EP2815822A2 - Method and installation for debinding and sintering of parts - Google Patents

Abstract

A method and apparatus for debinding and sintering parts are described. The parts are debinded and presintered in a first batch oven and subjected to a sintering process in a second batch oven. The pre-sintering process is carried out convectively in the same batch furnace as the debindering process with circulation of a process gas and / or protective gas. In this way, the debinding and sintering of such parts can be done time-saving and energy-saving.

Description

The present invention relates to a process for debindering and sintering parts, in particular parts made by MIM, PIM or CIM processes, in which the parts are debinded in a first batch furnace and sintered in a second batch furnace.

Debinding is understood to mean the removal of binders, in particular polymeric binders, from blanks. The debinding method used depends on the particular binder. There are binder systems with thermally decomposable binders, e.g. To grow. Other binders are removed with solvents such as water or acetone. The most common method is catalytic debinding, because it ensures the shortest debindering times.

The binder can consist of two components, whereby only one component is removed during the preliminary binder removal. The second component is necessary to give the blank the necessary strength so that it can still be handled during subsequent sintering. This second component is called residual binder and can be removed in a second debinding step (residual removal).

The process described here serves both for the preliminary debindering, encompassing all possible binder removal processes, and for residual debinding.

An important process step in powder metallurgy is sintering. The blanks or compacts produced from metal powders according to different solidification processes initially have only low strength and are subjected to solidification to a heat treatment close to the absolute melting temperature. This process is called sintering. Because of the oxidation sensitivity of most sintered materials, sintering must be carried out under a protective gas atmosphere or under vacuum.

Sintering is thus understood to mean a heat treatment process in which the loose powder structure is compacted to form the finished component. It comes to an almost complete filling of the free pore space with matter. Analogously, this also applies to ceramic parts, which takes place predominantly under air.

The present method generally relates to the debindering and sintering of parts, especially metal parts or metal moldings, but also of ceramic parts or ceramic moldings.

In particular, the invention relates to parts made by MIM, PIM or CIM processes. In the MIM process (Metal injection molding method) is prepared by extruding a metal powder and a binder of a metal powder and a binder system existing plasticized powder, which serves as a homogeneous raw material for subsequent injection molding. By the subsequent injection molding molded part are injection-molded, which still have about 10 wt.% Binder share. To remove this binder content, a subsequent debinding or residual debinding step takes place, resulting in a unsintered porous metal. This metal part is finally solidified by a sintering step to the final product.

In the CIM process ceramic moldings are produced in a similar manner.

A method of the type described above is known from DE 10 2005 022 242 A1 known. This publication describes a plant for debindering / residual debinding and sintering of powder-metallurgically produced metal parts. In the known method, debindering / residual debinding is carried out in a first batch furnace. The treated parts are introduced into a second batch furnace in which a sintering process is carried out.

The present invention has for its object to provide a method of the type described above, with which parts can be produced with a particularly good quality and is particularly quickly feasible.

This object is achieved in a method of the type specified in that the parts are subjected to debinding in the first batch oven in this furnace a pre-sintering process, according to which they convection with circulation of a process gas and / or inert gas to a process temperature in one area be heated from 650-950 ° C.

In the method according to the invention, a pre-sintering process is thus performed in addition to debindering in the first batch furnace. This has the advantage that the sintering process can be carried out in the second batch furnace with pre-sintered parts, whereby a considerable time saving is achieved. Since the parts treated in the second batch furnace (sintering furnace) are already pre-sintered, the actual sintering process can proceed more quickly. In particular, the heating phase of the sintering furnace can be carried out more quickly. For presintering in the first batch furnace, the temperature level already present there by the debinding process or residual debinding process can be utilized, whereby time and energy can be saved. Thus, investigations have shown that the process according to the invention requires, for example, in the first batch furnace for debinding and sintering a period of 9 hours and in the second batch furnace for sintering a period of about 7 hours. In a conventional process, in which only the binder is removed in the first batch furnace and the complete sintering process is carried out in the second batch furnace, a total time span of about 24 hours resulted.

An essential feature of the method according to the invention is that the pre-sintering process is convective, i. under circulation of a process gas and / or protective gas is performed. This ensures that the parts are subjected during / after debindering a homogeneous temperature level and a homogeneous gas quality, so that the implementation of a high-quality pre-sintering process is ensured. The parts to be treated are applied directly with the respective process gas and / or inert gas. The realized gas circulation ensures a uniform contact of the parts with the corresponding gas atmosphere.

The term "process gas and / or inert gas" as used herein is intended to cover all gases used for the pre-sintering process, i. also air. In particular, it is intended to cover gases or gas mixtures which undergo chemical reactions or gases or gas mixtures which serve exclusively for protective purposes. Of course, gases or gas mixtures are to be covered, which fulfill both tasks simultaneously.

