EP0292354B1 - Installation with a pump for spraying a coating product - Google Patents

Description

The invention relates to an installation of coating product such as, for example, a paint or a varnish, of the type comprising a pump intended to supply at least one projector with such a product. The invention relates more particularly to several improvements relating to the implementation of such a pump; it also targets several applications of its principle in installations of different natures.

A known paint spraying installation, preferably provided with a programmed automatic pilot color change system, comprises a plurality of circuits for circulating paint of different colors which will be called hereinafter "primary circuits", in each of which a paint circulates continuously over a relatively large path, means for supplying rinse aid, also in the form of a continuous circulation circuit, means for supplying compressed air and a set of controlled valves and systems pilot forming what is generally called a "color change block" comprising at least one output connected to one or more projectors located in a paint spray booth. The objects to be painted pass through said cabin. This type of installation is more particularly encountered in the automobile industry where one of the most severe operating constraints, resides in the fact that two objects (bodywork) succeeding each other in the cabin are generally not intended to be painted of the same color, which means being able to carry out a whole color change cycle for a short period of time not exceeding the time necessary to bring a new object into position in the cabin.

In this type of installation, it is known to bring the coating products to a relatively high pressure (6 to 7 bars) upstream of the color change block, that is to say in the primary circuits, to have sufficient pressure at the level of the projector. A pressure regulator is generally provided in the vicinity of the projector and the conduit in which the paint circulates between the color change block and the projector is of relatively large section to limit, as much as possible, the pressure drops. This results in the loss of significant amounts of paint and rinse aid (solvent) with each color change cycle. The time to make a color change can also, in some cases, become excessive. Furthermore, these problems are accentuated if it is necessary to provide a significant length of conduit in the cabin, which is particularly the case when the projector or projectors are mounted on multi-axis robots designed to move inside. of said cabin.

Faced with such difficulties, it has been proposed to insert a pump and in particular a pump whose flow rate is proportional to its drive speed, of the gear pump type, between the color change block and the paint sprayer (s), see for example document DE-A-3221326. The pump being placed in the vicinity of the color change block, it is possible to compensate for the pressure losses in the conduit, whatever its length and even significantly reduce the section of this conduit, which makes it possible to limit the losses of products during '' a color change cycle, while reducing the time required to complete such a cycle. We can also afford to reduce the pressure in the primary circuits, which is typically reduced from 6-7 bars to 3-4 bars. The invention relates to improvements to this type of installation. Such installations have indeed proved unreliable over time by making it necessary to frequently touch up the pump flow. The invention results from research undertaken on the causes of such unreliability.

It has thus been possible to demonstrate that the organs of the gear pump, used under such conditions, wear out more quickly than for other industrial applications and this wear results in an internal leak, i.e. the existence of a fluid flow rate not directly linked to the drive speed of the pump. In fact, this leak exists, although very small, when the pump is new; it is its variation over time that becomes detrimental to the proper functioning of the system. The direction and the importance of this internal leakage depend, among other things, on the pressure difference between the inlet and the outlet of the pump and on the fluidity of the product passing through it. The invention firstly provides a solution to this problem.

In this spirit, the invention essentially relates to an installation for spraying liquid coating product, of the type comprising at least one circuit comprising a pump inserted upstream of at least one projector and connected thereto by a flexible conduit, characterized in that said pump is controlled by means for controlling the flow of liquid in said conduit.

It should be noted that if the pump, mentioned above, is preferably a gear pump, in particular because this type of pump is flushed relatively easily, the basic concept of the invention can be applied for any type of pump.

For its drive, the pump is coupled to an electric motor; it is preferably a self-controlled synchronous motor.

According to another important characteristic of the invention, the aforementioned servo means comprise a flow sensor inserted downstream of the pump in said circuit. This flow sensor will preferably have a structure similar to that of a gear pump, while presenting a pressure drop as small as possible.

