EP0737755B1 - Method and apparatus for heat treating workpieces - Google Patents

Description

The present invention relates to a method of heat treatment of parts, in particular of small dimensions, according to the preamble of claim 1, thus than an installation for implementing this process.

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

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

Regarding the subsequent quenching, there are two large families qualified respectively as gas quenching and liquid quenching, due to the used to ensure rapid cooling of the parts.

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

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

However, it has been observed that when the treated parts are quenched in liquid medium, they are subjected to a significant thermal shock, and the phenomenon cooling occurs in a non-homogeneous way due in particular to the appearance of heat-sheaths due to boiling of the liquid. In addition, these sheaths appear on the surface of the hardened parts, which changes the coefficients of heat transfer between the parts and the medium, and what causes distortions or part distortions, especially if they are not very massive and if they have thinned shapes, as is generally the case with small dimensions.

It is therefore understood that quenching in a liquid medium is difficult to apply to heat treatment of small parts, generally having shapes complex, whose geometric stability, whether in shape or in size, must be assured if you want to avoid subsequent recovery operations, such as machining.

In addition, it should be noted that quenching in a liquid medium requires setting up work of washing parts after treatment, which increases considerably the cost of treatment per piece. Furthermore, the standards anti-pollution require 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 the exploitation of this type quenching.

Liquid quenching heat treatment facilities which have been for currently offered for the treatment of small parts, are installations known as parade, that is to say in which the displacement of the parts in the furnace of processing occurs in an essentially horizontal plane. In these facilities, quenching takes place by dropping the pieces into the quenching bath, at the outlet of the oven, under the effect of gravity.

We also know an alternative to quenching in a liquid medium, which is the gas quenching, applied specifically to medium or weak steels allies. This type of quenching is characterized by the use of gas pressures which can be higher than 15 bars. However, the use of high pressures does not can be justified only for the quenching of parts having a very high added value or for very massive parts, for example tools, and again because significant operating costs.

We therefore understand that there is no technological solution today economical and rational allowing the tempering of small parts, since all the solutions listed above have drawbacks having consequently an implementation, either incompatible, or too expensive.

We can indeed see that, for small parts, the application, by analogy, of the quenching conditions in liquid medium to the conditions gas quenching cannot be done without an appropriate adaptation of the installations and methods since, in particular in the case of parade treatment, it is inconceivable with a gas quenching cell to drop the parts in the cell, leaving the oven, since the quenching medium is not capable of braking the falling pieces.

These could therefore be injured or deformed, which would make this type of heat treatment not applicable.

In addition, if for the treatment of small parts, it is desired actually design a heat treatment process and installation at parade with a gas quenching cell, we encounter the following obstacles.

Indeed, the objective being to obtain a brutal quenching, for the application to all types of steel, conventional means of transport are no longer suitable since they are sources of significant heat losses between the exit of the oven and entry into the quench cell.

We could obviously increase the temperature inside oven correspondingly, but this would result in a far too large an increase in the grain size of the material, deterioration which, as we know, has the effect of seriously weakening the properties final mechanical aspects of the part (s) treated.

In addition, conventional parade processing facilities include one or more several watertight airlocks at the inlet and outlet of the oven, and at the inlet and outlet of the cell.

However, the operations of opening a sealed airlock at the outlet of the oven and opening a watertight airlock at the entrance to the quenching cell, during the transfer of parts, cause the oven enclosure to cool down and cause Consequently again a lowering of the temperature of the oven and the parts contained in it.

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

So while we are trying, on the one hand, to avoid the establishment of a too heavy mechanization in the construction of the airlocks, to ensure the transfer of parts from the oven to the cell without temperature loss in areas transition, we see that we must, on the other hand, avoid interaction at all costs between the two environments, respectively of the oven and the cell, on the one hand so as not to cause the oven to cool, and, on the other hand, to reduce the risk of explosion at 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 gas to absorb the heat contained in the parts to be treated, plays an important role in the quality of the 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 the facilities conventional heat treatment with gas quenching is not optimal in all conditions. Thus, for parts with high massiveness or for parts produced in steels which require cooling rates such as that gas quenching cannot give quenched parts final hardness desired, it may be desirable to use an installation whose hardening takes place in liquid media.

