US2331479A - Electrographitic brush - Google Patents

Description

Patented Oct. 12,1943."

" fshapigcarbea, baking the shapes vto Carbonne f mated Alife 'andvloW fricto'nand-possess'excellenlt'elecfgobi commutation'. lTl'us lack of cleaning and operation. y

. 23enne n t Y eine :ne empa oie a fa 'corporationeof Pennsylvania case-the'inorganicmatterftof-be"vlatilized. Co'n- 'W'itlfioutfir`ifiia'r'eiznan'tfs.-l f'secuntly, electrographitcbrushes d olnotpossess Still another object is to ploviei *any substantial *abra'dant or-f clean'ingfraptiin. arialinghelectrogaphitclrushe This'has inilitatedfagainsttheirmorewidespread e t -iinetal-Ylcarleide'sY as'"ia,leia'siveL use despite the fact that such brushesexhibitilong: i525# iW-hiehfs simplei'easlylpracticed#"etluiresnb inaerial change.iinexistingkmodesiofsmakm le f '1 .latrae-r'apl'iitiebrushes,l and rissproductiz@sofi-brushes Xvzhielfifenabodygoed;electrical;eliaifaeteristics '.abradingzactionmalees necessary-frequent vservicn lwhihsthe abrasive :character ,-,ofwv -th f-'caloicl'es` ^ing"of commutators. used :with I:eleCtrograpljlitiei.A v-risgfully. available.` `vbrushes,v especiallywherefvlratiom,thecoinpcs Yet;` anotherjobject., is.A toyprovideeapre y *i *,'tion'ioft-he ati'nospher'efin'Whihfthey eperfatejaiid` fthsftype in which -hardmetalgcarbide is '-irlcc) 1 other factors increase the difeulty faprope'r I *poratedsinitiallyj a;carb0nmixfor VVarious means have 'beenipropo'sed for-fcen4 ferringfcleaning ractionupon `electrographitic wbrushes. -Manyryearspag0itlwasproposedtoiin- Y exhibited -little additional gcleaningfaction, andv pr'opo'sedto make electrographitic brushes' fromy aV t,

I is *'-then subjected. to 1afg raphitizing 'temperature l and A1in Aally -iinpre' corporate lhard Ymetal carbides. ksuchfa'stungsten carbide or boron carbiclain these. brushes; but 'with 'poor success because thev graphitized'sbrushesi5514 laca, in; j "y mixture of carbon and. hard mtalcrb'iiefwhich gaat eing hat 'othe grapliitizing have caused the finely divided advantageous in the practice of theinvention beparticles of carbide to become fused, or at least incipiently fused at the sharp edgesl whichconi tribute abrasive action, so that thev particles orV their edges became round. Thus, although the carbides were retained inthe graphitized vbrush their desired eiect was not had because'the rounding'of the' particles or their edges caused them to slide or roll on the commutator instead of exerting the expected scouring or cleaning action.

I have discovered further, and it is upon thisV D that my invention is predicated in part, that the j foregoing diculty is avoided and electrographitic brushes possessing the desired cleaning or scouring action may be made from-carboncarbide compositions by eiecting the grapliitiza4 tion at a temperature belowthat which causes fusion or incipient fusion of the carbide particles.

In this way the desirable electrical characteristics `of graphite are obtained While the carbide `dis-- tributed through the graphite body retains' its abradingv action. Such brushes fpossess ,satisfactorylife in addition-'tegoed conimutating characteristics.

,In general, the materials and procedures used' for the manufactureof brushes can be followed Y in the practice of the presentI invention, due regard being had to the graphiti'zing temperature las just stated. Generally speaking, the Vbrushes are made lfrom amixture of carbon base material,

nfinely divided hard metal carbide, and a binder.

4The base materials may be such as are commonly used, such asY lamp black vor a calcine of lamp black and a carbonaceous binder, such as tar or pitch, which has been baked andpulverized. .Other forms -of carbon such as coke, gas black, graphite, or the like, or mixtures of `them l ywith lamp black, may beused. For mostpurposes it is preferredto use a carbonaceous binder, such as tar, pitch, or the like material productive 'y of a carbon bond.

V',lhe, finely divided hard metal, carbide may be added totliecarbon our in a mixer, preferably heated, and the dry flourmixed for fifteen to twenty minutes, `or vlong enough to obtain a uniform" blend. The pitch, or other binder, is thenA added and mixing continues'V until the carbon and carbide particlesare well coated,and generally from one to two hours Will sufce for this Epurpose. This basevmix is then removed from the` @mixe-r, cooled, pulverized and molded into plates which are then baked in'ovens, for instance `from A between-1800" to 2200 F.,'to carbonize the binder. Thereafter the plates are baked at a graphitizi'ng temperature, and either batch or continuous type electrical ovens may be used for this purpose.

` Thepresentinvention is dependentV upon this last, or graphitizing, step, which is critical in obtaining the results which ,characterize the in-vV vention'. Accordingly, the temperature of the furnace is controlled so as to graphitize vthecar bonA of the plates Vbutto be below thatk which will cause the nely divided particles of carbide to become rounded, or to round their edges.' This `maximum temperature is, of course, dependent cause of easier and closer control of the temperature.` e

I have found that where the carbides of zirconium, colulinbium,l tantalum and titanium are used it is satisfactory to graphitize, in accordance with this invention, at temperatures between about 27001and 3000 'C., in which temperature v range the'abrasive character ofthose carbides is not detrimentally affected. Tungsten and vanadium carbides, ihowevei,` require lower graphitizing temperatures.

