EP2167693B1 - Method for the heat treatment of castings using an air quench and system for implementing the method - Google Patents

Description

The field of the invention is that of heat treatments of castings made of aluminum-based alloy.

The invention relates to a method of heat treatment of breech type casting parts in which an air quenching of the parts is carried out, and a system for carrying out the method.

The heat treatment of aluminum alloys generally consists of a succession of operations.

First of all, a high-temperature dissolution operation is carried out, typically between 490 ° C. and 545 ° C. for silicon-containing foundry alloys (between 5 and 9%) and copper (between 0 and 3%). and magnesium (between 0 and 0.7%).

This operation is performed at the highest possible temperature to accelerate the dissolution of the hardening elements of the alloy, and dissolve as much as possible, while avoiding to remelt even locally the alloy (phenomenon called burn) . By this operation, a solid solution of hardening elements is obtained in the matrix of the alloy.

A quenching operation is then carried out to freeze the solid solution of the hardening elements in the matrix, by cooling rapidly from the solution temperature to room temperature or to the tempering temperature.

Finally, a revenue operation is carried out in the form of an oven residence at a moderate temperature, typically between 150 and 245 ° C., which causes the hardening elements of the alloy to recombine in the form of fine precipitates distributed within the matrix of the alloy, and thereby increases its resistance.

In this sequence of operations, the quenching operation is tricky.

Indeed, in order to keep the hardening potential as high as possible, those skilled in the art tend to perform this quenching in an effective cooling medium, water in general, which proves satisfactory from the point of view of mechanical characteristics.

However, the quenching with water introduced, especially for parts of complex geometry, significant residual stresses due to the fact that during quenching the various elements of the room can not cool at the same speed. This phenomenon is further accentuated by the appearance of bubbles in bubbles and film on the surface of the part during quenching with water, which disturbs the heat exchanges.

These residual stresses can locally reach the value of the cold elastic limit of the alloy, and can be very detrimental to the service life of the part, especially in fatigue stress, if their sign is that they are added to the external stresses applied to the piece.

The increase in the temperature of the quenching water is a technique well known to those skilled in the art for reducing the residual stresses of complex parts. This technique, however, has limited effects from the point of view of the reduction of residual stresses, while causing a significant reduction of properties. This reduction is all the more important as the temperature of the water increases and approaches the boiling temperature of the water.

The use of quenching additives (brine, for example) is also a well-known technique for the reduction of residual stresses. However, it poses problems of discharges and treatment of quench water, which generates additional costs.

An alternative quenching technique is to use ambient air rather than water as a cooling medium. Although air quenching is relatively easy to apply to single-unit or low-mass loads, it does not give satisfactory results in the case treatment of loads of large and massive parts, for example yokes for internal combustion engines, which because of their compactness and complexity of shapes (in particular the presence of multiple internal cavities) do not offer a favorable surface for extraction calories by the airflow.

This insufficiency of air quenching is further accentuated in the case of heat treatment of parts in the usual "batch" mode of treating a batch of aluminum alloy casting parts. In this "batch" mode, the parts of the batch of parts to be processed are put into baskets. Several baskets, generally made of steel, are stacked in a first layer on a base support, then in a second layer of baskets placed on the first, or possibly even other layers of baskets. The assembly consisting of the base support, successive layers of baskets and parts contained in the baskets forms what is called the heat treatment load, or more simply the load.

A vertical and horizontal space between the baskets is generally arranged so as to promote heat exchange during quenching.

The charge is successively introduced into the solution furnace, extracted from this furnace to be subjected to quenching (for example immersed in water in the case of quenching with water, or brought under a ventilation system in the case of quenching with air), then out of the quenching medium and introduced into the tempering furnace, finally extracted from the latter to be returned to the ambient air of the workshop at the end of the heat treatment.

This batch mode is particularly flexible, and is therefore interesting for the operator. In particular, each load can undergo treatment solution dissolution or income different from that of other loads. The quenching media can also be split, which adds to the flexibility (for example by using two quench tanks with water at different temperatures).

This mode is also interesting from an energy point of view. The charges being placed in furnaces whose door is closed after charging, the thermal leakage is minimal and the entire treatment is carried out in a closed space and well isolated vis-à-vis the outside.

In this respect, the document EP 1,531,185 a solution furnace and an air quenching unit. This document teaches that the foundry pieces are arranged in several layers of pieces superimposed on each other, both in the solution furnace and in the quench unit.

However, in the usual design of heat treatments in batch mode, a significant part of the energy is used to heat the steel baskets in the furnaces, then to cool the quenching water for the heat input portion related to these baskets, which is irrelevant for the main function of the heat treatment of aluminum parts.

The invention aims to overcome these disadvantages of the batch mode heat treatment of castings, including castings of aluminum alloys, and to ensure high and homogeneous properties regardless of the part in the load.

For this purpose, and according to a first aspect, the invention relates to a method of heat treatment of a lot of castings, comprising a solution-making operation carried out in a furnace charged with the parts of the batch arranged in several layers of superimposed parts to each other, characterized in that, following the extraction of the parts of the furnace dissolution, the parts are maneuvered to form a single layer of parts consisting of the parts of the batch, it brings the single layer in an air quenching unit having a ventilation system and air quenching is applied to the batch pieces arranged in the single layer.

