US1929396A

US1929396A - Resistance element

Info

Publication number: US1929396A
Application number: US445851A
Authority: US
Inventors: Glen F Benkelman
Original assignee: CONTINENTAL CARBON Inc
Current assignee: CONTINENTAL CARBON Inc
Priority date: 1930-04-21
Filing date: 1930-04-21
Publication date: 1933-10-03
Anticipated expiration: 1950-10-03

Description

Oct. 3, 1933.

G. F, BENKELMAN RESISTANCE ELEMENT Filed April 21, 1930 I NVENTOR EWE/ww E l ATTORNEYS UNITED STATES PATENT, OFFICE 1,929,396 EEsrs'rAncE ELEMENT Glen F. Benkelman, Cleveland, Ohio, assignor to Continental Carbon, Inc., Cleveland, Ohio, a

corporation of Ohio Application April 21, 1930. Serial No. 445,851

19 Claims.

This invention relates to resistance elements and has special reference to those of the carbon-rod type such as are often used in radio apparatus, telephone apparatus, photophone apparatus, television apparatus, and measuring apparatus, clocks, signal systems, and Wherever an inexpensive, reliable, resistance is desired.

These resistance elemgnjsare..enerallyxglade in t erformmog a rod orhbar, and consist of scTitfnr f'nmwnely divided carbon, (e. g. coke, graphite, gas-carbon, or lamp-black), mixed with a iinely divided insulating-material, (e. g. clay, sand, mica, cement, crushed-rockfetc), and a suitable inert and non-conducting binder '(e. g. bakelite, shellac, pitch, tar, rosin). The whole is baked at some temperature (e. g. between 250 Fahrenheit and 500 Fahrenheit) until it becomes suciently hard and the proper resistance value is attained. This resistance depends upon three factors, any one of which can be varied, namely: the proportion of carbon to inert material, the pressure used in compacting the mass, and the temperature (and time) employed in baking. As indicating the importance of an accurate adjustment of proportions, 3% of carbon with 97% of insulating material may produce a device having one million ohms resistance; 4% of carbon with 96% of insulating material may give one hundred thousand ohms; 5% of carbon with 95% of insulating material may give ten thousand ohms; and 10% of carbon With 90% of insulating material one thousand ohms. These iigures are approximate only and the result depends also upon the neness of the carbon and of the insulating material and the nature of the binder. By varying the pressure and controlling the temperature and time of baking it becomes possible to produce elements of accurately determined resistance. The longer and hotter the baking the lower the resistance becomes, and inasmuch as the effect of an electric current flowing in a resistance is to generate heat, these carbon resistance devices have heretofore tended in actual use to become progressively less resistant. The

' foregoing is common knowledge and practice in the art. y(

I have discovered that by treating these' resistance elements with certain materials or classes of materials this final change in resistance during use can be mostly or Wholly prevented and the resistance rendered permanent in amount so long as used within its rated capacity.

This material I herein term a xer. It consists of a resin having the ability to tend to dissolve the binder employed, but is applied under conditions which present its dissolving that binder already in place, but which serve to deposit it in the pores of the resistance-element ready to dissolve or attack that binder whenever as a result of heating its established condition shall tend to vary. The word dissolve as used here signies some form of penetration from free miscibility on the one hand to producing merely a swelling such as takes place when agar, sago or tapioca is soaked in Water. This resin is most easily employed after solution in a solvent or diluent of some kind which does not dissolve the binder already in place. Some examples of such a solvent or diluent are bayberry-Wax, carnaubawax, candelilla-wax, Montan-wax, parafiine-wax, beeswax, talloW, linseed--oil, tung-oil, pine-oil, turpentine, rosin, stearic acid, Japan-wax, or other fatty-acid or fatty-acid-ester. These materials may be of mineral, vegetable or animal origin as indicated by the above mentioned examples. Other examples of materials of mineral origin which I have found highly satisfactory in use are what are known commercially as halowax (a chlorinated naphthalene) and aroclor wax (a chlorinated diphenyl), both of which are coal tar derivatives. These materials are employed in melted or dissolved form, after the element has been originally formed and baked, care being only exercised not to employ the fixer in such form or concentration or for such length of time as to redissolve the original binder.

