US3181326A - High-speed production of magnet wire - Google Patents

Description

May 4, 1965 H. L. HOLLINGSWORTH ETAL 3,181,326

HIGH-SPEED PRODUCTION OF MAGNET WIRE Filed July 20, 1962 2 Sheets-Sheet 1 FIG. la

INVENTORS.

HENRY L. HOLUNGSWTH VERNE ILLAUSEN y 1965 H. HOLLINGSWORTH ETAL 3,181,326

HIGH-SPEED PRODUCTION OF MAGNET WIRE Filed July 20, 1962 2 Sheets-Sheet 2 FlCilb' INVENTORS. HEIVR Y L. 1/0 I'M-V007 VERA/E H. LAl/SEN 47' TOPIVEYJ- United States Patent 3,181,326 HIGH-SPEED PRUDUCTHON 01F MAGNET WERE Henry L. Hollingsworth, Perryshurg, Ohio, and Verne ll. Lausen, Fort Wayne, Ind; said Hollingsworth assignor to Phelps Dodge Copper Products Corporation, New York, N.Y., a corporation of Delaware Filed July 20, 1962, Ser. No. 223,283 5 Claims. (Cl. 72-46) This invention relates to the production of magnet Wire and more particularly to an improved method and apparatus for this purpose which enables such wire to be produced continuously at a substantially higher production rate than has been feasible heretofore.

Hereto'fore, magnet Wire has been manufactured from hare wire wound on spools which are arranged in supply racks. Bare wire of the gauge desired in the final product is continuously unwound from the spool and pulled through a treating path where insulating enamel is coated in liquid form and then baked or cured on the wire, this procedure being repeated to provide the desired insulation build on the wire as it travels along the treating path. Generally, the baking or curing is effected in an oven through which the wire is pulled back and forth in multiple passes by a capstan, and idler rollers are provided at the opposite ends of the oven for guiding the wire in these passes and directing it through an enamel applicator at the beginning of each pass. From the final coating and baking pass, the coated wire is pulled continuous- 1y to a take-up device serving to wind the wire on a spool or spools on which it is sold for ultimate use.

*From the viewpoint of efficiency, it is desirable to move the wire through these operations at the highest possible linear speed consistent with providing a final product of good quality. Through recent improvements in automatic spooling of the finished wire, and inthe enamel applicators and the drying or curing rate of such enamels, it is possible to perform the enameling and takeup operations at much higher speeds than previously used. Despite these improvements, however, the operating speeds used commercially have not increased substantially, operating speeds in excess of about 200 feet per minute being rare and the speeds commonly used being much lower than this.

A major factor contributing to this speed limitation has been the difficulties arising from the supply spools for the bare wire, and which may be summarized as follows:

(1) The bare wire has previously been drawn down to the desired gauge from larger gauge wire and then reeled on the supply spools, these drawing and reeling operations being performed at high speed in the wire mill. As

a result, flaws or imperfections occur in the reeling or" the Wire on the spools which eventually supply the bare wire to the enameling operations. While such flaws can be tolerated in the enameling operations at the present low speeds commercially used, they could not be tolerated in high-speed enameling operations, where they would cause excessive wire breakages, coating imperfections, etc.

'(2) If the bare wire is dereeled from the supply spool by rotation of the spool as the Wire is pulled off tangentially, there is a practical limit to the amount of wire which the spool can supply without creating excessive tensions in the wire. For example, a spool of 44-gauge wire weighing more than 10 pounds is impractical because too much tension would he required to rotate such a by resort to the well-known over-theend dereeling wherein the spool is held stationary while the wire is payed-off over one end under the action of a spinner. However, the latter method of dereeling has been impracticable for Supplying enameling operations because of the resulting twists in the wire, which would impair the desired application of a uniform coating and, particularly at high speeds and in line wire sizes, would increase the risk of breaking the wire as it is pulled through the enameling operations.

Another factor which has limited the wire speed through the enameling operations is the need to maintain a close control of the wire tension. Normally, it is desirable to heat the wire to about its annealing temperature in the oven, and at this temperature copper wire has very low tensile strength. Even at their present low operating speeds the wire transport means commonly used for pulling the wire through the enameling operations will impose tensions near (and all too frequently exceeding) the breaking point of the wire, at least with fine gauge wire. For example, in a typical Wire transport means one power-driven capstan, to which the finished wire travels, serves to pull the bare wire off the supply spool, around a guide post, over five idler guide rolls at opposite ends of the oven and through four enamel applicators. Such transport means are therefore unsuited for the much more demanding conditions required for highspeed operation.

