniques for the automatic dosing apparatus that allows the individual components to be recirculated through the dosing head. Said recirculation device would ensure that no pigment sediments would be produced in the individual paint doses, thereby increasing the precision associated with mixing in batches of paint components. This invention is directed to offer such improvements. Broadly speaking, the present invention features a recirculation device associated with an automatic dosing apparatus that utilizes pressurized supply tanks for the individual fluid components to be dosed and a recirculation circuit that allows the fluid components to be recirculated through the head dispenser and return them to their respective pressurized supply tanks. The recirculation device according to the present invention more specifically includes shock-absorbing containers that are in fluid communication with the dosing head and a respective pressurized supply tank. In the course of an operating mode of recirculation, the fluid material supplied to the dosing head will be forced to recirculate through channels defined in the dosing head and is then directed to the buffer vessel. The recirculated paint builds up in the cushion container until the recirculation operating mode has been completed. At that moment, an operational mode of transfer is started, in order to make the buffer vessel pressurized with a pressure higher than that existing in the supply tank. This higher pressure in the buffer vessel will thus serve to forcibly transfer the recirculated paint accumulated therein to feed the tank. Any number of such recirculation / flow circuits can be provided in the automatic apparatus of this invention., according to the quantity of individual components of fluid material that must be mixed in precisely measured quantities. With this invention, the fluid components are completely recirculated through the dosing head in order to purge the flow lines towards the dispensing nozzle of the dosing head and ensure high precision dosing. This and other advantages of the present invention will become apparent after carefully reading the following detailed description of the preferred embodiment example. BRIEF DESCRIPTION OF THE DRAWINGS Reference will now be made to the accompanying drawings, in which the same reference numbers of the different figures correspond to similar structural elements and in which: Figure 1 is a schematic representation of an automatic dosing apparatus of paint including the recirculation device of the present invention; Figure 2 is a partial cross-section showing the flow path within the dosing head for a paint component; Figure 3 is a front elevation view of an automatic paint dosing apparatus including the recirculation device according to the present invention; Figure 4 is a rear elevation view of the automatic paint dosing apparatus of Figure 3; Figures 5a and 5b are longitudinal sections of a buffer vessel used in the recirculation device according to this invention, in full and empty state, respectively; Figures 6a and 6b are, respectively, an exploded view and a partial section of a check valve having the recirculation device of the present invention. DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT The present invention can be used successfully for virtually any material capable of flowing (eg, liquids, pastes, grouts, etc.) or that can be induced to adopt a flowable state (e.g. eg thixotropic materials). Hence, in the present and the appended claims, the terms "fluid component" or "fluid material", etc. they mean any material that is capable of flowing during the operating modes of recirculation and transfer of equipment. FIG. 1 shows a diagram of an automatic dosing device 10 according to this invention. The equipment 10 has two paint flow circuits 10A, 10B. However, it is understood that automatic dosing equipment 10 can have any number of flow circuits to satisfy particular applications, depending on the number of components that need to be dosed. For example, the particular embodiment of the dosing equipment 10 shown in Figs. 3-4 can expend 36 individual components, although equipment with greater or lesser vending capacity are also within the scope of this invention. The dosing equipment 10 includes a dosing head 12 which serves to expend individual paint components fed thereto by means of the supply tanks 14A, 14B associated with the flow circuit 10A, 10B, respectively. The expended paint components are received in an overhead open mixing container 16 which rests on a platform of a scale 18 ', associated with a precision gravimetric balance 18. When the paint components are expended within the container 16, the balance Gravimetric 18 will emit a signal indicative of the cumulative weight of the paint in the container 16 to a controller based on a PC 20. An appropriate supply of each paint component is maintained in the supply tanks 22A, 22B, each of which it is provided with rotating agitators 22A ', 22B', respectively. The agitators 22A ', 22B'are operatively coupled to a drive chain 23 (see Figs 3-4), housed within a closed