EP0093060B1 - Rotary hearth furnace for thermic, thermochemical or electrothermic treatment of metals in a diluted atmosphere - Google Patents

Abstract

1. A rotary hearth furnace for thermic, thermochemical or electrothermic treatment of metal parts in a diluted atmosphere characterized in that it comprises : - a sealed metal enclosure (1), which may include a double wall, with an interposed cooling layer, this enclosure (1) comprising a side wall (2) preferably having a circular horizontal section, a cover (3) and a bottom (4) - means for creating, within the enclosure, an atmosphere for treatment under reduced pressure ; - a circular rolling path provided inside the enclosure on said bottom, in a peripheral region substantially adjacent the cylindrical wall ; - an annular tunnel (12) made of a heat isolating material, situated above the rolling track, this tunnel being open on its lower surface opposite the rolling track, this tunnel including means (13) for thermic, thermochemical or electrothermic treatment ; - a rotary hearth (22) consisting of a ring made of a heat isolating material, this hearth being movable on the rolling track and arranged so as to close the aperture of the lower part of the tunnel and thus provide continuity of the thermic isolation of the tunnel (12) as far as its lower surface is concerned ; - means for rotating the rotary hearth (22) by a motor (24) preferably lodged outside the enclosure ; - elements for supporting the parts (S) evenly distributed on the rotary hearth (22) ; - a hardening cell, comprising, on the one hand, a chamber forming a lock (6), also serving for charging and discharging the parts to be treated, this chamber being mounted against the side wall (2), inside the enclosure and communicating with the inner volume of the tunnel (12) by a first door and, if need be, a movable separating wall, and with the outside by a second door so as to allow the introduction and discharge of the parts to be treated inside the tunnel, and, on the other hand, a hardening a hardening vat (9) lodged below said chamber (6), this hardening cell comprising handling means (10) for depositing the parts on or taking them away from the rotary hearth, and for plunging them, at the end of treatment, into the hardening vat (9).

Description

The present invention relates to a rotary hearth furnace for the thermal, thermochemical or electrothermal treatment of metals under a rarefied atmosphere.

It applies more particularly to the thermal or thermochemical treatment of metals, optionally by ion bombardment, comprising, at the end of the treatment cycle, a final treatment, of limited duration, such as quenching.

It is known that there are already many types of heat or thermochemical vacuum treatment ovens with incorporated quench tank. These ovens generally include a cell equipped with heating and possibly cooling means for the thermal or thermochemical treatment as well as incorporated quenching equipment involving a chamber provided with a quenching tank and communicating with the treatment cell. , via a removable and watertight partition, means being further provided for transferring the parts, from the cell to the quenching tank and vice versa.

The disadvantage of these ovens then lies in the underuse of the quenching equipment, due to the fact that the duration of the quenching is generally negligible compared to the duration of the actual treatment. As a result, the profitability of the entire installation is reduced and the cost of treatment is relatively high.

• - une enceinte métallique étanche pouvant comprendre une double paroi, avec interposition d'une couche de refroidissement, cette enceinte comportant une paroi latérale qui présente, de préférence, une forme de section horizontale circulaire, un couvercle et un fond;
• - des moyens permettant de réaliser, à l'intérieur de l'enceinte une atmosphère de traitement à pression réduite;
• - un chemin de roulement circulaire prévu à l'intérieur de l'enceinte sur ledit fond, dans une région périphérique sensiblement adjacente à la paroi cylindrique;
• - un tunnel annulaire, en un matériau thermiquement isolant, disposé au-dessus du chemin de roulement, ce tunnel étant ouvert au niveau de sa face inférieure, face au chemin de roulement, ce tunnel renfermant des moyens de traitement thermique, thermochimique ou électrothermique;,
• - une sole tournante consistant en une couronne réalisée en une matière thermiquement isolante, cette sole étant mobile sur le chemin de roulement et agencée de manière à fermer l'ouverture de la partie inférieure du tunnel et à assurer ainsi la continuité de l'isolation thermique du tunnel au niveau de sa face inférieure;
• - des moyens pour entraîner la sole tournante en rotation, à partir d'un moteur situé, de préférence, à l'extérieur de l'enceinte;
• - des éléments de support des pièces uniformément répartis sur la sole tournante;
• - une cellule de trempe comprenant, d'une part, une chambre formant un sas qui sert également au chargement et au déchargement des pièces à traiter, cette chambre étant montée contre la paroi latérale, à l'intérieur de l'enceinte et communiquant avec le volume intérieur du tunnel par une première porte et éventuellement une cloison mobile et avec l'extérieur par une deuxième porte, de manière à permettre l'accés et la sortie des pièces à traiter à l'intérieur du tunnel et, d'autre part, un bac de trempe situé en dessous de ladite chambre, cette cellule de trempe comportant des moyens de manutention pour déposer ou extraire les pièces de la sole tournante et pour les plonger, en fin de traitement, dans le bac de trempe.

