US2547047A

US2547047A - Method of producing insulated magnet wire

Info

Publication number: US2547047A
Application number: US749804A
Authority: US
Inventors: Harry L Saums; John H Vail; Howard W Sturgis
Original assignee: Anaconda Wire and Cable Co
Current assignee: Anaconda Wire and Cable Co
Priority date: 1947-05-22
Filing date: 1947-05-22
Publication date: 1951-04-03
Anticipated expiration: 1968-04-03

Description

April 3, 1951 +1. SAUMS 'ET AL 2,547,047

METHOD OF PRODUCING INSULATED MAGNET WIRE Filed May 22, 1947 3 Sheets-Sheet 1 April 3, 1951 H. L. SAUMS ETAL METHOD OF PRODUCING INSULATEDMAGNET WIRE 3 Sheets-Sheet 2 Filed May 22, 1947 A W. G. WIRE SIZE 0 0 a w 2 mPDZZZ mum .rmmm awman O2 OU A.W. G. WIRE SIZE S m m S R w M m w M Y NRN R A m H BY A??o RNEYs i @rmq April 1951 H. L. SAUMS ETAL 2, 47,047

METHOD OF PRODUCING INSULATED MAGNET WIRE Filed May 22, 1947 s Sheets- Sheet s INVENTORS HARRY L. SAU MS JOHN H. V 1i HOWARD vW.STURGIS ATTORNE JS Patented Apr. 3, 1951 METHOD OF PRODUCING INSULATED MAGNET WIRE Harry L. Saums, John H. Vail, and Howard W.

Sturgis, Muskegon, Mich., assignors to Anaconda Wire and Cable Company, a corporation of Delaware Application May 22, 1947, Serial No. 749,804

4 Claims.

This invention relates to insulated wire, particularly wire of the character known to the trade as magnet wire. The invention provides an improved method for producin such insulated wire, and novel apparatus in which the method of the invention may be carried out. Wire produced in accordance with the invention is a new product possessing improved characteristics, and. the wire is itself therefore included within the scope of the invention.

A common type of magnet Wire consists of a metallic wire having an insulating enamel coating. Methods heretofore known for producing such wires involve applying to the wire a number of coats of oleo-resin enamel, or some similar enamel, and baking the wire after applying each coat to dry and harden the enamel on the wire. The baking step has always been necessary in the commercial production of enameled magnet wires, because the only enamels heretofore successfully employed have been of the type requiring evaporation of solvent, with or without oxidation of the vehicle, to dry and harden the enamel film on the wire. The film produced by only one coat of these baked enamels is so thin as tobe inadequate for electrical insulating purposes, and accordingly it has been commercial practice to apply a minimum of three coats and sometimes as many as twelve coats, with a baking step intermediate the application of each coat. The need for applying a number of coats of enamel has the effect, of course, of diminishing the amount of finished wire that can be produced per unit of time with a given amount of wire-enameling equipment.

Production of enameled wire by heretofore known methods is a slow process for still another reason. The drying and hardening of each coat of enamel requires baking for an appreciable length of time. There is a practical limit to the size of enameling ovens that can be built and operated economically, and even in ovens of the largest size deemed practical the rate at which" the wire can be passed therethrough, and still allow adequate time for baking the enamel coat,

is lowvarying say from about feet per minute for No. 10 A. W. G. (American Wire Gauge) wire to about 55 feet per minute for No. 39 A. W.G.

In order to obtain maximum production from an lenameling oven, it must be operated at the highest temperature consistent with the maximum temperature the enamel can withstand without deterioration (in order to permit passage of the wires through the oven at the greatest possible speed), and the wires must be closely spaced in the oven. Thus, enameling ovens are generally operated at a temperature of about 300 to 360 C., and the wire spacing is about one-half inch. If the enameled wire is allowed to remain in the oven under these conditions for a period of time only slightly exceeding the normal baking time, due either to a variation in wire speed or toa break in the wire, the resulting overbaking will cause such deterioration of the enamel coating as to make the wire valueless. A high degree of skill is required of the operators of such ovens to avoid any such damage to the wire and to insure the production of long lengths of uniformly baked enameled wire suitable for use in the electrical trade.

We have discovered that insulated magnet wire of excellent quality can be produced by passing a wire through a gelable lacquer maintained at above its gelation temperature, and cooling the lacquer coated wire rapidly upon. its withdrawal from the lacquer to a temperature below the gelation temperature of the lacquer. The resulting lacquer coated wire. has been found to have excellent insulating qualities, adequate for many commercial uses, when only a single coat of such gelable lacquer is applied. The wire may be produced commercially in this manner without baking and at speeds even ten times or more faster than is possible by wire-enameling procedures heretofore known. Uniformly coated wire may be thus produced without skilled attention, and the coating operation may beSlOwed or even completely stopped without deleteriously affecting the quality of the applied coating.

