US1821390A - Composition of matter - Google Patents

Description

- asbestos and an inorganic Z nitro-cellulose,

Patented Sept. 1, 1931 PATENT OFFICE LEON MCCULLOGH, OF

ELECTItIG & MANUFACTURING COMPAN PITTSBURGH, PENNSYLVANIA, ASSIG-NOR TO WESTINGHOUSE Y, A CORPORATION OF PENNSYLVANIA COMPOSITION OF MATTER No Drawing.

My invention relates to compositions of matter and more particularly to insulating or friction material which is coherent at high temperatures.

The principal object of my invention 1s to provide a composition of matter. comprising binder that is nonvolatile at high temperatures.

Another object of my invention is to pro- Ilo vide an insulating or friction material comprising asbestos, an organic binder and chromic sulphate.

A further object of my invention is to provide a process of producing a coherent 1.5.mass of asbestos which comprises impregnating asbestos fibers with an aqueous solution of chromic sulphate, either alone or with organic binders, and heating the impregnatedmateria'l at an elevated temperature to at least partially dehydrate the chromic sulphate and bind the fibers together in a coherent mass.

Heretofore, it has been the practice to employ organic binding agents, such as starch, oils, pitch and varnishes, as a binding agent for'asbestos fibers, which agent also serves to cement the insulation to electric wires and cables. tures, these binding agentsare not entirely satisfactory because the organic material either decomposes or volatilizes and leaves the asbestos in a loose condition. In insulating material employed in such apparatus as electrical stoves, where high temperature is encountered, this undesirable property of the organic binding agents is especially noticeable. The organic material is also inflammable and thisfactor increases the fire hazard when it is employed in connection with inflammable material.

During my researches on this subject, I have discovered a suitable inorganic binding agent .that isstable at elevated'temperatures.. I have found that, when chromic sulphate is employed as a binding agent, the

asbestos fibers will be bonded together permanently, even though the material is exposed .to a high temperature, and this will be true even though some organic material is present.

At high tempera- Application filed May 31, 1930. Serial No. 458.895.

' My invention is especially suitable for providing a flame-proof insulation for conductors because it avoids the necessity of utilizing an excessive amount of organic matter.

In practicing my invention, I employ commercial chromic sulphate which is dissolved in water, preferably with the aid of .heat, to obtain a solution containing a substantial amount of chromic sulphate, which is then allowed to cool. The asbestos is then immersed in, or drawn slowly through, the chromic-sulphatesolution, drained and dried in an oven at a temperature of 150 C. to 300 C. for a sufficient length of time to at least partially dehydrate the sulphate. If desired, the asbestos fibers may be bonded together by a small amount of an organic material and drawn through, or immersed in, the solution, or the asbestos may first be applied to electrical conductors and the coated conductors may then be drawn through, or immersed in, the solution.

As a result ofthe baking operation, the commercial chromic sulphate, which, in its hydrated form. is soluble in water, becomes practically insoluble, after being partially or completely dehydrated by baking.

The following specific example will serve to explain and illustrate my invention. A Monel-metal stranded cable, havin one felted coat and one braided coat of asfioestos was immersed in an aqueous solution containing 27.5% of chromic sulphate, by weight, for-a period of two minutes. The cable was then removed and the surplus chromic sulphate was allowed to drain off for three minutes. The cable was then baked in an oven for a period of one hour at a temperature of 150 C. In testing the insulation, it was found that it was capable of resisting 800 volts.

Since the amount of chromic sulphate in the solution may be varied widely, I do not desire to limit myself to any particular proportions. I have found that a solution containing from 10% to- 50%, by weight, of chromic sulphate is preferable. Furthermore, it is not necessary to employ water as the solvent, as other solvents may be employed, such as alcohol or a mixture of cal reasons,

- able binding agent,

Water and alcohol. However, for economi- I prefer to utilize an aqueous solution of chromic sulphate as the impregnating medium.

The baking period may also be varied considerably and will be dependent upon the thickness ofthe impregnated material and the temperature. The time and temperature should be suiiicient to, at least partially, dehydrate the chromic sulphate and to render it insoluble. At temperatures below 150 (1, the chromic sulphate will not be dehydrated, while, if the temperature is raised above 300 C., the asbestos begins to disintegrate, and the chromic sulphate undergoes partial decomposition.

In some cases, the asbestos fibers may be held together bya small amount of a suitsuch as nitrocellulose, The material is then impregnated with chromic sulphate and baked at a suflicient temperature and for a sufliicent length of time to eliminate the solvent, and, at least a portion of, the water of hydration. When it is desired .to produce asbestos cemented together partially by an organic binder and partially by chromic sulphate, the baking temperature must be maintained below the point of decomposition of the organic binder, which temperature, however, must be above the dehydration temperature of the chromic sulphate.