Examples of such gases or gas mixtures are in particular air, nitrogen or hydrogen.

The method according to the invention is therefore characterized in that two processes are carried out in a single batch furnace, namely a debindering process and a subsequent presintering process. With respect to the debinder process, a pre-deduction process and a residual deduction process can be performed. In the inventive Method, the sintering process is divided into a pre-sintering process and the actual sintering process, both processes are performed in different furnaces. This division results in the above-described advantages in terms of time savings, energy savings and product quality.

In a further development of the method according to the invention, the parts are convectively subjected to a binder removal process prior to the pre-sintering process with the circulation of a process gas and / or protective gas. In particular, in this case, the parts are subjected to a pre-debinding and / or residual debinding process. Of course, other parts already debranched in the first batch furnace can only undergo a residual debinding process.

Therefore, according to the invention, convective work is also carried out for debindering, ie a corresponding process gas and / or protective gas is circulated and contacted with the parts to be treated in order to carry out the corresponding debindering. The gas circulation takes place here as in the pre-sintering process. Even in this process phase thus a homogeneous gas contact and a homogeneous temperature level are ensured within the furnace chamber. Depending on the nature of the binder removal (with solvent, catalytic or thermal) different gases are used which fulfill reactive functions or protective functions. Nitric acid is used in particular for the catalytic debindering.

Depending on the type of process stage - pre-debinding, residual debinding - different temperatures are used, for example 100-120 ° C for pre-debinding and up to 700 ° C for residual debinding. The gases used depend on the respective product.

In order to further shorten the process according to the invention, the parts are preferably subjected to a cooling process after the pre-sintering process. Here too, preferably a convective cooling takes place with circulation of a cooling gas. Thus, a homogeneous cooling gas atmosphere and a uniform temperature level are also achieved.

The heating and the convective treatment of the parts during the binder removal process and / or pre-sintering process is preferably carried out so that the parts are heated indirectly via heaters arranged in a space separated from the parts and are directly exposed to the circulated process gas and / or inert gas. The cooling is preferably carried out by circulation of cooling air within the space in which the heaters are arranged. According to the invention thus the convective region in which the parts to be treated are arranged, separated from the heating and cooling area. By this measure, a particularly gentle homogeneous heating of the parts to be treated is achieved.

A further object of the present invention is to provide a system with which parts of particularly good quality can be produced or treated particularly quickly.

This object is achieved by a system for debinding and sintering of parts, in particular produced by the MIM, PIM or CIM process parts, with a first batch oven for debinding and a second batch oven for sintering the metal parts, wherein the first batch furnace comprises a furnace chamber, a furnace shell, a furnace cover, a process gas and / or inert gas introduction device, a gas circulation device, a gas extraction device, a charge receiving device and heating devices. This plant is according to the invention characterized in that the first batch furnace in the furnace chamber has a retort, in which the batch receiving means and the gas circulation means are arranged and in which the gas introduction means and the Gasabzugseinrichtung open, and that the heating means for forming a hot wall oven furnace furnace or are arranged adjacent to the furnace shell.

As stated above, an essential feature of the invention is that the debinding process and the pre-sintering process are carried out in one and the same batch furnace, convective with the circulation of a process gas and / or inert gas. The parts to be treated are in this case in a batch receiving device, which is arranged within a retort, which is located in the actual furnace chamber. Gas recirculation takes place within the retort, while the heaters are located outside the retort directly on the furnace shell or adjacent to the furnace shell, thus forming a hot wall furnace and thereby indirectly the parts to heat and to realize a gentle temperature control. Furthermore, the condensing of gaseous products on the furnace shell is thereby to be avoided. Rather, this is to ensure that such products are removed in the gaseous state via the gas extraction device from the oven.

The present invention thus relates only to the first batch oven of the plant, which simultaneously serves for debindering and pre-sintering. The second batch oven, i. Sintering furnace, may be formed in a conventional manner and will therefore not be described in detail here. The debinded and presintered parts are removed from the first batch oven after appropriate cooling and introduced into the second batch oven for further processing (for sintering).

An essential feature of the invention is that measures are taken to ensure convective treatment of the parts during the debinding and pre-sintering process in the first batch furnace. For this purpose, the first batch oven preferably has inside the retort the gas intake device at least partially surrounding gas guiding devices. The gas circulation device is in this case arranged in particular between the retort and the gas guiding devices. Preferably, the gas circulation means is in the form of a fan in an end region of the retort and directs the corresponding gas in the space between the retort wall and the gas guide means to the opposite end region of the retort, in which a gas inlet opening within the gas guide means located. In this area, the gas undergoes a reversal of direction by 360 ° and flows through the arranged within the gas guide devices charge receiving device with the parts to be treated back to the gas circulation device and is sucked by this again in the space between retort wall and gas guide devices. This gas circulation process within the retort therefore ensures within the retort for a homogeneous temperature and gas atmosphere and a uniform loading of the parts to be treated.

