Apparatus for coating metallic foil

BACKGROUND OF THE INVENTION

1. Field of The Invention

The invention relates in genera] to metallic foil, and more specifically to apparatus and methods for uniformly coating metallic foil with electrical insulating means.

2. Description of the Prior Art

Metallic foil, such as aluminum, is used to form the windings of certain types of electrical apparatus, such as transformers. The metallic foil is tightly wound into a coil, with the turns of the coil being superposed. Thus, some form of electrical insulating means must be used to separate the turns of the coil from one another. Since the turn-to-tum voltage is relatively low, the insulation should be as thin as practical, in order to increase the space factor of the coil. While separate extremely thin filmlike insulating materials, such as those of the polyester type, have been bifilarly wound with uninsulated metallic foil, to form an electrical coil, the development of excellent insulating coating materials for metallic foil, as well as techniques for applying uniform, thin coatings on metallic foil has made it more economical to apply a thin coating of insulating material to each side of the foil. For example, coatings of one-half to 1 mil thick per side are practical in production.

When the coating techniques were being developed, and coated foil was used on a limited basis, the speed of the coating lines was not important, and in general was under 25 feet per minute. With the increased usage of coated foil, the speed of the foil or strip is very important as it directly affects the capital investment required to produce the required amount of coated foil, and the floor space required. For example, it would be desirable to increase the strip speed while it is being coated with insulating means, up to about 100 feet per minute.

Increasing the strip speed through the coating process, how ever, is not as simple as providing the oven capacity for drvins τι.„ . _c and curing the insulating coatings. It was found that th! _manif _ld J™ ^perfor™2 ^{the method} includes methods and apparatus used for applying the coatings were ^ma'[°^{lds or alr} P^ads connected to an appropriate air supply, not suitable when the strip speed was increased, especially for ⁴⁰ th ^Pf I ^COnSt™^{Cted to apply the desired} P^res' the very thin foils, or were not suitable for coating both sides J ^β °‘ ^{Spaced a} P^rcdetermied dimension ,/..1. . . . . ° —— tneretrom wifhnut rtictnrhinrv of the foil before drying and curing the insulating coatings. For example, running the metallic foil through a bath of liquid insulating material at high speeds was found to produce a different coating thickness on the two major sides of the foil, and passing the foil over metering pins caused tearing of the foil when certain strip speeds were exceeded. Spraying the insulating material on both sides of the foil and passing the foil over metering pins suffers the same disadvantages. It provides satisfactory results at strip speeds below about 25 feet per minute, but results in tearing of the foil at higher speeds.

Applying the liquid insulating material to an applicator roll, passing the foil over the applicator roll such that the foil contacts about 10“ of the circumference of the applicator roll, and < ς 7 ----I----1------------ ““ ““ Wiom rotating the applicator roll in opposition to the advancing foil, cording to another embodiment of the invention; and enables thin coatings to be applied to the foil at high strip speeds. However, any imperfections in the foil, or irregularities in foil flatness such as due to gage bands, or floppy edges, and/or faulty foil tension adjustment of the foil drive, allows the foil to lift from the applicator roll which results in uncoated areas. Increasing the foil tension is not a satisfactory solution to this problem, as the maximum strip tension is determined largely by the drying and curing temperatures. ------------------------------------_- . „ ,_uoulaul

Too high a tension in the foil will stretch, wrinkle, or break the 65 material or enamel. FIG. 1 illustrates the steps of coatine fnil u/hpn it ic frs tlin _____{_}_____ ___. ·»· <·. ·. .. . . . _ ° foil, when it is subjected to the elevated oven temperatures.

A backup roller arranged to press the foil against the applicator roll may be used to coat the first side of the foil, but judicious use of the coating apparatus and floor space requires that the other side of the foil be coated before the foil is introduced into the drying and curing ovens. A backup roll cannot be used when the second side is being coated by an applicator roll, as the backup roll would disturb the wet coating on the first side of the foil. Passing the foil through two ap.. -· --ri--------— mviuuva an auuiiLdlUl JU11 pheator rolls arranged such that each is the backup for the 75 22, a pickup roll 24, a reservoir 26 which contains the liquid other, severely limits the degree of wrap of the foil on each roller, and also may introduce a “pinch effect, which limits the line speed. In order to successfully coat thin foil, such as two mil foil, at strip speeds over 25 feet per minute, the degree of wrap on the foil must be limited, and restrictions in the line, such as those due to pinch rollers, must be avoided.

