EP0649919B1 - Installation for surface treatment of metallic workpieces by cataphorese, particularly of car bodies - Google Patents

Description

The invention relates to an installation for treating surfaces by cataphoresis of metal parts, in particular motor vehicle bodies.

The invention relates more particularly to a surface treatment installation by cataphoresis, supplied by direct current, which comprises a tank whose edges carry anodes, an overhead conveyor which brings the parts to be treated spaced at a regular pitch λ, and which door of current supply mobiles in contact with at least one current conducting rail mounted on at least one support and located above the tank, and in which the parts to be treated constitute the cathodes.

It is known to produce a surface treatment installation by cataphoresis in which a rail is regularly divided at intervals λ into portions separated by an insulating material.

It is also known to make an installation of the same type in which two parallel rails are divided into portions separated by an insulating material so that the fractionation zones are in correspondence from one rail to the other, each rail portion being supplied by a different rectifier.

In these two cases when contacting the current supply mobiles with the fractionation zones, the rectifiers are switched off for the entire installation in order to avoid short circuits between rectifiers.
The metal part is then no longer supplied with current, which can cause coating defects of the part by sedimentation during these power cuts.

Furthermore, this operation reduces the effective quenching time of the part in the tank, resulting in an obligation to lengthen the tank to obtain the quenching time necessary for processing the part, or to use a very low rate.

The subject of the invention is an installation for treating surfaces of metal parts, indifferently comprising one or more current conducting rails, which makes it possible to specialize the treatment for each of the parts without the latter being subjected to a power cut in order to overcome the problems. appearance of the treated parts.

The invention also relates to an installation for treating surfaces by cataphoresis adaptable to any rate without the need to lengthen the installation.

Another object of the invention is to allow control of the voltage and current received at all times by the parts to be treated and precise knowledge of the voltage and current values.

The invention also relates to a surface treatment installation in which the number of rectifiers required is equal to the number of parts simultaneously in the tank.

According to a first alternative embodiment of the invention, the rail is regularly divided at intervals substantially equal to λ / 2 into portions separated by an insulating material and connected to the negative terminals of rectifiers of the supply current of the installation.

According to a second alternative embodiment of the invention, the installation comprises two parallel conductive rails and is characterized in that the two rails are divided in a manner known per se regularly into portions separated by an insulating material and connected to the negative terminals of rectifiers of the installation supply current and that the fractionation zones are offset from each other between the two rails.

• la figure 1 est une représentation schématique partielle d'une telle installation selon une première variante de réalisation,
• la figure 2 est une représentation schématique partielle d'une telle installation selon une seconde variante de réalisation.

Other characteristics and advantages of the invention will appear on reading an exemplary embodiment of a cataphoresis painting installation of motor vehicle bodies, with reference to the drawing in which:

• FIG. 1 is a partial schematic representation of such an installation according to a first alternative embodiment,
• Figure 2 is a partial schematic representation of such an installation according to a second embodiment.

In the following description, the common members of the different figures will be designated by the same references.

According to Figures 1 and 2, the installation comprises a paint tank 1, the edges of which carry anodes 2 connected to the positive terminals 32 of rectifiers 3 of the direct current supplying the installation.

The installation also includes an overhead conveyor (not shown) which causes the bodies 5 to be treated spaced apart at a regular pitch λ and which carries current supply mobiles constituted by carriages 4 equipped with two contact pads 41 and 42 mounted on two rails 11 and 12 parallel conductors mounted on at least one support not shown and located above the tank 1.

• soit par des chariots 4 équipés d'au moins un patin 41 de contact monté sur le rail 11, et portés par des balancelles qui supportent les carrosseries 5,
• soit par une navette au contact d'une série de patins fixes qui constituent un conducteur équivalent au rail et dont les portions correspondent alors à un ensemble de patins fixes.

