EP1268865B1 - Method and device for thermal treatment of steel wire - Google Patents

Description

• une formation d'un lit fluidisé par passage d'un agent fluidisant à travers un milieu particulaire fluidisable,
• un chauffage du lit fluidisé, et
• un défilement à travers le lit fluidisé chauffé dudit au moins un fil métallique à traiter, dans un sens, de manière à assurer une montée de température dudit au moins un fil à traiter et son maintien à cette température pendant une période d'égalisation de température au sein de la masse métallique dudit au moins un fil.

The present invention relates to a method of heat treatment of steel wire, comprising

• forming a fluidized bed by passing a fluidizing agent through a fluidizable particulate medium,
• a heating of the fluidized bed, and
• scrolling through the heated fluidized bed of said at least one metal wire to be treated, in one direction, so as to ensure a rise in temperature of said at least one wire to be treated and its maintenance at this temperature during a period of temperature equalization within the metal mass of said at least one wire.

a) oxydantes dans la première phase d'échauffement des produits de façon à brûler les résidus de diverses natures pouvant se trouver à leur surface,

b) réductrices par rapport au produit, lorsque ce dernier a dépassé la phase de transformation allotropique afin d'éviter une oxydation et une décarburation en surface des produits.

Conventionally, the heating of the yarn or the sheet of yarns in wire patenting processes is carried out either in open fire furnaces or in tube furnaces, without fluidized bed intervention. In the case of unalloyed steel, the heating is generally carried out in open fire furnaces whose atmospheres, obtained by combustion of a gas and an oxidizer, are adjusted so as to be:

a) oxidizing in the first heating phase of the products so as to burn the residues of various types that may be on their surface,

b) reducing with respect to the product, when the product has passed the allotropic transformation phase in order to avoid oxidation and surface decarburization of the products.

When it comes to alloy steel, a particular surface condition is generally sought after. The products are, therefore, heated by radiating tubes through which a protective gas maintain an impeccable surface finish to products throughout warm-up phase.

In both cases, the heating time is relatively long given the low heat transfer coefficients, either by convection in the case of open fire furnaces, either by pure radiation in the case of tube ovens.

The length of the furnace required for heating the wire to a austenitization temperature, for example of the order of 950 ° C., takes then an importance that plays to the detriment of the next process, the temperature equalization period within the metal mass of the (soaking) which can only be short (normally a few seconds) to maintain oven dimensions in acceptable limits for oven users. This results in a poor dissolution of cementite present at grain boundaries of austenite during the heating of the wires.

Moreover, we have already known for some years ovens wire heating system using a fluidized bed, as indicated at the beginning. The current applicant has already placed on the market such furnaces, in particular for the diffusion of Cu-Zn coatings in steel wires.

The plaintiff has indeed found that a good exchange heat could be obtained between heated bed particles fluidized, which are somehow bombarded on the surface of the wires in scrolling in the bed, and the wires themselves (see DE-A-3623890).

A process, as indicated above, has also been described in Japanese patent 2623004. The heating of the bed is carried out according to a embodiment using the fluidizing agent which consists of fumes resulting from the combustion of a combustion gas in air, this fluidizing agent being injected into the bottom of the fluidized bed by means of perforated lances, very sophisticated to prevent penetration particles of the bed in the spear. According to another form of realization, the fluidizing agent is air and a source of heat external to the fluidized bed is formed of burners located above the bed fluidized and projecting a flame or hot gases vertically onto this one.

The process according to this prior document makes it possible to attain in the fluidized bed a temperature only moderate from 470 to 550 ° C. In its first embodiment, it is limited by the complexity of spears feeding the bed fluidizing agent, such spears can not withstand the aggressiveness of flue gas from a too high, at the risk of having to be replaced very regularly. As for the vertical heating from the top, it presents the disadvantage of being inefficient and especially of causing a lack uniformity in bed temperature. Indeed, the burners used have each has a punctual impact on the bed with the consequence of small very hot bed surfaces and surrounding areas a lot less, which is obviously to be avoided to obtain treatment adequate son.