Thus, it would be desirable to provide a new and improved method of uniformly coating both sides of metallic foil with liquid insulating means, prior to the curing of the coatings, as well as new and improved apparatus for performing the new method, which enables the line speed to be substantially increased above 25 feet per minute, for example as high as 100 feet per minute, when coating metallic foil in the size range of 2 to 8 mils. Further, the new and improved method and apparatus must be able to uniformly coat imperfect foil, i.e., foil having gage bands or other irregularities in foil flatness.

SUMMARY OF THE INVENTION

Briefly, the invention is a new and improved method, and apparatus for performing the method, which enables both sides of imperfect metallic foil to be uniformly coated by two spaced applicator rolls, prior to drying and curing the applied coatings. The new and improved method of roll coating includes the steps of applying liquid insulating means to an applicator roll, advancing the metallic foil over a predetermined circumferential length of the applicator roll, rotating the applicator roll in opposition to the advancing strip, and pressing the foil against the applicator roll with air directed to the side of the foil opposite to the side in contact with the applicator roll. The force exerted by the air on the foil is selected to be of sufficient magnitude to hold the foil against the coating roll and insure uniform coating of the imperfect foil, but not of such magnitude that the air velocity would disturb and ripple a liquid coating previously applied to the side of the foil against which the air is directed:

therefrom, without disturbing a wet coating of insulating material previously applied thereto.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages and uses of the invention will become more apparent when considered in view of the following detailed description and drawings, in which:

FIG. 1 diagrammatically illustrates a method of coating metallic foil material according to the teachings of the invention:

FIG. 2 is a perspective view of an air pad or manifold constructed according to an embodiment of the invention;

FIG. 3 is a perspective view of an air pad constructed ac, J

FIG. 4 is a perspective view of still another air pad constructed according to the teachings of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring now to the drawings, and FIG. 1 in particular, there is illustrated a diagrammatic view of a coating line 10, which uniformly coats both major sides of a web of metallic foil 12, such as aluminum or copper, with a liquid insulating ______ metallic foil according to the teachings of the invention, which enables imperfect foil in the range of 2 to 8 mils to be coated at line speeds up to about 100 feet per minute. The foil 12 may be any suitable commercial width.

The foil 12 is unwound from storage reel 14 and guided into first and second vertically spaced applicator stations 16 and 18, respectively, via idler roll 20, which successively coats the first and second major sides 13 and 15, respectively, of the foil 12. Applicator or coating station 16 includes an applicator roll

3,589,331 insulating means or enamel, means 28 for applying the enamel to the pickup roll 24, such as a plurality of pipes 3® spaced across the length of the pickup roll 24, with the pipes being connected to a supply manifold 32, and means 34 for collecting the enamel which drops from the pickup roll 24 and for returning the enamel to the reservoir 26.

The applicator and pickup rolls 22 and 24 are connected to suitable adjustable speed drive means (not shown), such as a gear motor, which rotates the applicator roll 22 in opposition to the direction of the advancing strip or foil 12. Thus, as shown in FIG. 1, the foil 12 advances past the applicator roll 22 in an upwardly direction, with its first major side 13 contacting a predetermined circumferential length of the applicator roll, while the applicator roll 22 is driven in a clockwise direction, as indicated by the arrow.

In order to coat imperfect foil at line speeds substantially greater than 25 feet per minute, it is essential that the degree of wrap of the foil 12 about the applicator roll 22 be limited. If foil 12 was perfectly flat, the degree of wrap could be reduced to almost a line contact. The foil, however, is not perfectly flat, having gage bands and other imperfections which dictate a greater degree of wrap for uniform coating. If the degree of wrap is reduced in an effort to reduce the restriction in the coating line, and thus enable the foil speed to be increased, the imperfect sections of the foil will not contact the applicator roll and thus will not be coated. Increasing the foil tension will not solve this problem, as even a slight increase in tension may cause stretching, wrinkling, or tearing of the thin foil when it is subjected to the drying and curing temperatures. A backup roll may be used in the first coating station 16, since the second side 15 of the foil 12 has not yet been coated.

