EP3256804A1 - Sintering furnace for components made of sintered material, in particular dental components - Google Patents

Abstract

The invention relates to a sintering furnace (1) for components (15) made of a sintered material, in particular for dental components, comprising a furnace chamber (2) having a chamber volume (VK) and a chamber inner surface (OK), wherein a heat-up device (5), a receiving space (9) having a gross volume (VB) located in the chamber volume (VK) and delimited by the heat-up device (5), and a useful region (10) having a useful volume (VN) located in the gross volume (VB), are disposed in the furnace chamber (2). The furnace chamber (2) has an outer wall (3) consisting of a plurality of walls having a wall portion (7) to be opened for introduction into the receiving space (9) of a component to be sintered (15) and having an object volume (VO). In the furnace chamber (2) the heat-up device (5) has a thermal radiator (6) having a radiation field (13) which radiator is disposed on at least one side of the receiving space (9). Said thermal radiator (6) has a specific resistance of 0.1 Ωmm2 /m to 1,000,000 Ωmm2/m and has a total surface, the maximum of which is three times the chamber inner surface (OK). With this sintering furnace (1) a heat-up temperature of at least 1100°C can be achieved within 5 minutes at a maximum power input of 1.5 kW.

Description

 description

Sintering furnace for components made of sintered material, in particular

 Dental components

Technical area

The invention relates to a sintering furnace for components made of a sintered material, in particular for dental components and in particular for components made of ceramic, comprising a

Oven chamber with a chamber volume and a Kammerinnenoberfläche, wherein in the oven chamber, a heating device, a receiving space with a lying in the chamber volume by the Aufhei zVorrichtung limited gross volume and a Nutzbereich with a gross volume lying in the useful volume are arranged and wherein the oven chamber consists of a plurality of walls Conversion with a wall opening to be opened in at least one of the walls for introducing a component to be sintered with an ob ektvolumen in the receiving space.

State of the art

Decisive for the design of a sintering furnace is the material to be sintered. Sintered are basically metallic or ceramic moldings, consisting of a

Powders were pressed and which were possibly further processed either directly or after a Ansinterprozess by a milling or grinding process. The material determines the necessary temperature profile. The size and quantity of components determine the size of the furnace and also the temperature profile. The hotter the oven should be, the thicker the insulation. The size of the

Furnace, the components and the desired heating rate determine the design of the heating system and the

Control behavior. The power supply also plays a role here Role. Ultimately, the size and also the available power supply distinguish a dental furnace for a laboratory from an industrial sintering furnace.

Heat treatment processes, in particular the complete sintering of dental restorations from presintered

Ceramics or metals using a sintering furnace typically last between 60 minutes and several hours. The manufacturing process of a dental restoration that also requires preparatory and subsequent steps is sustainable interrupted by this time required a single ^¬ step. As required by the sogenann ^¬ te speed sintering of zirconium oxide at least 60 min.

The so-called super-speed sintering for zirconium oxide today only requires a minimum of 15 minutes of process throughput time. However, this assumes that the sintering furnace, in particular ^¬ sondere because of its mass, is preheated to the intended holding ^¬ temperature, which takes depends on the Products Available ^¬ ren mains voltage between 30 and 75 minutes. Furthermore, the oven must be loaded after preheating via an automatic loading sequence, so that special temperature profiles can be maintained and the oven does not cool unnecessarily.

From WO 2012/057829 a method for rapid sintering of ceramic materials is known. In a first

Embodiment forms a water-cooled copper pipe a

Coil connected to a high frequency power supply.

The coil surrounds a susceptor called thermal

Emitter in which the material to be sintered is located.

The susceptor is heated while the heated

Susceptor as a thermal radiator passes the heat to the material to be sintered. In a second embodiment, the coil is connected to a high frequency power supply having a sufficiently high frequency and power to generate a plasma which then heats the material. A disadvantage of preheating and subsequent loading, however, is that the oven, in particular its insulation and its heating elements are exposed to a high thermal cycling, which has a reducing effect on the Gerätele ^¬ bensdauer.

The object of the present invention is therefore to provide a sintering furnace, which allows a correspondingly short production time, without preheating the sintering furnace and / or a special Beladesequenzen are necessary.

