US3018199A

US3018199A - Method of coating wire and apparatus therefor

Info

Publication number: US3018199A
Application number: US698169A
Authority: US
Inventors: Harry B Lit; Robert E Dunton
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1957-11-22
Filing date: 1957-11-22
Publication date: 1962-01-23
Anticipated expiration: 1979-01-23
Also published as: FR1214396A

Description

Jan. 23, 1962 H. B. LlT ETAL 3,018,199

METHOD OF COATING WIRE AND APPARATUS THEREFOR Filed Nov. 22, 1957 llll n AAAA u 27b 27b mun n 25a. 25 iiiffifh 1 Roberf E'- D m n,

United States Patent 3,018,199 METHOD OF COATING WIRE AND APPARATUS THEREFOR Harry B. Lit, Pittsfield, Mass, and Robert E. Dunton, Canaan, N.Y., assignors to General Electric Company, a corporation of New York Filed Nov. 22, 1957, Ser. No. 698,169 17 Claims. (Cl. 117-431) The present invention relates to a method of coating elongated articles such as wire or the like and is more particularly concerned with an improved process of applying a viscous liquid coating composition on rectangular wire and with apparatus for carrying out such process.

The invention is especially suitable for use in coating rectangular electrical wire with viscous resin solutions, such as polyvinyl formal, to form an electrically insulating enamel coating thereon.

In providing such insulating coatings on wire, it is standard practice to apply the resinous coating material in a number of successive stages, such as by passing a Wire a number of times through a bath of the coating material and baking each coating layer on the wire immedi ately after it is applied. The number of passes of the wire through the continuous coating apparatus is determined by the desired thickness of the final coating deposit. In practice an important factor which governs the number of passes required to produce a desired coating thickness is the maximum amount of coating material which can be uniformly deposited in each pass of the wire through the coating apparatus. Attempts to deposit larger amounts than normally applied, using prior processes, have generally resulted in the formation around the wire of a non-uniform film having a so-called dog-bone shape, wherein excessive amounts of coating material collect on the flat surfaces of the wire adjacent the corners. This effect appears to result from the flow of material, due to its surface tension, away from the corners of the wire to the flat surfaces. The non-uniform coating consequently produced is wasteful of material and results in wire having a poor space factor.

On the other hand, limiting the amount of material deposited per pass to ensure uniformity of layer thickness has made necessary heretofore a relatively large number of passes of the wire through the coating apparatus to build up the desired over-all thickness of insulating coating. As a result, the capacity and productivity of the coating apparatus and associated baking oven is limited, and the coating process is time consuming and uneconomical.

It is an object of the invention to provide an improved process of coating wire or the like having at least one flat side, and particularly rectangular wire, which avoids the above disadvantages of prior coating processes.

It is another object of the invention to provide a method of coating rectangular wire and the like wherein a uniform coating of greater thickness may be deposited with each coating application than heretofore possible, so that a greater overall build of uniform coating may be obtained with the same number or fewer applications than heretofore required.

A further object of the invention is to provide relatively thick enamel coatings on rectangular wire or the like while avoiding distorted coatings such as evidenced by the dog-bone effect heretofore produced by known processes.

It is still another object of the invention to provide a' wire coating apparatus for effectively carrying out the above improved process.

Other objects and advantages of the invention will become apparent from the following description and appended claims.

ice

With the above objects in view, the present invention relates to a method of coating wire having at least one fiat side, such as rectangular wire and the like, which comprises applying a film of hardenable liquid coating material on the wire so that the thickness of the liquid film on the flat side is substantially greater in the central portion of said flat side than on the remaining portions thereof, and, after allowing the films of different thick ness to merge into a uniformly thick coating, hardening the liquid coating material on the wire.

It will be understood that wire of square cross section may also be rectangular wire as the latter expression is used herein.

In a preferred embodiment of apparatus adapted for carrying out the above method, there is provided in accordance with the invention a wire-engaging die member which is particularly constructed for producing a film of differential thickness on each flat side of the wire, the contact edge face of the die member being preferably formed with a centrally arranged recess means which serves to apply a greater thickness of liquid coating material to the central portion of the flat wire surface than to the remaining portions thereof.

