Dental firing apparatus

Abstract

The present invention provides a dental firing apparatus that allows for a reduction in the thickness of the heat insulating structure and enables miniaturization of the firing apparatus. [Solution] The invention comprises a heating means 3 for heating an object to be fired, and an insulating structure that surrounds the heating means 3. The insulating structure is characterized by having a structure in which a first insulating material 17 is provided opposite to the heating means 3, and a second insulating material 18 is provided outside the heating means 3 and has lower heat resistance and lower thermal conductivity than the first insulating material 17.

Description

Technical Field

[0001] The present invention relates to a dental firing apparatus that fires ceramics or the like by using a heater provided in a heat insulation structure.

Background Art

[0002] Conventionally, ceramic restorations have been used as dental restorations. For example, Patent Document 1 below discloses an apparatus for firing a restoration by a heating element installed in a furnace.

[0003] In recent years, due to excellent aesthetics, restorations made of zirconia have been widely used as dental restorations. As the heating element, a resistance heating element such as molybdenum disilicide or silicon carbide is generally used, and molybdenum disilicide is often used for firing zirconia restorations that require firing at high temperatures.

[0004] A molybdenum disilicide heater has a SiO2 protective film formed on its surface, but this protective film may peel off due to repeated heating and cooling of the heater and adhere to the fired restoration. For such a heater that can generate heat at high temperatures, for example, a heat insulating material mainly composed of alumina fiber may be used.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] In a dental firing apparatus, for example, by using a heat insulating material mainly composed of alumina fiber as described above, the dental firing apparatus has sufficient heat resistance against a maximum temperature of 1600°C. However, in order to ensure a high heat insulation effect, it is necessary to thicken the heat insulating material, and there is a problem that it is difficult to miniaturize the apparatus. [Means for solving the problem]

[0007] In view of the above issues, the dental firing apparatus according to the present invention is A heating means for heating the object to be fired, A heat insulating structure covering the periphery of the heating means and It has, The aforementioned heat insulating structure includes a first heat insulating material provided opposite to the heating means, The heating means is characterized by a structure in which a second insulating material, which has lower heat resistance and lower thermal conductivity than the first insulating material and is provided on the outside of the first insulating material, is laminated. [Effects of the Invention]

[0008] The thickness of the insulating structure can be reduced, allowing for a smaller firing apparatus. [Brief explanation of the drawing]

[0009] [Figure 1] Side cross-sectional view illustrating the firing apparatus in this embodiment. [Figure 2] Side cross-sectional view illustrating the state in which the stage of the firing apparatus in this embodiment has been lowered. [Figure 3] Diagram illustrating the configuration of the firing apparatus in this embodiment. [Figure 4] Cross-sectional view of the furnace body in Example 1 [Figure 5] Cross-sectional view illustrating a modified example of the furnace body in Example 1. [Figure 6] External view of the furnace body in Example 1 [Figure 7] Cross-sectional view of the furnace body in Example 2 [Figure 8] Graph illustrating the thermal conductivity of the second insulating material in Examples 1 and 2. [Modes for carrying out the invention]

[0010] The dental firing device according to this embodiment is shown in Fig. 1. Fig. 1 is a side sectional view for explaining the firing device in this embodiment. The dental firing device 1 includes a heater 3 for heating the furnace chamber 2, a first heat insulating material 17 in the side direction surrounding the furnace chamber 2, a second heat insulating material 18 outside the first heat insulating material 17, an upper heat insulating material 21 in the upper surface direction, a stage 7 for taking in and out the prosthesis 6 fired by this firing device into and out of the furnace chamber 2, and a lifting device 8 for lifting and lowering the stage 7.

[0011] For the heater 3, a resistance heating element such as molybdenum disilicide, silicon carbide, or carbon is used. Particularly for firing zirconia, which has been frequently used as a material for prostheses in recent years, molybdenum disilicide heaters are widely used.

