US 2118795 A
Description (OCR text may contain errors)
May 24, 1938. J. T. LITTLETON INSULATOR Filed Sept. 21, 1931 INVENTOR s.$ Z41 rue ro/v.
ATTORNEY Patented May 24, 1938 UNITED STATES PATENT OFFICE.
INSULATOB Application September 21, 1931, Serial No. 564,188
This invention relates to insulators, particularly to those which are used in the open and hence are exposed to varying weather conditions.
It is known that in wet weather the surface resistance of an ordinary insulator is lower than it is in dry weather. This is due to the tendency of water to adhere to the surface of the insulator and to form a thin film having a low resistance. This film in extreme instances will com pletely envelop the exposed surface of the insulator. As a result an insulator which under dry conditions will have a high surface resistance tends to lose its efllciency under wet conditions with consequent leakage of power. In view of the fact that on a single line there are a great many insulators, the importance of maintaining a uniform high surface resistance is obvious.
Furthermore, marker type" insulators of the prior art which are coated with paints of disgo tinctive color have not been entirely satisfactory because the paint vehicle upon which adhesion of the paint depends is broken down after a relatively short time by weathering.
Considerable difficulty is also experienced with as high tension insulators of the prior art in that they produce what is commonly known as corona which causes radio interference and is otherwise undesirable in that it constantly consumes power. Corona is an electrical discharge or series of disso charges through air from a conductor and may be explained as follows.
When a high potential is impressed upon a conductor it creates an electrical field of force, the lines of which start from the conductor and 36 end on conductors of opposite potential. Such a field of force, for instance, is created between the energized line wire and the pin of an insulator on which it is supported. Now with the insulator thus positioned in the field, if an air layer 0 be interposed between either or both of the conductors and the insulating medium, this air layer due to its relatively low dielectric constant will carry a high proportion of the electrical stress and the thinner the air layer with respect to the insulating medium, the greater the stress. Since insulators of the usual type are of such a geometric shape that at all times thin films of air must be interposed in the field between the conductors in the region of the insulator body, the air in the neighborhood of these points becomes highly and if the voltage gradient be sumeient a discharge or break downof the air takes place. Such a discharge will occur along any line of force where the potential 56 gradientexceedsacertaincriticalvalueinthe air and hence takes place over a well defined region of the insulator surface in the neighborhood of the line and tie wires and the pin. This critical value is known to be 31.5 kv./cm. and is somewhat dependent upon the temperature, pressure and atmospheric composition.
Moreover, the interposition of an air film, however thin, between a conductor and an insulator greatly increases the liability of that insulator to puncture or break-down. The cause of this is as follows. The dielectric constant of air approximates one-fourth that of glass and when the voltage is sufilcient to break down the air gap between the conductor and the insulator, the resulting discharge will accumulate an additional amount of energy and continues with accumulative action towards the destruction of the insulator. Discharges of sufilcient intensity will penetrate short distances into the insulating medium. This deterioration tends ultimately to allow the insulator to puncture at voltages below which it might be expected to puncture had these discharges been suppressed.
The above considerations apply not only to insulators made of glass but also to insulators made of porcelain or other insulator compositions, all of which may be termed ceramic insulators.
The primary object of the present invention is to increase the surface resistance of insulators under wet weather conditions.
Another object is to preserve the surface of insulators against deterioration due to weathering effects.
A further object is to facilitate the production of "marker type" insulators.
Still another object is to prevent corona through the air between the conductor and the insulator.
A still further object is to increase the resistance of an insulator to puncture or break-down.
The above and other objects may be accomplished by practicing my invention which embodies among its features applying to the surface of an insulator while it is hot metallic salt in a manner to be hereinafter more fully disclosed which is converted into an oxide through the heat and through contact with air and forms a thin coating which is so closely and permanently incorporated with the surface of the insulator as to become in reality a part thereof.
