EP1077267B1 - Apparatus for the continuous heat treatment of metal workpieces separately or in batches - Google Patents

Abstract

The first channel (11) of the two-channel cooling zone (8) has, along its length, a temperature gradient such that the temperature of the wall directly above the articles (2) is at least that of the condensation temperature of the elements. The second channel (12) walls have a temperature below the condensation temperature of the elements. Heat treatment furnace for metal articles (2) liable to give off elements having high evaporation pressure according to furnace temperature and gas flow and furnace composition comprises, in succession: (a) at least one inlet zone (1) for the articles (2); (b) at least one heating zone (3); (c) at least one cooling zone (8); (d) at least one device (13, 14) for feeding the articles (2) through the zones; and (e) at least one gas flow introduction device (15). The cooling zone (8) comprises two successive different sections (9, 10). The first section (9) extends from the end of the heating zone (3), or the heating channel, to the start of the second section (10), and comprises a channel (11) having, along the whole or part of its length, a temperature gradient such that the temperature of the wall directly above the articles (2) is at least that of the condensation temperature of the elements. The second section (10) comprises a channel (12) whose walls have a temperature below the condensation temperature of the elements.

Description

The present invention relates to a thermal treatment installation of metal pieces in batches or individually at the parade. More specifically the invention relates to such an installation comprising means allowing avoid the accumulation of condensate from the elements of the alloy parts above it in areas of the installation where the parts to are not yet fully solidified.

The parade heat treatment, which successively includes a warm-up phase, a temperature maintenance phase, and finally a cooling phase, of loose or unitary parts in alloy containing elements with high vaporization pressure (designated by thereafter by EPVE), under an oxidizing, inert or protective gas flow reducer presents many difficulties arising from vaporization or of the sublimation of these same elements.

Indeed, when warming up from and above the sublimation temperature, which for a given alloy is a function of the partial pressure of oxygen PO2, therefore of the composition of the atmosphere of treatment, there is an evaporation of the EPVE contained in the alloy. Through example for zinc in a copper base alloy under N2, this temperature is of the order of 400 ° C.

The vapors thus created mix with the atmosphere of the oven and form partly cold condensates.

In the cooling phase of the parts, sublimation stops at a temperature below the sublimation temperature.

Currently, the only industrial possibilities for heat treatment continuously small loose parts, typically monetary sides, in alloys containing EPVE, are rotary retort ovens with a cooling by dropping the parts in a water tank. Parts processed with this type of furnace show traces of impacts and deformations, due to shocks between the parts during transport. This alteration of coins is hardly acceptable in the case of monetary sides and quite inadmissible for rings used for the manufacture of parts bimetallic currency.

Heat treatment furnaces, with transport system for parts through the furnace through continuous movement or discontinuous of a support on which the parts to be treated are arranged, for example a conveyor belt made of a weaving of high-strength alloy wires temperature, allow annealing treatments to be carried out without physical alteration treated parts.

These ovens assimilated to a heated enclosure, with accesses, for example doors or simply openings on either side of the entrance and exit parts, typically consist of an entry area with a channel rectangular or circular sheet metal section, followed by a heating zone, then a cooling part consisting of a box cooled for example by through a double wall in which a cooling fluid circulates (water, air, etc.) and finally an exit zone, these various zones being assembled the to each other, for example by means of bolted flanges.

As described in US Patent 1,906,092, the cooling portion can be formed of a first chamber allowing a start of cooling and a second chamber having an additional cooling device allowing to obtain a faster and more homogeneous result.

For an annealing heat treatment installation, under an atmosphere of inert reducing or oxidizing protection of alloys containing EPVE, works under economically viable conditions, it is desirable that the oven be worn at a temperature higher than the sublimation temperature of the EPVE, so as to have the shortest possible treatment cycles, which is otherwise incompatible with the surface quality requirements of the treated parts. Indeed, condensate accumulation in the cold part of the installation, i.e. at the inlet of the heating zone (inlet channel, start of the oven) and at the start of the cooling, causes by falling tasks which irreparably alter the rooms.

In the furnace inlet area, the accumulation of condensate at the ceiling, brought about by the condensation of vapors generated in the heating zone and swept by the flow of shielding gas in part towards the entry area, can lead to the formation of particles which, when detached from the ceiling, cause a irreparable alteration of the parts. Indeed these condensate particles falling on the pieces at the entrance to the oven are brought to the fusion and form by solidifying during the passage of the parts in zone of cooling of the oven, encrusted particles which can no longer be removed by physico-chemical methods for treating conventional surfaces, for example by the shining technique used in the money industry. These incrustations thus cause an irreversible deterioration of the parts.

