EP1294512B1 - Method and device for sintering aluminium based sintered parts - Google Patents

Abstract

The invention relates to a method for sintering aluminium-based sintered parts which are, initially, guided with the aid of a transport system T through a de-binding area (3) before being guided through followed by a sintering area (2) and finally being guided through a cooling area (4). Inert gas atmosphere prevails in the sintering area (2), provided with an oxygen content, corresponding to a thawing point of, maximum, 40° C. The sintered parts (23) are heated to the required sintering temperature of 560-620° C., by means of convection, whereby the inert gas atmosphere is accordingly heated, flowing around said sintered parts in a corresponding manner.

Description

a) die Sinterteile werden entbindert;

b) die Sinterteile werden auf Sintertemperatur gebracht und auf dieser eine bestimmte Zeit gehalten;

c) die Sinterteile werden kontrolliert abgekühlt;

sowie
eine Vorrichtung zum Sintern von Aluminium-basierten Sinterteilen mit

a) einem Entbinderungsbereich, in dem die Sinterteile durch Erwärmen von Bindehilfsmitteln befreit werden;

b) einem Sinterbereich, in dem die Sinterteile durch Erwärmen auf Sintertemperatur einem Sinterungsprozeß unterzogen werden und der hierzu entsprechende Heizeinrichtungen aufweist;

c) einem Kühlbereich, in dem die Sinterteile nach dem Sinterungsprozeß kontrolliert abkühlbar sind,

d) einem Transportsystem, welches die Sinterteile kontinuierlich durch die verschiedenen Bereiche führt;

e) Schleusen, welche die Atmosphären der verschiedenen Bereiche getrennt halten und die von den Sinterteilen beim Verlassen eines bestimmten Bereiches durchquert werden müssen.

The invention relates to a method for sintering aluminum-based sintered parts, the sintered parts being passed continuously through a sintering furnace, in which the following steps are carried out in separate atmospheres in spatially separated areas:

a) the sintered parts are debindered;

b) the sintered parts are brought to the sintering temperature and held there for a certain time;

c) the sintered parts are cooled in a controlled manner;

such as
a device for sintering aluminum-based sintered parts with

a) a debinding area in which the sintered parts are freed of heating aids by heating;

b) a sintering area in which the sintered parts are subjected to a sintering process by heating to the sintering temperature and which has heating devices corresponding thereto;

c) a cooling area in which the sintered parts can be cooled in a controlled manner after the sintering process,

d) a transport system that continuously guides the sintered parts through the different areas;

e) Locks which keep the atmospheres of the different areas separate and which have to be crossed by the sintered parts when leaving a certain area.

The sintering of aluminum wins in view of the positive Properties that adhere to this metal on the most diverse technical fields, but especially in Automotive engineering, increasingly important. In the latter The area of application plays particularly the weight saving a big role with the use of aluminum connected is.

In general, pure aluminum powder is not processed; rather, powder mixtures are preferred or alloyed powders, which are used in particular as Additional silicon included. All powders that are important Component containing aluminum are summarized here Called "aluminum-based" and are at risk of to form oxides during sintering. Are particularly desired Aluminum sintered parts with a relatively high silicon content. However, with increasing silicon content the the sintering process more difficult. Another difficulty when sintering aluminum-based powders consists of that they have a higher content of binding agents during the pressing process need. For example, during sintering of iron such binding agents, which simultaneously serve as a lubricant for the press tool, a Make up a content of about 0.7 to 1.0 percent by weight, need about 1.0 to 1.5 percent by weight to sinter aluminum Binding aids are added. These binding aids must be complete again before the sintering process be removed. Overall, all the requirements are Accuracy, reproducibility and homogeneity the temperature distribution when sintering aluminum-based Powder much more critical than when sintering other powder, especially iron. For this So far, aluminum sintered parts are not yet wherever this is used for and on would be desirable.

A method and a device of the aforementioned Kind are described in DE-PS 197 19 203. This concerns a sintering process for Molded parts made of metal powder, for which purpose linguistically aluminum powder would also be counted. But actually this method and device are only for sintering determined from iron-based powders, since only for such Powder the rapid cooling of the sintered parts claimed there under a "Maitensitstartlinie" is conceivable.

It is also known from GB-B-1 115 465 a process for sintering Al-based parts in a muffle furnace under controlled conditions (Dew point and temperature).

The object of the present invention is a method of the type mentioned above, with the high quality Aluminum-based sintered parts can be produced.

This object is achieved in that in process step b) an inert gas as the atmosphere is used, the oxygen content of a dew point of at most -40 ° C, and that the sintered parts by circulating the appropriately heated inert Gases heated to a sintering temperature of 560 - 620 ° C. become.