Furthermore, as will be seen below, the invention advantageously applies to the use of two-component coating products (paint or varnish + hardener) by doubling the defined circuit. above. The ratio of the mixture of the two components can be adjusted with precision by means of the two flow control means thus implemented jointly.

A manually operated coating product sprayer can easily be used in the context of the invention. For this, it suffices to copy with a suitable transducer the movements given by the user to the control unit of the manual headlamp and to use the signal delivered by the transducer as a variable setpoint signal of said servo means. .

Finally, according to a variant, provision is made to insert a pressure regulator upstream of the or each pump. Such a pressure regulator is a subset known per se, commonly used in the art under consideration. The invention thus makes it possible to better exploit the installation connected to means forming a "color change block", themselves supplied by a plurality of primary circuits, for example conveying paints of different colors, a rinsing product and compressed air. The addition of this pressure regulator makes it possible to further reduce the booster pressure of the pump, but also to vary this booster pressure as desired, during the completion of a predetermined operating cycle of the installation.

• ― La figure 1 est un schéma-bloc d'une installation conforme au principe de l'invention;
• ― la figure 2 est un autre schéma-bloc illustrant l'application du principe de l'invention à la mise en oeuvre d'un produit de revêtement à deux composants;
• ― la figure 3 est un autre schéma-bloc illustrant l'application du principe de l'invention pour l'utilisation d'un projecteur à commande manuelle; et
• ― la figure 4 est un schéma-bloc d'une autre variante de l'installation.

The invention will be better understood and other advantages thereof will appear more clearly in the light of the following description of several embodiments of installations in accordance with its principle, given solely by way of example and made in reference to the accompanying drawings in which:

• - Figure 1 is a block diagram of an installation according to the principle of the invention;
• - Figure 2 is another block diagram illustrating the application of the principle of the invention to the implementation of a two-component coating product;
• - Figure 3 is another block diagram illustrating the application of the principle of the invention for use a manually operated projector; and
• - Figure 4 is a block diagram of another variant of the installation.

Referring more particularly to Figure 1, there is shown a painting projection installation with color change system. This installation comprises several primary circuits 11 for circulation of paints of respective different colors, a color change block 12, known per se, a motor-pump unit 13 in which essential elements of the invention are found, and at least one projector. of paint 14 placed in a cabin 15 in which circulate objects to be painted (not shown). It should be noted that the location of these subsets is not indifferent. Thus, the motor-pump unit 13 is placed near the color changing block 12 (at a distance of the order of one meter) and outside the cabin 15. Therefore, the length of the conduit 16 between the output of the motor-pump unit 13 and the headlamp 14 is relatively large (typically of the order of 12 meters), especially if the headlamp 14, mounted on a robot, must be able to be moved inside the cabin during a phase projection of paint. The section of the duct 16 is nevertheless chosen to be relatively small, the presence of a pump making it possible to compensate for the pressure losses.

