Description of the Cordeaux insulator

CORDEAUX'S PATENT IMPROVED

METHOD OF FIXING INSULATORS.

In the ordinary method of fixing telegraphic insulators, the bolt by which the insulator is supported from the arm of the telegraph pole is usually connected with the insulator by one end being inserted and cemented in a hole in the interior of the insulator, the other end of the bolt being fixed in the arm by the screwed end of the bolt being passed through a hole in it, and secured by a screw nut. This method of fixing renders the removal of the insulator for cleaning, repair, or replacement troublesome. The screw nut has to be unsecured and the insulator as well as the bolt removed from the arm whenever a new insulator is required. The rusting of the screw nut and screw sometimes renders the unscrewing of the nut very difficult.

This difficulty of removing the insulators has been attempted to be overcome by more than one inventor. The most apparently obvious method is to make the porcelain portion of the insulator to screw direct on to the bolt; this method, however, is not by any means one which could be practically successful. It is absolutely necessary that the porcelain cup be firmly screwed to the bolt, and the consequence is that the expansion of the iron is certain to split the porcelain. Another method which has been suggested is to cement an iron cup into the porcelain and to screw the bolt into the former, the difficulty first pointed out, however, with reference to the bolt and nut, viz., the rusting of the two portions of the iron together, would apply equally to such a method. It has been found, indeed, that an attempt to unscrew an insulator mounted in this manner has resulted in the porcelain being wrenched out of the iron cup secured to it; the adhesion, through rust, between the bolt and the cup being greater than that between the cup and the porcelain to which it is cemented.

Mr. Cordeaux, of the Postal Telegraph Department, has had these and other difficulties in view, and has devised a method of fixing the porcelain cup to the iron bolt, which is as efficient as it is simple. The method he adopts is as follows:—

A screwed hole is formed in the insulator in place of the plain or unscrewed hole ordinarily made. On that end of the bolt which enters the insulator a screw thread of a size and form proper to engage with the concave or hollow screw or screwed hole in the insulator is cut. The screwed end of the bolt is separated from the plain part of the bolt by a flange or collar or shoulder. In fixing the insulator, a ring or washer of cork, india-rubber, leather, or other yielding substance is placed on the screwed end of the bolt; the insulator is screwed on the screwed end of the bolt, the washer being compressed between the insulator and the shoulder on the bolt when the insulator is screwed home, the- washer by its elasticity holding the insulator tightly on the screw and preventing its removal by vibration or other accidental cause.

When it is wished to remove the insulator for any purpose, its removal may be effected by giving it an unscrewing motion when it separates from the bolt, leaving the bolt attached to the arm of the telegraph pole. Fig. 1 represents in elevation and fig. 2 in vertical section, an insulator fixed to its supporting bolt according to Mr. Cordeaux's method.

Fig. 3 represents in section the insulator separately, and Fig. 4 in elevation the upper part of the supporting bolt separately.

a is the porcelain portion of the insulator; b is the bolt by which the insulator is supported, and which is connected to the arm of the telegraph pole in the ordinary manner. In the axis of the insulator and near its head a screwed hole c is made, and on the upper end of the bolt b is a screw thread d of a size and form proper to engage with the concave or hollow screw thread of the screwed hole c in the insulator a. Between the screwed end d of the bolt b and the plain part of the said bolt is a flange collar or shoulder e, and supported on the said flange collar or shoulder e is a ring or washer f of india-rubber surrounding the lower screwed part d of the bolt in the manner represented in figs. 2 and 4.

In fixing the insulator a, the ring or washer f is first placed on the flange e, as represented in fig. 4, and the insulator a is then screwed on the screwed end d of the bolt b in the manner represented in figs. 1 and 2. On screwing home the insulator a the ring a or washer f is compressed between the internal shoulder a2 of the insulator a and the shoulder e on the bolt, as seen in fig. 2, the washer f by its elasticity holding the insulator a tightly on the screw d and preventing the removal of the insulator by vibration or other accidental cause.

A remarkable feature in this method of fixing is the very high insulating property it gives to the insulator, due, no doubt, to the use of the India rubber washer, and also to the fact that the screwed portion of the iron bolt is not in close contact with the mass of the porcelain of the cup.

From a reference to a table given on page 190 of the number of this Journal for May 1st, in which the insulator, with Mr. Cordeaux's method of fixing is indicated under the name "Porcelain D.S.P.O. large new," the first on the list, it will be seen that the average resistance of a number of tests showed a result as high as 13,374 megohms per mile of 23 insulators.

We understand that the Postal Telegraph department is largely adopting Mr. Cordeaux's method of fixing.

Messrs. Jobson Bros., Phoenix Works, Dudley, are the manufacturers of the insulators.