The gelable lacquers referred to herein are known to the chemical industry as such, or sometimes, as gel lacquers or gelation lacquers. They are solutions of complex organic compounds, usually in the category of synthetic resins or plastics, which are fluid at moderately elevated temperatures (usually in the range of 120 to 200 F.) and solidify to a non-flowing selfsupporting state by gelation upon cooling to a temperature below F. (usually near ordinary room temperature-about 70 F). These gelable lacquers as such do not constitute a part of our present invention. Lacquers in which a cellulose ester is the solute constituent are being and have been developed. For example, United States patents to Fordyce et al. Nos. 2,319,051 through 2,319,055, describe gelable cellulose ester lacquers which are fluid at temperatures above F. but form self-supportin non- .flowi g gels when the temperature is lowered to 3 below 100 F., and usually to about 70 F. or below. Our invention contemplates using such heretofore known lacquers, including those described in the above-noted patents and others as well, in the production of insulated magnet wire by our novel procedures and in our novel apparatus.

G'clable lacquers have heretofore been emlacquer can run back into the body of the hot solution. The rate of withdrawal is usually about one inch every six to twelve seconds, amounting to a linear speed of about 0.4 to about 0.8 foot per minute. This slow withdrawal rate is necessary because gelable lacquers in the liquid state are characterized by having a high viscosity, and an excessively thick and irregular accumulation of lacquer is formed on the article if it is withdrawn more rapidly. Upon cooling to a temperature below the critical gelation temperature, the

lacquer sets in the form of a thick coating about 0.006 to about 0.030 inch in thickness. Although the thick lacquer coating may be gelled by cooling to a non-flowing state very quickly after removal of the article from the hot lacquer solution, the coated article must be allowed to dry for ten to twenty minutes or longer before the coating is sufiiciently hard to withstand moderate handling; and in order for the coating to be hard enough to withstand the handling incident to normal use, it must be allowed to dry for a much longer time (usually a matter of hours).

Although the characteristics of the dip-coating procedures heretofore known for coating articles with a gelable lacquer, and the characteristics of the coatings so produced, have indicated that such procedures could not be used in the insulation of magnet wire (which must be with drawn from the coating bath at a linear speed far in excess of that used in dip coating articles,

and which must be handled by mechanical supports within an extremely short time interval after the wire is withdrawn from the coating solution), we have found it possible nonetheless to use such gelable lacquers to produce wholly satisfactory insulated wire.

We have found that when magnet wire is provided with such a coating of a gelable lacquer having a thickness less than 0.005 inch, and advantageously about 0.000l to about 0.002 inch. the applied hot lacquer coating may be cooled to its gelation temperature and substantially complete evaporation of the lacquer solvent may be effected during passage of the wire at a relatively high speed from the coating bath to the first wire-supporting element positioned a reasonable distance from the bath. Contact of the coated wire with a supporting element such as a pulley wheel or sheave may be made safely without damaging the coating in about 1.5 minutf s or less, and down to 0.075 minutes when fine wires are being coated, after application of the coating. By the end of this period the lacquer has gelled and the solvent has evaporated to such an extent as to permit such handling of the wire. The coated wire may be wound upon a spool or in the form of an electrical coil within about 0.15 to 3 minutes after the wire passes through the coating solution, the actual time depending more or less on the size of the wire.

In any practical wire-coating operation, the linear speed of the wire implicit in the time figures given above is such that the coating thickness specified (less than 0.005 inch) is much less than can be obtained simply by drainage of the lacquer at its natural flow rate from the moving wire as it emerges from the lacquer bath.

Based on the foregoing findings, the method of our invention involves passing a wire beneath the surface of a body of gelable lacquer maintained at above its gelation temperature, limiting the thickness of the lacquer film remaining on the wire upon its withdrawal from the body of lacquer to less than that obtainable by the natural fiow rate of the lacquer, and cooling the lacquer film on the wire to below its gelation temperature promptly upon withdrawal of the wire from the body of lacquer. It is generally advantageous, and in many cases possible, to regulate the thickness of the lacquer film so that normal magnet wire insulation is provided in a single pass of the wire through the body of lacquer. The rate at which the wire is passed through the body of lacquer is, in accordance with the invention, enormously greater than the rate at which gelable lacquers may be applied as dip coatings by the procedures heretofore known, and may even exceed by a substantial margin the rate at which magnet wires can be enameled by wireenameling methods known heretofore. It is also possible to coil wire coated in accordance with the invention much sooner after application of the coating than has been possible in the production of magnet wires by heretofore known enameling methods. 1:

Apparatus for producin magnet wire in accordance with the invention comprises basically a lacquer vessel, means for heating a body of gelation lacquer in said vessel to above its gelation temperature, a cooling zone maintained at a temperature below the gelation temperature of the lacquer, and means for continuously passing a wire to be insulated first through the body of lacquer and therefrom through the cooling zone. The same vessel which contains the lacquer advantageously also defines the cooling zone. In such an arrangement, the body of lacquer is 'in the lower portion of the vessel, and is heated therein to above its gelation temperature by heating coils or otherwise. In the upper portion of such vessel, above the surface of the lacquer, cooling coils or other cooling means are provided to maintain the temperature of the atmosphere below the gelation temperature.

