EP0737755A1 - Method and apparatus for heat treating workpieces - Google Patents

Abstract

Thermal treatment of components on a treatment line (LT) incorporating at least one furnace (2) and one hardening cell (4) comprises: (a) arranging the components (22) in individual charges (C), in some boxes or baskets (20), to form distinct lots with a volume (V) of components having a height (H) chosen to be clearly less than the other dimensions (L1,L2) of the volume; (b) introducing the individual charges (C) into the furnace (2) and heating them to the treatment temperature; (c) transporting the charges (C) from the inside of the furnace (2) to the inside of the hardening cell (4) by means of a transporter (T); and (d) guiding the displacement of the charges (C) on the transporter (T) along the treatment line (LT) in a manner that the charges (C) are displaced along this line, locally, at different speeds (V1,V2,V3). The installation used implement this method is also claimed, and incorporates at least one furnace (2), one hardening cell (4) and a transporter (T) forming a treatment line (LT).

Description

The present invention relates to a method of heat treatment of parts, in particular of small dimensions, as well as an installation for the implementation of this method.

Conventional heat treatment installations comprise one or more ovens which are associated with at least one quenching cell, these elements cooperating with transport means allowing the movement of the parts to be treated between the oven (s) and the cell.

The ovens are kept at relatively high heating temperatures, capable of processing the parts which must, for this purpose, remain in the ovens for a certain period of time in order to reach the desired treatment temperature.

With regard to the subsequent quenching, there are two large families qualified respectively as gas quenching and liquid quenching, because of the media used to ensure rapid cooling of the parts.

Gas quenching, as it has been implemented to date, is generally limited in its application to high-alloy steels or so-called "self-hardening".

Conversely, common steels, such as structural steels, carbonitriding steels or bearing steels must be quenched in liquid media, consisting for example of water, polymers, oil or salts in order to obtain significantly higher quenching rates.

However, it has been found that when the treated parts are quenched in a liquid medium, they are subjected to a significant thermal shock, and the cooling phenomenon occurs in a non-homogeneous manner due in particular to the appearance of heat-recovery sheaths due at boiling of the liquid. In addition, these sheaths appearing on the surface of the hardened parts, which modifies the heat transfer coefficients between the parts and the medium, and which gives rise to deformations or distortions of the parts, in particular if they are not very massive and if they have thinned shapes, as is generally the case with small parts.

It is therefore understood that quenching in a liquid medium is difficult to apply to the heat treatment of small parts, generally having complex shapes, the geometric stability of which, whether in shape or in size, must be ensured if operations are to be avoided. subsequent recovery, such as machining.

In addition, it should be noted that quenching in a liquid medium requires the implementation of parts washing operations after treatment, which considerably increases the cost price of the treatment per part. In addition, anti-pollution standards impose the use of equipment for cleaning pollution from washing baths and require strict observance of limits as to the proportion and nature of the products rejected, which, we understand, further complicates advantage of using this type of quenching.

The liquid quenching heat treatment installations which have been proposed for the treatment of small parts for the moment are so-called run-through installations, that is to say in which the movement of the parts in the treatment furnace occurs in an essentially horizontal plane. In these installations, the quenching is carried out by the falling of the parts in the quenching bath, at the outlet of the oven, under the effect of gravity.

There is also known an alternative to quenching in a liquid medium, which is gas quenching, applied specifically to medium or low alloy steels. This type of quenching is characterized by the use gas pressures which can be higher than 15 bars. However, the use of high pressures can only be justified for the quenching of parts having a very high added value or for very massive parts, for example tools, and this again because of the significant operating costs.

It is therefore understandable that today there is no economic and rational technological solution allowing the quenching of small parts, since all the solutions listed above have drawbacks resulting in an implementation, either incompatible or too expensive.

It can indeed be seen that, for small parts, the application, by analogy, of quenching conditions in a liquid medium to the quenching conditions with gas cannot be done without an appropriate adaptation of the installations and processes since, in particular in the case of parade treatment, it is inconceivable with a gas quenching cell to allow the pieces to drop in the cell, at the outlet of the oven, since the quenching medium is not capable of curbing the falling of the pieces.

They could therefore injure themselves or deform, which would make this type of heat treatment inapplicable.

In addition, if for the treatment of parts of small dimensions, it is actually desired to design a process and an installation for thermal treatment on parade with a gas quenching cell, the following obstacles are encountered.

Indeed, the objective being to obtain a brutal quenching, for the application to all types of steels, conventional means of transport do not prove to be any more adapted since they are sources of considerable heat losses between the leaving the oven and entering the quenching cell.

One could obviously increase the temperature inside the oven correspondingly, but this measure would result in a much too large increase in the grain size of the material, alteration which, as is known, has the effect of very seriously weaken the final mechanical properties of the treated part (s).

In addition, conventional parade treatment facilities include one or more airlocks at the entrance and exit of the oven, and at the entrance and exit of the cell.

However, the operations of opening a watertight airlock at the outlet of the furnace and of opening a watertight airlock at the entry of the quenching cell, during the transfer of the parts, cause the oven enclosure to cool. and consequently again results in a lowering of the temperature of the furnace and of the parts contained therein.

In addition, the presence of gas in the quenching cell, whether in pure form or in the form of a mixture, brings about significant risks of explosion due to the incompatibility between the two media, respectively of the oven and of the cell. .

