EP4284577A1 - Apparatus for debinding and sintering a workpiece - Google Patents

Abstract

The invention relates to an apparatus for debinding and sintering a workpiece. The apparatus comprises a retort furnace (2) with an interior (21) for receiving, debinding and sintering the workpiece (1), a double-walled tank (3), which surrounds the retort furnace (2) gas-tightly and comprises an inner wall (31), an outer wall (32) and a temperature-control system (33) between the inner wall (31) and the outer wall (32), and an acid reservoir (41), which is fluid-mechanically connected to the interior (21) of the retort furnace (2) and is designed and intended to receive an acid necessary for chemical debinding and to provide the acid (4) to the interior for a chemical debinding of the workpiece (1) in the gaseous state. Second heating means (42) are associated with the acid reservoir (41). Control means (5) are provided and designed, by adjustment of the temperature of the second heating means (42), to control the amount of acid (4) necessary for chemical debinding which is provided by the acid reservoir (41) to the interior (21) of the retort furnace (2), to control the temperature in the interior (21) of the retort furnace (2), and to control the temperature of the inner wall (31) of the tank (3).

Description

Device for debinding and sintering a workpiece

Description

The invention relates to a device for debinding and sintering a workpiece.

A green body or green body is a component that consists of a powdery material, such as a metal or ceramic powder, which is held in shape by a binder. The green body is an intermediate product which, although it has all the geometric properties of the workpiece to be produced, still requires further processing steps. Normally, in a further step, the typically organic binder is dissolved out of the green body and the part is then sintered. Debinding turns the green body into a so-called brown body or brown compact, which in turn becomes the workpiece to be manufactured through sintering. The sintering is associated with a shrinking process.

It is known to use binder systems made from polyoxymethylene (POM) or other organic substances as binders. In particular, a catalytic Debinding is known, in which a green body is treated in a gaseous, acidic atmosphere of hydrogen halides, formic acid or nitric acid at elevated temperature. Corresponding methods are described, for example, in EP 0 413 231 A1, EP 2 686 286 A1 and CN 106270506 A1, to which reference is made in this respect. An example of a catalytic process is the so-called Catamold® process from BASF SE, in which nitric acid and nitrogen form a gaseous, acidic atmosphere that is used in childbirth. A catalytic debinding with oxalic acid is known from WO 94/25205 A1.

In the case of catalytic debinding, the debinding process typically comprises two phases. In the first phase, the binder is largely chemically removed in a gaseous, acidic atmosphere, leaving a residual binder, which is then thermally decomposed in the sintering furnace in a second phase. The first phase takes place in a debinding station that is suitable for receiving the gaseous acid.

A disadvantage of known systems is that the workpiece has to be transported to different processing stations in order to run through different processing steps. The workpiece is particularly fragile following chemical debinding due to the extensive detachment of the supporting binder, and there is a risk that the workpiece will be damaged during transport.

Accordingly, the object of the invention is to provide a device for effective debinding and sintering of a workpiece.

This object is achieved by a device having the features of patent claim 1 and a method having the features of patent claim 22 . Developments of the invention are specified in the dependent claims.

Accordingly, the present invention contemplates an apparatus for debinding and sintering a workpiece. The device comprises a retort furnace with an interior space for receiving, debinding and sintering the workpiece (which is a green part) and first heating means arranged outside the interior space, the interior space being heatable via the first heating means. The device further comprises a double-walled vessel which encloses the retort furnace in a gas-tight manner and has an inner wall, an outer wall and a temperature control system between the inner wall and the outer wall includes. The inner wall of the double-walled boiler can be cooled or heated via the temperature control system. The temperature control system is therefore intended and designed to cool or heat the inner wall. The device also has an acid reservoir which is fluidically connected to the interior of the retort furnace and is designed and provided to receive an acid required for chemical debinding and to provide the acid to the interior for chemical debinding of the workpiece in the gaseous state. The acid reservoir has second heating means for heating the acid reservoir.

Furthermore, the device comprises control means that are provided and set up to control the amount of acid required for chemical debinding, which the acid reservoir provides to the debinding chamber by adjusting the temperature of the second heating means, to control the temperature in the interior of the retort furnace, and to control the temperature of the inner wall of the boiler.

The invention is based on the idea of integrating a debinding station and a sintering furnace in a single device. In this way, transport of the workpiece, which is particularly fragile after debinding, and the use of mechanically moved parts is not necessary and processing of the workpiece is simplified.

The retort furnace is used for thermal debinding and sintering of the workpiece, with the boiler being designed so that gaseous acid cannot escape from the device. The inner wall of the boiler can be heated by the temperature control system, so that during debinding with gaseous acid, if it escapes from the retort furnace in small quantities, which cannot be prevented, it does not condense on the inner wall of the boiler. This prevents acid residues from being deposited in the boiler or in the device, which is to be prevented due to the aggressive nature of the acid.

In addition, the heating of the inner wall of the vessel ensures an even temperature distribution in the vessel, resulting in improved process stability and repeatability of chemical debinding. The inner wall can also be cooled via the temperature control system, so that at high temperatures in the retort furnace, for example during sintering or thermal debinding, the boiler wall is not heated too much and, in particular, the boiler seals, which For example, seal the boiler door, avoid damage. The temperature of the inner wall of the boiler can therefore be controlled via the temperature control system.