The invention therefore aims to eliminate all these drawbacks. To this end, it offers a heat or thermochemical treatment oven with a rarefied atmosphere comprising more particularly:

• - A sealed metal enclosure which may include a double wall, with the interposition of a cooling layer, this enclosure comprising a side wall which preferably has a shape of circular horizontal section, a cover and a bottom;
• - Means making it possible to produce, inside the enclosure, a treatment atmosphere at reduced pressure;
• - A circular raceway provided inside the enclosure on said bottom, in a peripheral region substantially adjacent to the cylindrical wall;
• - An annular tunnel, made of a thermally insulating material, placed above the raceway, this tunnel being open at its lower face, facing the raceway, this tunnel containing means of thermal, thermochemical or electrothermal treatment; ,
• - a rotating floor consisting of a crown made of a thermally insulating material, this floor being movable on the raceway and arranged so as to close the opening of the lower part of the tunnel and thus to ensure the continuity of the thermal insulation the tunnel at its underside;
• - Means for driving the rotary hearth in rotation, from a motor preferably located outside the enclosure;
• - parts supporting elements uniformly distributed on the rotating floor;
• - a quenching cell comprising, on the one hand, a chamber forming an airlock which is also used for loading and unloading of the parts to be treated, this chamber being mounted against the side wall, inside the enclosure and communicating with the interior volume of the tunnel by a first door and possibly a movable partition and with the outside by a second door, so as to allow access and exit of the parts to be treated inside the tunnel and, on the other hand , a quenching tank located below said chamber, this quenching cell comprising handling means for depositing or extracting the parts from the rotary hearth and for immersing them, at the end of treatment, in the quenching tank.

It should be noted that in order to allow the parts to be isolated when they are introduced onto the hearth, the invention possibly provides a thermally insulating mobile carrier closing the tunnel on one side of the airlock door, preferably on the side where the parts arrive at the end of treatment.

According to another embodiment of the invention, the above-mentioned annular tunnel is interrupted in a sector, of length at least equal to that of the support elements of the parts to be treated, so as to delimit a zone for transferring the parts, this zone transfer located at the right of the interior door of the airlock.

In this case, to avoid excessive heating of the interior volume of the enclosure, two vertical retractable doors, made of a thermally insulating material, are preferably provided, to ensure the closure of the two ends of the annular tunnel, on both sides. other from the transfer area.

The oven can also include cooling means arranged in the enclosure, outside the annular tunnel, these cooling means being intended to permanently evacuate the heat energy dissipated inside the enclosure by the annular tunnel. , especially when the doors are opened and by the parts in the transfer area at the end of the treatment.

Furthermore, it should be noted that the processing means equipping the annular tunnel can be distributed uniformly along this tunnel. They can also consist of a succession of autonomous elements which can be controlled separately by means of a programmable system, in particular to allow custom processing of the parts. These processing means may consist of radiation heating means and / or of ion bombardment processing means. In this half case, a series of electrodes is then provided, namely a series of carried anodes through the tunnel and a series of cathodes which may consist of the support elements on which the parts to be treated are arranged. These cathodes are supplied by means of an electrical circuit with a rotating joint or else by means of a circular track mounted on the rotating floor ot on which brushes come to bear.

This furnace therefore makes it possible to carry out all types of treatment by ion bombardment such as nitriding, carbonitriding, boriding, various cementations, metallic deposits, etc.

The advantage of the previously described thermochemical or thermochemical treatment oven is obvious: firstly, the time of use of the installation of the quenching equipment is multiplied by the number of parts contained inside the oven and its profitability is increased.

The simplicity of the structure of the oven and its mechanisms makes it possible to considerably reduce its cost price. In addition, it turns out that all the mechanical parts of the oven are located in the areas of the oven at low temperature (especially because of the cooling means) and are made of conventional materials and therefore inexpensive.

• La figure 1 est une coupe axiale verticale d'un four à sole tournante selon l'invention
• La figure 2 est une coupe médiane horizontale du four représenté figure 1.

An embodiment of the invention will be described below, by way of nonlimiting example, with reference to the appended drawings in which:

• Figure 1 is a vertical axial section of a rotary hearth furnace according to the invention
• Figure 2 is a horizontal median section of the oven shown in Figure 1.

As previously mentioned, the rotary hearth furnace shown in these drawings first of all comprises a sealed enclosure 1 connected to means, not shown, for producing a treatment atmosphere inside the enclosure, for example a relative vacuum . This enclosure 1 comprises a substantially cylindrical vertical side wall 2 as well as a cover 3 and a curved bottom 4. The assembly rests on a base 5 produced in a conventional manner.

