US 3469430 A
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p 30, 1969 R. S.-BRAY ETAL Mam EDGE CONTOURING OF METAL STRIP AND METAL STRIP PRODUCT Filed Sept. 15, 1967 I N VEN TORS ROBERT S. BRAY y LUIS J. LOZANO ATTORNEYS United States Patent 3,469,430 I EDGE CONTOURIN G 0F METAL STRIP AND METAL STRIP PRODUCT Robert's. Bray, Cheshire, Luis J. Lozano, Southington, and Peter J. Kabelka, Torrington, Conn., assignors to Anaconda American Company, Waterbury, Conn., a
corporation of Connecticut Filed Sept. 15, 1967, Ser. No. 668,096 Int. Cl. B21d 19/00; C21c 9/56 US. Cl. 72200 6 Claims I ABSTRACT OF THE DISCLOSURE The edges of a metal strip are melted to a liquid state and the inherent surface tension is used to produce a BACKGROUND OF THE INVENTION This invention relates to a method of rounding the edges of a metal strip and to the metal strip per se.
In the manufacture of metal strip, particularly thin' metal strip which has been cut from wider widths of metal strip, such as in the manufacture of copper strip for winding electrical transformers, it is important that the flat sharp edges of the strip be removed, preferably by contouring these edges to a generally semi-circular cross-sectional configuration so that upon subsequent coating of the strip with the insulation there will be no sharp edges which would penetrate through a thin insulating coating.
One method which has been followed in the art heretofore has been to mechanically roll the edges of the strip to the desired curvature. But this has generally resulted in an unsatisfactory product because rolling the edges imparts a stress which produces a ripple of the edges out of the flat plane of the strip to form a ribbon candy structure. More recently a method has been disclosed in US. Patent 3,323,342 in which the edges were grooved and then heated to a flowable state. The patent discloses that the resulting structure had longitudinal undulations which required subsequent rolling to flatten out the strip and also roll the edges. The method of the invention goes beyond the prior art teachings in that it relies on the heretofore undiscovered principle that melting the edge area to the liquid state under controlled conditions which balance the surface tension of the metal against the force of gravity will result in the desired rounded contour at the edge of the strip without mechanical rolling. The edges, having been heated to the liquid state, are characterized by a long columnar grain structure (a characteristic of a cast metal as opposed to the small grain structure which would characterize metal in the wrought condition that had not reached the liquid state).
With the method of the invention the strip can be contoured .at its edge at speeds of 300 feet per minute while preserving the flatness of the strip and without any rippling as would occur with a mechanical contouring of the edges. Strips subsequently coated with a lacquer insulation provide a uniform insulation over the surface because of the absence of any sharp edges which might tend to weaken the insulation.
SUMMARY OF THE INVENTION The invention provides a method of rounding the edges of metal strip comprising passing the strip through a heat source and melting the edge of the metal to'a liquid state and removing the metal strip from the heat source'before the force of gravity acting on the volume of liquid metal exceeds the surface tension force acting on the liquid metal and holding it in a rounded cross-sectional edge configuration. The liquid edge is then solidified by cooling so that it retains itssemi-circular edge configuration and is characterized by longcolumnar grains extending 15 rounded cross-sectional configuration at the liquid edges 1' laterally outward in the plane of the strip along that edge portion of the strip which had been melted to the liquid state.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevation of a schematic of apparatus for practicing the method of the invention;
FIG. 2 is a fragmentary plan view taken along line 2-2 of FIG. 1;
FIG. 3 is an enlarged section taken along of FIG. 2;
FIG. 4 is an enlarged section taken along line 44 of FIG. 2; and
FIG. 5 is a photomicrograph of a cross-section of edge contoured copper strip produced according to the method of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIGS. 1 and 2, metal strip is unwound from a feed roll 10 through a melting zone 11 and rewound on a wind-up roll 12. At the melting zone 11 are provided two pairs of rollers 13 and 14 which serve to position the side edges of a strip 15 accurately in relation to tungsten inert gas heating elements 16 and 17 which are slightly spaced from the side edges of the strip 15.
In one example a copper strip nominally .020" thick was passed through apparatus as shown in FIGS. 1 and 2 and the tungsten inert gas heating elements were spaced a distance sufficient to melt only a segment of the edges to the liquid state. The strip was passed through the heating zone at a speed of 28 feet per minute and this was sufiicient to melt the flat edge 18 as shown in FIG. 3 to a liquid state and for a time insufiicient for the force of gravity to overcome the inherent surface tension along the flat broad faces of the strip and thereby retain the rounded configuration shown in dotted in FIG. 3 and rounded in FIG. 4. Had the volume melted exceeded the surface tension of the strip the segment would have teardropped or taken some other configuration depending upon the position of the edge of the strip with respect to the force of gravity. Melting at this speed and quick removal of the strip from the melting zone is sufficient to cool the strip and retain the desired configuration. It is also proposed to pass the melted strip through a roll sized with the radius of curvature desired, after the strip has cooled to a solid state but while it is still soft to refine the edge contour already formed.
As shown in FIG. 4, the rounded contour eliected by this melting operation is generally semi-circular in crosssection and free of sharp edges. It is therefore eminently suitable for coating with a lacquer or other insulation. It has also been found that the radius of curvature which will satisfy the balance between the surface tension and force of gravity is generally in the order of one-half the thickness of the metal strip. Thus in the example given the radius of the edge was .010 inch.
In FIG. 5 an end edge segment of a copper strip which had been made according to the method just described is shown and it is characterized by long columnar grains lines 3-3 which indicate that the edge reached the liquid state,
asevidenced by this classicalcast structure."
1. A method of rounding'the edge of metal strip comprising passing'the strip through a heat source and melting, the edge of the metal to a liquid state, removing the metal strip, from the heat source before the force of gravity acting on the volume of liquid metal exceeds the surface tension force acting on the liquid metal and holding it in a rounded'cross-sectional edge configuration and solidifying the edge by cooling so that it retains its rounded edge configuration characterized by long columnar grains extending laterally outward in the plane of the'strip along that edge portion of the strip which had been melted to the liquid state.
' 2. A method according to claim 1 in which the rounded edge is semi-circular in cross-section and has a radius of curvature equal to about one-half the thickness of the metal strip.
3. A method according to claim 1 wherein refinement of the contour of the edges after heating is eflected by a gentle rolling operation.
4. A method according to claim 1 wherein both edges of the strip are processed simultaneously.
5. A flat metal strip produced according to the method of'claim 1 having rounded edges which are characterized by long columnar grains "extending laterally outward in the plane of the strip along the curved segment at the edge of the strip.
6. A strip according to claim 5 in which the radius of curvature in cross-section of the rounded edges is equal to that of one-half the thickness of the 'metal strip.
CHARLES w. LANHAM, Primary Examiner E. M. COMBS, Assistant Examiner US. Cl. X.R.