As an example of my improvements: a resistance element is made of a mixture of 5% gra nite, 90% of moming sand and 15% ormlac. heSeIWground, lated, and mixed and allowed to cool into a lumpy condition, after which the mixture is crushed, moistened with alcohol, and compressed in dies to the des'red form and size. The resulting rods or bars are then baked for such a time and at such a temperature as to afford the desired resistance per unit, after which suitable terminals are attached as by winding wires about the ends of the rods, soldering wires or caps to the ends of the rods, or by electro-plating the ends of the rods, or such other expedient as may be adopted for the purpose. The rods may then be dipped brieiiy into a molten mixture of rosin 25 lbs. and bayberry-wax 100 lbs., the immersion lasting from around one-half minute in the case of a small resistance up to several minutes in the case of a large rod. The elements are then allowed to cool and dry, after which they can, if desired, be painted, lacquered, enameled, or otherwise coated to protect them from climatic or accidental injury. Such a 'rod Will maintain its rated resistance almost indefinitely when employed Within its rated capacity. Furthermore such a resistance Will not absorb moisture like an untreated resistor and so vary in resistance With climatic conditions, but is substantially immune to atmospheric variations even though used Without coating with paint, enamel, or the like.

The flxers above named can be used in a great many other forms or combinations, for example:

made to employ rosin alone without admlxture, the resistance element would probably be destroyed completely, either by actual disintegration or certainly by an indefinite increase in the resistance, but by employing the rosin in admixture with one of these diluents the immediate disintegration of the article is prevented while a condition fs created which renders the device permanent in character. In the absence of such a fixer as I have described, the effect of localized internal heating by the electric current is gradually to decrease the resistance, probably as a result of progressive decomposition of the binder, whereas with thls fixer present no added decomposition occurs until the fixer has been completely baked out which under ordinary operating conditions can hardly occur. The proportions of resin and diluent can be varied and different effects can thereby be produced. If the proportion of resn be increased sufciently it is possible to produce a device which even tends to increase gradually in resistance With use, and the proportion of resin may also be varied With reference to the tendency of the original binder to become dissolved thereby. Thus with a binder of hard bakelite the percentage of resin can desirably be increased.

By resin I means to designate a fatty acid or an ester of a fatty acid, but I preferably employ the cheapest and commonest of its class, namely rosin because of its ready availability. The reason I preferably employ bayberry-wax as a diluent therefor is because the composition melts at a convenient temperature producing a mixture which is sufficiently fiuid to readly penetrate the bars or rods, and that it also dries and hardens readily forming an article which is dry and pleasant to handle and which readily accepts a coat of paint or lacquer. Other diluents like paraffine will operate successfully in most respects exl cepting that paint or lacquer will not satisfacpart of this invention I have shown certain forms of resistors to which my invention is applicable. Fig. l is a side elevation of a resistor and Fig. 2 is a smilar view of a modified form.

Each of these resistors comprises a rod or bar 1 of the composition described, having suitable terminals attached to the end which in the form shown in Fig. 1 consists of wires 2 tightly Wound about the end of the rod; and in Fig. 2 consists of metal end caps 3 suitably applied and secured thereto. The rods vary in size from one inch or less to one foot or more in length and can be made with a Very wide range of resistance and carrying capacities, although this type of device is most valuable under conditions Where rather high resistances are desired and the currents employed are rather small.

However, I do not limit myself to any of the details herein described except as the same are specifically set forth in my several claims which I desire may be construed severally, each independently of limitations contained in other claims.

Having thus described my invention what I claim is:

1. The process of stabilizing a resistance element consisting of\ carbon, an insulating filler and a carbonaceous bi'drbaked together, which contains the step of impregnating said element after baking with a resin in a fatty acid solution which does not appreciably dissolve the binder When cold but begins to do so at the established operating temperature of the said element.

2. The process of stabilizing a resistance element consisting of carbon, an insulating filler and a carbonaceous binder baked together, which contains the step of impregnating said element after baking with a molten solution of a resin in an organic solvent which does not appreciably dissolve the binder when cold but begins to do so at the established operating temperature of said element.

3. As an article of manufacture and sale, a resistance element consisting of a baked mixture of finely divided conducting and non-conducting particles imbedded in a carbonaceous binder, the whole baked mixture being impregnated with a solution of a vegetable resin in an organic solvent said solution being inert to the binder when cold but which begins to dissolve the same when heated to a temperature at the established operating temperature of said element.

4. As an article of manufacture and sale, a resistance element consisting of a baked mixture of conducting and non-conducting materials imbedded in a carbonaceous binder, the Whole baked mixture being impregnated with a solution of a vegetable Wax in a vehicle of bayberry-Wax in which the said Wax does not appreciably dissolve the binder when cold but tends to do so upon a predetermined rise in temperature of the vehicle.