At the start of the cooling zone, the walls of which are at a temperature lower than the EPVE condensation temperature, and where the rooms have temperatures higher than the sublimation temperature of EPVE there is condensation of the vapors on all the walls.
The accumulation of these condensates, particularly those located at the ceiling level, generate particles which, by falling on parts having a temperature higher than the melting temperature of said particles, incrustations which bring as in the previous case an irreversible deterioration of the heat treated parts.

This phenomenon of sublimation of EPVE can be significantly reduced or even avoided by using a strongly oxidizing protective gas, by example an O2 + N2 mixture, a wet gas, mixtures of N2 and water or N2 and H2 and water, or just air. However these atmospheres cause a strong oxidation of the treated parts, with for consequence, especially for the monetary flanks, an increase sensitive physico-chemical treatment times for surface finishing, commonly called brightening. In addition the material losses which result of these operations are important.

To overcome the drawbacks of this prior art, the invention consists, during heat treatments of loose, batch, unit or continuous (such as strips, wires or profiles) in a passage furnace under protective atmosphere likely to cause formation of vapors from the parts to be treated, to avoid any possibility of fallout of condensate particles from these vapors on the parts, when these are, or will be brought to temperatures higher than the temperatures of these particles. In other words, the invention consists in avoiding that the EPVE cannot condense above the parts bed.

To this end, the invention relates to a treatment installation thermal treatment of metal parts in batches or units on parade in an oven gas flow circulation channel, said parts being composed of at least less an alloy capable of emitting elements at vapor pressure high (EPVE) depending on the oven temperature and the composition of the gas flow and said oven, successively comprising at least one zone at the entrance to the rooms, at least one heating zone and at least one heating zone cooling, formed of a first sector and a second sector from which the treated parts as well as at least one means of driving the parts to through these different zones and at least one device for introducing the gas flow, characterized in that the first sector channel, has on at least part of its length of the means for cooling the lower part to a lower temperature at the condensation temperature of the EPVE and the means for maintaining upper part temperature at a temperature greater than or equal to the temperature of condensation of the EPVE, and in that the channel of the second sector includes means allowing the walls to be brought to a temperature below the temperature of condensation of EPVE.

• la figure 1 montre une coupe schématique longitudinale d'un four de traitement au défilé selon l'invention;
• la figure 2 montre une vue en coupe de l'entrée du four selon la ligne II-II de la figure 1, et
• la figure 3 montre une vue en coupe de la sortie du four selon la ligne III-III de la figure 1.

The invention will be better understood on reading the following description of an embodiment given by way of nonlimiting example with reference to the accompanying drawings in which:

• Figure 1 shows a schematic longitudinal section of a parade treatment oven according to the invention;
• FIG. 2 shows a sectional view of the inlet of the furnace along the line II-II of FIG. 1, and
• FIG. 3 shows a sectional view of the outlet of the furnace along the line III-III of FIG. 1.

