FR2874079A1 - THERMOCHEMICAL CEMENT TREATMENT MACHINE - Google Patents

Abstract

The thermochemical treatment machine under low atmospheric pressure, for carburizing and optionally the carbonitriding of metal parts, comprises at least one cell (3) carburizing temperature, a cell (4) surface enrichment, a carbon diffusion cell (5) and a quenching cell (6) arranged one after the other. The cells (3, 4, 5) are of standard form and of length (L) adaptable. The length of a cell is proportional to the duration of the treatment performed in this cell. The transfer between two cells is performed at a predetermined pressure. The machine may comprise, upstream of the carburizing temperature setting cell (3), a cell (1) for cleaning the parts and a cell (2) for preheating parts, and downstream of the cell (6) of quenching, a cell (7) of income.

Description

Thermochemical Cementation Processing Machine Technical Field

the invention

  The invention relates to a thermochemical treatment machine under low atmospheric pressure, for the carburizing and optionally the carbonitriding of metal parts, comprising means for setting carburizing temperature, surface enrichment means and diffusion means of the invention. carbon from the surface to the heart of the pieces, respectively during a first phase, a second phase and a third successive treatment phase.

  STATE OF THE ART There are numerous thermochemical treatment systems for carburizing and carbonitriding of metal parts, in particular case-like systems with a solid cementitious material, uncontrolled atmosphere systems, controlled atmosphere systems with a carbon potential. constant or low pressure systems, of the order of 5mbar to 20mbar, sometimes even up to 100mbar.

  Carburizing and carbonitriding generally require a partial pressure of cementing gas, consisting of a hydrocarbon, for example methane (CH4), ethylene (C2H2) or propane (C3H8), and optionally a nitriding gas, for example. example of ammonia (NH3). The carburizing operations, namely a carburizing treatment treatment, a surface enrichment treatment and a carbon diffusion treatment, are preferably carried out under nitrogen partial pressure. To avoid oxidation during carburizing treatment and during transport to the quenching cell, the parts are not exposed to air at any time.

  The quenching operation, which generally follows the carburizing treatment, consists of rapidly cooling the parts. It is carried out either in a bath of oils or molten salts, or under high pressure gas and stirred, such as nitrogen, helium or various mixtures of neutral gases, such as carbon dioxide or hydrogen.

  These different operations, namely the different phases of the carburizing treatment are generally performed in the same chamber, the quenching being performed in a separate cell.

  Patent EP-A-0922778, in particular, describes a heat treatment plant comprising a plurality of cells for the heat treatment of a set of metal parts. The cells are all connected to a central chamber in equipression with the treatment cells. The parts are transferred from one cell to another via transport and handling rails. After carburizing in the corresponding cell, the cemented parts are transferred into the quenching cell through the central chamber, so there is no contact with the ambient air.

  Other installations consist of independent cells connected together by a mobile cell, whose function is either the loading and transfer operations to the quenching cell, or the loading, transfer and quenching operations simultaneously. under pressurized gas.

  Other installations consist of a single cell of the pushed trays type, partitioned and comprising an inlet lock and a quenching cell under gas.

  In all cases, all the phases of the cementation treatment, namely at least one carburization tempering phase, a phase of enrichment of the surface of the parts and a phase of diffusion of carbon from the surface to the core pieces, are performed successively in one and the same cell.

  OBJECT OF THE INVENTION The object of the invention is to overcome these drawbacks and is to design an efficient, flexible thermochemical processing machine capable of adapting and integrating into existing production lines of heat treatment. large parts.

  According to the invention, this object is achieved by the fact that the machine comprises at least one carburising temperature cell, a surface enrichment cell and a carbon diffusion cell, arranged one after the other , the cells being of standard shape and length adaptable to the duration of the treatment carried out in each cell, transfer means from one cell to the next and closure means for isolating a cell from adjacent cells during the treatment phases.

  According to a development of the invention, a cell comprising at least two bottoms and a standard section disposed between the bottoms, the desired length of a cell is obtained by setting up additional standard sections.

  According to a preferred embodiment, the carburizing, surface enrichment and carbon diffusion cells can be cold-walled.

  According to another development of the invention, the transfer between two cells is performed at a predetermined pressure.