 Presentation of the invention

This object is achieved by a sintering furnace for components made of a sintered material, in particular for dental components and in particular for components made of ceramics, comprising a furnace chamber having a chamber volume and a Kamme- groove surface and in which a Aufheizvorrich ^¬ tung, a receiving space and a Nutzbereich are arranged. The receiving space occupies a volume lying in the chamber volume and limited by the heating device gross volume. The working area has a useful volume and is located in the receiving space. The furnace chamber furthermore has a wall consisting of several walls with at least one opening wall section for introducing a component to be sintered in the receiving space. The heating device in the furnace chamber has at least one thermal radiator with a radiation field, which is arranged on at least one side of the receiving space and in the radiation ^¬ field at least the useful volume of the working area is. The maximum possible distance of the component to be sintered ^¬ part to the radiator corresponds at most to the second largest dimension of the maximum usable volume.

The thermal radiator has a resistivity of 0, lQmm ² / m to 1000000 Qmm ² / m and has a

Total surface, which is a maximum of 3 times, preferably at most 2.5 times the chamber inner surface.

The furnace chamber, also called combustion chamber, forms the part to be sintered receiving and heating, ie the core of the sintering furnace. The entire volume enclosed by the furnace chamber is called chamber volume. The free space remaining between the heating device arranged in the oven chamber can accommodate the component to be sintered and is therefore referred to as the receiving space. The volume of the receiving space results essentially from the remaining between the heater and possibly the chamber walls width and height and is therefore referred to as gross volume.

 The useful range is the area of the sintering furnace in which the necessary or necessary for the sintering process or

desired temperature is achieved by means of the heater. The useful range is thus the region in which the radiation field generated by the thermal radiator having the necessary intensity and / or uniformity for the sintering process and in which the component for the sintering is positio ned ^¬. The component has an ob ectvolumen. This useful range thus results essentially from the radiation field or from the arrangement of the heating device and its radiation characteristic and can be correspondingly smaller than the gross volume. For a successful sintering process, the object volume of the object to be sintered should therefore be at most the size of the useful volume exhibit. On the other hand, for the most efficient and fast sintering operations, the size of the useful volume should be at most the size of an upper estimate of the sintering to be sintered

Whether ektvolumen have. The total surface of the thermal radiator consists of the useful volume facing surface, ie an inner side and also from the wall of the furnace chamber facing surface, ie an outer side and from the surfaces for connecting the inside and the outside. In a thermal radiator in the form of a ring, the total surface is therefore the inner surface, the outer surface and the two end faces together. In a thermal radiator in the form of a closed hollow cylinder, the entire surface is formed by the outer surface and the inner surface.

The chamber inner surface is determined by the walls of Ofenkam ^¬ mer. In a cylindrical furnace chamber, there are the bottom, the lid and the lateral surface, which together form the chamber inner surface. In a block-shaped furnace chamber the six side walls form the Kammerinneno ^¬ berfläche.

In an advantageous development, a furnace is provided for a thermal radiator with an overall surface in the range of 1.0 to 3 times the chamber inner surface, which allows a sufficiently rapid heating of the component. Particularly advantageously, a ratio of more than 1.3 has been found, since a good sufficient heating is achieved here, although the thermal radiator covers the furnace chamber only partially. If the oven is to be used for sintering or for heating objects of different sizes, for example, for sintering individual tooth crowns and bridges, so It may therefore be advantageous to design the thermal radiator of the heating device so that the size of the receiving space, that is to say the gross volume, and in particular the size of the useful area, ie the useful volume, can be adapted to the size of the object.

 The useful volume can also be reduced by reducing the useful range and adapted to the size of the object. For example, with an insulating door insert a part of the receiving space can be blocked out. By making the best possible use of the gross volume, that is, a useful volume which is as large as possible in relation to the gross volume, the volume to be heated during the sintering process can be kept as low as possible, whereby a rapid heating and in particular that

Saving a preheating process is possible.

Dental objects typically have sizes of only a few millimeters to centimeters, so that a corresponding

Useful volume in the range of centimeters is typically sufficient. For single-tooth restorations to be sintered, such as crowns or copings, for example, a useful volume of 20 × 20 × 20 mm ^{3 may} suffice. For larger dental objects, such as bridges, a useful volume of

20x20x40 mm ³ suffice. Accordingly, the maximum possible distance of the component to be sintered to the radiator for a dental sintering furnace can be limited or ensured, for example, to 20 mm.

