A multi-gauge composite metal strip is produced from a plurality of individual metal strips of different thicknesses. The individual strips are heated, passed through an oxide reducing atmosphere and are then directed between a pair of work rolls with their adjacent edges arranged in a mutually overlapping relationship. The rolling action effects a reduction in the thickness of each strip while simultaneously effecting solid phase bonding of their overlapping edges. The resulting composite multi-gauge strip is subjected to tensile stresses which exceed the yield strength of the strip materials at the time and in the condition at which the composite strip exits from between the work rolls.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates generally to the production of multi-gauge metal 
strips, and is concerned in particular with a method of producing such 
strips with one or more relatively thin web segments having width to 
thickness ratios greater than about 50 to 1. 
2. Description of the Prior Art 
Multi-gauge strips have been produced by a number of known methods, 
including for example continuous casting, continuous hot forging, 
continuous rolling, milling or machining, welding and extrusion. 
A continuously cast product has a relatively rough surface and a low 
strength "as cast" crystal structure. Moreover, only one alloy can be 
continuously cast at a time, and then only at relatively slow speeds in 
the range of 8 to 60 inches per minute. 
Continuous forging is also characterized by relatively low production 
speeds as well as poor accuracy, and the resulting products have 
relatively rough surfaces, making it necessary to resort to further 
machining in order to achieve desired surface finishes and tolerances. 
Continuous rolling requires multiple roll passes, each having specially 
machined rolls. Intermediate annealing is usually required, and the 
resulting product in often plagued by non-uniform stresses which in turn 
result in distortions, e.g., twist and camber. 
Milling or machining entails the cutting away or removal of metal, thereby 
producing considerable scrap. Production speeds are again relatively low, 
usually in the range of 4 to 8 feet per minute, this being due in large 
part to the necessity of avoiding excessive heat build up in the product 
as well as the cutters. The resulting product surface is also frequently 
mared by cutter striations. 
Welding requires a high energy source to melt the metal and thereby cause 
fusion. Thickness variations are produced at the weld site, and the weld 
area is characterized by a relatively low strength as cast crystal 
structure. Moreover, the welds are subject to imperfections such as 
blow-holes and insufficient penetration. Welding rates rarely exceed 20 
feet per minute, and insoluble material such as silver and nickel cannot 
be bonded by this technique. 
Extrusion is limited to one metal or alloy at a time, and then only to 
those metals which have a low recrystallization temperature and a low 
modulus of elasticity, e.g., copper, silver and aluminum alloys. Metals 
which gaul e.g., nickel and the platinum group metals cannot be extruded. 
Many of the foregoing difficulties are exacerbated as the width to 
thickness ratios of the thinnest sections of the desired end products 
increase. When this ratio exceeds about 50 to 1, it becomes virtually 
impossible to successfully produce an acceptable product on a commercial 
scale with any of the above-described conventional methods. 
The production of composite strips by means of solid phase bonding is also 
known. However, difficulties stemming from differential rolling stresses 
and resulting curvature distortion have prevented this method from being 
employed successfully in the production of multi-gauge products with width 
to thickness ratios exceeding about 50 to 1. 
A general objective of the present invention is to provide an improved 
method of producing a multi-gauge metal strip which avoids the 
above-described shortcomings and problems of the prior art. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, at least two strips having 
different thicknesses and of the same or different metals are heated to a 
solid phase bonding temperature. The thus heated strips are next passed 
through an oxide reducing atmosphere before being guided in parallel 
alignment with their adjacent edges in an overlapping relationship into a 
roll pass defined by a pair of driven work rolls. The roll pass is 
configured to effect solid phase bonding of the overlapping strip edges 
while simultaneously reducing the thickness of each strip, thereby 
producing a composite strip exiting from the roll pass with a stepped 
cross section made up of at least two segments of different thicknesses. 
The resulting composite strip is immediately subjected to tensile stresses 
which exceed the yield strength of the strip material in the condition at 
which it exits from the roll pass.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT 
Referring initially in FIG. 1, a plurality of individual metal strips A, B 
and C are unwound from storage reels 10 and are directed towards a single 
roll pass defined by a pair of work rolls 12, 14. The strips can comprise 
the same or different metals or alloys. High modulus metals such as steels 
can be employed, as can metals that gaul or metals that have high 
recrystallization temperatures. As can be best seen in FIG. 2, the lower 
roll 14 has a cylindrical surface 16, whereas the upper roll 12 has end 
collars 18 separated from a central barrel section 20 by grooves 22. 
