DE102013010237A1 - Method and apparatus for debinding and sintering parts - Google Patents

Abstract

A method and system for debinding and sintering parts are described. The parts are debinded and pre-sintered in a first batch furnace and subjected to a sintering process in a second batch furnace. The pre-sintering process is carried out convectively in the same batch furnace as the debinding process while circulating a process gas and / or protective gas. In this way, debinding and sintering of such parts can be carried out in a time-saving and energy-saving manner.

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, such. B. waxing. 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 the residual binder and can be removed in a second debinding step (residual debinding).

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 (Metal Injection Molding) process, by extruding a metal powder and a binder, a plasticized powder consisting of metal powder and a binder system is prepared 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 by the fact 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 pre-sintering in the first batch furnace, the temperature level already present there by the debinding process or residual debinding process can be utilized, saving time and energy can. 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 convectively, d. H. 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. H. 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 method according to the invention, the sintering process is divided into a pre-sintering process and the actual sintering process, wherein both processes are carried out 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 binder removal, ie H. a corresponding process gas and / or inert gas is circulated and contacted with the parts to be treated in order to perform the appropriate 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 comprises 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. The gas circulation takes place within the retort, while the heating means are arranged outside the retort directly on the furnace shell or adjacent to the furnace shell to form in this way a hot wall furnace and thereby indirectly heat the parts 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, d. H. 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 recirculation 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 is located within the gas guiding means. 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 herein 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 oven shown in longitudinal section 1 serves for debindering (debinding and residual debinding) and for pre-sintering metal parts produced by powder metallurgy, in particular of metal parts produced by MIM processes. The furnace is in the shape of a horizontal cylinder and has a cylindrical furnace shell 13 which has an opening on one side (end). This opening is through a furnace lid 2 locked. Between furnace shell 13 and oven lid 2 there is a suitable seal 10 ,

The in the furnace jacket 13 End provided opening serves to introduce the treated metal parts and to remove the treated metal parts. The metal parts are for this purpose on a batch receiver (a batch carrier) 9 arranged by means of which they are introduced into the oven and removed again from this. The batch receiving device is approximately in the middle of the batch oven in the operating state 1 arranged.

The batch oven 1 also has a retort inside 3 which is also approximately cylindrical and has a substantially closed end side and an opposite open end side. The retort 3 is at a distance from the furnace shell 13 arranged between the retort 3 and the furnace shell 13 formed gap on the open side of the retort also through the seal 10 is sealed. Inside the retort 3 There are suitable gas management facilities 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 management facilities 4 is the batch receiver 9 ,

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

In the operation of the batch furnace is via the gas introduction 7 a process gas or inert gas or an acid in the space within the gas guide devices 4 near the batch receiver 9 introduced. By the operation of the gas circulation device 6 gets out of the space inside the gas routing facilities 4 Gas sucked in and into the space between retort 3 and the gas guiding devices 4 issued. The gas circulation device 6 thus ensures a gas circulation, with the gas passing through the space between retort 3 and the gas guiding devices 4 towards the furnace lid 2 is directed, there undergoes a reversal of direction by 360 ° and longitudinally through the batch receiving device 9 is returned to the gas circulation device. In this way, those in the batch receiving device 9 parts 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, after various Umwälzvorgängen by opening the gas extraction device 8th deducted.

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

On the inside of the oven jacket 13 There are suitable heating devices 14 that can be formed in the usual way. About these heaters 14 on the one hand the furnace shell 13 and on the other hand the retort 3 heated, such that the process temperatures required for a Vorentbinderungs-, Restentbinderungs- and Vorsinterprozess can be adjusted.

In order to achieve a rapid cooling of the treated parts after debindering and pre-sintering, the batch oven has 1 a cooling air supply device 11 and a cooling air extraction device 12 on. The cooling air introducing device 11 flows 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 down so that they can be removed from the furnace.

The following is an example relating to the debinding and pre-sintering of parts in the described batch oven described. In a first step, the corresponding metal parts using the batch receiver 9 introduced into the oven. After that, the furnace lid 2 closed. Next, the working space of the furnace is purged with nitrogen, for example.

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

After the completion of the cycle time for the catalytic debindering a heating of the work space takes place by means of the heaters 14 except for a suitable process temperature for thermal debindering / residual debindering. 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.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102005022242 A1 [0010]

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 are subjected to a Vorentbinderungs- and / or Restentbinderungsprozess. 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 jacket, 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 a retort ( 3 ), in which the batch receiving device ( 9 ) and the gas circulation device ( 6 ) are arranged and in which the gas introduction device ( 7 ) and the gas extraction device ( 8th ) and that the heating devices ( 14 ) for forming a hot wall oven on the furnace shell ( 13 ) or adjacent to the furnace shell ( 13 ) are arranged. Plant according to claim 7, characterized in that the first batch furnace ( 1 ) within the retort ( 3 ) the batch receiving device ( 9 ) at least partially surrounding gas guiding devices ( 4 ) having. Plant according to claim 7 or 8, characterized in that the gas circulation device ( 6 ) between the retort ( 3 ) and the gas-conducting devices ( 4 ) is arranged. Plant according to one of Claims 7 to 9, characterized in that the gas-conducting devices ( 4 ) and the gas circulation device ( 6 ) of the first batch furnace ( 1 ) are arranged so that the batch receiving device ( 9 ) is flowed through in the longitudinal or transverse direction. Installation according to one of claims 7 to 10, characterized in that the gas introduction device ( 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 cooling air supply and extraction devices ( 11 . 12 ) is provided. Installation according to one of claims 7 to 12, characterized in that the first batch furnace ( 1 ) coolable sealing devices ( 10 ) between furnace lid ( 2 ) and furnace shell ( 13 ) having. Installation according to one of claims 7 to 13, characterized in that the first batch furnace ( 1 ) as a horizontal oven with side oven lid ( 2 ) is trained.

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