The foregoing and other features of the invention are described below in some detail, with reference to the accompanying drawings, in which 7 Fig. 1 is a cross section through apparatus for producing wire in accordance with the invention; Fig. 2 is a'view on an enlarged scale of the grooved rotatable wheels shown in Fig. 1, taken substantially along the line 22 of Fig; 1; j Fig. 3 is a semi-logarithmic plot showing th linear speed at which wires of different sizes may be coated by enameling methods heretofore commercially employed compared with the method of the invention;

Fig. 4 is a semi-logarithmic plot of the time within which wires of different sizes, enameled by heretofore known commercial methods, may be 'ing means.

coiled after application of the enamel, compared with the time within which wires coated in accordance with the invention may be coiled;

Fig. 5 is a schematic cross section through a modified form of the apparatus shown in Fig. 1; and r Fig. 6 is a schematic cross section through another modified form of the apparatus shown in Fig. 1.

The apparatus shown in Figs. 1 and 2 comprises a vessel l0 containing a body of gelable lacquer solution II. A spiral heating coil [2 immersed in the solution is provided to maintain the lacquer at above its gelation temperature. An inlet connection l3 and an outlet connection'M are provided for admission and withdrawal of steam, hot oil or water, or other heating fluid. It i of course evident that various other heating means, such as a heating jacket surrounding the lower portion of the vessel Ill, electrical heating windings inside or surrounding the lower portion of the vessel, or even a screen-enclosed flame impinging on the bottom of the vessel, or a hot plate on which the vessel rests, may serve as the heat- The temperature at which the gelable lacquer is maintained by the heating means advantageou -1y is thermostatically controlled.

The normal surface level of the fluid gelation lacquer is well below the top of the vessel l0. Cooling coils [6 are arranged in the upper portion of the vessel 1 I] to cool the atmosphere in the cooling zone I! (above the surface of the lacquer) to a temperature below the gelation temperature of the lacquer. This cooling zone not only serves to cool the lacquer coating on the wire to its gelation temperature, but also serves to condense the lacquer solvent vapor emanating from the body of heated lacquer solution, so as to assist (by gravity return to the solution of the condensed solvent vapor) in maintaining the composition of the solution. An inlet I 8 and outlet |9 provide for the admission and withdrawal of cooling water or other cooling fluid to and from the cooling coils l6. As in the case of the heating coil l2, many other alternatives to the cooling coils l6 shown in the drawings may be provided for maintaining the temperature in the zone I! at the proper value. In some cases, where room temperature is safely below the gelation temperature, no special provision for cooling need be made, other than to insure that the wire comes to the temperature of the room atmosphere.

A wire 2!! to which a lacquer coating is to be applied is drawn from a spool 2i mounted at the side of the vess l 50. A freely rotatable idler wheel or roller 22 directs the wire from the spool 2| downwardly into the vessel and into the lacquer solution H. The wire passes around one of a pair of freely rotatable periph rally grooved

wheel

23 and 24. These wheels are mounted so that they project a short distance into the body of lacquer I I, and the wire is coated with lacouer in the course of its passa e th rearound. The

grooves in the wheel peripheries define an o ening, between their abutting faces through which the coated wire 25 emerges from the lacquer into the cooling zone I1.

From the cooling zone the coated wire passes around one or more wire-supporting pulleys 26 to a capstan 21. Conventional motive means are provided to rotate the capstan and draw the wire from the spool 2| continuouslythrough the lacquer and thence through the cooling zone. The wire passes from the capstan to a traverse mechanism 28 which feeds it back and forth across 6 the face of a. spool or other coll form 29-mounted on the spindle 30 of a suitably. driven coiling head.

The arrangement of the peripherally

grooved wheels

23 and 24 is shown on an enlarged scale .in Fig. 2. Each of these wheels is freely rotable on short axles 3 l and 32, respectively. Collars 33 on the outer ends of the axles bear against the hubs '34 of the wheels and hold them in position. One

of the wheels 23, preferably that around which the wire 20 passes, is mounted on an arm 35 depending from a bracket 36 and rigidly connected thereto. The other wheels 24 is mounted on a similar depending arm 31, but one which is pivotally mounted on the bracket 36 by a pivot pin 38. A tension spring 39 urges the pivoted arm 31 and the wheel 24 carried thereby toward the mating wheel 23, so that normally the peripheries of the two wheels abut.

Each of the wheels is formed with a peripheral groove 49, so that an opening 4| is defined at the abutting peripheries of the wheels. It is through this opening that t e coated. wire 25 emerges to pass into the cooling zone I! of the vessel l0. Since the amount of lacquer that remains on the wire after its emergence from between the wheels depends on the size of the opening H in relation to the size of the wire, the grooves 40 should be of such size as to produce the desired thickness of the coating film.

