EP1236810A1 - Process and apparatus for the partial thermochemical treatment of metallic workpieces - Google Patents

Abstract

Process for partially vacuum treating metallic workpieces comprises simultaneously treating several workpieces (1) with defined hollow chambers (2) in a molded body (11) and allowing a carbon-containing atmosphere to enter the hollow chambers of the workpiece. No thermo-chemical treatment takes place on the external surfaces of the workpiece. An Independent claim is also included for a device for carrying out the partial vacuum treatment of metallic workpieces. Preferred Features: At least one surface region of the hollow chamber of the workpiece is shielded against thermo-chemical treatment using a sleeve (8) whilst a further surface region of the hollow chamber is subjected to thermo-chemical treatment. The thermo-chemical treatment can be carried out using a plasma.

Description

The invention relates to a method for partial thermochemical Vacuum treatment of metallic workpieces according to the upper frame of claim 1 and a device therefor according to the preamble of claim 22.

The thermochemical treatment of workpieces made of metals in one Gas atmosphere from decomposable carbon and / or nitrogen compounds, possibly in a mixture with other gases, e.g. Inert gases and / or Hydrogen is known. DE 41 15 135 C1 describes a method for treating hollow bodies such as injection nozzles or of components with similarly difficult to access holes. In doing so the workpieces as bulk goods in the batch room without special arrangement or alignment placed. The result is a difficult to control Depth of penetration with a preference for the outer surfaces of the workpieces. If the outer surfaces are to be subsequently machined, so this is made difficult or impossible, because hardening after the Processing is ruled out due to the delay in hardness.

EP 0 818 555 A1 also deals with the carburizing of hollow bodies with blind holes, but the carburizing is preferred the outer surface of the hollow body takes place.

EP 0 695 813 A2 discloses the use of a carburizing agent Plasmas with a pulsating voltage between 200 and 2000 volts. Also however, the entire outer surface of the workpieces is always used carburized.

The applicant's company publication "Vacuum-assisted coaling processes with high pressure gas quenching ", Imprint: W2004d / 9.97 / 2000 / St, discloses complete processes in both a single chamber vacuum furnace as well as in a multi-chamber continuous system. Is described specifically the treatment of the outer surfaces of gear parts such as Gears and shafts. EP 0 313 888 B2 deals specifically with the High pressure gas quenching for hardening steel workpieces.

It is also known to workpieces in conventional gas carburizing partially carburize by not hardening outer "Sealed" surface areas with a covering paste. Such masking pastes are however neither for vacuum processes nor for plasma processes suitable because the masking pastes do not bombard the plasma with ions withstand. One has also tried threading through capsules or To cover the stopper mechanically, but it also comes through different dimensions easily to "crawl under" the covers, which is often laborious and causes destruction can be removed. They are also thermally treated Threads often no longer true to size after treatment.

From DE 29 20 719 A1 it is known individual ring-shaped workpieces such as gears, coupling parts, races for roller bearings and to carburize the like in zones by not carburizing Zones through reusable cladding against that Shields carbonization gas. This happens e.g. in that the end faces of the workpieces through disc-shaped molded parts made of metal or briquetted Metal powders are partially covered with annular flanges engage in the bore of the workpieces, an annular groove for the Protect the ends of the workpieces or are graduated. In each The largest proportion of the inner and outer surface areas should fall be exposed to the coal gas. By carburizing and Hardening of the outer surfaces will be followed by subsequent mechanical processing, e.g. difficult by threading. Ongoing manufacturing by placing it on a porous conveyor belt and transporting it through a continuous furnace is disclosed, but it is always the treatment of individual parts. Injection parts for engines and the Non-carburizing of the outside of these parts is not disclosed.

From WO 00/58531 A1 it is known when coating workpieces with aluminum and / or chrome and their connections the workpieces, e.g. the feet or roots of turbine blades, thereby against the influence of the coating material protect that these parts with reusable masks or caps with ceramic components that do not match the Workpieces react. However, it is always about "masking" individual workpieces and the coating of outer surfaces of the workpieces. Injection parts for engines are not disclosed, especially not the non-carburizing of all the outside of these parts.

It is also known from WO 99/13126 that a partial length, i.e. the end of tubular workpieces, e.g. Drill elements, thereby against to protect a thermochemical surface treatment that the End of the workpiece with a cap that the said partial length against the influence of thermochemical surface treatment shields. The largest part of the outer surface is the thermochemical Exposed to treatment. However, this is also the case "Masking" the ends of individual workpieces. Injection parts for engines are not disclosed.

From DE 35 02 144 A1 it is known that the inner surfaces of annular Workpieces with flat end faces such as slotted piston rings to protect against a nitriding treatment that these inner surfaces provides protection that e.g. from a copper coating, Nickel, chrome or tin exists. By axially lining up and congruent clamping of the end faces of several workpieces against each other on a carrier can also be achieved that only the cylindrical outer surfaces are exposed to the nitriding treatment. This is just the opposite of the invention in which all of the exterior surfaces should be protected against thermochemical treatment. For other than annular and plane-parallel workpieces the procedure is neither intended nor suitable.

