Sintering Furnace

Abstract

A sintering furnace (1) for sintering a dental workpiece (2) includes a heating element (3) having a storage space (4) for storing the workpiece (2) during the sintering process. The storage space (4) is a partial area of ​​an internal space (5) inside the heating element (3). The heating element (3) includes or is made of silicon carbide. The heating element (3) is a cylindrical member having slits formed at least partially therein. The slits (6) in the heating element (3) are spirally formed, forming the cylindrical member in a heating area (7) surrounding the storage space (4).

Description

[Technical field]

[0001] The present invention relates to a sintering furnace for sintering dental workpieces, the sintering furnace comprising a heating element having an accommodation space for accommodating the workpiece during the sintering process, the accommodation space being a partial area of ​​an internal space inside the heating element, the heating element including or made of silicon carbide. [Background technology]

[0002] In the prior art, sintering furnaces of various configurations for sintering dental workpieces are known. Various design variants of sintering furnaces have been proposed (see US Pat. No. 5,399,313). In these variants, a crucible made of, for example, silicon carbide is provided and is heated inductively from the outside by a rotating coil. In FIG. 5 of US Pat. No. 5,399,313 is very diagrammatically shown a heating element in the form of a wire-like heating spiral, inside which a receiving space for receiving the workpiece during sintering is arranged. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] European Patent Publication EP3132217B1 Summary of the Invention [Problem to be solved by the invention]

[0004] The aim of the present invention is to design a sintering furnace of the above mentioned type which is as efficient as possible, thereby allowing rapid high temperature sintering with it. [Means for solving the problem]

[0005] In order to solve this problem, the present invention provides a heating element designed as a tubular member in which slits are formed at least partially, the slits in the tubular member constituting the heating element being configured in a spiral manner in the heating area in which the heating element surrounds the receiving space. The heating element is positioned horizontally in the operating position. To provide.

[0006] Due to the heating element being configured as a tubular member at least partially slitted, which slits are helical in the heating area, a highly efficient sintering furnace is realized with very high sintering temperatures required for high-temperature sintering. This allows the heating time to be as short as possible with an appropriate energy consumption and allows the sintering furnace according to the invention to sinter dental workpieces at very high temperatures and very fast. Sintering temperatures of up to 1600°C are preferably achieved in the accommodation space surrounded by the heating area of ​​the heating element. The heating rate of the sintering furnace according to the invention is preferably comprised within the range of 5°C / min to 350°C / min. According to the invention, a wide variety of dental workpieces, such as crowns, onlays, bridges, artificial teeth, etc., can be sintered in the sintering furnace. The heating element is preferably an active heating device or heating device which generates heat from electrical energy. The heating element is preferably a resistive heating element, i.e. a heating element which generates heat when an electric current flows through it. The accommodation space for accommodating the workpieces is arranged inside this heating element during sintering, so that the accommodation space can be heated quickly to the required sintering temperature as a whole.

[0007] The heating element may contain silicon carbide or may consist exclusively of silicon carbide. The use of a tubular element with helical slits in the heating area is superior to heating elements in the form of a wire spiral known from the prior art in that a spatially very uniform and corresponding high temperature distribution can be generated in the receiving space. The high temperatures required for rapid sintering of the workpieces are achieved overall with relatively little electrical energy. The design of the heating area as a tubular element with helical slits results in a significantly more uniform high temperature distribution in the receiving space than when using a heating element designed as a wire spiral according to the prior art.

[0008] In this sense, at least in the heating area, where the slits in the tubular member are formed in a spiral, the ratio between the width of the slits in the pipe in which the slits are formed and the width of the bridge arranged between two adjacent slits is preferably within the range of 1:1 to 1:10, more preferably 1:3 to 1:7. In other words, in the heating area, i.e. in the area of ​​the tubular member in which the slits are formed in a spiral, the bridge between two adjacent slits in the tubular member in which the slits are formed has the same width as the slit or slits, preferably wider than said slits. The bridge is part of the wall of the tubular member in which the slits are formed, which generates heat when the heating element is operating and generates the required temperature in the receiving space.

[0009] In order to concentrate the temperature or heat required for sintering in the accommodation space, in a preferred variant of the invention, the internal space located inside the heating element and spaced apart from the accommodation space is at least partially filled with insulating material, preferably refractory material.

[0010] In a preferred, if not absolutely necessary, variant of the invention, the heating element is arranged lying horizontally in the operating position of the sintering furnace, so that the longitudinal axis of the tubular member forming the heating element extends horizontally in the operating position, the tubular member being preferably a hollow cylinder with a circular base area and with one or more corresponding slits formed in the cylinder jacket wall.