Although V-shaped grooves 40 are shown in the drawings, the shape of the grooves is not critical. The advantage of V-shaped grooves is that a form tool for cutting such grooves to the correct depth is easily made. The grooves may, however, be semi-circular or rectangular in cross section, or of any other desired shape, provided only that they serve to define an opening of the proper size through which the wire can pass between the abutting peripheries of the wheels.

The peripherally grooved

wheels

23 and 24, by their action in limiting the amount of lacquer remaining on the wire upon its withdrawal from the lacquer solution, insure production of an even coating of desired thickness about the wire. The small amount of flow necessary for the lacquer passing through the rectangular opening 4| to form film of even thickness about the periphery of the circular wire occurs quite readily in the short time interval before the lacquer coating gels. It is for this reason that the shape of the grooves in the

wheels

23 and 25 is not particularly critical. scribed are capab e of applying a uniform coating of the desired thickness regardless of the linear speed of the wire. The grooved Wheels have been found to operate effectively with lacquersolutions at viscosities up to about 300 poises, the maximum encountered in practice, and are capable of applying a coating of the desired thickness independently oi:- the normal flow rate of the viscous lacquer solution.

W e have found that die plates having simply a hole therein through which the wire is drawn are not particularly satisfactory in coating wires with gelation lacquers. keep the wire centered at all times in the opening of such die plates, and in consequence such plates generally remove more lacquer from one side of the wire than from the other. Unless the rate of production is unduly limited the lacquer gels before it has an opportunity to flow to the extent necessary to form an even coating of uniform thickness completely about the periphery of the wire.

The lacquer solution H which fills the lower Grooved wheels of the characted de- It is impossible in practice to portionofthe vessel may be any gelable lac- .quer which is fluid at a moderately elevated temperature but which gels to a non-flowing selfsupporting solid, without evaporation of the solvent, when the temperature thereof is sufficiently lowered. Many lacquers of this character are known, and the preparation of still others is within the skill of workers in this field. Among the lacquers that we have used with success are those in which the solute constituent is an ester of cellulose and at least one fatty acid of one to four carbon atoms. Either a single ester such as cellulose acetate, or a mixed ester such as cellulose acetate-butyrate or cellulose acetate-propionate, may be used. Such lacquers are prepared by dissolving the cellulose ester in a suitable solvent, or mixture of solvents, in the correct proportions, and heating to a temperature above the gelation temperature. Many suitable solvents for gelable cellulose ester lacquers are available. For example, gelable cellulose ester lacquers have been prepared using one or more of the following solvents: alkylene dichlorides (e. g. propylene or butylene chloride) aliphatic alcohols, particularly the lower aliphatic monohydric alcohols containing five carbon atoms or less (e.g. ethyl alcohol,

isopropyl alcohol, etc.), toluene, benzene, xylene and ,ligroin.

While we have obtained particularly satisfactory results using cellulose ester lacquers of the character referred to above and as disclosed in the aforementioned Fordyce et a1. and other patents relating to such lacquers, the invention is not limited to the use of cellulose ester gelation lacquers. Gelation lacquers in which the solute constituentis polyethylene (polymerized ethylone) have also been used successfully. Gelation lacquers incorporating still other resinous plastic compositions as the solute, such as polyvinyl chloride, copolymers of vinyl chloride and vinyl.

acetate, and ethyl cellulose (a polymer prepared by reaction of ethyl chloride and cellulose), may also be employed in accordance with the invention.

We have obtained excellent results using a gelable lacquer composition composed of about 18% cellulose acetatebutyrate, 16.4% isopropanol and 65.6% commercial xylol. This lacquer had a viscosity between 900 and 1000 centipoises at 122 F. and a gelation temperature of about 70 F. The lacquer was maintained at a temperature between 140 and 160 F. in the vessel !0, although the lacquer could be maintained at a higher temperature up to that at which bubbling occurs (usually about 200 F.). wires, meeting or exceeding the specifications established for commercial enameled magnet wires, have been obtained by passing bare metallic wire through this lacquer solution, in the apparatus described above, at speeds ranging from '75 to 160 feet per minute. Equally satisfactory results are ,obtained using a cellulose acetate gelable lacquer composed of about 1'7 cellulose acetate, about 58% propylene chloride, and about 25% isopropyl alcohol; and using a cellulose acetate-propionate lacquer composed of about 20% cellulose acetatepropionate, 24% isopropyl alcohol, and 56% toluene.

We have also coated magnet wires in accordance with the invention with a gelable lacquer solution composed of 20% to 23% of an ethyl cellulose obtained on the market as standard SO-centipoise, medium ethoxy ethyl cellulose dissolved in commercial xylol. This lacquer solution was maintained at a temperature of about Excellent coated 200 F. in the vessel l0 and'had' a gelation temperature of about 70 F. Similar ethyl cellulose gelable lacquers were used in which the solvent was modified by the addition of a low boiling range aliphatic hydrocarbon solvent having a boiling range of 230 to 280 F. We have also modified the physical characteristics of coatings produced by such lacquers, by incorporating in the lacquer solution agents such as the Paraplex resins (copolymers of sebacic acid, glycerol," and ricinoleic acid).