'An object of this invention is to provide a method for producing magnet wire at high speed, up to 1,000 feet per minute, without impairing the quality of the final product. A further object is to provide improved apparatus for carrying out the new method.

According to the invention, the bare wire to be processed is supplied from the supply spool at a relatively low linear speed but at a gauge or thickness considerably in excess of that desired in the finished magnet wire. The wire thus supplied is passed continuously through a wire-drawing zone where it is drawn down to substantially the finished wire gauge,'with the result that it is considerably elongated, preferably to several times its starting length, incident to such drawing. From the drawing zone, the wire is pulled continuously through a treating path at a high linear speed which exceeds the starting speed by an amount commensurate with this elongation; Liquid enamel is continuously and repeatedly applied to the drawn wire and baked on it as it is pulled through the treating path, to form the desired build of multiple coatings; and the coated wire is withdrawn from the treating path at substantially the aforesaid high speed and passed to a high-speed spooling device.

With this method, the magnet wire can be produced at a linear speed which is much higher than the speed at which bare wire is dereeled from the supply spool, so that the dereeling can be effected in a safe and simple manner at relatively low speed. Moreover, the bare wire can be supplied by over-the-end dereeling from the spool, with its attendant advantages, because the resulting twists in the wire are removed by the action of drawing down the wire in the drawing zone as the wire passes to the enameling operations. This drawing action also removesflaws such as twists resulting from imperfect spooling of the bare wire in the wire mill. In addition, the surface of freshly drawn copper wire seems to have greater and more uniform wetability for the enamel application than bare wire which has aged even a day or two.

An apparatus made according to the invention comprises wire-drawing die means and power-driven means for continuously pulling the bare Wire from the supply spool through the die means, the latter forming a drawing zone preferably having a series of die holes which progressively decrease in size in the direction of the wire travel, so that the drawing operation is effected in stages. The

3 power-driven means are operable to pull the drawn wire from the die means at a high linear speed substantially greater than that at which it is dereeled from the supply spool, to take into account the considerable elongation of the wire as it passes through the die means. The apparatus also comprises enamel applicator means for coating the wire, heating means for baking the coated enamel to a solid film on the wire, wire transport means for continuously pulling the elongated wire from the first pulling means successively through the applicator means and the heating means in multiple passes at substantially said high linear speed, and a high-speed spooling device for continuously taking up the coated wire from the transport means. Preferably, the Wire pulling means includes a power-driven stepped capstan for pulling the wire through the last two or three stages of the multi-stage drawing operation; and the wire transport means includes an extension of this capstan located opposite one end of an oven '(forming the heating means) and which serves to pull each pass of the wire to or from only one guiding idler roll located opposite the other end of the oven. Thus, the hot wire is required to turn only one idler roll (which may be a sheave) in each double pass to and from the capstan. This makes the condition of the guiding idler means less critical for a given wire size and enables the insulation of finer gauges of wire without breaking or even stretching the wire.

For a better understanding of the invention, reference may be had to the accompanying drawings in which FIGS. 1a and lb are schematic views (FIG. lb being a continuation of FIG. 1a) of a preferred form of the new apparatus for carrying out the method, and

FIG. 2 is a detail view, in front elevation, of the dual capstan shown in FIG. In for pulling the wire through the last few drawing stages and also for pulling the drawn wire through the subsequent enameling operations.

Referring to FIGS. 1a and 1b (jointly designated FIG. 1), the apparatus there shown comprises a bare wire supply source indicated generally at 10, die means forming a multi-stage drawing zone 20, wire pulling means arranged in two series 30 and 40' for pulling the bare wire W through the drawing zone 20, a dual capstan 42 forming part of the wire pulling means 40 and also serving to pull the drawn wire W1 through an oven 50 in multiple passes, enamel applicators 60-61 at opposite ends of the oven for applying liquid enamel to the wire passes, and a spooling device 70 for continuously taking up the coated wire W2 from the oven.

