Instructions for use of graphite rod in vacuum furnace

2020-12-1729

        The graphite rod with good red heat uniformity in the heating part is selected. The poor uniformity of red heat of the rod will affect the furnace temperature uniformity and shorten the service life of the rod. In the process of use, the uniformity of the red heat of the rod will gradually become worse, and the rod will be broken in serious cases.

        2. The higher the service temperature is, the shorter the service life of graphite rod is. Especially when the surface temperature of the rod exceeds 1500 ° C, the oxidation speed is accelerated and the service life is shortened. Attention should be paid not to let the surface temperature of the graphite rod too high.

        3. When graphite rods are heated in air, a dense silica film is formed on the surface of graphite rods, which becomes an anti-oxidation protective film, which can prolong the service life. Intermittent use, with the rise and fall of furnace temperature, the protective film on the rod surface will be broken, the protective effect will be weakened, and the resistance value of the rod will be increased.

        In order to ensure the furnace temperature stability and meet the needs of rapid temperature rise, the supporting electrical control system should have enough voltage adjustment margin - that is, when the new rod is used, it can meet the kiln design and use power at a lower voltage; with the extension of service time, the resistance value of the rod increases, so the use voltage should be correspondingly increased to meet the furnace design and power.

        Voltage margin value: the voltage of graphite rod is 1.5-1.7 times of that of new one. According to the difference of voltage regulation mode and wiring mode, the upper limit of later voltage is generally calculated as 220 V or 380 v.

        It is suggested to adjust the power by adjusting the voltage. Silicon controlled rectifier or voltage regulator is recommended as the voltage regulating mode of graphite rod. Generally, it is not adjusted by changing the number of cycles of the power regulator.

        4. Generally, the surface load density of graphite rod is obtained by the relationship between furnace temperature and graphite rod surface temperature. It is suggested to use the power of 1 / 2-1 / 3 value of graphite rod surface load density. The greater the current applied to the graphite rod, the higher the surface temperature of the graphite rod. It is recommended to use as little surface load density (power) as possible.

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

        5. When the graphite rod is used continuously, the voltage should be increased slowly to maintain long life.

        6. Graphite rods should be connected in parallel as far as possible. If the resistance value of graphite rod is different, the load of graphite rod with high resistance is concentrated in series, which leads to the rapid increase of resistance of a certain graphite rod, and the life is shortened.

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