FR2863629A1 - Device for the hot physicochemical treatment of mechanical components, notably for the cementation of steel components comprises hot cleaning enclosure, hot physicochemical enclosure and transport system - Google Patents

Abstract

A device (10) for the hot physicochemical treatment of mechanical components (24, 32) comprises: (A) a hot cleaning enclosure (30) for the components; (B) a hot physicochemical treatment enclosure (12); (C) a transport system (34, 36) for automatically transporting cleaned components from the cleaning enclosure to the inlet (17, 20) of the physicochemical treatment enclosure with a transport time such that the difference between the temperature of the cleaned components leaving the cleaning enclosure and the ambient temperature outside the cleaning enclosure reduces by half. An independent claim is also included for a method of hot physicochemical treatment using this device./.

Description

METHOD AND DEVICE FOR HOT PHYSICOCHFIC TREATMENT OF

  TECHNICAL FIELD The present invention relates to a method and a device for the physicochemical heat treatment of mechanical parts.

  An example of a physicochemical heat treatment is the carburizing of steel mechanical parts which involves introducing carbon into the surface of the parts to improve the hardness.

  A case-hardening treatment consists, for example, in subjecting the parts to be treated, in an air-tight enclosure, to an alternation of enrichment stages in the presence of a low pressure cementation gas and diffusion under vacuum or in a low pressure neutral atmosphere. The respective durations of the enrichment and diffusion steps and their number depend in particular on the desired carbon concentration and cementation depth in the pieces, and these treatments are well known in the art. An example of a low pressure carburization process is described in the French patent application No. 2,678,287 of the applicant.

  Any cementation treatment is followed by at least one quenching step performed by means of a quenching liquid or by means of a quenching gas. The main purpose of quenching is to obtain rapid cooling of the cemented parts without altering the surface state obtained.

  Another example of a physicochemical heat treatment is carbonitriding, the only difference from cementation being the enrichment gas used, to which ammonia is generally added. The result, well known, is the formation of nitrides (instead of carbides for cementation) on the surface of the piece. It should be noted that everything that will be exposed later in connection with cementation also applies to carbonitriding.

  Before being introduced into the cementation plant, the parts to be treated must be cleaned to have a surface state compatible with the carburizing treatment. Cleaning is generally obtained by performing a superficial oxidation of the parts to be treated, in a separate enclosure of the cementation plant and called oxidation chamber, so as to burn all the impurities covering the parts to be treated. The parts to be treated are generally oxidized to a small thickness, which also improves the reactivity properties of the surfaces of the parts to be treated during the cementation enrichment steps.

  Parts having undergone superficial oxidation are generally temporarily stored for subsequent transport to the cementation plant. However, handling operations of the superficially oxidized parts from the oxidation chamber to the storage area and from the storage area to the cementation plant may result in the deposit of unwanted impurities on the parts to be treated. In addition, it is necessary to provide a storage area for the superficially oxidized parts, which increases the total cost of the cementation treatment. In addition, such manipulations require the presence of operators, which also increases the total cost of the cementation treatment. In addition, it is necessary to provide a waiting time for the cooling of the output parts of the oxidation chamber before handling, which complicates the flow management of the parts to be treated. Finally, since the superficially oxidized parts are at ambient temperature when they are introduced into the cementation plant, a large amount of energy is used to heat the superficially oxidized parts to the temperatures necessary for carrying out the cementation treatment.

  The present invention relates to a method and a device for physicochemical heat treatment of mechanical parts comprising a prior step of cleaning the mechanical parts to prevent pollution of the parts between the cleaning step and the subsequent physicochemical heat treatment, particularly in avoiding any manipulation by operators of parts having undergone the cleaning step.

  The present invention also allows an efficient management of the flow of parts between the cleaning chamber in which the preliminary cleaning step is carried out and the physicochemical heat treatment installation, in particular by avoiding the storage of parts between the step of cleaning. cleaning and subsequent physicochemical heat treatment.

  The present invention also allows a reduction in the energy consouânation of the cementation plant.