The supply source comprises a replaceable spool 11 on which the bare wire W is wound and which is held stationary in any suitable manner. The wire is payed otf over the upper end of the spool by a spinner 12 mounted on the spool for free rotation about the spool axis. From the periphery of the spool, the wire extends through an outer guide 13 of the spinner and then upwardly and inwardly through an axial guide 14 of the spinner, so that the wire clears the upper flange of spool 11 in passing from guide 13 to guide 14. As the wire is pulled from the spool through these guides, the spinner 12 is rotated by the wire to pay it off over the upper end of the spool at whatever rate is called for by the pulling action, as is well known in the art. From supply spool 11, the-bare wire W is pulled over guide sheaves 15 and 16 to the wiredrawing zone 20.

The drawing zone 20 is constituted by a series of wiredrawing dies which are shown as being eight in number, designated 22 through 29, respectively. These dies, which may be of the conventional type, form a corresponding number of die holes (not shown), each die being operable to draw down the wire so as to reduce its diameter as the wire is pulled through the corresponding die hole. The dies are held stationary in the usual die block (not shown) and are supplied in the usual manner with a liquid for cooling and lubricating purposes. It will be understood that the holes in dies 22-29 are of progres- 4. sively decreasing diameter starting with the first die 22, so that the last die 29 will have the hole of smallest diameter corresponding to the gauge desired in the finished magnet wire. The dies are replaceable, as is common in wire mills, to provide for dirferent gauges of the wire supply and of the drawn wire.

Due to the elongation of the wire as it is drawn down in diameter, the wire must be pulled away from each die at a linear speed greater than that at which it is delivered to the die. For this purpose, the wire pulling reans 30 comprise a power-driven capstan 31 having steps 32, 33, 34, 35 and 36 of progressively increasing diameters, and an idler roll 37 mounted in spaced parallel relation to the capstan. The capstan 31 is driven from an electric motor 38 through an adjustable speed transmission 39. From guide sheave 16, the wire W passes over idler roll 37, through the first die 22, around the smallest diameter step 32 of capstan 31, back to and around the idler roll 37, through the second die 23, around the next larger step 33, and so on through the successive dies by way of idler 37 and the next step of the capstan. Thus, the first step 32 pulls the wire from the first die 22 at a linear speed greater than that at which the wire passes to this die and delivers the wire at that greater speed to the next die 23, from which the wire is pulled and delivered to the next die 24 at still greater speed by the second step 33, etc.

The wire pulling means of the second series 46 comprise an adjustable speed transmission 41 through which motor drives the dual capstan 42, a series of progressively increasing steps 43, 44 and 45 on capstan 42, and an idler guide roll 45 mounted in spaced parallel relation to these steps. From the last drawing stage of the die group 22-26, the wire passes by way of the pulling step 36 to guide roll 46, thence through die 27, around step 43, back to and around guide roll 46, through the next die 28, around the next larger step 44, and so on through the last die 29 and around the final step 45 of drawing capstan 4-2.

For simplicity, the idler guide means 37 and 46 are each shown as a single roll; but it will be apparent that they may be replaced by individual idler sheaves for the respective wire turns or by stepped idler rolls, to take into account the increasing speeds of the successive wire turns.

The oven 50 has work tubes 51 and 52 extending through the oven from front to back, one above the other. These tubes are relatively small in height dimension but are wide enough to accommodate the desired number of wire passes back and forth through the oven. The upper tube 52 receives the wire passes from an extension 48 of capstan 42 located opposite the front end of the oven, these upper passes extending through the upper tube to an idler roll 49 located opposite the back of the oven. The lower wire passes from idler roll 49 extend through the lower tube 51 and back to the capstan extension 48." The guide means shown as the single idler roll 49 may, of course, be in the form of individual idler sheaves for the respective Wire turns. Above the upper work tube 52 is an annealing tube 53 extending through the oven from front to back. Thus, the tubes 51-53 form wire inlet and outlet openings at opposite ends of the oven.

From the final capstan step 45 of the wire-pulling means 4%, the drawn wire W1 extends by way of a guide 55 through the annealing tube 53, around idler 49, through lower tube 51, around capstan extension 48, back through upper tube 52, around idler 49, and so on through the desired number of passes between the capstan extension 48 and guiding idler 49. As shown in FIG. 2, the steps 43, 44- and 45 of dual capstan 42 have peripheral flanges 47 for guiding the wire around the respective flanges; and the extension 48 has peripheral grooves 49a in which the respective wire turns from lower tube 51 are guided around this extension. To allow for slight extension of the wire under the heating action of the oven '0, while maintaining the wire taut, the grooves 4% may be made of slightly increasing diameters progressing from left to right (FIG. 2), although these diameter increases will be too small to be noticeable in the drawings.