pressurization manifold 24 by means of a flexible torque cable 22A ", 22B", respectively. The drive chain 23 of the manifold 24 is driven by an electric motor 26. Therefore, the operation of the motor 26 serves to drive the drive chain 23 within the manifold 24, so as to turn the flexible torque cables in turn. # 22A ", 22B" and therefore rotate the agitators 22A ', 22B', respectively. A manifold 28 supplies pressurized fluid (eg a gas such as nitrogen or more preferably air) to the pressurizing manifold 24 along line 28a. The pressurized fluid of the manifold 28 will then pass through a pressure regulator 28b which adjusts the fluid pressure at a selected level (eg 1.5 to 2.5 bar). The pressurizing fluid of the manifold is then introduced into each supply tank 22A, 22B via the pressurization conduits 30A, 30B, respectively. The pressurizing conduits 30A, 30B coaxially surround the torque wires 22A ", 22B", so as to create an annular space through which the pressurizing fluid can pass into the supply tanks 22A, 22B, respectively. As a result, the supply of paint to the supply tanks 22A, 22B is maintained at a pressure greater than atmospheric pressure. Each of the tanks 22A22B is provided with a pressure relief valve 31A, 31B, respectively, to be able to withdraw the pressure from the tanks when necessary. Although it is currently preferred to use coaxial torque cables 22A ", 22B" and pressurization conduits 30A, 30B, respectively, such structures can also be provided independently of each other, that is to say they are possible as an alternative arrangement, in which case the means of driving the agitators f ^^ ~ 22A ', 22B' is structurally independent of the ducts used to pressurize the tanks 22 A, 22B. When it is desired to dispense a dose of paint, the controller 20 will emit a control signal to one of the normally closed precision metering valves 32A, 32B. The metering valves 32 A, 32 B will then open in response to a corresponding control signal from the controller 20. Since the supply of paint within the tanks 22A, 22B is pressurized, as described above, the operation of one of the 32 A, 32B dosing valves will cause the paint to be removed from one of the tanks 22S, 22B via ducts 34A, 34B and then directed to the dosing head via ducts 14 A, 14B, respectively. The one-way check valves 36A, 36B are provided with respective conduits 14A, 14B to prevent reflow of the paint. In addition, when a relatively viscous liquid is used (eg automotive finishing paint) as a fluid component, the check valves 36A, 36B serve to prevent uncontrolled dripping of the fluid component from the discharge head 12. That is to say that arranging the check valves 36A, 36B very close to the discharge head 12 (and preferably directly connected thereto), the discharge of the » Fluid component will effectively end when the dispenser operating mode is finished. Therefore, it is not imperatively necessary to provide separate shut-off valves for each of the nozzles of the discharge head 12 to avoid the possibility of the nozzles being clogged with dry material, due to the presence of the check valves 36A, 36B. Relief valves 38A, 38B are provided in bifurcated conduits 39A, 39B (which are in fluid communication at the junction of piping 14A / 34A and 14B / 34B) to allow the escape of air or gas that would have been retained under pressure or dissolved in the paint. The electronic gravimetric balance 18 is responsible for the feedback control of the dosing valves 32A, 32B on the basis of the weight of the paint expended in the container 16. That is to say that the controller 20 will be programmed according to desired recipes that require the addition of precise amounts of paint components. For example, after checking that the correct dose of paint has been delivered from the supply tank 22A by means of the weight signal emitted by the gravimetric balance 18, the controller 20 will in response send a control signal to the metering valve 34A for that it closes and thus ends the operation of selling paint from the main tank 22A. Therefore, according to a preprogrammed recipe, the controller can then issue a control signal to the other metering valve 32B to open and thus allow the paint to be expended into the container 16 from the main tank 22B. Also in this case, when the controller 20 has verified that the paint dose of the supply tank 22B is correct, according to the preprogrammed recipe and has emitted the cumulative weight signal of the gravimetric balance 18, it will emit a control signal to the valve 32B to close and terminate the flow of paint from the supply tank 22B. This procedure is repeated for each individual component that is needed to meet the requirements of a particular preprogrammed recipe. At this time, the dosage of each component is essentially approximate (eg, 95-98%) of the total amount of material needed to fulfill the recipe. Therefore, in order to obtain the final amount of material needed, the controller 20 receives a signal from the electronic balance 18 and calculates the missing amount of each individual component. Then, the metering valves 32A, 32B may be operated in