Thus, while we seek, on the one hand, to avoid the implementation of too heavy mechanization in the construction of the airlocks, to ensure the transfer of parts from the oven to the cell without loss of temperature in transition zones, we note that on the other hand, we must avoid at all costs the interaction between the two environments, respectively of the oven and the cell, on the one hand not to cause cooling of the oven, and, on the other hand, to reduce the risk of an explosion on the operating site.

Added to this are the drawbacks inherent in gas quenching for which, as opposed to quenching in a liquid medium, the heat exchange capacity is very low. This heat capacity which is nothing other than the capacity of the gas to absorb the heat contained in the parts to be treated have an important place in the quality of quenching, because it is also this absorption characteristic which very strongly conditions the quenching speed.

For this reason, it must be recognized that the implementation of conventional heat treatment installations with gas quenching is not optimal under all conditions. Thus, for parts with a high mass or for parts produced in steels which require cooling rates such that gas quenching cannot give quenched parts the desired final hardness, it may be desirable to use an installation whose quenching takes place in liquid media.

We could determine that to increase this heat capacity in the case of gas quenching, that is to say this heat exchange, three conditions had to be met, namely the presence of a cold gas before the operation of quenching, a large gas flow and a turbulent regime of the gas flow in the cell.

However, if the parts are in the form of a bed, the gas heats up passing through the bed of parts, so that there are inside this bed of parts levels subjected to different quenching conditions , that is to say who are in contact with a gas whose temperature has increased. In addition, it can be seen that the presence of turbulence within the bed of parts can only be maintained on the first few levels.

To all of this is added, in gas quenching installations, another condition which is the stability of the controlled atmosphere inside the furnace, in order to maintain a constant quality of thermochemical treatment, for all types of treatment. whether for austenitization under nitrogen, austenitization under synthesis gas, austenitization under potential equilibrium, case hardening, carbonitriding or even for nitrocarburization.

It is known that all these types of thermochemical treatment require draconian regulation of the treatment atmosphere. The quality of the thermochemical treatment is therefore directly a function of the precision and the stability of the characteristics of this atmosphere which cannot undergo significant variations. However, the transfer of parts between the oven and the outside may cause such disturbances.

Finally, it should be noted that the construction of a heat treatment installation and the implementation of a specific process must meet the requirements of any industrial installation, namely, technological simplicity, profitability, reliability, in particular for mechanical working hot, safety, and finally manufacturing and maintenance with the lowest possible costs.

Thus, the object of the present invention is to provide an installation and a method of heat treatment which allow the treatment of small parts, without limitation of their material, and which avoids the problems and obstacles mentioned above while meeting all the requirements criteria raised.

• à disposer les pièces à traiter en charges individuelles dans des bacs ou paniers, pour constituer des lots distincts formant un volume V de pièces, dont la hauteur H est choisie nettement inférieure aux autres dimensions du volume,
• à introduire les charges individuelles dans le four pour porter lesdites pièces à la ou aux températures de traitement,
• à transporter les charges, d'une part, à l'intérieur du four, et d'autre part, à l'intérieur de la cellule de trempe, ainsi qu'entre le four et la cellule par l'intermédiaire de moyens de transport, et
• à piloter le déplacement des charges sur les moyens de transport, le long de la ligne de traitement de sorte que les charges se déplacent, le long de cette ligne, localement, à des vitesses différentes.

To this end, the invention relates to a process for the heat treatment of parts, in particular of small dimensions, on a process line for parade comprising at least one oven and a quenching cell, characterized in that it consists:

• placing the parts to be treated in individual loads in trays or baskets, to constitute separate batches forming a volume V of parts, the height H of which is chosen to be much lower than the other dimensions of the volume,
• introducing the individual charges into the oven to bring said parts to the treatment temperature or temperatures,
• to transport the charges, on the one hand, inside the oven, and on the other hand, inside the quenching cell, as well as between the oven and the cell by means of transport means , and
• to control the movement of the loads on the means of transport, along the processing line so that the loads move, along this line, locally, at different speeds.

The invention also relates to a thermal treatment installation for implementing this method, this installation being characterized in that it is provided for treating a set of trays or baskets arranged to receive the parts to be treated and group them into charges individual to constitute separate batches forming a volume of parts whose height is much lower than the other dimensions of the volume, the means of transport further being made up of several drive devices which can be controlled individually by means of regulation at least three characteristic speeds respectively of entry, treatment and exit to divide the line of treatment into sectors ensuring locally, on this line, a displacement of the trays or baskets at different speed levels.

• La figure 1 est une vue de côté d'une installation de traitement thermique selon un premier mode de réalisation de l'invention, cette installation étant représentée ici de façon très schématique, avec un diagramme de vitesse de déplacement des charges,
• la figure 2 est une vue en coupe longitudinale de l'installation de la figure 1, représentant essentiellement des dispositifs d'entraînement à bandes de cette installation,
• la figure 3 est une vue similaire à la figure 2 mais représentant des dispositifs d'entraînement formés de groupes de rouleaux,
• la figure 4 est une vue de dessus d'un des groupes de rouleaux de la figure 3,
• La figure 5 est une vue similaire à la figure 1, mais représentant un deuxième mode de réalisation de l'installation selon l'invention, munie uniquement de trois dispositifs d'entraînement,
• la figure 6 est une vue en coupe similaire à la figure 2, mais représentant l'installation selon le deuxième mode de réalisation, et
• la figure 7 est une vue de côté d'une installation selon un troisième mode de réalisation de l'invention, montrant une application à la trempe en milieu liquide.