• d'une zone d'entrée 1 s'étendant entre la section d'entrée des pièces 2 dans l'installation et le début du four proprement dit comprenant au moins une zone de chauffe 3 et comprenant par exemple un canal métallique 4 de forme rectangulaire ou circulaire qui dans certains cas peut être le prolongement du canal situé dans la zone de chauffe 3,
• d'une zone de chauffe 3 constituée d'un canal métallique de forme quelconque, entouré d'une couche de matériau isolant 6 et de moyens de chauffe 7 qui peuvent être des brûleurs à gaz ou des corps de chauffe électriques conventionnels. La température dans la zone de chauffe est régulée au moyen de dispositifs de mesure de température (par exemple des thermocouples) et de régulateurs conventionnels du marché, non représentés,
• d'une zone de refroidissement 8 destinée au refroidissement des pièces constituée d'un moins deux secteurs, le premier secteur 9 s'étendant de la fin de la zone de chauffe 3 ou de la fin du canal 5 de la zone de chauffe du four à une distance partir de laquelle la température des pièces 2 traversant le four ne produisent plus d'EPVE (typiquement 400°C pour les pièces contenant du zinc), le deuxième secteur 10 de la zone de refroidissement s'étendant de la fin du premier secteur 9 jusqu'à la sortie des pièces 2 de l'installation. Les deux secteurs 9, 10 de la zone de refroidissement comportent un canal respectivement 11 et 12. On peut cependant imaginer qu'un seul canal soit suffisant dans les deux secteurs de refroidissement. Le premier secteur est caractérisé par le fait que l'on assure que la température de la surface intérieure du canal 11, ou de toute surface disposée directement au dessus des pièces, est maintenue à une température telle que la condensation des EPVE n'est pas possible sur cette surface aussi longtemps, ou respectivement sur une distance suffisante pour permettre aux pièces d'atteindre une température inférieure à la température de fusion des condensats,
• d'un dispositif d'entraínement 13 des pièces 2 au travers des différentes zones de l'installation constitué d'un jeux de tambour ou de rouleaux motorisés entraínant une bande ou une chaíne de transport 14 qui supporte les pièces. D'autres modes de réalisation sont bien évidemment possibles comme le remplacement de la bande de transport 14 par des rouleaux entraínés disposés tout le long de l'installation, et
• d'un dispositif d'injection des gaz de traitement, constitué par exemple de buses de gaz à flux orientables 15 constituées d'un tube fendu à son extrémité et placé orthogonalement au sens de défilement des pièces ou simplement d'un tube dont le point d'injection est placé dans le sens du flux de gaz désiré.

Referring more particularly to FIG. 1, it can be seen that the treatment furnace according to the invention is typically constituted:

• an inlet zone 1 extending between the entry section of the parts 2 into the installation and the start of the oven proper comprising at least one heating zone 3 and comprising for example a metal channel 4 of rectangular shape or circular which in some cases can be an extension of the channel located in the heating zone 3,
• a heating zone 3 consisting of a metal channel of any shape, surrounded by a layer of insulating material 6 and heating means 7 which can be gas burners or conventional electric heating bodies. The temperature in the heating zone is regulated by means of temperature measuring devices (for example thermocouples) and conventional regulators on the market, not shown,
• a cooling zone 8 intended for cooling the parts made up of at least two sectors, the first sector 9 extending from the end of the heating zone 3 or from the end of the channel 5 of the furnace heating zone at a distance from which the temperature of the parts 2 passing through the furnace no longer produce EPVE (typically 400 ° C. for parts containing zinc), the second sector 10 of the cooling zone extending from the end of the first sector 9 until the exit of parts 2 of the installation. The two sectors 9, 10 of the cooling zone comprise a channel 11 and 12 respectively. It can however be imagined that a single channel is sufficient in the two cooling sectors. The first sector is characterized by the fact that it is ensured that the temperature of the internal surface of the channel 11, or of any surface disposed directly above the parts, is maintained at a temperature such that the condensation of the EPVE is not possible on this surface as long, or respectively over a distance sufficient to allow the parts to reach a temperature below the melting temperature of the condensates,
• of a drive device 13 for the parts 2 through the various zones of the installation consisting of a set of drums or motorized rollers driving a band or a transport chain 14 which supports the parts. Other embodiments are obviously possible such as replacing the conveyor belt 14 with driven rollers arranged throughout the installation, and
• a device for injecting the treatment gases, consisting for example of orientable flow gas nozzles 15 consisting of a tube split at its end and placed orthogonally to the direction of travel of the parts or simply of a tube whose point injector is placed in the direction of the desired gas flow.

The different channels 4, 5, 11 and 12 are linked together by means of example of flanges 16. One can however easily imagine that the channels 4 and / or 11 are replaced by an adequate extension of the channel 5.

Figure 2 describes in more detail the entrance area 1 according to the plan of section II-II defined in Figure 1.

According to the invention, the entry area 1 consists of a channel 4 of cylindrical or parallelepipedic section, for example the extension of the heating channel 8 or an attached part coupled to the heating channel for example by means of a flange 16. The length of the entry zone 1 depends on the passage height of channel 4 but is typically less than the length of the heating zone 3.

The entry area 1 comprises in the upper part, above the parts to be treated, a physical separation 17 arranged so as to spare a space between its upper part and the inlet channel and intended, for channel the flow of vapor-laden gas between the canal ceiling and this separation and, to collect the condensates, thus avoiding any fallout of particles that can cause irreparable damage to the parts.

This separation can consist for example of a plate maintained by supports 18 integral with the channel, for example brackets, pins. The same effect can be achieved through a bent sheet in the shape of an inverted U, the sides of which rest on the bottom of the channel.