The gas guiding devices and the gas circulation device of the first batch furnace are preferably arranged so that the charge receiving device is flowed through in the longitudinal or in the transverse direction.

The gas introduction device opens into the space inside the gas guiding devices and is preferably designed as a gas introduction lance. The gas extraction device preferably opens into the intermediate space between the retort wall and gas guiding devices. About this device, the corresponding gases are withdrawn and possibly subjected to thermal afterburning.

Preferably, the first batch furnace is provided with Kühlluftzuführ- and -abzugseinrichtungen that open into the gap between retort and furnace shell and depart therefrom. The space inside the retort is therefore not cooled directly by cooling air admission, but there is an indirect cooling over the space in which the heaters are located.

Preferably, the first batch furnace is designed as a horizontal furnace with side furnace cover. A training as a standing oven is also possible. Between the furnace cover and furnace shell suitable sealing means are arranged, which are preferably coolable to withstand the high temperatures, in particular during the pre-sintering process (by 900 ° C).

The terms "gas introduction device" and "gas introduction lance" used here also cover the introduction of the debinding acid or combinations of both systems (gas and acid).

The invention will be explained below with reference to an embodiment in conjunction with the drawings in detail. The single figure shows a longitudinal section through a first batch furnace of a plant for binder removal and sintering of parts.

The first batch furnace 1, shown in longitudinal section, serves for debindering (debinding and residual debinding) and for presintering of metal parts produced by powder metallurgy, in particular of metal parts produced by MIM processes. The furnace is in the form of a horizontal cylinder and has a cylindrical furnace shell 13, which has an opening on one side (end). This opening is closed by a furnace lid 2. Between furnace shell 13 and furnace cover 2 is a suitable seal 10th

The end provided in the furnace shell 13 opening serves to introduce the metal parts to be treated and to remove the treated metal parts. For this purpose, the metal parts are arranged on a batch receiving device (a batch carrier) 9, by means of which they are introduced into the oven and taken out of it again. The batch receiving device is arranged approximately centrally in the batch oven 1 in the operating state.

The batch furnace 1 further has in its interior a retort 3, which is also approximately cylindrical and has a substantially closed end side and an opposite open end side. The retort 3 is arranged at a distance from the furnace shell 13, wherein the gap formed between the retort 3 and the furnace shell 13 on the open side of the retort is also sealed by the seal 10. In the interior of the retort 3 are suitable gas guiding means 4, which also have approximately the shape of a horizontal cylinder and are substantially closed on the one end side and open on the opposite end side. Within the gas guiding devices 4, the charge receiving device 9 is located.

A suitable gas circulation device 6 in the form of a circulation fan is located in the end space between the retort 3 and the gas guide means 4 and has a drive shaft extending through the furnace shell 13, which is provided with suitable insulation, leading to a drive motor arranged outside the furnace , One in the form of a gas and / or acid introduction lance 7 formed Gaseinführeinrichtung also extends through the furnace shell 13 into the space inside the gas guide means 4 inside. A gas extraction device 8 in the form of a tube extends through the furnace shell 13 into the end-side gap between the retort 3 and the gas guiding devices 4.

During operation of the batch furnace, a process gas or inert gas or an acid is introduced into the space within the gas-conducting devices 4 in the vicinity of the charge-receiving device 9 via the gas introduction device 7. By the operation of the gas circulation device 6 4 gas is sucked from the space within the gas guide means and discharged into the space between the retort 3 and the gas guide means 4. The gas circulation device 6 thus ensures a gas circulation, wherein the gas is passed through the gap between the retort 3 and the gas guiding devices 4 in the direction of the furnace cover 2, there undergoes a direction reversal by 360 ° and is guided in the longitudinal direction by the charge receiving device 9 to the gas circulation device. In this way, the parts located in the batch receiving device 9 are exposed to the appropriate gas atmosphere.

A part of the circulated gas, which is then optionally provided with corresponding waste products of the binder is withdrawn after various recirculation processes by opening the gas extraction device 8.

When no gas is to be supplied or withdrawn, the gas supply device 7 and the gas discharge device 8 closed. If no circulation process is to take place, the gas circulation device 6 is switched off.

On the inside of the furnace shell 13 are suitable heaters 14, which may be formed in a conventional manner. About these heaters 14 of the furnace shell 13 on the one hand and on the other hand retort 3 is heated on the one hand, in such a way that the process temperatures required for a Vorentbinderungs-, Restentbinderungs- and Vorsinterprozess can be adjusted.