[0011] The heating element comprises a connection area in addition to the heating area, in which a preferably straight elongated slit is formed in the tubular member constituting the heating element, which extends in the longitudinal direction of the heating element. The heating area in which the slit of the tubular member constituting the heating element is formed in a spiral shape is the part of the heating element that generates heat during operation. It is also called a hot zone. In a preferred embodiment, the connection area of ​​the heating element does not generate heat even during operation of the sintering furnace. Rather, the connection area is an area of ​​the heating element where the heating element is held inside the sintering furnace and can be electrically connected. In this sense, it is preferred that the electrical connection of the heating element is realized at the end of the connection area opposite the heating area. The elongated slit in the connection area divides the tubular heating element in the connection area into two electrically separated areas, and an electrical connector may be connected to each of these areas. The elongated slit in the connection area may extend in a straight line, linear shape, or may extend in a different shape. In any case, since the slit in the connection area is not spiral, the heating element in the connection area is not heated as much when a current flows through it as in the heating area. An electric current is suitably supplied to the heating element via the electrical connector of the heating element, so that this current flows through the heating element in the connection area and the heating area in order to generate the required temperature or heat, thereby heating the heating area accordingly. Since the connection area is not heated as much as the heating area during the operation of the sintering furnace, said connection area is used both for fixing the heating element to the sintering furnace and for attaching the electrical connector. The connection area is preferably at least as long as the heating area, and preferably longer than the heating area. In this connection, it is preferred that in the longitudinal direction of the heating element, the ratio of the length of the heating area to the length of the connection area is comprised in the range of 1:1 to 1:5, preferably in the range of 1:2 to 1:4. The total length of the heating element is preferably comprised in the range of 150 mm to 300 mm.

[0012] In the sintering furnace according to the invention, the heating element preferably has an inlet opening for introducing the workpiece to be sintered into the receiving space, which inlet opening is preferably closable by a furnace door of the sintering furnace, which is preferably arranged so as to be linearly displaceable. In this connection, it is preferred that a workpiece support is fixed relative to the furnace door, and the workpiece to be sintered is introduced into the receiving space supported by the workpiece support and is held by the workpiece support during the sintering process. The workpiece support may preferably be a tongue-shaped elongated element protruding from the furnace door. The workpiece support is preferably made of silicon carbide. The workpiece support is suitably arranged in the closed position of the furnace door in such a way that the workpiece placed thereon is as centrally located as possible in the receiving space.

[0013] The sintering furnace includes a chamber wall made of a heat insulating material and a furnace chamber surrounded by the chamber wall, and the heating element is disposed inside the furnace chamber, and the chamber wall is preferably at least partially separated from the heating element in the heating area. The gap between the heating area of ​​the heating element and the chamber wall of the furnace chamber prevents damage to both the heating element and the chamber wall. However, the heating element may be in direct contact with the chamber wall. The gap between the chamber wall and the heating element is preferably at least partially included in the range of 0 mm to 30 mm in the heating area.

[0014] Further features and details of preferred embodiments of the invention are explained on the basis of an embodiment of a sintering furnace according to the invention with the aid of the following figures. [Brief description of the drawings]

[0015] [Figure 1] FIG. 2 is a schematic cross-sectional view of an embodiment of a sintering furnace according to the present invention in an open state. [Diagram 2] FIG. 2 is a schematic cross-sectional view of one embodiment of a sintering furnace according to the present invention in a closed state. [Diagram 3] FIG. 3 is a side view of the heating element used in FIGS. 1 and 2; [Figure 4] FIG. 2 is a front view of the heating element in the area of ​​the inlet opening. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] 1 and 2 show a schematic vertical cross-section of an embodiment of a sintering furnace 1 according to the invention. The sintering furnace 1 comprises a housing 30, shown here only diagrammatically, and a chamber wall 22 surrounding a furnace chamber 23. The chamber wall 22 may, for example, consist of firebricks or other suitable thermal insulation material. The heating element 3 of the sintering furnace 1 is arranged inside the furnace chamber 23. The heating element 3 according to the invention is designed as a tubular member, in which slits are formed at least partially. The slits 6 of the tubular member forming the heating element 3 are formed in a spiral shape in a heating area 7. The heating area 7 is a part of the heating element 3 surrounding a receiving space 4 for receiving the workpiece 2 in the sintering process. The receiving space 4 is an area of ​​a part of the internal space 5 inside the heating element 3. In this embodiment, the heating element 3 is entirely made of silicon carbide, except for the electrical connector 16. In the heating area 7, in which the slits 6 in the pipe are formed in a spiral shape, the slits 6 preferably have a width 8 in the range of 2 mm to 10 mm. In a preferred variant of the invention, the bridge 10 arranged between two adjacent slits 6 of the tubular member in which the slits are formed has a width 9, preferably between 2 mm and 25 mm. The width 9 of the bridge 10 (web) is preferably at least the same as the width 8 of the helical slit 6, more preferably greater than the width 8 of the helical slit 6. As mentioned above, the ratio between the width 8 of the slit 6 in the heating area 7 and the width 9 of the bridge 10 between the parts of two adjacent slits 6 is preferably included in the range of 1:1 to 1:10, more preferably in the range of 1:3 to 1:7. The bridge 10, which is relatively wide with respect to the slits 6, ensures a uniform spatial heat distribution inside the receiving space 4 during the sintering process. From Fig. 1 and Fig. 2 it can be seen that the heating element 3 is arranged horizontally in the operating position of the sintering furnace 1. A preferred embodiment of the invention provides that in the area of ​​the heating element 3 outside the heating area 7 the internal space 5 inside the heating element 3 is at least partially filled with a heat insulating material 11. The heat insulating material 11 is preferably fireclay or firebricks.Due to the fact that the internal space 5 of the heating element 3 is filled with insulating material 11 away from the accommodation space 4, the heat required for the sintering process, generated in the heating area 7 of the heating element 3, is concentrated in said area, i.e. in the accommodation space 4.