Other characteristics and advantages of the invention will appear on reading the detailed description which follows, given with reference to the appended drawings which are given solely by way of example, and in which:

• FIG. 1 is a side view of a thermal treatment installation according to a first embodiment of the invention, this installation being shown here very schematically, with a diagram of the speed of displacement of the loads,
• FIG. 2 is a view in longitudinal section of the installation of FIG. 1, essentially representing belt drive devices of this installation,
• FIG. 3 is a view similar to FIG. 2 but showing driving devices formed by groups of rollers,
• FIG. 4 is a top view of one of the groups of rollers in FIG. 3,
• FIG. 5 is a view similar to FIG. 1, but showing a second embodiment of the installation according to the invention, provided only with three drive devices,
• FIG. 6 is a sectional view similar to FIG. 2, but showing the installation according to the second embodiment, and
• FIG. 7 is a side view of an installation according to a third embodiment of the invention, showing an application to quenching in a liquid medium.

Referring to FIGS. 1 and 2, a thermal treatment installation according to the invention will be described below, in accordance with a first embodiment.

This heat treatment installation, which is identified by the general reference 1 comprises, in this embodiment, an oven 2 in the longitudinal axis of which is disposed a gas quenching cell 4. Of course, the invention is not limited to an installation having only one oven and only one cell, but it also applies to installations having several ovens and several cells, with selected combinations of numbers for these two elements.

In this installation, the direction of movement of the parts to be treated, which is carried out here from left to right, is represented by the arrow D. This movement takes place essentially linearly and more particularly in the same horizontal geometrical plane, via means of transport T, belt or roller.

The oven 2 is constituted by a thermally insulating carcass 2a which defines an enclosure or treatment cavity 2b inside which are arranged a plurality of heating elements 2c, only one of which has been referred to here.

The heating elements 2c are constituted, for example, by a set of electrical resistors capable of heating the enclosure 2b by convection and / or by radiation and of bringing this enclosure to selected treatment temperatures. These resistors are conventionally connected to a programmable power supply unit, not shown.

The processing temperatures used are common, and are chosen from the conventional temperature ranges used in the methods of heat treatment of metal parts.

The oven 2 is open at the end at its two ends by openings 2d and 2e, formed in the carcass 2a and respectively forming an inlet opening and an outlet opening of the oven 2. These openings have a width referenced LO (FIG. 2 ).

The enclosure 2b comprises three characteristic regions referenced respectively R1, R2 and R3.

The first region, referenced R1, forms the inlet of the furnace 2. It is arranged upstream relative to the other two, the directions “upstream” and “downstream” being defined with reference to the direction of movement D of the parts in the installation. .

The second region, referenced R2, which is contiguous with the first region R1, and which is arranged downstream thereof, constitutes, in the enclosure 2b of the furnace 2, the region of greatest length. It is indeed this which is intended to ensure the heating of the parts to be treated up to the selected treatment temperature.

Finally, the third characteristic region, referenced R3, which is contiguous with the second region R2, and which is likewise arranged downstream thereof, is called exit region since it is from this third region that the parts being treated will be moved towards the outside of the furnace, up to the gas quenching cell 4.

The installation 1 also includes an inlet E and an outlet S allowing the introduction and recovery of the parts. The inlet E and the outlet S are shown in FIG. 1 by the two open ends of the transport means T.

It will also be noted that the installation 1 comprises a first channel or tunnel called the inlet C1, extending from the inlet E of the facility to the opening 2d of the furnace 2.

The installation 1 comprises a second channel or tunnel called the outlet C2, extending from the outlet opening 2e of the oven 2 to an intermediate zone Z provided between the outlet of the oven 2 and the inlet of the cell 4 .

The two channels or tunnels C1 and C2 which are tightly fixed to the carcass 2a of the furnace 2, are thermally insulated and unheated. They communicate respectively with the regions R1 and R3 of the enclosure 2b of the furnace 2.

The two channels C1 and C2 have lengths K1 and K2 respectively. The length K2 is chosen at least equal to the width LO of the openings 2d and 2e (the representation in the figure is not to scale).

The channel C1 is provided at its entry with a non-watertight door P1, while the channel C2 is provided at its exit with a non-watertight door P2 of the same type.

It will be noted that the doors P1 and P2 can be controlled in opening and closing (here by pivoting) independently.

At the exit door P2, the installation 1 also comprises means making it possible to isolate the atmosphere prevailing in the enclosure of the furnace 2, vis-à-vis the atmosphere of the quenching cell 4, these means being achieved by the creation of a protective screen, here not shown, obtained, according to a first variant, by the combustion of the treatment gas or another gas. For this purpose, there is provided at the outlet door P2 of the oven 2 a pilot light Ve allowing the process gas to be ignited in a controlled manner in this region.

This protective screen can also be obtained, according to a second variant, by the establishment of an inert gas curtain (not shown) projected by a nozzle B, in the same region.

The protective screen is formed when the door P2 is open, but also when it is closed, since this door is not sealed, it leaves an open space through which the treatment gas can be ignited, in contact with air , through the pilot, if the gas is flammable. If it is not flammable, the overpressure of oven 2 creates the gas curtain.

When the door P2 is opened, the protective screen seals between the oven 2 and the ambient air and prevents the atmosphere in the oven 2 from being destabilized. This prevents gas from the oven 2 from either driven in the quench cell 4.