[0012] The heater shape is usually formed into a rod shape and then bent and processed into a U shape, a W shape, or a coil shape. The heater 3 is supplied with power from a power source (not shown) via an electric wire 9 and heated to a temperature corresponding to the material of the prosthesis 6.

[0013] The object to be fired is fired inside the furnace. As materials for dental prostheses that require firing, lithium disilicate and zirconia are usually used. In the case of zirconia, it is fired at a temperature of 1500 - 1600 °C for several tens of minutes to about 2 hours.

[0014] Conventionally, firing zirconia usually took 7 - 8 hours, but in recent years, materials that can be fired in 90 minutes or less have emerged due to material development.

[0015] The temperature inside the furnace is detected by a thermocouple 10, and the heater temperature is controlled according to a preset heating program.

[0016] For the thermocouple 10, platinum, platinum rhodium, tungsten - rhenium alloy, etc. that can withstand high temperatures are used, but it is not limited to these.

[0017] In this embodiment, in order to suppress the variation in the position of the tip of the thermocouple, it is placed in a ceramic protection tube such as alumina and fixed to the upper heat insulating material 21.

[0018] The tray 11 is a container for placing the patch 6, and ceramics such as alumina and silicon carbide are used because it is used at high temperatures.

[0019] The tray 11 is covered with a tray lid 12 and fired. In this embodiment, a through-hole into which the tip of the thermocouple 10 can be inserted is provided at the center of the tray lid. During firing, the tip of the thermocouple 10 is inserted into the tray 11, and the temperature near the workpiece is detected to control the heater temperature.

[0020] The tray 11 is placed on the firing table 13, and the firing table 13 is further placed on the stage 7.

[0021] The set of the patch 6 is performed with the stage lowered as shown in FIG. 2. FIG. 2 is a side cross-sectional view for explaining the state where the stage of the firing apparatus has descended. After putting the patch 6 into the tray 11 and covering the tray 11 with the tray lid 12, the lifting device 8 of the firing apparatus is raised to introduce the patch 6 into the furnace chamber 2.

[0022] By this upward movement, as shown in FIG. 3, the tip of the thermocouple 10 passes through the through-hole of the tray lid 12 and is inserted into the tray 11. FIG. 3 is a diagram for explaining the configuration of the firing apparatus. As shown in FIG. 3, the thermocouple 10, the tray 11, the tray lid 12, the firing table 13, and the stage 7 are positioned so that the tip of the thermocouple 10 does not collide with the tray lid 12.

[0023] In this embodiment, positioning pins 14 are set on the stage, and the firing table 13 is placed by fitting the positioning holes 15 to the positioning pins 14.

[0024] A depression is carved on the upper surface of the firing table 13, and the tray 11 is placed by fitting it into this depression.

[0025] [[ID=2,8]] Furthermore, the tray lid 12 has a stepped structure and is placed so as to fit into the opening of the tray 11. The positioning means is not limited to these, and heat-resistant pins, guides, hole machining, etc. can be arbitrarily used. [[ID=3,0]] [[ID=3,1]]

[0026] Since the firing stand 13 is made of brittle insulating material that can withstand high temperatures, such as alumina fiber or ceramic fiber, repeated placement and removal of the tray 11 will cause wear on the outer circumference of the depressions formed in the firing stand 13. As a result, the position of the tray 11 will vary, and consequently, the position of the through-hole in the tray lid 12 relative to the thermocouple 10 will also vary, increasing the likelihood of the thermocouple 10 and the top surface of the tray lid 12 colliding.

[0027] Therefore, the central through-hole of the tray lid 12 may have a wide, mortar-shaped chamfer at the top. By making it mortar-shaped, even if the position of the through-hole varies, the tip of the thermocouple 10 will be guided by the mortar shape as it is inserted into the through-hole, preventing damage to the tray lid 12 or the thermocouple 10.