We were able to determine that to increase this heat capacity in the case from gas quenching, i.e. this heat exchange, three conditions had to be combined, i.e. the presence of a cold gas before the quenching operation, a flow of significant gas and a turbulent regime of gas flow in the cell.

However, if the parts are in the form of a bed, the gas heats up in crossing the bed of rooms, so that there are levels of parts subject to different quenching conditions, i.e. which are in contact with a gas whose temperature has increased. Furthermore, it can be seen that the turbulence in the parts bed cannot be maintained only on the first few levels.

Added to all this, in installations with gas quenching, another condition which is the stability of the controlled atmosphere inside the oven, in order to maintain a constant quality of thermochemical treatment, for all types of treatment whether for austenitization under nitrogen, austenitization under gas from synthesis, austenitization under equilibrium potential, carburizing, carbonitriding or for nitrocarburization. These process gases can be flammable.

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

Finally, it should be noted that the construction of a thermal 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 hot working mechanics, safety, and finally a manufacturing and maintenance with the lowest possible costs.

International application WO 94/09164, to which the preamble corresponds of claims 1 and 6, describes a method of heat treatment of small parts metallic in an installation successively comprising a zone of preheating, an oven equipped with burners, an airlock and a cold air quenching cell. The parts to be treated are deposited directly on a roller conveyor which is subdivided into three sections operating at respective respective speeds. A first section at predetermined speed depending on the thickness of the pieces transports these through a hot air preheating channel and a region oven inlet. A second section transports the pieces across the region warmer from the oven at a higher speed to prevent carburization or decarburization and then a third section transports them to a even higher speed to make them cross the exit airlock and the quenching. We can see that these gradual increases in transport speed have to space out parts on the roller train, but may require to lengthen the final parts of the installation, in particular the quenching cell. Through elsewhere such an installation does not allow treatment under an atmosphere including flammable gases.

In patent DE 31 50 576 C1, provision is made for passing small parts metal through a heat treatment furnace by placing these parts in containers which are arranged in a line on rollers, the line of containers being step by step each time the container at the end of an initial region of the oven has reached a predetermined temperature. So all the containers move forward together and there are no differences in speeds along the processing line. Furthermore, no quenching cell is provided in this treatment line. Besides, the means of transport described would be unable to transfer quickly oven parts to a quench cell.

Thus the present invention aims to provide an installation and a heat treatment process 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.

• on dispose les pièces en charges individuelles, dans des bacs ou paniers, pour constituer des lots distincts formant un volume de pièces dont la hauteur est choisie nettement inférieure aux autres dimensions dudit volume,
• on utilise un premier moyen de transport à vitesse variable pour introduire les charges individuelles dans la région d'entrée du four, le premier niveau de vitesse étant choisi pour assurer une introduction rapide des charges dans le four,
• on utilise un deuxième moyen de transport pour déplacer les charges dans la région centrale du four, le deuxième niveau de vitesse étant inférieur au premier,
• on utilise au moins un troisième moyen de transport à vitesse variable pour déplacer les charges de la région de sortie du four en direction de la cellule de trempe, et on pilote lesdits moyens de transport de sorte que, pour le passage d'une charge du premier moyen de transport au deuxième, on diminue la vitesse du premier jusqu'au niveau de vitesse du deuxième et, pour le passage d'une charge du deuxième moyen de transport au troisième, on diminue la vitesse du troisième jusqu'au niveau de vitesse du deuxième.