From DE 28 51 983 B2 it is used when carburizing hollow bodies different wall thicknesses, e.g. for nozzles for diesel engines, known, the surface areas of the thin-walled sections in To accommodate wrappings in which a carburizing process with lower intensity than on the other surface areas, to avoid so-called "carbonization" and embrittlement. This also applies to the embodiment in which several thin-walled Sections of the nozzles through holes in a common, box-shaped cavity are introduced. For all embodiments applies, however, that all surface areas, including the outer surfaces of the Workpieces that are to be carburized and that the surroundings are both the thick-walled and the thin-walled sections of the hollow body throttled with each other, e.g. via the nozzle bores themselves, on the Participate in periodic gas changes in a vacuum oven. The carburization and subsequent hardening of the outer surfaces is for a subsequent one Machining the workpieces extremely disadvantageous.

1. Das Abdecken unregelmäßiger und/oder rauher Oberflächen, die z.B., durch Guß- oder Schmiedeverfahren entstanden sind, gegen das Eindringen von z.B. Kohlungsgasen gestaltet sich schwierig, wenn nicht gar unmöglich.

2. Beim Aufheizen auf die üblichen Temperaturen für Gasbehandlungen, die bei 900 °C und darüber durchgeführt werden, kann durch Wärmeverzug, unterschiedliche Ausdehnung etc. die Abdeckwirkung vermindert oder aufgehoben werden.

3. Dünnwandige Fortsätze von ansonsten dickwandigen Werkstücken neigen erheblich stärker zum Verspröden.

4. Beim partiellen Abdecken von Werkstücken kann durch unterschiedliche thermische Ausdehnungen die Grenze zwischen behandelten und unbehandelten Oberflächenbereichen während der Behandlung verschoben werden,

5. Werkstücke größerer Chargen, Insbesondere bei einer Serienfertigung sind in allen vorgegebenen Oberflächenbereichen identischen Verfahrensparametern auszusetzen.

None of the above writings deals with the following problem:

1. The covering of irregular and / or rough surfaces, which have arisen, for example, by casting or forging processes, against the penetration of, for example, carburizing gases, is difficult, if not impossible.

2. When heating to the usual temperatures for gas treatments, which are carried out at 900 ° C and above, the covering effect can be reduced or eliminated by heat distortion, different expansion, etc.

3. Thin-walled extensions of otherwise thick-walled workpieces are much more likely to become brittle.

4. When partially covering workpieces, the boundary between treated and untreated surface areas can be shifted during treatment due to different thermal expansions,

5. Workpieces of larger batches, in particular in series production, identical process parameters must be exposed in all specified surface areas.

The invention is therefore based on the object of a method of the beginning Specify the type described with which several workpieces or batches of many workpieces partially, i.e. only at precisely specified inner surface areas, especially in defined cavities of workpieces, precisely specified and of workpiece too Workpiece at least largely identical and over many treatment cycles reproducible process parameters are exposed. So it's not just about making the workpieces of a batch even to be partially treated, but also the work piece or work pieces below Batches.

The solution to the problem is the one specified at the beginning Method according to the invention by the features in the characteristic of Claim 1 and according to the invention in the device specified at the outset by the features in the characterizing part of the claim 22nd

The object is completely achieved by the invention, i.e. a method and a device of the type described at the outset Genre improved in that several workpieces with it or batches of many workpieces partially, i.e. only on precisely defined Surface areas in cavities of workpieces, thermochemically can be treated. This happens with precisely specified and at least largely identical from workpiece to workpiece and Process parameters that can be reproduced over many treatment cycles. It is especially about not only the workpieces of a batch evenly and partially treated, but also the workpieces subsequent batches, e.g. in continuous or quasi-continuous Processes.

The essence of the invention is the outer surfaces of the workpieces not to be treated thermochemically, e.g. carburizing, nevertheless the thermochemical treatment of the inner surfaces, in whole or in part.

To a certain extent, the invention is an inversion of the classic Procedure: It is no longer the largest part of the workpiece surface exposed to thermochemical gas treatment, with smaller ones Parts of the surface (s) covered against gas treatment or are isolated, but it is by the molded body according to the invention the entire outer workpiece surface, with one exception only of the inner surface areas to be treated, against the influence of gas protected. It is also not absolutely necessary that the Shaped body according to the invention the workpieces in complementary Shape without gaps and joints, but it is sufficient, e.g. at the Treating the interior of hollow workpieces To seal the molded body against the ends of the workpieces, if necessary with the interposition of sleeves, and between the sealing points in the To leave several mold cavities free inside the molded body Surround workpieces and in which no gas treatment can take place.

