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Causes, precautions and solutions for the fracture of corundum tubes in tube furnaces

  The tube used in the tube furnace is a corundum tube. Below, Kejia Electric Furnace Company briefly introduces the matters that need to be paid attention to when using the corundum tube of the tube furnace. The corundum tube is a very important part of the tube furnace because it is made of corundum. , its ability to withstand rapid cooling and rapid heating is poor, and its service life is very limited. Therefore, there will be many problems if used improperly during use. Let's take a look at the related problems and solutions, the causes and precautions for tube furnace corundum tube breakage, and how to solve them.
alumina ceramic tube
High purity alumina ceramic tube

1. The corundum furnace tube of the tube furnace has the characteristics of high purity and high temperature, but the corundum material has poor thermal shock resistance and is not resistant to rapid cooling and rapid heating. It needs to be operated with caution during use, otherwise the furnace tube will burst and cause work interruption. causing unnecessary losses.

2. Under normal circumstances, we recommend that customers keep the heating and cooling rate at 5 ℃/Min. A slower rate is better. During the cooling process, a cooling curve must be set. Do not allow it to cool naturally from high temperature to room temperature directly. In this way, the pipe will be very It is easy to burst. The temperature at which pipes are prone to bursting is generally 800-1000°C.

3. When using a tube furnace corundum furnace tube to burn the sample to about 1300, the moisture content is required to be low. For samples with high crystal water and moisture content generated during the heating process, it is recommended to pre-burn the sample first to drain the water. Then it is placed in a corundum furnace tube for sintering. The newly purchased furnace tube must be heated to 1300°C and baked once at a heating rate of 5~8/min before being used for work to eliminate stress and contaminants. The heating rate should not be too fast, and a cooling curve should be set for cooling. The heating rate should not be higher than 10/min, and the cooling rate should be lower than 10/min. Be sure to set the cooling rate, and avoid pausing the program directly at high temperatures.

4. Do not exceed 140 degrees when setting out and sampling. High temperature sampling and sampling may cause the corundum tube of the tube furnace to break. Remember not to touch the furnace tube at high temperature with low-temperature objects. When using corundum pipe, a heat insulation plug should be placed in the pipe. If it is necessary to vent the atmosphere, the air flow should not be excessive to avoid large temperature differences causing the furnace tube to break. When using high-temperature corundum furnace tubes, brackets should be added to both sides of the tube to avoid deformation and fracture caused by gravity.

5. The main reason for the explosion of the furnace tube is that the temperature difference is too large. The heating and cooling rate of the high-temperature furnace tube is preferably 5 degrees per minute. Rapid cooling and rapid heating are important causes of corundum furnace tube breakage. Afterwards, the tube must be kept clean and the inner wall of the furnace tube must be cleaned so that no sample remains in the tube.

6. New corundum tubes or corundum that has not been used for a long time need to be baked at about 300-400 degrees for 5-6 hours to bake out the moisture in the corundum tube. This will help extend the life of the corundum tube. Moisture is an important factor in the fracture of the corundum tube. reason.

7. Keep the inside of the tube furnace tube clean and sanitary. Substances that react with AL2O3 should not remain in the tube. When burning materials, in order to extend the service life of the furnace tube, do not put the material directly on the furnace tube. Use a boat-shaped crucible to hold it. 

8. When heating, please be sure to put alumina furnace plugs in the furnace tube, 2 on each side, 4 in total. The distance between the inner ends of the furnace plugs on both sides can be about 360mm. If the furnace plugs are not placed, the temperature at both ends of the tube furnace tube will be higher. , the O-ring in the flange cannot withstand high temperatures, resulting in poor air tightness. Placing furnace plugs at both ends of the furnace tube is beneficial to forming a balanced temperature field.

9. The flanges at both ends of the corundum tube need to be supported by support frames so that vertical stress will not be exerted on the corundum tube and the corundum tube will not bend at high temperatures or break due to stress.

10. Please do not put materials directly into the tube of the tube furnace to avoid contaminating the furnace tube. If the materials to be burned are volatile materials, you can use different tubes for different materials. The furnace tube of this furnace is easy to disassemble.

11. If you need to use the furnace continuously, you can only lower the temperature of the furnace to about 200°C and maintain it without lowering it to normal temperature. This will benefit the service life of the furnace tube. The temperature resistance of the corundum tube of the tube furnace is related to its purity. The higher the purity, the higher the temperature resistance, but the worse its ability to withstand rapid cooling and rapid heating.

12. Due to the high internal pressure of the gas cylinder, when passing gas into the tube furnace tube, a pressure reducing valve must be installed on the gas cylinder. It is recommended to purchase a pressure reducing valve from our company. The range of our company's pressure reducing valve is 0.01MPa. -0.1MPa, safer to use.

13. For sample heating experiments, it is not recommended to close the exhaust valve and air inlet valve at the flange end of the tube furnace. If you need to close the air valve to heat the sample, you need to always pay attention to the pressure gauge indication. If the air pressure indication is greater than 0.02MPa, you must open the relief valve immediately to prevent accidents (such as furnace tube rupture, flange flying out, etc.). When the temperature is >100°C, do not open the furnace cover to avoid cracks in the furnace tube.

14. The air pressure in the furnace tube should not be higher than 0.02MPa.

15. Graphite crucible cannot be used in corundum tube.

16. When the temperature of the tube furnace body is higher than 1500°C, the furnace tube must not be in a vacuum state.

17. The gas flow rate should be limited. The gas flow rate entering the furnace tube must be less than 200SCCM (or 200ml/min) to avoid the impact of cold atmospheric flow on the heating quartz tube.

18. Do not introduce corrosive gases such as sulfide and chloride, otherwise the furnace tube may rupture.

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