  To achieve these objects, the present invention provides a device for physicochemical heat treatment of mechanical parts comprising a hot cleaning chamber receiving mechanical parts to be treated and providing cleaned mechanical parts; a physicochemical heat treatment chamber for carrying out a physicochemical heat treatment of the cleaned mechanical parts; and transport means for automatically transporting cleaned mechanical parts from an outlet of the hot cleaning enclosure to an inlet of the physicochemical treatment enclosure in a transport time shorter than the duration for which the difference between the temperature of the cleaned mechanical parts exiting the hot cleaning enclosure and the ambient temperature outside the hot cleaning enclosure decreases by half.

  According to one embodiment of the invention, the transport time is less than three minutes.

  According to one embodiment of the invention, the temperature of the mechanical parts cleaned at the outlet of the hot cleaning chamber is greater than 300 C.

  According to one embodiment of the invention, the hot cleaning enclosure is an oxidation chamber adapted to superficially oxidize the parts to be treated.

  According to one embodiment of the invention, the mechanical parts are made of steel and the physicochemical heat treatment chamber is a cementation chamber comprising a low pressure carburizing furnace.

  According to one embodiment of the invention, the conveying means provides at least one conveyor belt.

  The present invention also relates to a method for the physicochemical heat treatment of mechanical parts comprising the steps, performed at least in part simultaneously, of hot cleaning mechanical parts to be treated in a hot cleaning chamber; automatically transporting cleaned parts from the hot cleaning enclosure to a physico-chemical heat treatment chamber in a transport time shorter than the time for which the difference between the temperature of the cleaned mechanical parts leaving the enclosure hot cleaning and room temperature out of the hot cleaning cabinet halves; and perform physicochemical heat treatment of the cleaned parts in the physicochemical heat treatment chamber.

  According to one embodiment of the invention, the transport time of a mechanical part cleaned from the hot cleaning chamber to the physicochemical hot treatment chamber is less than three minutes.

  According to one embodiment of the invention, the hot cleaning step is performed by surface oxidation of the mechanical parts to be treated at a temperature above 300 C.

  According to one embodiment of the invention, the mechanical parts are made of steel and the physicochemical heat treatment is cementation.

  These and other objects, features, and advantages of the present invention will be set forth in detail in the following non-limiting description of particular embodiments in connection with the single figure which schematically shows a plan view of an embodiment of a physicochemical heat treatment device according to the invention.

  As shown in FIG. 1, the processing device 10 according to the invention comprises a cementation plant 12 as described in the applicant's European patent application No. 922,778, to which reference may be made for further details. .

  The cementation plant 12 comprises a sealed chamber 14 in the form of a cylinder (of section not necessarily circular) with a horizontal axis. Both ends of this cylinder 14 are plugged by removable waterproof covers 15. Processing cells are connected laterally to the sealed enclosure 14 and are in the same horizontal plane. For example, four carburizing cells 16 (for example each of which may contain a charge to be cemented) are arranged in pairs facing each other and open into the sealed enclosure 14. A load-unloading cell 17 is placed facing a quenching cell 18, these cells being connected to the sealed enclosure 14. The carburizing cells 16 and the quenching cell 18 are separated from the sealed enclosure 14 by unrepresented movable doors. The load-unloading cell 17 is separated from the sealed enclosure 14 by a movable door 19, shown in dotted lines, and the external medium by an external door 20.

  A handling device is in the form of a carriage 21 which moves in the sealed enclosure 14 in parallel with the axis of the enclosure 14. The carriage 21 moves, for example, on rails 22 '. extending along the sealed enclosure 14. The carriage 21 is provided with a telescopic fork 23 which is capable of stretching on either side of the carriage 21 to the center of each of the cells 16, 17, 18 to take and deposit a charge during treatment. The carriage 21 is shown in solid lines at the cells 17 and 18, the telescopic fork 23 entering the load-unloading cell 17 to take a load 24. Of course, the load-unloading cell 17 was previously put at the low pressure of the chamber 10 to be able to open the door 19 which constitutes, with the outer door 20, an entrance lock. In dashed lines, the carriage 21 is shown at the level of the carburizing cells 16 medians. An installation as illustrated in Figure 1 is modular, that is to say that one or more additional modules each consisting of a sealed chamber portion provided with rails and one or two cells can be connected axially to the sealed enclosure 10 at the covers 15 to complete the sealed enclosure 10.

