US2824819A

US2824819A - Method for oxide insulating aluminum conductors

Info

Publication number: US2824819A
Application number: US584325A
Authority: US
Inventors: Millard F Smith
Original assignee: Individual
Current assignee: Individual
Priority date: 1956-05-11
Filing date: 1956-05-11
Publication date: 1958-02-25
Anticipated expiration: 1975-02-25

Description

M. F. SMITH Feb. 25, 1958 METHOD FOR OXIDE INSULATING ALUMINUM CONDUCTORS Filed May 11, 1956 INVENTO'R Millard Z ,S'mzl t/z ATTORNEY United States METHOD FOR OXIDE INSULATING ALUMINUM CONDUCTORS Millard F. Smith, Westport, Conn. Application May 11, 1956, Serial No. 584,325

6 Claims. (Cl. 148-63) This invention relates to a method and apparatus for insulating metal strip. More particularly, the invention relates to a method and apparatus for insulating metal foil, such as aluminum, by oxidizing the surfaces thereof.

Small electrical coils, such as inductance coils, may be Wound from metal strip, one material which has been used therefor with some success being aluminum foil. Such foil in strip form is ideally suited for the making of small coils where space is at a premium, but in the past difliculty has been experienced in prope ly insulat ing the surface thereof. Heretofore attempts have been made to insulate aluminum foil strip by the use of various varnish coatings but these were found difficult to apply and control in thickness. The resulting coatings were usually found to be too thick resulting in fractures and imperfect insulation as well as excessive use of space. Also, the edges of this aluminum foil strip are slightly irregular or ragged and it was found difficult to cover these completely with the varnish, making for imperfect insulation. Aluminum oxide is known as a good electrical insulator and thus attempts were made to insulate aluminum foil strip by oxidizing the surface. However, in the past attempts to do so met with difiiculty because the oxide was often too thin and hence easily rubbed off or too thick, resulting in coating fractures. When aluminum foil is exposed to normal atmosphere, an uneven film of aluminum oxide forms containing many impurities resulting from the action of various gases on the strip. The insulating properties of the film suffer from the presence of such unevenness and impurities which also inhibit further oxidation to form effective insulation. Consequently, if any of such oxide was on the surface of the aluminum before the oxidation process an imperfect insulating coating was bound to be the result.

Accordingly, one of the objects of this invention is to provide a method of insulating foil strip, such as aluminum, resulting in an insulating coating free from defeet and capable of forming electrical coils. Another object of this invention is to provide a method of the above character in which a continuously moving aluminum strip is oxidized with an insulating coating of substantial uniform thickness. Another object of this invention is to provide a method of the above character wherein a foil strip may be continuously and cheaply oxidized for purposes of insulation. Another object of this invention is to provide a method of the above character in which the thickness of the oxide coating may be automatically and uniformly controlled. Another object of this invention is to provide a method of the above character which will result in a durable coating well able to withstand the winding operation. Another object of this invention is to provide an apparatus in which foil strips such as aluminum may be continuously and cheaply oxidized with a durable coating of controlled thickness. Other objects will be in part obvious and in part pointed out hereinafter.

The invention accordingly comprises the several steps and the relation of one or more of such steps with respect to each of the others, and the apparatus embodying fea tures of construction, combinations of elements and arrangements of parts which are adapted to effect such steps, all as exemplified in the following detailed disclosure aud the scope of the invention will be indicated in the claims.

Referring now to the drawings in which is shown one of the various possible embodiments of this invention,

Figure 1 is a perspective view of a roll of aluminum foil of the type to be oxidized by the method and apparatus described herein.

Figure 2 is a fragmentary plan view on a greatly enlarged scale of a portion of the metal strip to be treated according to the method described herein, and

Figure 3 is a diagrammatic sectional view of the ap paratus which may be used in the practice of my method.

Similar reference characters refer to similar parts throughout the several views of the drawings.

Generally speaking, my process utilizes aluminum foil strip which is usually received from the fabricator in large rolls such as illustrated in Figure 1. From such rolls small continuous strips of foil may be cut in any convenient manner and continuously run through the apparatus shown in Figure 3 to oxidize the surface thereof. This is done prior to entering Winding apparatus of conventional design for automatically winding electrical inductance coils or the like. Thus, the strip from the roll is passed through a chemical bath where all foreign matter, such as grease and oxides, is removed from the surface thereof. After this it passes to a chamber for thorough drying and then is exposed to an ozone-containing atmosphere, preferably produced by ultraviolet radiation, to form very quickly a continuous aluminum oxide coating over the entire surface and edges of the strip thereby providing an excellent electrical insulating cover for the strip. The strip then passes to the winding equipment for formation into the desired coils.

More specifically the aluminum strip to be treated is cut from a roll generally indicated at 10 in Figure 1, and this may be achieved in any desired manner. For example, the roll may be vertically sliced to desired thickness and each resultant small roll processed in the manner to be described. On the other hand the entire roll may be mounted in the apparatus for processing and suitable mechanism provided for continuously cutting a small strip of the desired width from the large roll to be fed through the processing apparatus.

In practice it has been found that even when the strip of foil is cut with great care the resultant edges of the strip are somewhat irregular or ragged as indicated at 10a in Figure 2. Because of such irregularities it has been found in practice that it is diflicult to completely cover such strip with an insulating coating. The irregularities tend to protrude through varnish coatings and certain other types of chemical coatings used in the past. My improved method described herein assures a continuous coating throughout the strip.

Referring now to Figure 3 a standard 12 supports a roll 14 of aluminum foil strip on a shaft 16. Suitable equipment (not shown) may be employed for rotating the roll at a desired rate of speed to feed the strip 18 therefrom to a tank, generally indicated at 20. As previously mentioned, roll 14 may be of considerable length and thus associated with suitable cutting equipment for cutting a narrow continuous length of strip 18 therefrom. On the other hand, roll 14 may comprise a narrow strip of the dimensions used in forming these miniature electrical coils.

