Tests on glass insulators including Hemingray

ABSTRACTS AND REVIEWS

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V. — Glass: Compositions and Founding Processes.

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636. Experiments on the Manufacture of Glass Insulators of High Grade Quality. G. TH. THAKIROV and L. A. MURAKH (Keram. i Steklo, 1933, 9, No. 1, p. 7). — Seven glasses of different chemical composition used for the manufacture of insulators were studied, including (No. 1) the Hemingray, U.S.A., glass. The compositions were :—

The tests of the superficial strength (electrical resistance) of the glasses were carried out by placing the insulators in a wooden cupboard of special design which was then filled with steam to complete saturation at 22—27°. Some porcelain insulators served for comparison purposes. The superficial strength of the glass insulators was very low, varying from 2400 to 1800 megohms, and in one case it reached only 9000 megohms. For porcelain insulators it was much higher and attained to 18,000 megohms. On the suggestion of Prof. T. V. Grebentschikov, the insulators were placed in small baths of galvanised iron with water heated previously to 60—70°. The water was then brought to boiling and held at that temperature for from 10 min. to 1 1/2 hrs. in different experiments. After this treatment the superficial strength determined in the steam cupboard had increased sharply, but to a different degree for the different glasses, for glass No. 7, reaching as high as 180,000 megohms. The most favourable duration of boiling was 20—30 mins. The quality of the water influenced the treatment. The best results were obtained with distilled water. With town water they were somewhat worse and distinctly worse with water from a pond. The treatment of the insulators with steam at 2.5—3 atmospheres proved less efficient than boiling. Treatment with FeCl3, HCl, and H2SO4 afforded no particular advantage. The glass insulators, after treatment with boiling water, could replace porcelain ones on telephone lines. M. A. B.

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