For most new jobs, Pecho and other project engineers walk to the floor and talk with operators about
how a certain job is to be rolled. And at CMRP, operators aren’t just rolling A36 steel to a single radius.
They’re working with duplex steel, various grades of
aluminum and stainless, and often they’re not rolling straightforward cylinders. They’re rolling cones.
They’re rolling elliptical shapes with multiple radii.
When working with elliptical and other complex
shapes with multiple radii, engineers and operators
talk through the CAD drawing, segmenting the infinitely variable radius in the original file into defined
radius segments, each tangent with the next, ensuring that the final product looks entirely smooth with
no bend lines. The veteran operator then makes the
proper radius adjustments at just the right places,
and the rookie watches and learns.
“No bend lines and no flats” in a rolled workpiece
is CMRP’s modus operandi. Most jobs, even those
with multiple radii, emerge from the plate roll with
no noticeable bend lines between different radius
segments. Some amount of flat is unavoidable—the
plate roll needs something to grab on to—but in most
cases CMRP tries to eliminate or minimize it.
The flat section at the seam becomes more noticeable the tighter you roll. Operators may roll a
plate that’s a little longer than needed so that they
can trim the ends with a plasma cutter. Or, if the customer doesn’t want to pay for a little extra material
(understandable with duplex steel and other pricey
plates), operators may prebend the plate in a press
brake to minimize the flat section to where it’s barely if at all noticeable.
About Observation
At CMRP, a rookie becomes a guru by taking note of
all these idiosyncrasies. Good observations lead to
good questions and, ultimately, good information,
which goes into a rookie’s notebook.
The rookie may listen to a veteran talk with engineers, who discuss the fact that the plate needs
to be taken over to the press brake for prebending.
This time the operators have excess material to
work with, so they could trim the ends. Why move it
to the brake for the initial bends?
The rookie ultimately finds out that the material,
well over an inch thick, exceeds the plate roll’s tonnage limits for prebending. He learns that it takes
far more tonnage to prebend than to roll this particular material at this radius, and he makes a note
of it in his notebook.
Working with the veteran, he stretches a string
across the plate edge coming out of the plate roll.
If any light shows from underneath the string, he
knows that there is (most likely) some crowning issue that needs to be addressed.
The company usually can process a plate with
a properly crowned top roll, with the right-sized
bulge in the center, farthest from the machine side
frames. But because CMRP processes an extremely
wide range of materials, adjustments for crowning
are sometimes unavoidable, and quite often this involves using shims, anything from thin sheet metal
to pieces of cardboard.
Crowning problems usually make themselves apparent in the prebend. A downward bow in the center, called barreling, points to insufficient crowning,
with the radius tighter on the sides than in the center. If the operator can’t adjust the rolling pressure,
he needs to resort to shims, placing them toward
the center.
A prebent plate edge bowing upward in the center is a sign of excessive crowning, with the radius
in the center tighter than on the edges, producing
an hourglass shape. So shims may need to be used
again, this time near the edges of the workpiece, toward the machine frame.
Operators continue to measure the initial radius
with radius gauges, taking into account any holes
or other windows cut into the material. As Pecho
explained, cutting those windows with a plasma or
oxyfuel torch may or may not have a significant effect on the final radius. It depends on the material,
radius, and location and orientation of the window.
“If [the window is] perpendicular to the roll direction, it’s usually not that bad,” he said. “But when it’s
parallel to the roll direction, the piece may not take
the radius, and you may get a kink in your material.”
Operators observe the effects of gravity on the
workpiece and know the importance of using side
and overhead supports. Without support, the material kinks and stretches. This applies not just for
cylinders, but for other rolled shapes as well.
For instance, CMRP rolls a fair amount of large
tank sections that are field-erected. These aren’t cyl-
inders but instead are gradual, sweeping radii that
can extend 20 or 30 ft. outside the machine. “These
may be 0.25 in. thick and 120 in. wide,” Pecho said,
“but they’re often more than 30 ft. long.”
In these cases, rookies fetch some of the com-
pany’s cranes with under-the-hook lifting devices
designed to handle these extremely large workpiec-
es emerging from the plate roll. This ensures that
these massive curved sections maintain their shape
throughout the rolling cycle without stretching or
kinking the material.
“You never want to stretch the material,” Pecho
said, “or it’s over. You’re not going to get that kink
out of the material, and no matter what you do, you
will not get that perfect, smooth radius throughout
the piece.”
High-yield material can exhibit high amounts of
springback. A radius may look ridiculously tight
coming out of the plate roll; but as the radius is
formed, it springs back significantly.
Pecho added that getting springback right relates
to good communication between engineers and the
plate roll operators. The company uses software to
predict springback, relating the material thickness
and grade with the forming radius at hand.
“We roll plenty of A36 carbon steel, but we also
work with grades like A514 and AR400, even duplex
material,” Pecho said. “AR400 really looks crazy when
it comes out of the machine. If you didn’t understand
“When you see there’s a connection,
it’s almost as if these guys are reading
each other’s minds. When one guy
is coming to a complete close [of a
cylinder], the other guy is setting up
the plasma cutter to trim the ends
[to eliminate the flat section near
the seam of the rolled workpiece].”
—Ken Pecho, Chicago Metal Rolled Products
Project Engineer Ken Pecho (on left) works with a plate rolling team to check the radius of a rolled workpiece.