Brief description of the drawings

  Other advantages and features will emerge more clearly from the following description of particular embodiments of the invention given as non-limiting examples and shown in the accompanying drawings, in which: FIG. 1 schematically represents a front view of a thermochemical treatment machine according to the invention comprising a plurality of treatment cells for carburizing.

  FIG. 2 schematically represents a view from above of an alternative embodiment of a thermochemical treatment machine according to the invention. FIG. 3 diagrammatically represents a particular embodiment of a surface enrichment cell of the thermochemical treatment machine according to FIG. 1.

  Description of particular embodiments

  In FIGS. 1 and 2, the heat treatment machine, for the low-pressure cementation of metal parts, comprises a plurality of processing cells 1 to 7, arranged one after the other. In the embodiment of FIG. 1, the cells are arranged alternately on each other, whereas, in the embodiment of FIG. 2, the cells, represented in plan view, are arranged alternately next to one another others. In any case, whatever the arrangement of the cells, each cell corresponds to a particular phase of the low pressure carburizing treatment and has a standard shape and a length L

adaptable.

  The machine includes a cell 1 for cleaning parts, to prepare the parts to be case hardened. By way of example, cell 1 is a washing or degreasing machine operating at atmospheric pressure or, possibly, partial pressure in the vapor phase.

  The machine comprises, after the cell 1 for cleaning parts, a cell 2 for preheating parts. For example, the cell 2 is a preheating furnace for heating the parts to a temperature, for example, of the order of 300 C to 500 C, before their introduction into the next cell. Preheating carried out in the cell 2 may result in particular oxidation of the parts and good activation of their surfaces. This phase is carried out in air at atmospheric pressure, preferably with a little additional nitrogen. Once the preheating phase is complete, the cell 2 is purged with vacuum before the transfer of the parts inside the next cell.

  Downstream of the cleaning cells 1 and preheating 2, the machine comprises a cell 3 of carburizing temperature. The treatment carried out in the cell 3 is intended to raise the temperature of the parts to the required carburizing temperature, of the order of 880 C to 1050 C. This phase is carried out at the cementation pressure, of the order of 5mbar at 20mbar, preferably with nitrogen. In special cases, the pressure can reach up to 100mbar.

  Downstream of the cementation temperature-setting cell 3, the machine comprises a cell 4 for surface enrichment. The treatment carried out in cell 4 consists in enriching the surface of the carbon, carbon and nitrogen parts in order to reinforce, after quenching, the hardness of the parts. This enrichment phase is carried out, for example, by an injection of nitrogen or of any other neutral gas, at a temperature of the order of 880 ° C. to 1050 ° C., supplemented at regular intervals by an injection of cementing gas. The pressure in the cell 4 is, for example, of the order of 5mbar and 20mbar depending on the cementing gas used. For example, in the case of the use of propane or acetylene as a cementing gas, the pressure inside the cell 4 is of the order of 10 to 12mbar. The nitrogen is injected continuously throughout the enrichment phase and, every 5 to 8 minutes, propane or acetylene, is injected for 1 to 3 minutes.

  After the surface enrichment cell 4, the pieces are transferred to a carbon diffusion cell 5. The treatment carried out in the cell 5 consists in diffusing the carbon in the thickness of the pieces, from the surface to the core of the pieces, according to the desired depth of the cemented surface and the desired percentage of carbon on the surface of the pieces. This phase of the treatment is carried out at the same pressure as that of the case-hardening and surface enrichment cells 4. The temperature is adjusted, preferably between 880.degree. C. and 1050.degree. C., to allow a good penetration rate. carbon in the parts and to obtain the optimal temperature of the parts before carrying out the quenching operation.

  Downstream of the cells 1 to 5, the machine also comprises a quenching cell 6, equipped with pressure-tight doors. For example, the cell 6 is a gas quenching cell, oil quenching, quenching in a salt bath or any other system for cooling the parts. In an alternative embodiment (not shown), the machine may comprise, downstream of the cell 5, two quenching cells, for example an oil quenching cell followed by a quenching cell under gas.

  The machine comprises, downstream of the quenching cell 6, a cell 7 of income. The income phase is carried out at a temperature, for example, of the order of 200 C to 300 C.

