Temperature control method for zirconia ceramic block sintering based on continuous kiln

Abstract

The invention relates to a temperature control method for zirconia ceramic block sintering based on a continuous kiln. A kiln of the continuous kiln is sequentially divided into a first preheating area, a first heat preservation area, a second preheating area, a third preheating area, a sintering area and a cooling area from the front end to the rear end. All the areas are divided according to different proportions occupying the length of the continuous kiln, and all the areas correspond to different temperatures and temperature change rates; and meanwhile, the continuous kiln runs at a corresponding propelling speed according to the length of the kiln. According to the continuous kiln, the interior of the continuous kiln is divided into a plurality of different preheating areas and the heat preservation areas are arranged among the preheating areas, so that the zirconia ceramic blocks are heated more uniformly, the temperature is increased stably, and the quality of finished products is effectively improved.

Description

Technical Field

[0001] The invention relates to the field of sintering of zirconium oxide ceramic blocks, in particular to a temperature control method for sintering zirconium oxide ceramic blocks based on a continuous kiln. Background Art

[0002] Zirconia ceramic blocks are widely used in the dental field, mainly for the production of porcelain teeth, dental veneers and inlays. These applications are mainly based on the high aesthetic effect, low shrinkage, high compressive strength, extremely high wear resistance and excellent biosafety of zirconia ceramic blocks. In the existing technology for preparing zirconia ceramic blocks, zirconia powder is first pressed into zirconia cakes, and then the zirconia cakes are fired; currently, they are generally heat treated by a push-plate kiln. During the heat treatment process, the zirconia cakes are gradually pushed into and through the interior of the push-plate kiln, and are heated stably by the operation of the push-plate kiln. During the heat treatment process, the zirconia ceramic blocks often crack and deform due to poor temperature control, which also affects their density and strength, and the quality of the finished product is not high. Summary of the invention

[0003] In view of the existing deficiencies, the present invention provides a temperature control method for sintering zirconia ceramic blocks based on a continuous kiln.

[0004] The technical solution adopted by the present invention to solve the technical problem is: a temperature control method for sintering zirconia ceramic blocks based on a continuous kiln, wherein the kiln of the continuous kiln is divided into a first preheating zone, a first heat preservation zone, a second preheating zone, a third preheating zone, a firing zone and a cooling zone from the front end to the rear end;

[0005] The temperature of the first preheating zone is 300±15°C, the heating rate is 20-23°C / h, and the length of the first preheating zone accounts for 10-11% of the length of the continuous kiln;

[0006] The temperature of the first insulation zone is 300±15°C, and its length accounts for 1-1.3% of the length of the continuous kiln;

[0007] The temperature of the second preheating zone is 800±50°C, the heating rate is 14-20°C / h, and the length of the second preheating zone accounts for 30-40% of the length of the continuous kiln;

[0008] The temperature of the third preheating zone is 950±50°C, the heating rate is 23-30°C / h, and its length accounts for 9-10% of the length of the continuous kiln;

[0009] The temperature of the firing zone is 1000-1080°C, and its length accounts for 10-11% of the length of the continuous kiln;

[0010] The cooling rate of the cooling zone is 38-60°C / h, and its length accounts for 9-10% of the length of the continuous kiln;

[0011] The advancement speed of the continuous kiln corresponding to each meter of the kiln length is 0.013±0.002 m / h.

[0012] Preferably, the first preheating zone, the second preheating zone and the third preheating zone are each divided into a plurality of sub-preheating zones, and the temperatures of the plurality of sub-preheating zones corresponding to the same preheating zone increase sequentially from the front end to the rear end at a certain temperature difference.

[0013] Preferably, the temperature of the first preheating zone is increased from 100-120°C to 300±15°C; the temperature of the second preheating zone is increased from 300±15°C to 800±50°C; the temperature of the third preheating zone is increased from 800±50°C to 950±50°C.

[0014] Preferably, the temperature difference range of each sub-preheating zone in the first preheating zone is 70±10°C; the temperature difference range of each sub-preheating zone in the second preheating zone is 45±10°C; the temperature difference range of each sub-preheating zone in the third preheating zone is 60±10°C.

[0015] Preferably, the sintering zone is divided into a heating zone and a second heat preservation zone from the front end to the rear end, the heating rate of the heating zone is 20-25°C / h, and its length accounts for 1 / 3 of the length of the sintering zone.