The invention will be better understood from the following description taken in conjunction with the accompanying drawing in which:

FIG. 1 is a view of a continuous coating apparatus which may be employed in practicing the present invention;

'FIG. 2 is an enlarged view of a wire coating die device which may be employed in the apparatus of FIG. 1; and

FIGS. 3, 4, 5 and 6 show various embodiments of die members which may be used in the present invention.

Referring now to the drawing, and particularly to FIG. 1, there is shown an arrangement for continuously coating a moving rectangular wire 1, wherein the wire passes from supply reel 2 through bath 3 of a suitable insulating coating liquid, such as polyvinyl formal, around a guide sheave 4. Wire 1 having coating material adhering thereto then passes through die device 5, which may have a construction as more fully described hereinafter. Die device 5 is carried upwardly by the moving wire until restrained from further upward movement by fixed spaced fingers 6 (see FIG. 2), or other suitable stop means, which permit free lateral and rotational movement of the die device 5 in response to any swaying or twisting movement of the wire. The wire, with a uniform coating formed thereon by the die device 5, then continues upwardly through a baking or drying oven 7 of any suitable or conventional type wherein the varnish coating applied by the die device 5 to the Wire is heathardened. Thereafter, wire 1 passes around sheave 8 and back to a position on guide sheave 4 spaced axially from the initial turn of wire. Wire 1 then passes through the coating and drying apparatus in repeated stages in the manner described until a coating of the desired thickness is finally built up, it being understood that a die device 5 and stop fingers 6 are provided for each strand of wire passing upwardly in the apparatus. The coated wire is ultimately conducted to a take-up reel 9 or other storage means.

FIG. 2 shows the structure of die device 5 in greater detail, and as illustrated therein the die comprises in a preferred embodiment a pair of flat plates 10 and 11 constituting the principal supporting frame of the die and having slidably arranged in grooves therein pairs of movable

laminar die members

12, 13, 14 and 15 which yield- :ably engage the surfaces of the rectangular wire 1 as it passes through the die device.

The die device 5 shown in FIG. 2 is disclosed and claimed in copendiug application Serial No. 594,044, Lit and Anderson, filed June 26, 1956, and assigned to the be suitably employed in connection with the present invention, it will be understood that other types of die coating devices may be used if desired.

In accordance with the invention the

die contacting members

12 and 13 which respectively engage the fiat sides of the rectangular Wire, whether employed in the device shown in FIG. 2 or other suitable type of die device, are provided with a special configuration on their contact edge faces for the purposes of the present invention, as described hereinafter. The remaining pair of die members 14 and 15 contacting the narrow edges of the wire may be of conventional construction.

In coating rectangular Wire with insulating enamel in the manner above described it has been standard practice to use die coating members which serve to initially apply uniformly thick films of the liquid coating material on the faces of the wire. Generally, the prior types of die members had their contact edges uniformly positioned with respect to the flat sides of the Wire. In some cases, the prior die members had straight continuous edge faces for contacting the wire, and in other cases the edge face was provided with serrations forming recesses of uniform depth. Where either form was used, however, it has been found that the finally hardened coating produced on rectangular wire was not uniform, due primarily to the fact that the originally applied liquid material tends to flow away from the corners and collect on the fiat surfaces of the wire. In particular, attempts to provide thicker individual layers, such as by using more deeply serrated die members, resulted in the dog-bone type of distorted layer mentioned above. In the finally built up coating which was thereafter produced by the usual process of successive coating applications as above described, such nonuniformity became magnified, and this resulted in a considerable waste of material. Further, wound coils and the like formed of such wire were substantially larger and heavier than was necessary.

In accordance with the invention, it has been found possible to substantially increase the thickness of each applied layer while still maintaining a uniform thickness in each layer, and thereby provide a greater over-all coating of uniform thickness with fewer applications than previously required, by using die members of the type exemplified in FIGS. 3-6 for applying the coating to the relatively wide faces of rectangular wire. In general, the die members of the present invention are provided with an edge face recessed in such manner that the opening in the central portion of the edge face has a greater volume than the opening in either of the end portionsof the edge face adjacent thereto, so that for each pass of the wire a greater thickness of liquid, coating film is deposited on the central portion of its flat faces than on the remaining portions adjacent thereto. As a result, it has been found that the thus applied liquid film thereafter assumes a uniform thickness, in which condition it is hardened by the baking procedure to which it is then subjected.