  Cells 1, 2 and 7, shown in Figures 1 and 2, are optional. Indeed, the machine for the low-pressure carburizing treatment can comprise only the cells 3, 4, 5 and 6, which correspond, respectively, to the three essential phases of a low-pressure carburizing treatment and to the quenching phase, which follows the cementation treatment. The treatment phases carried out upstream in cells 1 and 2 and downstream in cell 7 are only complementary and optional phases of the low-pressure cementation treatment.

  The three cells 3, 4, 5, corresponding to the three mandatory phases of low pressure carburizing treatment, are cold-walled, so as to be non-polluting and non-hazardous. The transfer of the parts between these three cells is carried out at a predetermined pressure, namely the cementation pressure, of the order of 5mbar to 20mbar. Pumping systems maintain the three cells in equipression, especially during the transfer periods.

  In the absence of cells 1 and 2, an upstream cell, constituting only an entry lock for parts intended to be case hardened, may be provided. In this case, care should be taken to perform a vacuum purge in the airlock, so that the pressure in the airlock is the same as that of the cell 3, before the introduction of the parts and that the air is almost completely purged.

  In all cases, the parts intended to be cemented pass compulsorily and successively, in order, by all the heat treatment cells arranged one after the other. The machine also comprises means for transferring a cell to the next and closure means for isolating a cell from adjacent cells during the different phases of the cementation treatment. For example, the machine comprises, between two adjacent cells, a compartment 9 adjacent to each cell for transferring parts. The compartments 9 of the machine have means for scrolling parts and may also include an isolation system from one cell to another during the processing phases.

  In FIG. 1, the cells are arranged on two levels, alternately low (cells 1, 3, 5 to 7) and high (cells 2 and 4). For example, the compartments 9 comprise elevators or elevators, in particular to go from a low cell (cells 1, 3, 5 to 7) to a high cell (cells 2 and 4). In FIG. 2, the cells are arranged on one level and the compartments 9 comprise, for example, transfer systems designed to move the parts from one cell to another.

  Moreover, the transfer between two adjacent cells, represented by arrows 8 in FIGS. 1 and 2, is performed at a predetermined pressure. The machine therefore comprises additional means (not shown) for adjusting and controlling the pressure during treatment, if necessary, during the transfer phases, inside the compartments 9.

  The closure means, intended to isolate a cell from adjacent cells during the treatment phases, may be constituted by any known means. In particular, the closure means disposed between the cell 2 for preheating the parts and the carburizing temperature-setting cell 3 comprise an optically sealed or pressure-tight door.

  By way of example, the cells 1 to 7 all have the same general shape, namely substantially cylindrical. In addition, according to the invention, at least the cells 3 to 5 are of standard form and of length L adaptable, which allows to precisely adjust the processing time of each cell for a given rate. The change of pace makes it possible, in particular, to reach different carburizing depths. The length L of a cell is therefore proportional to the duration of the treatment carried out in this cell.

  The cells 3 to 5 are shaped according to the same model, standard, adapted to each function (heating, enrichment and diffusion). In particular, as shown in FIG. 3, the surface enrichment cell 4 of the thermochemical treatment machine shown in FIG. 1 is of substantially cylindrical shape and comprises two curved bottoms 10, each of which can contain a load 11 of metal parts. Each bottom 10 is connected to a corresponding compartment 9, namely a compartment 9 for the arrival of the pieces (arrow pointing upwards) and a compartment 9 for the exit of the pieces (arrow pointing downwards). In Figure 1, the cell 4 is located on a high level. The load 11 is therefore transferred from the previous cell, for example, via an elevator and is transferred to the next cell also via, for example, an elevator. Cell 4, like cells 3 and 5, standard, also includes heating equipment, a gas injection circuit and pump outlets for vacuum pumps (not shown).

  Between the funds 10, the cell 4 comprises, like the cells 3 and 5, at least one standard section 12 which can contain two charges 11 being processed. The introduction of several sections 12 between the funds 10 makes it possible to vary the length L2 (FIGS. 1 and 2) of the cell 4. At the same rate, the greater the number of sections 12, the greater the degree of cementation. important.