[0017] In this embodiment, the heating element 3 comprises a connection area 12 in addition to the heating area 7. In the connection area 12, a slit 14 is formed, which preferably extends linearly in the longitudinal direction 13 of the heating element 3. A connector 16 of the heating element 3 for supplying electrical energy or current to said heating element 3 is arranged at an end 15 of the connection area 12 opposite the heating area 7. The connection area 12 is significantly cooler than the heating area 7 when the sintering furnace 1 is in operation and may be used to fasten the heating element 3 to the sintering furnace 1 there. Furthermore, the connection area 12 ensures that the electrical connector 16 is sufficiently spaced from the heating area 7 so that said electrical connector 16 is not damaged or destroyed. In the longitudinal direction 13 of the heating element 3, the connection area 12 is preferably at least as long as the heating area 7 or longer. In a preferred embodiment, as mentioned above, the ratio of the length 17 of the heating area 7 to the length 18 of the connection area 12 in the longitudinal direction 13 of the heating element 3 is in the range of 1:1 to 1:5, preferably in the range of 1:2 to 1:4.

[0018] All of the slit areas of the tubular member constituting the heating element 3 are formed by a single continuous slit 6 or 14. However, a plurality of slits 6 or 14 may be provided in the tubular member.

[0019] In this embodiment, the chamber wall 22 of the sintering furnace 1 made of a thermal insulating material is at least partially separated from the heat generating element 3 in the heating area 7, preventing damage to both the heat generating element 3 and the chamber wall 22. As described above, the heat generating element 3 may be in direct contact with the chamber wall 22. The distance 24 between the heat generating element 3 or its heating area 7 and the chamber wall 22 is preferably within the range of 0 mm to 30 mm.

[0020] In this embodiment, at the end of the heating area 7 opposite the connection area 12, an inlet opening 19 is provided, through which the workpiece 2 to be sintered is introduced into the receiving space 4 inside the heating element 3 and can be removed again from the receiving space 4 after the sintering process is completed. The inlet opening 19 can preferably be closed by a furnace door 20 of the sintering furnace 1. The furnace door 20 is preferably mounted linearly displaceable with respect to the housing 30 of the sintering furnace 1. In FIG. 1, the sintering furnace 1 is in an open state with the furnace door 20 exposing the inlet opening 19. In FIG. 2, the sintering furnace 1 is in a closed state and the sintering process is also carried out. In the closed state shown in FIG. 2, the furnace door 20 closes the inlet opening 19. The linear guide 26 in this embodiment, which advances or retreats the furnace door 20 between the open position shown in FIG. 1 and the closed position shown in FIG. 2, is only shown diagrammatically in FIG. 1 and can be realized in a manner known per se in the prior art.

[0021] In this embodiment, as in the other preferred variants, the workpiece support member 21 is fixed to the furnace door 20. This has the result that the workpiece support member 21 moves together with the furnace door 20 when the furnace door 20 moves back and forth between the closed and open positions. The workpiece 2 to be sintered is supported by the workpiece support member 21 when it is introduced into the accommodation space 4 for the sintering process. In the sintering process, the workpiece 2 is placed on the workpiece support member 21. As mentioned above, the workpiece support member 21 is preferably elongated in the shape of a tongue, as shown in Figs. 1 and 2. The workpiece support member 21 is also preferably made of silicon carbide. As is clearly shown in Fig. 2, during the sintering process, the workpiece 2 to be sintered is held by the workpiece support member 21 in an approximately central position of the accommodation space 4 inside the heating element 3 or heating area 7.

