US2133768A - Insulator - Google Patents

Description

Oct. 18, 1938. J. c. HOSTETTER ET AL 2,133,758.

INSULATOR Filed Sept. 7, 1937 CONDUCTING 7; mzo/zo COAT/NG- INVENTOR. Jb/v/y C. //o a 7'5 rrzla ATTORNEYS.

Patented Oct. 18, 1938 UNITED STATES PATENT OFFICE IN SULATOR ration of New York Application September 7, 1937, Serial No. 162,774

6 Claims.

This invention relates to insulators and partieularlyto those which are used in the open and hence are exposed to varying weather conditions.

In a prior Patent No. 2,118,795, issued May 24, 1938, to Jesse T. Littleton, there is described an insulator, a portion of which is coated with tin iridizing whereby an extremely thin layer of tin compound having an appreciable electrical conductivity is formed on its surface. Such a coating eliminates the electrical brush discharge known to-the art as corona by preventing the building up of a potential gradient between the line wire and the surface of the insulator. The potential gradient, which normally is present between any conductor of high potential and a dielectric in contact therewith, is in this case spread out and dispersed over the slightly conducting tln iridized coating. It is further shown in the above mentioned application that other iridized coatings, such as those produced by iridizing with silicon tetrachloride and salts of tungsten andmolybdenum which under proper conditions likewise produce conducting coatings, have a similar effect.

Insulators so treated are known as no static insulators and are very desirable for power transmission at high voltages, because the absence of corona therein not only prevents leakage of power but completely eliminates the static or radio interference which has been a source of annoyance in radio reception in the vicinity of power lines and which was long sought to be overcome.

We have found that no static" insulators, such as those that are tin iridized, are subject to a certain amount of deterioration in service in that exposure to the weather and attendant electrolytic action causes a change in the iridized film, which results in a gradual loss of its conductivity.

It is the object of this invention to prevent loss of efliciency of conducting iridized coatings on insulators.

We have now discovered that the weathering of conducting iridized coatings on insulators may be prevented by applying over such a coating another iridized coating which has an extremely high resistance particularly at relatively low voltages and is hereinafter called a non-conducting iridized coating. Although we believe that any non-conductin'g iridized coating will have a protective effect as indicated by experiments made with various non-conducting coatings produced by iridizing with chlorides of iron, titanium, aluminum and silicon, we prefer to use iron iridizing or titanium iridizing since these are relatively easy to apply.

The invention therefore consists in the article and the method of preparing it to be more fully described in the following specification, claimed in the appended claims and illustrated in the accompanying drawing which shows an insulator partly in section having an exaggerated tin iridized zone which is covered over with iron iridizing, also greatly exaggerated, in accordance with our invention.

In practicing our invention it is preferable to apply the coatings to the insulator as it is taken from the mold at which time its temperature is about 600 C. to 750 C., but on account of un even cooling in some types of insulators it is desirable first to place the insulator in a reheating kiln held at about 650 C. in order that the parts to be coated may be brought to proper temperature. The above named temperatures are effective for insulators made of low expansion borosilicate glass, such as the glass B2 of the Sullivan and Taylor Patent No. 1,304,623, but softer glasses will require relatively lower temperatures as may be determined by trial.

The insulator is coated or iridized while hot, either by spraying it with a solution of metal salt ,or by exposing it to the fumes of the salt. For example, a tin iridized coat is first applied by spraying .or atomizing on the part to be coated, a water solution of stannous chloride containing enough hydrochloric acid to prevent hydrolysis or the vapor staunic chloride may be directed against theinsulator by blowing dry air through liquid anhydrous stannic chloride in a suitable container such as an Erlenmeyer flask provided with a delivery tube. This salt is readily vaporized without the use of heat and the amount of fumes is controlled merely by regulating the current of air. Best results are obtained by introducing some moist air into the vapor jet as it strikes the heated insulator surface. An extremely thin iridescent layer of oxide having a low electrical resistance, approximately 1001 ohm per centimeter cube, is formed on the surface of the glass and permanently incorporated therewith. Various other salts of tin will produce the same result. I

Obviously only a portion of the insulator is to be so coated with such a conducting coating and this is accomplished by placing the hot insulator on a rotating table and protecting the portion which is not to be iridized with an asbestos mask. The pinhole of the insulator may be iridized by means of an additional nozzle or Jet placed in the center of the rotating table. An exposure to the spray or vapor for about flve to fifteen seconds will sufice to produce the desired result.