The primary circuits 11, which are only partially shown at their respective connection points with the color changing block 12, are in fact long conduits each defining a closed circuit. Each circuit 11, in which paint is continuously circulating, is in communication with a paint tank of a given color, located remotely in the factory. Each primary circuit 11 is therefore connected to the corresponding input of the or each color change block 12. A circuit for circulating solvent or rinsing product 20, analogous in structure to a primary circuit for painting circulation, is connected to one specific input of the color change block 12. Another circuit 21 distributes compressed air and is connected to another specific input of the color change block 12. All this arrangement is well known, the control and sequencing of the openings and valve closures which are integrated into the color change block, are conventional and are not part of the invention. The output 25 of the color change block 12 is connected to the projector 14 by means of a circuit 22 successively including the motor pump group 13 and the conduit 16. The motor pump group 13 successively comprises a pump 28, here of the gear type, the input of which is directly connected to the output 25 of the color changing block, a bypass valve 29, of the three-way type, a flow sensor 30 and flow control means 32 arranged in a control loop between the sensor 30 and the pump 28. These control means are conventional in themselves and will only be briefly described. An electric motor 34 is mechanically coupled to the pump 28 to drive it in rotation. It is a self-controlled synchronous motor, known per se, and therefore associated with control means 36 designed to develop an alternating voltage of variable frequency, supplying the motor. The control means are themselves controlled by a signal from a comparator 38 producing an error signal from a first signal applied to a setpoint input 40 and a second signal directly or indirectly produced by the flow sensor 30. The mechanical part of the latter is here very similar, structurally, to a gear pump; the fluid being channeled to pass between two pinions engaged with each other, driving them in rotation. One of the pinions is integral with an axis linked to any transducer (not shown) capable of delivering an electrical signal which can be used by the comparator 38. The bypass valve 29, of the three-way type, has two outputs and one input . The latter is here connected to the output of the pump 28. One of the outputs is connected to the input of the flow sensor 30 and the other to its output. With this arrangement, it is possible to switch off the flow sensor 30 during a color change cycle or a part thereof and consequently to spare it the operating jolts resulting from the succession, in the conduits. , products of very different nature and viscosity such as paint, solvent or air. This can prevent wear or damage to the flow sensor. Various safety devices are also provided, such as, for example, a safety valve 42, connected in parallel to the pump 28, a pressure sensor 44 upstream of the pump and a pressure sensor 46 downstream of the flow sensor 30 The two pressure sensors thus make it possible to monitor the presence of a product when the pump 28 is actuated. Indeed, a pump of this kind "flu" quickly if it runs empty. In addition, the sensor 46 makes it possible to avoid accidents resulting from a rise in pressure when the projector (s) 14 are closed. The safety valve 42 is calibrated to open from a certain pressure (for example 15 bars) and recycles the product in the event of overpressure.

As mentioned previously, the presence of the pump 28 makes it possible both to cause a lower pressure to prevail in the primary circuits 11 and to reduce the cross section of the duct 16, the pressure drops being compensated by the action of the pump. In addition, any variation in the internal leakage of the pump 28 is corrected by the servo means 32, which gives very good operating stability and reliability, and avoids frequently changing the pump 28. The means used according to the invention also make it possible to improve productivity by achieving an appreciable time saving when changing color. It is indeed now possible, shortly before the end of a paint spraying phase to "push" the paint already engaged in the circuit 22 and in particular in the conduit 16, with solvent or product of rinsing. We therefore begin to clean the circuit 22 before the end of the application of paint on the object being treated. This was not previously practiced due to the difference in viscosity between the paint and the rinse aid, which would have caused a significant variation in the paint flow rate at the outlet of the projector 14. From now on, the pushing by the solvent remains perfectly stable due to flow regulation. It is therefore sufficient that the valve switches in the color change block are controlled to anticipate the introduction of the rinsing product into the circuit 22, with respect to the end of the paint spraying phase on a given object in the cabin 15 Consequently, the various elements of the motor-pump unit 13 are already almost cleaned when the actual rinsing cycle begins, characterized by a succession of injections of rinsing product and air into the circuit 22. The flow sensor 30 in particular is quickly cleaned because of its structure, which then makes it possible to protect it by switching the valve 29.

FIG. 2 represents an installation for spraying a two-component coating product, one of them playing, for example, the role of a hardener. It may, for example, be a paint requiring such a hardener for its implementation, or even a varnish. In an automatic installation, it is desirable to mix the two components continuously, as the mixture is consumed. However, the dosage between these two components must be extremely precise. The invention achieves this objective. In the example shown, all the structural elements similar to those of FIG. 1 have the same reference numbers and will not be described in detail again. In addition, the elements conveying the "base" of the paint or varnish are identified by the index a while the elements conveying the hardener are identified by the index b . We see that the part, in which the "base" of the paint or varnish circulates, is in all respects comparable to the installation of the Figure 1 and comprises a circuit 22 a provided with a pump 28 a and control means 32 a . The circuit 22 a is associated with a color changing block 12 a . This is generally not the case for circuit 22 b which is simply connected to a single circuit 11 b for circulation of the hardener. However, in the case where several types of hardeners could be selectively used to be mixed with different "bases", circuit 22 b could be associated with a system analogous to the color change system already described. The two flexible conduits 16 a , 16 b are selectively connected to the two inputs of a mixer 50 placed in the vicinity of the projector 14 or incorporated into it. The proportion between the "base" and the hardener can be easily and precisely predetermined by adjusting the value of the setpoint signals applied to the inputs 40 a and 40 b .