The invention is therefore based on a double finding: Because the oxygen content of the inert atmosphere a maximum limit is guaranteed that there are no undesirable oxides in the sintering process can form, which adversely affects the sintering product influence. In that, unlike the subject of above-mentioned DE-PS 197 19 203 not the sintered parts by radiant heat but by convection heat be heated, for which the aforementioned high purity inert Gas is put into a circulation flow takes place the heating of the sintered parts with a homogeneity, that could not be achieved otherwise. Only in total These characteristics result in the high quality desired of the sintered products.

Nitrogen is preferably used as the inert gas. This leaves is commercial with the required purity available and compared to noble gases, which are basically could also be considered, much cheaper.

Another object of the present invention is a To design the device of the type mentioned at the beginning that they are going to manufacture high quality aluminum-based Sintered parts are suitable.

f) die Atmosphäre im Sinterbereich von einem inerten Gas gebildet wird, dessen Sauerstoffgehalt einen Taupunkt von höchstens -40° C entspricht;

g) der Sinterbereich mindestens eine Heizeinrichtung für die Sinterteile aufweist, die indirekt beheizte Wärmetauschflächen, ein Gebläse und eine Luftleiteinrichtung derart umfaßt, daß sich eine die Sinterteile umfließende Zirkulationsströmung des inerten Gases einstellen läßt.

This object is achieved in that

f) the atmosphere in the sintered area is formed by an inert gas, the oxygen content of which corresponds to a dew point of at most -40 ° C;

g) the sintered area has at least one heating device for the sintered parts, which comprises indirectly heated heat exchange surfaces, a blower and an air guiding device such that a circulating flow of the inert gas flowing around the sintered parts can be set.

The meaning of these characteristics and the achievable with them Advantages coincide with what above for the invention Procedure was said.

The advantages of those specified in claims 4 and 5 Exemplary embodiments were described above with reference to the invention Procedure already indicated.

The sintering area of a sintering device must have a length have at the selected transport speed corresponds to the time required for sintering. In general it is recommended if a longer sintering area has several has zones delimited by partitions, each a heating device with heat exchange surfaces, blower and have air equipment. This allows defined everywhere even with longer sintering areas Set flow conditions.

Especially in the heating zone of the sintered area the temperature of the inert gas in the direction of movement successive zones of the sintered area differ.

To particularly good sintering results because of the high The design leads to homogeneity of the temperature profile of the invention, in which the flow around the sintered parts in zones one behind the other in the direction of movement of the sintered area is different. So they can Sintered parts, for example, once from bottom to top, the other time from top to bottom, the one time from one rotating clockwise Flow, the other time from one moving seen flowing counter-clockwise become.

It is also advantageous if a nozzle plate is provided over which the circulating inert gas is opposed the sintered parts is straightened. This allows the flow in the area of the sintered parts and thus also the warming that the sintered parts experience continues equalize.

As already mentioned above, careful cleaning plays a role a very special atmosphere in the sintering area Role. As a result, the sintered parts must be introduced in the sintering area and discharge from the sintering area special attention. Especially It is preferred if the gates of the locks that adjacent to the inlet and / or outlet of the sintered area are not fully sealable and if the inert gas in the sintering area is under pressure stands. Because of the wanted "leak" in that of the two Lock gates, which are adjacent to the sintering area is a purging flow of the inert gas out of the sintering area into the respective lock maintain with which on the one hand the Interior of the lock is flushed and with the other hand the penetration of foreign atmosphere from the lock into the sintering area is prevented.

Figur 1

schematisch einen Sinterofen zum Sintern von Aluminium-basierten Sinterteilen;

Figur 2

einen Schnitt in vergrößertem Maßstab durch den Sinterofen von Figur 1 im Bereich der Sinterzone.

An embodiment of the invention is explained below with reference to the drawing; show it

Figure 1

schematically shows a sintering furnace for sintering aluminum-based sintered parts;

Figure 2

a section on an enlarged scale through the sintering furnace of Figure 1 in the region of the sintering zone.

FIG. 1b shows a sintering furnace in vertical section, designed for sintering aluminum-based sintered parts is. The entire sintering furnace is divided into different zones or Area divided into the mapping in Figure la Figure 1b are shown schematically. The ones to be sintered Parts 23 (see FIG. 2) are made using a transport system T in the continuous run in the drawing led from left to right through the sintering furnace. The Sintering furnace contains one after the other, as seen in the conveying direction an inlet area 8, a debinding area 3, a Sintering area 2, a cooling area 4 and an outlet area 9. Each of these areas 2, 3, 4, 8, 9 of the sintering furnace is a separately driven and controllable conveyor Associated with T2 through T9, which together form the above Form conveyor system T.