After the tin iridized coat has been applied as above described; and before the insulator cools to any great extent, an'iron iridized coating is immediately applied thereover. This may be accomplished by atomizing a water solution of ferric chloride or by heating the solid salt in a closed container provided with a delivery tube. The spray or vapor is directed against the parts to be coated as before for about five to fifteen seconds. In this case it is desirable to use a different mask of such size and shape as will permit the iron iridized coating to extend beyond the limits of the tin iridized coat and preferably to extend-to the edge of the insulator skirt as shown in the drawing. If desired, the iron iridized coating may cover the entire insulator. This insures that the tin iridized coat will be completely covered and the entire upper surface of the insulator which is most exposed to the direct action of the weather will becovered with a highly resistant protective coating.

In lieu of iron iridizing, titanium iridizing may be applied by using the vapor of titanium tetrachloride in a similar manner or other non-conducting iridized coatings disclosed in the above mentioned prior patent may be used. For best results, however, the iron or titanium iridizing is preferred.

Analytical investigation has shown that these iridized coatings, both conducting and non-conducting, as described above, are composed of an oxide of the metal whose salt is employed in the iridizing process.

After the electrically conducting iridized coating and overlying non-conducting iridized coating have been applied, the insulator, if desired, may be annealed in the usual manner. The insulator could be annealed and cooled after the application of the tin iridized coat to be followed by reheating, application of the iron iridized coat and subsequent annealing, but this procedure would obviously be uneconomical.

No static insulators, which have been treated D in the above described mannerwith an overlying non-conducting iridized coating, will resist weathering efiects better than those to which only a conducting iridized coating has been applied. Contrary to expectations, the application oi a arsavea non-conducting coating over the conducting coating does not hinder the corona-preventing effect of the conducting coating and, although the reason for this may not be thoroughly understood, it is believed that due to the thinness of the nonconducting coating the charging current from the line and tie wires builds up practically the same potentials over the conducting coating beneath as would exist were the non-conducting coating not present. In the case of some coatings, such as the iron oxide coating, it has-been found that the outer'or insulating coat becomes conducting under the high voltage gradient .of the 1ine-to-pin potential so that the conducting under coat has practically the same potential and potential distribution as it would were it not covered, and hence the corona'formation is prevented in the normal manner. Yet this insulating coat is a perfect insulator to the low voltages causing the electrolytic destruction of the tin oxide coat. It is believed that the protective non-conducting coating should not be excessively thick at the point where it contacts the line and the tie wires. When such coatings are applied too thickly they lose their iridescent appearance. The proper thickness will not be exceeded if the above recited instructions are observed.

We claim:

1. Aninsulator provided with an electrically conducting iridized zone and a non-conducting iridized coating on the conducting iridized zone.

2. An insulator having an iridized conducting metallic oxide surface and an iridized non-conducting metallic oxide coating on the conducting surface.

3. An insulator provided with a tin iridized zone and an iron iridized coating on the tin iridized zone.

4. An insulator provided with a tin iridized zone and a titanium iridized coating on the tin iridized zone.

5. An insulator having an iridized surface of tin oxide and an iridized coating of iron oxide overlying and extending beyond the limits of the tin oxide surface.

6. An insulator having an iridized surface of tin oxide and an iridized coating of titanium oxide -w and extending beyond the limits of the tin oxide surface.

30m! C. HOSTETTER. JESSE T. a I. 5'. "1o

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