It will also be noted that the arrangement of the channels C1 and C2, and the mounting of the non-watertight doors P1 and P2 at the free end of these channels removes the potential source of disturbance from the atmosphere of the furnace 2 and therefore contributes to improving the stability of the thermochemical characteristics of treatment prevailing in the enclosure of the furnace 2.

It will also be noted that the implementation of this arrangement is facilitated by the fact that the parts are treated in loads, in batches having a height smaller than the width, as will be explained below in detail.

Similarly, the quenching cell 4 is provided at its inlet and at its outlet with two watertight or non-watertight doors P3 and P4.

This quenching cell 4 comprises a turbulence generating device, not shown, formed by a wind box or a propeller. The speed and the flow rate of the gas are also ensured by fans, likewise not shown.

The fluid used in this cell to ensure the quenching operation is designated in as being a gas, but it will be specified that a two-phase medium can be used, that is to say a mixture formed of a gas and a liquid of another nature, in spray form, in droplets.

The means of transport T are formed (FIG. 2) for example by a belt system constituting several independent drive devices, here four in number, respectively referenced DE1, DE2, DE3 and DE4. These four independent devices are placed in the installation 1 one after the other, at a short distance, on the same level, and they form, in this installation, the movement plan of the parts.

The first drive device DE1 which extends from the inlet E of the installation, into the first region R1 of the oven 2, through the channel C1 and the inlet opening 2d of the oven, is intended receiving the parts to be treated after they have been placed by a conventional feeding device, not shown here. This first drive device DE1 is also intended to ensure the rapid introduction of the batches of parts to be treated beyond the door P1 and, as in the example shown, as far as the oven 2, and more particularly as far as the first region R1.

The second drive device DE2 extends in the central region R2 of the enclosure 2b, over the major part of this enclosure, however leaving sufficient space between the end of DE2 and the end of the region R3.

The third drive device DE3 extends from an end part of the region R2, it crosses the region R3 and it enters the outlet opening of the furnace referenced 2e, in the vicinity of the channel C2.

Finally, the fourth device DE4 extends, on the one hand, from the channel C2 to the outlet S of the installation, and on the other hand, through the transition zone Z and the quenching cell 4 which it crosses right through.

As can be seen in FIG. 2, each drive device DE1 to DE4 comprises for example a flexible conveyor belt, driven and supported in rotation by one or more drive rollers R, only one being here referenced.

The four drive devices DE1 to DE4, and more particularly their bands b1 to b4, as well as the furnace 2 and the quenching cell 4 form, extending on the same longitudinal axis, a linear processing line LT. The installation 1 according to the invention can therefore be described as a parade installation, the oven 2 being a passage oven.

The rollers R which support the bands b1 to b4 are pivotally mounted in bearings (not referenced), some of which are fixed to the carcass 2a of the furnace 2, the others being supported by conventional support benches, not shown.

The bands b1, b2, b3 and b4 are respectively associated with independent motors M1, M2, M3 and M4.

The motors M1 to M4 are electric motors of conventional construction and will therefore not be described here in more detail. It will simply be mentioned that the drive between each motor and one of the rollers of the four drive devices DE1 to DE4 is done by mechanical means, such as for example a chain 6 (only one being referenced) engaged on two toothed pinions united in rotation respectively of the motor and the corresponding motor roller ensuring the drive of the strip.

The four motors M1 to M4 are all connected, for example, electrically to an electrical control unit UC, constituted, in this example, by a programmable controller. Thus, these motors can be controlled independently at different rotational speeds to allow the actuation of the four drive devices DE1 to DE4 at different speed levels, according to selected operating sequences.

Referring now to Figures 3 and 4, there will be described below a heat treatment installation with only roller drive devices.

This installation differs from the installation shown in FIG. 2 only by the absence of flexible drive bands, the four drive devices DE1 to DE4 being here constituted by groups of drive rollers, rollers whose structure is of the type of that of the rollers equipping the drive devices of FIG. 2.

In each group of drive rollers, a motor roller Rm (FIG. 4) is mechanically connected, as in the previous embodiment, to one of the motors M1 or M4, by means of two pinions 8 and 10, secured respectively to the motor and the motor rollers, and by means of a chain 6 meshing on these two pinions. In each group of rollers, the drive roller Rm is connected to the other driven rollers Re (two being referenced) by a transmission chain 12 meshing, on the one hand, with a second pinion 14 integral in rotation with the drive roller Rm, and d on the other hand, with pinions 16 (two being referenced) fixed respectively to one end of the driven rollers Re to provide them with a rotational movement, in synchronism.

Some of these rollers, as is the case with the rollers of the drive device DE2 which is shown in detail in FIG. 4, are rotatably mounted in bearings 18 (two being referenced), for example ball bearings, fixedly engaged in the carcass 2a of the oven 2, and in particular in its side walls, not referenced.

The other rollers of the devices DE1 to DE4 which are not supported by the carcass 2a of the furnace 2, are mounted free to rotate in conventional support benches, not shown.

Referring now to Figures 1 and 2, will be described below in more detail the advantageous arrangement of the parts to be treated, inside the installation.

Indeed, the installation 1 is further characterized in that it is provided in its dimensions and in its operating mode for treating a set of trays or baskets 20 which are arranged to receive the parts to be treated 22 (only one being referenced) and to group them into individual charges C. The pieces 22 are represented in FIGS. 1, 2 and 3 very schematically by symbols of square shape, but it is understood that small pieces of any shape can be treated by the installation and the method according to the invention.