It will be understood that the idler rolls 37, 46 and 49 may be formed with grooves (not shown) for guiding the wire turns around these rolls, and the steps of capstan 31 may be flanged like the steps 43-45 for guiding purposes.

The oven 50 may be heated in any desired manner, as by gas or electricity. By whatever heating means are used, the annealing tube 53 is generally maintained at a temperature sufficient to anneal the drawn wire before it picks up enamel from the applicators 6&61, while the work tubes 51-52 are generally maintained at a somewhat lower temperature sufficient to cure or bake each enamel coating to a dry film before the wire picks up the next coating. Cooling of the wire is effected in the course of its passage from the oven and around the capstan extension 48 or idler 4-9. To maintain the closest possible temperature control, electric heating is preferable, as by resistance-heating of the metal tubes 51-53, with individual thermostatic controls in the heating circuits for the respective tubes. For a particular enamel, the ideal temperature to be maintained in the working tubes can be determined by those skilled in the art, with a given oven length and speed of wire travel through the oven.

The applicator 60 is mounted between the front of the oven and the capstan extension 48, in position to apply liquid enamel to the upper wire passes before they enter upper tube 52. The other applicator 61 is mounted between the back of the oven and idler 49, in position to apply liquid enamel to the lower wire passes before they enter the lower tube 51.

The applicators 60 and 6-1 may be of any suitable type adapted to apply a uniform enamel coating to wire travelling at high speed, preferably up to 1,000 feet per minute, such as applicators of the roller-die or fiat-wipe type now in commercial use. However, it has been found that applicators of the so-calledfelt type, known in the art, are well suited for this purpose. As shown, each felt-type applicator comprises a hollow base 62 and an upper section 63 which directly underlie and overlie, respectively, the wire passes to be coated by the applicators and which support the wire-engaging felts below and above these passes. The coating enamel is supplied from a vented container 64 through pipe lines 65 and 66 leading to the bases of the respective applicators 60 and 61, these pipe lines including metering pumps 67 and 68, respectively. These pumps, which are adjustable as to pumping rate, are regulated to meter the liquid enamel to the respective applicators at precisely the rate required to coat the wire at its particular speed of travel through the applicators. The applicator felts wipe the enamel on the moving wire and smooth the enamel film on the wire exactly as required.

The spooling device 70 is of the type in which the sales spool 71 is removably mounted on a power-driven spindle 72 for rotating the spool to take up the wire under constant tension and which, when the spool is full, enables rapid transfer of the incoming wire to an empty spool.

An example of such a device is disclosed in T. T. Bunch Patent No. 2,868,468 granted January 13, 1959, for Strand Reeling Apparatus. A preferred form of this device is disclosed in a copending application of H. L. Hollingsworth and V. H. Lausen, Serial No. 125,243, filed July 19, 1961, for High-Speed Wire TakerUp and. Spool Changer. In the latter form, the spindle 72 is driven through an eddy current coupling and is carried by a rotatable head 73 which also carries a second spindle 72a similarly driven, the rotation axis of the head lying between these spindles. As the winding of spool 1 nears completion, the head 73 is rotated clockwise through several revolutions plus one-half a revolution, with timed displacements of the incoming wire path over the end of spool 71, thereby making several turns of the wire around replacement spool 71a on spindle 72a as spool 71 continues to reel in the wire. Then, with spool 71a in the loading position previously occupied by spool 71, the head 73 is stopped and the single wire pass between the two spools is cut so that spool 71a can reel in the wire in the usual manner, the rotation of spool 71 being braked in the unloading position previously occupied by spool 7111 to enable replacement of the filled spool 71 by an empty spool.

The apparatus may also include a wire accumulator shown generally at 80, through which the coated wire W2 passes from the wire transport means 48-49 on its ways to the take-up device 70. The purpose of accumulator 80 is to build up a wire reserve for offsetting any slight interruption in the operation of the wire take-up device 70. Thus, if the take-up of wire W2 by the spooling device is to be stopped temporarily, due, for example, to replacement of a sales spool, the accumulator is set in operation to take up the wire from the transport means 4849 during this stoppage, after which the sp'ooling device 70 may be operated temporarily at above-normal speed to remove the wire reserve frorn accumulator 80. As accumulators for this purpose are known in the art, the accumulator 80 need not be described in detail and is illustrated only generally.

