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This invention relates to the dividing or severing of a metal piece, such
as a sheet, strip or plate, into parts with the heating of the metal piece
by high frequency electrical current along the line where parts of the
piece are to be separated from each other.
BACKGROUND OF THE INVENTION
It is known in the art to heat the abutting faces of metal parts to forge
welding temperature along a line by means of high frequency electrical
current supplied to a first contact engaging one part, or the parts, at
one end of the line and through a proximity conductor overlying the line,
to a second contact engaging the one part, or the parts, at the other end
of the line, and then, to force the parts together along the line to form
a forge weld between the parts. See, for example, U.S. Pat. No. 3,591,757.
In general, the frequency of the current is selected so that when the
parts are overlapping, the reference depth of the current in the part
nearer the proximity conductor is greater than the thickness of such part.
When the parts are in end abutting relation, the reference depth is at
least equal the thickness of the abutting ends. The meaning of "reference
depth", or "depth of penetration" is set forth in said patent, and
reference depths for several metals at current frequencies of 10 KHz and
450 KHz are also set forth in said patent.
The object of the methods set forth in said U.S. Pat. No. 3,591,757 is to
weld two metal parts together. There is also a need in the industry to cut
larger pieces of metal into smaller pieces, and the edge faces of the
smaller pieces need not, in many cases, particularly if the edge faces are
to be subsequently welded to another part or parts, be relatively smooth
or precisely perpendicular to the major faces of the pieces. In the prior
art, the larger piece has been cut or severed by mechanical means, such as
by saws or shears, or by gas torches. These processes are relatively slow
and use equipment subject to relatively rapid wear or result in
undesirable environmental conditions.
BRIEF SUMMARY OF THE INVENTION
In accordance with the invention, apparatus and electrical conditions of
the type set forth in said patent are employed to heat a metal piece to be
severed into smaller pieces, or parts, to a temperature at which its
tensile strength is substantially reduced, but below its melting
temperature, along a line where the severing is to occur. In the preferred
embodiments of the invention, the portions of the heated piece at opposite
sides of the line are pulled apart while the metal along the line is of
reduced tensile strength to separate such portions from each other. In
this way, depending upon the thickness of the metal, a larger metal piece
can be severed into two pieces in from one to three seconds without
mechanical cutting and without any substantial adverse environmental
effects.
Since the metal at parting line tends to "neck down" as the portions of the
metal piece at opposite sides of the parting line are pulled apart, the
invention also provides methods for reforming the edge faces while they
are still relatively soft. In one method, the portions are pushed toward
each other before they are pulled apart. In another method, the edge faces
are pushed toward each other after the portions are pulled apart. In a
further method, the edge faces are pushed against an anvil after the
portions are pulled apart. In a still further method, the portions are
moved transverse to the direction in which they are pulled apart before
they are pulled apart.
In an alternative, less preferred, embodiment of the invention, the pieces
at opposite sides of the line of heating are not pulled apart after the
metal has been heated to cause separation of the pieces. Instead, a jet of
oxygen is directed on the heated metal to "burn" out the heated metal
leaving a gap between the pieces.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be better understood from the detailed description of
preferred embodiments thereof set forth hereinafter, which description
should be considered in conjunction with the accompanying drawings in
which:
FIG. 1 is a schematic, side elevation view of apparatus which can be
employed in the method of the invention;
FIG. 2 is a schematic, perspective view of the proximity conductor and
contacts of FIG. 1 in association with a plate or strip of metal to be
severed;
FIG. 3 is a side elevation view of the embodiment shown in FIG. 2 with
components omitted and illustrates the heating of a plate or strip of
metal to be severed;
FIG. 4 is a side elevation view illustrating the shape of the plate or
strip ends after the metal has been heated and the portions of the plate
or strip on opposite sides of the heated area have been merely pulled
apart;
FIG. 5 is a side elevation view illustrating the shaping of the heated
metal either prior to pulling the portions of the plate or strip apart or
after such portions have been pulled apart and then pushed together while
the facing ends are hot enough to be relatively easily reformed;
FIG. 6 is a side elevation view illustrating the shape of the ends of the
metal portions after the ends have been reformed as shown in FIG. 5 and
the portions are pulled apart;
FIG. 7 is a side elevation view illustrating the shaping of the ends of the
metal portions by pressing the ends against an anvil while such ends are
hot enough to be easily reformed;
FIG. 8 is a side elevation view of the ends of the metal portions when the
heated metal has been removed by subjecting it to a gas such as oxygen;
FIGS. 9 and 10 are plan views illustrating the severing of the metal plate
or strip by first laterally moving the portions on opposite sides of the
heated metal and then pulling such portions apart.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 illustrates, diagrammatically, apparatus for performing the methods
of the invention and FIG. 2 illustrates, diagrammatically, the electrical
portion of the apparatus in an association with a metal piece to be
severed into parts.