• le système de ventilation délivre un flux d'air de débit supérieur à 1000 m³/h et par pièce, de préférence supérieur à 1700 m³/h et par pièce ;
• lors de l'opération de mise en solution, les pièces sont disposées dans des paniers superposés les uns aux autres, et la manoeuvre des pièces consiste à désempiler les paniers ;
• les pièces sont posées horizontalement dans les paniers et espacées de moins de 100mm, de préférence de moins de 50 mm ;
• les paniers sont séparés par des cloisons et les pièces sont posées verticalement dans les paniers ;
• les cloisons forment un ensemble d'alvéoles, les pièces sont disposées à raison d'une pièce par alvéole de telle sorte que l'espace entre la pièce et l'alvéole soit inférieur à 60 mm, et de préférence inférieur à 30 mm ;
• les pièces sont suspendues ou maintenues par des supports dans les paniers ;
• la manoeuvre des couches de pièces consiste à déposer successivement chaque couche de pièces sur un chariot de réception adapté pour recevoir une couche unique de pièces ;
• le temps de transfert entre l'ouverture du four à l'issue de la mise en solution, et la mise en route du refroidissement à l'air est inférieur à 6 minutes, de préférence inférieur à 3 minutes 30 secondes ; et
• suite à la trempe, on manoeuvre les pièces pour les redisposer sur plusieurs couches, et on réalise une opération de revenu des pièces réalisée dans un four chargé avec les pièces du lot disposées sur plusieurs couches.

Some preferred, but not limiting, aspects of this method are as follows:

• the ventilation system delivers a flow of air with a flow rate greater than 1000 m ³ / h and per room, preferably greater than 1700 m ³ / h and per room;
• during the dissolution operation, the parts are arranged in baskets superimposed on each other, and the parts operation consists of unstacking the baskets;
• the pieces are laid horizontally in the baskets and spaced less than 100mm, preferably less than 50 mm;
• the baskets are separated by partitions and the pieces are placed vertically in the baskets;
• the partitions form a set of cells, the parts are arranged at a rate of one piece per cell so that the space between the part and the cell is less than 60 mm, and preferably less than 30 mm;
• the parts are suspended or held by supports in the baskets;
• the maneuver of the layers of parts consists of successively depositing each layer of parts on a receiving carriage adapted to receive a single layer of parts;
• the transfer time between the opening of the oven after the dissolution, and the start of the air cooling is less than 6 minutes, preferably less than 3 minutes 30 seconds; and
• following quenching, the parts are maneuvered to rearrange them in several layers, and a coin-making operation is performed in a furnace loaded with the pieces of the batch arranged in several layers.

According to a second aspect, the invention relates to a heat treatment system of a batch of castings comprising a solution furnace such that the batch parts are arranged in several layers of parts superimposed on each other when the furnace is charged, an air quenching unit having a ventilation system for causing a flow of cooling air, characterized in that it comprises means for extracting the parts of the solution furnace and for the disposing in a single layer of pieces, and means for bringing the single layer of pieces in the air quenching unit so as to apply air quench to the batch pieces arranged in a single layer.

• le système de ventilation est configuré pour délivrer un flux d'air de débit supérieur à 1000 m3/h et par pièce, de préférence supérieur à 1700 m3/h et par pièce.

Advantageously, but optionally, the heat treatment system of a batch of castings according to the invention further comprises the following characteristic:

• the ventilation system is configured to deliver a flow of air of flow greater than 1000 m3 / h and per room, preferably greater than 1700 m3 / h and per room.

• les figures 1a-1c représentent la charge constituée du support de base, de couches successives de paniers, et de pièces de fonderie contenues dans les paniers, selon un premier mode de réalisation possible de l'invention ;
• les figures 2a-2g représentent la séquence d'opérations d'un premier mode de réalisation possible du procédé selon l'invention ;
• les figures 3 et 4 représentent des moyens utilisés dans un premier mode de réalisation possible de l'invention pour désempiler les paniers dans lesquels les pièces sont disposées ;
• la figure 5 est un schéma d'une unité de trempe utilisée dans le cadre de l'invention pour réaliser la trempe à l'air des pièces de fonderie ;
• les figures 6a-6b sont des schémas représentant des distributeurs d'air pouvant être utilisés dans l'unité de trempe ;
• les figures 7 et 8 représentent une vue en perspective et une vue en coupe d'un support de charge multicouches utilisé dans le cadre d'un second mode de réalisation possible de l'invention ;
• les figures 9 et 10 illustrent un support de manutention sous la forme d'un râteau multi-peignes utilisé dans le cadre du seconde mode de réalisation possible de l'invention ;
• les figures 11a-11e son des schémas d'une séquence d'opérations illustrant la manoeuvre de la charge dans le cadre du seconde mode de réalisation possible de l'invention ;
• la figure 12 représente le principe d'un mode de réalisation possible du support de manutention de type râteau multi-peignes ;
• la figure 13 est un schéma représentant les chariots de réception pouvant être utilisés dans le cadre du seconde mode de réalisation possible de l'invention.