To this end, the invention relates to a method of heat treatment of parts, in particular of small dimensions, on a treatment line comprising at least one oven, a quenching cell and successive means of transport making it possible to move the parts to the inside the oven and the quenching cell, as well as between the oven and the quenching cell, so that the parts move along the processing line locally at different speeds which include a first speed level for introducing the parts in an inlet region of the furnace, where said parts are brought to the processing temperature or temperatures, a second speed level for moving the parts in a central region of the furnace and a third speed level for moving the parts d '' an outlet region from the oven to the quenching cell, the third speed level being higher than the second to ensure rapid transport of the charges between the oven and the quenching cell, characterized in that:

• the pieces are placed in individual charges, in tubs or baskets, to constitute separate batches forming a volume of pieces whose height is chosen to be significantly lower than the other dimensions of said volume,
• a first variable speed means of transport is used to introduce the individual charges into the inlet region of the oven, the first speed level being chosen to ensure rapid introduction of the charges into the oven,
• a second means of transport is used to move the loads in the central region of the oven, the second speed level being lower than the first,
• at least one third variable speed means of transport is used to move the charges from the exit region of the furnace towards the quenching cell, and said means of transport are piloted so that, for the passage of a charge from the first means of transport to the second, the speed of the first is reduced to the speed level of the second and, for the passage of a load from the second means of transport to the third, the speed of the third is reduced to the level of speed of the second.

In a preferred embodiment, the method includes processing thermochemical under controlled atmosphere in the furnace, in particular a austenitization, carburizing, carbonitriding or nitrocarburizing, oven inlet region being preceded by an unheated inlet channel, communicating with the oven and provided with a first door, and the region of exit from the oven being followed by an unheated outlet channel, communicating with the oven and provided a second door. To pass a load from the first means of transport to the second and the passage of a load from the second means of transport in the third, we pilot the three means of transport at the second speed level without any of said doors being opened. In addition, the operations for introducing charges into the oven and extracting charges from the oven so that only one of said doors is open.

• au moins un four de traitement capable de porter les pièces à traiter à des températures de traitement,
• au moins une cellule de trempe disposée en aval du four, ce four et cette cellule formant une ligne de traitement, et
• des moyens de transport permettant de déplacement lesdites pièces le long de la ligne de traitement localement à des vitesses différentes,

   l'installation étant caractérisée en ce qu'elle est prévue pour traiter un ensemble de bacs ou paniers agencés pour recevoir les pièces à traiter et les regrouper en charges individuelles pour constituer des lots distincts formant un volume V de pièces dont la hauteur H est nettement inférieure aux autres dimensions du volume,

en ce que lesdits moyens de transport comprennent au moins trois dispositifs d'entraínement successifs qui sont être pilotés individuellement, par des moyens de régulation, à au moins trois vitesses respectives d'entrée, de traitement et de sortie pour diviser la ligne de traitement en secteurs assurant localement, sur cette ligne, un déplacement des bacs ou paniers à des niveaux de vitesses différents, le premier dispositif d'entraínement s'étendant jusqu'à une région d'entrée du four, le deuxième dispositif d'entraínement s'étendant dans une région centrale du four et le troisième dispositif d'entraínement s'étendant à partir d'une région de sortie du four en direction de la cellule de trempe,

et en ce que les premier et troisième dispositifs d'entraínement sont à vitesses variables, leur permettant de fonctionner tantôt au même niveau de vitesse que le deuxième dispositif d'entraínement, tantôt à des niveaux de vitesse respectifs plus élevés.

The invention also relates to a thermal treatment installation for implementing this process comprising:

• at least one treatment oven capable of bringing the parts to be treated to treatment temperatures,
• at least one quenching cell placed downstream of the oven, this oven and this cell forming a treatment line, and
• transport means making it possible to move said pieces along the treatment line locally at different speeds,

the installation being characterized in that it is provided for treating a set of tanks or baskets arranged to receive the parts to be treated and grouping them into individual charges to constitute separate batches forming a volume V of parts whose height H is clearly smaller than the other dimensions of the volume,

in that said means of transport comprise at least three successive drive devices which are to be controlled individually, by regulating means, at at least three respective speeds of entry, treatment and exit to divide the line of treatment into sectors ensuring locally, on this line, a movement of the trays or baskets at different speed levels, the first drive device extending to an inlet region of the oven, the second drive device extending in a central region of the oven and the third drive device extending from an exit region of the oven towards the quenching cell,

and in that the first and third drive devices are at variable speeds, allowing them to operate sometimes at the same speed level as the second drive device, sometimes at respective higher 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'entraínement à bandes de cette installation,
• la figure 3 est une vue similaire à la figure 2 mais représentant des dispositifs d'entraínement 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'entraínement,
• 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 drive devices formed from 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 Figures 1 and 2, we will describe below a thermal treatment installation according to the invention, in accordance with a first mode of production.