The provision of an acid required for the debinding process in a separate acid reservoir, in which the acid provided for the process can be adjusted via the temperature of the acid reservoir, enables precise dosing of the amount of acid that is converted into a gaseous state and flows into the interior of the retort furnace and is thus provided for debinding the green part.

In this case, the heat input or the temperature of the acid can be adjusted via the second heating means on the acid reservoir and the associated control such that a controlled phase transition of the acid takes place. The second heating means for heating the acid reservoir, which is arranged independently of the interior of the retort furnace, in conjunction with the control means, thus enable improved dosing of the acid supplied for debinding, independently of the temperature in the interior of the retort furnace.

Thanks to the improved dosing of the acid, the debinding process can be controlled and run with maximum effectiveness, so that, for example, too rapid debinding, which could damage the workpiece with inclusions, can be avoided. At the same time, the separation of the interior of the retort furnace and the acid reservoir increases safety, since the possibility of contact with the acid, for example when inserting the workpiece into the interior of the retort furnace, is reduced.

In general, industrial furnaces are known as retort furnaces, which are used, for example, for the sintering of components. For example, the interior according to the invention can be heated to an interior temperature of 1380° C. by the first heating means for sintering stainless steel 316L.

Any connection that enables gas exchange between the acid reservoir and the interior of the retort furnace is considered to be a fluidic connection within the meaning of the present invention. It is formed, for example, by a tube or a passage. It is provided that the tank is sealed off from the environment, particularly at the point at which the fluidic connection occurs through the double-walled tank. The workpiece consists of a metal and/or ceramic powder mixed with a binder (green body). For example, the workpiece can include a printed part that is manufactured in layers from a filament using a 3D printing process. The filament consists of a metal or ceramic powder mixed with a binder. In a 3D print, for example, a filament is used that has a metal powder made of copper, stainless steel or tempered steel. Examples of materials are 17-4PH or 316L stainless steels and 42CrMo4 heat-treatable steels. For the use of ceramic powder, exemplary embodiments provide that the ceramic powder consists of aluminum oxide or zirconium oxide or generally an oxide ceramic, nitride ceramic or carbide ceramic or a mixture of such ceramics.

Alternatively, the workpiece can be an injection molded part, for example, in which a binder is used to bond the metal and/or ceramic powder during the injection molding process. Suitable materials that form the metal powder or as ceramic powder are described, for example, in EP 2 686 286 A1. Alternatively, the workpiece can also have been manufactured in a further primary forming process, in particular in a primary forming process from a liquid, plastic or pulpy state.

Electronic control means, for example a control computer, are preferably provided as the control means, which are electronically connected to the various components for setting the temperature. Provision is made for the control means to be connected to the first and second heating means and to the temperature control system. Furthermore, provision can be made for the control means to be connected to one or more temperature sensors. The temperature sensors can be arranged, for example, on the acid reservoir, on the interior of the retort furnace, on the temperature control system and/or on the interior of the double-walled boiler between the retort furnace and the inner wall of the boiler. The device can also have other sensors connected to the control means, for example sensors for determining the acidity or the pressure.

In one embodiment, the control means are provided and designed so that for chemical debinding the interior is provided with the acid required for debinding by adjusting the temperature of the second heating means, the interior is heated to a first debinding temperature by the first heating means and the inner wall of the double-walled vessel is heated to a heating temperature by the temperature control system. In principle, the interior of the retort furnace is designed to be as gas-tight as possible. Nevertheless, it cannot be ruled out that acid in gaseous form gets into the interior of the boiler between the retort furnace and the inner wall of the boiler, i.e. in the area between the retort furnace and the boiler. The heating of the inner wall of the boiler to the heating temperature serves to ensure that the gaseous acid in the interior of the boiler between the retort furnace and the inner wall of the boiler does not cool down on the inner wall and does not condense on it.

For thermal debinding, the control means are provided and designed so that the interior is heated to a second debinding temperature by the first heating means and the inner wall of the double-walled vessel is cooled to a first cooling temperature by the temperature control system, with the acid reservoir not providing any acid.

It is provided, for example, that the control means control the first heating means in such a way that a ramp gradient with a temperature change in the interior of e.g. 3 Kelvin per minute is achieved and the interior is heated to approximately 600°C. The control means are designed so that during thermal debinding the inner wall of the boiler is cooled by the temperature control system connected to the control means. Furthermore, the control means are designed so that the second heating means on the acid reservoir does not heat it up during thermal debinding, so that no acid is provided in the interior in a gaseous state.

For sintering the workpiece, the control means are provided and designed so that the interior is heated to a sintering temperature by the first heating means and the inner wall of the double-walled vessel is cooled to a second cooling temperature via the temperature control system, with the acid reservoir, analogous to thermal debinding, not providing any acid from the acid reservoir. The sintering temperature is in the range between 1300°C and 1500°C, for example.