Other aspects, objects and advantages of the present invention will appear better on reading the following detailed description of preferred embodiments thereof, given by way of non-limiting example, and with reference to the appended drawings in which: :

• the Figures 1a-1c represent the load consisting of the base support, successive layers of baskets, and castings contained in the baskets, according to a first possible embodiment of the invention;
• the Figures 2a-2g represent the sequence of operations of a first possible embodiment of the method according to the invention;
• the Figures 3 and 4 represent means used in a first possible embodiment of the invention for unstacking the baskets in which the parts are arranged;
• the figure 5 is a diagram of a quenching unit used in the context of the invention for performing the air quenching of castings;
• the Figures 6a-6b are diagrams showing air distributors that can be used in the quenching unit;
• the Figures 7 and 8 represent a perspective view and a sectional view of a multilayer load carrier used in the context of a second possible embodiment of the invention;
• the Figures 9 and 10 illustrate a handling support in the form of a multi-comb rake used in the context of the second possible embodiment of the invention;
• the Figures 11a-11e its schemas of a sequence of operations illustrating the operation of the load in the context of the second possible embodiment of the invention;
• the figure 12 represents the principle of a possible embodiment of the multi-comb rake handling support;
• the figure 13 is a diagram showing the reception trolleys that can be used in the context of the second possible embodiment of the invention.

According to the first aspect, the invention relates to a process for the heat treatment of a lot of castings, in which air quenching of the parts of the batch is carried out. The invention also relates to a heat treatment system of a batch of castings comprising means capable of performing the implementation of the method according to the first aspect of the invention.

As previously discussed, the pieces of a batch are generally arranged in stackable baskets, and the baskets are stacked on a base support to form two or more layers of baskets.

The figure 1a represents a load carrier 1 conventionally used to support successive layers of baskets, and the parts contained in the baskets.

The load support 1 comprises housing 2 feet of baskets and is shaped to be driven in translation, for example by rolling on roller conveyors which are the usual mechanization of loads in batch furnaces.

The figure 1b is a cross-sectional view of the load support 1 on which two layers of baskets are stacked: an upper layer P1 of baskets (for example an upper set of two baskets) stacked on a lower layer P2 of baskets (for example a lower set of two baskets), the latter resting on the load support 1. Foundry pieces 3 are arranged in the baskets of layers P1 and P2.

We also represented on this figure 1b , the motorization M of the heat treatment plant. This is for example a motorized roller raceway.

The figure 1c are a perspective view of a basket 4. This has a honeycomb structure and is provided with external walls 5 sheet. The honeycomb structure allows the disposition of a piece 3 by cell.

The basket 4 has spaces 6 for the female / male stack of the basket feet.

As has been seen previously, the load consisting of the support 1, stacked baskets P1, P2 and parts arranged in the baskets is conventionally loaded in a conventional batch oven in order to carry out the dissolving, then extracted from this oven and fed to a quenching unit to be quenched, and then quenched from the quench unit, charged to a conventional batch oven to achieve the income. Thus, during the heat treatment, and in particular during the quenching operation, the parts of the batch are distributed over different layers.

In the context of the invention, it is proposed to apply an air quench to the batch pieces arranged in a single layer.

Prior to quenching, that is to say typically at the outlet of the solution furnace, the pieces are conventionally arranged in several layers.

The invention then proposes, following the extraction of the load from the solution furnace, to manipulate the pieces to form a single layer of pieces made up of the parts of the batch. The single layer is then brought under a ventilation system in the quenching unit, the ventilation system stirring the ambient air to cause a flow of cooling air. In this way, an air quench is applied to the single layer of pieces.

According to a first embodiment of the invention, the conventional case of parts arranged in stackable baskets is considered. In this embodiment, the operation of the parts to form the single layer of parts may consist of unstacking the baskets.

According to a second embodiment of the invention which will be described in more detail below, a particular multilayer load carrier is proposed which has a plurality of support means for a layer of parts in the form of spaced apart sleepers. others. In this embodiment, the operation of the parts to form a single layer of parts may consist in successively depositing each layer of parts on a receiving carriage.

The operating systems of the parts which will be described later in connection with the presentation of the first and second possible embodiments of the invention are given by way of non-limiting examples. Those skilled in the art can in particular design alternative embodiments respecting the basic principles set out in connection with the presentation of these exemplary embodiments.

With reference to Figures 2a-2g , there is shown a sequence of operations according to the first possible embodiment of the method according to the invention.

The figure 1a illustrates the taking of the load constituted by the support 1, the layers P1 and P2 of stacked baskets, and parts arranged in the baskets. The reference 7 represents a transfer carriage having several locations for stacks of baskets. A first location has a motorized roller bearing path 8, while a second location 9, adjacent to the first one, does not have a motorized path but is equipped with basket feet similar to the housings 2 present on the support 1 ( cf. figure 1a ).

The carriage 7 preferably has a ventilated structure, so as to let the air.

The figure 2b represents the loading of the load on the transfer carriage. The stack of baskets P1, P2 is arranged at the first location of the carriage 7 by installing the support 1 on the path 8.

The Figure 2c illustrates the movement, shown schematically by the arrow 12, of the transfer carriage 7 to a solution furnace 10.

The oven 10 is a conventional batch oven comprising a laboratory (useful working space of the oven) essentially closed, thermally insulated, equipped with an air mixing system, provided with heating systems and control of the heating from thermocouples measuring the temperature of the oven or air in the oven, the oven laboratory being accessible through a door 11 for loading or unloading the load.

The figure 2d illustrates the loading of the solution furnace 10, the charge being introduced into the furnace according to the arrow 13a. Once the load is fully charged, the door 11 is closed, and is carried out in solution.