More particularly, according to this method, there are, in a first step, the parts to be treated 22 in individual charges C, in the trays or baskets 20, to constitute separate batches which form a volume V of parts whose height H is advantageously chosen much smaller than the other dimensions of the volume.

The other dimensions of the volume V are given here (FIGS. 1 and 3) by the size of the sides of this volume, quantities referenced L1 (width) and L2 (length) respectively. For information, we choose a height H at least twice smaller than the sizes L1 and L2. In an exemplary embodiment, the height H is equal to approximately 200 mm, while the width L1 and length L2 are each equal to approximately 400 mm to 800 mm.

This particular dimensioning of the volume of the charges allows all the pieces of a charge to be crossed, during the subsequent quenching by a flow of gas, a two-phase mixture or by a liquid whose characteristics do not vary or little for the different levels of parts within the load.

It is further noted that the outlet and the inlet of the furnace 2, that is to say the inlet and outlet openings 2d and 2e of the carcass 2, and, in this example, the outwardly opening openings of the channels C1 and C2 have a height h of the order of the height of the batches of parts, with the ready spaces necessary for the passage of the conveyor belts and for the introduction of the baskets into the openings.

Then, after having placed the parts to be treated in loads C, each load C is placed at the inlet E of the installation, on the end of the first drive device DE1.

After opening the door P1, the drive device DE1 is actuated to allow the load C thus dimensioned and placed to be introduced quickly into the furnace 2, up to the first region R1.

The load C therefore passes the gate P1, then it passes through the channel C1 and the inlet opening 2d of the carcass 2a at a first speed level V1 for example of the order of 250 to 400 cm / min . The door P1 is then closed to minimize contamination of the furnace atmosphere and limit the consumption of gas.

It will be specified here that the length of the strip b1 is not shown to scale in FIGS. 1 and 2 because it must allow the load C to take sufficient acceleration to reach the speed of introduction V1. This process has been illustrated with a constant acceleration of the charge, leading to a linear increase in its speed, but another form of acceleration can be chosen. In addition, this speed V1 may likewise not be constant. It can vary around the value V1, if the device DE1 undergoes between the input E and the region R1 accelerations or decelerations. This is why reference is made here to "levels" of speed. This remark generally applies to the appearance of the other characteristic speeds of the installation, referenced V2 and V3.

When the load C arrives in the first part of the region R1, its speed is reduced by slowing down the motor M1, so that the load C which is still on the first drive device DE1 reaches a speed level V2 lower than the level V1 . This second characteristic speed level is for example equal to about 50 to 100 cm / min.

Simultaneously, the second drive device DE2 is controlled so that it takes up speed V2 via an appropriate supply to the motor M2, under control of the central regulation unit UC. The load C will therefore be moved at speed V2 but now by the second drive device DE2 over the entire length of the strip b2.

When the load approaches the third drive device DE3, the latter is controlled, via its motor M3, so that it also takes the speed level V2, and that it can receive the load C.

The load C is therefore displaced throughout the region R2 of the furnace 2 at speed level V2, speed at which the load C of parts 22 undergoes the chosen treatment temperature.

When the load C arrives in the exit region R3, the third drive device DE3 is actuated, via an appropriate control of the motor M3, so that it strongly accelerates the strip b3 and the load C, and so that this load C take a speed level V3, at least higher than the level V2 and, in this example, also higher than level V1. The speed level V3 which is used for the rapid extraction of the charges is chosen in this example between approximately 500 and 800 cm / min.

Simultaneously, the door P2 from the oven outlet is opened and the door P3 from the quenching cell is opened.

In addition, the fourth drive device DE4 is brought via a control of its motor M4 to speed level V3, to ensure the rapid transfer of the load C between the oven 2 and the quenching cell 4, through the channel C2 and doors P2 and P3.

It will be understood that the control of the motors M1 to M4 at specific speeds enabling the speed levels V1 to V3 to be reached is controlled by the central control unit UC which in this installation constitutes means for regulating the speed of the control devices. drive DE1 to DE4, in order to reach the differentiated levels of speeds V1 to V3.

As can be seen in FIG. 1, the displacement of the charges C is regulated along the processing line LT, by appropriate control of the two drive devices DE3 and DE4 under control of the central control unit UC, from so that we create between the last charge (referenced Cd), located in the quenching cell and the upstream charge (referenced Ca) present in the furnace, in the outlet region R3, a distance L, capable of 'ensuring the stability of the temperature of the parts 22 and the stability of the thermochemical characteristics prevailing in the enclosure 2b of the furnace 2. This distance L is typically equal to two to four times the length L2 of a charge.

Thanks to this arrangement, it is possible to dip a batch of parts without influencing the processing of the batch or batches upstream.

Referring now to Figures 5 and 6, there will be described below an installation according to a second embodiment.

The installation shown in these figures differs from the installation previously described only in that the means of transport T no longer comprise four, but three drive devices DE1, DE2 and DE3 '. The first two drive devices DE1 and DE2 as well as the other components of this installation are identical to those described above.

The drive device DE3 'which is likewise controlled by the central unit UC via the motor M3' extends, like the two devices DE3 and DE4 of the first embodiment which it replaces, from the terminal part of the region R2 and it passes through region R3, the outlet opening of the furnace 2e, the outlet channel C2 and the transition zone Z to reach the quench cell 4. In the example shown, the drive device DE3 ' also passes through the quenching cell 4 and leads to the outlet S.