In one embodiment of the invention, the temperature control system has a liquid that flows between the inner wall and the outer wall of the boiler, with the temperature control system adjusting the temperature of the liquid. It is envisaged that the liquid will flow in such a way that the temperature exchange between the liquid and the inner wall of the vessel is as efficient as possible. Here is for example provided that the liquid flows flatly around the inner wall and guide elements are arranged between the inner wall and the outer wall of the tank, which ensure a meandering flow along the inner wall. The liquid is, for example, water or thermal oil.

In a further embodiment, the temperature control system can have heating and/or cooling elements arranged between the inner wall and the outer wall of the boiler.

In a preferred embodiment, the temperature control system is designed to heat the liquid to the heating temperature during chemical debinding. The temperature control system can have a heating device that is designed to heat the liquid to the heating temperature. Such a heating device can be provided, for example, by a flow heater or a heatable boiler.

In a further embodiment of the invention, the temperature control system is designed to set the liquid to the first or second cooling temperature (which can be identical or different) during thermal debinding and during sintering. The temperature control system can have a cooling device that serves to cool the liquid. In principle, however, the temperature control system can also be fed by a liquid that has already been preheated to a cooling temperature in advance.

In one embodiment, the first debinding temperature and the heating temperature are in a range from 120°C to 160°C, in particular in a range from 140°C to 150°C. On the one hand, this temperature range enables a chemical impediment to be carried out in an effective manner. On the other hand, condensation of acid escaping from the retort furnace is prevented on the inner wall of the boiler. However, the debinding temperature and the heating temperature do not have to be identical, but are preferably in the same range.

In a further configuration, the first and the second cooling temperature have a temperature in a range from 10°C to 50°C, in particular in a range from 25°C to 35°C. In this case, the first and the second cooling temperature do not have to be identical. In a variant of the invention, the device has a first gas inlet for introducing a protective gas and a first gas outlet for discharging the protective gas. The first gas inlet connects the interior of the retort furnace to a feed line arranged outside of the boiler, and the first gas outlet connects the interior of the retort furnace to a discharge line arranged outside of the boiler.

The introduction of protective gas serves to displace ambient air from the interior of the retort furnace and from the interior of the boiler for process stability. Particles or gases that could cause an unwanted chemical reaction or contamination of the workpiece are removed. The use of nitrogen, for example, is envisaged as the protective gas.

In a further variant of the invention, the device has a second gas inlet and a second gas outlet. The second gas inlet serves to introduce the protective gas and connects the interior of the boiler between the retort furnace and the inner wall of the boiler to a supply line arranged outside of the boiler, and the second gas outlet serves to discharge the protective gas from the interior of the boiler between the retort furnace and the inner wall of the boiler to a discharge line arranged outside of the boiler.

It can be provided that the first gas inlet and the second gas inlet are connected to the same feed line and the first and the second gas outlet are connected to the same outlet line.

In a further variant of the invention it can be provided that a pressure difference between the interior of the retort furnace and the interior of the boiler between the retort furnace and the inner wall of the boiler can be adjusted via the control means, the first and second gas inlets and the first and second gas outlets. The gas inlets and the gas outlets can have means for influencing the gas flow, such as valves or pumps, not shown, via which a pressure difference can be set. In particular, a vacuum pump, which is connected to the first and/or second gas outlet, can be provided, which serves to evacuate the gaseous acid. The vacuum pump can also be used to deoxygenate the interior of the retort furnace and the interior of the vessel at the beginning of the debinding process for an improved debinding process. In addition, it is possible to use the vacuum pump for improved thermal debinding under negative pressure conditions. The amount of protective gas that is fed into the interior of the retort furnace and/or the interior of the boiler can be metered via a gas flow controller. It is thus possible to precisely control the negative pressure in the interior of the retort furnace and/or in the interior of the boiler.

The control means are designed so that during chemical and thermal debinding the pressure in the interior of the vessel between the retort furnace and the inner wall of the vessel is greater than the pressure in the interior of the retort furnace. If the interior of the retort furnace is not perfectly sealed gas-tight and the gas can basically flow through a leakage opening, the existing pressure difference prevents or further reduces the gaseous acid from escaping from the retort furnace. This minimizes the possibility of the gaseous acid provided for debinding escaping.

Alternatively or additionally, it can be provided that the control means are designed such that during sintering the pressure in the interior of the retort furnace is greater than the pressure in the interior of the vessel between the retort furnace and the inner wall of the vessel. The difference in pressure creates a protective gas flow from the interior into the interior of the boiler between the retort furnace and the inner wall of the boiler. This directs fresh protective gas over the workpiece and prevents any contamination.

In a further embodiment of the invention, the discharge line can be connected to an exhaust gas flare for the combustion of exhaust gases. In this embodiment, it is provided that the first and the second gas outlet are connected via a common derivation line, the derivation line leading to the exhaust gas flare. Burning the exhaust gases prevents the escape of toxic gases that are produced by the debinding and sintering processes. For debinding under negative pressure conditions, it is provided that the discharge line has a valve which closes the discharge line with regard to the exhaust gas flare during negative pressure operation.