This heat treatment facility, which is identified by the general reference 1 includes, in this exemplary embodiment, a furnace 2 in the longitudinal axis which has a gas quenching cell 4. Good understood, the invention is not limited to an installation having only one oven and only one cell, but it also applies to installations with several ovens and multiple cells, with combinations chosen 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 is done by essentially linear and more particularly in the same horizontal geometric plane, by by means of means of transport T, with belts or rollers.

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

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

The processing temperatures used are common, and are chosen from the conventional ranges of temperatures used in treatment processes thermal of metal parts.

Oven 2 is open at both ends by openings 2d and 2e, formed in the carcass 2a and respectively forming an entrance opening and a oven outlet opening 2. These openings have a width referenced LO (Figure 2).

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

The first region, referenced R1, forms the entrance to the oven 2. It is arranged upstream with respect to the two others, the "upstream" and "downstream" directions being defined in reference to the direction of movement D of the parts in the installation.

The second region, referenced R2, which is contiguous to the first region R1, and which is arranged downstream of this constitutes, in the enclosure 2b of the furnace 2, the longer region. It is indeed this which is intended to heat the rooms to treat up to the selected treatment temperature.

Finally, the third characteristic region, referenced R3, which is contiguous to the second region R2, and which is likewise arranged downstream thereof, is called exit region since it is from this third region as parts being processed will be moved out of the oven, until the gas quenching cell 4.

The installation 1 also has an input E and an output S allowing the introduction and resumption of rooms. Input E and output S are materialized on Figure 1 by the two through ends of the means of transport T.

Note also that installation 1 has a first channel or tunnel called input C1, extending from input E of the installation to the opening 2d of the oven 2.

Installation 1 has a second channel or tunnel said outlet C2, extending from the outlet opening 2e from 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 fixed from tightly sealed to the carcass 2a of the oven 2, are thermally insulated and unheated. They communicate respectively with the regions R1 and R3 of the enclosure 2b from the oven 2.

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

The C1 channel is provided with a door not watertight P1, while the channel C2 is provided at its outlet of a non-watertight door P2 of the same type.

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

Installation 1 at the exit door P2 also includes means for isolating the atmosphere prevailing in the oven 2, vis-à-vis of the atmosphere of the quenching cell 4, these means being made by creating a protective screen, here not shown, obtained, according to a first variant, by combustion of process gas or another of gas. For this purpose, it is provided at the door of P2 outlet of oven 2 a Ve pilot light allowing ignite the process gas in a controlled manner in this region.

This protective screen can also be obtained, according to a second variant, by establishing a 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, because this door is not waterproof, it leaves a space open by where the process gas can be ignited, on contact with air, through pilot, if gas is flammable. If he is not flammable, the overpressure of oven 2 allows create the gas curtain.

When door P2 is opened, the screen protection ensures the seal between the oven 2 and the air ambient and avoids the destabilization of the atmosphere of the oven 2. This prevents the gas from oven 2 from being driven in the quenching cell 4.

Note also that the arrangement of channels C1 and C2, and the mounting of non-watertight doors P1 and P2 to the free end of these channels keep the source away potential for disturbance of the furnace 2 atmosphere and thereby contributes to improving the stability of prevailing thermochemical processing characteristics inside the oven 2.

It will also be noted that the establishment of this arrangement is facilitated by the fact that the parts are processed as charges, in batches more tall smaller than the width, as will be explained below in detail.

Likewise, the quenching cell 4 is provided at its entry and exit from two watertight doors or not waterproof P3 and P4.

This quenching cell 4 includes a device turbulence generator, not shown, formed by a wind box or propeller. Gas speed and flow are also provided by fans, similarly not represented.

