How to use graphite rod in vacuum furnace
1. Choose graphite rod with good red-heat uniformity in the heating zone. The poor uniformity of the red heat of the rod will affect the uniformity of furnace temperature and shorten the service life of the rod. In the process of application, the red heat uniformity of the rod will gradually become worse, and in severe cases constitute broken rod.
2. Graphite rod with the higher the temperature the shorter the life spans of use, especially in great appearance temperature above 1500 ° C in the future, oxidation rate speeds up, life spans shorter, pay attention to try not to let the graphite rod appearance in high temperature.
3. After the graphite rod is heated in the air, its appearance forms a fine silicon oxide film and becomes an anti-oxidation maintenance film to prolong its life. Intermittent operation, following the temperature rise and fall of the furnace, will lead to the appearance of the rod maintenance film rupture, maintenance effect weakened, accelerating the bar resistance value increased.
In order to ensure the temperature of the furnace is stable and meet the demand of rapid temperature rise, the supporting electrical control system should leave a satisfactory voltage adjustment margin -- that is, when the new rod is installed, the furnace planning and operating power can be satisfied at a lower voltage; With the extension of operating time, the resistance value of the rod increases, and the demand increases accordingly to use voltage to satisfy the furnace planning and operating power.
Voltage margin value: the voltage at the later stage of using graphite rod is generally 1.5-1.7 times of the operating voltage of the new rod. Depending on the voltage regulation method and wiring method, the upper limit of the later voltage is generally 220V or 380V as the accounting value.
The method of adjusting the power of graphite rod advocates the method of adjusting the power by adjusting the voltage. The voltage regulating method of graphite rod is recommended. Generally, the method of adjusting the power modulator by changing the cycle number is not adopted.
4. In general, the external load density of graphite bars is obtained from the relationship between the temperature in the furnace and the external temperature of graphite bars, and it is suggested to use the power of the maximum external load density of graphite bars of 1/2 to 1/3. The higher the electric flux applied to the graphite rod, the higher the external temperature of the graphite rod. Advocate the use of as small as possible external load density (power).
Please note that the value recorded at the cold end of the graphite rod is the current and voltage measured at the scale of 1050+-50 in the air, which is not necessarily consistent with the actual application.
5. When graphite rods are continuously used, it is expected to slowly add voltage to maintain long life.
6. Parallel graphite bars as far as possible. If the resistance value of the graphite rod is different, the load of the graphite rod with high resistance in series will be concentrated, leading to the rapid addition of a graphite rod resistance and shorter life.
A set of values to be reinforced together, i.e. the resistance values of the same set of bars should be as close as possible. Generally, the resistance value error of the same group of rods in parallel shall be within 10%-15%, and that in series shall be within 5%-10%. The higher the furnace temperature, the smaller the required resistance error.
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