The foil 12 may be advanced over applicator roll 22 with a small degree of wrap, such as 10°, and obtain a uniform coating of enamel thereon, without increasing the strip tension, and without utilizing a backup roll, by using the teachings of this invention which include the step of pressing the metallic strip material 12 against the applicator roll 22, with air directed against the second side 15 of the strip 12. As illustrated in FIG. 1, air pressure is applied to the second side 15 of the foil 12, immediately adjacent the applicator roll 22, by means 39 which includes a manifold or air pad 4® connected to means 42 for supplying air to manifold 40. Manifold 40, as will be hereinafter described in detail, has a plurality of openings which direct air against the second side IS of the strip 12. Since the second side 15 of the foil or strip 12 has riot yet been coated with liquid insulating means, the force applied to the foil 12 is not critical. It should merely be of sufficient magnitude to press the foil 12 uniformly against the applicator roll 22. The pressure of the air supply, the number of openings in the manifold 40, the size of the openings, and the spacing of the manifold 40 from the foil 12, are all selected to provide the desired force on the foil.

After the first side 13 of the foil 12 has been uniformly coated with enamel, the foil immediately advances into the second coating station 18 where the second side 15 of the foil 12 is provided with a uniform coating of enamel. The second station 18 is similar to the first, except in this station it is essential that an air pad be used to press the second side 15 of the foil 12 against the applicator roll, as a backup roll is now completely unacceptable due to the fact that it would disturb the wet coating of enamel already applied to the first side 13 of the foil 12. Also, the construction of the air pad is now important, as the air pad must provide the desired force on the foil without disturbing or rippling the wet coating of enamel.

More specifically, the second coating station 18 includes an applicator roll 44, a pickup roll 46, a reservoir 48 of liquid coating material or enamel, means 50 for applying the enamel to the pickup roll, such as a plurality of spaced pipes 52 connected to a distribution manifold 54, and means 56 for collecting the enamel which drops from the pickup roll and for returning it to the reservoir 48. The horizontal and vertical spacings of the centerlines of the applicator rolls 44 and 22 are adjusted, to obtain the desired degree of wrap of the foil about each applicator roll, such as 10°.

While the method of pressing the foil 12 against the applicator roll using air was desirable in the first coating station 16 because it enables the degree of wrap to be reduced while still obtaining a uniform coating, without resorting to mechanical backup rolls, the method of pressing the foil against the applicator roll using air as taught by this invention, is very important in the second coating station 18. Thus, means 57 which includes an air pad or manifold 58 is disposed near the first side 13 of the foil 12, immediately adjacent applicator roll 44, with manifold 58 being connected to receive air at a predetermined pressure from air supply 60. The air pressure means 57 of the second station requires a construction which will provide the desired force on the first side 13 of the foil 12 without disturbing the wet coating of enamel just applied to the first side. Thus, air pressure means 57 must meet requirements not imposed on the first air pressure means 39. However, both may be constructed in a similar manner, if desired, for purposes of interchangeability, such that air pressure means 39 has the same characteristics as air pressure means 57. Suitable air pressure means will be described in detail hereinafter. Similar to the first coating station 16, the applicator roll 44 is driven or rotated in a direction which is in opposition to the direction of the advancing foil 12.

After the second side 15 of the foil 12 has been uniformly coated with enamel, the foil is directed into heating means, such as oven 64, via idler roller 68, where the liquid insulating coatings are dried and cured. The temperature to which the foil is heated will depend upon the specific coating material utilized. For example, using an oil modified polyester enamel, as disclosed in U.S. Pat. No. 3,389,015, which is assigned to the same assignee as the present application, typical drying and curing temperatures are 300° C. and 350° C., respectively.