In a variant of the invention, thermal insulation elements are arranged between the retort furnace and the inner wall of the boiler. The thermal insulation elements are accordingly in the interior of the boiler between the retort furnace and the inner wall of the boiler and serve to connect the retort furnace to the to thermally separate the first heating means from one another with regard to the inner wall with the temperature control system during thermal debinding and in particular during sintering.

The thermal insulation elements can include graphite felt, carbon fiber reinforced carbon (CFC) panels, refractory metal panels (e.g. molybdenum or tungsten), or ceramic fiber panels.

In a further variant of the invention, it is provided that a wall of the retort furnace consists of graphite, ceramic and/or refractory metal (e.g. molybdenum or tungsten) or contains at least one of these materials. The wall delimits the interior of the retort furnace and is heated by the first heating elements.

In a further variant of the invention, the first heating means and/or the second heating means comprise graphite, carbon fiber reinforced carbon (CFC), cermet (e.g. molybdenum disilicide) and/or refractory metal (e.g. molybdenum or tungsten).

In a further variant of the invention, the boiler is sealed off from its surroundings by means of seals. In this case, for example, seals made from fluoroelastomers, for example so-called VITON seals, can be used. These are typically stable up to a temperature of 200 °C, so that the cooling of the kettle during thermal debinding and sintering must ensure this temperature of the kettle wall.

An embodiment of the invention provides that the acid required for the chemical debinding of the workpiece is present in the acid reservoir at room temperature (20° C.) as a solid which changes directly into the gaseous state from a sublimation point. The second heating means are controlled by the control means, for example, in such a way that the temperature of the acid reservoir is above or below the sublimation point. As a result, the amount of gaseous acid provided can be controlled in a particularly simple and effective manner. The acid can also be handled and transported particularly well in its solid form. In one embodiment, the acid is present in granular form in the acid reservoir. In one embodiment, oxalic acid is used as the acid for the chemical debinding of the workpiece. Oxalic acid has a low hazard class compared to other acids. For a sublimation of the oxalic acid, it is provided that the heating means of the acid reservoir, in conjunction with the control means, are designed to heat the oxalic acid to 157° C., 157° C. being the sublimation point of oxalic acid.

Furthermore, it can be provided that the device has a fan arranged in the interior of the retort furnace and air baffles for homogeneous material and temperature distribution. In order to operate the fan, it can be provided that a motor, which drives the fan via a shaft projecting into the debinding chamber, is arranged outside of the debinding chamber. A seal is provided at the entrance of the shaft into the boiler, which represents a gas-tight and acid-tight rotary union and prevents gas from escaping.

The liquid of the temperature control system includes a thermal oil, for example. In an alternative embodiment, the fluid of the temperature control system is pressurized water.

In a further invention aspect, the invention concerns a procedure for reducing a workpiece that is arranged in an interior of a retort furnace that is enclosed by a heated and coolable double -walled boiler, whereby the process includes the steps: o A chemical release of the workpiece, in which the interior of the retort oven is provided for an acid that is required for dismit -free acid reserves , the interior is heated to a first release temperature and an inner wall of the boiler surrounding the return oven is heated to a heating temperature, o A thermal release of the workpiece, in which the interior of the retort furnace is heated to a second desolation temperature and the inner wall of the boiler is cooled to a first cooling temperature, the acid reserves not produced and or one Internally, in which the interior heats to a sintering temperature and the inner wall of the boiler is cooled to a second cooling temperature, the acid reservoir does not provide acid from the acid reservoir. One embodiment of the method provides that a protective gas is introduced into the interior of the retort furnace and/or the interior of the boiler between the retort furnace and the inner wall of the boiler.

In a further embodiment, when the protective gas is introduced into the interior of the retort furnace and/or into the interior of the boiler between the retort furnace and the inner wall of the boiler, a pressure difference is generated between the interior of the retort furnace and the interior of the boiler between the retort furnace and the inner wall of the boiler.

It can be provided that during the chemical and thermal debinding the pressure difference is adjusted in such a way that the pressure in the interior of the vessel between the retort furnace and the inner wall of the vessel is greater than the pressure in the interior of the retort furnace and/or that during sintering the pressure in the interior of the retort furnace is greater than the pressure in the interior of the vessel between the retort furnace and the inner wall of the vessel.

The invention is explained in more detail below with reference to the figures of the drawing using several exemplary embodiments. show:

1 shows an exemplary embodiment of a device for chemical debinding, thermal debinding and sintering of a workpiece;

FIG. 2 shows a side view of the device from FIG. 1, the device having a door, shown in FIG. 2, for inserting and removing the workpiece; and

3 shows a flow chart of a method for chemical debinding, thermal debinding and sintering of a workpiece.

Figures 1 and 2 represent an embodiment of a device for debinding and sintering a workpiece 1. The workpiece 1 can be a metallic and / or ceramic pressure part, which consists of a metal or ceramic powder mixed with a binder. The printed part is created, for example, in a manufacturing process known as “Fused Deposition Modeling” (FDM) or “Fused Filament Fabrication” (FFF). In this manufacturing process, a filament is manufactured in layers in a printer unit to form a metallic or ceramic printed part. The Filament comprises a metal or a ceramic powder mixed with a typically organic binder. Alternatively, the base body is produced, for example, by metal powder injection molding or ceramic powder injection molding. The present device makes it possible to carry out the steps of chemical debinding, thermal debinding and sintering of a workpiece 1 by means of different settings in one device.

