EP0157057B1 - Method of consecutively galvanizing a metallic wire with two different coatings - Google Patents

Abstract

PCT No. PCT/FR84/00176 Sec. 371 Date Nov. 15, 1985 Sec. 102(e) Date Nov. 15, 1985 PCT Filed Jul. 23, 1984 PCT Pub. No. WO85/04427 PCT Pub. Date Oct. 10, 1985.The invention consists in a process for consecutively coating a metal band with at least two different coating alloys, on one production line, whereby, to pass from a first product to the second, a secondary tank (8) containing the second alloy is disposed in the main tank (2). The process is used for the continuous production of coated metal sheets.

Description

The coating of a metal strip with a zinc alloy is carried out today by means of an installation called a galvanizing line along which the strip passes and undergoes various treatments. Thus, after an unwinding station at the head of the line, there is successively a cleaning station, a preheating station with or without atmosphere control, a so-called laboratory station where generally the heating of the strip continues in a very reducing atmosphere, possibly a cooling station to finally arrive in a bath of molten zinc alloy. On leaving the bath, the strip is wrung out and cooled to be either wound up or conducted through subsequent treatment stations (such as, for example, heat treatment or surface treatment stations, etc.).

One can realize that such a galvanizing line is a complex installation which is intended for strong continuous productions of a single product. However, it may be advantageous to be able to manufacture products with different coatings. On the same galvanizing line, this modification requires, in addition to the adjustment of all the treatment doors in the amount of the alloy bath, the emptying of the tank containing this bath, which is a delicate and long operation, therefore expensive, taking into account in particular heating means used (induction) which function correctly only in the presence of a bath in the tank. In addition, the correctly emptied tank must undergo an extremely thorough cleaning, in certain cases, in order to then be able to receive the new coating alloy which may not tolerate, even in very small concentration, one or more of the elements constituting the previous alloy.

The manufacture of two different products therefore often required the use of two galvanizing lines, specialized for each of them in one or the other of the products. No further explanation is needed to understand that this solution involves a considerable investment which can only be justified by depreciation on very large productions. However, two tanks were produced on the same line which could be alternately put into service by transverse translation in the direction of travel of the metal strip. This solution also has the disadvantage of immobilizing large quantities of molten metal and of maintaining a bath in the molten state out of service during the use of the other with the energy consumption that this represents.

the invention intends to propose another solution for the production, on the same galvanizing line, of two different products, that is to say coated with different alloys, successively, by means of a galvanizing process . The arrangements of the invention advantageously allow a change of bath with a minimum of handling of molten metal, maximum safety in particular for the temperature maintenance device and finally in a relatively short time, that is to say without incidence appreciable on the production capacity and therefore on the cost price of the finished product.

To this end, the subject of the invention is a method for producing consecutively on a single production line at least two metal foil products coated with different metal alloys, the production line comprising in particular a fixed tank of molten alloy in which the metallic sheet scrolls.

According to one of the main characteristics of the invention, this process consists, to go from the first to the second product, to place in the bath of said fixed cube, a removable tank of volume smaller than that of the fixed tank, containing the one of the aforementioned alloys different from that contained in the fixed tank and in passing said metal sheet through the bath of the removable tank, and, to move from the second to the first product, in removing said removable tank, the metal sheet then passing through the fixed tank.

It is advantageous in this method to constitute at least one bath initiator in the removable tank before the establishment of this tank in the bath of the fixed tank.

One of the phases of the process resides in the fact that, prior to the installation of the removable tank, the stationary tank is partially emptied then, after this installation, the two baths are completed to an identical level.

The invention will be better understood during the description given below by way of purely indicative and nonlimiting example which will make it possible to identify the advantages and the secondary characteristics thereof.

• a figure 1 est une vue schématique en coupe d'une installation connue de galvanisation dans la zone du bain d'alliage fondu;
• la figure 2 illustre par une même coupe schématique une installation pour mettre en oeuvre le procédé selon l'invention.

Reference will be made to the appended drawings in which:

• Figure 1 is a schematic sectional view of a known galvanizing installation in the area of the molten alloy bath;
• FIG. 2 illustrates by the same schematic section an installation for implementing the method according to the invention.

Referring first to Figure 1, we see a portion of the galvanizing line at the bath of molten zinc alloy. This bath 1 is contained in a fixed tank 2 which has heat supply elements known in themselves and not shown, such as inductors.

The means for guiding the metal strip 3 in the bath 1 during its circulation in the direction A consist of a return roller 4 immersed in this bath by which the strip passes from its plunging path to its substantially vertical extraction path. This guidance is supplemented by a descaling roller 5.