  The treatment device 10 according to the invention includes an oxidation chamber 30 through which charges to be oxidized transported by a first conveyor 34 circulate, a charge 32 being represented in FIG. 1 at the inlet of the enclosure The conveyor 34 is, for example, a conveyor belt. Conventionally, the oxidation chamber 30 comprises an inlet lock and an outlet lock (not shown) for isolating the charges to be oxidized. A second conveyor 36 is provided at the outlet of the oxidation chamber 30 and allows the transport of one or more charges between the first conveyor 34 and the load-unloading cell 17. The second conveyor 36 is for example, a conveyor belt. The second conveyor 36 can move a load in two opposite directions, that is to say from the first conveyor 34 to the load-unloading cell 17 or from the load-unloading cell 17 to the first conveyor 34. A module supervision 38 controls the operation of the first and second conveyors 34, 36, the oxidation chamber 30 and the cementation plant 12. In particular, the supervision module 38 controls the second conveyor 36 for the transport of a load from the first conveyor 34 to the load-unloading cell 17 or from the load-unloading cell 17 to the first conveyor 34.

  According to an example of operation of the device 10, each load consists of, for example, a set of toothed rings, synchronizing rings, hubs, etc., which may represent a total weight of several hundred kilograms. The charges to be treated are successively introduced into the oxidation chamber 30, in which they are cleaned by a superficial oxidation step at temperatures of the order of 400 to 500 ° C. for several hours. For example, the oxidation chamber 30 can simultaneously perform the oxidation of six charges, the entry lock and the exit chamber of the oxidation chamber 30 can then further each contain a load.

  A charge leaving the oxidation chamber 30 is immediately transported by the first conveyor 34 and the second conveyor 36 to the load-unloading cell 17 of the cementation plant 12.

  In the carburizing plant 12, the load is for example first moved to a carburizing cell 16 in which it is heated to a temperature of 920 to 1000 C for 1 to 2 hours. At the same time, the pressure is lowered to a value of 5 to 20 mbar. Then, the charge is subjected to several stages of enrichment under carbon atmosphere, alternated with as many diffusion steps under nitrogen. The respective durations of the enrichment and diffusion steps are chosen in a conventional manner and are preferably decreasing for the enrichment and increasing stages for the diffusion steps. The total duration of the enrichment and diffusion steps is, for example, a hundred minutes. The charge is then moved to the quenching cell 18 in which it is subjected to gas quenching, for example quenching in air or an inert gas. When the carburization treatment is completed, the load is again moved to the second conveyor 36 via the load-unloading cell 17. The second conveyor 36 then transports the load to the first conveyor 34 which transports it. finally to a receiving area where finishing operations are performed if necessary.

  The supervision module 38 controls the flow of the charges 32 to be treated between the oxidation chamber 30 and the cementation plant 12 so that the oxidized parts superficially coming out of the oxidation chamber 30 are preferably directly supplied to the cementation plant 12. The transport time of a charge between the oxidation chamber 30 and the cementation plant 12 is less than the duration for which the difference between the temperature of the cleaned mechanical parts leaving the the oxidation chamber 30 and the ambient temperature outside the oxidation chamber 30 decreases by half. For example, the transport time between the outlet of the oxidation chamber 30 and the inlet of the cementation plant 12 varies from 30 seconds to about three minutes, and preferably from 30 seconds to one minute, to limit the cooling of the superficially oxidized charge. The charges entering the carburizing chamber 12 thus retain substantially the temperature they have at the outlet of the oxidation chamber 30 which is generally greater than 300 ° C., and preferably of the order of 400 ° C. to 500 C. The temperatures present in a cementation cell 16 up to 900 C, energy savings are realized since a lesser amount of energy must be supplied to the charges entering the cementation plant 12 to bring them to carburizing temperatures.