This makes it possible to work with almost any geometry and / or with irregular and / or rough surfaces, e.g. by casting or forging processes have arisen, exactly thermochemically treated areas and when heating to the usual Temperatures for gas treatments carried out at 800 ° C and above the influences of heat distortion, different Reduce extensions etc. on the masking effect or entirely off. Thin-walled extensions of otherwise thick-walled ones Workpieces are cooled more evenly and thus get one more favorable residual stress condition. The boundaries between treated and untreated surface areas are characterized by different thermal expansions no longer shifted during treatment. In particular, there are workpieces of larger batches in all predetermined surface areas identical process parameters exposed.

The use according to the invention of those which include the workpieces Shaped body and the shaped body itself, to a certain extent Represent housing, can be opened and also as boxes, Boxing or the like can be designated, allow after their messaging with the workpieces not only the transport in and through a Treatment plant with several process stages, but surprisingly also the most diverse treatments that occur in practice such as heating, carburizing (or embroidering), diffusing, quenching and aftertreatment in other systems (e.g. freezing and tempering), without the individual workpieces being "unpacked" and reloaded should be. This surprising effect applies in particular to the Case of high-pressure gas quenching to be carried out in a few seconds, such as in EP 0 313 888 B2 and in the introduction mentioned company publication of the same applicant is described.

As a thermochemical gas treatment can not only a vacuum gas treatment used without plasma excitation at pressures up to 30,000 Pa be in which the molded body and possibly also the intermediate Sleeves also made from an electrically non-conductive material Ceramics can exist. Rather, it is in particular also possible Apply the method of plasma treatment, wherein the shaped body for this case preferably from an electrically conductive material, preferably made of graphite, so that the molded body as an electrode (Cathode) for plasma excitation. More details and advantages result from the detailed description.

• jeweils mindestens ein Oberflächenbereich des Hohraums des Werkstücks durch eine eingesetzte Hülse gegen die thermochemische Behandlung abgeschirmt wird, während mindestens ein weiterer Oberflächenbereich des Hohlraums der thermochemischen Behandlung ausgesetzt wird,
• die thermochemische Behandlung unter Plasmaeinwirkung durchgeführt wird und wenn der Formkörper aus einem elektrisch leitfähigen Material besteht,
• ein Formkörper mit mehreren Formhohlräumen für die Ausnahme jeweils eines Werkstücks verwendet wird,
• der Formkörper als Gehäuse mit einem Oberteil ausgebildet ist und wenn zumindest das Oberteil Öffnungen aufweist, die mit den Hohlräumen in den Werkstücken kommunizieren und durch die die kohlenstoffhaltige Atmosphäre in die Werkstücke eintritt,
• zwischen nicht zu behandelnden Oberflächenbereichen der Werkstücke und dem Formkörper zur Abdichtung Hülsen eingesetzt werden,
• mehrere Formkörper zu einer Charge vereinigt werden,
• das Verfahren im Vakuumbereich zwischen 10 Pa und 3000 Pa, vorzugsweise zwischen 50 Pa und 1000 Pa, durchgeführt wird,
• das Verfahren mit Plasmaspannungen zwischen 200 und 2000 Volt, vorzugsweise zwischen 300 und 1000 Volt, durchgeführt wird,
• das Plasma impulsförmig eingesetzt wird, wobei vorzugsweise die Einschaltdauer zwischen 10 und 200 µs und die Pausendauer zwischen 10 und 500 µs gewählt werden,
• als kohlenstoffhaltiges Gas mindestens ein Kohlenwasserstoff aus der Gruppe Methan, Ethan, Propan und Azethylen ausgewählt wird,
• dem kohlenstoffhaltigen Gas mindestens ein Gas aus der Gruppe Argon, Stickstoff und Wasserstoff zugesetzt wird, wobei der Anteil des mindestens einen Kohlenwasserstoffes zwischen 10 und 90 Volumens-% gewählt wird,
• als Material für die Formkörper Grafit oder CFC verwendet wird, insbesondere wenn als Material für die Formkörper ein Werkstoff verwendet wird, der zumindest bis zu einer Temperatur von 1050°C, vorzugsweise bis 1200°C, keine Verzugserscheinungen aufweist,
• die plasmaseitigen Enden des mindestens einen Formhohlraums der Formkörper gegenüber dem jeweiligen Werkstück plasmadicht ausgebildet werden, und/oder, wenn
• die Werkstücke innerhalb des Formkörpers
• a) vor der Aufkohlung einem Aufheizvorgang,
• b) nach der Aufkohfung einem Diffusionsvorgang,
• c) nach dem Diffusionsvorgang einer Hochdruck-Gasabschreckung,
• d) nach der Hochdruck-Gasabschreckung einer Weiterbehandlung durch Tiefkühlung und Anlassen
ausgesetzt werden.