Advantageously, the useful volume to the chamber volume of the furnace chamber in a ratio of 1:50 to 1: 1 and the gross volume of the receiving space in a ratio of 1:20 to 1: 1. Advantageously, the chamber volume of the sintering furnace is between 50 cm ³ and 200 cm ³ .

It is advantageous if the maximum total surface area of the radiator and thus of the heating device is about 400 cm ".

The less volume and the less mass must be heated in total, the faster a desired tempera ^¬ ture in the oven chamber or in the payload can be achieved and the sintering process is carried out successfully. For example, the chamber volume of the furnace chamber may be 60x60x45 mm ³ and the gross volume may still be 25x35x60 mm ³ . These details mean that the dimensions of each

Volume 60 mm x 60 mm x 45 mm or 25 mm x 35 mm x 60 mm are.

Advantageously, the object volume can be a maximum of 20 x 20 x 40 mm ^3. The dimensions are then 20 mm x 20 mm x 40 mm.

The useful volume for the component to be sintered to Objektvo ^¬ lumen of the component can be sintered at a ratio of 1500: be 1: 1 to. 1

 The smaller the difference between the useful volume of the useful range and the object volume of the to be sintered

Component is, the more energy efficient and faster the sintering process for the component is feasible. With this sintering furnace can therefore be achieved within 5 minutes due to the optimal dimensioning with a maximum power consumption of 1.5 kW, a heating temperature of at least 1100 ° C.

Advantageously, the heating element or the thermal radiator can be heated resistively or inductively. Inductive heating elements or resistance heating elements represent simple design variants for a heating element of a sintering furnace that represents a thermal radiator.

Advantageously, the thermal radiator of the heating device made of graphite, M0S1 ₂ , SiC or glassy carbon ^¬ substance, since these materials have a resistivity in the range 0, lQmm ² / m to 1000000 Qmm ² / m.

Advantageously, the walling has a chamber wall which is impermeable to and / or returns to the radiation field and which, in particular, carries a reflective coating or is designed as a reflector.

By means of a reflective coating, the intensity of the radiation field of the thermal radiator in the useful area, ie within the useful volume, can be increased. Is the thermal radiators arranged only on one side of the receiving space ^¬, so a more homogenous and / or intensity stronger radiation field in the payload can be achieved by means of a, for example, opposed reflective coating or an oppositely arranged reflector.

Advantageously, the heating device has a heating ^¬ element as a thermal radiator with a heating rate in the useful range of at least 200 K / min at 20 ° C. Advantageously, the useful volume can be a maximum of 20 × 20 × 40 mm ³ and the dimensions of the usable volume are not more than 20 mm × 20 mm × 40 mm.

 According to a development, the thermal radiator can be designed as a crucible.

Brief description of the drawings The invention will be explained with reference to the drawing. Show it :

1 shows a part of a sintering furnace according to the invention for components made of a sintered material, in particular for dental components;

 Fig. 2A, B an inductively heatable heating device with a crucible and coil existing thermal radiator;

Fig. 3 is a plate-shaped inductively heatable

 thermal radiator with integrated coil;

Fig. 4A, B resistively heatable Aufheizvorrichtungen with rod-shaped heating elements existing thermal radiator;

5 shows a heating coil as a resistance heating element.

FIG. 6 shows a thermal radiator consisting of heating coil and reflector; FIG.

FIG. 7 shows a thermal radiator consisting of U-shaped heating elements; FIG.

FIG. 8 shows a thermal radiator consisting of flat heating elements; FIG.

9-16 different arrangements of the thermal radiator and the useful volume in the furnace chamber.

embodiment

Fig. 1 shows a part of a sintering furnace 1, which has a furnace chamber 2 with a chamber volume VK, whose walls 3 are provided with an insulation 4 for shielding the hot furnace chamber 2 from the environment. The chamber volume VK is between 50 cm ³ and 200 cm ³ . For heating the furnace chamber 2, a heating device 5 with two thermal radiators 6 is provided in the furnace chamber 2 arranged. The oven chamber 2 has an openable

Wall section 7 for introducing a component 15 to be sintered in the furnace chamber 2, which here is the lower wall portion, ie the bottom of the furnace chamber 2. The component 15 to be sintered has a volume of at least

10x10x10 mm ³ on. The maximum size of the component 15 is 20x20x40 mm ^3.