This second installation operates according to sequences S1, S2 and S3 which are identical or similar and at the same speed levels V1, V2 and V3.

However, after the batch of parts has passed the door P1 and it has been brought to speed V1 to the end of the first device DE1, the three drive devices DE1 to DE3 'are simultaneously driven at the same speed V2, for a time T, to allow the newly introduced load, located on the device DE1, to come to be placed completely on the device DE2 (as shown in broken lines) and to allow the last load which was positioned initially at the end of the second device DE2 also come to be placed completely on the device following DE3 '(as also shown in broken lines). This operation is carried out without any of the doors P1 and P2 having to be opened.

The displacement of the batches of loads C up to the end of the two devices DE1 and DE2 is obtained by piloting the control unit UC which orders acceleration, deceleration and possibly stopping of the motors M1 to M3 'accordingly.

Finally, when the load is on the third device DE3 ', the doors P2 and P3 are then opened and the device DE3' is brought to speed V3 so that the load is quickly transported to the quenching cell 4. The door P2 is immediately closed as soon as the load leaves the channel C2 and the door P3 is closed when the load C is entirely in the quenching cell 4.

It will be noted that in this embodiment of the invention, the second drive device DE2 has a length LD2 which is a multiple of the length L2 of the loads, apart from the gaps left between the loads.

Thus, as for the first embodiment, the installation operates according to three characteristic sequences with a rapid insertion speed V1, a slower processing speed V2 (V1> V2) and a very rapid quenching speed towards the quench cell. V3 which is at least greater than V2 (V3> V2) and which can also be greater than V1 (V3> V1> V2).

Although this is not described here, it should be pointed out that the installations according to the invention can also be provided with mechanical stops housed at least partly in the enclosure 2b of the oven 2 and which can be controlled from the outside, for example by the control unit UC, to position themselves at the end, for example, of the first two drive devices DE1 and DE2 or at the end of the three devices DE1 to DE3 'to ensure that the loads stop the end of these devices in defined positions on the processing line LT. Such a stop may be constituted for example by a pivotally mounted cleat or by a linear displacement finger actuated by jack and capable of projecting at the end of the strips b1, b2 and possibly b3 'or between two rollers.

It is understood that in this particular control mode, the batches of loads C are stopped at the end of the drive devices and that these batches have a zero speed (V = 0) at the end of each sequence S1, S2 and S3 (the speed variations with this type of control have been shown, compared to the continuous control mode, or broken lines). To avoid friction of the baskets on the strips or rollers, the movement of the drive devices associated with these movable stops is preferably stopped by an appropriate control of the control unit UC, when the stops act on the corresponding loads.

As can be seen in FIG. 7, the treatment in charge of small parts described in conjunction with the above sequences also applies to quenching in a liquid medium.

The installation shown in FIG. 7 comprises a quenching cell 4 ′ which comprises a tank 30 containing a liquid medium M such as water, a mixture of polymers, oil or molten salts. The tank 30 is partially positioned under a sealed transfer airlock 32 which is integral with the carcass 2a and which is immersed in the medium M.

The airlock 32 includes a door P5 which can be actuated by a jack 34.

Inside the tank 30 is housed an elevator 36 which includes a support 38 capable of receiving the load at the end of the third drive device DE3 '.

On this support 38 are placed rollers 40 linked together by a chain or any other drive means, not shown. The rollers 40 can come in the plane of the last drive device DE3 ′ and they are associated on a first side with a wheel or a drive roller 42 which is designed to come into contact with either another wheel or a roller or the free end of the strip to be driven in rotation by the drive device DE3 '. This wheel or roller 42 being linked by a chain or any other means to the rollers 40, it drives the rollers 40 in rotation when the support 32 is in the high position as shown in FIG. 7.

When a load C is placed on the support 38, the elevator 36 lowers this support 38 and the load C in the tank 30 to ensure quenching (arrow B in the figure). The elevator then moves laterally to the right (arrow L) then it raises the support 38, and the load C in the open air (arrow R) so that the load C can be taken up, either by a lifting device, either by an external drive device DE5 also formed by a group of rollers or a band b5. In the case where the load is taken up at its exit by a group of rollers or a band b5, a second wheel 44, opposite to the first wheel referenced 42, can be provided on the other side of the support 38 to engage with this strip and to ensure the drive of the rollers 40 of the support 38 in order to allow the release of the load on the strip b5 (to the right in the figure).

In this example, the elevator 36 therefore forms part of the means of transport T of the loads C in the installation, the processing line LT extending in several orthogonal directions.

Retractable mechanical stops, not shown, can be provided on each side of the support 38 to ensure the precise positioning of the load on this support.

These stops can be constituted for example by vertical plates which are, on the one hand, mounted on either side of the support 38 on compression springs keeping them in the high position and which are, on the other hand, associated with control members, such as a finger or an orthogonal plate, which can bear under the rollers or the strip of the driving devices DE3 ′ and DE5, during the movements of raising the elevator 36, in order to control the lowering the corresponding stop plate and allow the passage of the load.

These stops can, according to yet another embodiment, be constituted by the members which support the wheels 42 and 44 on either side of the support 38 if these members are rotatably mounted on this support and can be released by the action of an elastic element when the wheels 42 and 44 are not in contact with the drive devices DE3 'and DE5, as shown in broken lines in FIG. 7, to the right of the support 38.

