poured insulation compositions based on thermosetting oligomers or monomers. They are used to impregnate (for insulation) transformer windings, reactors of electrical machines, and articles of radio-engineering and electronic apparatus, as well as for filling the gaps (potting) between parts of electrical machinery or apparatus. The main advantage of poured insulation is the possibility of producing electrical-engineering articles in the form of small units of any configuration that do not require additional finishing. Polymer compounds also include some less frequently used compounds based on thermoplastics (such as bitumen, oils, rosin, and ceresin); these compounds have a hard or waxy consistency and are liquefied before use by heating.
The materials usually used as oligomers in preparing polymer compounds are epoxy resins, polyester resins, and liquid organosilicon rubbers; the raw materials for the synthesis of polyacrylates and polyurethanes are used as monomers. Epoxy polymer compounds are the most widely used materials. The composition of polymer compounds includes not only monomers and oligomers but also plasticizers, fillers, cure accelerators or polymerization initiators, and pigments.
The requirements for uncured polymer compounds are absence of volatile components, minimum shrinkage upon hardening or polymerization, low viscosity (which ensures good impregnation and potting properties), and sufficient resistance to aging. Cured polymer compounds must have good dielectric properties (see Table 1) and high strength. The hardening of polymer compounds occurs at room temperature or higher.
|Table 1. Dielectric properties of Soviet cured compounds at 20°C|
|Name and brand||Tangent of dielectric phase angle1||Specific electric resistance (ohms-cm)||Electric strength at 50 Hz (kV/mm)||Dielectric constant1|
|1Frequency (in hertz) is shown in parentheses|
|Epoxy and epoxy-polyester|
|EZK-9||0.009 (106)||1015||—||4.3 (106)|
|D-8||0.03 (105)||1014||—||4.5 (106)|
|EPK-101||0.015 (50)||9.9 X 1014||22||4.8 (50)|
|KGMS-1 polyester||0.04 (50)||5 X 1013||25||4.0 (50)|
|MBK-1 methacrylic||0.07 (50)||1014||20||4.0 (50)|
|K-31 Polyurethane||0.02 (106)||1014||27||3.5 (196)|
|K-67 organosilicon||0.005 (50)||1015||20||3.0 (50)|
REFERENCESCherniak, K. I. Epoksidnye kompaundy i ikh primenenie, 3rd ed. Leningrad, 1967.
Cherniak, K. I. Nemetallicheskie materialy v sudovoielektro-iradioteknicheskoi apparature: Spravochnik. Leningrad, 1966.
Volk, M., J. Lefforge, and P. Stetson. Germetizatsiia elektrotekhnicheskoi i radioelektronnoi apparatury. Moscow-Leningrad, 1966. (Translated from English.)
M. A. GOLUBENKO