This physical separation 17 partially extends 17a in the heating zone without, however, crossing it entirely. Typically, this separation 17a extends into the heating zone up to a distance substantially equal to where the parts reach temperature evaporation or sublimation of EPVE.

The vapors swept away by the flow of shielding gas introduced into the oven or in the channels constituting the interior of the oven, the heating zone towards the oven inlet, via an injection system, consisting of example of directional flow gas nozzles 15, condense preferably on top of the sheet forming the separation which is therefore easily removable for cleaning. Cleaning frequencies are essentially a function of the quantities of EPVE contained in the parts treat.

According to another embodiment of the invention, in particular for some applications, producing a large amount of condensate by example for the annealing of brass parts with a high percentage of zinc, the physical separation system 17 can be completed with a device heated 19 to maintain the temperature of the wall above the parts at a temperature higher than the condensation temperature of vapors from EPVE.

The heater 19 is for example made up of a metal coil of type armored heating body, whether or not integral with the partition 17, in order to maintain its temperature at a temperature higher than the temperature of condensation of vapors from EPVE.

In this case, the physical separation 17 need not necessarily extend to the interior of the heating zone 3. The regulation of the separation temperature is conventionally operated by means of a measurement of the temperature (for example a thermocouple) and of a regulator of conventional temperature, not shown.

It is also possible, in another embodiment, to delete the physical separation 17 and heat the upper part of the inlet channel 4 on the same heating mode as that proposed for example for the physical separation.

In order to limit pollution of the installation environment, the parallelepiped section can be fitted at the ceiling with a duct vapor evacuation (not shown), typically a section tube cylindrical directly welded to the channel, or with a removable junction by through flasks. Gas extraction can be natural or forced, for example by venturi effect, supplemented if necessary by a system of mechanical filtering or condensation of vapors by vacuum.

In the heating zone 3, the temperature of the walls of the channel 5 in look of the parts is higher than the condensation temperature of the vapors from the sublimation of EPVE contained in the parts there therefore there is no risk of formation of condensates liable to pollute the rooms.

In the cooling zone 8 where the sublimation phenomena occur continue until the pieces reach a temperature below sublimation temperature, e.g. approx. 400 ° C for zinc in copper alloys, this is to avoid any formation of condensate above parts, condensates which falling down would cause damage irreversible of the parts, if these are at a temperature higher than the condensate melting temperature.

Figure 3 shows a section, along the plane III-III of Figure 1, of first sector 9 of the cooling zone 8 and consists of at least minus a parallelepipedic or circular channel 11, depending on the geometry of the upstream and downstream interfaces.

The first sector 9 of the cooling zone 8 extends from the end the heating zone or the heating channel 5 if it extends slightly further than the heating zone 3 proper.

The first sector is characterized by the fact that it is ensured that the temperature of the inner surface of channel 11 or any surface placed directly above the parts is maintained at a temperature such that condensation of EPVE is not possible on this surface too a long time, or a sufficient distance respectively, to allow pieces to reach a temperature below the melting temperature condensates.

The extent of the first sector of the cooling zone depends on the processing temperature in the heating and dissipation area energy of the parts (cooling) in the cooling zone. Typically, the length of the first sector 9 of the cooling zone 8 is 2 to 4 meters for a total length of the cooling zone 8 of about ten meters and a length of the heating zone 3 of 4-6 meters.

According to the invention, the first sector 9 of the cooling zone is characterized in that the upper surface 21 located above the parts (which can be the surface of channel 11 or another surface) is not cooled as is the case in a conventional processing oven. This surface 21 is on the contrary thermally insulated by means of an insulator thermal 24 whose thickness is adapted accordingly (typically 100 300 mm) disposed inside or outside the channel 11, said surface 21 can also be provided with a heating system 20.

The heating system 20 can be arranged either outside or at inside the channel 11 and does not have to extend over the entire distance from the first sector of the cooling zone. Heating 20 can be achieved using conventional electric heaters or through a gas burner. Temperature regulation desired on the surface is conventionally carried out by means for example of a temperature measurement and a conventional temperature controller, not shown.

At the exit of the heating zone 3 or start of the first sector 9 of the cooling zone 8, it is not absolutely necessary to isolate thermally or heat to maintain the surface temperature 21 above the desired temperature. Indeed, the pieces coming out of the oven suffice to maintain this surface above the critical temperature.