When the foil 12 leaves oven 64 and idler roller 68 it is directed via idler rollers 70 and 74 through cooling means 72, which may be a plurality of pipes disposed on both sides of the foil 12, which are connected to a supply of air, which circulate air over the foil to remove the heat therefrom. The cooled foil 12 may then advance about idler rollers 76 and 78 into an “S” bridle drive arrangement, which includes driven rollers 80 and 82, and then the foil 12 is wound into a roll 84 on an adjustable speed, controlled tension recoiler.

Thus, the coating line 10 uniformly coats both sides of the metallic foil 12, utilizing a process which enables imperfect foil to be satisfactorily coated. Even 2 mil foil may be processed up to a speed of about 100 feet per minute, or more, as there are no large degree wraps about metering pins, or other small rolls.

While FIG. 1 illustrates only one coat of insulating material being applied to the metallic foil 12, it will be understood that the foil 12 may be subjected to any desired plurality of coating and heating steps, to obtain the total build desired. For example, four coats may be applied % mil at a time, to achieve a total build dimension of Ά mil per side.

As hereinbefore stated, the force applied to the foil 12 must be sufficient to press the foil uniformly against the applicator roll, and when the air is applied against a side of the foil which has a wet coating of insulating enamel thereon, the air must develop a force of the desired magnitude without disturbing the enamel coating. If the air movement across the wet enamel is such that there is movement withing the wet film, the enamel will ripple.

The construction of the air pad or manifold, and factors such as the pressure of the air supply, the cross-sectional area of the manifold, the size and number of apertures in the manifold, the spacing of the manifold from the foil, and the viscosity and thickness of the coating, all must be coordinated to provide the desired results. Further, the force against the foil may be selected to be largely due to the velocity of the air from the apertures or orifices, or largely due to pressure buildup, or due to a combination of both, depending upon the construction of the manifold or air pad. Thus, the manner in which one desires the force to be developed will dictate the range of certain of the variables hereinbefore enumerated, or the ranges chosen for the variables will dictate the manner in which the force is developed.

3,589,331

FIG. 2 is a perspective view of an air pad or manifold 100 constructed according to a first embodiment ofthe invention, which develops a force on the foil due almost entirely to the velocity of the air. Manifold 100 includes an enclosure 102, having a cross-sectional configuration which is about 2 inches square, with a length determined by the width ofthe foil. The enclosure 102 is closed except for fitting 104 adapted for connection to the air supply, and a plurality of openings or apertures 106 disposed through one of the sides of the enclosure. In a specific embodiment of manifold 100 two rows of apertures, each having a diameter of .040 inches were utilized, with the rows being three-eighths of an inch apart, and the apertures being spaced three-eighths inch apart. The fitting 104 was connected to a source of compressed air having a pressure of about 80 pounds per square inch. The manifold was spaced from the foil, adjacent the applicator roll, with a spacing of about one-half inch between its surface which contains the apertures 106 and the foil. The resulting velocity of the air which emanates from the small apertures 106 was found to be sufficient to press the foil into intimate contact with the applicator roll, without disturbing a wet coating of enamel already applied to the side of the foil subjected to the force of the air.

FIG. 3 is a perspective view of the manifold 100 shown in FIG. 2, modified with a pressure chamber 108 disposed about the apertures 106. In this embodiment, the outwardly extending edges of the members which form the pressure chamber 108 are spaced about one-sixteenth of an inch from the foil, which confines the air withing the boxlike pressure chamber to buildup a pressure against the foil. Thus, the force against the foil in this instance is a combination of the velocity of the air from the openings and the elevated pressure in the partially closed pressure chamber. Since the air pressure now aids in pressing the foil against the applicator roll, the velocity of the air escaping from the apertures may be reduced, by reducing the pressure of the air in the manifold.