To isolate the atmospheres in areas 3, 2, 4 and 9, locks 7 are arranged between these areas, which each have two mechanical gates 6. These gates 6 are each in a front shaft of the corresponding Area 3, 2, 4, 9 arranged and preferably vertically movable, each lock 7 also separately controllable and adjustable conveyor (in the drawing not shown) is assigned.

Details of the locks 7 can be seen in FIG. 4 or the above mentioned DE-PS 197 19 203 are taken.

The one preceding the sintered area 2 in the conveying direction Debinding area 3 is designed as a muffle furnace. That is, above and below the movement path of the to sintered parts there is a partition 20 through electric heating elements 21 or the like at temperature brought, essentially by radiant heat the sintered parts conveyed past are heated and from them drives out the binding aids.

While in the described in DE-PS 197 19 203.3, Sintering furnace intended for sintering iron powder parts the sintered area also works with radiant heat, the sintered area 2 of the present differs Sintering furnace thereof in a manner that is now based on of Figure 2 is described.

Figure 2 shows a section perpendicular to the direction of movement of the sintered parts in the area of the sintering zone 2. The housing 22 provided with insulation is on all places where air can enter the outside atmosphere or the escape of gases the interior atmosphere would be possible, well sealed. in the The lower area of the housing 22 is the transport system T2 shown, the exact construction deliberately open is left. It is characterized by good gas permeability in the vertical direction; particularly suitable are, for example, roller or link belt systems. With the help of the transport system T2, the sintered parts 23 conveyed perpendicular to the plane of Figure 2, in illustrated example on a carrier plate 24, the ideally well permeable even in the vertical direction should be.

The area of the interior lying above the sintered parts 23 of the housing 22 is parallel to one another Direction of movement of the sintered parts 23 and substantially vertically extending partition 25 in two chambers 26 and 27 divided. In the one on the left in Figure 2 Chamber 26 contains the heat exchanger surfaces 28 an indirect heater 29, for example electrically can be operated. Located at the top of chamber 26 air baffles with a central opening 30, which represents the suction opening of a blower 31.

The fan 31 is by a on the top of the Housing 22 attached motor 32 driven.

The outlet side of the fan 31 stands over an opening 33 with the chamber 27 on the right in FIG. 2 of the interior of the housing 22 in connection. This chamber 27 is at her lower end, just above the sintered parts 23, through a nozzle plate 34 completed.

The entire sintered area 2 contains, in particular FIG. 1b shows a plurality of identical, sintering zones constructed in the manner described above, which are separated from one another by partitions 35. The partitions 35 essentially only contain openings, which just allow the passage of the sintered parts 23.

The cooling area 4 is essentially the same Designed as in DE-PS 197 19 203.3 is described. The way in which the sintered parts temperature controlled and cooled in this area are not of interest in the present context. This is also shown in the drawing a kind of "muffle furnace" with a similar construction, like it is used in the debinding zone 3.

The sintering furnace described works as follows:

The pressed sintered parts 23 are in the inlet area 8th placed on the conveyor system T8, from this on a simple gate 6 is introduced into the debinding zone 3 and taken over by the T3 conveyor system there. With help the radiated heat emitted by the heated partition walls 20 the binding aids from the sintered parts 23 expelled and essentially subtracted. Since all inner surfaces in the debinding zone 3 are hot, there is a risk of "sooting up" No binding aids. The sintered parts 23 occur individually or in small groups next to and / or one above the other Sintered parts 23 through the first gate of the Lock 7 that between the Entbinderungsbereich 3 and the sintered area 2 lies in the space between the two gates of this lock 7. That for the sintering area 2 leading second gate of this lock 7 remains closed. Alternatively, it is possible to use this second goal to keep open with a small gap and that Interior of the sintering area 2 of the sintering furnace 1 below operate with a certain pressure. Then constantly from the sintering area 2 the gas atmosphere prevailing there, which will be discussed below in the space lick between the two gates of lock 7 and rinse this space.

After the group of sintered parts 23 into the lock 7 has occurred, the first becomes debinding zone 3 leading gate closed and the gap between the lock 7 rinsed and / or pumped out. The sintered parts 23 are thereby, as already mentioned above, from its own transport system T7 promoted, the speed of which varies the speed in the other areas of the sintering furnace can make a brief distinction to the overall system hold.

After a certain time in the lock 7 the gate adjacent to the sintered area 2 opens the lock 7. The sintered parts 23 are now on the Transfer conveyor system T2 and from it to a heating zone which, for example, are passed through the extends through the first three zones of the sintered region 2. In the other zones of the sintering area 2 the actual sintering at a temperature between 560 and 620 ° C instead.

The temperature of the existing in the individual zones Gas is released by one near the movement path of the sintered parts 23 arranged temperature sensor 40 (cf. FIG. 2) who monitors the via a control loop Heater 29 controls.