FIG. 1 shows a device for debinding a workpiece 1, a plurality of workpieces 1 being arranged on shelves 10 in an interior space 21 of a retort furnace 2. The or each workpiece 1 is first chemically and then thermally debound before it is sintered.

To provide an acid 4 for chemical debinding, the device has an acid reservoir 41 which is connected to the interior 21 of the retort furnace 2 via a fluidic connection 43 . Second heating means 42 are arranged on the acid reservoir 41 and can heat the acid reservoir 41 in such a way that acid 4 located in the acid reservoir 41 converts to the gaseous state and can be supplied to the interior 21 . Oxalic acid is provided as the acid 4 . In alternative embodiments, the use of nitric acid is envisaged. The acid 4 can be entered as a solid or granules in the acid reservoir 41 and then heated to a sublimation temperature. Here, the acid 4 changes directly from the solid to the gaseous state.

In an embodiment variant that is not shown, a valve is arranged on the fluidic connection 43 which can prevent a gas flow between the acid reservoir 41 and the interior of the retort furnace 2 .

The retort furnace 2 has a wall 23 which delimits the interior space 21 . First heating means 22 of the retort furnace 2 for heating the interior 21 are arranged outside the wall 23 . A double-walled vessel 3 with an inner wall 31 and an outer wall 32 surrounds the retort furnace. Thermal insulation elements 10 are arranged between the vessel 3 and the retort furnace 2 in the interior 8 of the vessel.

The thermal isolation elements 10 include graphite felt, carbon fiber reinforced carbon (CFC) sheets, refractory metal sheets (eg, molybdenum or tungsten), or ceramic fiber sheets. The wall 23 of the retort furnace 2 includes graphite, ceramic and/or refractory metal (e.g. molybdenum or tungsten). The first heating means 22 and/or the second heating means 42 comprise graphite, carbon fiber reinforced carbon, cermet (eg molybdenum disilicide) and/or refractory metal (eg molybdenum or tungsten).

The wall 23 of the retort furnace cannot be designed to be perfectly gas-tight, but necessarily has leakage openings so that gaseous acid 4 located in the interior 21 can escape from the interior 21 of the retort furnace 2 into the interior 8 of the boiler 3 between the retort furnace 2 and the boiler. In particular, it is not possible to construct a gas-tight door (not shown separately) in the wall 23, through which the workpieces 1 can be inserted and removed, since there are no seals available that would be resistant to the high temperatures occurring during sintering in the range between 1300° C. and 1500° C.

The area between the retort furnace 2 and the inner wall 31 of the boiler 3 is referred to below as the intermediate space 9 .

The device has a temperature control system 33 for setting the temperature on the inner wall 31 of the double-walled vessel 3 . In this case, a heated or cooled liquid 34 is conducted between the inner wall 31 and the outer wall 32 . The liquid 34 is fed via supply lines 36 to a heating and/or cooling device 35 which heats or cools the liquid 34 to a predetermined value. In alternative embodiments, heated or cooled liquid 34 can also be supplied from a pre-tempered liquid reservoir. In this case, the heating and/or cooling device 35 can consist of separate devices through which flow is carried out via a valve control only for heating or cooling. The liquid 34 is, for example, thermal oil or pressurized water.

To introduce a protective gas, the device has gas inlets 61 , 62 and gas outlets 71 , 72 , each with an assigned inlet line 6 and outlet line 7 arranged outside of the boiler 3 . A first gas inlet 61 connects the interior 21 of the retort furnace 2 and a second gas inlet 62 the

Space 9 with the supply line 6. Correspondingly, the first gas outlet 71 connects the interior 21 of the retort furnace 2 and the second gas outlet 72 the

Intermediate space 9 with the discharge line 7. Any harmful residues from the debinding burned off and sintering process. The gas inlets 61 , 62 and the gas outlets 71 , 72 have means for influencing the gas flow, such as valves or pumps, not shown, via which a pressure difference can be induced between the interior 21 of the retort furnace 2 and the intermediate space 9 .

A vacuum pump is connected to the supply line 6 or the discharge line 7 in exemplary embodiments that are not shown. The vacuum pump is used for improved debinding, in which the interior 21 of the retort furnace 2 and/or the interior 8 of the vessel 3 is freed from oxygen at the beginning of the debinding process for an improved debinding process.

In addition, such a vacuum pump can be used for improved thermal debinding under negative pressure conditions. In this case, the amount of protective gas that is fed into the interior 21 of the retort furnace 2 and/or the interior 8 of the boiler 3 is metered, for example via a gas flow controller. Thus, precise control of the negative pressure in the interior 21 of the retort furnace 2 and/or in the interior 8 of the boiler 3 is possible.