In order to achieve rapid cooling of the treated parts after debindering and pre-sintering, the batch furnace 1 has a cooling air supply device 11 and a cooling air extraction device 12. The cooling air introducing device 11 opens into the space between the furnace shell 13 and retort 3, as well as the cooling air extraction device 12. By introducing cooling air, the parts are cooled so far that they can be removed from the oven.

In the following, an example relating to the debinding and pre-sintering of parts in the illustrated batch furnace will be described. In a first step, the corresponding metal parts are introduced by means of the batch receiving device 9 in the oven. Thereafter, the furnace lid 2 is closed. Next, the working space of the furnace is purged with nitrogen, for example.

In the present example, a catalytic Vorentbinderung should be performed. Nitric acid is therefore introduced via the gas introduction device 7 and evaporated in the working space and circulated. The heaters 14 keep the process temperature at about 120 ° C.

After the completion of the cycle time for the catalytic debindering a heating of the work space by means of the heaters 14 takes place up to a suitable process temperature for the thermal debindering / Restentbinderung. After completion of the cycle time for the thermal debindering is further heated to a presintering temperature of about 900 ° C. After completion of the pre-sintering cycle, the heaters are switched off and cooling air is introduced until a temperature of about 60 ° C is reached at which the treated parts can be removed from the furnace.

For the metal moldings (PIM or MIM) treated here, the catalytic debinding is carried out using nitric acid and N ₂ . If a drying phase is carried out for aqueous binder parts, this is carried out under N ₂ or H ₂ or N ₂ / H ₂ mixed gas. The thermal debinding is carried out under N ₂ or H ₂ or N ₂ / H ₂ mixed gas. The pre-sintering and cooling can also be carried out under N ₂ or H ₂ or N ₂ / H ₂ mixed gas. All process steps are carried out convectively.

In the case of ceramic moldings (CIM), the working space is preferably supplied with air.

Claims (14)

Method for debindering and sintering parts, in particular parts produced by MIM, PIM or CIM processes, in which the parts are debinded in a first batch oven and sintered in a second batch oven, characterized in that the parts after debinding in the first batch furnace in this furnace, they are subjected to a presintering process in which they are convectively heated to a process temperature in a range of 650-950 ° C. while circulating a process gas and / or inert gas. A method according to claim 1, characterized in that the parts are subjected before the pre-sintering process while circulating a process gas and / or protective gas convective a debinding process. A method according to claim 1 or 2, characterized in that the parts a Vorentbinderungs and / or Restentbinderungsprozess be subjected. Method according to one of the preceding claims, characterized in that the parts are subjected to a cooling process after the pre-sintering process. Route according to claim 4, characterized in that the parts are cooled convection while circulating a cooling gas. Method according to one of the preceding claims, characterized in that the heating of the parts takes place indirectly via arranged in a space separated from the parts of the heating means and that the parts are subjected directly to the circulated process gas and / or inert gas. Apparatus for debinding and sintering parts, in particular parts produced by the MIM, PIM or CIM process, comprising a first batch oven for debinding and a second batch oven for sintering the parts, the first batch oven having a Furnace chamber, a furnace shell, a furnace cover, a process gas and / or inert gas introduction device, a gas circulation device, a gas extraction device, a batch receiving device and heating devices, characterized in that the first batch furnace (1) in the furnace chamber has a retort (3), in the batch receiving device (9) and the gas circulation device (6) are arranged and into which the gas introduction device (7) and the gas discharge device (8) open, and that the heating means (14) for forming a hot wall oven furnace furnace (13) or adjacent to the furnace shell (13) are arranged. Installation according to claim 7, characterized in that the first batch furnace (1) within the retort (3) the charge receiving means (9) at least partially surrounding gas guiding means (4). Installation according to claim 7 or 8, characterized in that the gas circulation device (6) between the retort (3) and the gas guiding means (4) is arranged. Installation according to one of claims 7 to 9, characterized in that the gas guiding means (4) and the gas circulation means (6) of the first batch furnace (1) are arranged so that the batch receiving means (9) is flowed through in longitudinal or transverse direction , Installation according to one of claims 7 to 10, characterized in that the gas introduction means (7) of the first batch furnace (1) is designed as a gas introduction lance. Installation according to one of claims 7 to 11, characterized in that the first batch furnace (1) with Kühlluftzuführ- and -auszugseinrichtungen (11, 12) is provided. Installation according to one of claims 7 to 12, characterized in that the first batch furnace (1) has coolable sealing means (10) between the furnace lid (2) and furnace shell (13). Installation according to one of claims 7 to 13, characterized in that the first batch furnace (1) is designed as a horizontal furnace with side furnace cover (2).

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