Modular thermochemical surface treatment facility

Abstract

The present description relates to a thermochemical treatment facility (10) comprising a plurality of treatment cells (30, 40) and a common sealed enclosure (16) provided with handling means (22, 26) for transferring a feedstock (28) from one treatment cell to another, wherein one of the treatment cells is a nitriding cell (30) comprising a nitriding enclosure, which is intended to receive the feedstock (28), the common sealed enclosure (16) being movable or being permanently connected to the treatment cells (30, 40).

Description

DESCRIPTION TITLE: Modular Thermochemical Surface Treatment Plant This patent application claims priority from French patent application FR24 / 13867, which will be considered an integral part of this description. technical field

[0001] This description generally relates to a thermochemical surface treatment installation for parts. Previous technique

[0002] There are various types of thermochemical surface treatments for parts, such as steel parts, to modify their mechanical properties, particularly to increase wear resistance and surface hardness. One example of a thermochemical surface treatment is nitriding, which involves incorporating nitrogen into the surface layer of a part. Another example is carburizing, which involves incorporating carbon into the surface layer of a part. A further example is carbonitriding, or nitrocarburizing, which involves incorporating both carbon and nitrogen into the surface layer of a part.

[0003] It is known to use a treatment cell to perform carbonitriding, carburizing, nitriding, and / or nitrocarburizing treatments. A nitriding and / or carburizing gas is injected into the cell containing the part to be treated. One drawback is that it can be difficult to control with The precision of the nitrogen enrichment profiles of the treated parts is crucial. Furthermore, the treatment time can be lengthy. Additionally, nitriding can lead to unwanted carbon enrichment of the treated parts. The processing conditions for carbon and nitrogen enrichment within a single treatment cell create stressful atmospheres for the cell, resulting in rapid component wear compared to typical industrial applications. Moreover, the high-temperature mixing of gases used in these processes induces the formation of undesirable reaction byproducts, such as hydrogen cyanide (HCN) compounds.On the other hand, it is known to carry out the carbonitriding process in three successive stages, including an initial heating, nitriding and then cementation, each carried out in dedicated and separate cells.

[0004] Furthermore, for reasons of manufacturing cost and processing speed, it would be desirable to have a modular thermochemical treatment cell installation without a "muffle" type design and with the heating elements directly in the thermochemical treatment atmosphere.

[0005] It would be desirable for the nitriding, or nitrocarburizing, process to be carried out under a variable pressure thermochemical treatment atmosphere.

[0006] It would be desirable for the same thermochemical surface treatment plant to be easily used to perform different treatments, for example nitriding, carburizing, nitrocarburizing, and / or carbonitriding, while still allowing for a consistent profile. nitrogen enrichment, and possibly carbon enrichment, of the treated parts that can be precisely controlled. Summary of the invention

[0007] One embodiment overcomes all or part of the disadvantages of known thermochemical surface treatment installations for parts.

[0008] One embodiment provides for a thermochemical treatment installation comprising several treatment cells and a common sealed enclosure equipped with handling means for transferring a load from one treatment cell to another, in which one of the treatment cells is a nitriding cell comprising a nitriding enclosure, intended to receive the load, heating elements in direct contact with the load treatment atmosphere, and thermal insulation elements in direct contact with the load treatment atmosphere, the heating elements and the thermal insulation elements not containing graphite, the common sealed enclosure being mobile or being permanently connected to the treatment cells.

[0009] According to one embodiment, the heating elements are metallic or ceramic.

[0010] According to one embodiment, the nitriding cell comprises a cooled-walled metallic enclosure, in particular a double-walled cooled enclosure.

[0011] According to one embodiment, the heating elements and the thermal insulation elements are contained within the cooled double-walled metal enclosure.

[0012] According to one embodiment, one of the treatment cells is a cementation cell, having a different structure from the structure of the nitriding cell.

[0013] According to one embodiment, the thermochemical treatment installation further includes a cell for loading the charge from outside the thermal treatment installation and for unloading the charge to the outside of the thermal treatment installation.

[0014] According to one embodiment, the thermochemical treatment installation further includes a quenching or cooling cell, under fluid, the fluid comprising a gas and / or a liquid.

[0015] According to one embodiment, the common enclosure comprises a horizontally axisd cylinder and lateral extensions connected to the treatment cells, and the handling means comprise a trolley moving parallel to the axis of the cylinder and serving the treatment cells by means of a telescopic element.

[0016] According to one embodiment, the trolley moves on rails attached to the common sealed enclosure.

[0017] According to one embodiment, the common enclosure includes a trolley on which the common enclosure rests, the trolley being configured to move the common enclosure between the processing cells.