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

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

The first DE1 training device that extends from the entrance E of the installation, up to the first region R1 of oven 2, through channel C1 and the 2d inlet opening of the oven, is intended to receive the parts to be treated after they have been installed by a conventional supply device, not shown here. This first drive device DE1 is also intended for ensure rapid introduction of batches of parts to be treated beyond gate P1 and, as in the example shown, even in oven 2, and more particularly up to the first region R1.

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

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

Finally, the fourth device DE4 extends, from a part, from channel C2 to exit S of the installation, and on the other hand, through the area of transition Z and the quenching cell 4 which it crosses from side to side.

As seen in Figure 2, each device DE1 to DE4 drive includes for example a band of flexible transport, 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 quench cell 4 form, extending on the same longitudinal axis, a processing line linear LT. The installation 1 according to the invention can therefore be qualified as a parade installation, oven 2 being a passage oven.

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

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

Motors M1 to M4 are electric motors of classic construction and therefore will not described here in more detail. We will mention simply that the drive between each engine and one rollers of the four drive devices DE1 to DE4 is done by mechanical means, such as by example a chain 6 (only one being referenced) engaged on two toothed pinions integral in rotation motor and motor roller respectively correspondent ensuring the training of the band.

The four motors M1 to M4 are all connected, by example, electrically to a control unit electric UC, constituted, in this example, by a programmable robot. So these motors can be independently controlled at rotational speeds different to allow the actuation of the four training devices DE1 to DE4 at levels of different speeds, according to operating sequences chosen.

Referring now to Figures 3 and 4, we will describe below a heat treatment installation with drive devices only rollers.

This installation is no different from the installation represented in figure 2 only by the absence of bands flexible training, the four devices DE1 to DE4 being here constituted by groups of drive rollers, rollers of which the structure is of the type of that of the rollers equipping the drive devices of Figure 2.

In each group of drive rollers, one motor roller Rm (figure 4) is mechanically connected, as in the previous embodiment, at one of motors M1 or M4, via two pinions 8 and 10, respectively secured to the motor and the rollers motor, and via a chain 6 meshing on these two gables. In each group of rollers, the motor 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 motor roller Rm, and other part, with pinions 16 (two being referenced) fixed respectively at 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 rollers of the DE2 drive which is shown in detail in Figure 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 do not are not supported by the carcass 2a of the oven 2, are free mounted in rotation in support benches conventional, not shown.

Referring now to Figures 1 and 2, we will describe in more detail below the provision advantageous parts to be treated, inside the installation.

Indeed, the installation 1 is further characterized by what it is planned in its dimensions and in its mode operating to process a set of bins or baskets 20 which are arranged to receive the parts to process 22 (only one being referenced) and for the group into individual charges C. Parts 22 are shown in Figures 1, 2 and 3 very schematic by square symbols but it's of course only small parts of any form can be processed by the installation and the method according to the invention.

More particularly, according to this method, we have, in a first step, the parts to be treated 22 in individual loads C, in trays or baskets 20, for constitute separate lots which form a volume V of pieces whose height H is advantageously chosen significantly lower than the other dimensions of the volume.

The other dimensions of volume V are given here (Figures 1 and 3) by the size of the sides of this volume, quantities referenced L1 (width) and L2 respectively (length). As an indication, we choose a height H at minus twice as small as the quantities L1 and L2. In an exemplary embodiment, the height H is equal to about 200 mm, while the width L1 and length L2 are equal to about 400 mm to 800 mm each.

This particular dimensioning of the load volume allows all the parts of a load to be crossed, during subsequent quenching by a gas flow, 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 arranged the parts to be treated in loads C, each load C is placed at the input E of installation, on the end of the first device DE1 drive.

After opening door P1, the device DE1 drive is operated to allow charging C thus dimensioned and set up to be introduced quickly in oven 2, to the first region R1.

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

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

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

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

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

Charge C is therefore displaced throughout the region R2 of oven 2 at speed level V2, speed at which the parts load C 22 undergoes processing temperature chosen.