The device has a controller 5 . It is designed to control the temperature of the interior 21 of the retort furnace 2 via the first heating means 22 and the temperature of the inner wall 31 of the vessel 3 via the temperature of the liquid 34 or via the heating and/or cooling device 35 . In addition, the controller 5 controls the discharge of acid 4 in a gaseous state from the acid reservoir 41 to the inner space 21 of the retort furnace 2 by controlling the second heating means 42 . Depending on the second heating means 42 and the corresponding temperature at the acid reservoir 41 , it can be controlled how much acid 4 converts into the gaseous state and flows into the interior 21 of the retort furnace 2 via the fluidic connection 43 . In addition, the controller 5 is connected to the means for influencing the gas flow.

The controller 5 is optionally connected to sensors for measuring temperature, pressure and/or gas content in the interior 21 of the retort furnace 2, on the inner wall of the boiler 31, on the temperature control system 33, on the acid reservoir and/or on the gas inlets and/or gas outlets. The controller 5 controls the individual steps and production parameters during chemical debinding, thermal debinding and sintering.

The device settings for chemical debinding are as follows: The interior 21 of the retort furnace 2 is provided with acid 4 in the gaseous state via the acid reservoir 41 . For this purpose, the second heating means 42 are controlled by the controller 5 in such a way that the acid 4 in the acid reservoir 41 is heated to a temperature of 120 to 150° C., so that the acid 4 changes to the gaseous state. If oxalic acid is used, the acid reservoir can also be heated to the sublimation temperature of oxalic acid, 157°C. The gaseous acid 4 then flows via the fluidic connection 43 into the interior of the retort furnace.

The interior 21 of the retort furnace 2 is set to a first debinding temperature by the first heating means 22 and the inner wall 31 of the boiler 3 is set to a heating temperature by the tempering system. The first debinding temperature and the heating temperature are in the range from 120° C. to 160° C., in particular in a range from 140° C. to 150° C., with the heating and debinding temperatures not necessarily having to be the same. To heat the inner wall 31 of the boiler 3 to the heating temperature, the liquid 34 is supplied to the heating device 35 via the supply lines 36 . In the heating device 35, the liquid 34 is heated to the heating temperature and then fed back between the inner wall 31 and the outer wall 32, where it releases its temperature.

A protective gas is conducted into the interior 21 of the retort furnace 2 and the intermediate space 9 via the gas inlets 61 , 62 and the gas outlets 71 , 72 . A pressure difference is induced between the two spaces 21, 9, at which the pressure in the interior 21 of the retort furnace 2 is lower than in the intermediate space 9.

The lower pressure in the interior 21 of the retort furnace means that gaseous acid 4 cannot escape through a leakage opening in the inner wall 23 into the intermediate space 9, but instead an opposite flow of protective gas flows out of the intermediate space 9 into the interior 21 of the retort furnace 2.

The heating of the inner wall 31 of the double-walled vessel 3 prevents acid 4 escaping in a gaseous state from the interior 21 of the retort furnace 2 and entering the intermediate space 9 from condensing on the inner wall 31 of the vessel 3 . In addition, the heating of the inner wall 31 to the heating temperature ensures an even temperature distribution in the boiler 3 and in the Retort furnace 2, so that there is improved process stability and repeatability of debinding.

The following settings are available for thermal debinding:

The interior 21 of the retort furnace 2 is heated to a second debinding temperature of approximately 600° C. by the first heating means at a ramp rate of 3 Kelvin per minute. The inner wall 31 of the boiler 3 is cooled to a first cooling temperature by the temperature control system 33 and the acid reservoir does not provide any gaseous acid 4 from the acid reservoir 41 . As in chemical debinding, a pressure difference is induced here, with the pressure in the intermediate space 9 exceeding the pressure in the interior 21 of the retort furnace 2 .

In this setting, the heating and/or cooling device 35 serves as cooling, which cools the liquid 34 to the first cooling temperature. In alternative exemplary embodiments, it is provided that the cooling device does not cool the liquid 34, but feeds the temperature control system 33 with new liquid 34 that has already been preheated to the first cooling temperature. The first cooling temperature is 10 to 50°C, in particular it is in a range from 25°C to 35°C.

The interruption of the supply of acid from the acid reservoir 41 is achieved in that the second heating means 42 no longer heat the acid reservoir 41 and the acid 4 located therein, so that a phase transition of the acid 4 into the gaseous state is prevented. In alternative exemplary embodiments, in which a valve is arranged on the fluidic connection 43 between the acid reservoir 41 and the interior 21 of the retort furnace 2, the valve can be closed.

As with chemical debinding, the present lower pressure in the interior 21 of the retort furnace 2 minimizes the escape of the gaseous acid 4 from the interior 21 of the retort furnace 2 into the intermediate space 9 .

The following settings are present during sintering:

The inner space 21 is heated to a sintering temperature by the first heating means 22 and the inner wall 31 of the vessel 3 is cooled to a second cooling temperature, with the acid reservoir 41 not providing any acid 4 . A pressure difference is induced in which the pressure in the interior 21 of the retort furnace 2 exceeds the pressure at the intermediate space 9 and .