The figure 2e illustrates the outlet of the load of the solution furnace 10 (output shown schematically by the arrow 13b), and the supply of the load (shown schematically by the movement of the transfer carriage 7 according to the arrow 14) to a system adapted to unstack the baskets.

As shown on the figure 2f , the carriage 7 is transferred to pass under a unstacking gantry 15, one embodiment of which will be described in more detail below with reference to the Figures 3 and 4 . When the first location 8 of the carriage is to the right of the gantry 15, the baskets of the upper layer P1 can be lifted using a gripping mechanism 16 integral with the gantry 15.

As illustrated on the figure 2g , the carriage is then advanced according to the arrow 14 until the second location 9 of the carriage 7 is at the right of the gantry 15. The gripping mechanism 16 is then controlled to drop the baskets of the upper layer P1 on the second location 9 of the carriage 7, which in the meantime has been advanced by the distance necessary for the upper layer P1 can be presented vertically feet 2 on the housing housing 7.

The set of baskets is then arranged in a single layer, the basket layers P1 and P2 being positioned side by side at the same level on the carriage 7.

We have shown on Figures 3 and 4 a possible embodiment of the gantry 15. The gantry 15 is here a structure fixed to the ground S, comprising a gripping mechanism 16 controlled by means of a jack 17 for lifting and depositing a layer of baskets.

The gantry comprises a cross member 18 extending horizontally from the ground, and in which a frame 19 (consisting for example of two vertical columns, a beam and a horizontal plate) supporting the gripping mechanism 16 can slide vertically under the action of the cylinder 17. The gripping mechanism 16 comprises a movable plate 20 forming part of the frame 19, and is provided with claws 21 adapted to be actuated by claw actuators 22 to engage with the upper layer of baskets P1.

Once the baskets have been unstacked using the gantry 15, the transfer carriage 7 on which the pieces are now arranged in a single layer is fed to the quenching unit in the air.

With reference to the figure 5 , the parts arranged in a single layer in the baskets P1 and P2 are brought to the right of a ventilation system 23 adapted to cause a flow of cooling air schematized by the arrows 24 and generally perpendicular to the single layer of parts.

So that the mechanical properties remain at a high level, the parts are subjected during the quenching air flow whose flow rate is preferably greater than 1000 m ³ per hour and per unit, and preferably greater than 1700 m ³ per hour and per room. By way of example, the air speed is of the order of 23 m / s for a flow rate of 1000 m ³ / h and per cylinder head, and of the order of 45 m / s for a flow rate of 1700 m ³ / h and per cylinder head.

Forced air cooling can be achieved until the rooms reach the room temperature, or the temperature of income, if income is subsequently made.

The quenching unit may be essentially closed by a wall 26 intended to recover the air after quenching, and act as a sonic barrier by evacuating the air through a sound absorber (the exhaust ducts of the air through the walls and sound dampeners are not represented on the figure 5 ).

The air passes through the cells of the baskets in which the parts are arranged, as well as a grid with trolley rails, to enter a chamber 30.

During quenching, the carriage 7 on which the single layer of parts is located is in a chamber consisting of walls 27 for confining the flow of air on the load.

Air distributors 28 are arranged above the load to channel the flow of air towards each of the rooms. An example of an air distributor in the form of a grid with honeycomb structure is shown on the figure 6a . Another example is represented on the figure 6b , on which the grid has a closed bottom surface, provided with an air passage slot in each of the cells.

The single part layer is spaced from the lower end of the air distributors 28 by a height H.

The quenching unit may further comprise a wind box 25 disposed between the ventilation system 23 and the air distributors 28 to provide sectional ratios between the ventilation system 23 and the air distributors 28.

In the context of this first embodiment, the parts can be laid horizontally in the baskets, which is the most satisfactory solution from the point of view of cooling. The parts can also be placed vertically in the baskets which increases the capacity of the heat treatment. Note here that "horizontally" or "vertically" refers to the largest area of the room.

Preferably, in horizontal position, the parts will be spaced less than 100 mm and preferably less than 50 mm.

In the upright position, the parts can be placed in baskets separated by continuous or partial partitions so as to keep them correctly close to the vertical position, these partitions also making it possible to channel the flow of air.

Preferably, in vertical position, these partitions will be made of steel forming a set of juxtaposed cells, each contiguous with its closest neighbors, in which the parts can be introduced at a rate of one piece per cell.

The space between the part and the cell, called E, is defined as follows for each dimension of the cell, for example the length and the width. For dimension characterized, 2 X E is equal to the difference between the envelope of the part built by surrounding the piece of a shape identical to the shape of the cell and the actual size of the cell.

Preferably, the shape of the cell is chosen such that in all dimensions E is approximately the same, to within a few mm, that is to say, by adapting the shape of the basket to the workpiece.

E thus defined will preferably be less than 60 mm, and more preferably less than 30 mm, its smallest dimension to be adjusted case by case, according to the actual geometry of the room to be able to maintain the air flow rates presented above. It can thus have a value of E close to zero, that is to say just the space required to load the piece into the cell, if by its intrinsic geometry the part leaves the required air passage.

The parts can also be suspended or held by supports in the basket. In this case, the cell previously described is not necessarily materialized, but we will keep the same preferences of values of E described above in relation to the space allocated to each room (the equivalent of the cell).