When charge C arrives in the exit region R3, we activate the third drive device DE3, via an appropriate command of the M3 motor, so that it strongly accelerates the band b3 and the load C, and so that this load C takes a speed level V3, at least higher than level V2 and, in this example, also higher than level V1. The speed level V3 which is used to rapid charge extraction is chosen in this example between about 500 and 800 cm / min.

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

In addition, we bring the fourth device DE4 drive via a command of its M4 engine at speed level V3, to ensure rapid transfer of the load C between the furnace 2 and the quenching cell 4, at through channel C2 and doors P2 and P3.

It is understood that the control of the motors M1 to M4 aux specific diets to achieve the levels of speeds V1 to V3 is controlled by the central unit of UC command which in this installation constitutes means for regulating the speed of the devices DE1 to DE4, in order to reach the levels differentiated speeds V1 to V3.

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

Thanks to this arrangement, a batch of parts without influencing the treatment of the batch or batches upstream.

Referring now to Figures 5 and 6, we will describe below an installation according to a second mode of achievement.

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

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

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

However, after the part lot has passed the door P1 and that it was brought to speed V1 up to the end of the first DE1 device, we train simultaneously the three drive devices DE1 to DE3 'at the same speed V2, for a time T, for allow the newly introduced charge, located on the DE1 device, to place itself completely on the DE2 device (as shown in broken lines) and to allow the last load that was positioned initially at the end of the second DE2 device of also come to place itself completely on the device along DE3 '(as also shown in lines interrupted). This operation is carried out without any doors P1 and P2 should not be opened.

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

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

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

So as for the first embodiment, the installation operates in three sequences features with fast insertion speed V1, a slower processing speed V2 (V1> V2) and a output speed to the very fast quench cell V3 which is at least greater than V2 (V3> V2) and which can be also greater than V1 (V3> V1> V2).

Although this is not described here, we will specify that the installations according to the invention can also be provided with mechanical stops housed at least in part 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 itself 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 'for stop the loads at the end of these devices by positions defined on the LT processing line. A such stop can be constituted for example by a cleat mounted swivel or by a linear displacement finger actuated by cylinder and capable of projecting the end of the bands b1, b2 and possibly b3 'or between two rollers.

We understand 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 speed null (V = 0) at the end of each sequence S1, S2 and S3 (speed variations with this type of control have have been represented, compared to the command mode in continuous, or broken lines). To avoid friction baskets on the strips or rolls, the movement of drive devices associated with these movable stops is preferably stopped by an appropriate command of the control unit UC, when the stops act on the corresponding charges.

As seen in Figure 7, processing in load of small parts described in conjunction with the above sequences also applies to quenching in liquid medium.

The installation shown in Figure 7 includes 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. Bac 30 is partially positioned under a sealed transfer lock 32 which is integral with the carcass 2a and which is immersed in the middle M.

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

Inside the bin 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 between them by a chain or any other means drive, not shown. 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 intended to come to the contact, either from another wheel, or from 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 the rollers 40, it ensures the rotational drive of rollers 40 when the support 32 is in position high as shown in Figure 7.

When a load C is placed on the support 38, the elevator 36 descends this support 38 and the load C in the tank 30 for tempering (arrow B in the figure). The elevator then moves laterally to the right (arrow L) then it goes up the support 38, and the load C to the open air (arrow R) so that the load C can be recovery, either by a lifting device or by a DES external training device also formed 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 the first wheel referenced 42, can be provided with the other side of the holder 38 to engage with this strip and to ensure the drive of the rollers 40 of the support 38 to allow the release of the load on strip b5 (to the right in the figure).

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

Retractable mechanical stops, not shown, can be provided on each side of the support 38 for 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 from on either side of the support 38 on springs of compression keeping them in the up position and which are, on the other hand, associated with control members, such than a finger or an orthogonal plate, which can take support under rollers or device strip DE3 'and DE5, during climb movements of elevator 36, in order to control the lowering of the corresponding stop plate and allow passage of load.

These stops can, according to yet another mode of achievement, be constituted by the organs 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 element elastic when the wheels 42 and 44 are not at contact of DE3 'and DES drive devices, such as shown in broken lines in Figure 7, at right of support 38.