'The cleaning or scouring-action of brushes made in accordance with the invention will be dependent upon `such factors as the particular carbide used and the amount present. Generally e. speaking, it is now preferred that the brush shall contain'from about 0.1 to 1.5 per cent by weight brush.` Ii the -carbide is too coarse it may cause v threading, and even groovingmf the commutator. On the other hand, if the carbide is too fine its cleaning action may beundesi'rably low, and even negligible. II-now prefer touse thecarbide ina form in which all of it passes a ZOO-mesh sieve.

Forsevere conditions of service, where considerableoleaning actionvis necessary, it is advisable tohave the majorityof the carbide yparticles towardthe coarser Yend, i. e.,"passingrbut close to 2G0fmesh, but where n'iore'of a p'olishingthan an abrading action `-isy desirable, the carbide may suitably be ,such as will pass a 325-mesh1screen.

Various modiiications are, ofcourse, permis- ,sible` "Thus, mixtures of carbides may be used, vfor instance as', a further means of controlling Y theabrading action', `and materials, `such as sulfur, may be incorporated in the mixesfor their known effects. i i i From what has been saiditwill belappreciated thatno .impregnation ofthe brushes is used, in the practice oi this invention. I have'found that i by proceedingas described the particles of carbide are held vnaturally in place so that the frtrouble and cost of impregnation with a` medium l intended to act asa binder for the carbide are As exemplifying the practice of the invention, brushes satisfactory for many applications are 'made from 100 parts by weight of lampblack calcinemixed with 55 4parts by weightxof lsoft pitch and` 3%; Dartby weight of `zirconium carbide (through S25-mesh) 'in .a heated mixer `for ninety minutes. TheLmixture is oooledand pul- `verized and the ilour is molded int'o plates approximately l inch thick. The plateseare packed :inl coke and baked to 1800., F. in a gas fired` oven,

' after which theyk are passed through acontinuupon the particularl carbide present inthe mix,

. andthe purity of the carbide, some carbides, containing small amounts of impurities4 which Willtend to lower -,the temperature `atwhich theV edges of -the particles will undergo incipient fusion.` The temperatureis, `of course, easily con- Y Vtrolled byadjustment o f thepower input to the 9ven,. vj 1h e Continuous method of `graphitiz inge is ,ous graphitizing oven maintainedat a temperature which graphitizes the carbon but does not cause fusion or rounding of the carbide particles.

.Brushesmade from this mix in this `manner possee-s distinct abrasive propertiesand,the-desirable corrimutatingf properties of ordinary` electrograplwiitio brushes.

lAccording to the'provisions of the ,patent statutes, I have explained` theprinciple and mode of practicing my inventiorigand have described what :lilou censiderrio representiis. basisinkomment. However, I desire to have it understood that, within the scope ofthe appended claims',

the invention may be practiced otherwise than as speciiically described. I claim: I l. That method metal carbide, and heating said mixture to "a graphitizing temperatureibut-below a tempera-l ture which causes rounding, of .the sharp edges y,

of said carbide particles.

of making an electrographitic brush which comprises forming a mixtureofvcarbon, binder, and at least one nely divided hard 2. That method of making an electrographitic brush which comprises forming shapes from a mixture of carbon, carbonaceous binder, and at least one nely dividedvhard metal carbide, heat-v ing said shapes to carbonize said binder y,and effeet bonding of said mix, and thenA heating the shapes to a graphitizing temperature but below` the fusion temperature of said carbide particles.

3. That method of making an electrographitic brush which comprises forming shapes from a mixture of a major proportion by Weight of carhon, a minor proportion of carbonaceous binder,`

and from about 0.1 to 1.5 per cent by Weight of at least one nely divided hard metal carbide, heating said shapes to carbonize said binder and effect bonding of said mix, andthen heating the shapes to a graphitizing temperature below a temperature which causes rounding of the sharp edges of said carbide particles.

brush which comprises kforming shapes `from a mixture Vof a major proportion by Weight of carbon,'a minor proportion of carbonaceorus'binder,v I Y and at least one finely dividedhard metalcary bide, heating said Vshapesto about- 1800i 1302200" hard metal carbide in the form of finely divided? sharp edged particles distributed through "andff bonded in place by said body, ,and the brush be'- ving adaptedto eXert a 'cleaning action upon a commutator.

An Al'electrographitic rbrush accordingr to claim 5, said carbide constitutingv about 0.1 vto v 1.5 per cent by weight of therbody K- brush according to i' 7. An electrographitic claim 5, `saidgraphitized carbon beingcarbon' bonded and said carbide constituting about 0.1`toY 1.5 per cent by Weight of the body. i Y 8. An electrographitic' brush according lto claim V5, said carbide being selected `from :the

group consisting o f carbides of zirconium, column A bium, tantalum, titanium, tungsten and'vana--` dum.

'4. `That 'method of making an emamgraphitic WALTER G. riRELL1\IER.