US317587A - Vulcanization of rubber coverings for electrical conductors - Google Patents

Description

UNITED STATES PATENT. OFFICE.

JOHN J. C. SlVllTH AND MICHAEL SMITH, OF PASSAIG, NEXV JERSEY.

VULCANlZATlON 0F RUBBER COVERINGS FOR ELECTRICAL CONDUCTORS.

SPECIFICATION forming part of Letters Patent No. 317,587, dated May 12, 1885.

Application filed August 1, 1884. (Specimens.)

To a. whom it may concern:

- Be it known that we, JOHN JosErH CHARLES SMITH and MIcHAEL SMITH, citizens of the United States, residing at Passaic, in the county of Passaic and State of New Jersey, have invented certain new and useful Improvements in Vulcanizing Rubber or other Vulcanizable Insulation Compounds used as Coverings of Electric Conductors, of which the following is a specification.

The object of this invention is to vulcanize such coverings in such a manner as to avoid the detrimental effects of moisture on the insulating-coverings of electric conductors while such coverings are in process of vulcanization.

\Ve have found that any moisture which may come in direct contact with the insulatingcovering of electric conductors while such covering is being vulcanized will seriously affect and impair, if it does not destroy, theinsulating qualities of the covering.

In order that those who are skilled in the art of producing highly-insulated electric conductors may fully understand the novelty and importance of our invention, we will first relate some facts which came within the scope of our observation while going through a long series of experiments on an extensive scale for the purpose of producing a high insulation of electric conductors by the use of a vulcanizedrubber compound.

Under the principal methods now used to vulcanize the covering of electric conductors, either the insulating compound is made so that it may be vulcanized in a dry-heat chamber, where no pressure can be applied to the compound during the process of vulcanization, or the covered conductors are packed in dry soapstone-powder and are placed in a vulcanizingvessel, where steam is admitted, which produces the required heat and pressure at the same time. The last-named is very troublesome on account of the difficulty of properly packing a long piece of insulated wire in the soapstone. In both cases the compounds used as insulating-coverings are made up with a view to being of such nature that they can be vulcanized in either one or the other way, and

therefore are not of such high insulating quali- 50 ties as they otherwise might be.

Many slight modifications of these systems are in use; but the principles remain the same.

lVhile carrying on our experiments we used both of these systems and manyof the sundry modifications in vogue; but found invariably thattheinsulation resistance of the compounds was very much lower after vulcanization than before, and too often was lost altogether. By close observation we found that the compound absorbed more or less moisture during vulcanization by one or the other mode. \Vhen vulcanized in dry heat without pressure, the compound was full of fine pores unless it was mixed in considerable quantity with heavy ingredients not suitable for producing high insulation. Such observation led us to adopt our present new method,the principle of which is to inclose the insulating-covering in 2. her metical envelope, through which moisture cannot penetrate under pressure, and to vulcanize the covering undersuch aprotection. This effectually prevents moisture from coming in contact with the compound while it is being vulcanized.

\Ve have carried our invention into effect with complete success in the following manner: lVe lay a sheet of the insulating compound firmly on a long sheet of heavy tin-foil, and then out both in long narrow strips, in the manner described by J. J. C. Smith in his Patent No. 276,725, dated May 1, 1883, with reference to cutting in long strips combined sheets of insulating and fibrous material. Such strips of tin-foil, in combination with the vulcanizable insulating material, we lay on the wire by means of the covering-machine described andclaimed by the said J. J. G. Smith in his Patent No. 276,72l, dated May 1, 1883.

Under our present invention the tin-foil answers the same purpose as the fibrous sheet in affording facility for laying and pressing the covering closely on the wire; but in addition to this it serves the very important purpose of providing an impervious envelope for the insulating covering, and protecting it fully against the influence of moisture during vulcanization, thus permitting the direct pressure and heat of steam without injurious effect. It also differs from the fibrous covering in that it does not become inseparably incorporated ICO megohms.

with the insulating-covering. Ithas long been known th at all vuleanizable compounds become much better and of closer texture if vulcanized under pressure. Many cannot be vulcanized in a solid condition without pressure. Others which can be vulcanized in dry heat without pressure possess this capability because heavily loaded with ingredients injurious to a good insulation.

WVhen the insulating-cover is to be vulcanized, we coil the covered wire on a large but light metallic reel in two or three layers. This reel is so arranged that it may be put readily in and out of the vulcanizer, and that it can be revolved horizontally in the vulcanizer while the same is closed and in operation. The revolving of the reel is accomplishedby' means of a shaft extendingthrough a stuffingboX in the head of the horizontal vulcanizer and provided with a driving-gear on the outl he reel may be advantageously made to contain about two miles of wire at one charge, and is rotated for the purpose of continually changing the position and weight of the wire and its covering, which keeps the wire central in the covering while it is softened by heat before the vulcanization takes place.

Then the vulcanization is completed, the wire is taken out, and the tin envelope, having performed its function, is removed from the insulatingcovering, leaving a smooth and dense surface.