In the course of further refinements of the method according to the invention, it is particularly advantageous if - either individually or in combination:

• at least one surface area of the cavity of the workpiece is shielded from the thermochemical treatment by an inserted sleeve, while at least one further surface area of the cavity is exposed to the thermochemical treatment,
• the thermochemical treatment is carried out under the influence of plasma and if the shaped body consists of an electrically conductive material,
• a molded body with several mold cavities is used for the exception of one workpiece,
• the molded body is designed as a housing with an upper part and if at least the upper part has openings which communicate with the cavities in the workpieces and through which the carbon-containing atmosphere enters the workpieces,
• sleeves are used between surface areas of the workpieces not to be treated and the shaped body for sealing,
• several shaped bodies are combined into one batch,
• the process is carried out in a vacuum range between 10 Pa and 3000 Pa, preferably between 50 Pa and 1000 Pa,
• the method is carried out with plasma voltages between 200 and 2000 volts, preferably between 300 and 1000 volts,
• the plasma is used in pulse form, the duty cycle preferably being selected between 10 and 200 μs and the pause duration between 10 and 500 μs,
• at least one hydrocarbon from the group methane, ethane, propane and acetylene is selected as the carbon-containing gas,
• at least one gas from the group of argon, nitrogen and hydrogen is added to the carbon-containing gas, the proportion of the at least one hydrocarbon being chosen between 10 and 90% by volume,
• graphite or CFC is used as the material for the shaped bodies, in particular if a material is used as the material for the shaped bodies which has no signs of distortion at least up to a temperature of 1050 ° C., preferably up to 1200 ° C.,
• the plasma-side ends of the at least one mold cavity of the moldings are designed to be plasma-tight with respect to the respective workpiece, and / or if
• the workpieces within the molded body
• a) before the carburizing, a heating process,
• b) after the decarburization, a diffusion process,
• c) after the diffusion process of high pressure gas quenching,
• d) after high-pressure gas quenching, further treatment by freezing and tempering
get abandoned.

• der Formkörper als Gehäuse ausgebildet ist und aus einem elektrisch leitfähigen Werkstoff besteht und wenn die Werkstücke im Formhohlraum derart einschließbar sind, daß sich bei der Anwendung von Plasma zwischen dem Formkörper und den Werkstücken kein Plasma ausbildet,
• der Formkörper zum Behandeln von Werkstücken mit Hohlräumen, die einer thermochemischen Vakuumbehandlung ausgesetzt werden, mehrere Öffnungen besitzt, die mit den Hohlräumen der jeweils zugehörigen Werkstücke kommunizieren,
• der Formkörper als Gehäuse mit einem Oberteil ausgebildet ist und wenn zumindest das Oberteil mehrere Öffnungen aufweist, die mit den Hohlräumen in den jeweils zugehörigen Werkstücken kommunizieren,
• der Formkörper ein Unterteil aufweist, das mehrere Öffnungen aufweist, und wenn die Achsen der Öffnungen im Oberteil und im Unterteil fluchten,
• zwischen Unterteil und Oberteil eine auf dem Umfang umlaufende Trennfuge angeordnet ist, die eine teleskopartige Bewegung zwischen Unterteil und Oberteil ermöglicht,
• die plasmaseitigen Enden der Öffnungen im Formkörper gegenüber dem jeweiligen Werkstück plasmadicht ausgebildet sind,
• Hülsen vorgesehen sind, die zwischen dem Werkstück und dem Unterteil einerseits und dem Werkstück und dem Oberteil andererseits einsetzbar und derart an das Werkstück angepaßt sind, daß nicht zu behandelnde Oberflächenbereiche der Werkstücke von der thermochemischen Behandlung ausgesschlossen sind,
• mehrere Formkörper durch ein Transportgestell zu einer Charge vereinigt sind, insbesondere, wenn das Transportgestell Traversen zur Aufstellung von Formkörpern mit Abständen nebeneinander und übereinander aufweist,
• als Material für die Formkörper Grafit oder CFC verwendet wird, insbesondere wenn als Material für die Formkörper ein Werkstoff verwendet wird, der zumindest bis zu einer Temperatur von 1050°C, vorzugsweise bis 1200°C, keine Verzugserscheinungen aufweist, und/oder, wenn
• der Formkörper innerhalb einer evakuierbaren Kammer mit einem Einlaß für mindestens einen Kohlenwasserstoff angeordnet und als Katode für eine Plasmaausbildung geschaltet ist.