FIG. 3 shows a preferred embodiment of a die member which is suitable for use in carrying out the invention. As shown, die member is provided with a differentially serrated edge face for making contact with the flat face of the wire 1. It will be understood that in practice two such die members would be positioned against the opposite fiat faces of rectangular wire, in the manner illustrated in FIG. 2. The serrations in the central portion 214 of edge face 21 are relatively deep as compared to the serrations on each side 21b thereof, the serrations on the illustrated embodiment gradually decreasing in degree of depth from the maximum in the central portion to the minimum in the outer portions. In a typical die member used for a rectangular wire of about 300 mils width, the deepest serrations in the center of the .die member would be about 22 mils in depth, while the outermost serrations would be about 12 mils in depth. It is not necessary to have the contact face serrated from one end to the other, but the length of the serrated portion should be sufiicient to extend over the entire Width of the wire face to be coated. Generally, the most satisfactory results have been obtained in so proportioning the serrations in contact with the wire that the centrally located, relatively deep serrations 21a occupy about two-thirds of the Width of the wire while the outer relatively shallow serrations 21b occupy about one-sixth of the Wire width on opposite sides of the central portion, the shallow serrations preferably being about one-half the depth of the central serrations.

FIG. 4 shows another embodiment of the present die member, and in this form die member 22 has an edge face 23 formed of a non-serrated, rectangular recess 23a flanked by serrated end portions 23b. As indicated in the figure, the depth of the end serrations 23b may be as great as (or even greater than) that of recess 23a and still apply a liquid coating film thinner than that of the central recess. This is readily apparent in view of the substantially smaller volume of liquid passing through the serrated portions as compared to that flowing through the central recess. As a rule, where serrations similar to those shown are employed, the amount of liquid passing through the serrated portion will be about half that passing through the rectangular recess when the recess and serrations are of equal depth and extent.

FIG. 5 shows still another embodiment, wherein the edge face 25 of member 24 is formed of a concave cen tral recess 25a and serrated end portions 25!). Here also the depth of the end serrations 25b may be as great as the deepest portion of recess 25a while still providing substantially thinner applied films adjacent the edges of the wire than in the intermediate portion thereof.

FIG. 6 illustrates still a further modification, wherein die member 26 has an edge face 27 formed with a serrated central portion 27a arranged between recessed nonserrated end portions 27 b, the projecting serrations riding on the wire to properly position the die member 26 relative to the wire face. In a typical arrangement of this embodiment, the recessed fiat portions 271) may be offset 5 to 6 mils behind the plane of the serration points, the depth of the serrations being about 24 mils.

It will be understood that the specific depth and arrangement of the serrations and recesses of the die members employed in particular cases may vary depending on such factors as the nature and viscosity of the coating liquid, the width of the wire, the form of the serrations, and other conditions. Further, the die members may have a shape and thickness different from that shown, and still provide the desired results.

The following are illustrative examples of procedures which may be carried out in practicing the invention, it being understood that it is not intended thereby to limit the scope of the invention in any way:

Example I Rectangular copper wire 250 mils in width and 60 mils thick was coated with polyvinyl formal having a viscosity of 5500 centipoises. A pair of die members were used on the opposite wide faces of the wire, each die member having a form similar to that shown in FIG. 3 wherein the central serrated portion had relatively deep grooves with a maximum depth of 21 mils extending over a length of mils and tapering in depth to end serrations about 12 mils deep extending over about 35 milson opposite sides of the central portion. A final coating was produced in eight passes of the wire through the coating apparatus which was uniformly 4 mils thick around the wire.

Previous experience using prior art types of die members under similar coating conditions showed that the same number of passes of the wire produced a uniform coating only 2 /2 mils thick.

Example II In a procedure using coating material similar to that in Example I, a rectangular wire 500 x 112 mils was provided with a coating employing thirteen passes of the wire through the coating apparatus. The die members in this process had a central serrated portion of maximum depth of 22 mils extending about 350 mils in length tapering to end serrations each covering about 75 mils in length and being about 12 mils in depth. A uniformly thick coating of 6 mils around the wire was produced by this procedure.

