US1638557A - Insulating compound - Google Patents

Description

' 1,638,557 1927' J. M. WILSON msumwme comrouun Filed July so, 1924 hrm/orr JM/Ml W/Zm/Z Patented Aug. 9, 1927.

UNITED STATES v 1,638,557 PATENT OFFICE.

JOHN 1!. WILSON, F BRONX, NEW YORK, ASSIGNOR TO WESTERN ELECTRIC COM- PANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

INSULATING COMPOUND.

Application filed July 30,

This invention relates to insulating compounds and specifically to electric insulating cements.

An object of the invention is to produce 5 an insulating cement which will be efficient under severe conditions of service.

Insulating cements used for insulation between metallic elements in lightning arresters and the like in telephone or other circuits frequently deteriorate with time in service to such an extent as to cause exces sive current leakage which results in objectionable transmission losses. Investigation has shown that such deterioration is often caused by freealkali or alkali-producing materials in the insulating cement which in the presence of moisture soon form leakage paths for the current.

The cement of the invention comprises materials as low in free alkali or alkali-producin materials as porcelain and having high insulation properties. Preferably, the cement comprises ground porcelain as a filler, a shellac as a bindingmaterial and an easily vaporizable material, such as alcohol, as a solvent for the shellac. From these materials'combined in suitable. proportions an insulating cement has been produced which will retain its insulation properties over long periods of time and under extreme conditions of service.

The invention will be clear from the following detailed description read in connection with the accompanying drawing:

The single figure shows a sectional view of a spark-gap arrester' of a well known grounded by being held in position against the metal strip 3 which is connected to ground through a binding post,not shown. The outer blocks 2 are held in place by contact springs 4 which extend through the porcelain base 5 and connect the blocks 2 to opposite sides of the line through the binding posts 6. A slight air-gap 7 is maintained between each carbon block 2 and the ground- 56 ed block 1 which it faces by strips of mica 1924. Serialno. 729,041.

not shown. Potentials exceeding a certain value, due to lightning or other causes, will jump across the air-gaps 7 from line to ground thus dissipating any static charge which may accumulate on the line due to the excessive potential. A recess in the lower part of the porcelain base 5is filled with the insulating cement 8 of the invention to insulate the two sides of the line from each other, from ground, and from the support on which the porcelain base 5 will rest. It has been found that with the insulating cement of the invention, the insulation in such a device as described will function satisfactorily for the lifetime of the device and under severe conditions of service.

As stated above the cement of the invention is made from a. binding material, such as shellac, a vaporizable solvent such as alcohol, and a filler, such as ground porcelain.

Any other materials having a degree of alkalinity not exceeding that of ground porcelain may be used in place of ground porcelain as a filler in the cement if they have the required insulation properties and are mechanicall suited for the purpose. Materials whic have been found to be satisfactory are certain grades of silica, such as New Jersey Pulverizing Companys extra quality silica infusorial earth, such as Elmer and Amends technical I infusorial earth, sand, such as Ottawa sand, and Cellite Producing Companys Sil-o-Cel.

The amount of shellac and alcohol to be used in the insulating cement of the invention will vary with the fineness of the filler. It is, of course, preferable to use a minimum of shellac so that the drying of the cement will not be retarded objectionably. The alcohol is used merely as a solvent and, of 05 course, must be used in such proportions as to insure complete volatilization in order that the final cement will have sufficiently good electrical and mechanical properties. The fineness of the filler should be governed 100 by its mechanical suitability for the proposed use as the degree of fineness is not important from an engineering standpoint provided the material is coarser than 50 mesh. Preferable roportions to be used in the 105 making of t e insulating cement in accordance with the invention are approximately by weight 80 per cent filler, having a fineness of 100 mesh or above, 10 per cent shellac and 10 per cent alcohol. It has been 110 found that a cement made from the above mentioned materials in approximately the proportions specified may be applied be-,

tween the elements to be insulated from each otherwithout the use of heat, and after a comparatively short exposure to the atmosphere will produce a material which in addition to its exceptionable insulating properties, has satisfactory adhesive qualities, and is substantially non-hygroscopic and non-flammable.

Although the invention has been described and illustrated in connection with its use as a sealing compound in lightning arresters,

'it is to be understood that it is not limited to such use but is capable of general application wherever good insulatlon properties are re uiredL, For example, it may be usedhave a sufiiciently low degree of alkalinity and have the required adhesive insulation or solvent ualit-ies.

What 1s claimed is:

1. An insulatin cement comprising by weight substantial y 10 per cent alcohol, 10 per cent shellac, and 80 per cent pulverized filler having a degree of alkalinity comparable to that of porcelain and low electrical conductivity.

2. An insulating cement comprising, shellac, an easily vaporizable solvent therefor and a pulverized filler having a degree of alkalinity at least as low as porcelain and having high insulation properties, said shellac and said filler being combined in the proportions of substantially one to eight, respectively.

- 3. An insulating cement comprising alcohol, shellac and substantially 80 per cent of ground porcelain. g

In Witness whereof, I hereunto subscribe my name this 28th day of July, A. D., 1924. JOHN M. WILSON.

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