The service life of graphite rods decreases with the increase of operating temperature, especially when the surface temperature of the rod exceeds 1500 ℃, the oxidation rate accelerates and the service life shortens. When using, be careful not to let the surface temperature of the graphite rod be too high. Graphite rods with good thermal uniformity in the heating area should be selected for application. The poor uniformity of the red heat of the bar will affect the uniformity of the furnace temperature and shorten the service life of the bar. During use, the uniformity of the red heat of the rod will gradually deteriorate, and in severe cases, it may lead to rod breakage.
After heating the graphite rod in the air, a dense layer of silicon oxide film is formed on the surface of the graphite rod, becoming a protective film against oxidation and prolonging its lifespan. Intermittent use, as the furnace temperature rises or falls, can cause the protective film on the surface of the rod to rupture, weaken the protective effect, and accelerate the increase in the resistance value of the rod.
In order to ensure the temperature stability of the kiln and meet the demand for rapid heating, the supporting electrical control system should have sufficient voltage regulation margin, that is, when installing new rods, lower voltage should be used to meet the design and power of the kiln; As the usage time prolongs, the resistance of the rod increases. At this point, it is necessary to increase the working voltage accordingly to meet the design and power requirements of the kiln.
Voltage margin value: The voltage of graphite rods in the later stage of use is generally 1.5-1.7 times that of new rods. According to the different voltage regulation wiring methods, the upper voltage limit in the later stage is generally 220V or 380V.
It is recommended to adjust the power of the graphite rod by adjusting the voltage. It is recommended to choose controllable silicon or voltage regulator as the voltage regulation method for graphite rods. It is generally not adjusted by changing the frequency of the power regulator.
Generally speaking, the surface load density of graphite rods is obtained by the relationship between the temperature of the furnace and the surface temperature of the graphite rod. It is recommended to use a power of 1/2-1/3 of the surface load density of graphite rods. The greater the current applied to the graphite rod, the higher the surface temperature of the graphite rod. Suggest using a small surface load density (power). Please note that the values recorded at the cold end of the graphite rod are the current and voltage measured in air at 1050-50 degrees Celsius, which may not be consistent with actual use.
When using continuous graphite rods, try to increase the voltage slowly to maintain a longer service life. Graphite rods should be connected in parallel as much as possible. If the resistance of graphite rods is different, the load of high resistance graphite rods in series will be concentrated, leading to a rapid increase in the resistance of a certain graphite rod and a shortened lifespan. 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 parallel resistance deviation of the same group of bars is within 10% -15%, and the series resistance deviation of the same group of bars is within 5% -10%. The higher the furnace temperature, the smaller the required resistance deviation.