抄録
It is the well-known fact from long ago that porcelain insulators are broken by using the cement as binding materials for porcelains and hardwares.
The causes have been considered as follows.
(1) the thermal expansion of cement
(2) the chemical expansion of cement
(3) the abnormal expansion of cement caused by CaO and MgO
(4) the expansion of cement caused by absorption of moisture
(5) the expansion of cement caused by freezing
Writers tried an experimental investigation on some deteriorated insulators and specimens exposed to open air for years. The specimens for the test are bars made of various kinds of cements and mortars, and porcelain cups filled up with cement. From the result obtained by this experiment, we have come to the following conclusion.
Of above-mentioned five causes, comm, (4) is the most significant, in general case, followed by (1) and the others are almost unimportant. But the failure of porcelain insulators can't be fully explained by these causes only.
Hardening and contraction by losing moisture in cement lead to give rise cracks in it. If it takes place these cracks are filled up with dusts and the deposition of soluble salts. In original, if the expansion by absorption of moisture take place on cement, which such a condition, its volume becomes far greater than the leads the porcelain insulators to break, In the process of this kind of action the thermal expansion of cement plays its part in some extent.