[0018] One embodiment also provides for the use of the thermochemical treatment plant as defined above comprising a heating step of the feed and a carbon enrichment or nitrogen enrichment step of the feed, the heating step being carried out in one of the treatment cells in which the nitriding or cementation steps are carried out.

[0019] According to one embodiment, a nitrogen enrichment operation of the feed in the nitriding cell is preceded by a heating step of the feed in the cementation cell and a carbon enrichment operation of the feed in the cementation cell is preceded by a heating step of the feed in the nitriding cell.

[0020] According to one embodiment, the nitrogen enrichment step of the feed is carried out in an atmosphere whose composition is controlled by a control system as a function of the pressure of the treatment atmosphere, said pressure ranging from 1000 Pa to 150000 Pa, said pressure being constant or variable. Brief description of the drawings

[0021] These features and advantages, as well as others, will be described in detail in the following description of particular embodiments, given by way of non-limiting example, in relation to the attached figures, among which:

[0022] Figure 1 represents, in a partial and schematic way, a top view of one embodiment of a modular thermochemical surface treatment installation;

[0023] Figure 2 represents, in a partial and schematic way, a side view in cross-section of the installation of Figure 1;

[0024] Figure 3 represents, in a partial and schematic way, one embodiment of a nitriding cell of the installation of Figure 1;

[0025] Figure 4 shows, in a partial and schematic manner, a top view of another embodiment of a modular thermochemical surface treatment installation; and

[0026] Figure 5 shows, in a partial and schematic manner, a side view in cross-section of the installation in Figure 4. Description of the embodiments

[0027] The same elements have been designated by the same reference numerals in the different figures. In particular, structural and / or functional elements common to the different embodiments may have the same reference numerals and may have identical structural, dimensional and material properties.

[0028] For the sake of clarity, only the steps and elements useful for understanding the implementation methods described have been represented and are detailed.

[0029] Unless otherwise specified, when referring to two connected elements, this means directly connected without any intermediate elements other than conductors, and when referring to two coupled elements, this means that these two elements can be connected or linked through one or more other elements.

[0030] In the description that follows, when referring to absolute position qualifiers, such as the terms "front", "back", "top", "bottom", "left", "right", etc., or relative position qualifiers, such as the terms "above", "below", "superior", "inferior", etc., or to orientation qualifiers, such as the terms "horizontal", "vertical", etc., unless otherwise specified, reference is made to the orientation of the figures or to a thermochemical surface treatment facility for parts in a normal operating position.

[0031] Unless otherwise specified, the expressions "approximately", "roughly", and "in the order of" mean to within 10% or 10°, preferably to within 5% or 5°.

[0032] Figure 1 illustrates in solid line a basic module 12 of a thermochemical surface treatment installation 10 according to one embodiment and in dashed line an additional module 14.

[0033] The basic module 12 comprises a sealed enclosure 16 in the form of a horizontally oriented cylinder. The two ends of this cylinder 16, fitted with flanges, are sealed by removable, watertight covers 18. Treatment cells 30, 40, 50, and 60 are connected laterally to the cylinder 16 and are located in the same horizontal plane. As an example, Figure 1 illustrates two thermochemical surface treatment cells 30 and 40 arranged opposite each other, a loading / unloading cell 50, and a quenching or cooling cell 60 positioned opposite the loading / unloading cell 50.

[0034] As can be seen more clearly in Figure 2, the cylindrical enclosure 16 has lateral cylindrical extensions 20 fitted with collars allowing the treatment cells to be fixed in a sealed manner, for example with bolts.

[0035] Conventionally, the communication openings between the heat treatment cells 30, 40 and the enclosure 16 are fitted with insulated doors 301, 401. In one embodiment, the doors 301, 401 are airtight. In another embodiment, the doors 301, 401 are not airtight, in cases where the pressure maintained in the enclosure 16, for example, on the order of 5 millibars (500 Pa), is the same as that required in the heat treatment cells 30, 40. The loading / unloading cell 50 and the quenching or cooling cell 60 are fitted with airtight doors. respectively 52 and 62, at the level of their communication openings with the enclosure 16. Indeed, the loading / unloading cell 50 has an external door 54 intended to insert the loads to be treated into the installation 10. The cell 50 must therefore be able to be brought to atmospheric pressure without disturbing the atmosphere of the enclosure 16. Similarly, in the cell 60, during quenching or cooling operations, there is a pressure generally higher than atmospheric pressure.

