ASTM International Standard Specification for Pressboard for Electrical Insulating Purposes ASTM D4063-99(2016)

This specification covers pressboard for electrical insulating purposes as well as for dielectrical or structural purposes in transformers and other electrical apparatus. Pressboards under this specification are of three types: Type 1 consists of high-purity (Grade 1.1) calendered pressboards, while Type 2 consists of normal-purity (Grades 2.1.1, 2.2.1, 2.3.1, and 2.3.2) calendered pressboards. Precompressed pressboards (Grades 3.1.1, 3.2.1, and 3.3) fall under Type 3. Not included in this specification, however, are pressboards comprised of two or more sheets laminated together using an adhesive. Pressboards shall be manufactured from unbleached kraft pulp, cotton pulp, or a combination of both, and shall conform to the thickness, density, surface texture (smooth calendered surface for Types1 and 2, and fine-textured finish for Type 3), and color (from tan to blue-gray, depending on the pressboard's grade) requirements specified. The pressboard must also be free of dirt, metal particles, and other foreign material. Tests for apparent density, thickness, moisture and ash content, aqueous extract conductivity, chloride content, tensile strength, pH of aqueous extract, dielectric strength in air and in oil, shrinkage, and compressibility shall be performed and shall conform to the requirements specified.