Also known are fluidized beds heated by combustion, to inside or on the surface of the furnace, a non-fluidizing agent fuel when introduced into the bed but made combustible thereafter during his ascent (see, for example, Reynoldson R.W., Anwendung von gasbeheizten Wirbelbetten zur Wärmebehandlung von Metallen, in Härtenei-Technischen Mitteilungen, Vol. 37 (1982), Munich, p. 109-119; Patent abstracts of Japan vol. 015, No. 231 (= JP03072036)). These heating processes have the disadvantage of being dangerous because they present a real danger of explosion and they produce huge flames directed upwards. They do not not allow a control of the uniformity of heating in the parts from the bed where the objects to be heated are located.

Fluidized beds are also known contained in tanks of small diameter and made using a non-combustible fluidizing agent. These beds are heated by surface injection by burners of a combustion mixture for thermally treating parts large metal and mass that remain static for the duration of a treatment, which can last up to 30 minutes (see Reynoldson R.W., supra).

The present invention aims to offer a solution to the often large size of ovens, especially ovens used in the austenitization of steel wire, while achieving treated son qualities equivalent or even superior and in allowing a treatment during the continuous scrolling of the son.

The present invention also aims to allow rapid and uniform heating of the fluidized bed and the son to be treated, and this to a good energy efficiency, so as to allow a period of temperature equalization within the metal mass largely higher than what is applied now, and without this being detrimental to the bulk of the overall apparatus.
The present invention also aims to thwart the disadvantageous effect of the fluidized bed particles drive, during the passage of son in it, with their migration from the entrance of the installation to the output.

The problems mentioned above are solved by a method of heat treatment of steel wires, as indicated at the beginning, in which said fluidizing agent is non-combustible, said heating is at least partially obtained by at least one heating of the fluidized bed which is introduced substantially tangentially to an upper surface average thereof, the method further comprising at least one pumping fluidized particulate medium over the fluidized bed and a discharging a jet of this particulate medium to the fluidized bed in a opposite direction to said direction of travel, said at least one heater tangential being performed at least partially through the medium jet particulate repressed.

As is known, a fluidized bed is formed of particles of solid material which are brought into suspension by the training of a fluidizing agent, normally a gas, which passes through the bed from bottom to top. During this crossing fluidizing riddle carries up the particles some of which are projected in the form of waves or protuberances higher than others. We thus obtain, in section cross-section of the bed, a very excited upper band, whose upper surface is continuously variable in height, and which represents a part of the bed less dense in particles.

By the expression upper middle surface of the fluidized bed, it is necessary to so hear according to the invention the surface that is at the height average between the troughs and peaks of waves existing at the upper surface of the bed.

By tangential heating to this average upper surface, the particles of the fluidized bed, which are there in a low density state, strongly dispersed, can be heated to extremely high temperatures high, close to incandescence. Particles so strongly heated, transfer heat to other particles that will be contact with the wires by obtaining an optimal heat exchange at a impossible to envisage in accordance with the teaching of the prior art. In addition, tangential heating is independent of the fluidizing agent and the perforated lances projecting this agent are not attacked by flue gas excessive temperatures.

Given the excellent coefficient of heat transfer by intermediate fluidized heated bed according to the invention, the temperature heating wires, during which austenitization of the wires occurs, can be drastically shortened, and so we can now consider a period of maintenance of austenitization temperature sufficient to achieve extensive dissolution of Fe carbides steel wire, without burdening the cost of installation at a level commercially indefensible and without making it a clutter insupportable. In addition, this embodiment makes it possible to break down the installation into two units, one relatively short, in the form of a fluidized bed furnace and the other consisting of a simple isolated tube or box where the threads scroll while being held at temperature by simple means such as heating elements electric, radiant type gas burners, fluidizing agent recirculated from the elongated oven, and / or a second fluidized bed.

The current embodiment can not only counteract the effect disadvantageous migration of particles to the outlet of the installation, but it makes it possible to take advantage of the pumping for increase the efficiency of tangential heating. Indeed, by the pumping, the particulate matter is repressed in the form of rain to a higher level at the peaks of the fluidized bed and in the middle of the bed. As a result, the heads of burners can according to the invention be arranged at level raised. It then becomes possible to arrange the burner heads out of reaching the particles, and thus the present embodiment significantly less risk of fouling of these burner heads by bed particles.