It does not appear necessary in the present invention to critically time the hardening step after the film applying step in order to provide a hardened film of uniform thickness. tions of the film left by the described die device merge together to a uniform thickness almost immediately after the wire passes through the die device and remains in that condition until hardened by the heat of the oven through which the wire then passes. While the exact fiow behavior of the liquid film applied by the described arrangement is not fully known, it appears likely that the initially applied thin portions of the film provided by the invention are augmented by the flow of excess coating liquid deposited along the corners of the wire to the adjacent flat surfaces, as well as by the flow of the thicker film at the central portions of the flat sides, with the net effect of avoiding the dog-bone deposit otherwise encountered and providing an even distribution of insulating enamel about the wire.

By virtue of the invention as thus described there is provided a wire coating process and apparatus therefor which produces on rectangular wire relatively thick enamel coatings of uniform depth around the wire, and which enables a reduction in the number of applications heretofore necessary to produce an over-all uniform build of any given thickness. As a result, the present types of continuous coating apparatus may be more economically operated and increased in capacity, waste of coating material is avoided, the coating process requires less time and the wire is subjected to fewer handling and flexing operations encountered in the coating procedure which tend to make the wire Work-hardened and less flexible.

While the present invention has been described with reference to particular embodiments thereof, it will be understood that numerous modifications may be made by those skilled in the art without actually departing from the scope of the invention. Therefore, the appended claims are intended to cover all such equivalent variations as come within the true spirit and scope of the invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

l. The method of coating wire or the like having at least one flat side which comprises applying -a film of hardenable liquid coating material on the wire so that the thickness of the liquid film on the fiat side is substantially greater in the central portion thereof than on the remaining portions thereof, and hardening the liquid coating material on the wire after the thus applied liquid film merges to a uniform thickness around the wire.

2. The method of coating wire or the like having at least one fiat side which comprises the steps of applying a film of hardenable liquid coating material on the wire so that the thickness of the liquid film on the flat side is substantially greater in the central portion thereof than on the remaining portions thereof, hardening the liquid coating material after the thus applied liquid film merges to a uniform thickness around the wire, and repeating said steps until a coating of predetermined thickness is produced on the wire.

3. The method of coating rectangular wire or the like having opposite flat sides which comprises applying a film of hardenable liquid coating material on the wire so that the thickness of the liquid film on each fiat side is sub- It appears that the thicker and thinner porstantially greater in the central portions thereof than on the remaining portions, and hardening the 'liquid coating material after the thus applied liquid film merges to a unifor-m thickness around the wire.

4. The method of coating rectangular wire or the like having opposite flat sides which comprises the steps of applying a film of hardenable liquid coating material on the wire so that the thickness of the liquid film on each of the flat sides is substantially greater in the central portion thereof than on the remaining portions thereof, hardening the liquid coating material after the thus applied liquid film merges to a uniform thickness around the wire, and repeating said steps until a coating of predetermined thickness is produced on the wire.

5. The method of providing a uniformly thick coating on a rectangular wire or the like having opposite flat sides, which comprises the steps of applying a thick film of hardenable liquid coating material on the wire, removing excess coating material from said wire while leaving a film of liquid coating material thereon which is thicker on the central portion of each flat side constituting about /3 the width thereof than on the remaining portions thereof, and hardening the thus applied liquid coating material after said liquid film merges to a uniform thickness around the wire.

6. In an apparatus for providing a coating on wire and the like having at least one flat side, said apparatus including means for applying hardenable liquid coating material on the wire, and means for hardening the liquid coating material on the Wire, the improvement which comprises die means for removing excess liquid coating material deposited on the wire by the applying means while providing a thicker liquid coating on the central portion of the flat side than on the remaining portions thereof, said die means comprising a die member having a wire engaging face adapted to contact said flat side of the wire and formed in the central portion thereof with a first recessed area and in the remaining portions thereof with second and third recessed areas, the volume of the opening in said first recessed area being greater than the volume of the opening in either of the second and third recessed areas.

