EP0338871A1 - Controlled paint spray installation using frequent colour changes, in particular for the motor car industry - Google Patents

Abstract

The installation comprises a coating product spray (14) fed, via a distribution circuit (12), with a combination of five primary colour change units (G to K), connected by controlled valves (1g-6g, 1h-6h, 1i-6i, 1j-6j, 1k-6k) to groups (A to E) of paint supply loops (1a-6a, 1b-6b, 1c-6c, 1d-6d, 1e-6e), through each of which a particular coating product passes, and a secondary colour change unit (L) connected to the outputs of the primary units (G to K) by intermediate ducts (11g to 11k). Thus, the only ducts in which the coating products could stagnate and deposit sediment are these intermediate ducts. In the usual case, these intermediate ducts are flushed and rinsed after use. However, in order to reduce losses of paint and solvent, the flushing and rinsing of a duct are inhibited if, according to the colour change predictions, on the first occasion the duct is used after being used with a particular colour, and within a fixed period of time, the same colour will be used. <IMAGE>

Description

The invention relates to a controlled installation for spraying coating product comprising at least one projector supplied, through a distribution circuit comprising means for propelling coating product, from a coating product change device. connected to a multiplicity of supply loops, each traversed by a particular coating product, by as many controlled valves, the apparatus also being selectively supplied with rinsing product and with air for drying under pressure.

The invention is more particularly applicable to the use of lacquers or metallic or solid bases of multiple colors, with rapid and frequent color changes of the coating product, in particular for the coating of automobile bodies.

Known paint spraying installations provided with a programmed automatic piloting color change system, comprising a plurality of circuits for circulating paints of different colors which will hereinafter be called "supply loops", 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 of control 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. Objects to paint pass through this cabin. This type of installation is encountered more particularly in the automobile industry where one of the most severe operating constraints, resides in the fact that two successive bodies in the cabin generally do not have to be painted the same color, which means that a complete color change cycle can be carried out 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 per se to use conventional equipment, in which a single color changer, for each sprayer, has its inputs connected to the supply loops, and also has two specific inputs connected to a solvent circulation circuit, and a pressurized air distribution circuit.

The supply loops are in fact long conduits each defining a closed circuit. Each loop, in which paint is constantly circulating, is in communication with a paint tank of a given color, located remotely in the factory.

Controlled valves allow the admission into the collector of the color change apparatus and therefore the arrival in the sprayer of as many different products as there are supply loops.

Valves allow injection into the distribution circuit of rinsing solvent and blowing and drying air.

In a conventional body paint application station, 9 sprayers are generally used. This station therefore generally comprises at least 9 similar circuits as just described, only the supply loops being common to all the sprayers.

All this arrangement is well known, the control and sequencing of the openings and closings of the valves which are integrated into the color change block, are conventional and allow successively to paint and rinse the circuits, then to paint again with another color. or another product without pollution of the new color by the old color.

The output of the color change block is connected to the projector via a distribution circuit successively including a motor-pump group and a conduit. The motor-pump unit consists of a pump of the rinsable gear type, short-circuitable during the color change sequence, the input of which is directly connected to the output of the color change block, and a motor. drive, for example of the step-by-step type, the speed of rotation of which is considered to be proportional to the quantity of paint withdrawn from the supply loop and discharged towards the sprayer. Pressure sensors monitor the inlet and outlet pressures of the pump.

These conventional systems have many drawbacks: they indeed require for each color change, a complete rinsing of the color change block, resulting in a significant loss of solvent and paint.

The color changing block or apparatus, always placed near the pump, is connected by a hose several meters in length to the supply loops, which leaves without movement and therefore without mixing the contents of the pipes which do not correspond sprayed product at the time. However, certain products such as bases or water products, consisting of suspensions, sediment when they are no longer in motion for a period of time exceeding a few tens of minutes.

To correct this last point, it has been proposed to put Y-shaped fittings at the inlet of each of the controlled valves of the product change device, so that each valve is connected to a branch of the Y, l 'arrival on a second branch and finally a paint return to the supply loop connected to the last branch of the Y. But experience has shown that, apart from the fact that it leads to an inextricable forest of pipes, the number of colors sometimes exceeding thirty, It also causes enormous difficulties in regulating the flow rate in the supply loop, which is permanently disturbed by the opening or closing of the valves of the various sprayers.

Finally, a major drawback of such systems lies in the fact that when one of the many controlled valves breaks down, in order to be able to dismantle it, it must close all of the manual sectioning taps when connected to the supply loops. and therefore stop the operation of the sprayer.

To overcome these drawbacks, the invention proposes a piloted installation for spraying coating product comprising at least one powered projector, through a distribution circuit comprising means for propelling coating product, from a change of switchgear. coating product connected to a multiplicity of supply loops, each traversed by a particular coating product, by as many controlled valves, the apparatus also being selectively supplied with rinsing product and air for drying under pressure, characterized in that said apparatus is divided into a plurality of coating product changing units, here called primary units, arranged in parallel in close proximity to the multiplicity of supply loops and each having an outlet, and in that '' a coating product change unit, here called secondary unit, has a plurality of inputs fitted with valves controlled, each connected through an intermediate pipe to the outlet of a respective primary unit, pipe rinsable after use from this respective primary unit.