The method according to the invention can also be extended to the production, in addition to the air quenching applied to the single layer, in carrying out the solution-setting operation prior to quenching and / or completion of the income transaction after quenching.

In such cases, solution and return are carried out by charging in the corresponding furnaces dissolution solution and income load consisting of baskets stacked on top of each other so as to best use the capacity of conventional batch oven . In other words, the dissolution and the income are made conventionally by loading the batch of parts distributed in several layers of parts in the oven.

After dissolution, the baskets are thus unstacked as described above, and the single layer of parts is brought into the quenching unit.

The transfer time between the dissolving furnace (time counted at the opening of the door) and the starting of the air cooling must not exceed 6 minutes, and preferably be less than 3 minutes. 30 seconds. The Applicant has surprisingly observed that despite these rather long transfer times, necessary to enable the de-stacking operations on large furnaces, the mechanical properties of the parts remained high, under these conditions, practically without any reduction of properties compared to an immediate quench after oven exit.

In the case where a revenue operation (of structural hardening) is performed after quenching, the baskets will preferably be re-stacked so as to reconstitute the load. The gantry 15 described above can also be used for this purpose.

According to a second possible embodiment of the invention, presented with reference to Figures 7 to 12 it is proposed to use a particular multilayer load carrier which has a plurality of superposed means for supporting a layer of parts. Each support means for a layer of parts comprises sleepers spaced apart from each other.

As a general rule for cylinder head loads, the weight of baskets and steel supports is of the order of 0.5 tonnes per 1 tonne of aluminum actually treated. This second embodiment is advantageous in that it allows to heat and cool only the parts, which is a substantial saving in energy consumption.

This multilayer load carrier 30 is shown on the Figures 7 and 8 . In these figures, the references N1, N2 and N3 represent the different levels on which the layers of parts are superimposed. The multilayer support 30 has a plurality of superimposed means for supporting a layer of parts in the form of crosspieces 31 spaced apart from each other.

On the figure 7 only the N1 level is shown for the sake of clarity, while on the figure 8 three levels are shown, a layer of parts 3 being positioned on each level N1-N3.

We have shown on Figures 9 and 10 40S handling support parts in the form of a multi-comb rake. This support has an arm 40 from which extends a plurality of combs 41, each comb being able to support a layer of parts. The combs 41 and the crosspieces 31 are shaped in such a way that the teeth of a comb can be introduced into the inter-cross space of a support means for a layer of parts of the multilayer filler support 30.

So, as is schematized by the arrows 47 on the figures 8 and 9 , the support 40S handling can be advanced towards the multilayer load carrier 30, the teeth 42 of each of the combs 41 being introduced between the crosspieces 31 of each of the support means of a layer of parts. Then, the support 40 can be reassembled so that each of the combs slightly raises a layer of parts. Finally, the support 40 can be removed from the support 30 to carry the different layers of parts.

Once the layers of parts present on the handling support 40, the parts can be transported on a load support similar to the multilayer support 30. It will be understood that the layers of parts can be deposited on the support 30 from the handling support 40 coming to introduce the teeth of the combs between the sleepers.

In particular, it is possible to deposit the parts on a multilayer support 30 suitable for being introduced into a batch oven, or on a multilayer support 30 present in a batch oven. The handling support 40S can thus be used for loading and unloading a batch oven in order to carry out a solution dissolving operation or a batch layer coin layer operation operation of the batch of pieces.

In particular after dissolution, the handling support 40S is used to unload the furnace so that the different layers of parts are arranged on the different combs of the handling support 40S.

In this second embodiment, the parts are then maneuvered to form a single layer of parts on a transfer trolley consisting of two half-trolleys (assuming two levels of parts are to be maneuvered to form the single layer), and in general the number of trolleys corresponding to the number of layers of parts.

This maneuver is represented on the diagrams of Figures 11a-11e .

With reference to the figure 11a , the handling support 40S is advanced according to the arrow 43 in the direction of half-carriages 44a, 44b (also referred to as receiving carriages thereafter). Each receiving carriage 44a, 44b is shaped to receive a layer of pieces, and presents in particular (cf. figure 13 ) means for supporting a layer of parts in the form of a comb having teeth 48 spaced apart from each other.

Once the handling support 40S is positioned to the right of a first receiving carriage 44b, said support 40S is lowered so that the teeth of the lower comb of the support 40S enter the inter-teeth spaces of the support means of the carriage 44b. Parts 3 of the lower layer are then deposited on the carriage 44b. The teeth of the lower comb of the support 40S are then removed from the inter-tooth spaces of the carriage 44b, and the handling support 40S is raised as shown in FIG. figure 11c .

The carriages 44a, 44b are then advanced, for example along a motorized path, and the same sequence of operations is repeated to deposit the layer of parts of the upper comb on the carriage 44a.

As shown on the figure 11d the pieces 3 of the batch are then distributed over the different receiving trolleys 44a, 44b in a single layer, and the trolleys are then brought to the quenching unit described above in connection with the first possible embodiment of the invention. , schematized in dotted lines on the figure 11e .

It should be noted here that an income transaction can be carried out following quenching. The handling support 40S is then used to manipulate the pieces after quenching in similar operations to those described above and reconstitute the multilayer load before baking in the batch oven income.