[0016] Preferably, the cooling zone is divided into a plurality of sub-cooling zones from the front end to the rear end, and the cooling rates of the plurality of sub-cooling zones gradually decrease from the two ends to the middle.

[0017] Preferably, the continuous kiln is provided with a front buffer zone before the first preheating zone and a rear buffer zone after the cooling zone; the length of the front buffer zone accounts for 3-3.5% of the length of the continuous kiln; the length of the rear buffer zone accounts for 13-15% of the length of the continuous kiln.

[0018] Preferably, the kiln length of the continuous kiln is 21 m, and the advancement speed of the continuous kiln is 0.27 m / h.

[0019] The beneficial effects of the present invention are as follows: the invention sets up a plurality of preheating zones in the kiln of the continuous kiln, and sets up insulation zones between the preheating zones. At the same time, different heating rates in each zone are used to ensure that the zirconium oxide cake material is heated more evenly, avoiding excessive temperature differences. The temperature in each zone of the continuous kiln can be controlled very accurately, solving the problem of uneven heating and improving the quality of the finished product. DETAILED DESCRIPTION

[0020] In order to more clearly illustrate the purpose, technical solutions and advantages of the embodiments of the present invention, the present invention will be further described in conjunction with the embodiments below, and a clear and complete description will be given. Obviously, the embodiments described are partial embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work belong to the protection scope of the present invention.

[0021] The embodiment of the present invention is a temperature control method for sintering zirconia ceramic blocks based on a continuous kiln, in which the kiln of the continuous kiln is divided into a first preheating zone, a first insulation zone, a second preheating zone, a third preheating zone, a firing zone and a cooling zone from the front end to the rear end. The continuous kiln can adopt any one of the existing tunnel kiln, roller kiln or push plate kiln, and divide the interior of the kiln into different preheating zones, thus forming different temperature control zones in the kiln, so that the temperature control in the kiln can be better and more accurately controlled, so that the zirconia ceramic blocks are heated more evenly during the heat treatment process, and no large temperature difference changes will occur, thereby improving the quality of the finished product. For example, the zirconium oxide cake to be sintered is made of multiple layers of zirconium oxide powder by cold isostatic pressing. Each layer of zirconium oxide powder is mainly composed of a mixture of zirconium oxide powder, hafnium oxide powder, yttrium oxide powder, iron oxide powder, erbium oxide powder, manganese oxide powder and aluminum oxide powder. The content of each component in each layer is different. In terms of mass percentage, the sum of the content of zirconium oxide and hafnium oxide in each layer ranges from 76.5% to 95%, the content of yttrium oxide ranges from 5% to 10%, and the content of iron oxide ranges from 10%. The proportion of zirconium oxide is 0.17-0.6%, the proportion of erbium oxide is 9.6-13.8%, the proportion of manganese oxide is 0.0005-0.035%, the proportion of aluminum oxide is 0-0.5%, and the sum of zirconium oxide and hafnium oxide in the final zirconium oxide cake is not less than 98.2%, the content of iron oxide is less than or equal to 0.3%, the content of erbium oxide is less than or equal to 1.0%, and the content of other components is less than or equal to 0.5%; the specific settings for each zone are as follows:

[0022] The temperature of the first preheating zone is 300±15℃, and its heating rate is 20-23℃ / h. Its length accounts for 10-11% of the length of the continuous kiln. This zone is located at the front end of the kiln, and the temperature rises from 100-120℃ to 300±15℃. In this zone, the moisture in the zirconium oxide cake can be effectively evaporated without causing the zirconium oxide cake to heat up sharply and crack. At this time, in order to more accurately control the heating temperature of the zirconium oxide cake, a plurality of sub-preheating zones are divided in this zone, which can be called the first sub-preheating zone. The temperature of the multiple first sub-preheating zones rises from the front end to the rear end in sequence with a certain temperature difference, and the temperature difference is based on the divided The temperature of each sub-preheating zone in the first preheating zone is 70±10°C. For example, if a temperature difference of 60°C is selected, the front temperature is 120°C, and the rear temperature is 300°C, then four first sub-preheating zones can be divided at equal intervals, namely, the first sub-preheating zones of 120°C, 180°C, 240°C, and 300°C. Since the first sub-preheating zone corresponding to 120°C is at the front end, its heating rate can be selected to be slightly higher than that of other sub-preheating zones, such as 22.4°C / h, and the heating rate of other sub-preheating zones can be selected to be 21.6°C / h.