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

In addition, it should be noted that the creation of charges in lots offers an interesting alternative in the case of soaking in a liquid medium, which takes place traditionally by falling pieces in the middle quenching. Indeed, the pieces falling in the middle quenching under the effect of gravitation collide and get injured the more easily they are previously brought to temperatures at which parts no longer have mechanical strength or hardness sufficient to allow them to accommodate shocks by elastic deformation.

In addition, the fact of constituting the parts as charges and transport the parts well through the oven allows these charges to be recovered on an elevator for introduce into the quenching medium, by a movement vertical descent orthogonal to linear displacement in the oven, at the same speed determined for all rooms.

Liquid quench medium can be agitated conventional by imposing on the fluid a movement according to an identical or opposite direction to that of the load.

This advantageous characteristic makes it possible to limit the deformations of parts and it makes it possible to avoid any risk of injury to parts when inserted in the quench medium.

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

We therefore understand from what has just been described that we carried out a process in which, after having introduces each individual charge into the oven to bring the workpieces to the temperature (s) of treatment, we transport the charge (s) 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 2 and the cell 4 via the means of transport T constituted by the displacement devices DE1 to DE4, by controlling the displacement of these loads C on the means of transport T, along the processing line LT, of so the charges C move along this line, locally, at different speeds V1, V2 and V3.

In this heat treatment installation at parade with a passing oven, so we planned drive devices DE1 to DE4 which can be individually piloted at characteristic speeds to divide the LT processing line into sectors S1, S2 and S3 (FIG. 1) providing locally, on this line LT, displacement at discontinuous speeds of the tanks or baskets forming the containers containing charges C, at levels of different speeds V1 to V3.

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

Thus, the transfer times of batches of pieces, when introduced into the oven, but also during extraction, for introduction into the quenching cell.

In addition, batch processing of small parts and the division of means of transport into several drive devices along the line of processing, allows to separate operations introduction of the batches into the oven and extraction of lots of the oven, so that only one of the doors P1 or P2 has need to be open. We limit again the risks of disturbing the atmosphere of the oven. So we have in this process and this installation dissociated the operations oven feed, oven feed and outlet from the oven, thereby locally accelerating transfers of charges.

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

This steering of training devices to the same pace over a given period, i.e. at the same speed level or according to the same acceleration after a load stop ensures load transfer from one device to another without speed variation between baskets that carry loads and bands or rollers that drive them.

It should be noted that although we have described a installation and process in which each load is moves along the LT processing line according to at minus three types of characteristic displacements, know 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 training and their sequences at speed levels V1 to V3, although described in reference to the embodiment of FIG. 2, also apply to the training of groups of rollers shown in Figures 3 and 4.

Claims (9)

1. Method for thermal treatment of pieces, particularly of small dimensions, on a treatment line (LT) including at least one furnace (2), a quenching cell (4) and successive transport means (T) enabling to displace the pieces within the furnace and the quenching cell, as well as between the furnace and the quenching cell, such that the pieces are displaced along the treatment line locally at different speeds comprising a first speed level (V1) for introducing the pieces into an input region (R1) of the furnace, where said pieces are brought to the treatment temperature or temperatures, a second speed level (V2) for displacing the pieces in a central region (R2) of the furnace and a third speed level (V3) for displacing the pieces from an output region (R3) of the furnace to the quenching cell, the third speed level (V3) being greater than the second one (V2) for assuring a rapid transport of the charges between the furnace and the quenching cell, characterized by the steps of:

   arranging the pieces (22) in individual charges (C), in trays or baskets (20), to constitute distinct batches forming a volume (V) of pieces whose height (H) is chosen to be substantially less than the other dimensions (L1, L2) of said volume,

   using a first variable speed transport means (DE1) for introducing the individual charges (C) into the input region of the furnace, the first speed level (V1) being selected for assuring a rapid introduction of the charges into the furnace,

   using a second transport means (DE2) for displacing the charges (C) in the central region of the furnace, the second speed level (V2) being less than the first one (V1),

