The Reason of the Tungsten Heater Loss in the Aluminizing Process ——Aging

Aging is one of the important factors in the consumption of tungsten heater. Under normal circumstances, the life time of the tungsten heater is more than 300 times, but if done incorrectly, heater element would change color into yellow, and then in the central of tungsten heater would have irregular cracks which cannot process the normal evaporation process of aluminum, that is the aging of wolfram heater. When the evaporation of aluminum, under the saturated vapor pressure (1.33Pa), evaporation temperature of aluminum is 1490K. If the voltage is too high during the evaporation process, the high input power would cause the temperature of heating element is too high, thus greatly reducing the life time of wolfram heater. Figure 1 is a graph showing the heater element voltage and lifetime relationships. From the figure it is clear that with the increase of the number of evaporation, the voltage would decline rather than rise. This is because that the use of time would accelerate the aging of materials, thereby reducing the heating element resistance. If you use the same or a higher voltage, which would undoubtedly increase the input power of wolfram heater, causing the rise of the temperature of wolfram heater, leading to significantly shorten its service life. However, due to the use of heating element time is inconsistent, the voltage cannot be unified adjusted unless replace all the tungsten wire, but this would affect production and increase costs. What’s more, the life time of the tungsten wire is not the same, so it is unrealistic to replace them unified.

For this problem, the operator can reduce time of evapotranspiration, generally holding for 20 ~ 30s, and minimize the compression time for wolfram heater in the premise of complete evapotranspiration. By reducing evapotranspiration time to reduce the time of overheating, thereby avoiding heater element temperature is too high, too fast aging. Figure 2 is a graph showing the heater element voltage and time relationships.

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