In the example shown, the enclosure 1 has double walls between which a cooling fluid can circulate in a conventional manner.

Access to the interior of the enclosure 1 is carried out by means of an airlock 6 mounted against the vertical wall 2 outside the enclosure 1, which is part of the furnace quenching installation. The airlock 6 comprises, giving on the outside, a conventional pivoting door 7 and, giving on the inside of the enclosure 1, a door 8 retractable laterally. It communicates in its lower part with a quenching tank 9 located below the airlock 6. A transfer means 10 allows the transfer of the parts from the outside to the inside of the enclosure 1 and vice versa, as well as immersion parts at the end of treatment in the quench tank 9.

On the bottom of the enclosure 1 in a peripheral region substantially adjacent to the cylindrical side wall 2, a circular raceway 11 is produced.

Above this raceway 11 is an annular tunnel 12, made of a thermally insulating material, open at its lower face, facing the raceway 11, and equipped with processing means suitable for the use of the furnace, such as electrical resistors 13, electrodes for ion bombardment, nozzles for injection of treatment gas, etc.

This tunnel 12 is also interrupted in a sector 14 of about 60 to 70 °, adjacent to the door 8 of the airlock 6, which serves as a transfer area. The two openings of this tunnel can be closed respectively by two thermally insulating doors 15, 16, which can take at least two positions, namely, a retracted position in the central part 17 of the enclosure 1, position obtained by horizontal radial translation, and a slightly raised position, obtained by vertical translation. The displacements of these doors are obtained by means of a system with pulley slides 19 and return cables 20 driven by a motor 21 situated outside the enclosure 1.

The lower part of the tunnel 12 is further closed by a rotating floor 22 consisting of a crown of thermally insulating material mounted on the raceway 11 by means of rollers 23 and driven in rotation by means of a motor 24 and a transmission system comprising a pinion 25 meshing with a ring gear 26 secured to the sole 22.

This sole 22 carries a series of radial support elements S ₁ to 5 ₉ intended to carry the loads to be treated, at the rate of three support elements S per load. In the example shown, the floor 22 is designed to carry 9 loads making between them an angular difference of 40 °.

It appears from the above description that, in the oven, only the lower volume of the annular tunnel 12, which is thermally isolated from the rest of the volume of the enclosure 1, is subjected to a high temperature. Consequently, all the mechanical parts of the oven are at a relatively low temperature. However, due to the heat losses from the tunnel 12, in particular when the doors 15, 16 are opened and when a load is present at the end of treatment in the transfer zone 14, the invention further provides a system cooling consisting of a coil 28, housed in the cylindrical volume 17 delimited by the tunnel 12 and connected to an external coolant circuit.

The general principle of the oven described above is very simple.

During each of the stages of stopping the sole 22, a load is introduced and / / the support elements S located in the transfer zone 14 are extracted, by the transfer means 10 equipping the airlock 6.

The charges thus introduced are then entrained by the floor 22 and circulate inside the tunnel 12 in a forward movement step by step.

The maximum duration of treatment of these charges corresponds to the time of passage of the charges inside the tunnel 12. In all cases, the return of the charges in the transfer zone takes place at the end of the final treatment phase .

The transfer device 10 which equips the airlock 6, comes to extract the charge which has just arrived in the transfer zone 14 and is still at the final treatment temperature, then immerses it in the quench tank 9. At the end of 'quenching operation, the load is extracted from the airlock 6 and the transfer device 10, can receive a new load.

It should be noted that the charge transfer zone 14 can correspond to the length of the charges to be treated. In this case there is provided between the loads a sufficient interval to allow the passage of the shutter doors 15 and 16. The sole 22 can then be animated with a stepwise movement whose pitch corresponds to the angular difference between two charges.

Furthermore, to avoid overheating of the interior volume of the enclosure 1, outside the tunnel the doors 15, 16 are controlled so as to close the end of the tunnel 12, at least during each of the stop periods of sole 22.

However, this solution has the drawback of requiring a relatively large interval between each charge, which therefore reduces the number of charges processed simultaneously.

The embodiment shown in Figure 2, at least partially eliminates this drawback.

According to this embodiment, the sole comprises nine groups, each comprising three support elements S ₁ to Sg, each of these groups being designed to support a load. The distribution of these groups of support elements S is such that the loads are substantially contiguous and are angularly offset by 40 °.

The transfer area extends over approximately 70 ° with a central area of 40 ° in the axis of the airlock. This transfer zone 14 therefore partially covers two groups of consecutive support elements S ₄ and S ₅ arranged symmetrically with respect to the axis of the airlock 6, as shown in FIG. 2.