Strip 18 is fed forwardly or to the right as viewed in Figure 3 over roller 22, under

rollers

24 and 26, and over roller 28.

Rollers

22, 24, 26 and 28 may be driven as desired at a proper speed for continuously feeding strip Ice Patented Feb. 25, 1958 18 through a chemical bath in tank 20. This chemical V winding of electrical coils. The continuous formation of 7 bath may be of any desired composition suitable for rean insulating oxide coating of substantially uniform thick- 7 moving foreign matter such ;as grease, oxides and im- 7 ness makes for a very cheap way'of making small elecpurities from the strip withoutattacking the metallic foil;. trical coils. l a e one of-the'arnines may be. used forthispurpose; It will thus be seen that the objects set forth above,fl

T'Strip 18 passes from roller 28 through "the" processing 7 among those made apparent from the preceding clescripchamber generally indicated at 30; Generallyspeaking, j tion, are efiiciently attained .and, since certain changes chamber-30 includes apparatus for firstthoroughly drying may bemade in c rrying ou the above m tho nd in he impurities which prevent the formation ofa'nfefiectrveiin- 0 '2. The c a the strip, and then subjecting it to ultra-violetjradiation'to 'COHSIfllctiOnlset :fdifli witholitidepafiilig fl'dlii th $501331 form an'oxide coating thereon.

0f the invention, it is iritended that all matter contained The strip enters'the chamber30lthrough an opening, in' the above description or shownin the accompanying over and suitably dispdsed'to'wipefboth sur faces'ofi the limitingzsense. strip 18 as it move's'into the'jchamber. The strip then r I clalm:

passes between infra-red lamps 38 extendingfrorn the 1. Inamethod ofr ctliilir i g oxide insulated aluminum a ,top of thechamber and suitably secured thereto anfdflamps fiondllflor, the p j f f d Said 601161110821 a 0011 upp neat on "a Shelf Q "-1i1 "4 z, 1n an atmosphere containing nascentroxygen to' remsulate Preferably the atmosphere .atathiis point in itheinterior of 3335 qf i ai e s fip Where. Cracking ot :the originali the chamber is kept substantially free fr m .w nd oxide r u l q a a V V r nation aenneagn'e ain; 1 L n when. sate sulating'film. l liacco'mplishediri anez'en -containing at Preferablyj the strip next-passes between' ultra-violet mospherei to 1' f- I: ll r i lamps or'other ozone producingapparatus-genera y in; 3. The Sc r'fibinatioii definedjini claim 1in vvhich said dicated at 44 and 46' and its surfaces are therebyfoxidi ti. i di g Is s acc'Q hpl jfihcdlinithe presence of ultra- 1 V The presence of the ozone i this portion of thech' 4 her iQl 't radiation h A 1 h w h mt fw 1 i -n min mtq ndvstot V has beenfound to accelerate the oxidation pr theirgit has been found inpractice' that ultra-v ation forms an oxide coating 'ove'rgthejentire su essentially 'niatter' lrorn the "sur ces of said strip 18including the ragged edges thereof. conductor d conduct r oxi ing- .said conf .this oxide coating is of substantially uniform} and substantially free 'fr'omlimpuritiesdher Q in an economical 'fa'shionadura'ble afidpraeti insulating covering 'for the 'strip.

i ventionalwinding equipment illustrativelyfind .such breakage, agnewloiide coating is forrried ofhfth'e breakage is repaire'dibe'fore th cracked pitiohfisieoyrefcl e The strip then ente rsfa compartment 48 cohtaiiiin conmospherel.w

for automatically forming electrical inductance cor s' or winding ste'plis 1n thefirSpceofi ultrathe like. It has been found inpr'acti'ce that there maybe violet radiation. V a I r r a some cracking of the oxide coacting' due toth'e'behdin of r V i T a i E 1 the strip during windingf Accordingly I 'have' to diit V Referencestli ted thedileof thls patent preferable to include in compartment 48, nu 'U rTgpsIarns, PATENTS ductor to insulate thesurfacfe" thereof, and Winding said conductor intoafcdilj inItlie' presenc o'fzna scent ortygenf 7 o v o .5 w h i Winding t s aq bfii'p i h -i z nesnt a rf a 59' 6. The cornbinatioii 54 411 I lamps 52 for direc'ting ultra-Violet radiation agar t v a I e I i a 1, 2 5 May 10.1927 stnp as 1t 1s bemg wound mto 0011. Thus, 1f there is any 7 9 p strip while it 'isbeingfweundto maintain'thedesired'elece 5' trical insulation. Thjozorieprdduced by hem tram le V lampsi forms such new coati very, rapidly; so that, thjef by another portion of the'eoil; c Accordingly; itcan 'be seen hitll havegprevraeaa d Ple and l mail-16d. bl/M5195 M 41* vol. 1 pages 262-272 pages 27'2 re1i'ed on. Fourth ed. sulating coatmgon anali rr numfoil strip or ithelike in s r 1 A r v z pub. 1911. Filed November 13, 1951. 1 V V a continuous fashion S0. that 1t may heutihzedm the. g

5o flRoscoe and. Schrolemmer: Trea'tis e on' Chemistr-y,

Claims

1. IN A METHOD OF COILING OXIDE INSULATED ALUMINUM CONDUCTOR, THE STEP OF WINDING SAID CONDUCTOR INTO A COIL IN AN ATMOSPHERE CONTAINING NASCENT OXYGEN TO REINSULATE THE AREA OF SAID STRIP WHERE CRACKING OF THE ORIGINAL OXIDE INSULATION HAS OCCURRED.