By placing the primary product change units in the immediate vicinity of the coating product supply loops, the product stagnation between the supply loops and the controlled valves of the primary units is eliminated, stagnation can only occur in the intermediate pipes, which are in reduced number, and can be cleaned by rinsing and blowing from the primary coating product change units. In addition, damage to a valve controlled by a primary unit can be repaired by isolating the primary unit from the only supply loops to which this unit is connected, while the rest of the installation continues to operate with the colors which do not correspond to the isolated primary unit.

In preferred arrangement, the installation is controlled by a computer where a forecast of sequence for changing the coating product is stored and this computer is programmed to inhibit the rinsing of an intermediate pipe after use with a particular coating product if this pipe must be reused at the first occurrence by the same coating product, within a specified period of time.

This reduces the frequency of rinsing of the intermediate pipes, and the amounts of lost coating product and rinse aid consumed, eliminating the rinsing each time the coating product remaining in the intermediate pipe would be reusable. Statistical studies on the frequencies of use of the various coating products, which will be discussed in more detail below, make it possible, by assigning the supply loops corresponding to the various primary units to the various coating products as a function of their frequency of use. use, to maximize the probability of occurrence of the successive use of the same product in the same intermediate pipe.

Preferably, the propulsion means comprise, at the output of the secondary coating product change unit, a pump driven by a variable speed motor controlled by a servo device sensitive to the difference between a signal emitted by a flow sensor in series with said pump, and a setpoint signal.

Considering that the precise adjustment of the flow rate of coating product to the sprayer is a primary condition efficiency and repeatability of the spray coating, it will be understood that the use of a flow-controlled pump allows such precise adjustment, regardless of the pressure under which the coating product is supplied to the distribution circuit; however, due to the multiplicity of supply loops, variations in the flow rate supplied by these loops, and pressure losses resulting from the length of the pipes through which the coating products circulate, the adjustment of the flow rate or sprayer of products powered by upstream overpressure is a source of considerable difficulty.

Preferably, a controlled valve is arranged in parallel with the pump. This valve will be open during cleaning cycles.

• - la figure 1 représente schématiquement une installation conforme à la présente invention;
• - la figure 2 représente schématiquement les moyens de propulsion de produit de revêtement vers le projecteur.

The characteristics of the invention, with their advantages will emerge more clearly from the description which follows by way of example, with reference to the appended drawings in which:

• - Figure 1 schematically shows an installation according to the present invention;
• - Figure 2 shows schematically the means of propelling coating product to the projector.

According to the embodiment chosen and represented in FIG. 1, a coating product projection installation according to the invention, with controlled change of coating product, is supplied by a multiplicity of supply loops (here 30) grouped in one plurality (here 5) of blocks A, B, C, D, E of six loops referenced 1 to 6 with the lowercase letter of its block. Each supply loop includes, as shown here for loop 5 d , a tank R, a circulation pump P, a supply line Q and a return line S.

On each supply loop Nx (N = 1 to 6, x = a-e) a nozzle is arranged with a manual valve N'x.

Each block A, B, C, D, E of six supply loops is associated with a primary unit for changing the coating product, respectively G, H, I, J, K, comprising six pneumatically operated valves Ny with N = 1 to 6 in correspondence with the supply loops, and y = g, h, i, j, k, in correspondence with the reference of the change unit of product.

In addition, each GK primary unit comprises two pneumatically operated valves 8 (gk) and 9 (gk), connected respectively to rinsing product 20 and air under blowing and rinsing pressure 21 lines, and an outlet 10 ( gk).

Note that the connections between the manual valves 1′a-6′a, 1′b-6′b, 1′c-6′c, 1′d-6′d, 1′e-6′e and the ordered valves 1g-6g, 1h-6h, 1i-6i, 1d-6d, 1k-6k, are as short as possible.

In addition, the five outputs 10g-10k of the recovery product change units are connected by pipes 11g-11k of length of the order of a meter to pneumatically operated valves 1 l , 2 l , 3 l , 4 l , 5 l respectively of a secondary unit L for changing the coating product, of conventional structure similar to that of the primary units GK. This secondary unit L also has pneumatically controlled valves 8 l and 9 l connected respectively to the pipes 20 and 21 for supplying rinsing product and blowing and drying air, and an outlet 10 l .

This secondary unit L for changing the coating product is located a short distance from the product projection booths. Its output 10 l is connected to a distribution circuit 12 comprising a product propulsion group 40 as a whole, which will be described in more detail with reference to FIG. 2, which flows into a flexible pipe 41 for connection to the projector 14.

In practice, a covering station for automobile bodywork can have up to 9 projectors, each powered independently by an installation as just described.