Figure 3 shows a variant that uses a improper installation essentially to that of Figure 1. It is not distinguished by the nature of the projector 14 is used. It is a manually controlled projector therefore comprising a manual control member 52 or "trigger", the position of which is representative of the flow of product, chosen by the user. According to one aspect of the invention, a transducer 54 is coupled to this control member 52 and the electrical signal output of this transducer is connected to the setpoint input 40. The flow rate of the pump is therefore made variable as a function the action that the user exerts on the control member of his coating product sprayer.

In FIG. 4, the elements similar to those described with reference to FIG. 1 bear the same numerical references increased by 100. These elements will therefore not be described again in detail any more than the way in which they are connected and cooperate with each other. . It will therefore simply be recalled that this installation comprises several primary circuits 111 for circulation of paint, a color change unit 112, a motor-pump unit 113 and at least one paint projector 114, placed in a cabin 115. As before, the motor-pump unit 113 is placed near the color changing block 112 (at a distance of the order of one meter) and outside the cabin 115. Therefore , the length of the conduit 116 between the outlet of the motor-pump unit 113 and the projector 114 is relatively large (typically of the order of 12 meters), especially if the projector 114, mounted on a robot, must be able to be moved to the interior of the cabin during a paint projection phase. The section of the duct 116 is nevertheless chosen to be relatively small, the presence of a pump making it possible to compensate for the pressure losses.

The installation also includes, as in the example in FIG. 1, a circuit for circulating solvent or rinsing product 120 and an air distribution circuit 121.

The output 125 of the color change block 112 is connected to the projector 114 via a circuit 122 including in particular the motor-pump group 113 and the conduit 116. The motor-pump group 113 successively comprises a pump 128, here of the gear type, a bypass valve 129, a flow sensor 130 and flow control means 132. These control means comprise an electric motor 134 mechanically coupled to the pump 128 to drive it in rotation and associated to control means 136 designed to develop an alternating voltage of variable frequency, supplying the motor. The control means are themselves controlled by a signal from a comparator 138 producing an error signal from a first signal applied to a setpoint input 140 and a second signal directly or indirectly produced by the flow sensor 130. The mechanical part of the latter is here very similar, structurally, to a gear pump.

Various safety devices are also provided as above, in particular a safety valve 142, a pressure sensor 144 and a pressure sensor 146.

In accordance with the variant described, a pressure regulator 150 is inserted upstream of the pump 128. More precisely, this regulator is interconnected between the output 125 of the color change block 112 and the input of the pump 128. In addition, additional means for supplying rinse aid, delivering the latter under relatively high pressure, are connected to the circuit 122 between the outlet of the pressure regulator 150 and the inlet of the pump 128. This rinse aid is taken here from another circuit 152 where it circulates in a closed loop, under high pressure. The connection is made by means of a selection valve 153. Another selection valve 154, of the three-way type, is interconnected between the outlet of the pressure regulator, the inlet of the pump 128 and a circuit of purge 155. More precisely, the output of the pressure regulator 150 is connected to the input of the valve 154, one of the outputs of this valve is connected to the input of the pump 128 and the other output of the same valve is connected to the purge circuit 155. The output of the valve 153 is connected to the circuit 122 between the valve 154 and the pump 128. Of course, the setpoint of the pressure regulator can be modified as the a predetermined operating cycle, by conventional control means.

The advantages of this arrangement are numerous.

