Temperature tests
Various kinds of magnets have different heat resistance. Exceeding the temperature limits leads to a gradual loss of magnetization. This transition consists of reversible and irreversible components and do not have a sharp boundary - see the expressions on magnetism - Temperature and time characteristics. The thermal resistance shows the basic measurement of hysteresis loops depending on the temperature - see Measurement of magnetic properties. For easy monitoring of thermal resistance is used the surface magnetic induction and magnetic flux measurement. The magnet is subjected to a temperature cycle to ... tk ... to, where to is room temperature and tested tk is the critical temperature. Exposure time tk is governed by the size of the magnet, at least 20 min. Temperature values before and after cycle are compared. The maximum allowable drop is 5%.
Temperature behavior of magnets is affected by the presence of magnetic field. At the favorable orientation with the vector of internal magnetization effects of temperature to some extent diminish, the opposite orientation on a contrary causes increases. This plays an important role in testing kits such as magnets in electric motors. In these cases, the heat resistance test must be conducted on the assembly similar to actual use.