In the course of further refinements of the device according to the invention, it is particularly advantageous if - either individually or in combination:

• the molded body is designed as a housing and consists of an electrically conductive material and if the workpieces can be enclosed in the mold cavity in such a way that no plasma forms between the molded body and the workpieces when plasma is used,
• the shaped body for treating workpieces with cavities which are subjected to thermochemical vacuum treatment has a plurality of openings which communicate with the cavities of the respectively associated workpieces,
• the molded body is designed as a housing with an upper part and if at least the upper part has a plurality of openings which communicate with the cavities in the respectively associated workpieces,
• the shaped body has a lower part which has a plurality of openings, and if the axes of the openings in the upper part and in the lower part are aligned,
• a separating joint running around the circumference is arranged between the lower part and the upper part, which enables a telescopic movement between the lower part and the upper part,
• the plasma-side ends of the openings in the molded body are designed to be plasma-tight with respect to the respective workpiece,
• Sleeves are provided which can be inserted between the workpiece and the lower part on the one hand and the workpiece and the upper part on the other and are adapted to the workpiece in such a way that surface areas of the workpieces which are not to be treated are excluded from the thermochemical treatment,
• several shaped bodies are combined to form a batch by a transport frame, in particular if the transport frame has crossbeams for setting up shaped bodies with spacings next to and on top of one another
• graphite or CFC is used as the material for the shaped bodies, in particular if a material is used as the material for the shaped bodies which has no signs of distortion at least up to a temperature of 1050 ° C., preferably up to 1200 ° C., and / or if
• the molded body is arranged within an evacuable chamber with an inlet for at least one hydrocarbon and is connected as a cathode for plasma formation.

An embodiment of the subject of the invention and its mode of operation are subsequently based on Figures 1 to 6 in connection explained in more detail with a thermochemical plasma treatment.

Figur 1

einen halben Vertikalschnitt durch eines der Werkstücke innerhalb des Formkörpers quer zu dessen Längsachse ,

Figur 2

eine Draufsicht auf ein Ende eines Formkörpers für zahlreiche Werkstücke in verkleinertem Maßstab,

Figur 3

eine Seitenansicht eines Transportgestells mit einer Charge, bestehend aus zwölf Formkörpern, in drei Etagen,

Figur 4

eine weitere Seitenansicht des Gegenstandes nach Figur 3 aus einer um 90 Grad verdrehten Blickrichtung,

Figur 5

einen Längsschnitt durch eine Durchlaufanlage zur Behandlung von Chargen nach den Figuren 3 und 4 in stark schematisierter Darstellung und

Figur 6

einen Ausschnitt aus Figur 5 in vergrößertem Maßstab und mit zusätzlichen Details.

Show it:

Figure 1

a half vertical section through one of the workpieces within the shaped body transversely to its longitudinal axis,

Figure 2

a plan view of one end of a shaped body for numerous workpieces on a reduced scale,

Figure 3

a side view of a transport frame with a batch, consisting of twelve moldings, in three floors,

Figure 4

3 shows a further side view of the object according to FIG. 3 from a viewing direction rotated by 90 degrees,

Figure 5

a longitudinal section through a continuous system for the treatment of batches according to Figures 3 and 4 in a highly schematic representation and

Figure 6

a section of Figure 5 on an enlarged scale and with additional details.

1 shows a sleeve-shaped workpiece 1 with an axis A-A, which has a cavity 2 in the form of a stepped bore from which the strongly rimmed inner cylindrical surface areas 3, 4 and 5 and the surface area 6, an annular end face, carburized should be, but not the other surface areas. The highlighted surface areas 3, 4, 5 and 6 are in treatment exposed to a plasma in a carbon-containing atmosphere.

The workpiece 1 has a tubular extension 1a, the outside of which 1b must be protected against plasma bombardment. This happens through a sleeve 7 with a collar 7a, which the extension 1a with encloses the smallest possible play to prevent penetration of the plasma prevent. The sleeve 7 can be made of a metallic material, but also consist of a non-metal that does not react with the workpiece 1 received. In the upper end of the workpiece 1, the cavity 2 this point has a larger diameter, another sleeve 8 is with a collar 8a used, which has an annular gap with respect to the workpiece 9 leaves blank to compensate for tolerances and / or thermal expansion. It is important that no plasma can penetrate into a parting line 10. Also the sleeve 8 can also be made of a metallic material, but also consist of a non-metal that does not react with the workpiece 1 received. The workpiece 1 and the sleeves 7 and 8 form to a certain extent a rotationally symmetrical stack that described below Function. However, the rotational symmetry is not mandatory.

The stack described above is in a two-part molded body 11 used, which consists of a lower part 12 and an upper part 13, whose frames 12a and 13a are plasma-tight on a Z-shaped parting line 14 and reach over telescopically. The lower part 12 has an opening 12b, in which the sleeve 7 - again plasma-tight - is inserted, and that Upper part 13 has an opening 13b, the edge of which the collar 8a of the sleeve 8 - again plasma-tight - overlaps. The axes of the openings 12a and 13a are aligned. This supports the upper part 13, a kind Cover, on the stack from the workpiece 1 and the sleeves 7 and 8.

The clearly shown vertical play at the parting line 14 serves to tolerances and / or to compensate for thermal expansion. In which the workpiece As a result, the mold cavity 15 enclosing it cannot become plasma form. The mold cavity 15 can tightly enclose each workpiece, however, it can also form free spaces around the workpiece, if only ensured is that between the openings 12a and 13a and the workpiece and / or the sleeves 7 and 8 no plasma can penetrate. Free rooms favor the insertion of workpieces with different Geometries.

