Unimpregnated fibrous electrical insulating materials. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Unimpregnated fibrous electrical insulating materials. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Electricity for beginners

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This group includes sheet and roll materials consisting of fibers of organic and inorganic origin. Fibrous materials of organic origin (paper, cardboard, fiber and fabric) are obtained from plant fibers of wood, cotton and natural silk.

The normal moisture content of electrical insulating cardboard, paper and fiber ranges from 6 to 10%. Fibrous organic materials based on synthetic fibers (nylon) have a moisture content of 3 to 5%. Approximately the same humidity is observed in materials produced on the basis of inorganic fibers (asbestos, fiberglass). Characteristic features of inorganic fibrous materials are their non-flammability and high heat resistance (class C). These valuable properties are in most cases reduced when these materials are impregnated with varnishes.

Insulating paper is usually made from wood pulp. The mica paper used in the production of mica tapes has the highest porosity.

Electric cardboard is made from wood pulp or from a mixture of cotton fibers and wood (sulfate) pulp fibers, taken in various proportions. An increase in the content of cotton fibers reduces the hygroscopicity and shrinkage of the cardboard.

Electric cardboard designed to work in air has a denser structure compared to cardboard designed to work in oil. Cardboard with a thickness of 0,1-0,8 mm is produced in rolls, and cardboard with a thickness of 1 mm or more is produced in sheets of various sizes.

Fiber is a monolithic material obtained by pressing sheets of paper, pre-treated with a heated solution of zinc chloride and washed in water. The fiber lends itself to all types of mechanical processing and molding after soaking its blanks in hot water.

Leteroid is a thin sheet and roll fiber used for the manufacture of various types of electrical insulating gaskets, washers and fittings.

Asbestos papers, cardboards and tapes are made from chrysotile asbestos fibers, which have the greatest elasticity and the ability to twist into threads. All asbestos materials are resistant to alkalis, but are easily destroyed by acids.

Electrically insulating glass tapes and fabrics are produced from glass threads obtained from alkali-free or low-alkali glasses. The advantage of glass fibers over vegetable and asbestos fibers is their smooth surface, which reduces the absorption of moisture from the air. The heat resistance of glass fabrics and tapes is higher than asbestos ones.

Author: Smirnova L.N.

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