  The present invention has many advantages: First, the charges being transported automatically from the oxidation chamber to the cementation plant, it is possible to limit any new pollution of the parts after the oxidation treatment, in particular by avoiding any manipulation parts by operators.

  Secondly, an optimization of the management of the flow of the charges to be treated is obtained by avoiding the storage of charges between the oxidation step and the cementation step.

  Thirdly, energy gain is achieved since the charges are supplied to the carburizing plant with a temperature higher than the ambient temperature.

  Of course, the present invention is susceptible to various variations and modifications which will be apparent in the art. In particular, although the invention has been described in connection with a low pressure cementation treatment, it is more generally applicable to any treatment in which similar problems arise. It may be, for example, a carbonitriding treatment, brazing and other applications under partial vacuum before quenching.

  In addition, the adaptation of the implementation data of the method of hot-chemical physicochemical treatment of the invention as a function of the type of parts, the volume of the load, and previous treatments is within the reach of the skilled person from the indications given above. In particular, it will be noted that the numerical indications of the particular example of cementation treatment indicated above are only an illustration of the feasibility of the invention, and that other values may be adopted. In addition, the automatic transport of the charges between the oxidation chamber and the cementation plant can be achieved by any suitable means, and in particular by a single conveyor belt. Finally, it should be noted that the invention can also be implemented in a treatment plant of the type described in European Patent Application No. 388,333 of the Applicant where several vertical treatment cells are distributed over an enclosure waterproof transfer of the load and on both sides of the quenching cell.

Claims (10)

  A device for heat physicochemical treatment (10) of mechanical parts (24, 32) comprising: a hot cleaning vessel (30) receiving mechanical parts to be treated and providing cleaned mechanical parts; a physicochemical heat treatment chamber (12) for performing a physicochemical heat treatment of the cleaned mechanical parts; and transport means (34, 36) for automatically transporting cleaned mechanical parts from an outlet of the hot cleaning enclosure to an inlet (17, 20) of the physicochemical treatment enclosure in a period of time. less than the duration for which the difference between the temperature of the cleaned mechanical parts leaving the hot cleaning cabinet and the ambient temperature outside the hot cleaning cabinet is reduced by half.   2. Device according to claim 1, wherein the transport time is less than three minutes.   3. Device according to claim 1, wherein the temperature of the mechanical parts cleaned at the outlet of the hot cleaning chamber (30) is greater than 300 C.   4. Device according to claim 1, wherein the hot cleaning chamber (30) is an oxidation chamber adapted to superficially oxidize the parts (24) to be treated.   5. Device according to claim 1, wherein the mechanical parts (24, 32) are made of steel and wherein the physicochemical heat treatment chamber (12) is a cementation chamber comprising a carburizing furnace (16) low pressure .   6. Device according to claim 1, wherein the transport means (34, 36) comprises at least one conveyor belt.   7. A method for the physicochemical heat treatment of mechanical parts (24, 32) comprising the following steps, carried out at least in part simultaneously: hot cleaning mechanical parts to be treated in a hot cleaning chamber (30); automatically transporting cleaned parts from the hot cleaning enclosure to a hot-water physicochemical treatment enclosure (12) in a transport time less than the time for which the difference between the temperature of the cleaned mechanical parts exiting the hot cleaning enclosure and the ambient temperature out of the hot cleaning enclosure halves; and performing a physicochemical heat treatment of the cleaned parts in the physicochemical heat treatment chamber.   The method of claim 7, wherein the duration of transport of a cleaned mechanical part (24) from the hot cleaning enclosure (30) to the physicochemical heat treatment chamber (12) is less than at three minutes.   9. The method of claim 7, wherein the hot cleaning step is performed by surface oxidation of mechanical parts (24) to be treated at a temperature above 300 C.   10. The method of claim 7, wherein the mechanical parts (24, 32) are steel and wherein the physicochemical heat treatment is carburizing.