The molded body 11 is preferably made of graphite or CFC, which the required properties with regard to service life, reusability, Temperature resistance, thermal expansion coefficient and has electrical conductivity. The sleeves 7 and 8 are not mandatory required, but can be advantageous if the molded body 11 consists of graphite, which carburizes at unwanted points in the Workpiece could favor. In addition, the interchangeable Sleeves 7 and / or 8 as an adapter for inserting workpieces with serve different geometries.

It is understood that the arrangement of Figure 1 within the Shaped body 11 can repeat as often as required, which is shown in FIG. 2 is shown.

FIG. 2 now shows a top view of one end of such a shaped body 11 on a reduced scale, namely on the upper part 13 with a plurality of such openings 13b, but without workpieces, the Use in use corresponds to the number of openings 13b. That too here the mold cavity 15 can around each workpiece closed, but it can also around some or all workpieces be continuous around. Should such a molded body 11 only partially Workpieces are filled, it is sufficient to leave the otherwise free Close openings 12a and 13a by blind plugs.

Figures 3 and 4 show side views of a transport frame 16 with a batch 17 consisting of twelve moldings 11 in three floors. The Transport frame 16 consists of a rectangular frame structure, whose individual frame elements coincide with the edges of the cuboid. A multitude of extends through the frame structure horizontal traverses 18 on which the shaped bodies 11 rest.

FIG. 5 shows a longitudinal section through a continuous system 19 Treatment of batches 17 according to Figures 3 and 4 in a highly schematic Presentation. The continuous system 19 has a row arrangement - counted in the working direction - a total of five chambers 20, 21, 22, 23 and 24, which are separated by inner lock valves 25, 26, 27 and 28 are separated or separable. Located at the entrance to the continuous system 19 there is a feed gate 29 and at the exit a feed gate 30. Through the slider 28 and 30, the last chamber 24 is used Quenching chamber, at the same time as a discharge chamber.

The chamber 20 is a lock-in chamber and has a parking space for one Charge 17. Chamber 21 is a heating chamber and has spaces for three batches 17 and three circulation fans 31. The chamber 22 is one Carburizing chamber and has a space for a batch 17. The Chamber 23 is a diffusion chamber and has spaces for two batches 17. Chamber 24 is a cold high pressure quenching chamber and has a parking space for a batch 17, a circulation fan 32 and one Gas cooler 33. The number of batches 17 in chambers 21, 22, 23 and 24 and the resulting corrugation times and chamber lengths are open a specific cycle time of 30 minutes, for example.

The heating process in chamber 21 is thus 90 minutes, and during this time, the batches move up every 30 minutes every 17 minutes. The carburizing process in chamber 22 is thus a maximum of 30 minutes, can however within this time and after reaching the given Carburizing depth by interrupting the power supply for the Plasma generation can be stopped. The diffusion process in the Chamber 23 is therefore 60 minutes, and during this time the Batches every 17 minutes every 30 minutes. The quenching process in the Chamber 24 is therefore a maximum of 30 minutes, but experience has shown briefly ended. The batches 17 are transported by a well-known walking beam system, but not for the sake of simplicity is shown.

During all treatment processes, the workpieces 1 remain in the Shaped bodies, so they do not have to be "unpacked" and reloaded. It has surprisingly been found that the encapsulation in the moldings also no negative influence on processes other than carburizing, especially on high pressure gas quenching. Much more the workpieces can be used even after complete quenching and for further after-treatments remain in the shaped bodies, for example in another plant for deep-freezing by gaseous Nitrogen of up to -150 ° C for the residual transformation of austenite and subsequent tempering.

FIG. 6 shows a detail from FIG. 5 on an enlarged scale and with additional details. The carburizing chamber 22 is shown an array of heating rods 34 on either side of the transport path are arranged, and a stand 35, which rests on insulators 36. On this stator, which is not shown, is the negative pole of a pulse voltage source connected for plasma generation while the Chamber walls 22a are at ground potential. The gas supply lines too for the different possible hydrocarbons like methane, Ethane, propane and acetylene and possibly inert gases such as nitrogen and argon and possibly a reducing gas such as hydrogen and mixtures of these gases are shown as little as the suction port of one Vacuum pump set.

Example:

In a continuous vacuum system 19 according to FIGS. 5 and 6 Batches 17 with the arrangement described in Figures 1 to 3 and Training treated thermochemically. The cuboid shaped bodies 11 according to Figures 1 and 2 consisted of graphite and had the outer dimensions L = 500 mm, W = 100 mm and H = 60 mm. The spatial distribution the sleeve-shaped workpieces 1, which are made of a conventional case hardening steel passed, and the sleeves 7 and 8 corresponded to Figure 1 in connection with Figure 2. The cyclical operation of the system is described above. The cycle time of the system was 30 minutes. The gas atmosphere in the Chambers 21, 22 and 23 consisted of 50 volume percent methane, 25 volume percent argon and 25 volume percent hydrogen. The Pressures were around 100 Pa.