In FIG. 1, a metal piece 1 to be severed into two parts or portions is
inserted beneath a proximity conductor 2, which can be copper tubing and
be water cooled, with the portion thereof at which the piece 1 is to be
severed beneath the proximity conductor 2. The conductor 2 should be as
close as possible to the line along which the piece 1 is to be severed
consistent with mechanical and electrical requirements.
Preferably, in order to further concentrate the heating current along the
line of severance, the conductor 2 is partly surrounded by a stack of
laminations 3 of magnetic material. Supports 4 and 5, preferably of a low
heat conductivity, are disposed at the side of the piece 1 opposite from
conductor 2 and at opposite sides of the line of severance.
If considered to be desirable, to prevent oxidation of the metal of the
piece 1, the space within the laminations 3 may be supplied with an inert
gas or hydrogen gas through one or more tubes 6 extending into such space
and connected to a conventional source (not shown) of such gas. In an
embodiment of the method described hereinafter, the gas supplied by tube 6
can be oxygen or an oxygen containing gas.
The metal piece 1 has a predetermined width W (see FIG. 2) and a
predetermined thickness T, the width W being less than the length of the
conductor 2. The piece 1 has a major surface 7.
The metal piece 1 may be made of various materials, but in view of the fact
that the reference depth of electrical currents is relatively small in
metals other than steel, (see Col. 7 of said Pat. No. 3,591,757), and
therefore, pieces of metal other than steel must be relatively thin for
the purposes of the invention and can be readily sheared, the methods of
the invention are principally applicable to steel pieces.
As is known in the art, the electrical current flowing in a metal part
concentrates as closely as possible to the proximity conductor when the
current in the proximity conductor flows, at any instant, in a direction
opposite to the direction of current flow in the metal part. Thus, the
heating pattern in the metal part has the shape of the projection of the
proximity conductor on the part. The invention will be described in
connection with a rectilinear proximity conductor 2 which will produce
heating of the metal piece 1 along a rectilinear severing line 8 indicated
by a dashed line in FIG. 2. However, it is to be understood that if the
severing line is not to be rectilinear, the conductor 2 may have other
configurations such as arcuate, sinusoidal, saw tooth, etc., in a plane
parallel to the major surface 7. See, for example, the configurations
shown in FIGS. 7, 8, 9 and 15 of said U.S. Pat. No. 3,591,757.
After the metal piece 1 is positioned as described and as illustrated in
FIG. 1, it is held in position by diagrammatically illustrated, known,
fluid operable, clamping assemblies 9, 10, 11 and 12. For purposes
hereinafter described, the assemblies 9 and 10 are movable in the
directions of the arrows 13 and 14 by fluid operable piston and cylinder
assemblies 15 and 16. Although in the embodiment of the apparatus shown in
FIG. 1, the assemblies 11 and 12 are fixed in horizontal position and the
assemblies 9 and 10 are movable horizontally, the assemblies 11 and 12 can
also be movable horizontally by assemblies like the assemblies 15 and 16.
FIG. 2 illustrates bifurcated contacts 17 and 18 which engage the side
faces 19 and 20 of the piece 1. Thus, the legs of the contacts 17 and 18
respectively engage the side faces 19 and 20 at opposite sides of the
severing line 8. However, if desired, other types of contacts can be used,
such as a single contact at each end of, and centered on, the severing
line 8.
After the metal piece 1 has been position as described and the contacts 17
and 18 are moved into engagement with the side faces 19 and 20, a current
of a frequency which will provide a reference depth in the metal of the
piece 1 at least substantially equal to the thickness T is supplied from a
high frequency source 21 to the contact 17 through a lead 22 and to the
contact 18 through the proximity conductor 2 overlying the severing line 8
for the time necessary to heat the metal along the line 8 to a temperature
at which the tensile strength of the heated metal is significantly
reduced, e.g. to about 10% of its strength at room temperature. Normally,
for steel, the temperature would be that used for forging or hot working
of the steel. For example, for carbon steel, the temperature would be in
the range from about 1600.degree. to about 2000.degree. F. and at such
temperature, the tensile strength of the heated metal would be about 10%
of its tensile strength at room temperature. At lower temperatures, a
higher separating force is required, and at higher temperatures in the
range, a significant reduction in the separating force is not obtained.
The length of time during which the metal is subjected to heating current
depends on the size of the source, the thickness T and the metal of the
piece 1. For example, with a piece of steel 7 3/8 in. wide and 1/8 in.
thick and a source 21 operating at 9 KHz and which provides approximately
90 kilowatts to the piece 1, the heating time was one second to produce
sufficient softening of the metal. The reference depth, when the metal is
heated above the Curie point, was approximately 0.25 in.