We have shown on the figure 12 , a diagram of a possible embodiment of the multi-comb rake type handling support 40S used in this second possible embodiment of the invention.

The support 40S may comprise a first carriage 45 rolling on rails to ensure longitudinal movement of the support 40S in the direction indicated by the arrow F ₄₅ . It may also include a second rolling carriage 46 adapted to move laterally on the first carriage C1 in the direction indicated by the arrow F ₄₆ . The support 40S may further have a Δ axis allowing the rotation of a main arm B, itself guiding a movable arm B 'integral with the combs.

Examples

Various examples of implementation of the invention are described below. In all these examples, in-line four-cylinder diesel cylinder heads were molded in static gravity into a metal mold, fire-facing downwards, with a steel plate cooled energetically so as to obtain a fine microstructure that can be characterized. by measuring the SDAS ("Secondary Dendrite Arm Spacing"), with values of the order of 30 microns in the area where the tensile specimens used to characterize the material are taken.

The metal temperature at casting is 720 ° C at the inlet in the casting cup of the mold, from which feed channels leave to fill the mold through attacks located at the foot of the room.

Putting millet, ratio between the weight cast (piece plus feeding system, plus weights) and the weight of the piece is 1.7. The molded piece weighs 14.1 kg.

All coring is carried out in cold box type process, for the realization of the inner forms: intake ducts, exhaust ducts, circulation of water, oil and for the realization of the core containing the weights, reserves of metal located above the piece itself and allowing the supply of liquid metal during the solidification and contraction of the piece.

The molding cycle time is of the order of 5 minutes from room to room.

The alloy is of AA 356 type, of first fusion, with a chemical composition given below in weight percentages: Yes Fe mn mg Ti Zn al 7.4 0.12 0.02 0.30 0.11 0.02 rest

The alloy has its eutectic structure modified by addition of strontium.

After casting, the piece is extracted from the mold and cooled in a forced air tunnel so that it is cooled to a temperature of 50 ° C. in a time of about 120 minutes.

• ✔ Essai n°1 : Traitement thermique hors du champ de l'invention comprenant :
  • Une mise en solution 6 h à 540°C dans un four conventionnel.
  • Une trempe dans de l'eau chaude à 70°C.
  • Un revenu de 6h à 200°C dans un four conventionnel.
• ✔ Essais N° 2 à 5 : Traitement thermique conforme à l'invention comprenant :
  • Une mise en solution 6 h à 540°C dans un four conventionnel.
  • Un positionnement des pièces verticalement dans des paniers à fond grillagé et à alvéoles (reposant sur le fond) dont la hauteur dépasse de 150 mm la surface supérieure de la culasse.
  • Un transfert des pièces du four de mise en solution vers l'unité de refroidissement à l'air pour la trempe, avec un support de manutention conforme à celui décrit en relation ave l'exposé du seconde mode de réalisation possible de l'invention en 1 minute 30 secondes.
  • Une trempe à l'air conforme à l'invention, avec les paramètres critiques de refroidissement suivants :
    • ∘ la surface supérieure des alvéoles est située à 50 mm de la surface inférieure du distributeur d'air de la boite à vent. La distance H entre les pièces et la partie inférieure de la distribution d'air située sous la boite à vent est donc de 200 mm.
    • ∘ Essai N°2
      • ▪ Débit d'air 1100 m³/h et pièce
      • ▪ Espace pièce alvéole : 15 mm en largeur et en longueur.
    • ∘ Essai N°3
      • ▪ Débit d'air 3200 m³/h et pièce
      • ▪ Espace pièce alvéole : 40 mm en largeur et en longueur.
    • ∘ Essai N°4
      • ▪ Débit d'air 3200 m³/h et pièce
      • ▪ Espace pièce alvéole : 15 mm en largeur et en longueur.
    • ∘ Essai N°5
      • ▪ Débit d'air 1700 m³/h et pièce
      • ▪ Espace pièce alvéole : 15 mm en largeur et en longueur.
• ✔ Essai N° 6 : Traitement thermique conforme à l'invention comprenant :
  • Une mise en solution 6 h à 540°C dans un four conventionnel.
  • Un positionnement des pièces verticalement dans des paniers à fond grillagé et à alvéoles (reposant sur le fond) dont la hauteur dépasse de 150 mm la surface supérieure de la culasse.
  • Un transfert des pièces du four de mise en solution vers l'unité de refroidissement à l'air pour la trempe, avec un support de manutention conforme à celui décrit en relation avec l'exposé du seconde mode de réalisation possible de l'invention, en 3 minutes.
  • Une trempe à l'air conforme à l'invention, avec les paramètres critiques de refroidissement suivants :
    • ∘ La surface supérieure des alvéoles est située à 50 mm de la surface inférieure du distributeur d'air de la boite à vent. La distance H entre les pièces et la partie inférieure de la distribution d'air située sous la boite à vent est donc de 200 mm.
    • ∘ Débit d'air 3200 m³/h et pièce
    • ∘ Espace pièce alvéole : 15 mm en largeur et en longueur.
• ✔ Essais N° 7 : Traitement thermique conforme à l'invention comprenant :
  • Une mise en solution 6 h à 540°C dans un four conventionnel.
  • Un positionnement des pièces horizontalement dans des paniers à fond grillagé.
  • Un transfert des pièces du four de mise en solution vers l'unité de refroidissement à l'air pour la trempe, avec un support de manutention permettant de remplir les fonctions décrites dans la variante de réalisation de l'invention en 1 minute 30 secondes.
  • Une trempe à l'air conforme à l'invention, avec les paramètres critiques de refroidissement suivants :
    • ∘ Les culasses sont placées face feu vers le haut
    • ∘ La distance H entre le haut des culasses et la base du distributeur d'air situé sous la boite à vent est de 150 mm.
    • ∘ Débit d'air 3200 m³/h et pièce
    • ∘ Espace inter-pièces: 40 mm environ (équivalent à E=20mm)

The cylinder heads are then subjected to the usual finishing operations (elimination of the filling systems, deburring, sawing of the weights, deburring) and the following different heat treatments.