All zones of the sintering area 2 are, as already above noted, essentially in that shown in Figure 2 Set up in such a way and with high purity nitrogen as inert Atmosphere filled. The oxygen content in this inert atmosphere may not exceed a dew point of - correspond to 40 ° C. In each zone of the sintering area 2 is a circulating current with the help of a fan 31 Maintain nitrogen atmosphere, which, in the area the left chamber 26 coming from below, on the heat exchanger surfaces 28 of the respective heater 29 by the chamber 26 to the blower 31, from there into the chamber 27 and through the nozzle plate 34 onto the sintered parts 23 is directed. These hot nitrogen gases flow around the sintered parts 23 penetrate the carrier plate 24 and the transport system T22 and from there again supplied to the heater 29, whereby the circuit is closed is.

Low leakage losses of the inert atmosphere within the Zones of the sintered area 2 are identified by corresponding ones Fresh gas supply balanced. The temperature at the inlet The heater 29 should differ from the temperature at the outlet distinguish the heater 29 as little as possible. This is synonymous with the statement that the circulating Nitrogen gases inside the housing 22 everywhere have substantially the same temperature.

To ensure uniform heating of the sintered parts 23 further improve, it is possible to change the flow direction of the nitrogen gases in the individual zones of the To have sintered area 2 alternated. In particular it is conceivable the flow in the area of the sintered parts 23 alternately from top to bottom and from bottom to bottom to let flow above.

At the end of the sintering area 2, the sintered parts pass through 23 between the sintering area 2 and the cooling area 4 lying, two gates including lock 7, where appropriate the same operations take place as above for between the debinding area 3 and the sintering area 2 lying lock 7 was explained. In the cooling area 4 then finds a controlled cooling of the finished sintered parts to a temperature at which the Sintered parts 23 via a further lock 7 from the Exit cooling area 4 and finally in the outlet area 9 removed or closed by the local conveyor system T9 can be transported to another location.

Claims (10)

1. A process for sintering aluminium-based sintered parts, the parts to be sintered being moved through a sintering furnace in a continuous pass, in which process the following steps are carried out in separate atmospheres and in spatially separate areas in each case:

   a) the parts to be sintered are de-bindered;

   b) the parts to be sintered are heated to sintering temperature and maintained at this temperature for a given time;

   c) the sintered parts are cooled in a controlled manner,

   characterised in that
   in process step b) an inert gas the oxygen content of which corresponds to a dew point not higher than -40°C is used as the atmosphere, and in that the parts (23) for sintering are heated to a sintering temperature of 560 to 620°C by circulation of the correspondingly heated inert gas.
2. Process according to claim 1, characterised in that nitrogen is used as the inert gas.
3. A device for sintering aluminium-based sintered parts, comprising

   a) a de-bindering area (3) in which the parts to be sintered are stripped of binding agents by heating;

   b) a sintering area (2) in which the parts to be sintered are subjected to a sintering process by heating to sintering temperature, which area has suitable heating arrangements for this purpose;

   c) a cooling area (4) in which the sintered parts can be cooled in a controlled manner after the sintering process;

   d) a transport system (T2-T4, T7-T9) which continuously conveys the parts for sintering through the different areas;

   e) airlocks (7) which keep the atmospheres of the different areas separate and through which the parts for sintering must pass on leaving a particular area, the sintering area being connected to an inert gas source,

   characterised in that

   f) the atmosphere in the sintering area (2) is formed by an inert gas the oxygen content of which corresponds to a dew point not higher than - 40°C;

   g) the sintering area (2) has at least one heating arrangement for the parts (23) for sintering which includes indirectly heated heat exchanging surfaces (28), a fan (31) and an air guidance arrangement (25) such that a circulating flow of the inert gas around the parts (23) for sintering can be induced.
4. Device according to claim 3, characterised in that the inert gas is nitrogen.
5. Device according to claim 3 or 4, characterised in that the inert gas is at a temperature of 560 to 620°C.
6. Device according to one of claims 2 to 5, characterised in that the sintering area (2) has a plurality of zones separated by dividing walls (35), each of which zones includes a heating arrangement with heat exchanging surfaces (28), a fan (31) and an air guidance arrangement (25).
7. Device according to claim 6, characterised in that the temperature of the inert gas differs between zones of the sintering area (2) located successively in the direction of movement.
8. Device according to claim 6 or 7, characterised in that the gas flow around the parts (23) for sintering differs between zones of the sintering area (2) located successively in the direction of movement.
9. Device according to one of claims 3 to 8, characterised in that a nozzle plate (34) by means of which the circulating inert gas is directed against the parts (23) for sintering is provided.
10. Device according to one of claims 3 to 9, characterised in that the doors of the airlocks (7) adjacent the intake and/or the outlet of the sintering area (2) are closable in a not completely sealed manner and the inert gases are at a pressure above atmospheric in the sintering area (2).

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