It will be noted that in this application to quenching in a liquid medium, the constitution of the parts to be treated as fillers whose dimensions are such that the height H of this charge is chosen to be significantly lower than the other dimensions of the volume, allows, as for quenching at gas, not to force the flow to cross too great a height in order to obtain homogeneous quenching conditions for the parts located upstream and downstream compared to the direction of circulation of the liquid by avoiding a rise in temperature of the liquid quenching at the passage between these levels.

In addition, it will be noted that the constitution of batch loads offers an interesting alternative in the case of quenching in a liquid medium, which is traditionally carried out by the falling of parts in the quenching medium. Indeed, the parts falling in the quenching medium under the effect of gravitation collide and injure themselves all the more easily as they are brought beforehand to temperatures at which the parts no longer have mechanical resistance, nor sufficient hardness allowing them to accommodate shocks by elastic deformation.

In addition, the fact of constituting the parts in loads and of transporting the parts thus through the furnace makes it possible to recover these loads on an elevator to introduce them into the quenching medium, by a movement vertical descent orthogonal to linear movement in the oven, at the same speed determined for all parts.

The liquid quenching medium can be agitated in a conventional manner by imposing on the fluid a movement in a direction identical or opposite to that of the charge.

This advantageous characteristic makes it possible to limit the deformations of parts and it makes it possible to avoid any risk of injury to the parts during their introduction into the quenching medium.

It will be noted here that in the detailed description which is made of the method according to the invention, reference is made to a load but that according to an appropriate dimensioning of the means of transport T, of the furnace 2 and of the cell 4, it is could obviously have side by side several loads C (that is to say several baskets) which would simultaneously undergo the same displacements at the three characteristic speed levels V1, V2 and V3 and which would move in parallel concomitantly from the entrance E of installation 1, until its exit S.

It will therefore be understood from what has just been described that a process has been carried out in which, after having introduced each individual charge into the oven to bring the parts to be treated to the treatment temperature or temperatures, the charges C, on the one hand, inside the furnace 2, and on the other hand, inside the quenching cell 4, as well as between the furnace 2 and the cell 4 via the means transport T constituted by the displacement devices DE1 to DE4, by controlling the displacement of these loads C on the transport means T, along the processing line LT, so that the loads C move along this line , locally, at different speeds V1, V2 and V3.

In this parade heat treatment installation having a pass-through oven, provision has therefore been made drive devices DE1 to DE4 which can be controlled individually at characteristic speeds to divide the LT treatment line into sectors S1, S2 and S3 (Figure 1) locally ensuring, on this LT line, displacement at discontinuous speeds of the tanks or baskets forming the containers containing charges C, at different speed levels V1 to V3.

Furthermore, this installation includes regulation means formed by the control unit UC associated with the drive devices DE1 to DE4 to control them at speed levels such that the batches of parts enter and leave the oven at higher speeds. at speed level V2 at which the batches are moved in the oven, during processing.

Thus, the transfer times of the batches of parts are reduced, during the introduction into the furnace, but also during the extraction, for the introduction into the quenching cell.

Furthermore, the batch processing of small parts and the division of the means of transport into several drive devices along the processing line makes it possible to separate the operations of introducing batches into the oven and extracting the lots of the oven, so that only one of the doors P1 or P2 needs to be opened. This again limits the risk of disturbing the atmosphere of the oven. In this process and this installation, therefore, the operations of feeding the oven, advancing in the oven and leaving the oven have been dissociated, thereby locally accelerating the transfer of charges.

It will also be specified that in the installation and the method according to the invention, the control unit UC controls the drive devices and their motor so that the adjacent ends of these devices are driven at the same speed during the transfer. of each charge from one device to another so that the load baskets C pass from the previous device to next device without excessive sliding between their bottom and, for example, the two bands which support them during the overlapping of the bottom of these baskets and adjacent bands.

This control of drive devices at the same speed over a given period, that is to say at the same speed level or according to the same acceleration after a load stop ensures the transfer of loads from a device to a other without speed variation between the baskets which transport the loads and the bands or rollers which drive them.

It will be noted that although an installation and a method have been described in which each load moves along the processing line LT according to at least three types of characteristic movements, namely fast, slow and faster, the invention is not limited to these three regimes but could include a higher number of speed levels, in combination with a number of training devices greater than four.

In addition, the types of drive and their sequences at speed levels V1 to V3, although described with reference to the embodiment of FIG. 2, also apply to the drive of the groups of rollers shown in FIGS. 3 and 4.