   using at least a third variable speed transport means (DE3) for displacing the charges (C) from the output region of the furnace towards the quenching cell, and regulating said transport means (T) such that, for passing a charge from the first transport means (DE1) to the second one (DE2), the speed of the former is decreased to the speed level (V2) of the latter (DE2) and, for passing a charge from the second transport means (DE2) to the third one (DE3), the speed of the latter is decreased to the speed level (V2) of the former (DE2).
2. Method according to claim 1, characterized by the step of regulating the displacement of the charges (C) along the treatment line so as to create, between a charge (Cd) located in the quenching cell (4) and a following charge (Ca) located upstream in the furnace (2), a distance L able to ensure the stability of the temperature of the pieces and the stability of the thermochemical characteristics present in the heating chamber.
3. Method according to claim 1 or 2, including a thermochemical treatment in a controlled atmosphere within the furnace, particularly austenitisation, case-hardening, carbonitruration or nitrocarburation, the input region of the furnace being preceded by a non heated input channel (C1), which communicates with the furnace and has a first gate (P1), and the output region of the furnace being followed by a non heated output channel (C2), which communicates with the furnace and has a second gate (P2),
      characterized in that, for passing a charge from the first transport means to the second one and for passing a charge from the second transport means to the third one, the three transport means (DE1, DE2, DE3) are regulated at the second speed level (V2) without any of said gates (P1, P2) being open.
4. Method according to claim 3, characterized in that the operations of introducing the charges into the furnace and outputting the charges from the furnace are made such that only one of said gates (P1, P2) is opened.
5. Method according to claim 3, characterized by the step of insulating the atmosphere of the furnace (2) from the atmosphere of the quenching cell (4) by creating at the output of the furnace, at least when the second gate (P2) is open, a protection screen formed by the combustion of a treatment gas contained in the furnace or another gas or by the establishment of an inert gas curtain.
6. Thermal treatment installation for the implementation of the method according to any one of the preceding claims, including :

   at least one treatment furnace (2) able to bring the pieces to be treated (22) to treatment temperatures,

   at least one quenching cell (4) located downstream from the furnace (2), said furnace and said cell forming a treatment line (LT), and

   transport means (T) enabling to displace said pieces (22) along the treatment line (LT) locally at different speeds,

      said installation being characterized in that it is arranged for treatment of a plurality of trays or baskets (20) adapted to receive the pieces to be treated (22) into groups in individual charges to constitute distinct batches forming a volume V of pieces whose height H is substantially less than the other dimensions (L1, L2) of the volume,

   in that said transport means (T) include at least three successive driving devices (DE1, DE2, DE3, DE3', DE4) which are individually regulated, by regulation means (UC), at at least three respective speeds, respectively an input speed, a treatment speed and an output speed, to divide the treatment line (LT) into sectors (S1, S2 and S3) ensuring locally, on said line, a displacement of the trays or baskets at different speeds levels (V1, V2 and V3), the first driving device (DE1) extending to an input region (R1) of the furnace, the second driving device (DE2) extending in a central region (R2) of the furnace and the third driving device (DE3, DE3') extending from an output region (R3) of the furnace towards the quenching cell,

   and in that the first and third driving devices (DE1 and DE3) are of variable speed types, enabling them to operate sometimes at the same speed level (V2) as the second driving device (DE2) and sometimes at higher respective speed levels (V1, V3).
7. Installation according to claim 6, characterized in that the input region (R1) of the furnace is preceded by a non heated input channel (C1), which communicates with the furnace and is equipped with an input gate (P1) of the furnace, and in that the output region (R3) of the furnace is followed by a non heated output channel (C2), which communicates with the furnace and is equipped with an output gate (P2) of the furnace, said gates being controlled by the regulation means (UC).
8. Installation according to claim 7, characterized in that the third driving device (DE3) extends to near the output channel (C2) and in that a fourth driving device (DE4) is disposed downstream from the third one and extends from the interior of the output channel (C2) at least to the interior of the quenching cell (4).
9. Installation according to claim 6 or 7, characterized in that the third driving device (DE3') extends to at least the interior of the quenching cell (4).

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