  The loads 11 moving in the direction of the arrow D during the treatment, the more the number of sections 12 of a cell is important, the more parts spend time in the cell. Moreover, in FIG. 3, a load 11 is represented in dashed lines inside the cell 4, at the outlet compartment of the rooms, since there can not be at the same time a load 11 facing the compartment 9 input and a load 11 opposite the compartment 9 output.

  The lengths L1, L2 and L3 (FIGS. 1 and 2), respectively of the cells 3, 4 and 5, can therefore be different according to the number of standard sections 12 that they comprise. Cells with standard sections thus allow great adaptability of the machine to perform the desired treatment.

  The heat treatment machine described above therefore has the following advantages. The machine is cold outside and non polluting, thanks to the cold walls of the cells 3, 4 and 5. The cells being of standard shape and length adaptable thanks to the sections 12, they can be inserted in any workshop existing machining and in any mass production facility. Productivity is therefore greatly improved. The flexibility of the installation also allows, depending on the commands or heat treatments to be performed, to insert or not optional cells, including cleaning cells 1, preheating 2 and income 7.

  The invention is not limited to the embodiments described above. In particular, the parts to be treated may be constituted by sets of parts arranged on a support. The cells can have any suitable shape. The transfer and closure means may be constituted by any appropriate means for ensuring sealing properties and predetermined pressure between two adjacent cells. The cementing gas may be propane or any other hydrocarbon capable of associating with the temperatures of the enrichment cell 4 to treat the surface of the parts.

  After the income cell 7, the machine may comprise additional transfer means (not shown), intended to transfer the parts to another machine, for example, finishing treatment (shot blasting, grinding).

  A carbonitriding treatment may optionally be applied in cells 3, 4 and 5. The enrichment of nitrogen can then be carried out by introducing a gas such as ammonia (NH 3) into the surface enrichment cells 4 and 4. diffusion 5, at a rate to be determined according to the desired result.

Claims (12)

claims   1. Thermochemical treatment machine under low atmospheric pressure, for the cementation of metal parts, comprising means for setting carburizing temperature, surface enrichment means and carbon diffusion means from the surface to the core parts, respectively during a first phase, a second phase and a third successive treatment phase, characterized in that it comprises at least one cell (3) carburizing temperature, a cell (4) for enrichment surface and a carbon diffusion cell (5) arranged one after the other, the cells (3, 4, 5) being of standard shape and length (L) adaptable to the duration of the treatment carried out in each cell, means for transferring from one cell to the next and closure means for isolating a cell from adjacent cells during the processing phases.   2. Machine according to claim 1, characterized in that, a cell having at least two bottoms (10) and a standard section (12) disposed between the bottoms (10), the desired length (L) of a cell is obtained by setting up additional standard sections (12).   3. Machine according to one of claims 1 and 2, characterized in that the transfer between two cells is performed at a predetermined pressure.   4. Machine according to any one of claims 1 to 3, characterized in that the transfer means between cells comprise a compartment (9) adjacent to each cell.   5. Machine according to any one of claims 1 to 4, characterized in that the pressure inside the cells for heating (3), surface enrichment (4) and carbon diffusion (5) is of the order of 5mbar to 20mbar.   6. Machine according to any one of claims 1 to 5, characterized in that the cells for heating (3), surface enrichment (4) and carbon diffusion (5) are cold-walled.   7. Machine according to any one of claims 1 to 6, characterized in that the cell (4) for surface enrichment is maintained at a temperature of the order of 880 C to 1050 C.   8. Machine according to any one of claims 1 to 7, characterized in that it comprises a quenching cell (6) downstream of the carbon diffusion cell (5).   9. Machine according to claim 8, characterized in that it comprises, downstream of the cell (6) quenching, a cell (7) of income.   10. Machine according to any one of claims 1 to 9, characterized in that it comprises, upstream of the cell (3) carburizing temperature, a cell (2) for preheating parts.   11. Machine according to claim 10, characterized in that it comprises, upstream of the cell (2) for preheating parts, a cell (1) for cleaning parts.   12. Machine according to one of claims 10 and 11, characterized in that the closure means comprise, between the cell (2) for preheating parts and the cell (3) carburizing temperature, a sealed door to pressure.