Although my invention is applicable to porcelain as well as glass insulators. I prefer to employ glass as the insulating composition and preferably low expansion borosilicate glass of the type disclosed in the Sullivan and Taylor Patent 1,304,623.
In the drawing:
Fig. 1 is a side view partly in section of an insulator constructed in accordance with this invention; and
Fig. 2 is a similar view of an insulator certain zones or which have been coated to suppress corona.
Referring to the drawing in detail, the insulator designated generally it] consists of a body ll, formed on its upper end with a head I2, the upper face of which is provided with a transversely extending groove l3 for the reception of a line wire or cable. Formed in the body ll immediately below the head I! is an annular groove M for the reception of tie wires by means of which the line wire is retained in place in the groove l3. Extending outwardly from the body immediately below the groove [4 is a flange l5 which is provided adjacent its outer edge with a downwardly curved portion forming a shed l6, and projecting downwardly from the inside of the flange is an annular rib I'I. Extending downwardly and outwardly from the body from a point intermediate its upper and lower ends is a skirt l8, and extending into the body from its lower end is a pin hole consisting of a tapered bore H! which terminates at its upper end in a threaded recess 20 for the reception of the threaded end of an insulator supporting pin (not shown).
In practicing my invention I prefer to apply my coating to predetermined portions of the insulator as it is taken from the mold, that is, when the temperature is about 600 C. to 750 C. but on account of uneven 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 insulator is then coated by spraying with a metallic salt solution or by exposing it to the fumes of a metallic salt.
The salt solution used for spraying the insulator preferably is forced from the nozzle by a stream of compressed air which produces a foglike spray of minute particles, the volume of which may be controlled by adjusting the flow of air through the nozzle. Fumes of the metallic salt may be generated (1) by heating a solid salt, for example ferric chloride, in a closed container provided with delivery tubes or; (2) in case the salt has a normally high vapor pressure, by passing air through the container as in the case of stannic chloride, titanium chloride or silicon tetrachloride, or; (3) by passing chlorine through a tube containing the metal or an oxide of the metal and carbon as in the case of iron, tungsten or molybdenum.
In performing this operation I prefer to place the insulator on a rotating table before a nozzle which is positioned to direct the spray or fumes onto the insulator. By the rotation of the table combined with proper direction of the jet, the outside of the hot insulator is coated with a uniformly thin film of oxide which is closely incorporated with the surface of the insulator in the form of a lustrous or iridescent coating whose thickness is approximately .001 to .03 mm. If it is desired to treatthe entire surface of the insulator as for instance in producing marker insulators as illustrated in Fig. 1, the pin hole may be held toward the spray or an additional nozzle may be placed in the center of the rotating table. After the insulator has been sprayed as above described it is placed in a lehr and annealed in the customary manner.
I have found that the coat produced by my process is not readily wet by water. Observation shows that when a drop of water contacts with glass so coated its angle of contact is greater than when a similar drop contacts with uncoated glass. This is due to the fact that the adhesion between water and uncoated glass is greater than that between water and glass which has been coated by my process. This property enables an insulator which has been coated by my process to shed water more readily than one which has not been so coated and any water that remains on the surface so coated will tend to collect into distinct drops rather than to spread into a thin film as is its tendency otherwise. Obviously by my process I am able to produce insulators whose surface resistance will remain relatively constant in dry or wet weather.
I have further found that my coating being closely incorporated into the surface of the glass and not being dependent upon a vehicle for its adhesion is resistant to abrasion or weathering over along period of time. Moreover,thesurfaces of insulators so treated are less liable to erosion than those of untreated insulators. This is especially true in the case of lime glass insulators but also applies though in a lesser degree to insulators made from borosilicate glass. These coatings absorb heat only slightly more than glass and hence do not cause the introduction of harmful temperature gradients.