5. The process of making permanent resistance elements which contains the steps of rst mixing together an electrically conducting material,

a non-conducting material, and a carbonaceous binder, compressing the mass into elements of desired size and shape, heating the same until the binder takes on a degree of set, and finally impregnating the pores of the device with a carbon compound which is inert to the binder when cold but has the property of tending to dissolve the binder when heated to a temperature at and above the established operating temperature of the device.

6. The process of stabilizing a resistance element consisting of a mixture of conducting and non-conducting materials imbedded and baked in a carbonaceous binder, Which contains the step of impregnating said element after baking with a vegetable resin which does not appreciably dissolve the binder when cold but tends to do so when hot.

7. The process of stabilizing a resistance element consisting of a mixture of conducting and non-conducting materials imbedded and baked in a carbonaceous binder, and which includes the step of Wholely impregnating the mixture after baking With a solution of a vegetable wax in a vehicle, in which the said Wax does not appreciably dissolve the binder when cold but tends to do so at and above the established operating temperature of the element.

8. The process of stabilizing a resistance element including carbon, an insulating filler, and a carbonaceous binder baked together, which contains the step of impregnating said element after baking with a molten solution of a carbon compound in an organic solvent which is solid at normal temperatures and tends to dissolve the binder at and above established operating temperatures of said element.

9. The process of stabilizing a resistance element, including carbon, an insulating ller, and a carbonaceous binder baked together, which contains the step of expelling the air from Within said element by permeating the voids naturally occurring therein with a molten solution of a carbon compound in an organic solvent, which is solid at normal temperatures and which begins to dissolve the binder at an established operating temperature.

10. The process of stabilizing a resistance element, including carbon, an insulating ller, and a carbonaceous binder baked together, which contains the step of permeating and lling the voids of said element with a coal tar derivative which is solid at normal temperatures and begins to dissolve the binder at operating temperatures.

11. The process of stabilizing a resistance element, including carbon, an insulating filler, and a carbonaceous binder baked together, which contains the step of expelling the air from Within said element by permeating the voids naturally occurring therein with a molten solution of a substance of vegetable origin which is solid at normal temperatures and tends to dissolve the binder at and above established operating temperatures.

12. The process of stabilizing a resistance element consisting of carbon, an insulating filler, and a carbonaceous binder baked together, which contains the step of impregnating said element after baking, With a molten solution of a ller including vegetable Wax in an organic solvent which is solid at normal temperatures and tends to dissolve the binder at and above the established operating temperatures of the element.

13. The process of stabilizing a resistance element consisting of carbon, an insulating filler, and a carbonaceous binder baked together, which contains the step of impregnating said element after baking with a resin in a solution of an ester of a fatty acid which solution does not appreciably dissolve the binder when cold but which tends to do so above the established operating temperature of the said element.

14. The process of stabilizing a resistance element including carbon, an insulating ller, and a carbonaceous binder baked together, which contains the step of impregnating said element after baking with a molten solution of a carbon compound in an organic solvent Which is solid at normal temperatures and tends to dissolve the binder above the established operating temperature of said element, whereby the localization of heat in portions of said element is prevented.

15. The process of stabilizing a resistance element including carbon, an insulating-filler, and a carbonaceous binder baked together, Which contains the step of expelling the air from Within said element by permeating the voids naturally occurring therein With a molten solution of a substance of vegetable origin which is solid at normal temperatures but which begins to penetrate the binder at and above established operating temperatures of the element whereby the localization of heat at portions of said element is prevented.

16. As an article of manufacture and sale, a resistance element consisting of a baked mixture of nely divided conducting and non-conducting particles imbedded in a carbonaceous binder, the Whole baked mixture being impregnated with a solution of a resin in an organic solvent said solution being inert to the binder when cold but which begins to dissolve the same when heated to a temperature at the established operating temperature of said element.

17. As an article of manufacture, a resistance element including a baked mixture of conducting and non-conducting material imbedded in a carbonaceous binder, the Whole baked mixture being impregnated with a molten solution of a carbon compound in an organic solvent which is solid at normal temperatures but which tends to dissolve the binder at and above the established operating temperatures of said element.

18. As an article of manufacture, a resistance element including a baked mixture of conducting and non-conducting material imbedded in a carbonaceous binder, the Whole baked mixture being impregnated with a molten solution of a carbon compound in an organic solvent, which is solid at normal temperatures and which begins to dissolve the binder at established operating temperatures of the element.

19. As an article of manufacture, a resistance element including a baked vmixture of conducting and non-conducting material imbedded in a carbonaceous binder, the whole baked mixture being impregnated with a coal tar derivative which is solid at normal temperatures and begins to dissolve the binder at operating temperatures.

GLEN F. BENKELMAN.