In the spraying phase of a paint, the booster pressure of the pump can advantageously be reduced to a value of the order of 2 bars, with primary circuits 111 carried between 4 and 5 bars. This booster pressure is also advantageously stabilized whatever the nature of the equipment upstream of the pump. On the other hand, the pressure can be increased beyond 3 bars, only during the filling phase of the circuit 122, after a color change cycle. The phase of "pushing" the paint with rinse aid can, for its part, be advantageously carried out under low pressure, the rinse aid being injected from the block of Color change. In all cases, the pressure at the inlet of the pump is relatively stabilized, which further increases its service life. In particular, the pump 128 no longer undergoes the variations transmitted by the primary circuits supplied by alternative pumps. From the same set of primary circuits, it is now possible to force-feed the pump 128 under low pressure for low flow rates and under higher pressure for high flow rate. One can also advantageously differentiate the booster pressure of the pump 128 according to whether one is in the spraying phase (where the pressure can be relatively lower) or rinsing. This is partly the role of the additional means for supplying rinse aid under high pressure, including the circuit 152. This arrangement also makes it possible to save time during the color change cycle. Indeed, while the part of the circuit 122 going from the pump 128 to the sprayer, is cleaned by high-pressure rinsing product, the part between the color change block 112 and the valve 154 is cleaned simultaneously but more quickly ( given its short length) with rinse aid from circuit 120. The rest of the time is used to start introducing the new paint until the outlet of valve 154, while cleaning of the circuit ends 122. This saves several seconds in each color change cycle.

Claims (13)

1. An installation for spraying a liquid coating product of the type comprising at least one circuit (22) including a pump (28) disposed upstream of at least one sprayer (14) and connected thereto by a flexible conduit (16), characterised in that said pump (28) is controlled by means (32) for controlling the flow rate of liquid in said conduit.

2. An installation according to claim 1 characterised in that said pump (28) is a per se known gear pump.

3. An installation according to claim 1 or claim 2 characterised in that said pump is coupled to an electric motor (34) to be driven thereby, preferably a self-regulated synchronous motor.

4. An installation according to one of claims 1 to 3 characterised in that said flow rate control means (32) comprise a flow rate sensor (30) disposed in said circuit downstrean of said pump.

5. An installation according to claim 4 characterised in that said flow rate sensor (30) is of the gear type.

6. An installation according to one of claims 4 and 5 characterised in that a controlled by-pass valve (29) is connected to said flow rate sensor.

7. An installation according to claim 6 characterised in that said by-pass valve (29) is a three-way valve comprising an inlet and two outlets, said inlet being connected to the outlet of said pump (28) and the two outlets being respectively connected to the inlet and the outlet of said flow rate sensor.

8. A coating product spraying installation according to one of the preceding claims characterised in that it comprises two said circuits (22a, 22b) in which two components of said coating product flow, and that the two circuits are connected to a mixer (50) disposed in said sprayer or in the vicinity thereof.

9. A coating product spraying installation according to one of the preceding claims wherein said flow control means comprise a reference input (40) for controlling the flow rate of the pump, characterised in that said sprayer is of the manually controlled type, that a transducer (54) is coupled to the control member of said sprayer and that the output of said transducer is connected to said reference input.

10. A coating product spraying installation according to one of the preceding claims comprising rinsing product feed means which are controlled by per se know switching means characterised in that said switching means are pilot-controlled so that the end of a sequence of spraying said coating product is preceded by the introduction of rinsing product into said circuit, said product urging the paint towards said sprayer.

11. A coating product spraying installation according to one of the preceding claims characterised in that it comprises a pressure regulator (150) upstream of the or each pump (128).

12. An installation according to claim 11 characterised in that said pressure regulator (150) is disposed between means forming a colour change unit (112) and the inlet of said pump (128).

13. An installation according to claim 11 or claim 12 characterised in that supplementary means (152) for the feed of rinsing product under relatively high pressure are connected by way of a set of selector valves (153, 154) between said pressure regulator (150) and said pump (128).

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