The coatings produced in the above described manner by use of ferric chloride and also the chlorides of titanium, tantalum, columbium, aluminum, antimony, zirconium, thorium and thallium, and also chromic anhydride have extremely high electrical resistance and hence are practically non-conducting. For this reason an insulator may be coated by the use of these salts so as to coverits entire surface without substantially decreasing its insulating properties. Since the color of the coating produced by use of ferric chloride varies from a light golden brown to a deep reddish brown, depending on the thickness of the coat, I am thus enabled to produce in a simple manner a distinctively and permanently colored marker type insulator whose color is not affected by weathering.
I have further found that with my coating I can practically eliminate corona by using tin chloride to form the coating. This may be applied by spraying the hot glass in the manner described above using a solution of stannous chloride in water and hydrochloric acid but I prefer to use the fumes of stannic chloride generated by passing dry air through liquid anhydrous stannic chloride in a suitable container such as an Erlenmeyer flask provided with delivery tubes. 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. In this case the stannic chloride vapor on coming into contact with the hot glass is immediately converted into an extremely thin layer of some compound of tin having a relatively low electrical resistance, approximately .001 ohm per centimeter cube as measured. This compound of tin insofar as I have been able to determine by numerous analyses and tests has the composition $1102 in spite of the fact that stannic oxide is stated to have an extremely high electrical resistance (International Critical Tables, volume VI. P e 153) and I am unable to account for this apparent contradiction of facts.
The coatings produced by the above described process are extremely thin, from .001 to .03 mm., and on this account give rise to the phenomenon known as interference colors, 'that is, they have an iridescent appearance. When the coating exceeds a certain thickness it no longer appears iridescent. The thickness of the coating may easily be increased by long or repeated exposure to the fumes or to the spray and, in general, in the case of the coating produced by tin salts, the conductivity of the coating increases with its thickness.
I have also found that other salts of tin will produce my conducting coating and I have successfully employed fumes of stannic chloride, stannous chloride and stannous iodide and sprayed solutions of stannous chloride, stannic chloride, stannous sulphate, stannic sulphate and stannous nitrate. I have even produced conducting coatings by applying solid stannous oxalate and also solid stannous oxide directly to the surface of hot glass. However, for producing my conducting coating I prefer to use the fumes of stannic chloride generated and applied as above described because they are more easily controlled and produce more uniform results.
I am also able to produce conducting coatings with salts of tungsten and molybdenum and also with silicon tetrachloride and ferric chloride but in doing this I have found it necessary subsequently to heat and cool the coated articles in a reducing atmosphere after the initial application of fumes or spray to the hot glass. That is, I take the article sprayed or fumed as above described by ferric chloride or silicon tetrachloride or chlorides of tungsten and molybdenum and I reheat the article and the coating in a gas flame burning with a slightly insufficient supply of air and then allow the article to cool, preferably in an atmosphere of illuminating gas. In lieu of a gas flame I may use an electric muflle and maintain therein an atmosphere of illuminating gas.
In the case of a conducting coating I spray only certain portions of the insulator, for instance, the head or threaded recess or both as illustrated in Fig. 2 and I preferably use an asbestos mask to protect those parts which are not to be so coated.
I have found that the conducting coating thus produced on an insulator practically eliminates corona because it prevents building up of a potential gradient between the line wire and the surface of the insulator so coated. The elimination of stress and the consequent discharge not only reduces radio interference but prevents loss of power and preserves the insulator supporting pins by preventing the formation of corrosive gases which are produced by such discharges. In order to effect a further reduction in radio interference I have found that by proper manipulation of the jet or spray I am enabled to decrease the thickness of the coating as its outer edge is approached and thereby increase its resistance per unit area. I have found that up to the full operating voltage of insulators the radio interference caused by my improved coated in sulator is entirely eliminated.
I have further found that my conducting coating increases the resistance of the insulator to puncture or break-down from fifty to one hundred percent. due to the fact that my coating is so closely incorporated with the surface of the insulator that there is no interposed air film between the two and the potential of the line wire resides thereby directly on the surface of the insulator. There is thus no possible building up of energy by discharge across an air gap.