According to one embodiment of the invention, said at least one Tangential heating is oriented transversally to the direction for scrolling said at least one wire to be heated. By its transverse and tangential orientation the heating of the fluidized bed allows uniform and spread heating over the entire width and bed length of particles suspended in the bed, which allows uniform heating of the son scrolling in the oven.

According to an advantageous embodiment of the invention, said at least one tangential heating comprises a projection of at least minus a flame and / or smoke jet tangentially to said surface upper average of the fluidized bed. With the help of such a process, burners directly heat the particles of the fluidized bed, without gases burned at high temperatures must not pass through a tube perforated, fragile under these conditions. The layout is simple and highly effective.

According to a particular embodiment of an invention, said at least one tangential heating comprises a heat exchange between a heating medium and the fluidized bed via at least one a tube which is arranged tangentially to said upper surface average of the fluidized bed and through which said heating medium passes. Thus, alloy steel wires can be heated efficiently and quickly which can not come into contact with flue gases. The exchange thermally occurs remarkably between a single tube, perforated, through which passes the heating medium and the sparse particles of the bed that lick the walls of the tube heated.

Other features of the process according to the invention are indicated in claims 1 to 7 which follow.

• un four de chauffage allongé,
• une zone de maintien en température, et
• des moyens d'entraínement d'au moins un fil d'acier à traiter qui les font défiler dans un sens à travers le four et la zone de maintien en température, de manière que ledit au moins un fil à traiter subisse une montée en température dans le four et soit maintenu à cette température dans la zone de maintien en température, et
• un lit fluidisé formé dans le four de chauffage par passage d'un agent fluidisant à travers un milieu particulaire fluidisable,

caractérisé en ce que l'agent fluidisant susdit est non combustible et en ce que le dispositif comprend en outre

• des moyens de chauffage du lit fluidisé comportant au moins des moyens de chauffage qui produisent un chauffage sensiblement tangentiellement à une surface supérieure moyenne de celui-ci, et
• au moins un dispositif de pompage de matière particulaire qui pompe celle-ci au-dessus du lit fluidisé et la refoule en un jet vers le lit fluidisé dans un sens opposé audit sens de défilement, au moins un moyen de chauffage produisant ledit chauffage tangentiel à travers le jet de milieu particulaire refoulé par au moins un dispositif de pompage susdit.

According to the invention, a device for heat treatment of steel wire, comprising

• an elongated heating oven,
• a temperature maintenance zone, and
• means for driving at least one steel wire to be treated, which makes them run in one direction through the oven and the temperature holding zone, so that the at least one wire to be treated undergoes a rise in temperature in the oven and is maintained at this temperature in the temperature maintenance zone, and
• a fluidized bed formed in the heating furnace by passing a fluidizing agent through a fluidizable particulate medium,

characterized in that the aforesaid fluidizing agent is non-combustible and in that the device further comprises

• means for heating the fluidized bed comprising at least heating means which produce heating substantially tangentially to an average upper surface thereof, and
• at least one pumping device of particulate matter which pumps it above the fluidized bed and delivers it in a jet towards the fluidized bed in a direction opposite to said direction of travel, at least one heating means producing said tangential heating at through the jet of particulate medium discharged by at least one aforesaid pumping device.

Other details concerning the devices according to the invention are indicated in the following claims 8 to 16.

Les figures 1 à 3 représentent une vue en coupe transversale de trois variantes de réalisation de four à lit fluidisé suivant l'invention.

La figure 4 représente une vue du dessus du four représenté sur la figure 1.

La figure 5 représente un dispositif comprenant deux unités successives, l'une pour la chauffe des fils et l'autre pour le maintien en température.

La figure 6 représente un graphique illustrant la variation de température du fil défilant dans le four en fonction du temps.

Les figures 7 et 8 représentent une vue en coupe transversale et une vue en coupe longitudinale d'une quatrième variante de réalisation de four à lit fluidisé suivant l'invention.

