US1762990A - Preparation of electrical resistance units - Google Patents

Description

Patented Junelfl, 1930 cRoss REFERENCE PATENT OFFICE LESTER L. JONEB,,OF omnnn, rmwannsny, aim JOSEPH a. rnnzznn, or Bacon, 1

NEW YORK, *ASSIGNOBS, BY DIRECT AND MESNE ASSIGNMENTS, TO TECENIDYN CORPORATION, 01' NEW YORK, N; 'Y.,'.l COBPQBATION OF NEW YORK v rnnrniurrox or'nnncrnrcnr. ansrsrmcn nm'rs R Drawing.

This invention'relates to the preparation of electrical resistance coatings, and has special reference to the manufacture of ca- 7 pacityand inductance-free high resistances. 5, As is well known, capacity and inductance-free high resistance elements are made in the art by any of a number of methods, such as by impregnatin pa er strips or other material with various ind s of carbon inks,

10 by surfacing paper or the like with graphite streaks or lines, b painting insulating bases with raphite an other compositions or by depositing'thin films of metal on insulating bases such as lass tubesor the like. These resistances, a though compact, inductance and capacit -free, possess a number of disadvanta es eit er in the process of mauufacture o the same or in service, the inked and graphited paper resistances being, for instance, quite mlcrophonic, generally destructible in use, and incapable of carrying any considerable current, the metallic film resistances being unstable. by reason of the change in the resistance value thereof which 26 takes place due to the crystallization or oxidation of the thin metal film, and the graphite'd painted or coated resistances bein comparativel diflicult to make, due to t e necessity o compacting the graphite layer by hand or other means. Some of these resistance elements are also open to the common and serious objection that the resistance values thereof for a iven type or make vary within wide: limits, .1tbeing difficult to manufacture the resistances of uniform value,especially where the same are produced by quantity reduction methods. The manu acture of resistance units which do not possess the above-stated objections 40 and drawbacks, and which arecharacterized by being non-microphonic, stable in value v or magnitude, of large current-carrying caacity, durable, and capable of being manuactured uniformly in desired values within A further prime object of our present invention' relates to the production of a re-,

Application filed October 8, 1985. Serial No. 81,328. 1/ w wide ranges, and especially without the nesistance material capable of being applied to almost any insulating substance such as glass, porcelain, bakelite, paper or fibre,'capable of being applied by simply coating or painting the same onto the insulatin base to produce the resistance'element, an having the property of compactingvthe conductin material into a homogeneous la er upon rying and capable of withstanding high temperatures in use without noticeable deterioration.

To theaccomplishment of the foregoing and such other object's as may hereinafter -appear,'our invention consists in the ethod,'the resistance elements and resi tance material hereinafter particularly described and sought to be defined in the claims.

lVe have discovered that the desired objects of the invention may be attained by employing a resistance material composed of ia bite and preferably of finely divided graplilfe, mixed with a binder capable of com pacting the graphite particles into a, homo geneous layer-upon drying, and ca able of withstanding high temperatures wit out deteriorationglilslie saidf binlder consisting olf a mor hous 'cate o so ium or water ass. In compounding the resistance material, tli e graphite is mixed with the water glass m r0 rtignsporresponding to the res stance so desire i, and weliave found that alm ost any ratid of graphite to water glass may be useddown "to about one part of graplnte' to seven parts of water glass by volume. This mixture of water glass and graphite which forms a suspended graphite solution roduoes an excellent resistance filaint, w 1 ch may be applied by coating to a 0st any 1nsulatin substance, the same adhering firmly to j and the like. The'water lass tends to form a smooth, even film when rushed on smooth surfaces, and in drying has the property of compactin the graphite into a homogeneous and durab e layer, so that manual or other '5 lcompacting operations hitherto found necessary to produce a uniform and homogeneous layer are obviated.

We have also found that after coating the resistance material on a base and drying the 100 "ExAmmi ass, porcelain, bakelite, paper, fibre solution, the resultin same, a more perfect coating may be obtained in forming a more homogeneous layer which is substantially non-microphonic and which adheres very firmly to the insulating base by heating the coatin or film of resistance material byexterna heat or b the passage of an electric current through t e resistance unit or element. By subjecting the coated resistance element to such heat, which is preferably at high temperatures, such for example as 300 centigrade, a permanent drop of resistance of the order of from one-half to one-fifth the original value is obtained, and the resistance coating becomes very hard, dense and homo-' In lieu of the ordinarv air floated ulverized ra hite we ma&employ coloidal ra- )Kite Efiown com rcially as Koila en the'resistance Ipaint or material comprises a mixture .of ollag and water glass forming a suspended or colloidal raphite coating is ound to be exceptionally uni orm in its resistance properties and appearance.- When the in-- vsulating base to which the coating is applied is of a material such as lglass or porcelain, which will withstand hi temperatures, we have found that the ba 'ng of the coated bases up to temperatures of' the order of -300 centigrade for about one-half an hour roduces an exceptionally hard surface coating which polishes readily under a bufiing wheel withpraetically no change of resistance, the graphite being so densely compacted that the same cannot be removed even when rubbed with considerable vigor.

Preferably the resistance elements thus formed are covered with a coatin sons to rotect the same from mechanica or other injury, and desirably such coating consists of a covering of water glass over the baked and finished resistance element, water glass being preferred because of its advantage of being able to withstand high temperatures.

The manner of compounding the resistance material and the making of the resistance elements will in the main be fully apparent from the above detailed description thereof. It will be further apparent that the resistance elements may be manufactured with great ease and facility by the use of our resistance material, .the operations of coatbases 'vaiue or m 7 8 i or painting the resistance bases and of ba 'n or otherwise heatin the so} treated ing ible of being carried'out with ease an rapidity and co uent economy by quantity production met ods. The resulting resistance elements have resistance values which may be predetermined with accuracy,' the said resistances being stable in agnitude and of large current-earcapac1ty.' A further mportant ad- 1,7e2,eeo

in circuit, for on account of the high tem the durability and capability of withstanding high'temperatures of the resistance unit, it may be stated .that'when glass tubes emplo 'ed for grid leak resistances are coated wit the resistance material of our invention, giving a value of two thousand ohms, a current of or milli-amperes may be passed through the resistance, giving rom 5 to 8 watts load; and in so doing, the glass becomes red-hot in the center portiolrwithout any deterioration of the resistance coating. While we have described the preferred form of our invention, it will be apparent that-many modifications and changes may be made therein without departing from the spirit of the invention, defined in the following claims.

\Ve claim:

1. A free flowing electrically conductive paint adapted to be applied in a thin homogeneous layer to a surface for the manufacture of resistances comprising a mixture of one part of "colloidal graphite, by volume,

with about seven parts of water glass, by volume, the mixture being proportioned to obtain a consistency such that when applied a smooth even film of desired uniform thinness is produced. v

2. The method of making a resistance ele ment which includes coating 8. base witha free flowing electrically conductive paint comprising a mixture of about one part of colloidal graphite, by volume, with about seven parts of water glass by volume, the mixture being proportioned to obtain a consistenc such that whenapplied a smooth even fi m of desired uniform thinness is produced, and thereafter heating the painted base to a temperature ofabout 300 C. or higher inorder to com act the gra hite film.

Signed at New Yor city, in t ecounty of New York and State of New York this LEST L. JONES.

vantage of the resistance units or elements so obtained is the ability to connect the same