[0028] Furthermore, it is preferable that the tip of the thermocouple 10 protrudes below the bottom surface of the tray lid 12 so that it can detect the temperature inside the tray 11, and it is even more preferable that it protrudes close to the prosthesis 6 without touching it.

[0029] While motors, pneumatic cylinders, hydraulic cylinders, etc., can be used as the drive source for the lifting device 8, a motor with excellent position control and speed control properties is particularly preferred.

[0030] The lifting device 8 may also have a collision detection means (not shown) that detects the load on the motor during lifting and stops the lifting operation if the load exceeds a predetermined level. Even if the tray lid 12 shifts and collides with the thermocouple 10, the collision detection means can prevent damage to the tray lid 12, thermocouple 10, etc.

[0031] In another embodiment, there is a drive device that can move the thermocouple 10 up and down, and a motor, pneumatic cylinder, hydraulic cylinder, etc., can be used.

[0032] In this embodiment, first the thermocouple 10 is retracted to the upper part of the furnace, and the firing stand 13, tray lid 12, tray 11, and prosthesis 6 are brought into the furnace. Subsequently, the thermocouple is lowered by the drive device and inserted through the through hole in the tray lid 12 into the interior of the tray 11.

[0033] This method allows the position of the thermocouple tip to be changed by the amount of movement of the drive mechanism, making it possible to measure the height of the workpiece in advance and adjust the position of the thermocouple to the appropriate location.

[0034] <Example 1> Embodiments of the present invention will be described below with reference to the drawings, but the present invention is not limited thereto.

[0035] Figure 4 shows a cross-sectional view of a furnace body according to Embodiment 1 of the present invention. The heater unit 16 shown in Figure 4, which serves as a heating means for heating the workpiece to be fired, is configured as an insulating structure by comprising a heater 3, a first insulating material 17 (side insulating material) provided opposite the heater to insulate against heat radiating in the circumferential direction of the heater, and a second insulating material 18 laminated on the outside of the first insulating material 17. An upper insulating material 21 is placed on the upper side of the heater unit 16 to insulate against heat radiating upward, and a lower insulating material 22 is placed on the lower side to insulate against heat radiating downward.

[0036] As the first insulation material 17, in this embodiment, an insulation material is used that is mainly made of alumina fiber containing 70% or more alumina, with binders such as silica and sodium silicate added. However, there are no particular limitations on the material, and general fibrous materials mainly composed of ceramics such as silicon carbide and brick can be used. Alumina fiber has a high heat resistance temperature and low thermal conductivity compared to general fibrous materials, so the thickness of the insulation material can be reduced.

[0037] Because the first insulation material 17 lowers the temperature at which heat is transferred from the heater, the second insulation material 18 can be made of an insulation material with a lower heat resistance temperature and higher thermal conductivity than the first insulation material 17. In this embodiment, an insulation material is used which is made by continuously laminating silica-calcia-magnesia-based alkali earth silicate wool containing 76% or more silica as ceramic fiber, forming it into a blanket shape, and then needle-punching it. However, there are no particular limitations on the material, and materials commonly used for insulation materials such as glass fiber or rock fiber can be used.

[0038] In this embodiment, the first insulating material 17 is an insulating material mainly composed of alumina fiber with a heat resistance temperature of 1700°C, which is higher than the firing temperature of the workpiece (1500-1600°C), and a thermal conductivity of 0.30 [W / m·K] when the insulating material is at 1400°C (measured by the hot-wire method using a platinum-rhodium alloy containing 13% rhodium as the positive side conductor and platinum as the negative side conductor, based on JIS R2616. The thermal conductivity will be measured in the same way hereafter). The second insulating material 18 is an insulating material mainly composed of ceramic fiber with a heat resistance temperature of 1300°C, which is lower than the firing temperature of the workpiece (1500-1600°C), and a thermal conductivity of 0.16 [W / m·K] when the insulating material is at 600°C, but is not limited to this. Note that the thermal conductivity of the second insulating material 18 increases in proportion to the temperature, as shown in the graph in Figure 8. It is sufficient for the first insulation material 17 to be usable in a temperature range lower than its thermal conductivity (low thermal conductivity range), and the thickness of the first insulation material 17 is set so that the temperature of the second insulation material 18 is in the low thermal conductivity range. In other words, the thickness of the first insulation material 17 is such that the temperature of the second insulation material 18 is in the low thermal conductivity range.

