Method of making electric resistance

Dec. 18, 1934.

A. HAROLDSON

METHOD OF MAKING ELECTRIC RESISTANCE

Filed May 1, 1930

1,985,166

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Patented Dec. 18, 1934

1,985,166

UNITED STATES PATENT OFFICE

1,985,166

METHOD OF MAKING ELECTRIC RESISTANCE

Arthur HaroldMn, Valparaiso, Ind., assignor, by mesne assignments, to Continental Diamond Fibre Company, Newark, Del., a corporation of Delaware

Application May 1, 1930, Serial No. 448,900

Claims. (CL 201—75)

My present invention relates in general’ to electrical conductor material particularly adapted for use in electrical resistance units.

The invention is particularly adapted for the 5 production of volume controls or fixed resistors particularly adaptable for radio apparatus where inexpensive but,accurate control of electrical cir, cults is important. The invention is also adapted for use in precision rheostats and other resistance 10 units used in electric circuits.

One of the objects of my invention resides in providing a method for making resistors wherein the measuring of predetermined quantities of the conductive substance of which the unit is 15 composed is accomplished in a simple and inexpensive manner, and wherein the same in its molded state is consolidated with a relatively thin base or carrier formed by means of a heat curable material. ₇

Yet another object of my invention resides in the provision of a resistance unit made by the method herein disclosed.

These and other objects of my invention will be apparent from a perusal of the following speci25 flcation when taken in connection with the accompanying drawing wherein:

Figure 1 is a bottom view of one form of die by means of which the shape and amount of conductive material may be applied directly to either 30 a sheet of treated or untreated material;

Figure 2 is a perspective view showing a sheet of tissue paper impressed by the die shown in Figure 1;

Figure 3 is a view showing said strip of tissue 35 paper superimposed upon a sheet of heat curable material in its unreacted state;

Figure 4 is a view of the laminated finished material provided with a number of the resistance units;

Figure 5 is a view similar to Figure 3 showing a manner in which the conductive materials are pressed by a die directly on a sheet of untreated thermo-plastic material but before the latter is heated and pressed to finished form;

⁴⁵ Figure 6 is a perspective view of a resistor which is provided with a graduated carbon deposition made in accordance with my invention; and

Figure 7 is a side view of the same.

In my improved method for forming a resist50 ance unit, I provide a die preferably of metal provided with one or more cavities of desired shape and cross section and adapted to contain a predetermined and measured amount of conductive material.

^M in the present instance, the die is illustrated as showing one or more impressions or cavities so that when impressed upon a sheet of material it will form simultaneously one or more shapes thereon, all of which are identical and each forming on the material impressed, a single or a se- 5 ries of units, each containing a measured or predetermined amount of such conductive material.

The conductive composition may include any type of conductive material such as graphite, car- 10 bon, aluminum, copper and the like, in finely divided form. I prefer to use graphite or carbon, preferably in the colloidal form. In the present instance I use colloidal graphite which is known among the trade as “Aquadag”. I may also form 15 a suspension of graphite or carbon in amyl acetate or the conductor material may be formed as a water suspension in gelatin, together with a trace of ammonia as a binder for the powdered conductor so as to assist the finely divided con- 20 ductive material in retaining a substantially moldable form for impressioii or deposition upon the carrier.

Instead of making single or multiple impressions from the die, I may provide a die of continu- 25 Ous and cylindrical construction to operate either continuously or periodically upon a strip or sheet of material fed in proximity to the die so that a continuous process may be afforded. The die is provided with means for intermittently or con- 30 tinuously filling the Impressions with conductive material and for scraping off the surplus material so that each cavity will contain the same amount of conductive material. This die is rotated or positioned so as to successively deposit upon the 35 periodically fed strip, a succession of such deposits.

In any case, in using either a single die or a rotary die, after the cavity in the die has been filled with the conductive material, the surplus ⁴⁰must be scraped off so as to have only a precise amount of material in the cavity whereby uniformity and accuracy in measurement is secured for each of the die impressions.

In another aspect of my invention, the con- ⁴⁵ducting material itself may be mixed witli an insulating material in various proportions in order to vary the conductivity and resistance per unit length in the resulting material. By properly controlling the ratio of conducting to non- ⁵⁰conducting material during manufacture, a material is maintained having any desired resistance and conductive characteristics. However, in the present instance, the resistance unit is disclosed as being formed of the conductive substance such ⁶⁵

1,985,166

Figures 6 and 7,, the same show a resistor or other element made in accordance with my invention comprising the base or carrier 10 of resin treated sheet material with the resistor consolidated therewith in accordance with the meth- 5 od hereinbefore set forth. In this instance, the carbon, graphite, or other deposition 12 is of tapering or graduated thickness, the end of the resistor at the left shown in Figures 6 and 7 being thicker with the deposition gradually thin- 10 ning toward the right, or toward the other end of the resistance element.

In the same manner, my invention contemplates the provision of a resistor having different zones of its surface provided with cross sectional 15 areas of conducting material of different thicknesses. This is of course controlled by the depth of the die cavity when the same is deposited upon the sheet material, as hereinbefore described. 20