This installation is described by way of nonlimiting example. Indeed, in particular for the first alternative embodiment of the invention shown in FIG. 1, the installation could have been envisaged with a single rail 11 where the mobiles for supplying the current would have been made up:

• either by carriages 4 equipped with at least one contact pad 41 mounted on the rail 11, and carried by swings which support the bodies 5,
• either by a shuttle in contact with a series of fixed pads which constitute a conductor equivalent to the rail and the portions of which then correspond to a set of fixed pads.

The rails 11 and 12 are divided into portions separated by an insulating material and connected to the negative terminals 31 of rectifiers 3 of the supply current of the installation.

The number of rectifiers 3 used is equal to the number of bodies 1 simultaneously present in the tank 1. It is however possible to provide an emergency rectifier 3 'as shown in FIGS. 1 and 2.

The negative terminals of the rectifiers 3 are respectively connected to diodes 16, the anodes 161 of which are connected to earth 17 of the tank 1 so that the diode connected to the rectifier of higher potential becomes conductive, thus avoiding problems of corrosion of the tank. 1.

According to the first alternative embodiment shown in FIG. 1, the rails 11 and 12 are divided regularly at intervals substantially equal to λ / 2 into portions 111 and 121 respectively.

The fractionation zones 15 thus obtained, made of insulating material, respectively 151 and 152 for the rails 11 and 12, are opposite and have a length less than that of the pads 41 and 42 in order to avoid an interruption of the supply of bodywork 5.

The portions 111 and 121 of the rails 11 and 12 opposite are connected by bridges 14 so that the two pads of the same carriage 4 are always subjected to the same supply.

The power supply to rail 11 will therefore be described below.

The latter consists of portions 111 and 111 ', a portion 111' being juxtaposed with a portion 111.

The portions 111 are supplied directly by a rectifier 3 while the portions 111 'are supplied by means of two thyristors 22 and 23 in opposition, each of them being connected to a different rectifier 3. Thus two juxtaposed portions have a different feeding mode.

The two thyristors 22 and 23 supplying a portion 111 ′ are each located at one of the ends of said portion, that is to say that the connections are made in the end zones of the portion.
For two portions 111 'adjacent to the same portion 111, the thyristor 22 of one of the portions 111' located near the portion 111 and the thyristor 23 of the other portion 111 'also located near the portion 111, are connected to rectifier 3 which directly supplies this portion 111.

The rail 12 is therefore also constituted by portions 121 and 121 ′, the bridges 14 between the two rails 11 and 12 being produced by each direct or indirect supply cable through a thyristor 22, 23.

It is easy to deduce from this description an installation according to the invention which would include carriages 4 carrying a single contact pad 41 mounted on a rail 11 as described above, the supply device differing from the previous only by absence of bypasses 14.

An example of the operation of such an installation will be described during the passage of a carriage from a portion 111 to the next portion 111 in the direction of the arrow shown in FIG. 1.

A carriage 4 passing through a portion 111 is supplied directly by a rectifier 3. When the carriage 4 reaches a fractionation zone 151, the voltage of the rectifier 3 is increased so that it is greater than that of the rectifier connected to the thyristor 22 of the next 111 'portion.

This command enables the thyristor 23 of this portion 111 ′ to pass and to block its thyristor 22 so that on either side of the fractionation zone 151 the rail 11 is supplied by the same rectifier 3.

The thyristors 22 and 23 permanently receive pulses to be primed. This arrangement allows during a possible false contact in the supply circuit or between a shoe 41 (42) and a rail portion 111 '(121') causing the extinction of the thyristor concerned, that the latter turns on immediately.

When the carriage 4 has entered the portion 111 ′, an increase in the voltage of the rectifier 3 connected to the thyristor 22 of this portion relative to the voltage of the rectifier previously used, enables the thyristor 22 to pass. The portion 111 ′ is then supplied by the rectifier 3 connected to the thyristor 22.

The passage through the following fractionation zone 151 takes place without change of state of the thyristors, since the next portion 111 is already connected directly to the same rectifier 3.