The base 7 also has an insulation 4, on which a base 8 is placed for the components 15 to be sintered, which is also referred to as a carrier 8. As a carrier 8 but also bow or a crucible or perpendicular pins made of ceramic or refractory metal come into consideration, on which the component 15 is placed.

By the heating device 5 and the thermal Strah1er 6, the example in Fig. 1 on two sides of

Furnace chamber 2 is disposed within the furnace chamber 2 results in a lower compared to the chamber volume VK free volume, which is indicated in Fig. 1 with a dashed line and is referred to as the gross volume VB. The space occupied by this gross volume VB is the receiving space 9 into which an object 15 to be sintered can be introduced. The heating device 5 in this case has an overall surface which is at most 2.5 times a chamber inner surface OK. The Gesamtoberflä- surface of the heating device 5 is not greater than 400 cm ". The material of the heating device 5 has a specific resistance which lies between 0, lQmm ² / m to 1,000,000 Qmm ² / m, wherein the heating device 5, for example made of graphite , SiC or glassy carbon may consist, M0S1. ₂

With the thermal radiator 6 of the heating device 5, a heating of the receiving space 9 is achieved, wherein at least a portion of the gross volume VB of the receiving space 9 is sufficiently strong and heated evenly. This area is referred to as useful area 10 and the volume as Nutzvo ^¬ lumen VN. The useful area 10 is shown schematically in FIG. 1 by a dot-dash line and a second largest dimension of the useful area 10 is shown as D _y . The size and position of the useful area 10 is essentially determined by the emission characteristic, that is to say the radiation field 13, and the arrangement of the radiators 6, wherein an arrangement of the radiators 6 on at least one side of the receiving space 9 ensures that the useful area 10 is within the receiving space 9.

The heating of the object 15 to be sintered can take place, for example, resistively or inductively. In FIGS. 2A and 2B, for example, an inductively heated thermal

Emitter 6 is shown as a heating device 5. The thermal radiator 6 is designed as a crucible 11, for example made of graphite, M0S1 ₂ , SiC or glassy carbon, with at least one rotating coil 12 for inductive heating, wherein the emission of the crucible 11, ie the thermal radiation 13, is indicated by arrows. In this example, the receiving space 9 is formed by the interior of the crucible. The payload 10 is also located in the interior of the crucible 11, wherein the ratio of the useful range VN Nutzvo ^¬ lumens 10 for the gross volume VB of the receiving space 9 is 1: 1.

Although not shown in FIG. 2A, a retort, for example a bell jar, may be provided, which in the FIG

Crucible is arranged and the component 15 surrounds.

The component 15 to be sintered is in the interior of the

Tiegel 11, in matching with the useful area 13 Reception room 9 arranged. The distance of the object to the thermal radiator 6, so here to the crucible 11 is referred to as d.

FIG. 3 shows a thermal radiator 6 formed from two plate-shaped elements, which is heated by means of integrated coils 12. The receiving space 9 is located between the two plate-shaped elements accordingly. In Fig. 3 the radiation field 13 of the rule thermi ^¬ radiator 6 is further illustrated with lines. Correspondingly results in a receiving space 9 arranged useful area 10, which covers a homogeneous as possible region of the radiation ^¬ field 13 with high intensity.

 The thermal radiators 6 shown in FIGS. 4A and 4B consist of three or four rod-shaped resistance heating elements 14.

Further variants of resistive, thermal radiators 6 and arrangements are shown in FIGS. 5 to 8. The thermal radiator 6 shown in FIG. 5 is designed as Heizspira ^¬ le 16, wherein the receiving space 9 and Nutzbereich 10 are cylindrical and arranged within the heating coil. 6, the thermal radiator 6 is a combination of a radiant heater, here a heating coil 16 and a reflector 17, wherein receiving space 9 and useful area 10 between the heating coil 16 and the reflector 17 are. FIG. 7 shows a thermal radiator consisting of two U-shaped heating elements 18 with a receiving space 9 arranged between the two U-shaped heating elements 18. FIG. 8 shows a thermal radiator 6 made up of two flat heating elements 19.