Batches 17 were individually charged via chamber 20 and first in chamber 21 within 90 minutes using the heating elements 34 heated to a temperature of 960 ° C. After that the last of the batches 17 for carburizing at 960 ° C in the chamber 22 transported, and the power supply of this batch was 17 switched on for 20 minutes. The pulsating or clocked Voltage was - 700 volts.

Then the carburized charge 17 was diffused for the absorbed Carbon is also transported into the chamber 23 at 960 ° C., in which, with a one-time conversion from the first to the second parking space vacated by spreading the last batch 60 minutes remained. The last batch was then 17 in the chamber 24 is spent and there with hardening of the carburized Sub-areas quenched taking into account the usual Z-T-U diagrams. Such a process is very detailed in EP 0 313 888 B2 described, so that further information is unnecessary here.

After the subsequent freezing with gaseous nitrogen from to to - 150 ° C and the usual tempering was applied to the carburized areas the workpieces 1 measured a hardness HV of over 700, and on a micrograph showed a very uniform hardening depth of 0.7 to 0.8 mm determined. The distortion of the workpieces was within the specified Tolerances, and the workpieces 1 were absolutely free of cracks. The moldings 11 could be used as often as required without being distorted.

As far as "defined" cavities 2 within a workpiece 1 are described, are those that occur during the thermochemical Treatment in at least one place from the outside for the Furnace atmosphere are accessible, for example by at least one the openings 12b and / or 13b assigned to each workpiece.

The surface area 6 to be treated, a circular ring-shaped end face, is assigned to the inner surface areas 3, 4 and 5, because this surface area 6 with the surface area 5, one Bore wall of the workpiece 11, is connected.

LIST OF REFERENCE NUMBERS

1

workpiece

1a

extension

1 b

outside

2

cavity

3

surface area

4

surface area

5

surface area

6

surface area

7

shell

7a

collar

8th

shell

8a

collar

9

annular gap

10

parting line

11

moldings

12

lower part

12a

frame

12b

opening

13

top

13a

frame

13b

opening

14

parting line

15

mold cavity

16

Caddy

17

Charge (n)

18

trusses

19

Continuous Flow System

20

chamber

21

chamber

22

chamber

22a

chamber walls

23

chamber

24

chamber

25

lock slider

26

lock slider

27

lock slider

28

lock slider

29

Einschleusschieber

30

Ausschleusschieber

31

circulating fan

32

circulating fan

33

gas cooler

34

heaters

35

stand

36

insulators

A-A

axis

Claims (35)

