LU83424A1 - IMPROVED PROCESS FOR THE CONTINUOUS COOLING OF MACHINE WIRE - Google Patents

Description

j / Claiming the priority of a patent application filed on June 13, 1980 under No. 883.833 BL-3161 / EM / BM C 2043/8006.

I * 'METALLURGICAL RESEARCH CENTER -CENTRUM VOOR RESEARCH IN DE METALLURGIE,

Non-profit association - vereniging zonder winstoogmerk in BRUXELLES, (Belgium).

Improved process for continuous cooling of wire rod.

The present invention relates to improvements in the continuous cooling processes of steel wire rod.

i At the exit of the wire rolling mill, the wire rod i j is subjected to a controlled cooling operation, including; characteristics depend on the final properties that one wishes i; impart to the wire.

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Taking into account the composition of the wire and the final properties that one seeks to give it, the duration, the number, the nature and the efficiency of the various phases of the complete cooling process can vary in significant proportions.

Another aspect of the problem is constituted by the importance of the installations making it possible to carry out the requested coolings, and in particular their bulk in the longitudinal direction, which can have a considerable impact on the investments necessary to carry them out. Finally, and this as- | pect is not the least, there is a major interest in producing a wire whose mechanical properties are uniform and homogeneous on! its entire length.

It follows that an improvement on any | that phases of a wire cooling process can have | an influence both on the quality of the wire, on the duration of the time necessary to cool the wire completely, on the size of the corresponding installations and consequently, on their cost both of operation and of first establishment, and on the homogeneity of mechanical characteristics.

There are currently many methods for subjecting, on leaving the rolling mill, a wire rod to a well-defined cooling sequence, most often specific to the quality of wire sought.

These processes frequently require a more or less prolonged stay on a conveyor with calm air, which results in a difference in cooling rate and therefore in microstructure and mechanical properties, between the parts of turns which are on the edges of the conveyor and the parts of turns being distant from the edges of the conveyor, that is to say in the central zone of the conveyor.

One of these processes, developed by the same applicant, consists in that, at the exit from the rolling mill, the t k

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3.- wire rod whose temperature has been brought between 900 ° C and 780 ° C, is deposited in the form of non-contiguous turns on a conveyor? the wire thus put in turns on the conveyor is cooled, by setting the cooling rate to a sufficiently low value so that, when the allotropic transformation has been carried out at least up to 80% and preferably greater than -95%, the ferritic grain has the desired size, preferably at least ASTM 9; still on a conveyor, the wire is then subjected to so-called rapid cooling, to a temperature between 350 ° C and 560 ° C, and preferably between 500 ° C and 560 ° C; „At the end of this rapid cooling phase, the wire is finally subjected to a second slow cooling phase in coils.

The so-called rapid cooling is advantageously obtained by immersing the wire in an aqueous bath, preferably brought to its boiling temperature, and which may contain surfactants.

This process makes it possible, in particular for extra-mild steel wires, to obtain a breaking load, an elastic limit and a particularly low E / R ratio, by means of an installation the length of which can be much less than those usually encountered in processes which do not include the rapid cooling phase in question.

The subject of the present invention is a method of the kind described above and which makes it possible to improve the uniformity in length of the wire which is subjected to it.

It is well known that when the wire rod is spread in non-concentric turns on a conveyor, most of the metal of the turns is accumulated in a relatively small volume, at the two lateral edges of the sheet of turns, while at the zone center of this sheet, the metal accumulation is less than at the edges. There follows a difference in. the cooling speed of the turns, the lateral edges of f

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4.- I>; ·}; the sheet cooling less quickly than the central zone, which I which does not favor the homogeneity of the structure of the wire over the whole of the same turn and leads, for the wire being i1 in the central zone, to properties less good mechanical than those obtained for the wire located in the lateral zones.

The object of the present invention, as said above, is to increase this homogeneity of structure, even in the case where the wire rod is arranged in turns spread out on a conveyor.