The individual strips A, B and C are initially heated to a solid phase 
bonding temperature by means of an electrical power source 24 connected as 
at 26 to one of the work rolls, and as at 28 by sliding or rolling 
contacts to each of the strips. The thus heated strips then enter a 
chamber 30 containing an oxide reducing atmosphere, e.g., hydrogen. A 
guide 32 then directs the strips from the chamber 30 into the roll pass. 
As shown in FIG. 3, the entering strips A, B and C are in parallel 
alignment, with their adjacent edges arranged in an overlapping 
relationship. In this particular embodiment the center strip B is thinner 
and wider than the two outboard strips A, C. 
The thus aligned strips are rolled in the roll pass to effect a solid phase 
bonding of their overlapping edges while simultaneously reducing the 
thicknesses of the strips. The thus rolled strips exit from the roll pass 
as a composite multi-gauge strip S having a stepped cross section with 
three segments A', B' and C'. The center segment or web B' is thinner than 
the two outboard segments A', C' and has a width to thickness ratio 
greater than about 50 to 1. The bond interface between segments B' and C' 
is indicated in dotted at 34 in FIG. 5. This interface extends laterally 
from both sides of a reference plane P containing the steps, and provides 
a continuous secure joint between the segments. A similar but mirror image 
bond interface is created between segments A' and B'. The entire cross 
section has a wrought or cold work crystal structure which provides good 
strength and ductility. 
A traction device 36 is employed to pull the composite strip S exiting from 
the roll pass. The pulling force subjects the composite strip to tensile 
stresses which exceed the yield strength of its materials at the time and 
elevated temperature condition at which they exit from the roll pass. 
Because strips A, B and C of different cross sections are being bonded 
together to produce the desired end shape, non-uniform internal stresses 
are minimized and subsequently negated by the imposition of higher 
substantially uniform tensile stresses created by the pulling action of 
the traction device 36. Therefore, greater percentage thickness reductions 
may be effected at the areas of strip overlap in order to enhance solid 
phase bonding, without causing twist, camber or other like distortions. 
After being subjected to tensile stresses by the traction device 36, the 
composite strip may be subdivided by a flying shear 38 or the like into 
discrete lengths. Alternatively, the composite strip may be accumulated in 
coil form on a take up reel (not shown). 
The following example illustrates the invention: three copper strips A, B 
and C were processed in accordance with the foregoing description. Each of 
the strips A, C had a width of 1.625" and at thickness of 0.200". The 
center strip B had a width of 2.085" and a thickness of 0.041". The strips 
were resistance heated to a temperature above 1000.degree. F. and were 
then directed through a hydrogen atmosphere in chamber 30 before entering 
the roll pass in the condition illustrated in FIG. 3. During rolling, the 
strips were each reduced in thickness by between 30-50%, with the areas of 
edge overlap experiencing a larger percentage reduction in thickness of 
about 69%. Solid phase bonding was achieved at the areas of overlap. The 
cross sectional configuration of the resulting composite strip S was as 
shown in FIG. 4. Segments A' and C' had widths of 1.5" and thicknesses of 
0.126", and the central web segment B' had a width of 2.0" and a thickness 
of 0.026", making its width to thickness ratio approximately 76.923. 
The exiting composite strip was subjected to tensile stresses on the order 
of 20,000 psi before being subdivided into discrete lengths by a shear. 
The resulting composite strip lengths laid flat without twist, camber or 
other like distortions in any of the segments A', B' and C'. 
The method of the present invention is not limited to the production of the 
composite strip shown in FIG. 4. Other and varied cross sectional 
configurations are possible. Thus, as shown in FIG. 6, the central web 
segment B' may be thicker than the side segment A', C'. Alternatively, as 
shown in FIG. 7, the side segments A', C' may protrude from opposite faces 
of the composite strip. These are but a few of the variations which are 
possible by solid phase bonding two or more metal strips in accordance 
with the present invention. 
The present invention is capable of continuous operation at production 
rates as high as 40 feet per minute and perhaps higher. Bonding is 
effected and a finished shape is produced in a single roll pass, without 
resorting to additional process steps such as annealing, grinding, 
polishing, etc. The resulting surface finish is that of ground tool steel 
rolls, i.e., 20 micro-inch RMS or less. The bonded product has a wrought 
or cold work crystal structure which provides good strength and ductility 
without internal discontinuities and imperfections of the type which 
characterize welded products. As compared with conventional milling or 
machining methods, scrap is minimal, making it possible to achieve 
acceptable product yields of 90% or better. The present invention can 
produce strips with web segments having width to thickness ratios of 
greater than about 50 to 1, with extreme accuracy in shape location and 
reproducibility.