We have in addition produced very satisfactory coated magnet wires by the process of the invention using a gelable polyethylene lacquer comprising, as far as we have been able to ascertain, about 20% polyethylene solids in toluol 'as a solvent. The lacquer was applied to the wire at a temperature of about 180 to F.

Plasticizers may be incorporated in the gelable lacquer solutions, but generally, for Wire coating purposes, it is preferable to omit the plasticizer. Unplasticized cellulose ester films deposited on wires in accordance with the invention are usually harder and more abrasion resistant than plasticized films, and yet are adequately flexible for the uses to which magnet wires are ordinarily put.

Colored and opaque coatings of gel lacquers can be produced by adding to the lacquer soldtion an appropriate dye or pigment which is compatible therewith. The dye should be soluble in the lacquer solution, and many such dyes 'are known which do not deleteriously affect the dc"- sirable characteristics of the gelled lacquer film on the wire. Pigments and other solid materials such as finely divided aluminum oxide, titanium dioxide, silicon dioxide, iron oxide, and the like, may be used as the coloring or opaquing agent. By appropriate choice of the pigment and the amount thereof used in the lacquer, it is possible to modify other characteristics of the coating besides its color or opacity. For example, a suf' ficient amount of a metal oxide pigment'in the coating will generally increase its resistance to heat.

In carrying out the method of our invention in apparatus such as that shown in Figs. 1 and 2, the wire 20 is drawn continuously from the spool 21 around the grooved wheel 23, whereby it is immersed in the body of lacquer ll. As the result of such immersion, the hot liquid lacquer wets and adheres to the surface of the wire. The temperature of the lacquer is maintained by the heating coils at above the gelation temperature and high enough to establish the desired lacquer viscosity, but preferably not so' high that bubbles form in the solution (ordinarily bubble formation begins about 200 F. or higher). The wire is drawn upwardly through the opening ll defined by the grooves in the abutting peripheries of the freely

rotatable wheels

23 and 24, ro-

tation of which is caused by the movement of the wire.

The opening 4| limits the thickness of the film of lacquer remaining on the wire after it has passed therethrough to less than could be obtained by the natural flow rate of the lacquer with the wire travelin at any reasonable coating speed. As the coated wire emerges from the opening 4!, the coating remains liquid for just about long enough to flow into and form a uniform coating about the wire, and it then solidifies by gelation to form a self-supporting film on the Wire.

In coating wire with a gelable cellulose acetate-butyrate lacquer maintained at a coating temperature of about 140 to 160 R, we. have found that gelation and solvent evaporation take place satisfactorily in the cooling zone I! without the aid of cooling by the cooling coils. The atmosphere at ordinary room temperature suffices to accomplish these results. However, improved gelation and, more particularly, improved solvent recovery by condensation of solvent vapor in the cooling zone l1, have been obtained by lowering the temperature of the cooling zone I! to below room temperature by the use of cold tap water circulating through the cooling coils.

Whether or not the cooling coils are used to cool the zone I! to below room temperature,

gelation and solvent evaporation take place so rapidly that, with the wire moving at normal coating speeds, the coated wire can be touched lightly with the fingers without damage to the film at a point about 2 or 3 feet above the top of the vessel It. Solvent evaporation continues as the coated wire 25 travels toward the sup portin pulley 26, and by the time the wire reaches it gelation is complete and solvent evaporation has advanced to the point that the coated wire may be passed over the pulley without damage to the coating film. In general, for ordinary coating speeds, a distance of about 15 feet between the

grooved wheels

23 and 24 and the upper pulley 26 is sufiicient to permit quite complete hardening of the coating. This distance may of course be varied, if desired, depending upon the wire size and coating speed and thickness. For example, in coating fine wires such as No. 37 A. W. G., a distance somewhat less than 15 feet is usually sufficient, whereas with relatively coarse wires such as No. 15 A. W. G. a somewhat greater distance may be preferable, particularly if a thick coating of the lacquer is applied. By establishing a distance between the upper pulley 26 and the capstan 21 approximately equal to the distance between the upper pulley 26 and the

grooved wheels

23 and 24, the coatin film will be sufliciently hard to withstand the distortion caused by the capstan and by the coiling operation, which may follow immediately.

Wires of any size may be coated by the method and apparatus of the invention. In the case of the larger wires, such as No. 14 to No. 20 A. W. G., the rate of solvent evaporation from the gelled coating may be increased by gently heating the coating on the wire over a portion of the distance between the top of the vessel I and the upper pulley 26. Such heating may be accomplished by passing the wire through a steam coil, or by infra-red heating lamps, or in any other desired manner.