The process, object of the present invention, in which the wire rod, directly at the outlet of the last rolling mill stand, is arranged on a conveyor in a sheet made up of non-concentric turns spread out to be subjected on this conveyor, to a cooling operation. comprising an immersion phase in an aqueous bath, is essentially characterized in that, during all or part of the stay of the turns on the non-submerged conveyor, the part of the ply of the turns located in the central zone of the conveyor, is subjected to less intense cooling than that of the edges of the sheet and in that the difference in cooling is adjusted, so as to obtain a homogeneous structure of the wire over all of its turns.

Several methods can be used to achieve this differential cooling. It is possible, for example, ♦ by means of a heat generator, to carry, at appropriate temperature j, a gaseous fluid which is projected onto the part

Ides turns being in said central zone, the temperature of the gas thus projected decreasing progressively, and in an appropriate way, in the central zone, in the direction of * movement of the conveyor. Any other heating moven! / r '5 * - {sheet of turns located in said central area can be used, without departing from the scope of the present invention.

Preference is, however, given to any means which, without precise supply of calories, contributes to slowing down in proportion, the cooling of said central zone, in particular, all other equal factors, by reducing it, compared to the flow of cooling used for the edges of the tablecloth, the flow of these same agents used for the said - central zone.

Another particularly advantageous means for implementing the method of the present invention consists in * placing above the central zone of the conveyor, and preferably nothing above it, at a certain distance from the sheet of turns and over all or part of its length, a screen whose effect is on the one hand, to slow down the circulation of any gaseous fluid on the said central zone and on the other hand, to reflect towards the upper part of the zone central of the layer of turns, the calories which emanate from it, in particular by radiation.

The effectiveness of the effects of this screen depends on its own parameters, dimensions, nature, distance above the turns, more or less specular state of the face of the screen located on the side of the turns. By way of example, such a screen, supported by a frame of aluminum-based profiles, consists of a steel plate, polished on its side on the turns side and blackened on its opposite side.

♦ The above process has been described in the case * of its particular use in the manufacture of wire rod made of extra mild steel, but this is only by way of example, since it can be used for all other categories of wire rod, for which cooling provides for a stay /

Claims (5)

1. An improved process for the continuous cooling of wire rod, in which the wire rod directly out of the last rolling mill stand is placed on a conveyor in a sheet made up of non-concentric turns spread out to be subjected on this conveyor to an operation of cooling, comprising a phase of immersion in an aqueous bath, characterized in that, during all or part of the stay of the turns on the non-submerged conveyor, the part of the ply of the turns situated in the central zone of the conveyor is subjected to a less intense cooling than that of the edges of the sheet, and in that the difference in cooling is adjusted so as to obtain a homogeneity of structure of the wire over all of its turns. 2. Method according to claim 1, characterized in that any means of heating the part of the ply located in said central zone can be used to produce this difference in cooling. 3. Method according to claim 2, character-. · Risé in that by means of a generator of heat, one brings to suitable temperature, a gaseous fluid which one projects on the part of the turns being in said central zone, the „temperature of the gas thus projected decreasing gradually, and ► 'appropriately, in the central zone, in the direction of movement of the conveyor. 4. Method according to claim 1, characterized in that use is made of any means which, without precise supply of calories, contributes to slowing down the cooling of j · said central zone, for example, all other equal factors, / by reducing, compared to the flow rate of cooling agents t 7.- irtrilised for the edges of the sheet, the flow rate of re-rusting agents used for the central zone of the sheet. 5. Method according to claim 4, character-îttjlss in that one has above the central area of the con-r.-trysur, and preferably just above it, at a certain v ^ stance of the ply of turns and on all or part of its lon-æsxuc, a screen intended on the one hand, to slow down compared to this -rrrt it is on the lateral zones of the ply, the circulation _-; cooling fluid on the said central zone and on the other hand, to reflect towards the upper part of the v * .-- r ^ trale zone of the sheet of turns, the calories which emanate therefrom, • - especially by radiation. "* * ♦