sequence (or simultaneously) to deliver precalibrated volumetric loads of material and thus obtain the precise total amount according to the recipe. Therefore, this combination of approximate gravimetric expenditures followed by volumetric loads offers several advantages in terms of less time of sale and greater precision in the sale. At the end of the multicomponent dosing, the total amount of material is checked by electronic balance 18, supplying a total weight signal to controller 20. Preferred dosing valves 32A, 32B, which are used in practicing this invention, are conventional In themselves. In this regard, dosing valves 32A, 32B are commercially available, manufactured by Cydec S.A. and have been described in more detail in US Pat. No. 5,108,074, the contents of which are incorporated herein by reference. It will be verified, however, that the preferred metering valves have only one intake and discharge. That is, the metering valves do not have any flow bypass function and consequently, when opened, they only allow the paint to flow towards the metering head 12. When it is desired to recirculate paint through the metering head 12 and back to its respective supply tank, a rigid plate 12a is inserted in the retainer 12b (see Fig. 3). Therefore, plate 12a blocks the flow of paint from the discharge nozzles, each of which is intended for a particular color of paint. The accompanying FIG. 2 presents a flow path of the paint within the dosing head 12 and the recirculation channels 14A and 44A, respectively, associated with the flow circuit 10A. The flow of paint through the supply channel 14A will displace the ball 36A 'from its seat, counteracting the force of the spring 36A "inside the one way valve 36. Then, the paint is allowed to enter through the supply inlet 46A. This supply inlet 46A is in fluid communication with its corresponding discharge noz48A via the supply channel 50A, however, since the outlet end of the discharge noz48A is blocked by the plate 12a, the paint enters the recirculation channel 54A displacing the ball 52A 'from its seat, counteracting the force of the spring 52A "associated with the internal one-way valve 52 A. The paint is thus forced to discharge into the recirculation duct 44A through the inlet recirculation 56A. The paint component flowing through the recirculation conduit 44A will be "introduced into a closed damper vessel 60A, associated with the flow circuit 10 A. During the recirculating operating mode, the damper vessel will be maintained at a pressure substantially less than the pressure inside the main tank 22 A. A one-way valve 62A serves to isolate the greatest pressure existing inside the supply tank 22A from the lowest pressure existing in the damper vessel 60 A during the recirculation mode of operation. maintained at atmospheric pressure by means of the three-way solenoid valve 64 A. That is to say that during the recirculation operating mode, the solenoid valve 64A will be in a position that allows to purge the interior space of the buffer vessel 60A to the atmosphere.

The damper container 60A is of sufficient size to admit a predetermined volume of recirculated paint (eg about 150 ml) during the recirculation operating mode. That is, with the valve 32A fully open during the recirculation operating mode, a control signal from the controller 20 will cause a known amount of paint per unit of time to flow through the conduit 14a and therefore recirculate through the conduit 44. A. Therefore, the internal volume of the buffer vessel 60A should be at least large enough to allow the entire conduit 14A to be purged with fresh and agitated paint removed from the supply tank 22A. At the start of the recirculation operating mode an internal clock associated with the controller 20 will be started. After sufficient time has elapsed, corresponding to the passage of the total volume of the paint necessary to ensure complete purging of the line 14A, the internal clock associated with the controller 20 will warn, stopping the recirculation operating mode and issuing a command signal to the valve 34A to close. The cushion container can be filled by operating the metering valve 32A to a fully open state and / or by calibrated volumetric loads. The damping vessel 60A is connected through the solenoid valve 64A to the manifold 28 via the pipe 66, so as to allow the contents of the damping vessel 60A to be pressurized by the pressurizing fluid. Therefore, after completion of the recirculation operating mode as described above, the controller issues a signal to the solenoid valve 64A so that it assumes a position in which, instead of purging the buffer vessel 60A a the atmosphere, put it in fluid communication with the pressurizing fluid supplied by the collector 28g. In this regard, a pressure regulator 68 disposed in the conduit 66 is adjusted to supply fluid under pressure at a pressure of approx. 