In the operation of the apparatus, the speed transmissions 39 and 41 are so adjusted, and the progressively increasing diameters of the successive capstan steps are so related to the drawing-down actions of the corresponding dies 22-29, that the bare wire is pulled continuously and smoothly through the drawing zone 20 by the wire pulling means 30 and 40, at a linear speed which increases at each drawing stage.

Let it be assumed, for example, that magnet wire of 44-gauge AWG (about 2 mils) is to be produced and that each of the dies 22-29 is adapted to draw the wire down by one gauge number, the last die 29 providing the desired final gauge. This means that bare wire W of 36-gauge (5 mils) is supplied from the source 10. Thus, if the bare wire is pulled from supply spool 11 at a linear speed of about feet per minute, it will be pulled from the final die 29 by the final capstan step 45 at over 900 feet per minute, since the finally drawn wire will have a length equal to its original length times about 2.5 squared. This illustrates how a high linear output speed of coated wire W2 can be obtained from a bare wire supply source 10 operating at low speed. Of course, by providing additional drawing stages and starting with bare wire of still larger diameter, the wire speed through the enameling and take-up operations can be further increased.

It will be apparent, therefore, that by passing the wire directly and continuously from the drawing to the enameling operations, a simple form of pay-off device may be used at the bare wire source 10 due to the fact that the wire is pulled from this source at a speed much lower than that at which it is passed through the enameling operations and while the wire has much greater resistance to breakage. Moreover, since the drawing operations serve to remove twists from the bare wire, the bare wire may be payed ofi by over-the-end dereeling at source 10, as shown, which means that each supply spool 11 can carry a much greater supply of bare wire. In this way, supply spool replacement can be relatively infrequent even when operating at high speed. Also, the present invention eliminates the unspooling and spooling operations which would normally be performed in the wire mill incident to drawing the bare wire down to the final gauge desired in the magnet wire.

A further advantage of the present invention is that it facilitates operation of the enamel applicators 6041 numbering as in the first line but with the letter a in applying a uniform coating to the bare wire while it moves at high speed, since this coating operation is effected promptly after the wire has been drawn in the drawing zone 20. That is, the freshly drawn surface of the wire W1 does not have an opportunity to pick up impurities to any appreciable extent, through oxidizing, aging, etc., so that it has improved wetability when the liquid enamel is applied.

The dual capstan 42 provides in eifect an operative connection between the wire transport means 4349 and the wire pulling means 3044, for pulling the wire through the oven 50 and through the preceding drawing zone 20, respectively. Thus, these two means are driven in unison to provide smooth and continuous travel of the wire through the drawing and enam-eling operations and to allow starting and stopping of the line in a simple manner through a common control (not shown) for the variable speed transmissions 39 and 41.

High speed operation is also facilitated by arranging the capstan 42 as shown, so that its extension 48 effects multiple pulling actions 'on the several wire passes extending through the oven 50. This provides close tension control because each pair of wire passes is required to turn only one idler, in contrast to the common arrangement wherein idler rolls or sheaves are located at both ends of the oven to guide the multiple passes and the capstan pulls only the single pass of wire coming from these idlers.

It will be understood that several wire lines similar to that described may be arranged in parallel, each line utilizing the oven 50 but having its own supply source 10, drawing zone 20, wire pulling means 3040, wire transport means 48-49, applicators 60-61, and take-up device 70. This enables several different wire sizes to be insulated simultaneously in the manner described, using only one oven. One such additional line is shown partially in FIG. 1, corresponding parts having the same added.

