7Goodoperatorscanfigureout We can run thicker materials
the proper roll gap settings. 9 with higher yield strength
than the machine’s name-
While that might have been true plate capacity.
when the only material processed was Straightening, flattening, and leveling
mild steel, new steels have yield machines are very sensitive to their
strengths from 30 kilopounds per upper capacity limits. One plant had
square inch (KSI) to 180 KSI. Steel been leveling 3⁄8-inch hot-rolled plate
and aluminum are processed on the on a machine built for 1⁄4-in. material.
same machine, and they all require The frames were sprung out of line
very different settings. Generally, and the machine had to be scrapped.
information on a new coil’s yield
“But we got that plate flat!” the senior
strength is not made available to line
operators. Today, operators cannot be
expected to just “figure it out.” At another plant, operators com-
Each range of yield strength and plained that they could not remove
material type needs a different gap edge wave from their coils. They were
setting to produce dead-flat and stable overloading a non-backed-up straight-
material. With today’s greater empha- ener never designed for wave or buck-
sis on improved productivity and le control. Their unsupported straight-reduced scrap loss, you cannot rely on ener rolls were deflecting, and they
trial-and-error methods. You need to were actually putting edge wave into
get different materials flat the first the material.
time. One plant had been running 3⁄8-in.
You should have computer-gener- aluminum on a machine built for 5⁄16-in.
ated entry and exit roll gap setting material with no damage to the
charts for each range of yield strength machine. The operator wasn’t closing
and each material, steel or aluminum. the entry roll gap enough to level the
Most machine builders can supply plate. Had he done so, the machine
them. would have been overloaded and
something would have bent or broken.
When asked about machine capac-
ity, some supervisors tell production
control, “Ask old Charlie to see if he
can run that thickness.” What hap-
pens if he can’t? Presumably, he breaks
a shaft or bends a roll pin. It’s better to
check the manufacturer’s data if
capacity limits are the issue.
10Our operator doesn’t
need to know the materi-
al’s yield strength.
When the only material processed was
that mythical mild steel at 60-KSI
tensile and 40-KSI yield, you could
build those numbers into your set-
tings. Now steels have increasingly
higher ranges of strengths. Light steel
plate with 180-KSI yields are com-
mon, and 80 to 90 KSI is easy to find.
The settings and thickness capacities
are not the same at all.
If you run prime material, the yield
strength should be on the mill test
reports. You should have that number
and know what it means to your
8The material comes out flat,
so we must be doing it right.
Certainly, the coils do come out flat
sometimes. One operator who made
this statement said that the material
got wavy if he worked it harder.
Something looked odd about the
operation—I found that the
machine’s work roll gap settings were
so light that the operator was not
stretching the material past its yield
strength. In fact, the work rolls barely
touched the metal.
The good strip coming out of the
machine was the same shape as when
it was going in. If he closed the roll
gap, the material became out-of-flat
because he did not know how to run
Does it matter? Yes. The purchasing manager was having trouble buying steel that their equipment could
flatten. That certainly cost them
money. They had the equipment to
run material with less than perfect
quality, but the operator did not know
how to do it.
The FABRICATOR | An FMA Publication
March 2007 | www.thefabricator.com
Want more information?
Visit www.thefabricator.com; enter the article number (digits only) in the
home page search box:
• “Protecting surface-sensitive materials in coil processing” 677
• “Holding the line on metal costs: Reducing coil line scrap” 1448
• “How to avoid slit-in coil slitting problems: Controlling variables prevents edge
wave width inconsistencies, burrs” 1285
11We can control waves
and buckles with our
One straightener manufacturer explained that by putting football-shaped work rolls in the straightener,
he could stretch the center of the
metal. He said he could stretch the
edges by overloading the entry roll
gap, bending the work rolls.
Of course, doing this threw all the
bearings and drive out of line. Roll gap
adjustment also is critical for proper
coil set and crossbow control. You
need the right tools for the job, and
this approach is a poor substitute.
12Iadjust our leveler’s
backup roller flights to
push down the buckles.
This is exactly the opposite of what
should be done. You need to stretch
the short part (the part between the
“hills”) of the sheet or coil.
If you’ve been in this business
awhile, some of these stories will be
familiar. No doubt, you could add a
few. If some hit a chord, have a laugh
and fix it tomorrow.
If there is a pattern, it probably
means you are relying on the old
crutch, “I didn’t look at it closely
because we have always done it that
Eric Theis is with Consultants to The
Industry, 603 Maple Lane, Sewickley, PA
15143, 412-741-2111, email@example.com.
Eric Theis will be presenting at FMA’s
Coil Processing Workshop, May 15-16
in Nashville. For registration information, please visit www.fmanet.org.
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