Other details and features of the invention will become apparent from the description given below, without limitation, of some embodiments of devices according to the invention, with reference to the accompanying drawings.

Figures 1 to 3 show a cross-sectional view of three embodiments of fluidized bed furnace according to the invention.

Figure 4 shows a top view of the oven shown in Figure 1.

FIG. 5 represents a device comprising two successive units, one for heating the wires and the other for maintaining the temperature.

Figure 6 is a graph illustrating the temperature variation of the wire moving in the oven as a function of time.

Figures 7 and 8 show a cross-sectional view and a longitudinal sectional view of a fourth embodiment of fluidized bed furnace according to the invention.

In the different drawings, the identical or analogs are designated by the same references.

In Figure 1, there is shown in cross section an oven elongate 1 containing a fluidized bed 2. The fluidized bed 2 is formed of particles relatively finely divided into a material resistant to high temperatures and preferably inert vis-à-vis the son to heat. For example, silica particles, zirconia, alumina or other refractory materials having a good ability to transmit heat to bodies that are in contact with they. Alumina sands can be particularly example of F90 particle size according to the FEPA 42F 1984 standard, or zircon sands.

A fluidizing agent, such as, for example, air, nitrogen, ammonia, is introduced at high pressure and in this case at the room temperature at the base of the fluidized bed, via a perforated lance 3. Any protective gas judiciously chosen in function of the nature of steel can be used for this purpose. By his pressure and its flow rate, the fluidizing agent carries the particles of the bed upwards and bring them into suspension. This swirling type suspension manifested at the top of bed 2 by wave formation, the surface upper middle of the bed being represented by a mixed line 4.

It should be noted that the fluidizing agent is not combustible in the process conditions. This one, cold or at room temperature, does not request the lance by which it is projected in the bed fluidized and the life of the lances is therefore very greatly increased compared to the lances according to the technique which serve both the fluidization and heating of the bed.

The fluidizing agent very hot after passing through of the bed is then recovered at the top of the oven by an exhaust pipe 5 (see Figure 5).

In the examples illustrated in the figures, a sheet of threads 6 runs in the oven following the longitudinal direction of the oven which is perpendicular to the plane of the drawing, at a speed which is calculated in function of a constant set by the imperatives of production and so of the capacity of the treatment line. This constant is equal to produces the diameter of the wire expressed in mm and the speed of the wire expressed in m / minute. So, the thinner the wire, the faster its speed scrolling will be fast and vice versa. It should be noted that one could consider running one wire at a time in the oven, or scrolling of several threads of different diameters, or the scrolling of several layers superimposed at a time.

As illustrated in FIG. 1, the heating means of the fluidized bed consist of several burners 7 (see also Figure 4) which are, in this example, arranged on either side of the sheet of son to heat and which project their flame or fumes transversely to the direction of scrolling son. The flames or fumes are in particular tangential to said upper surface average 4 of the fluidized bed, thereby heating the particles directly suspended in a band of the bed where they are less dense and therefore more easily worn almost incandescent. It is obvious that, if in the examples shown the so-called tangential direction of the flame or fumes coincides perfectly with the surface 4 shown, it is conceivable to arrange the burners slightly oblique in relation to this flame or these fumes, provided that always get a heating well spread on the surface of the bed and that the wires are not affected by flames or fumes.

The flame of the burners and the fumes produced at the exit of the burner result in a common way of the combustion of a fuel and an oxidizer, for example a combustible gas or liquid, such as CH ₄ , fuel, etc. ..., and air, enriched or not in oxygen, or even oxygen considered industrially pure. The flue gases formed are then recovered through the exhaust duct 5, simultaneously with the heated fluidizing agent.

As can be seen in FIG. 4, the burners are arranged alternating way to the left and right of the sheet of threads and the flame and the jet of hot gas burns that accompany it extend transversely over the entire width of the oven. This provision offers the advantage of allowing a very uniform heating of the fluidized bed and therefore son to treat.