To illustrate the importance of a tin-foil or other metallic foil covering on the outside of the insulation-covering as a protective envelope during vulcanization, we will state the results of a number of experiments in vulcanization by other methods,and the results when we used the metallic envelop An insulation compound such as is used in one of the best-known manufactories of lllSlllated wire, and which we designate as compound No. 1, was laid one twenty-fourth of an inch thick on one thousand feet of No. 14 copper wire. Before vulcanization the insulation resistance of the cover was one hundred and eight megohms. It was then vulcanized in a dry-heat chamber without pressure. Ater vulcanization the insulation resistance of the covering stood only twenty-seven and onehalf megohms, and it fell to fifteen megohms after immersion in water for three days. This proved that fine pores must have formed during vulcanization, which absorbed moisture, thereby injuring theinsulation. Another one thousand feet of wire, covered with the same compound No. 1 one twenty-fourth of an inch thick, showed one hundred and twelve megohms before vulcanization. It was vulcan- 7 ized in a dry soapstone-powder bed carefully packed and heated. under steam-pressure. After vulcanization the insulation resistance of this covering was thirty-seven and one-half Three days immersion in water brought it down to twenty-three megohms. A third piece one thousand feetlong was covl I in J. J. C. Smiths application filed the 7th of l l l l l ered with the same compound No. 1 to the same thickness, and was protected by what is commonly called a waterproof tape. This piece was vulcanized in steam under pressure generally cured. After vulcanization it in less than three hours immersion in water it came down to one-half megohm. A fourth piece of one thousand ,feet was covered with I the same compound the same thickness, but protected by our metallic envelope. Before vulcanization this piece indicated one hundred and thirteen megohms insulation resistance. It was vulcanized in steam under sixty- After vulcanization this pOLllldS pressure. picce'indicated an insulation resistance'of one -three megohms, which showed a great increase of the insulation resistance. Three days immersion in water proved it to ,be unalterable.

The rubber compound described and claimed hundred and sixty April, 1884, showed still more remarkable results. This compound is absolutely waterproof and one of the best insulators. It was laid on one thousand feet of No. 14 copper wire, one twenty-fourth of an inch thick, the same thickness as in the previous experiments with compound No. 1. When raw, this compound showed an insulation resistance of two hundred and forty megohms. After vulcanization in dry soapstone-powder under pressure of steam, it showed an insulation resistance of ninety-two megohms, falling to fortyseven after three days immersion. A second piece covered with the said Smiths compound and with water-proof tape as a proteetion,and vulcanized in steam under pressure, showed only seventy-two megohms insulation after vulcanization, -falling to forty megohms after three days immersion in water. A third piece of one thousand feet of wire covered with Smiths compound, but protected by our metallic envelope, was vulcanized in steam under pressure. After vulcanization it showed an insulation resistance of five hundred and seventy megohms. Immersion in water for weeks had no influence upon it. Repeated trials with the same compounds and many others showed corresponding results, proving the fact thatif an electric conductor insulated with a vulcanizable compound is covered with a metallic envelope in the manner described, and'is vulcanized under such a protection,the insulation resistance of the covering is very much improved. All the named trials were made with equal accuracy, and all tests and measurements taken with the most sensitive instruments and galvanometers.

In order to avoid any possibility of mistake about one or the other compound,we took hardrubber or ebonite compound, which is known as one of the best insulators.

first sample vulcanized showed an insulation resistance of ninety-seven showed only seven megohms insulation, and

in the manner in which soft-rubber goods are 1 30 It was laid on the wire the same thickness as the other. The in dry soapstone megohms, but fell to forty after immersion. The second example vulcanized in steam showed only one-half megohm after vulcanization. The third sample was vulcanized under the protection of the metallic envelope. After vulcanization .it stood two hundred and eighty megohms, and did not change by immersion in water. These trials proved conclusively that all vulcanizable compounds suffer in their insulating qualities when Vl1lC2L11-,

ized in such a manner that moisture may come in contact with the material lll'PIOCGSS of vulcanization. If vulcanized in dry heat or soapstone, it suffers from want of pressure on the compound, and a fine porous formation takes place, or the compound must be so much loaded with other ingredients as to affect its insulating qualities.

"We are well aware that tin-foil or other metallic sheets are used in the manufacture and vulcanization of rubber goods to obtain smooth surfaces,or to keep the rubber in shape, or to facilitate molding and pressing in special forms; but it will be apparent that the impervious metallic envelope performs an essentially different and novel function in our process of vulcanizing insulation-coverings of electrical conductors. i

We use the tin-foil or other pliable metal sheets as an envelope that cannot be penetrated by moisture, so that we may fully protect our insulating compound against the detrimental influence of moisture while it is vulcanized, permitting us to use direct action of steam as the best and most convenient medium to produce the required heat and pressure at the same time.

What we claim as new, and by Letters Patent, is-

The mode or process herein described of vulcanizing the insulating-covering of electrical conductors, the same consisting in enveloping the covered wire in a tight and impervious cover of tin-foil or other pliable metal, and subjecting it to the combined and simultaneous action of heat and pressure.

.T. J. 0. SMITH. MICHAEL SMITH.

lVitnesses:

JOHN B. PUDNEY, EUGENE 0. SMITH.

desire to secure