As pointed out above, the linear speed with which wires can be enameled in conventional enameling ovens depends on the size of the wire; and the same is more or less true in coating wires in accordance with the invention. The coating speeds involved in the method of the invention are indicated in Fig. 3 of the drawings, wherein coating speeds in feet per minute are plotted against the size (A. W. G.) of the wire being coated. The line ab on Fig. 3 indicates substantially the maximum linear speed with which it has been possible heretofore to enamel wires in commercial practice with oleo-resin enamels requiring baking. An important commercial advantage of the new method is that it permits coating to proceed at a much higher linear rate of travel of the wire. The .line c.d

of Fig. 3 indicates a rair. averagenormal coating speed for coating wires of different sizes in accordance with the invention, although in particular cases a somewhat. lower or substantially higher coating speed may be preferable; and. the line e--,f is indicative of speeds that actually have been attained in some cases. Ordinarily commercial wire coating in accordance with the invention will be conducted at speeds at least about double thosev attainable in baking-enamel coating operations. If the linear rate of withdrawal of articles being coated by the dip methods heretofore known for applying elable lacquers were plotted to scale on Fig. 3, the speed of application of such thin coatings as are re.- quired for magnet wire insulation would lead to a curve that would be. virtually indistinguishable from the Wire Size axis of the plot. It is evident from this plot that wires can be coated in accordance with the invention much more rapidly than with enamels that require baking (i. e., they can be coated at a rate in excess of the rate shown by the line ab of Fig. 3), and enormously more rapidly than would be possible by heretofore known dip methods.

Related to the high coating speed attainable is the very short time that need. elapse. between applying the lacquer and coiling a wire coated in. accordance with the invention. Coiling may be either on spools for convenience in handling, or in the form of finished electrical coils for the electrical industry. Fig... i isa plot, against wire size, of the time elapsed between, application of the coating and coiling of the wire. in the cases (1) of wires, coated accordance with the invention and. (2) in accordance with here tofore known commercial methods. Thev line g-h of Fig. 4, indicates the minimum time int-h..- in which wires of .difierent sizes may he coiled commercially after coating with. oleoresin enamels and baking. The elapsed time between immerson of any section of the wire in the lacquer and coiling of said section may, in accord: ance with the invention,v be less than that indicated by the line gh. The line of Fig. .1 indicates; a, ,fair; average, time to allow in. ordinary cases between. application of. lacquers. in accordance with. the invention and ceiling of the coated wire. It is clear from this pilot that wire coated. in accordance with the inventionrnay be coiled much sooner aftera-pplication of the coat.- ing composition than is the case in the. commercial wire-enameling procedures heretofore known. The short time interval between coating andcoileing that is attainable in accordance with the invention may be contrastedwith the time. of several hours required for drying and hardening the thick gelable lacquer coatings formed by heretofore known dipping methods on tool nan-.- dles and other such articles.

The line m-n plotted on Fig. e indicates the very short time, interval that need elapse lee..- tween application of the enamel andv passage. of the coated wire over the. first supporting p111- ley .or sheave. after emergence of the wire from the body .of lacquer. Within this period of time the lacquer may be gelled and suiiicientv solvent evaporated to produce a hard enough coating to withstand the forces to which it is subjected in being drawn over the support. In general the normal maximum elapsed time between the passage of any section of the wire through the lacquer and passage of the same section over the supporting sheave is less than about 3.5 minutes, and in the case of .finev wires (say No. 40 A. W. .G.)

it may be only 4.5 seconds (0.075 minute) or less.

As hereinbefore stated, wire prepared in accordance with the invention may be wound into finished electrical coils directly after coating, as a last step in a conjoint wire-coating and coilwinding operation. This represents the fulfilment of a desire that has long been felt in the magnet wire industry, but one that previously has not been attained because of the limitations imposed by the wire-enameling procedures heretofore commercially available. In winding electrical coils it is generally necessary from time to time to start and stop the movement of wire to the coil winder, and sometimes to vary the linear speed of wire travel. It is not feasible to interrupt the passage of wire through an enameling oven, or vary the speed with which it passes through the oven, for the reasons already given. Furthermore, it is not economically practical to limit coil winding to the speeds attainable in producing baked-enamel coated wires, or to subject it to the production hazards incident to breakage of the wire during the course of the coating operation. Our new wire coating method is not subject to these limitations. The coating speeds attainable are commensurate with commercial coil winding speeds, and passage of the wire through the body of gelable lacquer may be slowed down or speeded up, or even stopped altogether, as the occasion to do so arises, without deleteriously affecting the thickness or quality of the coating on the wire. Whereas an interruption in the passage of wire through a commercial wire enameling oven almost invariably results in ruining the wire, an interruption in the new coating operation has no significant effect on the wire, and the passage of the wire through the gelable lacquer may be resumed after an interruption without discarding any portion of the wire.

Various modifications may be made in the method and apparatus described above. For example, in producing wires with fairly thick coatings, it may be desirable to modify the apparatus as shown in Fig. 5. This modification involves providing an'idler pulley or sheave '42 below the first pulley 26 over which the wire passes after emerging from thelacquer, and a second idler 43 about at the elevation of the first pulley 26. The coated wire passes upwardly around the first pulley 26, downwardly and around the idler 42, and thence upwardly and around the second idler 43 to the capstan 21. The extra wire path length provided in this modification between the coating bath and the capstan allows, at a given wire speed, some additional time for solvent evaporation, in those cases where such is desirable.