1 bar higher than the pressure set by the regulator 28b. Accordingly, once the valve 64A puts the buffer vessel 60A in fluid communication with the pressurizing fluid of the conduit 66, the volume of paint recirculation within the buffer vessel 64A will be under the influence of a pressure that is greater ( eg about 1 bar) than the pressure inside the supply tank 22A. As a result of said fluid communication between the buffer vessel 60A and the pressurization conduit 66, the recirculated volume of paint within the buffer vessel 60A is transferred through the conduit • ^^^ - > 70A, through the one way valve 62A, to the supply tank 22A. It will be understood that such fluid communication between the buffer vessel 60A and the pressurizing conduit 66 should only be set momentarily for a time sufficient to allow the transfer of the paint content from the interior of the buffer vessel 60A to the supply tank 22A. Therefore, in response to the internal clock associated with the controller 20 that is interrupted during the transfer operation mode, a signal will be issued for the solenoid valve 64A to reestablish communication between the container 60A and the atmosphere. In Nl ^ - that moment, the one way valve 62A will return to its seat again to maintain the pressure, which is now greater, within the supply tank 22A. The recirculation and transfer operating modes that have been described with respect to the flow circuit 10A are similar to those corresponding to the flow circuit 19B (and any other flow circuit associated with the apparatus 10). That is to say that the cushion container 60B, the one-way valve 62B, the conduit 70B and the three-way solenoid valve 64B (which momentarily fluidizes the container 60B with the pressurization conduit 66 in response to a command signal emitted by the controller 20) are identical to those described with respect to similar structures associated with the flow circuit 10A.

A preferred arrangement of the different structural components described above can be seen more clearly in Figs. 3 and 4 attached. In Figs. 2-3, the structures associated with the flow circuit 10A and the support / auxiliary structures of the automatic dosing apparatus 10 are shown in full lines for clarity. The structures associated with other flow circuits are shown mainly in dotted lines and, although they have not been described in detail, it is understood that they have functions similar to the structures of the flow circuit 10A that have been described. The automatic dosing apparatus 10 includes an appropriate frame 100 having several horizontally disposed support grids 100a which serve to hold a desired quantity of supply tanks. The supply tank 22A is shown in the lower row of the holding grid 100a and is of high capacity compared to other tanks arranged in upper rows of the grid. As a re, the most frequently used colors can be placed in tanks of the lowest row / s to provide a ready paint voter without frequent refilling. The frame 100 also supports equipment / electronic cabinets (see Fig.3) to accommodate the necessary electronic and peripheral devices. The dosing head 12 is also supported by the frame 100 at a central location, on a pedestal 104 and its associated platform 104a on which the gravimetric balance and the dispensing container 16 are located. The solenoid valves, the cushion containers and the Dosing valves are supported by the frame 100 in horizontally organized rows 106, 108 and 110, respectively. Therefore, the solenoid valve 64A, the buffer vessel 60A and the metering valve 32A, associated with the flow circuit 10A are arranged, each within their respective organized rows 106, 108 and 110 with associated structures similar to each other flow circuits. Preferably, a cable groove 112 is provided which creates a space through which the necessary electrical / signal wiring and the like passes to the associated structures. While not specifically shown in Figs. 3 and 4, the pressurizing conduit 28a is connected to the closed and hermetic manifold 24 in which the drive chain 23 and the conduit 66 are arranged, which in the preferred embodiment is also a multiple hermetic structure. Therefore, the connection of the solenoid valve 64A to the manifold 66 via the nip 114A serves to establish the fluid communication between the solenoid valve 64A and the pressurizing fluid provided via the manifold 28 (not shown in Figs. .3 and 4 but in Fig. 1). Similarly, the solenoid valve 64B (and the other solenoid valves of row 106) is in fluid communication with the manifold 66 via its respective nipple 114B. In the recirculation duct 44A it is connected to the transfer duct 70A at a T-junction 116A. The T 116 serves, therefore, to establish fluid communication of the conduits 44A and 70A with each other, as well as with the cushion container 60A via nipple 118A. Similarly, a T-junction 116B and a nipple 119B serve to connect the tubes 44B, 70B and with the buffer vessel 60B, associated with the flow circuit 10B. The other flow circuits not described specifically have similar fluid communications. Accordingly, only a single entry disposed at the bottom of each buffer vessel is needed to allow both entry and exit of the paint during the recirculation and transfer modes of operation described above, thus simplifying the structure of the cushion container. In order to prevent reflow of