I have also found that insulators coated with a non-conducting coating, for instance by means of ferric chloride, have a greatly increased resistance to puncture or break-down. In view of the assumption that the increased resistance to puncture depends upon the presence of a conducting coating, I am unable to explain why the non-conducting coating made by use of ferric chloride should also have this effect.
The process of producing iridescent coatings on glass articles by exposing them while hot to the fumes or sprayed solutions of metallic salts is known in the glass art as "iridizing but insofar as I am aware the methods used in iridizing have never been employed to produce coatings on insulators for the purpose of providing a uniform surface resistance during wet and dry weather, eliminating corona and improving resistance to puncture.
As stated in my previous application, SeriaiNo. 474,661, before referred to, the peculiar lustre obtained by the process just referred to renders the iridized insulators readily discernable and hence especially valuable for use as "marker insulators and the coating thus obtained is thin enough not to absorb heat with the result that danger of cracking the glass due to rapid temperature changes is avoided.
By the expression, permanently incorporated with its surface" in the appended claims, I mean the close incorporation and the resulting lasting adhesion of the film to the glass which is obtained by my invention as distinguished from the adhesion of a paint or the like, due to the adhesive qualities of its vehicle.
The words tin iridized as used in the claims is intended to comprise a deposit on the glass of a tin compound formed under the influence of heat.
This application is in part a continuation of my co-pending applications: Serial No. 321,665 filed November 24, 1928 and Serial No. 474,661 filed August 11, 1930.
Having thus described my invention, what I claim is:
1. A glass insulator having permanently incorporated in its surface a coating of a substance which resists the adhesion of water.
2. A glass insulator having permanently incorporated in its surface a coating which is substantially transparent to solar heat.
3. A clear glass insulator having a lustrous surface coating of oxide which is substantially transparent to solar heat.
4. An insulator having a. part of its surface coated with an electrically conducting oxide of tin.
5. An insulator having its head coated with an electrically conducting oxide of tin.
6. An insulator having a portion of its surface coated with an electrically conducting layer of tin oxide. the resistance of the layer increasing as its edges are approached.
7. An insulator having a portion of its surface coated with an electrically conducting layer of tin oxide which is permanently incorporated in the surface of the insulator.
It is assumed that this is l 8. An insulator provided with a tin iridized zone.
9. An insulator provided with a tin iridized head.
10. An insulator provided with a plurality of tin iridized zones.
11. An insulator provided with a tin iridized head and a tin iridized threaded recess.
12. An insulator having a tin iridized coating intimately associated with certain zones thereof, the resistance of the coating increasing as its edges are approached.
13. A glass insulator having permanently incorporated with its surface an iridescent coating of iron oxide.
14. A clear glass insulator having a surface coating oi. iron oxide which is substantially transparent to solar heat.
15. A ceramic insulator having a non-conducting iridescent coating of a. metallic compound applied thereto.
-l6. An insulator having an iridized metallic oxide surface.
17. An insulator having an iridized conducting metallic oxide surface. 18. An insulator having an iridized non-conducting metallic oxide surface.
19. An insulator provided with an iridized conducting zone of a metallic oxide.
20. An insulator provided with an iridized conducting head surface containing a metallic oxide.
21. An insulator for electrical conductors comprising a body of vitreous material having a surface layer of a metallic oxide of high electrical resistivity and high interfacial tension with water.
22. A ceramic insulator for electrical conductors having a substantially non-conducting coating of a metallic oxide more resistant to electrical leakage under moist conditions than the material forming the main body of the insulator.
23. An insulator for electrical conductors comprising a body of vitreous material having a reentrant undersurface, said surface having a sub stantially non-conducting superficial coating of a metallic oxide more resistant to electrical leakage under moist conditions than the main body of the insulator.
24. An insulator of ceramic material having permanently incorporated with its surface an iridescent coating of an oxide which resists the adhesion of water.
25. A ceramic insulator having permanently incorporated with its surface an iridescent coating of a. metallic oxide which is transparent to solar heat.
JESSE 'i'. LI'I'ILETON.