Vacuum furnace graphite rod
Notes on the use of graphite rods in vacuum furnaces:
1. Choose graphite rods with good uniformity of red heat in the heating zone. The poor red heat uniformity of the rod will affect the temperature uniformity of the vacuum furnace and shorten the service life of the rod. In the course of use, the red-heat uniformity of the rod will gradually deteriorate, and the rod will be broken when it is serious.
2. The longer the service life of the graphite rod is, the shorter the service life is. Especially after the surface temperature of the rod exceeds 1500 degrees C, the oxidation speed is accelerated and the service life is shortened. Attention should be paid to keeping the surface temperature of the graphite rod as high as possible in use.
3. When graphite rods are heated in air, a dense silicon oxide film is formed on the surface, which becomes an anti-oxidation protective film, thus prolonging the life of graphite rods. Intermittent use, with the change of vacuum furnace temperature, will lead to the breakdown of protective film on the rod surface, the protective effect will be weakened, and the resistance value of the rod will be increased.
In order to ensure the temperature stability of the vacuum furnace and meet the needs of rapid heating, the matching electrical control system should leave enough voltage adjustment allowance, that is, when the new rod is used, the design and power of the vacuum furnace can be satisfied at a lower voltage; with the continuous use of time, the resistance value of the rod becomes larger, at this time, it is necessary to increase the applied voltage accordingly to meet the design and work of the vacuum furnace. Rate.
Voltage margin value: The voltage of graphite rod is 1.5-1.7 times of that of new rod. According to the different voltage regulation and wiring modes, the upper limit of the later voltage is generally 220 V or 380 V.
It is suggested to adjust the power of graphite rod by adjusting the voltage. It is recommended that graphite rod be regulated by SCR or voltage regulator. Normally, it is not adjusted by changing the cycle number of the power regulator.
4. Generally, the surface load density of graphite rod is calculated by the relationship between the temperature in vacuum furnace and the surface temperature of graphite rod. It is suggested that the power of 1/2-1/3 of the large surface load density of graphite rod be used. The higher the current applied to the graphite rod, the higher the surface temperature of the graphite rod. It is recommended to use the smallest surface load density (power).
Please note that the values recorded at the cold end of the graphite rod are currents and voltages measured in the range of 1050 (+) 50 (+) in the air, which do not necessarily correspond to the actual use.
5. Continuous use of graphite rods, we hope to increase voltage slowly to maintain a long life.
6. Graphite rods are connected in parallel as far as possible. If the resistance value of graphite rod is different, the load of graphite rod with high resistance concentrates in series, which leads to the rapid increase of resistance and shorter life of a graphite rod.
At the same time, it is necessary to strengthen the grouping of resistance values, that is, the resistance values of the same group of rods are as close as possible. Generally, the resistance deviation of the same group of bars in parallel is less than 10%-15%, and that of the same group of bars in series is less than 5%-10%. The higher the temperature of vacuum furnace, the smaller the deviation of resistance required.