paint from the damping vessels to their associated solenoid valves during the recirculation mode of operation and to prevent the overflow of pressurization fluid from the damping vessels during the transfer operation modeEach damping vessel is provided with an internal floating valve, as seen in Figs. 5a and 5b attached. Figs. 5a and 5b describe the damping vessel 60A associated with the flow circuit 10A, representative of the other damping vessels included in the apparatus 10. As seen in Figs. 5a and 5b, the cushion container 60A consists, in general, of a cylindrical body 60A? whose open upper end is hermetically closed by means of a screw cap 60A2. The nipple 114A is thus in fluid communication with the interior space created within the body 60A, via an upper opening 60 A3, defined in the lid structure 60 A2. The pressurizing fluid can be introduced into the interior of the buffer vessel 60A during the transfer operation mode, as described above. A spherical floating valve 120A is disposed in the interior space of the cushion container 60A. The floating valve 120A is selected so that it can float and be chemically resistant to the fluid inside the buffer vessel 60A. Eg, when automotive paint is used in the apparatus 10 of this invention, it is preferable that the floating valve be made of n-butyl rubber. Preferred floating n-butyl rubber valves can be purchased from Harper Leather Goods, Chicago, Illinois, Model CT335. Fig. 5a describes the state in which substantially all of the volumetric capacity of the cushion container 60A has been filled with recycled paint PR during the recirculation operating mode. Since the floating valve is floating in the recirculated PR paint, it will rise with the level of the paint. Normally, the paint level in the cushion container 60A does not rise to the lower end of the aperture 60 A3. However, in the event that the level of paint in the buffer vessel 60A rises to an abnormal level, the float valve 120A will be forced to settle into a segmented (or conical) concavity 60 A4 formed at the lower end of the opening 60 A3 (see Fig. 5b). It will be recalled that during the recirculation operating mode, the solenoid valve 64A is vented to the atmosphere. Therefore, after settling in the concavity 60A4 the flow of recirculated paint PR into the cushion container 60A will cease until the pressure in the recirculation duct 44A is not greater than the pressure inside the supply tank 22A. As a result, the float valve 120A functions as a safety valve during the recirculation operating mode to prevent reflow of paint to the solenoid 64A (and possibly the pressurization conduit 66) in the event of controller or similar dysfunction. The floating valve 120A also serves as a safety valve during the transfer operating mode as shown in Fig. 5b attached. That is, during the transfer operating mode, the solenoid valve 64 A will be in fluid communication with the pressurizing fluid in order to pressurize the interior space of the cushion container 60A and thereby transfer substantially all of the recirculated paint to the supply tank 22A by conduit path 70A. However, it is desirable to prevent both the entrainment of pressurization fluid (eg air) in the recirculated paint as well as the transfer of pressurization fluid to the main tank 22 A. As the diameter of the spherical float valve 120A is slightly smaller that the inner diameter of the body dOAj of the buffer vessel 60A, the floating valve 120A will serve as a barrier for the entrainment of pressurizing fluid in the recirculated paint when said fluid enters the buffer vessel 60A during the transfer operating mode. In addition, since the lower end of the body 60 Aj of the cushion container 60 A is hemispherical in shape, will be forced by the pressurizing fluid to settle on the lower opening 60A5 when substantially all of the recirculated paint has been transferred to the main tank 22A. As a result, the pressurization fluid is prevented from entering the conduit 70A and hence the supply tank 22A. The floating valve 120A thus isolates the higher pressure of the pressurizing fluid from the conduit 66 from the lower pressure of the pressurizing fluid in the supply tank 22A (provided via manifold 24 and conduit 34A). In addition, due to the relatively high speed of the fluid during the transfer mode within the buffer vessel 60A, the float valve 120A also serves to avoid any atomizing effect of the air / fluid mixture within the conduit 70A and the consequent entrapment of air in the material. Figs. 6a and 6b attached show a particularly preferred form of vent valve that can be used according to this invention. In Figs. 6a and 6b, the vent valve 38A is shown, associated with the flow circuit 10A, which is considered representative of the vent valve 38B associated with the flow circuit 10B, as well as the other valves that can be used in the apparatus 10 of this invention. In essence, the vent valve 38A consists of a pair of ventilation valves coupled in sequence 38Aj and 38A2, which are in themselves, essentially conventional. That is, the vent valves 38Aj and 38A2 are more preferably spherical