In this case the movement of the sole is no longer a simple step-by-step movement, but a pilgrim's step movement, comprising a movement of recoil of the sole 22 by 20 ° making it possible to bring a group of support elements S, loaded or not on the central area 30, and then a forward movement of 60 °, so that the result of these two movements corresponds to a forward movement of 40 °. During these movements the doors 15 and 16 will be retracted in the case of the passage of a support group S, provided with a load, or simply lifted in the case of the passage of a support group S without load. During the shutdown phases of the sole 22 the doors will be retracted in the case where a load is in their path or completely closed in the case where a group of empty support elements S is in their path. In the latter case, the doors 15 and 16 will pass between two consecutive support elements S.

Of course, the invention is not limited to the embodiments described above. Thus, for example in the case where an uninterrupted tunnel is used, access to the interior of the tunnel from the quenching tank could be effected either by means of the watertight door of the quenching tank and / or by a heat shield parallel to this door. In this case, the internal wall of the tunnel will only be interrupted for a possible door (15 or 16) isolating the hot zone from the part which has just received the new load.

Claims (10)

1. A rotary hearth furnace for thermic, thermochemical or electrothermic treatment of metal parts in a diluted atmosphere characterized in that it comprises:

- a sealed metal enclosure (1), which may include a double wall, with an interposed cooling layer, this enclosure (1) comprising a side wall (2) preferably having a circular horizontal section, a cover (3) and a bottom (4)

- means for creating, within the enclosure, an atmosphere for treatment under reduced pressure;

- a circular rolling path provided inside the enclosure on said bottom, in a peripheral region substantially adjacent the cylindrical wall;

- an annular tunnel (12) made of a heat isolating material, situated above the rolling track, this tunnel being open on its lower surface opposite the rolling track, this tunnel including means (13) for thermic, thermochemical or electrothermic treatment;

- a rotary hearth (22) consisting of a ring made of a heat isolating material, this hearth being movable on the rolling track and arranged so as to close the aperture of the lower part of the tunnel and thus provide continuity of the thermic isolation of the tunnel (12) as far as its lower surface is concerned;

- means for rotating the rotary hearth (22) by a motor (24) preferably lodged outside the enclosure;

- elements for supporting the parts (S) evenly distributed on the rotary hearth (22);

- a hardening cell, comprising, on the one hand, a chamber forming a lock (6), also serving for charging and discharging the parts to be treated, this chamber being mounted against the side wall (2), inside the enclosure and communicating with the inner volume of the tunnel (12) by a first door and, if need be, a movable separating wall, and with the outside by a second door so as to allow the introduction and discharge of the parts to be treated inside the tunnel, and, on the other hand, a hardening a hardening vat (9) lodged below said chamber (6), this hardening cell comprising handling means (10) for depositing the parts on or taking them away from the rotary hearth, and for plunging them, at the end of treatment, into the hardening vat (9).

2. Furnace according to claim 1, characterized in that it comprises a movable heat isolating door adapted to close the tunnel (12) at one side of the door of the lock chamber (6), preferably at the side where the parts arrive at the end of treatment.

3. Furnace according to claim 1, characterized in that said annular tunnel (12) is interrupted for a section at least equal in length to that of the elements supporting the charges to be treated, so as to delimit a region (14) for transferring the parts, said transfer region (14) being in line with the outer door of the lock chamber (6).

4. Furnace according to claim 3, characterized in that, in order to avoid excessive heating of the inner volume of the enclosure (1), it comprises two retractable vertical doors (15, 16) made of heat isolating material, for closing the two ends of the annular tunnel (12) at either side of the transfer region (14).

5. Furnace according to claim 1, characterized in that the access from the hardening vat to the inner space of the tunnel takes place by means of the sealing door of the hardening vat and, if need be, by a thermic screen which is parallel to said door, and in that, in this case, the inner wall of the tunnel is only interrupted, if need be, by a door (15 or 16) isolating the hot region from the part which just received the new charge.

6. Furnace according to one of the preceding claims, characterized in that it comprises cooling means (28) arranged in the enclosure (1) outside the annular tunnel (12), these cooling means (28) being designed to permanently evacuate the thermal energy dissipated inside the enclosure (1) by the annular tunnel (12), especially when the doors (15, 16) are opened, and by the parts being located in the transfer region (14) at the end of treatment.

7. Furnace according to one of the preceding claims, characterized in that the means for treatment (13) are evenly distributed inside the tunnel (12).

8. Furnace according to one of claims 1 to 6, characterized in that the means for treatment (13) consist of a succession of independent elements which may be separately controlled by a programmable device, especially for job- treatment of the parts.

9. Furnace according to one of the preceding claims, characterized in that the hearth (22) is driven by a rotary movement of the step-by-step type or of the forward and partial backward type.

10. Furnace according to one of the preceding claims, characterized in that the doors (15 and 16) can take at least two positions, namely: a retracted position in the central part (17) of the enclosure (1) by horizontal translation, and a slightly raised position by vertical translation.

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