抄録
The break of tungsten filament and deformation of the electron tube heater in their on-off cycling test are the subjects of our present study with respect to their tensile strength at room temperature after their heat treatment, and also with respect to their metallographic structure. The heat treatment of the tungsten filament was made by the method presented in our previous report5). The on-off cycling test of the heater was carried on by applying heater voltage higher than normal rating. The results are summarized as follows.
(1) The tungsten filament with tensile strength that remains high at room temperature after the heat treatment does not break even at the on-off cycling test where heater voltage higher by 60% than normal rating is applied. In order to prevent the break of the filament or the deformation of the heater, it is necessary that the tungsten filament will have tensile strength higher than 50g/MG at room temperature, and maintain it after being subjected to heat treatment at 1600°C for 20 seconds.
(2) The tungsten filament with low tensile strength at room temperature easily breaks and the heater gets deformed after heat treatment or at on-off cycling test, and their metallographic structure shows grain growth considerably.
(3) As evidenced by repeated experiments the tensile strength of the tungsten filament has a great deal to do with the condition of the filament itself and of the electron tube heater after their heat treatment and on-off cycling test, whether both the filament and the heater are safe and sound or whether there will be the break of the filament and deformation of the heater. This evaluation method of tungsten filament will thus guarantee prevention of break of the filament and deformation of the heater.