In the embodiment illustrated in FIG. heat can not come into contact with flue gases for maintain their surface state. The heating of the bed is done here too tangentially to the average upper surface 4 of the bed but by through an unperforated tube 8 that lick the waves particles of the bed, which are thus brought to high temperature. The burnt gases exit through an outlet duct 9 through which they can be recovered.

The embodiment illustrated in FIG. 3 is of the same type than that shown in Figure 2. However, in this case, we have provided a box 10 located below the fluidized bed and in communication with the projection lance 3. One or more burners 11 are arranged in this box and make it possible to obtain fumes warm to a moderate temperature, higher than the ambient temperature, for example of the order of 400 to 500 ° C, where the fumes are not yet overly aggressive for spears 3. This embodiment allows an even greater efficiency of the fluidized bed heating. It is understood that one could also foresee this arrangement with that of the open flame burners as illustrated on Figure 1.

The son to be treated in the furnaces according to the invention are example of the steel wires that will be subjected to an operation of patenting.

The patenting operation is a well-known process in the world of wire drawing, it consists in carrying, first of all, the temperature of a wire or a ply of wire at a level such that we obtain a transformation of ferrite and perlite or perlite and austenite cementite.

In a second step, we realize what we call a isothermal quenching so as to retransform the austenite (previously obtained by heating) in fine perlite in order to obtain good mechanical properties and, especially, excellent drawing ability.

During the step of heating the wire, it is necessary to reach a temperature of the order of 950 ° C to obtain austenitization of steel. However, before going to the quench, a period temperature equalization within the metal mass, called "soaking", is favorable to dissolve the carbides present in the austenite grain boundaries.

As illustrated in Figure 5, in one example of device according to the invention we will be able to provide two units separate units, a heating unit 1 and a unit of equalization temperature 12.

The heating unit consists of a furnace 1 with a fluidized bed 2, such as than previously described, which can be relatively short, given the excellent heat transfer coefficient of this type of oven. Wire 6 scrolls continuously through this oven which may have a length of Example 5 to 6 m. In the bottom of the oven, a box 10 of the type of one schematically shown in FIG. 3 is arranged to allow pre-heating of the fluidizing medium. Temperature heated fluidized sand according to the invention can advantageously reach about 1000 ° C.

The wire 6 thus leaves oven 1 at a temperature of about 950 ° C. and then passes into the temperature equalization unit 12, by through a sealed hopper 13. The unit 12 consists of a box or tube perfectly insulated from the thermal point of view. In this one just need to maintain the acquired wire temperature of 950 ° C and a heat exchange for heating is no longer necessary. In the illustrated case, this temperature maintenance is carried out by a recirculation of flue gases from unit 1 through the exhaust duct 5. The burnt gases released are fed to a filtering means, for example example a cyclone 14, and the filtered gases still hot or partially heated in a complementary manner are brought to using a pump 15 to the unit 12 for maintaining the temperature of the wire. Dissolution of carbides (cementite) is accomplished in unit 12, which can have a length of about 4 m and in which, by scrolling, the wire remains for a time sufficient to obtain the dissolution of carbides. At the output of the unit 12, the wire passes to a quenching device 16 only partially represented.

The total device of this example therefore has a length quite acceptable in terms of footprint of about 9 to 10 m.

In FIGS. 7 and 8, there is shown the pumping devices 17 which are provided to counteract the migration of fluidized bed particles since the oven entrance to the exit. The particles are indeed driven mechanically by the movement of scrolling son.

These pumping devices 17 include in the example illustrated a tube 18 arranged substantially vertically, which is connected to its lower part to a collecting cone 19. This is advantageously arranged above a perforated lance 3. In its upper part the tube 18 is connected to a watering nozzle 20 which is oriented in a opposite direction to the direction of travel 21 son 6 to be treated. Advantageously, the spray nozzle 20 is further oriented in oblique towards the central part of the oven, as is apparent from the figure 7.

In the present embodiment, the perforations in the lances 3 are arranged downwards.