Thus, in known manner, the strip 3 is brought into the bath through a sheath 6 for confining the atmosphere which has an end 6a plunging into the bath to seal the internal volume of the sheath relative to outside. On leaving the bath, beyond the roller 41, the strip enters a wringing device 7 which may be mechanical by rollers or by spraying gas. It will be noted that the roller 4 (and the roller 5) is carried by an arm 4a (5a for the roller 5) which is detachably fixed to a fixed structure of the line extending above the tank 2 and which also carries the sheath 6.

In Figure 2 we retoruve a line structure of galvanizing at the level of the bath 2 of molten alloy substantially identical to that of FIG. 1, at least in its main components. Note however that the end 6a of the sheath 6, and the rollers 4 and 5 are brought together in a zone of the bath 1 of predetermined volume. This volume must be smaller than that inside of a removable tank 8 which can be suspended in the fixed tank 2 by means of fixed suspension devices (represented by a frame 9) which extend above the tank 2 and which are integral with the above fixed structure. When the tank 8 is in place, its position relative to the tank 2 is such that it is almost completely immersed in the bath 1 of molten alloy which constitutes a means of heat transfer between the fixed heating equipment by induction of the tank 1 and a bath 10 contained in the tank 8. It can therefore be seen that there is an advantage in having the maximum contact surface between the tank 8 and the bath 1, therefore in immersing it as much as possible. Nevertheless, it is possible to provide an additional heating means integral with the tank 8.

The establishment of the removable tank 8 requires clearing access to the fixed tank 2. To do this, provision will be made for the rollers 4 and 5 to be removable, as well as the blowing nozzles 11 for the wiping gas mounted at sliding on rails, not shown, transverse to the direction of travel of the strip. As regards the sheath 6, one can provide either its retraction by an appropriate articulation on the fixed structure, or a telescopic construction, or finally a lower part carrying the end 6a (or shoe) easily removable.

The implementation of the method according to the invention is carried out with an installation in accordance with that of FIG. 2. It can be seen that in the absence of the removable tank 8 the metal strip plunges into the alloy bath 1 and is therefore coated with a first coating characterizing a first product from the galvanizing line.

The production of a second product, distinguished from the first by a coating of a different nature, can be carried out on the same line. It is then advisable, after the latter has been stopped, to disassemble or retract the members 4, 5, 6, 7 and / or 11 and, by means of a lifting bridge, to approach the tank 8 of the fixed tank 2 that we will have partially emptied of its content. The tank 8 will preferably contain a start of bath 10 of a second alloy which will have been created for example by means of an oven or by means of an auxiliary heating which it may comprise. It is known in fact that the ingot of ingots is faster when they are in contact with a bath already created. The tank 8, then attached to the devices 9, soaks in the bath part 1 remaining in the tank 2 which provides it with the calories necessary for the maintenance of the beginning of the bath. Then proceed to replace the organs 4, 5, 6, 7 and / or 11 and complement each of the baths 1 and 10 by providing ingots or for bath 1, a portion of the drain portion of the initial bath which could have been maintained in the liquid state. The metal strip then passes through the bath 10 and is coated with the aforementioned second alloy.

The operation consisting in the commissioning of the auxiliary tank is relatively quick so that the downtime of the galvanizing line is not prohibitive as regards its impact on the production cost price. In addition, the method according to the invention allows the passage without any danger from one alloy to another since these are contained in two different tanks without any possible solution of a component of the first bath in the second. For example, on a single line, one can produce sheets coated with an alloy containing lead and with a zinc-aluminum alloy in which it is known that the lead must be free.

The invention is not limited to the example which has just been given, but on the contrary covers all the variants which could be made to it without departing from its scope.

Claims (4)

1. Process for consecutively producing on a single production line at least two metal band products (3) coated with different metal alloys, the production line comprising a fixed tank (2) of molten alloy (1) in which a metal band advances, characterized in that it consists, in order to change from the first to the second product, in placing in the bath (1) of said fixed tank (2) a removable tank (8) of smaller volume containing one of the said alloys different from that contained in the fixed tank and in passing said metal band through the bath (10) of the removable tank (8), and, to change from the second to the first product, in withdrawing said removable tank (8), the metal band then passing trough the fixed tank.

2. Process according to Claim 1, characterized in that the temperature of the bath (10) of the removable tank is maintained by regulating the temperature of the bath (1) in the fixed tank (2).

3. Process according to Claim 1, characterized in that at least one start of bath is constituted in the removable tank (8) before placing it in the bath (1) of the fixed tank (2).

4. Process according to any one of preceding claims, characterized in that, prior to placing the removable tank (8) the fixed tank (2) is partially emptied then, after this placing, the two baths (1,10) are adjusted to an identical level.

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