Standard Test Method for Thermal Endurance of Rigid Electrical Insulating Materials

Importancia y uso:

6.1 Thermal degradation is often a major factor affecting the life of insulating materials and the equipment in which they are used. The temperature index provides a means for comparing the thermal capability of different materials in respect to the degradation of a selected property (the aging criterion). This property needs to directly or indirectly represent functional needs in application. For example, it is possible that a change in dielectric strength will be of direct, functional importance. However, more often it is possible that a decrease in dielectric strength will indirectly indicate the development of undesirable cracking (embrittlement). A decrease in flexural strength has the potential to be of direct importance in some applications, but also has the potential to indirectly indicate a susceptibility to failure in vibration. Often, it is necessary that two or more criteria of failure be used; for example, dielectric strength and flexural strength.

6.2 Other factors, such as vibration, moisture and contaminants, have the potential to cause failure after thermal degradation takes place. In this test method, water absorption provides one means to evaluate such considerations.

6.3 For some applications, the aging criteria in this test method will not be the most suitable. Other criteria, such as elongation at tensile or flexural failure, or resistivity after exposure to high humidity or weight loss, have the potential to serve better. The procedures in this test method have the potential to be used with such aging criteria. It is important to consider both the nature of the material and its application. For example, it is possible that tensile strength will be a poor choice for glass-fiber reinforced laminates, because it is possible that the glass fiber will maintain the tensile strength even when the associated resin is badly deteriorated. In this case, flexural strength is a better criterion of thermal aging.

6.4 When dictated by the needs of the application, it is possible that an aging atmosphere other than air will be needed and used. For example, thermal aging can be conducted in an oxygen-free, nitrogen atmosphere.

Subcomité:

D09.07

Referida por:

D1711-24A, D4502-92R19, F2953-12R21, D0709-17

Volúmen:

10.01

Número ICS:

29.035.01 (Insulating materials in general)

Palabras clave:

 a-c breakdown voltage; flexural strength; heat aging; rigid plates; rigid sheets; thermal endurance; thermosetting laminates; water absorption;