In order to reduce the length of the first cooling sector 9, the part of the system below the parts can be cooled by example by means of a double wall 22 in which a fluid circulates cooling (water, air, etc.). This double coat can be placed at inside or outside of channel 11. Possible condensation of EPVE on the bottom of the channel 11 thus cooled is of no consequence since the cold surfaces are located under the parts and no damage to the surface of the parts is not to be feared. We can provide openings that allow the bottom of channel 11 to be cleaned from time to time.

In case of insufficient gas flow dynamics, the system can be equipped with a vapor evacuation device (not shown), typically a cylindrical section tube directly welded to the system ceiling channel, or with a removable junction via flanges. The aspiration of gases can be natural or forced, for example by effect venturi, supplemented if necessary by a mechanical filtering system or vapor condensation by vacuum.

In this case the vapor exhaust system must be accessible for the in situ cleaning of condensates, the solution of a junction removable - for example by flanges is therefore preferable.

The second sector 10 of the cooling zone 8 can be typically consisting of a double mantle 23 or channel in which a coolant, including at the top which is voluntarily cooled to accelerate the cooling of the parts.

This part can also be equipped with a convection device shielding gas and a heat exchanger to allow cool the parts faster and decrease the length of the cooling 12.

Between the two sectors 9, 10 of the cooling zone 8 or towards the end of the first cooling sector 9 or at the start of the second sector 10 cooling, gas treatment or protection of parts (e.g. nitrogen, hydrogen, argon or mixtures gas) is injected to allow the gas to impart a movement whose direction is the opposite of that of advance of the pieces through the zone of cooling.

The installation which has just been described can be adapted by the person skilled in the art. art, without departing from the scope of the invention according to the alloys entering into the composition of the parts to be heat treated.

Thus, the invention overcomes the disadvantages of the prior art by providing a heat treatment installation for susceptible parts to issue EPVEs in which the processing time is relatively short without causing an irreversible change in the appearance of parts surface.

Claims (11)

1. Apparatus for the continuous heat treatment of metal workpieces (2) separately or in batches in a channel furnace with gas flow circulation, said workpieces (2) being formed of at least an alloy capable of giving off high evaporation pressure elements (EPVE) as a function of the temperature of the furnace and the composition of the gas flow, and said furnace successively including at least one inlet zone (1) for the workpieces (2) at least one heating zone (3) and at least one cooling zone (8), formed of a first section (9) and a second section (10) from which the treated workpieces exit and at least one driving means (13, 14) for driving the workpieces (2) through said various zones and at least a gas flow introduction device (15), characterized in that the channel (11) of the first section (9) comprises, over at least a portion of its length, means for cooling the lower portion to a temperature lower than the condensation temperature of the EPVE and means for maintaining the temperature of the upper portion at a temperature greater than or equal to the condensation temperature of the EPVE, and in that the channel (12) of the second section (10) includes means for bringing the walls to a temperature lower than the condensation temperature of the EPVE.
2. Heat treatment apparatus according to claim 1, characterized in that the cooling means for the lower portion of the first section (9) are formed by a double wall (22) allowing a cooling fluid to circulate.
3. Heat treatment apparatus according to claim 1, characterized in that the means for maintaining the temperature of the first section (9) use a heat insulator (24).
4. Heat treatment apparatus according to claim 3, characterized in that the heat insulator (24) further includes heating means (20).
5. Heat treatment apparatus according to claim 1, characterized in that the gas flow circulates in a direction opposite the movement of the workpieces (2) over a major portion of the first section (9) of the cooling zone (8) .
6. Heat treatment apparatus according to claim 1, characterized in that the inlet zone (1) is constituted of at least one channel (4) in which a physical separation (17) over at least one portion of its length is further disposed, in order to provide a space between the upper surface of the channel (4) and said physical separation (17).
7. Heat treatment apparatus according to claim 6, characterized in that the physical separation (17) extends partially inside the heating zone (3) .
8. Heat treatment apparatus according to claim 6, characterized in that the physical separation (17) further includes heating means (19).
9. Heat treatment apparatus according to claim 6, characterized in that at least the upper portion of the channel (4) of the inlet zone (1) includes heating means.
10. Heat treatment apparatus according to claim 1, characterized in that the second section (10) of the cooling zone is surrounded by an envelope (23) in which flows a cooling fluid.
11. Heat treatment apparatus according to claim 1, characterized in that the different zones and sections are individual elements assembled and connected in series by means of connecting flanges (16).

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