In preparing a material containing an organic material and chromic sulphate, the asbestos may be drawn through a solution containing chromic sulphate and starch or dextrin or both of such materials, and the impregnated material is baked at a temperature above the dehydration temperature starch or dextrin.

of the chromic sulphate but below the temperature of decomposition of the starch or dextrin, or, if desired, the fibers may be boundtogether by nitrocellulose and the material passed through, or immersed in, a solution containing chromic sulphate and an organic material, such as starch or dextrin, or both of them, and the material allowed to drain. The impregnated asbestos is then baked at a sufficient temperature and for a sufiicient length of time to dehydrate the chromic sulphate and decompose the nitrocellulose without decomposing the starch or dextrin.

Dehydrated chromic sulphate is superior to sodium silicate as a binding agent, because it is a better insulator and is c0mpar attively non-hygroscopic. In' view of its amorphous characteristics, it is superior to a crystalline binding agent, because it forms a glasslike film that covers, andadheres to, the fabric. It adhere v extremely well to the meshes of a fabric and is stable at tem peratures at which organic binding agents volatilize or decompose.

effected therein, without While I have described chromic sulphate as being especially suitable as a binding agent for asbestos when utilized as an insulation for electrical wires and cables, I do not desire to limit my invention in this respect, as the material may obviously be employed for various other purposes, such as for the brake bands of automobiles, for friction. purposes, heating pads, or, in general, wherever asbestos is employed at the present time.

The term asbestos, as employed in the specification and claims, refers to commercial asbestos which comprises asbestos fibers loosely held together by suitable means, such as cotton threads.

lVhile I have described my invention in considerable detail and have given specific examples, it will be understood that the examples should be construed as illustrative and not by way of limitation, and, in view of the numerous modifications which may be departing from the spirit and scope of my invention, it is desired that only such limitations shall be imposed as are indicated in the appended claims.

I claim as my invention:

1. A composition of matter comprising asbestos fibers cemented together by a binding agent comprising chromic sulphate that is, at least partially, dehydrated.

composition of matter comprising asbestos, an organic binding agent, and a chromic sulphate that is, at least partially, dehydrated.

3. An insulating material comprising asbestos fibers cemented together by a binding agent including chromic sulphate that is, at least partially, dehydrated.

4. An insulating material comprising asbestos fibers cemented together by a binding agent comprising an organic material and chromic sulphate that is, at least partially, dehydrated.

5. An article of manufacture consisting of a conductor coated with an insulating material comprising asbestos fibers cemented together by a binding agent including chromic sulphate that is, atleast partially, dehydrated.

6. The method of binding asbestos fibers together which comprises immersing them in a solution containing chromic .sulphate, withdrawing the material and then baking at a sufiicient temperature to partially dehydrate the chromic sulphate.

7. The method of binding asbestos fibers together which comprises immersing them in a solution containing 10% to 50% chromic sulphate, by weight, withdrawing said material and then baking it at a temperature of from 150 C. to 300, C. for a sufficient length of time to, at least partially, dehydrate the sulphate.

hydrate the 8. The method of binding asbestos fibers together which comprises immersing them in an aqueous solution of chromio sulphate containing from 10% to 50%, by weight, of chromic sulphate, withdrawing the impregnated fibers and then baking at 150 C. to 300 C. for a sufiicient length of time to, at least partially, dehydrate the 'chromic sulphate and bind the fibers together.

9. The method of binding asbestos fibers together which comprises impregnating them with an aqueous solution containing an organic binding agent and chromic sulphate, withdrawing the impregnated material, and then baking at a temperature sufficient to, at least partially, dehydrate the sulphate.

10. In the method of binding asbestos fibers together, the step which comprises impregnating the fibers with a solution of chromic sulphate that is, at least partially, dehydrated.

11. In the method of binding asbestos fibers together, the steps which comprise impregnating the fibers with chromic sulphate and then heating to, at least partially, dechromic sulphate.

12. The method of forming an insulated conductor which comprises felting or braiding asbestos around the conductor, impregnating the felted or braided material with a solution containing chromic sulphate, and then heating at a suflicient temperature to, at least partially, dehydrate the chromic sulphate.

13. The method of forming an insulating material which comprises cementing asbestos fibers together by a binder that will be decomposed at a comparatively low temperature, impregnating the same with a solution containing chromic sulphate, and then heating at a sufficient temperature to decompose the organic binder and to, at least partially, dehydrate the chromic sulphate.

In testimony whereof, I have hereunto subscribed my name this 29th day of May,

LEON MGCULLOCH.