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2 Maszyny Elektryczne : zeszyty problemowe

2 2008

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Mechanical properties of epoxy/glass/mica composite at high temperature

Boček V., Vik R.

Maszyny Elektryczne : zeszyty problemowe

2008

Nr 80

83-85

The stator windings of large rotating machines are insulated with mica-glass fabric impregnated with epoxy resin. These composites are exposed to thermal, mechanical and electrical stresses. The mechanical behaviour of two different forms (foil and tape) of cured epoxy/glass/mica composite was studied during this experiment. Specimens were made of calcinated mica paper and a glass cloth, bonded together with epoxy-novolac resin. These materials are used for the insulation of coils and bars of the electric machines in thermal insulation class F. The aim of this experiment is to compare the present material with the modified one. The improvement is based on the use of innovated glass cloth and in modification of epoxy-novolac bonding resin. Tensile and bending strength of these materials are investigated at room temperature and at temperatures 130, 155 and 180 °C. Decreasing of tensile strength and bending strength of both materials with increased temperature is shown.

Influence of dicy crystals on electrical and mechanical behaviour of the epoxy/glass composite

Kučerová E., Vik R.

Maszyny Elektryczne : zeszyty problemowe

2008

Nr 80

87-89

Epoxy/glass composites are widely used in the manufacture of quite a number of electrical machines and equipment. These composites (epoxy/glass laminates) are frequently prepared from prepregs. The prepregs are made by coating woven glass fabric with an epoxy resin, usually cured to the B-stage. Dicyandiamide (DICY) is used as a curing agent for the epoxy resin. In usual conditions the curing agent is fully depleted during the curing process. However in undesirable conditions DICY crystallizes and these crystals can adversely affect insulation properties of the material. This paper deals with term specification, when the DICY crystals occur and determination of their influence on mechanical and electrical properties of epoxy/glass laminate. Based on the results is evident that the influence of residual dicyandiamide on electrical properties of epoxy/glass laminate is insignificant.