[0036] A handling device is in the form of a trolley 22 moving parallel to the axis of the cylinder 16. This trolley 22 moves, for example, on rails 24 extending along the length of the cylinder 16. The trolley 22 is equipped with a telescopic fork 26 which can extend from either side of the trolley 22 to the center of each of the cells 30, 40, 50, 60 to pick up and place a load 28 being processed. The load 28 corresponds, for example, to a set of parts, such as steel parts.

[0037] In Figure 1, the trolley 22 is positioned between cells 50 and 60, shown in solid line. The telescopic fork 26 enters cell 50 to pick up a load 28. Cell 50 has been pre-pressurized by the enclosure 16 to allow the door 52 to be opened. As shown in Figure 2, the load 28 rests on supports 29, raising it above the bottom of cell 50 and allowing the fork 26 to pass underneath. The fork 26 is raised to lift the load 28 from the supports 29, then retracted to bring the load 28 back onto the trolley 22. Next, the trolley 22 moves to the desired cell, for example, to the position shown in dashed line in Figure 1. The fork 26 is then extended and lowered to deposit the load 28 into the cell.

[0038] According to one embodiment, in the basic module 12 of the installation 10 in Figure 1 (shown in solid line), cell 30 is a nitriding cell, also called a nitriding furnace, and cell 40 is a carburizing cell, also called a carburizing furnace. Alternatively, the carburizing cell 40 is not present. Alternatively, cell 40 is also a nitriding cell, which allows two batches 28 to be processed practically simultaneously. The single quenching or cooling cell 60 is then sufficient because the quenching or cooling operation is particularly fast compared to the nitriding operations.

[0039] As shown in Figure 2, the installation can include a loading / unloading cell 50 and a quenching or cooling cell 60 using a gas or oil-based quenching fluid. Gas quenching is suitable for a wide range of materials. To achieve a good balance between the power required to circulate the quenching gas and the diversity of materials that can be quenched under gas, nitrogen or a mixture containing at least 50% nitrogen can be used.

[0040] The handling device 22, 26 is powered by conventional means. For example, the trolley 20 can move along the rails 24 thanks to an onboard electric motor equipped with a pinion that meshes with a rack positioned parallel to the rails. The telescopic fork 26 can be extended and retracted by a chain or lever system. Raising and lowering the fork can be achieved by a cam or eccentric system.

[0041] Figure 3 schematically represents an example of an embodiment of the nitriding cell 30. The nitriding cell 30 comprises a sealed enclosure 302 delimiting An internal volume 303 in which the charge to be treated 28 is placed on a suitable support 304. According to one embodiment, the enclosure 302 is a cooled-walled metallic enclosure, preferably a cooled double-walled metallic enclosure. In Figure 3, the door 301 of the nitriding cell 30 is not visible. The sealed enclosure 302 contains thermal insulation elements 305 that thermally insulate the internal volume 303 from the external environment. The pressure in the internal volume 303 can be controlled by means of an extraction line 306 connected to an extractor 307, comprising, for example, a vacuum pump. An injector 36 allows gases to be introduced in a distributed manner into the internal volume 303. As an example, gas inlets 308, 309, 310 respectively controlled by valves 312, 313, 314 have been shown. According to one embodiment, the temperature in the internal volume 303 is fixed by heating elements 316.According to one embodiment, the heating elements 316 are in direct contact with the treatment atmosphere present in the internal volume 303.

[0042] In one embodiment, the components within the internal volume 303 do not contain graphite. In particular, the sealed enclosure 302, the support 304, the thermal insulation elements 305, and the heating elements 316 do not contain graphite. In one embodiment, the sealed enclosure 302 is made of steel. In one embodiment, the support 304 is made of steel. In one embodiment, the thermal insulation elements 305 include a felt layer. In one embodiment, the heating elements 316 are metallic electrical resistors. In one embodiment, the heating elements 316 are made of metallic or ceramic material, and are composed, in particular, of selected materials. in the group comprising tungsten (W), molybdenum (Mo), alumina (Al2O3), or a mixture of these compounds. In one embodiment, the load 28 is directly exposed to the radiation emitted by the heating elements 316, i.e., there are no mechanical parts interposed between the load 28 and the heating elements 316. This advantageously allows for a faster temperature rise of the load 28 than that obtained when the heating elements 316 are located outside the internal volume 303, at least one of the walls of the enclosure 302 being interposed between the heating elements 316 and the load 28.