• Test No. 1 : Heat Treatment Outside the Field of the Invention Comprising:
  • Dissolving for 6 h at 540 ° C. in a conventional oven.
  • Quenching in hot water at 70 ° C.
  • An income of 6 hours at 200 ° C in a conventional oven.
• ✔ Tests N ° 2 to 5 : Thermal treatment according to the invention comprising:
  • Dissolving for 6 h at 540 ° C. in a conventional oven.
  • The positioning of the parts vertically in baskets with a grid bottom and with cells (resting on the bottom) whose height is 150 mm higher than the upper surface of the cylinder head.
  • A transfer of the pieces of the solution furnace to the air cooling unit for quenching, with a handling support according to that described in relation to the disclosure of the second possible embodiment of the invention in 1 minute 30 seconds.
  • An air quench according to the invention, with the following critical cooling parameters:
    • ∘ the upper surface of the cells is located 50 mm from the lower surface of the air distributor of the wind box. The distance H between the parts and the lower part of the air distribution located under the wind box is 200 mm.
    • ∘ Test N ° 2
      • ▪ Air flow 1100 m ³ / h and room
      • ▪ Cell space gap: 15 mm in width and length.
    • ∘ Test N ° 3
      • ▪ Air flow 3200 m ³ / h and room
      • ▪ Cell space gap: 40 mm in width and length.
    • ∘ Test N ° 4
      • ▪ Air flow 3200 m ³ / h and room
      • ▪ Cell space gap: 15 mm in width and length.
    • ∘ Test N ° 5
      • ▪ Air flow 1700 m ³ / h and room
      • ▪ Cell space gap: 15 mm in width and length.
• Test No. 6 : Heat Treatment According to the Invention Comprising:
  • Dissolving for 6 h at 540 ° C. in a conventional oven.
  • The positioning of the parts vertically in baskets with a grid bottom and with cells (resting on the bottom) whose height is 150 mm higher than the upper surface of the cylinder head.
  • Transfer of the parts of the solution furnace to the air cooling unit for quenching, with a handling support according to that described in relation with the disclosure of the second possible embodiment of the invention, in 3 minutes.
  • An air quench according to the invention, with the following critical cooling parameters:
    • ∘ The upper surface of the cells is located 50 mm from the lower surface of the air distributor of the wind box. The distance H between the parts and the lower part of the air distribution located under the wind box is 200 mm.
    • ∘ Airflow 3200 m ³ / h and room
    • ∘ Space alveolus piece: 15 mm in width and in length.
• ✔ Tests No. 7 : Heat treatment according to the invention comprising:
  • Dissolving for 6 h at 540 ° C. in a conventional oven.
  • Horizontal positioning of the pieces in baskets with a grid base.
  • A transfer of the pieces of the solution furnace to the air cooling unit for quenching, with a handling support to fulfill the functions described in the embodiment of the invention in 1 minute 30 seconds.
  • An air quench according to the invention, with the following critical cooling parameters:
    • ∘ The cylinder heads are facing fire up
    • ∘ The distance H between the top of the cylinder heads and the base of the air distributor located under the wind box is 150 mm.
    • ∘ Airflow 3200 m ³ / h and room
    • ∘ Space between rooms: about 40 mm (equivalent to E = 20 mm)

In all the tests No. 2 to 7 in accordance with the invention, the parts are cooled by the quenching operation to room temperature and then subjected to the same income as for test No. 1, ie: 6 hours at 200 ° C in a conventional batch oven.

It is for this alloy and for all the examples mentioned, a heat treatment of T7 type, that is to say with an over-income beyond the peak of maximum hardening of the alloy.

Characterization of the cylinder heads

The cylinder heads have been characterized at room temperature in traction and hardness.

The tensile properties are measured according to standard AFNOR EN 10002-1 in the fire side, at the level of the inter-valve bridges by tensile specimens with a diameter of 6.18 mm and a calibrated length of 36.2 mm. Each measurement is the average of 4 test pieces per piece, for 3 pieces.

Brinell hardness is measured according to the AFNOR EN ISO 6506 - 1 and ASTM E10-06 standards in the fire side as well. One measurement is made per piece, for five pieces.

In addition, thermocouples were placed in the yokes at the heart of the tablature towards the fire side of the cylinder head to measure the cooling rate, which was characterized by the time required to bring the cylinder head from 430 ° C to 70 ° C. ° C.