[0022] In Fig. 3 the heating element 3 used in Figs. 1 and 2 is shown with the other components of the sintering furnace 1 omitted. The spiral configuration of the slits 6 in the heating area 7 of the heating element 3, which is cylindrically formed, is shown. In the connection area 12 the slits 14 are designed as slits extending linearly on both sides, so as not to create a short circuit between the two electrical connectors 16 at the rear or end 15 of the connection area 12 opposite the heating area 7.

[0023] FIG. 4 shows a front view of the cylindrical heating element 3 in the area of ​​the inlet opening 19, i.e. the receiving space 4 arranged in the inner space 5 or heating area 7 of the heating element 3.

[0024] In a preferred variant of the invention, the inner diameter 27 of the heating element 3, in particular the heating area 7 shown in FIG. 4, is comprised between 20 mm and 70 mm. The wall thickness of the heating element 3, in particular in the heating area 7, is preferably comprised between 2 mm and 7 mm. In particular, the ratio of the inner diameter 27 of the heating element 3 to the outer diameter 28 of the heating element 3, in the heating area 7, is preferably comprised between 1:1.2 and 1:1.5. The length of the heating area 7 in the longitudinal direction 13 of the heating element 3 is preferably comprised between 20 mm and 70 mm, particularly preferably between 30 mm and 60 mm. [Explanation of symbols]

[0025] 1 sintering furnace, 2 workpiece, 3 heating element, 4 containment space, 5 inner space, 6 slit, 7 heating area, 8 width, 9 width, 10 bridge, 11 insulation, 12 connection area, 13 longitudinal direction, 14 slit, 15 end, 16 electrical connector, 17 length, 18 length, 19 entry opening, 20 furnace door, 21 workpiece support, 22 chamber wall, 23 furnace chamber, 24 spacing, 26 linear guide, inner diameter 27 outer diameter 28, 29 wall thickness, 30 housing.

Claims

1. A sintering furnace (1) for sintering a dental workpiece (2), comprising: The sintering furnace (1) comprises a heat generating element (3) having a receiving space (4) for receiving a workpiece (2) during a sintering process, The storage space (4) is a part of the area of ​​the internal space (5) inside the heating element (3), The heating element (3) comprises or consists of silicon carbide; The heating element (3) is configured as a cylindrical member having slits formed at least partially therein, and the slits (6) in the heating element (3) forming the cylindrical member in a heating area (7) surrounding the accommodation space (4) of the heating element (3) are formed in a spiral shape; The heating element (3) is arranged horizontally in the operating position of the sintering furnace (1), the heating element (3) has an inlet opening (19) for introducing the workpiece (2) to be sintered into the receiving space (4), the inlet opening (19) being adapted to be closed by a furnace door (20) of the sintering furnace (1) or by a linearly displaceable furnace door (20); A workpiece support member (21) or a workpiece support member (21) made of silicon carbide is fixed to the furnace door (20), and the workpiece (2) to be sintered is placed on the workpiece support member (21) and introduced into the receiving space (4), and can be placed on the workpiece support member (21) during the sintering process. Sintering furnace (1).

2. A sintering furnace (1) according to claim 1, At least in the heating area (7) where the slit (6) in the tubular member is formed in a spiral shape, the ratio of the width (8) of the slit (6) to the width (9) of the bridge (10) of the tubular member arranged between two adjacent sections via the slit (6) is in the range of 1:1 to 1:10 or in the range of 1:3 to 1:

7. Sintering furnace (1).

3. A sintering furnace (1) according to claim 1 or 2, The interior space (5) of the heating element (3) separate from the accommodation space (4) is at least partially filled with a heat insulating material (11) or a fireproof material. Sintering furnace (1).

4. The sintering furnace (1) according to any one of claims 1 to 3, The heating element (3) has a connection area (12) in addition to the heating area (7), and in the connection area (12), a slit (14) extending in the longitudinal direction (13) of the heating element (3) or extending linearly is formed in the tubular member forming the heating element (3). Sintering furnace (1).

5. A sintering furnace (1) according to claim 4, An electrical connector (16) of the heating element (3) is formed at an end (15) of the connection area (12) opposite the heating area (7). Sintering furnace (1).

6. A sintering furnace (1) according to claim 4 or 5, In the longitudinal direction (13) of the heating element (3), the ratio of the length (17) of the heating area (7) to the length (18) of the connection area (12) is in the range of 1:1 to 1:5 or 1:2 to 1:

4. Sintering furnace (1).

7. The sintering furnace (1) according to any one of claims 1 to 6, The sintering furnace (1) has a chamber wall (22) made of a heat insulating material (11) or a refractory material, and a furnace chamber (23) surrounded by the chamber wall (22), The heating element (3) is disposed in the furnace chamber (23), The chamber wall (22) is at least partially spaced from the heat generating element (3) in the heating area (7). Sintering furnace (1).

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