It is ordinarily possible and desirable to apply a coating of adequate thickness to provide normal magnet wire insulation in a single pass of initially bare wire through the body of gelable lacquer. Coating thicknesses between 0.0001 inch and 0.002 inch are quite easily produced in accordance with the invention in a single pass through the lacquer, and thicknesses in this range (commonly near 0.0005 inch) are those usually desired for magnet wire insulation. Hence a feature of the invention is that in many cases the wire may be packaged for the electrical trade (either as a spool or coil of. wire for convenient handling, or as a finished electrical or magnet coil) after but a single pass through the gelable lacquer coating solution.

For some purposes magnet wires havingcoat 12 ings up to 0.005 inch are desirable, and for producing such wires apparatus modified as shown in Fig. 6 may be used with advantage. In this modification a second set of coating rollers 44 and 45, similar to the first set of

rollers

23 and 24 described above, is mounted in the vessel ID at the gelable lacquer surface. A second supporting pulley or sheave 46 similar to the first such pulley 26 also is provided. The incoming wire 28 passes down and through the body of gelable lacquer, around one of the rollers 24, and up to and around the supporting pulley 26. Thence the wire passes again into the body of lacquer and around a roller 34 of the second set to the second supporting pulley 46, from which it passes to the capstan 21. Thus two coats of the lacquer are applied to the wire in a single operation. We have found that a considerable number of coats may be applied thus directly after gelation of the previous coat, without injuring the coat or coats previously applied. There is no advantage, so far as insulating magnet wires are concerned, however, in applying more than two coats. We have been able to develop coating thicknesses up to 0.016 inch in only two passes of the wire through the lacquer, and so two coats may be regarded as the maximum necessary forordinary wire coating operations even in those cases Where thicker-than-usual coatings are desired.

Magnet wire produced in accordance with the invention is the equal of conventional enameled magnet wire in many respects, and it is superior in some respects. For ,example, magnet wire comprising a metallic conductor having thereon a thin, substantially continuous insulating film of an ester of cellulose and one or more fatty acids containing one to four carbon atoms (e. g. cellulose acetate-butyrate) applied directly incontact with the conductor surface, easily passes the quality acceptance tests established for ordinary enameled wire. The cellulose ester coating possesses high abrasion resistance. It is substantially insoluble in and not appreciably softened by petroleum oils, water or other liquids to which it is likely to be exposed in service. The wire may be bent on a mandrel of its own diameter without cracking the coating, even when the coating is unplasticized. The insulation resistance is high, even after prolonged exposure at a temperature of 120 F. to an atmosphere saturated with water vapor. The dielectric strength is likewise high. Continuity of the film is substantially equal to that of ordinary enameled wire. The Q value of coils wound from the new wire generally is substantially higher than that of coils wound from ordinary enameled wires. (The Q value of an electrical coil indicates the magnitude'of the ratio of the amount of energy stored in the coil to the amount of energy dissipated therein for cycle of an alternating current flowing therethrough. A high Q value, which indicates that the coil will dissipate only a small amount of the power supplied to it or passed through it, is much desired in magnet wire coils employed in radio circuits and other fairly high frequency alternating current devices.)

Another feature of wires coated with a gelable lacquer in accordance with the invention is the ease with which the coating may be removed from the wire. for making electrical connections. For example, the insulation may be removed readily from wires coated with a cellulose acetate-butyrate gel lacquer by dipping the wire in acetone. This leaves a clean wire surface to which electrical connections may easily be made by soldering or otherwise. This is an outstanding advantage of the gel lacquer coated wire over baked enamel coated wire from which the enamel can be removed only by scraping or by the use of an abrasive such as Sandpaper, or by powerful solvents. Sandpapering is slow and frequently causes breakage of fine Wires, and the solvents which will remove heretofore known baked enamels are expensive, toxic, must be handled carefully and must be thoroughly washed from the wire.

Coatings applied to wires in accordance with the invention do not adhere to the wire as do baked enamel coatings, but this is not a disadvantage, and is even an advantage in that it permits easy mechanical stripping of the coating if a suitable solvent is not at hand. Solvent evaporation that ensues after gelation of the coating is accompanied by shrinkage of the coating tightly about the wire, so that there is no danger of the coating slipping on the wire accidentally.

It is evident from the foregoing that the invention provides a magnet wire possessing in a large measure the properties desired in such wires, and yet that can be madeby the method and with the apparatus of the invention much more rapidly and with much less costly equipment than heretofore known enameled wires.

We claim:

1. The method of producing insulated magnet wire which comprises passing a wire through a body of gelable lacquer which i maintained at substantially atmospheric pressure and which is maintained in the liquid state by being heated to above its gelation temperature, withdrawing the Wire from the body of lacquer and substantially simultaneously limiting the thickness of the lacquer film on the wire to less than 0.005 inch and less than that obtainable by the natural flow rate of the lacquer by passing the wire through a restricted opening formed by two arcuate memb rs, at least one of which rotates in a direction such that its edge adjacent the wire moves in thesame direction as the movement of the wire through the opening, and cooling the lacquer film on the wire to below its gelation temperature promptly upon withdrawal of the wire from the restricted opening.