7. In an apparatus for providing a coating on wire and the like having at least one flat side, said apparatus including means for applying hardenable liquid coating material on the wire and means for hardening the liquid coating material on the wire, the improvement which comprises die means for removing excess liquid coating mate rial deposited on the wire by the applying means while providing a thicker liquid coating on the central portion of the flat side than on the remaining portions thereof, said die means comprising a die member having a wire engaging face adapted to contact said flat side of the wire, said wire engaging face being formed with serrations extending therealong, said serrations being deeper in the central portion thereof than in the remaining portions, the volume of the opening in the serrated central portion being greater than the volume of the opening in either of the remaining serrated portions.

8. In an apparatus for providing a coating on wire and the like having at least one flat side, said apparatus including means for applying hardenable liquid coating material on the wire and means for hardening the liquid coating material on the wire, the improvement which comprises die means for removing excess liquid coating material deposited on the wire by the applying means while providing a thicker liquid coating on the central portion of the fiat side than on the remaining portions thereof, said die means comprising a die member having a wire engaging face adapted to contact said flat side of the wire, said wire engaging face being formed with a continuous recess extending along the central portion thereof and with serrations in the remaining portions, the volume of the opening in said continuous recess being 7 greater than the volume of the opening in either of the remaining serrated portions.

9. The arrangement as defined in claim 8, wherein said recess of said die member is rectangular.

10. The arrangement as defined in claim 8, wherein said recess of said die member is concave.

11. In an apparatus for providing a coating on wire and the like having at least one flat side, said apparatus including means for applying hardenable liquid coating material on the Wire and means for hardening the liquid coating material on the wire, the improvement which comprises die means for removing excess liquid coating material deposited on the wire by the applying means while providing a thicker liquid coating on the central portion of the flat side than on the remaining portions thereof, said die means comprising a die member having a wire engaging face adapted to contact said flat side of the wire, said wire engaging face being formed with serrations in the central portion thereof and with a recess, on opposite sides of said central portion, the volume of the opening in said central serrated portion being greater than the opening in either of the recessed portions.

12. A die device for use in apparatus for coating wire having a flat side, comprising a member having a wire engaging face formed in the central portion thereof with a first recessed area and the remaining portions thereof with second and third recessed areas, the volume of the opening in said first recessed area being greater than the opening in either of the second and third recessed areas.

13. A die device for use in apparatus for applying a hardenable liquid coating material on the wire, comprising a member having a wire engaging face formed with serrations extending therealong, said serrations being deeper in the central portion thereof than in the remaining portions, the volume of the opening in the serrated central portion being greater than the volume oi the opening in either of the remaining serrated portions.

14. A die device for use in apparatus for coating wire having a flat side with hardenable liquid coating material, comprising a member having a wire engaging face formed with a continuous recess extending along the central portion thereof and with serrations in the remaining portions, the volume of the opening in said continuous re- 0655 bcinggrea'ter than the volume of the opening in either of the'reniaining serrated portions.

15. A die device as defined in claim 14, wherein said recess is rectangular.

16. A die device as defined in claim 14 wherein said recess is concave.

17; A die device for use in apparatus for coating wire having a flat side with hardenable liquid coating material comprising a member having a wire engaging face formed with serrations in the central portion thereof and with a recess on opposite sides of said central portions, the

volume of the opening in said central serrated portion being greater than the opening in either of the recessed portions.

References Cited in the file of this patent UNITED V STATES PATENTS 2,287,589 Wilson et a1 June 23, 1942 2,345,390 Flynn Mar. 28, 1944 2,346,697 Mungall Apr. 18, 1944 2,433,642 Bailey Dec. 30, 1947 2,447,521 Miller et a1. Aug. 24, 1948 2,812,741 OConnor Nov. 12, 1957 2,875,725 Lit et a1. Mar. 3, 1959

Claims

1. THE METHOD OF COATING WIRE OR THE LIKE HAVING AT LEAST ONE FLAT SIDE WHICH COMPRISES APPLYING A FILM OF HARDENABLE LIQUID COATING MATERIAL ON THE WIRE SO THAT THE THICKNESS OF THE LIQUID FILM ON THE FLAT SIDE IS SUBSTANTIALLY GREATER IN THE CENTRAL PORTION THEREOF, THAN ON THE REMAINING PORTIONS THEREOF, AND HARDENING THE LIQUID COATING MATERIAL ON THE WIRE AFTER THE THUS APPLIED LIQUID FILM MERGES TO A UNIFORM THICKNESS AROUND THE WIRE.