We claim:

1. Apparatus for high-speed production of magnet wire, which comprises a wire source for continuously supplying a length of bare wire, a series of wire-drawing dies operable to draw the wire down to a final cross-sectional area at which the wire length is at least double its length at said source, means for continuously pulling the bare wire lengthwise from said source at a first linear speed and successively through said dies, said pulling means including a driven drawing capstan operable to pull the drawn wire from the dies at a linear speed at least double said first speed, a source of liquid insulating enamel, applicator means connected to said source for receiving liquid enamel therefrom and operable to coat said enamel on the wire, an oven for baking the coated enamel to a solid film on the wire, wire transport means for continuously pulling the elongated wire from said pulling means successively through the applicator means and the oven in multiple passes, whereby the wire in each pass receives a liquid coating which is baked on the wire prior to the next pass, said transport means including a second driven capstan in driving engagement with the wire passing from each alternate 'one of said passes to the next one of said passes, a powerdriven packaging device for continuously taking up the coated wire from the transport means, and an operative connection between said capstans for driving said transport means at a rate to pull the elongated wire at said greater speed at which the drawn wire is pulled from the dies.

2. Apparatus according to claim 1, in which one of said capstans is an integral extension of the other capstan to provide said operative connection.

3. Apparatus according to claim 1, in which one of said capstans is an integral extension of the other capstan to provide said operative connection, said one capstan and its extension forming a dual capstan, said applicator means being interposed between the dual capstan and the oven.,

4. In an apparatus for high-speed production of magnet Wire, the combination of an oven having wire inlet and outlet openings at opposite ends of the oven, a source of liquid insulating enamel, enamel applicator means located opposite each end of the oven and connected to said source for receiving enamel therefrom, wire transport means for continuously pulling a wire successively through one of said applicator means, the oven, the other applicator means and back through the oven by way of said openings, to provide multiple passes of the Wire through the applicator means and the oven, said transport means including a rotary transport capstan for pulling the Wire and means for guiding the wire through said passes and at least partly around the transport capstan in moving from one pass to the next, a wire source for continuously supplying a length of bare wire, die means forming a series of successive wire-drawing stages operable to draw the wire down to a final cross-sectional area at which the wire length from the last stage of said series is at least double its length at said source, means for continuously pulling the bare wire lengthwise from said source at a first linear speed and successively through said wire-drawing stages, said pulling means including a rotary drawing capstan for pulling the wire from said last stage and delivering the wire to said transport capstan, said pulling means and transport means also including a coupler connecting said capstans for synchronous rotation and means for driving said capstans to pull the wire from said last stage and through said multiple passes at a second linear speed at least double said first linear speed, and a spooling device for continuously withdrawing the wire from the transport means at substantially said second linear speed.

5. Apparatus according to claim 4, in which said coupler is a rigid connection between said capstans, whereby one of the capstans is an integral extension of the other, said capstans being located between said die means and one end of the oven.

References Cited by the Examiner UNITED STATES PATENTS 573,573 12/96 Daniels 205-19 960,016 5/10 Horton 205-l9 1,248,107 11/ 17 Hathaway 205-17 1,948,664 2/34 Johnson 205l9 1,972,746 9/34 Mcllvried 20519 2,023,998 12/35 Fustier 205-21 2,045,726 6/36 Richards 20519 2,928,527 3/60 Frankenfield 205-19 MICHAEL V. BRINDISI, Primary Examiner. CHARLES W. LANHAM, Examiner.

Claims (1)

1. APPARATUS FOR HIGH-SPEED PRODUCTION OF MAGNET WIRE, WHICH COMPRISES A WIRE SOURCE FOR CONTINUOUSLY SUPPLYING A LENGTH OF BARE WIRE, A SERIES OF WIRE-DRAWING DIES OPERABLE TO DRAW THE WIRE DOWN TO A FINAL CROSS-SECTIONAL AREA AT WHICH THE WIRE LENGTH IS AT LEAST DOUBLE ITS LENGTH AT SAID SOURCE, MEANS FOR CONTINUOUSLY PULLING THE BARE WIRE LENGTHWISE FROM SAID SOURCE AT A FIRST LINEAR SPEED AND SUCCESSIVELY THROUGH SAID DIES, SAID PULLING MEANS INCLUDING A DRIVEN DRAWING CAPSTAN OPERABLE TO PULL THE DRAWN WIRE FROM THE DIES AT A LINEAR SPEED AT LEAST DOUBLE SAID FIRST SPEED, A SOURCE OF LIQUID INSULATING ENAMEL, APPLICATOR MEANS CONNECTED TO SAID SOURCE FOR RECEIVING LIQUID ENAMEL THEREFROM AND OPERABLE TO COAT SAID ENAMEL ON THE WIRE, AN OVEN FOR BAKING THE COATED ENAMEL TO A SOLID FILM ON THE WIRE, WIRE TRANS-

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