While a frequency having a reference depth at least equal to the thickness
T is preferred, a frequency having a reference depth slightly less, e.g.
10% less, than the thickness T can be used with longer times of heating
because even though the current in the portion of the metal below the
reference depth is smaller, heat is transmitted to such portion by
conduction. In general, and except for the embodiment described
hereinafter, the reference depth, power and heating time are selected so
that the metal is reduced in tensile strength, or softened, throughout its
thickness along the heating or severing line without causing any of the
metal to become molten. Normally, the metal will be heated along the
severing line to a few hundred degrees below its melting point, and a
typical temperature for steel is in the range from 1600.degree. F. to
2000.degree. F.
FIG. 3 illustrates the heating pattern produced with the method of the
invention. Thus, along the severing line 8, the metal is heated in the
shaded heating pattern 23 which is wider nearer the proximity conductor 2
and narrower at the lower surface of the piece 1.
After the metal has reached softening temperature, the portions of the
metal piece 1 on opposite sides of the severing line 8 are separated from
each other. If they are merely pulled apart by actuating the assemblies 15
and 16, the facing end surfaces of the portions will generally be tapered
as illustrated in FIG. 4 which may be acceptable for some purposes. As
shown in FIG. 4, the portions 24 and 25 have tapered end surfaces 26 and
27.
The end surfaces may be treated in several ways to improve the shape of the
end surfaces. For example, while still heated and malleable, e.g. at a
temperature at which it can be deformed without deforming the metal
adjacent to the heated metal, the facing end surfaces may be pushed toward
each other to create bulges 28 and 29 of metal as shown in FIG. 5, and
then again pulled apart to provide end surfaces having the shapes shown in
FIG. 6. Alternatively, prior to pulling the portion 24 away from the
portion 25, and after heating the metal to the reduced tensile strength,
or softening, temperature, the portion 24 may be pushed toward the portion
25 creating the bulges 28 and 29 shown in FIG. 5. Thereafter, the portion
24 is pulled away from the portion 25 producing edge surfaces of the shape
shown in FIG. 6.
In another method for shaping the edge surfaces 26 and 27, the edge
surfaces, while still heated and malleable, are pressed against the planar
faces of an anvil 30. Thus, after the portions 24 and 25 are separated, an
anvil 30 can be inserted between the faces 26 and 27 and the portion 24
can be pushed toward the anvil 30 which, in turn, presses against the face
27 and modifies the edge faces as illustrated in FIG. 7. Of course, both
portions 24 and 25 may be pushed toward the anvil 30, and if desired, the
portions 24 and 25 may be quickly moved to separate pushing apparatus with
a fixed anvil for forming the edge surfaces 26 and 27.
Another method for modifying the shapes of the edge surfaces is illustrated
in FIGS. 9 and 10. In this method, after the metal along the severing line
8 has been heated to its softening temperature, the portion 24, the
portion 25 or both is moved in a direction transverse to the length of the
piece 1 by a small amount, as shown in FIG. 9, and then, the portion 24 is
pulled away from the portion 25 as shown in FIG. 10.
Although, in the preferred methods described, the portions are separated in
a direction parallel to the plane of a major surface 7 of the metal piece
1, it will be apparent that they can be separated in another direction,
e.g. transversely to the plane of the surface 7.
If edge surfaces at the point of separation of the type which are obtained
by torch "burning" are acceptable, the method of the invention can be
modified to separate the portions of the metal piece 1 without pulling one
portion with respect to the other. In the modified method, the metal of
the piece 1 is heated along the severing line 8 by the apparatus and
electrical current described to a temperature at which it will "burn", and
while the portions 24 and 25 are held in fixed positions, a stream of
oxygen, or oxygen containing gas, is directed on the hot metal, such as by
way of tube 6, or additional tubes 6, causing the hot metal to drop or
"burn" out. For example, with carbon steel, the temperature would
typically be 2000.degree. F. but can be as high as the melting temperature
thereof. With carbon steel, the reaction of oxygen therewith does not
become exothermic until the temperature is at least 1600.degree. F.
Therefore, with temperatures below about 1600.degree. F., the oxygen would
merely tend to cool the heated metal, and the temperature should be at
least about 1600.degree. F. so that the steel would "burn" in a
selfsustaining reaction.
FIG. 8 illustrates the portions 24 and 25 after such "burning". With this
method, pulling apparatus can be omitted, the metal piece 1 merely being
clamped during the separation of the portions 24 and 25.
Although preferred embodiments of the present invention have been described
and illustrated, it will be apparent to those skilled in the art that
various modifications may be made without departing from the principles of
the invention.
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