How to choose graphite rod heating element for vacuum furnace

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The vacuum furnace should use graphite rods with good red heat uniformity in the heating part as the heating element.

Instructions for the use of graphite rods for vacuum furnaces

1. Use graphite rods with good red heat uniformity in the heating part. The poor red heat uniformity of the rod will affect the uniformity of the furnace temperature and shorten the service life of the rod. During use, the red heat uniformity of the rod will gradually become worse, and the rod will be broken in severe cases.

2. The life of the graphite rod will be shorter as the use temperature is higher, especially when the surface temperature of the rod exceeds 1500°C, the oxidation rate will increase and the life will be shortened. Please be careful not to make the surface temperature of the graphite rod too high during use.

3. After the graphite rod is heated in the air, a dense silicon oxide film is formed on the surface, which becomes an anti-oxidation protective film, which prolongs the life. Intermittent use, as the temperature of the kiln rises and falls, the protective film on the surface of the rod will be broken, the protective effect will be weakened, and the resistance value of the rod will increase.

In order to ensure the stability of the furnace temperature and meet the needs of rapid heating, the supporting electrical control system should leave enough voltage adjustment margin-that is: when the new rod is new, it can meet the furnace design and operating power at a lower voltage ; With the continuation of the use time, the resistance value of the rod becomes larger. At this time, it is necessary to increase the use voltage accordingly to meet the furnace design and use power.

Voltage margin value: The voltage of the graphite rod in the later period of use is generally 1.5-1.7 times the voltage of the new rod. According to the different voltage regulation methods and wiring methods, the upper limit of the later voltage is generally 220V or 380V as the calculated value.

To adjust the power of the graphite rod, it is recommended to adjust the power by adjusting the voltage. It is recommended that the graphite rod is used to adjust the pressure by using a silicon controlled rectifier or a voltage regulator. Generally, it is not adjusted by changing the frequency of the power regulator.

4. Under normal circumstances, the surface load density of graphite rods is obtained from the relationship between the furnace temperature and the surface temperature of the graphite rods. It is recommended to use the power of the maximum surface load density of the graphite rods 1/2-1/3. The greater the amount of current applied to the graphite rod, the higher the surface temperature of the graphite rod. It is recommended to use the smallest possible surface load density (power).

Please note that the value recorded on the cold end of the graphite rod is the current and voltage measured in the air in the range of 1050℃+-50℃, which may not be consistent with actual use.

5. When using graphite rods continuously, hope to increase the voltage slowly to maintain a long life.

6. Graphite rods are connected in parallel as much as possible. If the resistance values ​​of the graphite rods are different, the load of the graphite rods with high resistance will be concentrated when connected in series, which will cause the resistance of a certain graphite rod to increase rapidly and its life will be shortened.

At the same time, it is necessary to strengthen the matching group of resistance value, that is, the resistance value of the same group of rods should be as close as possible. Generally, the resistance value deviation of the same group of rods in parallel is within 10%-15%, and the deviation of the resistance value of the same group of rods in series is within 5%-10%. The higher the furnace temperature, the smaller the required resistance deviation.

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