The selection of the various coating products includes, analogously to the conventional process of change of product, the opening of the valve controlled in group 1a-6a, 1b-6b, 1c-6c, 1d-6d, 1e-6e, which corresponds to the supply loop assigned to the desired coating product, and simultaneously that of the valve of group 1 l -5 l of the secondary unit L which corresponds to the suitable group in the plurality AK of supply loops. When the projection is finished, and during the replacement of the painted bodywork with the next one in the cabin, the secondary product change units L and that of the primary units GK which has been used are rinsed, as well as the distribution circuit 12.

A priori, that of the intermediate pipes 11g to 11k which has just been used should be purged of the paint it contains, then rinsed and dried from the primary unit for changing the coating product at the outlet from which it is connected. However, purging and cleaning of this intermediate pipe is unnecessary if the next use of the same pipe must be with the same coating product, and before the product which remains stagnant in the pipe has started to sediment. It will be understood that if the computer has memorized the forecast sequence of use of the coating products for a duration greater than the duration of non-sedimentation of the products, it is within the reach of the skilled person to program this computer to identify the occurrence of the succession of use of the same product in the time interval of non-sedimentation, and controlling in response the inhibition of the purging and cleaning operation of the intermediate pipe of the plurality 11g-11k.

However, to optimize the savings in coating and cleaning products, it is necessary to seek to obtain the greatest possible frequency of these occurrences.

However, if the succession of colors corresponding to customer orders is random, the attractiveness of the various colors for customers means that the frequency of choice of different colors, or probability of use of each coating product is determinable.

Without going into the details of probability calculations, it will be noted that the probability of occurrence of successive use of the same coating product increases with the probability of use of this product. In addition, as each intermediate pipe 11g-11k corresponds to a group of coating products, the probability of occurrence of successive use increases with the probability that after a first use, the demands for other products occur in other groups. of covering product loops. Thus, after having estimated the frequencies of choice of the different colors, we will assign the five most requested colors to each of the five groups of supply loops A to E, then the five colors of lower frequency and so on in descending order of frequency, by operating for the different groups of five colors of the permutations to best equalize the probabilities of use of the five primary units G to K of product change.

It will also be appreciated that if a fault occurs in one of the primary coating product change units G to K, in particular on a pneumatically controlled valve, it is possible to continue working with the other primary units and product change coating, while we will intervene on the deficient member after closing the manual valves 1′x to 6′x of group X of supply loops corresponding to the primary unit Y broken down.

It will be noted, moreover, that the drop in manufacturing yield compared to the programmed orders will be substantially the same regardless of the damaged primary unit, since the coating products have been distributed to the primary units G to K to equalize at best their probabilities of use.

As shown in FIG. 2, the propulsion means 40 comprise a rinsable pump 55, of the type to gear, driven by a motor 50 with rapid response time, and further connected to the output 10 l of the secondary unit L for changing the coating product. The motor 50 is powered by servo electronics 51 with a comparator 52 which receives on the one hand, a flow signal delivered by a flow sensor 53, and on the other hand, on an input 54, a setpoint signal developed by an automatic management principle known in itself. In parallel, on the pump 55, there is a controlled valve 56 which can be opened, either to discharge the pump in the event of downstream overpressure, or to bypass the rinse aid when the pump is not running. Between the pump 55 and the flow sensor 53 is disposed a three-way valve 57, which allows the rinsing product to be diverted parallel to the flow sensor, which does not have to work in the rinsing phase.

Pressure sensors 58, 59 respectively upstream and downstream of the propulsion means 40 provide the safety functions to protect the pump 55 and the flow sensor 53.

Claims (4)

1- Controlled installation for coating product projection comprising at least one powered projector (14), through a distribution circuit (12) comprising means (40) for coating product propulsion, from a changeover device of coating product (G, H, I, J, K, L) connected to a multiplicity of supply loops (1a-6a, 1b-6b, 1c-6c, 1d-6d, 1e-6e) each traversed by a particular coating product, by as many controlled valves, the apparatus being additionally supplied in a selective manner with rinsing product and air for drying under pressure, characterized in that said apparatus is divided into a plurality of change units of coating product (G to K), here called primary units, arranged in parallel in close proximity to the multiplicity of supply loops (1a to 6e) and each having an outlet (10g-10k), and in that a coating product change unit (L), here called secondary unit, pr has a plurality of inputs with controlled valves (1 l -5 l ), each connected through an intermediate pipe (11g-11k) to the outlet of a respective primary unit (G to K), pipe rinsable after use at from this respective primary unit. 2- Installation according to claim 1, the control of which is ensured by a computer where a forecast of sequence for changing the coating product is stored, characterized in that the computer is programmed to inhibit the rinsing of an intermediate pipe (11g -11k) after use with a particular coating product if this pipe must be reused at the first occurrence, by the same coating product, within a determined period of time. 3- Installation according to one of claims 1 and 2, characterized in that said propulsion means (40) comprise at the outlet (10 l ) of the secondary unit (L) of change of coating product a pump (55), preferably of the gear type, driven by a variable speed motor (50) controlled by a device (51, 52), of a control sensitive to the difference between a signal emitted by a flow sensor (53) in series with said pump (55) and a setpoint signal (54). 4- Installation according to claim 3, characterized in that a controlled valve (56) is arranged in parallel with the pump (55).

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