Method for partial thermochemical vacuum treatment of metallic workpieces (1), in particular for carburizing and case hardening of workpieces (1) made of case hardening steel in a carbon-containing atmosphere, surface areas (3, 4, 5, 6) to be treated and surface areas not to be treated colliding with one another, and wherein the surface areas not to be treated during the treatment of the remaining surface areas (3, 4, 5, 6) are covered by reusable moldings (11) made of a temperature-resistant material, characterized in that for the simultaneous treatment of several workpieces (1) with defined cavities (2) the workpieces (1) are accommodated in a molded body (11) with at least one mold cavity (15) and a plurality of openings (12b, 13b) through which the carbon-containing atmosphere enters the cavities (2) of the workpieces (1), the molded body (11) enclosing the workpieces (1) in such a way that no thermochemical treatment takes place in the outer surface areas of the workpieces (1), A method according to claim 1, characterized in that at least one surface area of the cavity (2) of the workpiece (1) is shielded from thermochemical treatment by an inserted sleeve (8), while at least one further surface area (3, 4, 5) of the Cavity (2) is exposed to thermochemical treatment, A method according to claim 1, characterized in that the thermochemical treatment is carried out under the action of plasma and that the molded body (11) consists of an electrically conductive material. A method according to claim 1, characterized in that a molded body (11) with a plurality of mold cavities (15) is used for receiving a workpiece (1). Method according to claim 1, characterized in that the molded body (11) is designed as a housing with an upper part (13) and that at least the upper part (13) has openings (13b) which are in contact with the cavities (2) in the workpieces (1 ) communicate and through which the carbon-containing atmosphere enters the workpieces (1). Method according to Claim 1, characterized in that sleeves (7, 8) are used for sealing between surface areas of the workpieces (1) and the shaped body (11) which are not to be treated. Method according to Claim 1, characterized in that a plurality of shaped bodies (11) are combined to form a batch (17). Process according to Claim 1, characterized in that the process is carried out in a vacuum range between 10 Pa and 3000 Pa, preferably between 50 Pa and 1000 Pa. Method according to claim 2, characterized in that the method is carried out with plasma voltages between 200 and 2000 volts, preferably between 300 and 1000 volts. Method according to Claim 9, characterized in that the plasma is used in the form of a pulse. A method according to claim 10, characterized in that the duty cycle between 10 and 200 µs and the pause duration between 10 and 500 µs are selected. Process according to Claim 1, characterized in that at least one hydrocarbon is selected from the group consisting of methane, ethane, propane and acetylene as the carbon-containing gas. A method according to claim 12, characterized in that at least one gas from the group of argon, nitrogen and hydrogen is added to the carbon-containing gas, the proportion of the at least one hydrocarbon being chosen between 10 and 90% by volume. Method according to claim 1, characterized in that graphite is used as the material for the shaped bodies (11). Method according to Claim 1, characterized in that CFC is used as the material for the shaped bodies (11). Method according to Claim 1, characterized in that a material is used as the material for the shaped bodies (11) which has no signs of distortion at least up to a temperature of 1050 ° C, preferably up to 1200 ° C. Method according to Claim 3, characterized in that the plasma-side ends of the at least one mold cavity (15) of the moldings (11) are designed to be plasma-tight with respect to the respective workpiece (1). Method according to Claim 1, characterized in that the workpieces (1) are subjected to a heating process inside the shaped body (11) before carburizing. Method according to claim 1, characterized in that the workpieces (1) within the shaped body (11) are subjected to a diffusion process after carburizing. A method according to claim 1, characterized in that the workpieces (1) within the molded body (11) are subjected to high-pressure gas quenching after the diffusion process. Method according to claim 1, characterized in that the workpieces (1) within the molded body (11) are subjected to at least one further treatment from the group of freezing and tempering after the high-pressure gas quenching. Device for use in a single-chamber system or in a multi-chamber continuous system for partial thermochemical vacuum treatment of metallic workpieces (1), in particular for carburizing and case hardening of workpieces (1) made of case hardening steel in a carbon-containing atmosphere, with surface areas (3, 4, 5 , 6) and surface areas that are not to be treated, and at least one reusable molded body (11) made of a temperature-resistant material is provided for covering surface areas that are not to be treated during the treatment of the other surface areas (3, 4, 5, 6), characterized in that a plurality of mold cavities (15) are provided in the molded body (11) for the insertion of several workpieces (1), the workpieces (1) being enclosable in the mold cavity (15) in such a way that on the outer surfaces of the workpieces (1 ) no thermochemical treatment takes place , Apparatus according to claim 22, characterized in that the molded body (11) is designed as a housing and consists of an electrically conductive material and that the workpieces (1) can be enclosed in the mold cavity (15) such that when plasma is used, there is between the molded body (11) and the workpieces (1) no plasma. Device according to Claim 22, characterized in that the shaped body (11) for treating the workpieces (1) with cavities (2) which are subjected to thermochemical vacuum treatment has a plurality of openings (12b, 13b) which are in contact with the cavities (2) communicate the associated workpieces (1). Apparatus according to claim 22, characterized in that the molded body (11) is designed as a housing with an upper part (13) and that at least the upper part (13) has a plurality of openings (13b) which correspond to the respective cavities with the cavities (2) Communicate workpieces (1). Device according to claim 25, characterized in that the shaped body (11) has a lower part (12) which has a plurality of openings (12b), and in that the axes of the openings (13a, 12a) in the upper part (13) and in the lower part (12 ) align. Apparatus according to claim 26, characterized in that between the lower part (12) and the upper part (13) of the shaped body (11) there is a circumferential parting line (14) which allows a telescopic movement between the lower part (12) and the upper part (13). allows. Apparatus according to claim 23, characterized in that the plasma-side ends of the openings (12b, 13b) in the molded body (11) are designed to be plasma-tight with respect to the respective workpiece (1). Device according to at least one of claims 22 to 28, characterized by sleeves (7, 8) which can be used between the workpiece (1) and the lower part (12) on the one hand and the workpiece (1) and the upper part (13) on the other and which are adapted to the workpiece (1) in such a way that surface areas of the workpieces (1) which are not to be treated are excluded from the thermochemical treatment. Apparatus according to claim 22, characterized in that a plurality of molded bodies (11) are combined to form a batch (17) by a transport frame (16). Apparatus according to claim 30, characterized in that the transport frame (16) has cross members (18) for the installation of shaped bodies (11) next to and above one another. Device according to claim 22, characterized in that the shaped body (11) consists of graphite. Device according to claim 22, characterized in that the shaped body (11) consists of CFC. Apparatus according to claim 22, characterized in that a material is used as the material for the molded body (11), which has no signs of distortion at least up to a temperature of 1050 ° C, preferably up to 1200 ° C. Apparatus according to claim 23, characterized in that the molded body (11) is arranged within an evacuable chamber (22) with an inlet for at least one hydrocarbon and is connected as a cathode for plasma formation.

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