The second cooling temperature is in a range from 10 to 50° C. corresponding to the first cooling temperature, in particular in a range from 25° C. to 35° C., it being possible for the first and second cooling temperatures to be different. For example, the sintering temperature for 316L stainless steel is 1380°C.

During sintering, the pressure difference between the interior 21 of the retort furnace 2 and the intermediate space 9 is the opposite of debinding: in contrast to thermal and chemical debinding, during sintering an increased pressure is induced in the interior, so that a flow of protective gas from the inner space 21 into the intermediate space 9 is created. In this way, fresh protective gas is passed over the workpiece 1 and any contamination of the workpiece 1 is prevented.

Following the sintering, a flow of protective gas is formed via the gas inlets 61, 62 and the gas outlets 71, 72 to cool the workpiece in order to cool the workpiece. After cooling, the component can be removed through a door shown in FIG.

FIG. 2 shows a side view of the exemplary embodiment shown in FIG.

The side view does not show the first heating elements shown in FIG. 1, the gas inlets and the gas outlets and the device for heating/cooling the liquid.

A door 37 is shown in the side view, through which the boiler 3 can be opened and through which the workpiece 1 can be removed from the device. The door 37 is sealed on the sides by particularly heat-resistant seals 38, such as VITON seals. The thermal

Open insulation elements 10 and the inner wall 23, for example, through a corresponding door (not shown). The seals 38 are resistant up to a temperature of 200° C., for example. The cooling of the inner wall of the vessel during thermal debinding and sintering ensures that the seals 38 do not heat up above the specified limit temperature. FIG. 3 summarizes the method described. Step 101 describes chemical debinding, step 102 describes thermal debinding and step 103 describes sintering. It should be understood that the invention is not limited to the embodiments described above, and various modifications and improvements can be made without departing from the concepts described herein. It is further pointed out that any of the features described can be used separately or in combination with any other features, provided they are not mutually exclusive. The disclosure extends to and encompasses all combinations and sub-combinations of one or more features described herein. If ranges are defined, these include all values within these ranges as well as all sub-ranges that fall within a range.