Fluidized bed particles and fluidization agent rush in the collecting cone. Since the mass of particles then has a much lower apparent density in the tube to that of the fluidized bed, this mass is projected higher than the ridges of the fluidized bed: the spray nozzles then return jets 22 of particles to the rear and towards the center of the bed, which allows counteract the migration of particles in the direction of scrolling son. As can be seen, this pumping does not imply, in the case illustrated, no additional energy expenditure.

These jets have the effect of raising the upper surface average bed that in the example shown is at the line level mixed 4 '. As can be seen in Figure 7, this level is higher as the peaks of the waves of the fluidized bed.

As can be seen from figures 7 and 8, heating by burners 7 is now performed according to the invention, tangentially to this upper middle surface 4 ', elevated, of way that the jet of gas from the burner passes through the projection of particles from the pumping device.

The tangential heating thus obtained is particularly effective. In addition, it offers the advantage that the heads of the burners 7 are out of reach of the particles that are projected towards the center of the oven. A fouling of the burner heads can thus be favorably avoid.

Examples of non-limiting embodiments will now be given to explain the invention in more detail.

Example 1

A eutectoid-type steel wire with a diameter of 3 mm is introduced into a fluidized bed furnace equipped according to the invention whose constant DV (wire diameter (mm) x speed of movement (m / min)) is The fluidized bed consists of Al ₂ O ₃ - F 90 with a particle size of 106 to 250 μm. It is kept in suspension by a fluidizing gas, in this case air, having a minimum pressure of 600 mm H ₂ O and a flow rate of 64 Nm ³ / hm ² . The fluidizing gas is introduced from the bottom of the fluidized bed at room temperature.
Burners project fumes from the combustion of gas and combustion air tangentially to the upper middle surface of the fluidized bed, so as to heat the particles of the fluidized bed almost to incandescence and to obtain a bed of a temperature average of about 1000 ° C. The fumes from the burners are in direct contact with the fluidized bed.

As can be seen from curve A of the graph given in the figure 6, the wire reaches a temperature of 950 ° C after about 20 seconds of scrolling, at most 30 seconds, that is to say that the length of the fluidized bed furnace according to the invention may be limited to a value about 5 m, for the DV constant chosen above.

Over a length of 4 m, which corresponds to a period of passage of 20 seconds of the wire, it is maintained in the unit 12 to the temperature of 950 ° C, for the dissolution of tertiary cementite.

For comparison, we scrolled through an identical thread through a conventional open fire furnace, without a fluidized bed, of high convection type. It can be seen on curve B that the wire must be heated during about 50 seconds to reach the austenitization temperature and that the temperature equalization period within the mass metal can not be made in an oven of the same length and with the same DV constant, as for 3 to 4 seconds, which is insufficient to obtain a good dissolution of carbides (cementite tertiary).

Example 2

A steel wire type XC70 (0.76% C) is subjected to the same processing conditions as in Example 1. The wire has a diameter of 1 mm and its constant DV is 36.
The wire reaches a temperature of 950 ° C after about 5 seconds of running and the length of the fluidized bed furnace can be limited to a value equal to or even less than 5 m.
Over a length of 4 m, which corresponds to a passage period of about 7 seconds, the wire is maintained at the temperature of 950 ° C for the dissolution of tertiary cementite.

Example 3

A steel wire type XC70 is subjected to the same processing conditions as in Example 1. The wire has a diameter of 5 mm and its constant DV is 36.
The wire reaches a temperature of 950 ° C after about 40 to 50 seconds of travel and the length of the fluidized bed furnace can be limited to a value of about 5.5 m.
Over a length of 4 m, which corresponds to a passage period of about 35 seconds, the wire is maintained at a temperature of 950 ° C.