[0039] In this case, for example, in high-temperature regions of 600°C or higher, if the ambient temperature is the same, the thermal conductivity of the second insulating material 18 is higher than that of the first insulating material 17.

[0040] The ceramic fiber used as the second insulation material 18 has lower heat resistance than alumina fiber, but it has lower thermal conductivity at low temperatures and is relatively inexpensive. Therefore, it is possible to reduce the size of the insulation structure while achieving both cost reduction and insulation performance.

[0041] In this embodiment, the first insulation material 17 and the second insulation material 18 are made of fibrous inorganic material, but the invention is not limited to this. Furthermore, although the insulation material is configured with two layers, it may also be configured with three or more layers.

[0042] Furthermore, as shown in the modified example in Figure 5, the insulation material may be fixed using multiple claw-shaped fixing parts 20. When multiple claw-shaped fixing parts 20 are used, it is not necessary to cover the entire material as with a strip-shaped fixing, and it is sufficient to fix the insulation material at positions corresponding to three points obtained by dividing the circumference of the insulation material into three parts using the claw-shaped fixing parts 20.

[0043] In this embodiment, the first insulation material 17 and the second insulation material 18 are formed in a cylindrical shape, and the second insulation material 18 is laminated on the outer circumference of the first insulation material 17. The cylindrical shape makes it easier to process than a polygonal shape.

[0044] The second insulation material 18 is formed in a strip shape. Since the strip-shaped insulation material needs to be fixed in a wrapped state, a belt-shaped fixing member 19 is arranged to cover the perimeter of the laminated structure, as shown in the external view of the furnace body in Figure 6, and then fixed in place. The fixing member 19 only needs to be able to fix the insulation material, and can be fixed by screwing, riveting, welding, etc.

[0045] An upper insulating material 21 is placed on the upper side of the heater unit 16 to insulate against heat dissipation in the upward direction, and a lower insulating material 22 is placed on the lower side to insulate against heat dissipation in the downward direction, forming a furnace body 26 for heating the object to be fired, with the heater unit 16 in between.

[0046] The upper insulation material 21 and the lower insulation material 22 are connected and fixed between the insulation material holding surface 23 that holds the insulation material and the upper surface of the upper insulation material 21 by four column-shaped holding members 24 and insulation material retaining parts 25. The holding members 24 restrict lateral movement, and the insulation material retaining parts 25 restrict vertical movement.

[0047] The four columnar holding members 24 are arranged so as to be diagonally opposite each other.

[0048] Furthermore, by making each holding member columnar, it is possible to avoid wiring protruding from the heater unit toward the rear of the device, and it also becomes easier to arrange the thermocouple wiring toward the rear of the device. In addition, the weight of the device can be reduced.

[0049] In this embodiment, the columnar holding members 24 are configured as four, but the number of columnar parts can be appropriately selected as needed.

[0050] Furthermore, if a member that restricts lateral movement is provided on the insulation material holding surface 23, the number of column-shaped holding members may be limited to two.

[0051] In the heater unit 16, we compare the thickness of the insulation material when the temperature inside the furnace is set to 1600°C and the surface temperature of the insulation material outside the furnace is assumed to be approximately 160°C.

[0052] When the firing apparatus is constructed using only the first insulation material 17, which is mainly composed of alumina fiber, a thickness of 100 mm of insulation material is required. However, when the first insulation material 17 is made mainly of alumina fiber and the second insulation material 18 is made mainly of ceramic fiber, equivalent insulation performance can be obtained with a thickness of 47 mm (32 mm for the first insulation material and 15 mm for the second insulation material), and the apparatus can be miniaturized by making the insulation material thinner.