[0023] The temperature of the first insulation zone is 300±15℃, and its length accounts for 1-1.3% of the length of the continuous kiln. The temperature of the first insulation zone is equivalent to the temperature at the rear end of the first preheating zone. The setting of the first insulation zone makes it possible for the zirconium oxide cake to be heated more evenly from the inside to the outside at this temperature after being preheated in the first preheating zone, and can also avoid the problem of excessive temperature difference between the inside and the outside of the zirconium oxide cake.

[0024] The temperature of the second preheating zone is 800±50℃, and its heating rate is 14-20℃ / h. Its length accounts for 30-40% of the length of the continuous kiln. After the zirconium oxide cake is kept in the first insulation zone, the temperature inside and outside are kept consistent and enter the second preheating zone. In the second preheating zone, the temperature is increased from the temperature of the first insulation zone to 800±50℃, that is, the temperature of the second preheating zone is increased from 300±15℃ to 800±50℃. If the temperature is increased from 300℃ to 800℃, the temperature in this area is in a slow heating state, and its heating rate is also lower than the heating rates of the first and third preheating zones, which can further ensure that the temperature inside and outside of the zirconium oxide cake is increased synchronously. For example, a heating rate of 14.4℃ / h is selected in the first half of this area, and a heating rate of 18℃ / h is selected in the second half. Similarly, in order to control the temperature more accurately, in this area, multiple sub-preheating zones can be divided according to the method of dividing the first sub-preheating zone into the first preheating zone, which can be called second sub-preheating zones. The temperature difference range of each sub-preheating zone in the second preheating zone is 45±10℃. For example, if a temperature difference of 50℃ is selected, increasing from 300℃ to 800℃, then ten second sub-preheating zones can be divided at equal intervals. In the second preheating zone, the second sub-preheating zone at the front end is 350℃, and the second sub-preheating zone at the rear end is 800℃.

[0025] The temperature of the third preheating zone is 950±50℃, the heating rate is 23-30℃ / h, and its length accounts for 9-10% of the length of the continuous kiln. In the third preheating zone, the temperature is increased from the temperature of the second preheating zone to 800±50℃, that is, the temperature of the third preheating zone is increased from 800±50℃ to 950±50℃. If the temperature is increased from 800℃ to 950℃, the heating rate is increased to avoid excessive temperature fluctuations during the preheating process. Similarly, in order to control the temperature more accurately, in this area, multiple sub-preheating zones can be divided according to the method of dividing the first sub-preheating zone in the first preheating zone, which can be called the third sub-preheating zone. The temperature difference range of each sub-preheating zone in the third preheating zone is 60±10℃.

[0026] The temperature of the firing zone is 1000-1080℃, and its length accounts for 10-11% of the length of the continuous kiln; the temperature of the zirconium oxide cake coming from the third preheating zone is 950℃, and it is quickly heated to 1000-1080℃ after entering the firing zone. If the temperature is raised to 1000℃, it is fired at this temperature. That is to say, the firing zone is divided into a heating zone and a second insulation zone from the front end to the rear end. The heating rate of the heating zone is 20-25℃ / h, and its length accounts for 1 / 3 of the length of the firing zone, such as a heating rate of 21.6℃ / h.

[0027] The cooling rate of the cooling zone is 38-60℃ / h, and its length accounts for 9-10% of the length of the continuous kiln. The fired zirconia ceramic blocks are cooled in the cooling zone. In order to avoid damage to the zirconia ceramic blocks during the cooling process, the cooling zone is divided into multiple sub-cooling zones from the front end to the rear end. The cooling rates of the multiple sub-cooling zones gradually decrease from the two ends to the middle. For example, a cooling rate of 54℃ / h is selected at the front end of the cooling zone, that is, the zirconia ceramic blocks are first reduced from 1000℃ to 850℃ at a rate of 54℃ per hour, a cooling rate of 40℃ / h is selected in the middle of the cooling zone and cooled to 700℃, and a cooling rate of 48℃ / h is selected at the rear end of the cooling zone and cooled to 500℃ or lower.

[0028] The advancement speed of the continuous kiln corresponding to each meter of the kiln length is 0.013±0.002m / h, that is, on the basis of the above conditions, the advancement speed is determined according to the selected length of the continuous kiln. For example, if the kiln is 21m long, the advancement speed is 0.27m / h, that is, when the kiln is 21m long, the continuous kiln advances 0.27m per hour, that is, 27.0cm. Similarly, when the kiln is 30m long, the advancement speed is 0.390m / h. In this way, no matter how long the kiln is, it can be fired within the firing cycle.