Claims (16)

1. Method of heat treating steel wire, comprising

   formation of a fluidised bed by the passage of a fluidising agent through a fluidisable particulate medium,

   heating of the fluidised bed, and

   movement through the heated fluidised bed of the said at least one metallic wire to be treated, in one direction, so as to provide at least a rise in temperature of said at least one wire to be treated and maintaining thereof during a temperature equalisation period within the metallic mass of the said at least one wire,

   characterised in that said fluidising agent is non-combustible, in that said heating is at least partially obtained by at least a heating of the fluidised bed which is produced substantially tangentially to a mean top surface thereof, and in that the method further comprises at least one pumping of the fluidised particulate medium above the fluidised bed and a driving of a jet of this particulate medium towards the fluidised bed in an opposite direction to the said direction of movement, said at least one tangential heating being effected at least partially through the jet of driven particulate medium.
2. Method according to Claim 1, characterised in that said at least one tangential heating is oriented transversely with respect to the direction of movement of said at least one metallic wire to be heated.
3. Method according to one of Claims 1 and 2, characterised in that said at least one tangential heating comprises a projection of at least one flame and/or jet of fumes tangentially to said mean top surface of the fluidised bed.
4. Method according to one of Claims 1 and 2, characterised in that said at least one tangential heating comprises an exchange of heat between a heating medium and the fluidised bed by means of at least one tube which is disposed tangentially to said mean top surface of the fluidised bed and through which said heating medium passes.
5. Method according to any one of Claims 1 to 4, characterised in that the heating of the fluidised bed also comprises a heating of the fluidising agent prior to its passage through the fluidisable particulate medium.
6. Method according to any one of Claims 1 to 5, characterised in that the heating makes it possible to achieve a temperature of the fluidised bed greater than 950°C, preferably greater than 1000°C, in a time of no more than 30 seconds.
7. Method according to any one of Claims 1 to 6, characterised in that it comprises the maintaining of said at least one wire at the austenitisation temperature in said fluidised bed and/or outside this fluidised bed.
8. Device for the heat treatment of steel wire, comprising

   an elongate heating furnace (1),

   a temperature maintaining zone (12), and

   means of driving at least one steel wire to be treated which makes them pass in a direction across the furnace and the temperature maintaining zone, so that the said at least one wire to be treated undergoes a rise in temperature in the furnace and is maintained at this temperature in the temperature maintaining zone, and

   a fluidised bed (2) formed in the heating furnace (1) by passing a fluidising agent through a fluidisable particulate medium,

   characterised in that said fluidising agent is non-combustible and the device also comprises

   means of heating the fluidised bed comprising at least heating means which produce heating substantially tangentially to a mean top surface thereof, and

   at least one device for pumping particulate matter which pumps it above the fluidised bed and drives it in a jet towards the fluidised bed in an opposite direction to said direction of movement, at least one heating means producing said tangential heating through the jet of particulate medium driven through at least one above mentioned pumping device.
9. Device according to Claim 8, characterised in that the tangential heating means comprise at least one burner (7) which projects a flame and/or fumes tangentially to said mean top surface (4) of the fluidised bed (2).
10. Device according to Claim 9, characterised in that it comprises several burners (7) disposed on each side of the moving wire or wires (6), preferably in alternation, and projecting their flame and/or fumes transversely to the direction of movement of the wire or wires.
11. Device according to Claim 8, characterised in that the tangential heating means comprise tubes (8) which are disposed tangentially to said mean top surface (4) of the fluidised bed (2), transversely to the direction of movement of the wire or wires, and through which a heating medium passes.
12. Device according to any one of Claims 8 to 11, characterised in that it also comprises means (11) of preheating the fluidising agent.
13. Device according to any one of Claims 8 to 12, characterised in that it comprises a short elongate furnace (1) in which the said at least one wire to be heated quickly reaches the austenitisation temperature and, following the furnace, a thermally insulated chamber (12) in which the wire is maintained at said predetermined maximum temperature by temperature maintaining means (5, 14, 15).
14. Device according to Claim 13, characterised in that the temperature maintaining means are electric heating elements, gas burners of the radiating type, means (5, 14, 15) of recirculating the fluidising agent leaving the elongate furnace (1), and/or a second fluidised bed.
15. Device according to anyone of Claims 8 to 14, characterised in that the means of heating the fluidised bed produce said substantially tangential heating between the troughs and the crests of the waves existing at the top surface of the bed.
16. Device according to anyone of Claims 8 to 15, characterised in that the means of heating the fluidised bed are arranged at a level higher than the fluidised bed.

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