Claims

patent claims 1 . Device for debinding and sintering a workpiece, which has: a retort furnace (2) with an interior (21) for receiving, debinding and sintering the workpiece (1) and with first heating means (22) arranged outside the interior (21), the interior (21) being heatable via the first heating means (22), - A double-walled vessel (3) which encloses the retort furnace (2) in a gas-tight manner and comprises an inner wall (31), an outer wall (32) and a temperature control system (33) between the inner wall (31) and the outer wall (32), via which the inner wall (31) can be cooled or heated, an acid reservoir (41) which is fluidically connected to the interior (21) of the retort furnace (2) and is designed and provided to receive an acid (4) required for chemical debinding and to provide the acid (4) to the interior (21) for chemical debinding of the workpiece (1) in the gaseous state, with the acid reservoir (41) being assigned second heating means (42) for heating the acid reservoir (41), and - Control means (5) which are provided and set up to control the amount of acid (4) required for chemical debinding, which the acid reservoir (41) provides to the interior (21) of the retort furnace (2) by setting the temperature of the second heating means (42), the temperature in the interior (21) of the retort furnace (2) to control, and to control the temperature of the inner wall (31) of the boiler (3). 2. Device according to claim 1, characterized in that the control means (5) are provided and designed so that for chemical debinding the interior (21) is provided with the acid (4) required for debinding via the temperature of the second heating means (42), the interior (21) is heated to a first debinding temperature by the first heating means (22) and the inner wall (31) of the double-walled vessel (3) is heated to a heating temperature by the temperature control system (33). , For a thermal debinding of the interior (21) by the first heating means (22) heated to a second debinding temperature and the inner wall (31) of the double-walled vessel (3) by the temperature control system (33) to a first Cooling temperature is cooled, wherein the acid reservoir (41) provides no acid (4), and - For sintering, the interior (21) is heated to a sintering temperature by the first heating means (22) and the inner wall (31) of the double-walled vessel (3) is cooled to a second cooling temperature via the temperature control system (33), the acid reservoir (41) not providing any acid (4) from the acid reservoir (41). Device according to Claim 1 or 2, characterized in that the temperature control system (33) has a liquid (34) which flows between the inner wall (31) and the outer wall (32) of the boiler (3), the temperature control system (33) adjusting the temperature of the liquid (34). Device according to Claim 3, insofar as it relates back to Claim 2, characterized in that the temperature control system (33) is designed to heat the liquid (34) to the heating temperature during chemical debinding. Device according to Claim 3 or 4, insofar as it relates back to Claim 2, characterized in that the temperature control system (33) is designed to adjust the liquid (34) to the first and second cooling temperature during thermal debinding and during sintering. Device according to one of the preceding claims, insofar as dependent on claim 2, characterized in that the first debinding temperature and the heating temperature are in a range from 120°C to 160°C, in particular in a range from 140°C to 150°C. Device according to one of the preceding claims, insofar as dependent on claim 2, characterized in that the first and second cooling temperatures are each in a range from 10°C to 50°C, in particular in a range from 25°C to 35°C. Device according to one of the preceding claims, characterized in that the device has a first gas inlet (61) which connects the interior (21) of the retort furnace (2) to a supply line (6) arranged outside the boiler (3) for introducing a protective gas, and a first gas outlet (71) which connects the interior (21) of the retort furnace (2) to a discharge line (7) arranged outside the boiler (3) for discharging the protective gas. Device according to one of the preceding claims, characterized in that the device has a second gas inlet (62) which connects the interior (8) of the vessel (3) between the retort furnace (2) and the inner wall (31) of the vessel (3) to a supply line (6) arranged outside the vessel in order to introduce a protective gas, and a second gas outlet (72) which connects the inner space (8) of the vessel (3) between the retort furnace (2) and the inner wall (31) to discharge the protective gas. of the boiler (3) with a discharge line (7) arranged outside of the boiler (3). Device according to Claims 8 and 9, characterized in that a pressure difference between the interior (21) of the retort furnace (2) and the interior (8) of the boiler (3) between the retort furnace (2) and the inner wall (31) of the boiler (3) can be set via the control means (5), the first gas inlets (61) and second gas inlets (62), and the first gas outlets (71) and second gas outlets (72). Device according to Claim 10, characterized in that the control means (5) are designed such that during chemical and thermal debinding the pressure in the interior (8) of the vessel (3) between the retort furnace (2) and the inner wall (31) of the vessel (3) is greater than the pressure in the interior (21) of the retort furnace (2). Device according to Claim 10 or 11, characterized in that the control means (5) are designed such that during sintering the pressure in the interior (21) of the retort furnace (2) is greater than the pressure in the interior (8) of the vessel (3) between the retort furnace (2) and the inner wall (31) of the vessel (3). Device according to one of Claims 8 to 12, characterized in that the discharge line (7) is connected to an exhaust gas flare (73) for the combustion of exhaust gases. Device according to one of the preceding claims, characterized in that thermal insulation elements (10) are arranged between the retort furnace (2) and the inner wall (31) of the boiler (3). Device according to claim 14, characterized in that the thermal insulation elements (10) are graphite felt, plates with carbon fiber reinforced carbon, Have plates made of refractory metal and / or plates made of ceramic fibers. 16. Device according to one of the preceding claims, characterized in that a wall (23) of the retort furnace (2) comprises graphite, ceramic and/or refractory metal. 17. Device according to one of the preceding claims, characterized in that the first heating means (22) and/or the second heating means (42) comprise graphite, carbon fiber reinforced carbon, cermet and/or refractory metal. 18. Device according to one of the preceding claims, characterized in that the boiler (3) has a door (37) which is sealed by seals (38). 19. Device according to one of the preceding claims, characterized in that the acid (4) required for chemical debinding of the workpiece is present in the acid reservoir (41) as a solid which changes directly into the gaseous state from a sublimation point. 20. Device according to one of the preceding claims, characterized in that the acid reservoir (41) for the chemical debinding of the workpiece (1) contains oxalic acid. 21. Device according to one of the preceding claims, characterized in that the retort furnace (2) has a fan and air baffles arranged in the interior (21) for material and temperature distribution. 22. Method for debinding and sintering a workpiece, which is arranged in an interior (21) of a retort furnace (2), which is enclosed by a heatable and coolable double-walled vessel (3), the method comprising the steps: o chemical debinding of the workpiece, in which the interior (21) of the retort furnace (2) is provided with an acid (4) required for debinding via a heatable acid reservoir (41). , wherein the interior (21) is heated to a first debinding temperature and an inner wall (31) of the vessel (3) surrounding the retort furnace (2) is heated to a heating temperature, o thermal debinding of the workpiece, in which the interior (21) of the retort furnace (2) is heated to a second debinding temperature and the inner wall (31) of the vessel (3) is cooled to a first cooling temperature, the acid reservoir (41) not containing acid (4 ) provides, o sintering of the workpiece, in which the interior (21) is heated to a sintering temperature and the inner wall (31) of the vessel (3) is cooled to a second cooling temperature, the acid reservoir (41) not providing any acid (4) from the acid reservoir (41). 23. The method according to claim 22, characterized in that an inert gas is introduced into the interior (21) of the retort furnace (2) and/or the interior (8) of the boiler (3) between the retort furnace (2) and the inner wall (31) of the boiler (3). 24. The method according to claim 23, characterized in that when the protective gas is introduced into the interior (21) of the retort furnace (2) and/or into the interior (8) of the boiler (3) between the retort furnace (2) and the inner wall (31) of the boiler (3), a pressure difference between the interior (21) of the retort furnace (2) and the interior (8) of the boiler (3) between the retort furnace (2) and the inner wall (31 ) of the boiler (3) is generated. 25. The method according to claim 24, characterized in that during chemical and thermal debinding the pressure difference is set such that the pressure in the interior of the vessel (8) between the retort furnace (2) and the inner wall (31) of the vessel (3) is greater than the pressure in the interior (21) of the retort furnace (2) and that during sintering the pressure in the interior (21) of the retort furnace (2) is greater than the pressure in the interior (8) of the vessel s (3) between the retort furnace (2) and the inner wall (31) of the boiler (3).