[0043] In one embodiment, the treatment carried out in the nitriding cell 30 comprises maintaining the feed 28 to be treated at a substantially constant temperature within the internal volume 303, and includes one or more nitrogen enrichment phases during which a nitriding gas is injected into the chamber. For example, the nitriding gas injected into the internal volume 303 is ammonia (NH3). Carrier gases, such as nitrogen (N2) and hydrogen (H2), may also be injected into the internal volume 303. The temperature in the nitriding cell 30 is adapted for nitrogen enrichment. In one embodiment, the temperature in the nitriding cell 30 is between 400 °C and 1000 °C. The pressure maintained in the internal volume 303 depends on the treatment being carried out. According to one embodiment, the pressure in the internal volume 303 varies between 10 mbar (1000 Pa) and 1500 mbar (150000 Pa).The durations of the enrichment and diffusion phases are adapted for nitrogen enrichment. This advantageously allows for precise and reproducible control of the nitrogen concentration profile obtained in the treated parts. Advantageously, since the nitriding cell 30 does not contain graphite elements, there is no unwanted carbon enrichment of the feed 28 during the nitriding process. Advantageously, since the nitriding cell 30 does not contain graphite elements, there is no formation of undesirable reaction byproducts, such as hydrogen cyanide (HCN) compounds.

[0044] According to one embodiment, the control of the atmosphere in the internal volume of the nitriding cell 30 allows treatment at different pressures, or allows the pressure to be varied during treatment, and takes into account the pressure of the nitriding cell 30 in addition to the measurements made by atmosphere sensors for the control of the atmosphere in the internal volume of the nitriding cell 30

[0045] The cementation cell 40 can have the same structure as the nitriding cell 30 except that it can include thermal insulation elements and heating elements containing graphite.

[0046] According to one embodiment, the treatment carried out in the carburizing cell 40 comprises maintaining the charge 28 to be treated within the chamber at a substantially constant temperature, and includes a single carbon enrichment phase during which a carburizing gas is injected into the chamber under reduced pressure and a carbon diffusion phase during which the injection of the carburizing gas is interrupted, or an alternation of carbon enrichment phases during which a carburizing gas is injected into the chamber under reduced pressure and nitrogen diffusion phases during which the injection of the carburizing gas is interrupted. For example, the carburizing gas injected into the internal volume 303 is acetylene (C2H2). Carriers, such as nitrogen (N2) and hydrogen (H2), can also be injected into the internal volume 303. The temperature in the carburizing cell 40 is adapted for carbon enrichment. In one embodiment, the temperature in the carburizing cell 40 is between 800 °C and 1200 °C. In another embodiment, the pressure in the enclosure of the carburizing cell 40 varies between 10 mbar (1000 Pa) and 1100 mbar (110,000 Pa). The durations of the enrichment and diffusion phases are adapted for carbon enrichment. This advantageously allows for precise and reproducible control of the carbon concentration profile obtained in the treated parts.

[0047] Referring again to Figure 1, if the plant's output is to be increased or additional processing capabilities are required, extra processing cells are needed. In this case, module 14, shown in dashed lines in Figure 1, is mounted on the basic plant. This module 14 comprises a cylindrical section 16' which is mounted as an extension of the cylindrical enclosure 16, replacing one of the covers 18. The removed cover 18 can then be used to close the free end of the cylindrical section 16'. As shown, module 14 may only have two additional cells, 30' and 40', connected opposite each other on the cylindrical section 16'.

[0048] Of course, additional modules can be mounted on the free ends of module 14 and base module 12 in place of covers 18. Several modules can thus be cascaded to create a heat treatment installation adapted to the user's needs.

[0049] In the case where the trolley 22 is mounted on rails 24, as shown, the module 14 may include 24' rails which connect to the 24 rails when module 14 is mounted on base module 12.

[0050] To access enclosure 16 or 16', simply remove one or both of the covers 18, which opens a corridor allowing a person to enter the installation and easily perform the necessary operations on the handling device 22, 26 and on the cells. If needed, the handling device is moved to one side or the other of the enclosure.

[0051] Figure 4 illustrates in solid line a basic module 12 of a thermochemical surface treatment installation 70 according to another embodiment and Figure 5 represents, in a partial and schematic way, a side view in cross-section of the installation of Figure 4.

[0052] The thermochemical surface treatment installation 70 shown in Figure 4 comprises all the elements of the thermochemical surface treatment installation 10 shown in Figure 1, except that the enclosure 16 and the covers 18 are not present, and it includes an enclosure 72 resting on the trolley 22, visible in Figure 5, configured to move the enclosure 72 between cells 50, 30, 40, 60. The trolley 22 can be a wheeled vehicle or a vehicle moving on rails, as in the installation 10 shown in Figure 1. The enclosure 72 is equipped with at least one door 76, two doors 76 being shown as an example in Figure 4. The doors 76 are preferably thermally insulated and airtight.