[0053] <Example 2> Next, a firing apparatus according to Embodiment 2 of the present invention will be described. The basic configuration of Embodiment 2 is the same as that of Embodiment 1. Therefore, in the following description, the same reference numerals will be used for the same parts, and their explanations will be omitted.

[0054] Figure 7 shows a cross-sectional view of a furnace body according to Embodiment 2 of the present invention. In Embodiment 1, the heater was bent into a U shape and fixed to the upper insulation material 21, but in this embodiment, it is bent into a zigzag shape 27 and held in place by fasteners fixed to holes drilled in the first insulation material 17.

[0055] By doing so, the number of parts is reduced, and in addition to providing insulation for safety outside the furnace, the furnace chamber 2 is formed, making it possible to miniaturize the device.

[0056] Furthermore, fewer through-holes are preferable in terms of insulation performance. In Example 1, three heaters are used, and six through-holes are provided in the upper insulation material 21. In this example, only one heater is used, so there are only two through-holes in the first insulation material, making it possible to improve insulation performance compared to Example 1.

[0057] Conventionally, through-holes were provided in the upper insulation material 21, but in this embodiment, since the thickness of the radial insulation material can be reduced, the through-holes are provided in the first insulation material 17. This makes it possible to shorten the length of the heater, which contributes to cost reduction. Also, as mentioned above, since the heater 3 is fixed to the first insulation material 17, it is sufficient to use a material with high heat resistance only for the first insulation material 17. [Explanation of Symbols]

[0058] 1. Dental firing apparatus 2 Furnace room 3 Heater 6. Prostheses 7 stages 8. Lifting device 9 Electric wire 10 Thermocouples 11 trays 12 Tray lid 13 Baking stand 14 Positioning pins 15 positioning holes 16 Heater Unit 17. First insulation material 18. Second insulation material 19 Fixing member 20 Fixing parts 21 Upper insulation 22 Lower insulation 23 Retaining member 24 Retaining member 25 Retaining member 26 Furnace body 27 Heater with a zigzag pattern

Claims

1. A heating means for heating the object to be fired, A heat insulating structure covering the periphery of the heating means and It has, The aforementioned heat insulating structure includes a first heat insulating material provided opposite to the heating means, A dental firing apparatus characterized in that, relative to the heating means, a second insulating material having lower heat resistance and lower thermal conductivity than the first insulating material is laminated on top of the first insulating material.

2. The dental firing apparatus according to claim 1, characterized in that the heating means is fixed to the first insulating material and the first insulating material forms a furnace chamber.

3. The first and second insulating materials have fixing members that cover the periphery of them, The dental firing apparatus according to either claim 1 or 2, characterized in that the fixing member is belt-shaped.

4. Having a retaining surface for holding the aforementioned heat insulating structure, The first and second insulating materials are formed in a cylindrical shape. The upper insulation material located on the upper surface of the first and second insulation materials, Lower insulation material located on the lower surface of the first and second insulation materials It has, The dental firing apparatus according to either claim 1 or 2, characterized in that the first and second insulating materials and the upper and lower insulating materials are fixed by connecting the insulating material holding surface and the upper insulating material with at least three columns.

5. The dental firing apparatus according to claim 1, characterized in that the first insulating material has a thickness such that the temperature of the second insulating material is in the low thermal conductivity range.

6. The dental firing apparatus according to claim 1, characterized in that the heat resistance temperature of the first insulating material is higher and the heat resistance temperature of the second insulating material is lower than the firing temperature of the workpiece fired by the heating means.

7. The dental firing apparatus according to claim 6, wherein the first insulating material is mainly composed of alumina fiber and the second insulating material is mainly composed of ceramic fiber.

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