The results are reproduced in the following table. testing Cooling rate: from the cylinder head in the range of 430 ° C to 70 ° C Mechanical properties of the cylinder head Traction Hardness H _B Limit at break Rm (MPa) Elastic limit R _0.2 (MPa) Lengthening A (%) No. 1 Reference (water quenching) > 200 ° C / min 287 245 5.4 106 n ° 2 Vertical cylinder head 1100 m ³ / h E 15mm H 200mm 21 ° C / min 243 201 5.8 90 n ° 3 Vertical cylinder head 3200 m ³ / h E 40mm H 200mm 47 ° C / min - - - - n ° 4 Vertical cylinder head 3200 m ³ / h E 15mm H 200mm 56 ° C / min 263 211 6.5 91 n ° 5 Vertical cylinder head 1700 m ³ / h E 15mm H 200mm 34 ° C / min 265 210 5.8 88 n ° 6 Vertical cylinder head 3200 m ³ / h E 15mm H 200mm Long transfer between dissolution and quenching 56 ° C / min 259 209 5.7 90 n ° 7 Horizontal cylinder head 3200 m ³ / h E 20mm H 150mm 61 ° C / min 265 212 5.7 88

All of these results show that it is possible to approach the mechanical characteristics of water-soaked cylinder heads (test No. 1) with heat treatments according to the invention using air quenching (tests). Nos. 2 to 7) applied to a single layer of pieces made up of the pieces of the batch.

This air quenching has the additional advantage of not generating residual stresses in the parts, which is generally very beneficial to the life of the yokes in service. This also widens the possibilities of income choice, as over-income is often imposed to try to reduce the residual stresses generated by water quenching.

In addition, the process according to the invention provides wide operating ranges from the point of view of the industrial operation.

It can be seen for example that for values of E of the order of 15 mm, as soon as we exceed an airflow of 1700 m ³ / h and per piece, the mechanical characteristics of the part reach an asymptote, that well. that the cooling rate continues to grow (tests 4 and 5).

It also appears that it is desirable not to go below 1700 m ³ / h and per piece (see test n ° 2) if one wants to remain close to the maximum level of resistance accessible by these methods of quenching with the air which justifies the preferential flow rates according to the invention.

We also see the interest of keeping E as small as possible (see tests 3 and 4).

It is also possible to soak the pieces horizontally or vertically.

The fact that 1 minute of transfer (i.e. the time elapsing between the opening of the solution furnace door and the beginning of forced air cooling) gives practically the same result as 3 minutes of transfer leaves the possibility of achieving in good mechanical conditions speeds and accelerations including the operations of maneuver the load to form the single layer of parts (tests 4 and 6). This very surprising result compared to the usual practices of the quenching which impose for casting alloys very short transfer times, of the order of 15 seconds maximum in general, has been the subject of multiple confirmations by the Applicant. On this occasion, it has been demonstrated that after 6 minutes 30 seconds of transfer time, the mechanical property reductions become significant.

Claims (12)

1. A method for heat treatment of a batch of castings, comprising a solutionization operation performed in an oven loaded with the parts of the batch positioned on several layers of parts superposed onto each other, characterized in that, following extraction of the parts from the solution heat treatment oven, the layers of parts are maneuvered in order to form a single layer of parts consisting of the parts of the batch, the single layer is brought into an air quenching unit having a ventilation system and quenching is applied to parts of the batch arranged in the single layer.
2. The method according to claim 1, wherein the ventilation system delivers an air flow rate greater than 1,000 m³/h and per part, preferably greater than 1,700 m³/h and per part.
3. The method according to any of claims 1 to 2, wherein during the solutionization operation, the parts are positioned into baskets superposed onto each other, and the maneuvering of the layers of parts consists of unstacking baskets.
4. The method according to claim 3, wherein the parts are laid horizontally in the baskets and spaced apart by at least 100 mm, preferably at least 50 mm.
5. The method according to claim 3, wherein the baskets are separated by partitions and wherein the parts are laid vertically in the baskets.
6. The method according to claim 4, wherein the partitions form a set of cells, the parts being positioned in an amount of one part per cell so that the space between the part and the cell is less than 60 mm, and preferably less than 30 mm.
7. The method according to claim 3, wherein the parts are suspended or maintained by supports in the baskets.
8. The method according to claim 1, wherein the maneuvering of the layers of parts consists of successively depositing each layer of parts on a receiving carriage adapted for receiving a single layer of parts.
9. The method according to any of claims 1 to 8, wherein the transfer time between the opening of the oven upon completion of the solutionization, and the starting of air cooling, is less than 6 minutes, preferably less than 3 minutes 30 seconds.
10. The method according to any of claims 1 to 8, wherein following quenching, the parts are maneuvered in order to re-position them on several layers, and an operation for tempering the parts is performed in an oven loaded with the parts of the batch positioned on several layers is performed.
11. A system for heat treatment of a batch of castings comprising a solutionization oven such that the parts of the batch are positioned on several layers of parts superposed onto each other when the oven is loaded, an air quenching unit having a ventilation system in order to cause a cooling air flow, characterized in that it includes means for extracting the parts from the solutionization oven and for positioning them in a single layer of parts, and means for bringing the single layer of parts into the air quenching unit so as to apply air quenching to the parts of the batch positioned in a single layer.
12. The system according to claim 11, wherein the ventilation system is configured to deliver an air flow rate greater than 1,000 m³/h and per part, preferably greater than 1,700 m³/h and per part.

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