Two commonly used annealing methods for thermocouples

In order to eliminate the stress inside the thermocouple and make its metallographic structure more regular, annealing treatment is necessary before using the thermocouple. There are usually two methods for annealing thermocouples, which can be divided into electrical annealing and furnace annealing. Below is a specific introduction to how to handle annealing:

1. Electrical annealing

Electric annealing is the process of hanging a thermoelectric electrode on a bracket using borax cleaning method, slowly adjusting the current to keep the electrode at a certain temperature for a certain period of time, and then slowly reducing the input current to zero. The temperature and time for annealing various thermocouples are specified.

The advantages of electric annealing are simple equipment, convenient operation, uniform heating along the hot electrode, and easy volatilization of surface impurities. The disadvantage is that the radial temperature of the thermoelectric electrode is affected by the surrounding air, and the surface metal is prone to volatilization, causing changes in composition. However, it can still meet the requirements for industrial thermocouples.

2. Furnace annealing

In furnace annealing is the process of threading a thermoelectric electrode through an insulating tube, placing it in a uniform temperature field of a specialized annealing furnace, holding it at a specified temperature for a certain period of time, and then cooling it down with the furnace. Its advantage is that the thermoelectric electrode is uniformly heated radially, which can eliminate the stress caused by pipe penetration. The disadvantage is uneven heating along the longitudinal direction of the hot electrode. Both annealing methods have their own advantages and disadvantages. If adopted separately, good results can be achieved.