check valves manufactured by Chudnow Valve Company, Part No. S470. Valves 38Aj and 38A2 ~ will therefore include respective valve bodies 38A3, 38A4, ball seals / seats 38A5, 38A6 and elastomer O-rings 38A7, 38A8. The valves 38Aj and 38A2 are modified, so as to include a series of balls 38A9, 38A13 and float in the paint supplied from the supply tank 22A. Balls 38A9, 38A13 are preferably made of polypropylene and are obtained from Machining Technologies, Inc. of Elmore, Ohio. A nipple connector 38AM couples the bifurcated line 39A with the body of the valve 38A4. When the paint flows through the valve 32A, into the duct 14A, a portion of the supplied paint will be directed into the bifurcated duct 39A (see Fig. 1). The paint in the duct 39A will serve to bind floating to the series of balls 38A9 38A13 which settle in the ball retainer seat 38A, thus preventing the flow of paint through the body of the check valve 38A4. However, in the event that air (or another gas used as pressurization fluid) arrives at the valve 38 A, it will remain inside the valve body 38A4. Consequently, the balls 38Ap-38A13 will not remain seated in the ball retainer seat 38A6 and will allow trapped air to escape downstream to the valve body 38A3 of the check valve 38Aj. In the event that there is no paint inside the check valve 38Aj, the air may be directed to any appropriate ventilation. As a result, the check valve 38A1 serves as a replica of the functions that the check valve 38A2 fulfills. In this way, the relief valve 38A allows to vent the pressurization fluid that may be trapped in the paint supplied to the dosing head. The apparatus 10 of this invention is compatible with virtually all automotive paints, including those containing aluminum and / or mica particles, which require careful handling to prevent the particles from being damaged. All the component parts of the apparatus 10 can be made of corrosion-resistant materials and solvents, so that it can operate both with paints containing solvents and with paints containing with water. In addition, the structures of the apparatus 10 have been designed explosion-proof and meet the safety regulations in force for equipment that work with flammable materials. That is to say that the supply / recirculation ducts have been provided in a physical place outside all electrical and electronic components, which are housed in explosion-proof or air-pressurized cabinets with appropriate cutting devices for the case of low air pressure. While the apparatus 10 of this invention has been described in connection with a preferred embodiment that allows automotive paint to be accurately and automatically dosed, it will be understood by those skilled in the art that other fluid liquid materials, in paste and / or slurry, can benefit from the same way with the structures / functions described in the present. Therefore, while this invention has been described in connection with an embodiment which is currently considered to be the most practical and preferred, it is understood that the invention should not be limited to the disclosed embodiment, but on the contrary, that it covers different modifications and equivalent provisions included in the spirit and scope of the following claims.

Claims (19)

1. # NOVELTY OF THE INVENTION CLAIMS 1. In an automatic dosing apparatus having a dispensing head for dispensing a dose of fluid material, a supply tank for maintaining a supply of fluid material subjected to a pressure Pl 5 a supply piping that establishes fluid communication between the supply tank and the dosing head and a flow valve disposed in the supply pipe having at least a closed state and an open state which prevent and allow * respectively that the fluid material flows towards the dispensing head, the improvement comprising a recirculation device that recirculates the fluid material during the recirculating operating mode to the supply tank, said recirculation device comprising: a cushion container; a recirculation channel inside the dosing head that establishes fluid communication with the supply pipe; a recirculation pipe that establishes fluid communication between the recirculation channel and the buffer vessel; < * a transfer piping that establishes fluid communication between the buffer vessel and the supply tank; a pressurization fluid manifold at a pressure P2 greater than the pressure P] [of the supply tank; a control valve operatively interconnecting the damping vessel and the pressurizing fluid manifold and having a venting state in which the damping vessel is vented and a state of pressurization in which the damping vessel is in fluid communication with the pressurization fluid manifold; and an automatic controller operatively connected to the flow and control valves to i) initiate an operating mode of recirculation by emitting a first signal to cause the flow valve to assume its open state and thus allow the fluid material to flow through the recirculating pipe to the buffer vessel, thereby accumulating a volume of recirculated fluid material within the buffer vessel and then ii) initiating an operational transfer mode by