[0053] To transport the load 28 from one cell to another, the trolley 22 is moved until the enclosure 72 is in contact with the cell into which the load 28 is to be taken or placed. In Figure 4, the enclosure 72 is in contact with cell 50. The door 76 of the enclosure 72 facing cell 50 is open and the door 52 The cell 50 is opened, so that the internal volume of the enclosure 72 communicates with the internal volume of the cell 50. The telescopic fork 26 is extended to enter the cell 50 and pick up the load 28. The fork 26 is then raised to lift the load 28 from the supports 29, and then retracted to return the load 28 to the enclosure 72 of the trolley 22. Next, the trolley 22 is moved to another cell into which the load 28 is to be deposited. When the enclosure 72 is moved by the trolley, the doors 76 are closed so that the enclosure 72 is sealed. The telescopic fork 26 is then completely contained within the enclosure 72.

[0054] Various embodiments and variations have been described. A person skilled in the art will understand that some features of these various embodiments and variations could be combined, and other variations will become apparent to a person skilled in the art.

[0055] Finally, the practical implementation of the described methods and variants is within the reach of the person in the trade, based on the functional indications given above.

Claims

DEMANDS 1. Thermochemical treatment installation (10; 70) comprising several treatment cells (30, 40) and a common sealed enclosure (16; 72) equipped with handling means (22, 26) for transferring a charge (28) from one treatment cell to another, in which one of the treatment cells is a nitriding cell (30) comprising a nitriding enclosure (302) , intended to receive the charge (28) , heating elements (316) in direct contact with the charge treatment atmosphere (28) , and thermal insulation elements (305) in direct contact with the charge treatment atmosphere (28) , the heating elements (316) and the thermal insulation elements (305) not containing graphite, the common sealed enclosure (16; 72) being mobile or being permanently connected to the treatment cells (30, 40).

2. Thermochemical treatment installation according to claim 1, wherein the heating elements (316) are metallic or ceramic.

3. Thermochemical treatment installation according to claim 1, in which the nitriding cell (30) comprises a cooled-walled metallic enclosure (302), in particular a cooled double-walled enclosure.

4. Thermochemical treatment installation according to claim 3, in which the heating elements (316) and the thermal insulation elements (305) are contained in the cooled double-walled metal enclosure (302).

5. Thermochemical treatment installation according to any one of claims 1 to 4, wherein one of the treatment cells is a cementation cell (40) , having a different structure from the structure of the nitriding cell (30) .

6. Thermochemical treatment installation according to any one of claims 1 to 5, further comprising a charge loading cell (28) from outside the heat treatment installation and a charge unloading cell (28) to outside the heat treatment installation.

7. Thermochemical treatment installation according to any one of claims 1 to 6, further comprising a quenching or cooling cell, under fluid (60), the fluid comprising a gas and / or a liquid.

8. Thermochemical treatment installation according to any one of claims 1 to 7, wherein the common enclosure comprises a horizontally axisd cylinder (16) and lateral extensions (20) connected to the treatment cells (30, 40) and wherein the handling means comprise a trolley (22) moving parallel to the axis of the cylinder (16) and serving the treatment cells (30, 40) by means of a telescopic element (26).

9. Thermochemical treatment installation according to claim 8, in which the trolley (22) moves on rails (24) integral with the common sealed enclosure (16).

10. Thermochemical treatment installation according to any one of claims 1 to 7, comprising a trolley (22) on which rests the common enclosure (72), the trolley (22) being configured to move the common enclosure (72) between the treatment cells (30, 40). 18 11. Use of the thermochemical treatment plant (10; 70) according to any one of claims 1 to 10, comprising a heating step of the feed (28) and a carbon enrichment or nitrogen enrichment step of the feed (28), the heating step being carried out in one of the treatment cells (30, 40) in which the nitriding or cementation steps are carried out.

12. Use according to claim 11, wherein the thermochemical treatment plant (10; 70) is according to claim 5, wherein a nitrogen enrichment operation of the feed (28) in the nitriding cell (30) is preceded by a heating step of the feed (28) in the carburizing cell (40) and wherein a carbon enrichment operation of the feed (28) in the carburizing cell (40) is preceded by a heating step of the feed (28) in the nitriding cell (30).

13. Use according to claim 11 or 12, wherein the nitrogen enrichment step of the feed (28) is carried out in an atmosphere whose composition is controlled by a control system as a function of the pressure of the treatment atmosphere, said pressure ranging from 1000 Pa to 150000 Pa, said pressure being constant or variable.

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