2. The method of producing insulated magnet Wire which comprises passing a wire through a body of gelable lacquer which is maintained at substantially atmospheric pressure and which is maintained in the liquid state by being heated to above its gelation temperature, withdrawing the wire from the body of lacquer and substantially simultaneously limiting the thickness of the lacquer film on the wire to less than 0.005 inch and less than that obtainable by the natural flow rate of the lacquer by passing the Wire through a restricted opening formed by two arcuate members at least one of which rotates in a direction such that its edge adjacent the wire moves in the same direction as the movement of the wire through the opening, and cooling the lacquer film on the wire to below its gelation temperature promptly upon withdrawal of the wire from the restricted opening, the rate of passage of the wire through the body of lacquer and through the restricted opening in relation to the size of the wire being at least about equal to the rate shown by the line c-d of Fig. 3 of the accompanying drawings.

' lacquer by passing the wire through a restricted opening formed by two arcuate members at least one of which rotates in a direction such that its edge adjacent the wire moves in the same direction as the movement of the wire through the opening, cooling the lacquer film on the wire to below its gelation temperature promptly upon withdrawal of the wire from the restricted opening, and winding the wire into an electric coil of desired size and shape directly after gelation of the lacquer coating and as the final step in a conjoint wire-coating and coil-winding operation.

4. The continuous method of producing a coil of insulated wire which comprises passing a me tallic wire through a body of gelable lacquer which is maintained at substantially atmospheric pressure and which is maintained in the liquid state by being heated to above its gelation temperature, withdrawing the wire from the body of lacquer and substantially simultaneously limiting the thickness of the lacquer film remaining on the wire to less than 0.005 inch and less than that obtainable by the natural fiow rate of the lacquer by passing the wire through a restricted opening formed by two arcuate members at least one of which rotates in a direction such that its edge adjacent the wire moves in the same direction as the movement of the wire through the opening, cooling the lacquer film on the wire to below its gelation temperature promptly upon withdrawal of the wire from the restricted opening, and winding the wire into a coil of desired size and shape directly after gelation of the lacquer coating and as the final step in a conjoint wire-coating and coiling operation, the elapsed time between immersion of any section of the wire in the body of lacquer and coiling of said section, in relation to the size of the wire, being not appreciably greater than the time shown by the line a'-lc of Fig. 4 of the accompanying drawings.

HARRY L. SAUMS.

JOHN H. VAIL.

HOWARD W. STURGIS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 862,935 Pfanstiehl Aug. 13, 1907 1,531,259 Turner Mar. 24, 1925 1,993,838 Hagedorn Mar. 12, 1935 2,044,970 Candy June 23, 1936 2,051,944 I-Iershberger Aug. 25, 1936 2,156,607 Schon May 2, 1939 2,197,622 Sendzimir Apr. 16, 1940 2,291,670 Wiley Aug. 4, 1942 2,308,638 Balthis Jan. 19, 1943 2,315,645 Newton Apr. 6, 1943 2,350,742 Fordyce June 6, 1944

Claims

3. THE CONTINUOUS METHOD OF PRODUCING AN ELECTRIC COIL WHICH COMPRISES PASSING A METALLIC WIRE THROUGH A BODY OF GELABLE LACQUER WHICH IS MAINTAINED AT SUBSTANTIALLY ATMOSPHERIC PRESSURE AND WHICH IS MAINTAINED IN THE LIQUID STATE BY BEING HEATED TO ABOVE ITS GELATION TEMPERATURE, WITHDRAWING THE WIRE FROM THE BODY OF LACQUER AND SUBSTANTIALLY SIMULTANEOUSLY LIMITING THE THICKNESS OF THE LACQUER FILM REMAINAING ON THE WIRE TO LESS THAN 0.005 INCH AND LESS THAN THAT OBTAINABLE BY THE NATURAL FLOW RATE OF THE LACQUER BY PASSING THE WIRE THROUGH A RESTRICTED OPENING FORMED BY TWO ARCUATE MEMBERS AT LEAST ONE OF WHICH ROTATES IN A DIRECTION SUCH THAT ITS EDGE ADJACENT THE WIRE MOVES IN THE SAME DIRECTION AS THE MOVEMENT OF THE WIRE THROUGH THE OPENING, COOLING THE LACQUER FILM ON THE WIRE TO BELOW ITS GELATION TEMPERATURE PROMPTLY UPON WITHDRAWAL OF THE WIRE FROM THE RESTRICTED OPENING, AND WINDING THE WIRE INTO AN ELECTRIC COIL OF DESIRED SIZE AND SHAPE DIRECTLY AFTER GELATION OF THE LACQUER COATING AND AS THE FINAL STEP IN A CONJOINT WIRE-COATING AND COIL-WINDING OPERATION.