emitting a second signal to cause the control valve to assume its status of pressurization, being * pressurizing the buffer vessel by the pressurizing fluid in response to the control valve adopting the pressurized state to cause the volume of recirculated fluid material within the buffer vessel to be transferred to the supply tank. In an automatic dosing apparatus of clause 1, the CHARACTERIZED improvement because the damping vessel includes an opening that is in fluid communication with the recirculation and transfer lines and thus allows the volume of recirculated fluid material to flow into and be discharged from the buffer vessel. * In an automatic dosing apparatus of clause 1, the enhancement CHARACTERIZED because the controller issues a third signal during the transfer operating mode to cause the flow valve to adopt its closed state. In an automatic dosing apparatus of clause 1, the improvement CHARACTERIZED because the control valve is vented to the atmosphere when it is in the state of venting. In an automatic dosing apparatus of clause 1, the improvement further comprises a bifurcated line in fluid communication with the supply line and a one-way relief valve disposed on the bifurcated line to allow the gas inside it to be purged In an automatic dosing apparatus of clause 1, the improvement CHARACTERIZED because the one-way relief valve includes a pair of check valves interconnected in series. In an automatic dosing apparatus of clauses 1 or 2, the improvement CHARACTERIZED because the damping vessel includes an internal floating valve that flows in the recirculated fluid material volume. In an automatic dosing apparatus of clause 7, the improvement CHARACTERIZED because the cushion container has a cylindrical body and because the internal floating valve is spherical and has a diameter very similar to the diameter of the cylindrical body of the cushion container. In an automatic dosing apparatus of clause 1, the improvement CHARACTERIZED because the control valve is a three-way solenoid valve. 0. In an automatic dosing apparatus of clause 1, the improvement CHARACTERIZED because the pressure P2 is approx. 1 bar higher than Pressure P1. 11. In an automatic dosing apparatus of clause 1, the improvement CHARACTERIZED because the dosing head includes a dispensing opening in fluid communication with the recirculation channel and a plate that obstructs the dispensing opening during the recirculation operating mode to make that the fluid material supplied to the dispensing head by the supply line is directed towards the recirculation line. 12. In an automatic dosing apparatus of clause 1, the enhancement CHARACTERIZED because it comprises a one-way valve in the supply line and disposed very close to the dosing head to prevent uncontrolled dripping of fluid material after a dose thereof has been sold. 13. A method for recirculating fluid material withdrawn from a pressurized supply tank through a dispenser head so that recirculated fluid material charged from the dispenser head is returned to the supply tank, the method comprising the following steps: "™ a ) to put a damping vessel in fluid communication with the dispensing head by means of a recirculation line and with the supply tank by means of a transfer line; b) establishing a state of pressure within the buffer vessel during the recirculation operating mode that is lower than the state of pressure within the supply tank to allow recirculated fluid material to be discharged from the dispenser head to accumulate within the buffer vessel; and then "A c) establishing a state of pressure within the buffer vessel during the transfer operating mode that is greater than the state of pressure within the supply tank to cause the fluid material to accumulate within the buffer vessel to be transferred to the supply tank through the transfer line 14. A method of clause 13, CHARACTERIZED because step c) is implemented by providing a pressurization fluid manifold having a pressure higher than the pressure prevailing within the supply tank and a control valve having an operative position that establishes fluid communication between the source of pressurization fluid and the buffer vessel and then operating the control valve to assume its operative position 15. A method of the clause 14, CHARACTERIZED because step b) is implemented by venting the control valve to the atmosphere when it is not in its operative position. 16. A method of clause 13, CHARACTERIZED because it also includes, venting the accumulated gas from the supply line. 17. A method of clause 13, CHARACTERIZED because it further comprises, an internal floating valve within the buffer vessel that floats in the recirculated material accumulated therein. 18. A method of clause 13, CHARACTERIZED because it further comprises preventing the controlled dripping of fluid material from the dispensing head after the dose has been expended. 19. A method of clause 18, CHARACTERIZED in that the step of preventing uncontrolled dripping of fluid material includes disposing a one-way floating valve in a fluid material supply line, ^^ __ L very close to the dispensing head.