[0029] As a further improvement, the continuous kiln is provided with a front buffer zone in front of the first preheating zone and a rear buffer zone after the cooling zone; the length of the front buffer zone accounts for 3-3.5% of the length of the continuous kiln; the length of the rear buffer zone accounts for 13-15% of the length of the continuous kiln; the front buffer zone facilitates the zirconia cake to enter the kiln from the kiln inlet, and also facilitates the temperature of the zirconia cake to be raised from room temperature to the starting temperature of the first preheating zone, and the setting of the rear buffer zone facilitates the further cooling of the zirconia ceramic block.

[0030] Although the present invention has been described in detail above with general descriptions and specific embodiments, it is obvious to those skilled in the art that some modifications or improvements can be made on the basis of the present invention. Therefore, these modifications or improvements made on the basis of not departing from the spirit of the present invention all belong to the scope of protection claimed by the present invention.

Claims

1. A temperature control method for sintering zirconia ceramic blocks based on a continuous kiln, characterized in that: The kiln of the continuous kiln is divided into a first preheating zone, a first heat preservation zone, a second preheating zone, a third preheating zone, a firing zone and a cooling zone from the front end to the rear end; The temperature of the first preheating zone is 300±15°C, the heating rate is 20-23°C / h, and the length of the first preheating zone accounts for 10-11% of the length of the continuous kiln; The temperature of the first insulation zone is 300±15°C, and its length accounts for 1-1.3% of the length of the continuous kiln; the temperature of the second preheating zone is 800±50°C, and its heating rate is 14-20°C / h, and its length accounts for 30-40% of the length of the continuous kiln; The temperature of the third preheating zone is 950±50°C, the heating rate is 23-30°C / h, and its length accounts for 9-10% of the length of the continuous kiln; The temperature of the firing zone is 1000-1080°C, and its length accounts for 10-11% of the length of the continuous kiln; The cooling rate of the cooling zone is 38-60°C / h, and its length accounts for 9-10% of the length of the continuous kiln; The advancement speed of the continuous kiln corresponding to each meter of the kiln length is 0.013±0.002 m / h.

2. The temperature control method for sintering zirconia ceramic blocks based on a continuous kiln according to claim 1, characterized in that The first preheating zone, the second preheating zone and the third preheating zone are each divided into a plurality of sub-preheating zones, and the temperatures of the plurality of sub-preheating zones in the same preheating zone increase sequentially from the front end to the rear end at a certain temperature difference.

3. The temperature control method for sintering zirconia ceramic blocks based on a continuous kiln according to claim 2, characterized in that : The temperature of the first preheating zone is increased from 100-120°C to 300±15°C; the temperature of the second preheating zone is increased from 300±15°C to 800±50°C; the temperature of the third preheating zone is increased from 800±50°C to 950±50°C.

4. The temperature control method for sintering zirconium oxide ceramic blocks based on a continuous kiln according to claim 2 or 3, characterized in that : The temperature difference range of each sub-preheating zone in the first preheating zone is 70±10°C; the temperature difference range of each sub-preheating zone in the second preheating zone is 45±10°C; the temperature difference range of each sub-preheating zone in the third preheating zone is 60±10°C.

5. The temperature control method for sintering zirconia ceramic blocks based on a continuous kiln according to claim 1, characterized in that The firing zone is divided into a heating zone and a second heat preservation zone from the front end to the rear end. The heating rate of the heating zone is 20-25°C / h, and its length accounts for 1 / 3 of the length of the firing zone.

6. The temperature control method for sintering zirconia ceramic blocks based on a continuous kiln according to claim 1, characterized in that The cooling zone is divided into a plurality of sub-cooling zones from the front end to the rear end, and the cooling rates of the plurality of sub-cooling zones gradually decrease from the two ends to the middle.

7. The temperature control method for sintering zirconia ceramic blocks based on a continuous kiln according to claim 1, characterized in that The continuous kiln is provided with a front buffer zone in front of the first preheating zone and a rear buffer zone after the cooling zone; the length of the front buffer zone accounts for 3-3.5% of the length of the continuous kiln; the length of the rear buffer zone accounts for 13-15% of the length of the continuous kiln.

8. The temperature control method for sintering zirconia ceramic blocks based on a continuous kiln according to claim 1, characterized in that :The kiln length of the continuous kiln is 21m, and the advancement speed of the continuous kiln is 0.27m / h.