Publication: Electrical World and Engineer
New York, NY, United States
Boch's "Glaze-Filled" Insulator.
In the controversy between the advocates of porcelain and glass insulators for high tension transmission lines, it is conceded for porcelain that it has the advantage in respect to mechanical strength. The difficulty has been to make high voltage insulators of porcelain uniformly free from flaws. When that has been accomplished there can be little doubt that glass insulators can no longer claim superiority in insulating quality over porcelain ones.
R. Thomas & Sons' Company, of East Liverpool, Ohio, claim that their manager, Mr. J. W. Boch, has accomplished the task of producing a flawless porcelain insulator of superior insulating qualities as well as of great mechanical strength in his "glaze-filled" insulator. This insulator has gone into practical use during the past few years on high tension lines all over the country and has met with marked success. It is of interest therefore to know how this insulator is made, especially as Mr. Boch's patent has been recently sustained by the United States Circuit Court.
Mr. Boch's invention is primarily based upon the fact known ever since pottery was invented, that a thin piece of clay will mould and vitrify better than a thick one. For this reason Mr. Boch builds up his insulator out of two or more shells nested together. In the photo-engraving are shown separately at 1, 2 and 3, the three shells of which Mr. Boch makes up his triple petticoat insulator. The inner piece 3 is moulded with a suitable threaded socket (see Fig. 4) for the usual pin. The outer shell 1 is provided with the usual notched head for the conductor and like the intermediate part 2 is made bowl-shaped, so that the three are relatively thin shells, to be nested into each other.
In the practice usually followed by R. Thomas & Sons' Company, in making these insulators, these separately-molded parts are first dried out separately, preferably in an oven or kiln in the usual manner of drying clay articles by the process known as "biscuit firing." The separate parts are then coated with glaze all over, as by dipping into liquid glazing material, and they are then fitted into each other and stoop upside down, that is, petticoats uppermost, as in the position shown at 5. Extra glaze material is supplied at the joints, that is, in the annular channels between the petticoats.
The parts thus put together and supplied with extra glaze at the joints are now put in the sagger with the petticoats of the insulator uppermost and placed in a kiln, in which under great heat the clay shrinks and becomes vitrified as usual and the glazing material melts and becomes of a glass-like character, flowing down into and filling all the spaces between the parts, such spaces either being there by lack of correct fit of the parts or arising during the shrinkage of the clay by the vitrification. The separately molded shells are thus welded together by seams of glass-like glaze, and this welding has been found to be of so tenacious a character that the insulators can be broken less easily along the lines of the "glaze-filled" seams than elsewhere. The completed insulator is shown at 5, while at 4 is shown one cut in two. This section clearly illustrates the three shells and the intermediate "glaze-fillings," which, needless to say, add to the electrical insulating qualities of the insulator as well as its mechanical strength.