According to the second variant embodiment of the invention shown in FIG. 2, the rails 11 and 12 are regularly divided into portions respectively 111 and 121 so that the fractionation zones 151, 152 are spaced apart on each of the rails 11, 12 of the not λ.

Thus, the fractionation zones 151 are offset linearly with respect to the fractionation zones 152, this offset is equal to λ / 2.

The supply of each portion 111, 121 of the rails 11 and 12 is carried out by means of a set 20 of thyristors 21 each of which is connected by its cathode to the negative terminal of a different rectifier 3 so that it it is possible to select, thanks to these thyristors 21, any of the rectifiers 3 to supply a determined portion.

• supérieure à celle d'un patin 41 (42) au contact d'un des rails 11 (12) de sorte à provoquer une extinction totale des thyristors connectés à ce rail 11 (12) au passage de ses zones de fractionnement 151 (152),
• et inférieure à λ/4 dans le but lors du passage des zones de fractionnement 151 (152) de modifier la commutation des thyristors 21 de chaque ensemble 20 relié au rail 11 (12), en déterminant ainsi le thyristor passant de chaque ensemble 20 avant que le chariot n'entre dans une nouvelle portion.

The fractionation zones 151 (152) have a length:

• greater than that of a shoe 41 (42) in contact with one of the rails 11 (12) so as to cause a total extinction of the thyristors connected to this rail 11 (12) when passing through its fractionation zones 151 (152) ,
• and less than λ / 4 in order to change the switching of the thyristors 21 of each assembly 20 connected to the rail 11 (12) when passing through the fractionation zones 151 (152), thereby determining the thyristor passing from each assembly 20 before that the carriage enters a new portion.

The thyristors 21 of the same set 20 are grouped together and located near the rails 11 and 12 in order to minimize the spark which occurs when the thyristors are extinguished by entry of the carriages 4 into the fractionation zones 151 and 152.
Indeed, this spark is due to the energy stored in the portion of cable containing the thyristor which was in operation and is therefore proportional to the inductance of the cable where the current was flowing, itself a function of the length of the latter.

An example of the operation of the power supply of the installation will be described during the evolution of the vehicle bodies in the tank, the arrow I representing the direction of movement of the bodies 5.

The two portions 111 and 121 in contact with the pads 41 and 42 of the same carriage 4 are supplied by the same rectifier 3.

When the carriages 4 pass through the fractionation zones 151 of one of the rails 11, all the thyristors 21 connected to this rail 11 are turned off.
The pads 42 in connection with the portions 121 remain supplied, each of them being connected by means of an assembly 20 to a rectifier 3.

During this extinction, an automatic or manual command makes it possible to select the thyristors 21 of the assemblies 20 of the rail 11 so that the pads 41 in contact with the portions 111 at the outlet from the fractionation zones 151 are supplied by the same rectifier as the pads 42.

The thyristors 21 are again primed when the carriages 4 leave the fractionation zones 151.
This priming is carried out by a train of pulses in order to compensate for possible false contacts as described above for the thyristors 22 and 23 of the first variant embodiment.

It is the same for the passage of the pads 42 in the fractionation zones 152 of the rail 12.

Thus everything happens as if each rectifier 3 was linked to a particular bodywork 5 and accompanied it during its evolution in the tank 1.

Whatever the variant, it is possible at any time to modify the voltage of each rectifier in order to modulate the polarization of the bodywork as a function of its advancement in the tank.

The control of these various instructions can be achieved by an efficient management system to which it would be necessary to provide the characteristics of the parts to be painted such as the size by using for example a bodywork monitoring such as photocells or detectors.

This exemplary embodiment of the installation is not limiting, the realization of such an installation can be envisaged for any surface treatment of metal parts by cataphoresis.