Claims (12)

Method of heat treatment of parts, in particular of small dimensions, on a treatment line (LT) comprising at least one furnace (2) and a quenching cell (4), characterized in that it consists: - arranging the parts to be treated (22) in individual charges (C), in trays or baskets (20), to constitute separate batches forming a volume V of parts whose height H is chosen to be much lower than the other dimensions (L1 , L2) of the volume, - introducing the individual charges (C) into the oven (2) to bring said parts to the treatment temperature or temperatures, to transport the charges (C), on the one hand, inside the oven (2), and on the other hand, inside the quenching cell (4), as well as between the oven and the cell, by means of transport (T), and - controlling the movement of the loads (C) on the means of transport (T), along the processing line (LT) so that the loads (C) move along this line, locally, at speeds (V1, V2 and V3) different. Method according to claim 1, characterized in that it further comprises: - to regulate the movement of the charges (C), along the treatment line (LT), to create, between the last charge (Cd) located in the quenching cell (4) and the charge upstream (Ca) present in the oven (2), a distance L, capable of ensuring the stability of the temperature of the rooms and the stability of the thermochemical characteristics prevailing in the heating enclosure. Method according to claim 1 or 2, characterized in that it further comprises: - To move each load (C) along the processing line (LT), according to at least three types of characteristic movement having successive speed levels V1, V2 and V3. Method according to claim 3, characterized in that it consists: - To move the charge (s) (C) from outside the oven (2) to a first interior region thereof (R1), called input, according to a first speed level V1 to ensure the rapid introduction of the charges into the oven, - moving the charge (s) located in a second region of the furnace (R2), called the central one, disposed downstream of said first region (R1), according to a second speed level V2, lower than the level V1, this level V2 being chosen to ensure the application of the treatment to the charge (s) in the furnace, and - moving the charge (s) (C) from a third region of the furnace (R3) called the outlet, disposed downstream of the second region, up to the interior of the quenching cell, according to a third speed level V3 , higher than level V2, this level V3 being chosen to ensure the rapid transfer of the charge (s) (C) between the oven (2) and the quenching cell (4). Method according to any one of the preceding claims, characterized in that it also consists of: - to close at least the oven outlet (2) by a non-leaktight closing door (P2), and - isolating the atmosphere of the oven (2) from the atmosphere of the quenching cell (4) by creating, at the outlet of the oven (2), at least when said door (P2) is open, a protective screen formed by the combustion of process gas or other gas or by the establishment of an inert gas curtain. Method according to any one of the preceding claims, characterized in that it also consists of: - passing the charges (C), immediately before entering the oven (2), through a first unheated channel (C1) thermally insulated, communicating with the oven (2), and - Passing the charges (C) immediately at the outlet of the oven (2), through a second unheated channel (C2) thermally insulated, also communicating with the oven (2). Installation for heat treatment for implementing the method according to any one of Claims 1 to 6, comprising: - at least one treatment oven (2) capable of bringing the parts to be treated (22) to treatment temperatures, at least one quenching cell (4) disposed downstream from the furnace (2), this furnace and this cell forming a treatment line (LT), and - means of transport (T) allowing the movement of the parts (22) along the processing line (LT), installation characterized in that it is intended to treat a set of trays or baskets (20) arranged to receive the parts to be treated (22) and group them into individual loads to constitute separate batches forming a volume V of parts whose height H is clearly smaller than the other dimensions (L1, L2) of the volume, said means of transport (T) also being made up of several drive devices (DE1, DE2, DE3, DE3 'and DE4) which can be controlled individually, by regulation means (UC), at at least three characteristic speeds of input (V1), processing (V2) and output (V3) respectively to divide the processing line (LT) into sectors (S1, S2 and S3) ensuring locally, on this line, a movement of the trays or baskets at different speed levels (V1, V2 and V3). Installation according to claim 7, characterized in that the regulation means (UC) are provided for controlling the drive devices at the speed levels (V1, V2 and V3) which are chosen so that the pieces enter and leave the oven at speed levels higher than the speed level at which the batches are moved in the oven during processing. Installation according to claim 8, characterized in that it comprises at least four drive devices (DE1 to DE4). Installation according to claim 9, characterized in that it comprises at least: a first drive device (DE1) extending from the inlet (E) of the installation, upstream of an inlet door (P1) of the furnace (2) and beyond the door ( P1) to allow the passage of batches of parts (C) beyond this door (P1) to a speed level (V1), - a second drive device (DE2) arranged downstream of the first and extending at least inside the oven (2), this second device (DE2) allowing the treatment of batches of parts (C) at one level speed (V2), lower than the previous level (V1), - A third drive device (DE3) disposed downstream of the second and extending from the interior of the oven to the vicinity of a channel (C2) secured to the oven (2), this third group (DE3) allowing the passage of the speed of movement of the batches from the speed level (V2) to a speed level (V3), higher than the previous level (V2), and - a fourth drive device (DE4) disposed downstream of the third and extending from the interior of the channel (C2) at least to the interior of the quenching cell (4), this fourth device (DE4 ) allowing the batches to be removed from the oven and introduced fast in the quenching cell (4) at the speed level (V3). Installation according to claim 7 or 8, characterized in that it comprises at least three drive devices (DE1, DE2 and DE3 ') and in particular: a first drive device (DE1) extending from the inlet (E) of the installation, upstream of an inlet door (P1) of the furnace (2) and beyond the door ( P1) to allow the passage of batches of parts (C) beyond this door (P1) to a speed level (V1), - a second drive device (DE2) arranged downstream of the first and extending at least inside the oven (2), this second device (DE2) allowing the treatment of batches of parts (C) at one level speed (V2), lower than the previous level (V1), and - a third drive device (DE3 ') disposed downstream from the second and extending at least as far as the interior of the quenching cell (4), this third device allowing the batches to be removed from the oven and their introduction fast in the quenching cell (4) at a speed level (V3), higher than the previous level (V2). Installation according to any one of claims 7 to 11, characterized in that it comprises two unheated channels (C1 and C2) thermally isolated, disposed respectively between an oven entry door (P1) and the entry (2d ) proper of the latter, and between the outlet (2c) of the oven and an outlet door of this oven (P2).

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