These typically have a surface radiation, whereby the useful area is a particularly large part of the between the flat heating elements 19 lying receiving space 9 occupies.

 With the sintering furnace 1 according to the invention, with a maximum power consumption of 1.5 kW, a heating temperature of at least 1100 ° C. can be achieved within 5 minutes.

The ratio of radiator surface to the surface of the chamber interior surface is specified with a maximum of 2.5. When specifying this value has been assumed that the chamber inner surface corresponded to the surface of the Nutzvolu ^¬ mens. When considering this maximum ratio was essentially based on an annular thermal radiator, as it is formed by the lateral surface of the crucible of Fig. 2A.

In rod-shaped thermal emitters as an embodiment example according to FIGS. 4a, 4b, 7 shows that the Oberflä ^¬ che such thermal radiators may be smaller than the surface of the oven chamber or as the surface of the

Useful volume. In a furnace construction with rod elements as thermal emitters, the chamber inner surface is interpreting ^¬ Lich greater than the useful volume, whereby the surface conditions go quasi zero. If instead the surface of the useful volume is selected, one arrives at a reasonable minimum ratio of radiator surface to the surface of the useful volume of 0.4.

The useful volume is defined as the limit within which a safe burning process is possible. It has geometrical dimensions, which can be given for example by the length, the width and the height (1 xbxh). If the size of the usable volume is increased, the specified ratio to the total surface area of the thermal smaller spotlight. However, such an oven can only be operated permanently with lower power.

It is also conceivable that the dimensions of the thermal radiator protrude beyond the boundary of the furnace chamber, for example to come about the ratio of 2.5. With an upper limit of the ratio of 3, a sufficient ^¬ the balance between the economic to be operated additional technical effort and the advantage of the invention is given here. The lower limit of 1 borders the

Invention in terms of performance against ovens with smaller thermal radiators.

Fig. 9-16 shows various arrangements of the thermal radiator and the useful volume in the furnace chamber. Thus, Fig. 9 shows a schematic structure of a furnace 21 with a furnace chamber 22 which is bounded at least partially by an inner and an outer door brick 23, 24, also referred to as upper and lower Türstein down. The door stone is laterally surrounded by the lower wall portion of the furnace chamber, which is formed in several parts in the present case, namely with three layers.

 On the lower wall portion 25 sits in the furnace chamber 22 arranged annular thermal radiator 26, which in turn is surrounded by an annular insulating wall portion 27. For reasons of clarity, the coils located further outside are inductive

 Heating of the thermal radiator 26 not shown.

Above the annular wall portion 27 is the

Oven chamber 22 bounded by the upper wall portion 28 which is formed as the lower wall portion 25 in multiple layers. Through the upper wall portion 28, a Thermoele ^¬ ment 29 projects into the oven chamber 22 and penetrates a little way into the thermal radiator 26 umschllos- senen interior 30 and limited so in the interior 30 arranged useful volume 31, since the arranged on the door brick 23, not shown component not with the

Thermocouple 30 may come into contact.

The surface of the oven chamber 22 is here formed by the furnace chamber facing surface of the wall portion 27 and from the top of the door stone 23 and the underside of the upper wall portion 28. The annulus around the thermocouple and gaps between the first door member and the lower wall member are neglected.

 FIG. 10A shows in detail the arrangement of the restricted useful area 31 with respect to the radiator 26 of FIG. 9, in order to face it in relation to a useful area 31 shown in FIG. 10B. The ratio of the total surface area of the thermal radiator and the furnace chamber does not change even if the ratio of the total surface area of the thermal radiator to the surface of the effective volume of FIG. 10A is lowered as shown in FIG. 10B.