Claims (13)

1. Installation for surface treatment by cataphoresis of metal pieces (5), particularly of bodies of automotive vehicles, supplied with direct current, which comprises a bath (1), the sides of which carry anodes (2), an aerial conveyor which conveys the pieces (5) to be treated spaced at a regular distance λ and which carries mobile current supply means (4) in contact with at least one current conducting rail (11) mounted on at least one support and situated above the bath (1), and in which the pieces (5) to be treated constitute the cathodes, characterised by the fact that the rail (11) is divided regularly at intervals substantially equal to λ/2 into sections (111) separated by an insulating material and connected to the negative terminals (31) of rectifiers (3) of the current supply of the installation.
2. Installation according to claim 1, characterised by the fact that some sections (111) of rail (11) are supplied directly by a rectifier (3) and that other sections (111') are supplied by means of two thyristors (22, 23) in opposition, each of them being connected to a different rectifier (3) so that two juxtaposed sections (111, 111') have a different method of supply.
3. Installation according to claim 2, characterised by the fact that the thyristors (22, 23) of each section (111', 121') are located respectively at its extremities, and that the thyristors (22) of sections (111', 121') adjacent to a common section (111, 121) directly supplied by a rectifier (3) located in the proximity of said section (111, 121) are connected to the rectifier (3) which directly supplies this section (111, 121).
4. Installation according to any one of claims 1 to 3, characterised by the fact that the mobile means are constituted in a manner known per se by carriages (4) fitted with at least one contact shoe (41) mounted on the rail (11) and carried by swing trays which support the pieces (5) to be treated and that the dividing areas (151) have a length which is less than that of a shoe (41).
5. Installation according to claim 4, characterised by the fact that the carriages (4) comprise two contact shoes (41, 42) mounted on two parallel conducting rails (11, 12) situated above the bath (1) and that the dividing areas (151, 152) face one another.
6. Installation according to claim 5, characterised by the fact that each cable for direct supply via a rectifier (3) or indirect supply across a thyristor (22, 23) forms abridge (14) between the two rails (11, 12).
7. Installation for surface treatment by cataphoresis of metal pieces (5), particularly of bodies of automotive vehicles, supplied with direct current, which comprises a bath (1), the sides of which carry anodes (2), an aerial conveyor which conveys the pieces (5) to be treated in swing trays spaced at a regular distance λ, each of them comprising a carriage (4) fitted with two contact shoes (41, 42) mounted on two parallel conducting rails (11, 12) situated above the bath (1), and in which the pieces (5) to be treated constitute the cathodes, characterised by the fact that the two rails (11, 12) are divided in a manner known per se regularly into sections (111, 121) separated by an insulating material and connected to the negative terminals (31) of rectifiers (3) of the current supply of the installation and that the dividing areas (151, 152) are offset with respect to one another between the two rails (11, 12).
8. Installation according to claim 7, characterised by the fact that the dividing areas (151, 152) of a same rail (11, 12) are spaced at intervals of λ and that the linear offset between the dividing areas (151, 152) situated on the two rails (11, 12) is equal to λ/2.
9. Installation according to any one of claims 7 or 8, characterised by the fact that the dividing zones (151, 152) have a length greater than that of a shoe (41, 42) and less than λ/4.
10. Installation according to any one of claims 7 to 9, characterised by the fact that each section (111, 121) of rail (11, 12) is connected to an assembly (20) of thyristors (21) each of which is connected to the negative terminal (31) of a rectifier (3).
11. Installation according to claim 10, characterised by the fact that the thyristors (21) of a same assembly (20) are grouped together and located in the proximity of the rails (11, 12).
12. Installation according to any one of claims 1 to 11, characterised by the fact that the negative terminals (31) of the rectifiers (3) are respectively connected to diodes (16), the anodes (161) of which are connected to the mass of the bath (1).
13. Installation according to any one of claims 1 to 12, characterised by the fact that the number of rectifiers (3) is equal to the number of pieces (5) present in the bath (1) at the same time.

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