FIG. 4 is a perspective view of an air pad or manifold 110 constructed according to still another embodiment of the invention. Manifold 110 is constructed such that it does not require compressed air from the plant compressor system, which is nominally 80 pounds per square inch. Manifold 110 has a greater cross-sectional area than the manifolds shown in FIGS. 2 and 3, and includes a plurality of small pressure chambers, each of which have at least one aperture which communicates with the inside of the manifold. In a specific embodiment of this manifold, a 4 inch O.D. pipe 112 having a closed end 113, and an open end 115, had its open end 115 connected to an air supply having a pressure of 15 to 20 inches of water, such as developed by a fan type blower. A plurality of three-sixteenths inch diameter openings or apertures 114 were longitudinally spaced about 1 inch apart across the pipe 112, with each opening being surrounded by an open end pressure chamber. The outwardly extending open ends of the pressure chambers where disposed about one-sixteenth of an inch from the surface of the foil. The pressure chambers may be formed by an assembly 116 which is bolted to the pipe 112, with a resilient gasket member 118 being disposed between the assembly 116 and the pipe 112 to insure that the air will escape from the manifold 110 only through the plurality of openings 114. The assembly 116 has a plurality of open ended boxes or pressure chambers 120, each of which have an opening 114 in its closed end which is aligned with similarly sized openings in the gasket 118 and pipe 112. The open ended pressure chambers 120, which have an opening about 2 inches square, are formed by two apaced upstanding members 122 and 124, which extend outwardly from a base member 126, with the two spaced members 122 and 124 being joined by a plurality of parallel spaced members 128.

Each of the individual pressure chambers 120 develop a pressure therein, when their open ends are spaced about onesixteenth of an inch or less, from the foil, with the pressure developed on the surface of the foil being in the range of .05 to 1 ounces per square inch. The pressure developed may be adjusted to provide the desired force without rippling the enamel, by adjusting the air pressure in the pipe 112 from the air supply, and/or changing the spacing from the ends of the plurality of pressure chambers 120 and the foil.

Utilizing a spacing of about one-sixteenth of an inch, or less, from the ends of the open pressure chambers 120 to the foil, develops pressure at the foil which is self-adjusting, automatically increasing when the foil is raised from the applicator roll. The pressure increase due to the foil being raised from the applicator roll is a function of the size of the opening or openings in each pressure chamber which communicate with the inside of the manifold, with the larger the aperture the greater the pressure buildup due to raised foil. Thus, the pressure will be increased when the foil is not in contact with the applicator roll, which forces the foil into intimate contact with the applicator roll.

In the embodiment of the invention shown in FIG. 4, a portion of the force developed on the foil is due to the velocity of the air from the aperture. By disposing baffles in the pressure chamber which arc spaced from the aperture and located such that the air from the aperture strikes the baffles, the effect of the velocity of the air may be substantially eliminated, with the force developed against the strip being almost wholly due to the pressure developed in the plurality of partially closed pressure chambers 120. Therefore, the manifolds or air pads may develop a force almost completely due to the velocity of the air from the apertures, such as the air pad 100 shown in FIG. 2, the air pads may develop a force almost completely due to pressure developed in partially closed pressure chambers, or almost any ratio of velocity and pressure may be used depending upon the specific structure of the air pads.

In summary, there has been disclosed a new and improved method of uniformly coating metallic strip or foil, which enables imperfect foil to be satisfactorily coated, and which removes restrictions placed on line speed by prior art arrangements. Further, both sides of the foil are coated before the coatings are dried and cured, without disturbing the coating applied to either side. The new and improved method eliminates passing the foil through a bath of enamel, or spraying the enamel onto the foil, as well as running the foil over metering pins to remove excess enamel, by utilizing a process which includes advancing the foil over an applicator roll, with only about a 10° wrap. Imperfections and nonflatness in the foil surfaces are overcome by pressing the metallic foil against the applicator roll with a force developed by air.

Further, new and improved apparatus for coating the foil according to the new method is disclosed, which enables the desired force to be developed against the foil without disturbing a wet coating of enamel previously applied to the side the air is being applied to. Depending upon the specific requirements of the application, the force due to the air may be either largely due to air velocity, or largely due to air pressure, or a combination of velocity and air pressure, in any desired ratio.

Since numerous changes may be made in the above described apparatus and different embodiments of the invention may be made without departing from the spirit thereof, it is intended that all matter contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative, and not in a limiting sense.