In Fig. 11, a thermal radiator 26 is shown, which also also has a bottom 32 and a cover 33, whereby the total surface of the thermal radiator 26 relative to the entire surface of the thermal radiator 26 of FIG. 9 increases. The useful volume 31 corresponds to that of FIG. 10B. In Fig. 12, the effective volume 31 by insulating

Wall sections 34, 35 reduced, the thermal radiator remains unchanged even with respect to Fig. 9 and 10A, 10B. This also reduces the surface of the

Furnace chamber and the ratio of the total surface of the thermal radiator and the furnace chamber is larger. FIG. 13 shows a furnace 41 with a furnace chamber 42 which extends above the interior 31 of the thermal radiator 43 upwards and downwards and continues into the upper and the lower wall sections 28, 25, so that the useful area is increased. This reduces the ratio of

Overall surface of the thermal radiator and the Ofenkam ^¬ mer.

In Fig. 14 is further reduced the useful region 13 over the useful region of FIG., By having the upper and the lower wall portion 28 ', 25' is no longer the same inner diameter as the thermal ^¬ radiator 43. The total surface area of the thermal radiator remains the same, but the surface area of the furnace chamber is reduced from that of FIG. 13.

In Fig. 15, a plurality of cylindrical thermal radiator 52 are shown in a predetermined oven chamber 51, here are shown 4 thermal radiators, in pairs at a distance zueinan ^¬ arranged, which extend into the plane. Between a radiator pair is the useful range. The ratio of the total surface area of the thermal radiators 52 and the surface of the oven chamber 51 is smaller as compared with the arrangement of Figs. 9-14.

This also applies if oblong surface heating elements 62 are used in your furnace chamber 61 instead of cylindrical thermal radiators, as shown in FIG. 16.

 The thermal radiators of FIGS. 15 and 16 can also be resistive radiators, which heat up due to the electrical resistance when passing an electrical current.

Claims

 claims Sintering furnace (1) for components (15) made of a sintered material, in particular for dental components and in particular for components (16) of ceramic comprising a Ofenkam ^¬ mer (2) with a chamber volume (CV) and a chamber inner surface (OK), wherein in the Furnace chamber (2) a heating device (5), a receiving space (9) with a in the chamber volume (VK) lying by the heating device (5) limited gross volume (VB) and a useful area (10) with a gross volume (VB) useful volume ( VN) are arranged and wherein the furnace chamber (2) has a wall consisting of several walls (3) with at least one opening Wandab ^{¬ section} (7) for introducing a component to be sintered (15) in the receiving space (9) characterized in that the heating device (5) in the furnace chamber (2) contains at least one thermal radiator (6) having a specific resistance of 0, lQmm ² / m to 1000000 Qmm ² / m and has a Ge ^¬ velvetic surface, which is a maximum of 3 times, in particular ^¬ a maximum of 2.5 times the chamber inner surface (OK). Sintering furnace (1) according to claim 1, characterized in that the chamber volume (CV) of the sintering furnace (1) Zvi ^¬ rule 50 cm ³ and 200 cm ^3.  Sintering furnace (1) according to claim 1, characterized in that the maximum total surface of the thermal radiator (6) is about 400 cm ". Sintering furnace (1) according to claim 1, characterized in that the ob ektvolumen (VO) is a maximum of 20 x 20 x 40 mm ³ . Sintering furnace (1) according to claim 1, characterized in that the thermal radiator (6) can be heated resistively or inductively. Sintering furnace (1) according to claim 1, characterized in that the heating device (5) consists of graphite, M0S1 ₂ , SiC or glassy carbon.  Sintering furnace (1) according to one of claims 1 to 6, characterized in that the walling for the radiation field (13) impermeable and / or this to ^¬ returning chamber inner wall which carries in particular a reflective coating or is designed as a reflector ^¬ gate.  Sintering furnace (1) according to one of claims 1 to 7, characterized in that the thermal radiator (6) of the heating device (5) has a heating rate in the useful range of at least 200 K / min at 20 ° C. Sintering furnace (1) according to one of claims 1 to 8, characterized in that the useful volume (VN) maxi ^¬ times 20x20x40 mm ³ and that the dimensions of the effective volume (VN) are at most 20 mm x 20 mm x 40 mm. Sintering furnace (1) according to one of claims 1 to 9, characterized in that the thermal radiator is designed as a crucible (11). Sintering furnace (1) according to one of claims 1 to 10, characterized in that the total surface min ^¬ least 1.0 times the chamber inner surface (OK) is.