Editor’s Note: As a consultant to the industry, the author has had the opportunity to discuss flat-rolled coil straightening and leveling
with many people. This article is an anecdotal review of 12 common misconceptions he
has encountered. This article was originally
published in the March 2006 issue of
STAMPING Journal®.
Many stampers, fabricators, and
coil processors have misconceptions about straightening
and leveling. Below are 12 common
misunderstandings.
1Our coils are dead flat
because the producer or
processor says they are.
Of course, I also hear the opposite:
“They say it’s flat, and it isn’t.” What
they might really have meant is, “It
looks flat” or “It is as flat as we can
get it.”
In these days of tightening tolerances and an expanded range of material properties, you are told to send the
material back if you don’t like it. But
that doesn’t return lost time or lost
customers.
Some of you don’t have flatness-measuring systems; others of you may
have highly sophisticated flatness-measuring systems. Accurately measuring and describing the degree of flatness of rolled sheets or plate is one
thing; producing flat metal is another.
One production plant recoils in
the hot condition. Operators cannot
measure what the flatness will be at
ambient temperature. They know it is
good material from experience, but on
any given day or for a specific coil,
they cannot know for sure.
You should have your own methods
for checking flatness, such as a flatness
table. Then, to put that data to good
use, you need to describe how flat is
flat enough for your stamping, fabricating, or coil processing operation. I-units, which measure wave height and
wavelength to describe flatness, are
being used more frequently.
2We don’t need a straightener,
flattener, or leveler if the coil
supplier gets it right.
Getting it right may not even be possible. Some variables might be beyond
the supplier’s control. Here are several
interesting possibilities:
First scenario: Your steel or aluminum coils probably have some coil
set simply because they have been
coiled. That is a fact of life. The
processor or producer might not be
able to do anything about it. If the
material is dead flat going into the
recoiler, then coil set should be the
only problem. A simple, non-backed-up spread-center straightener or flattener is all you need.
Second scenario: Most mill coils
have some crossbow. Slitting also may
put alternating up-down crossbow
into the cut strands at each
male/female knife setup. This, too, is
one of the facts of life. In a perfect
world, with perfect setups every time,
there would be no such crossbow.
Perfect slitter setups more often are
found in the operator’s manual than
on the shop floor. The result can be
that one slit strand gives you good
parts, while the next strand produces
too many rejects.
One stamper told me his coils had
no crossbow. A quick check of his
inbound coils with a straight edge
proved that wrong. He also said he
had too many rejects on about half of
his coil strands. It took some patience,
but I found the pattern was in every
other coil.
Crossbow requires straightening or
flattening equipment that can stretch
the strip surface three times more than
is needed to remove coil set, and that
takes more vertical force and more
horsepower. You will need a leveler in
the slitting line following the slitter or
a backed-up, close-center straightener
or flattener in the press feed line.
Third scenario: Buckles and waves
may be a problem with wide coils or
sheets. If you have a leveler in your
slitting line, buckles or waves should
be under control, unless your stamping
or roll forming dies are causing the
shape problem. In that case, you will
need a leveler in your line, not for flat
coils but for shape control and consistent product quality. This requires leveling equipment with controlled work
roll bend that also can stretch the
metal surface three times more than a
simple straightener or flattener can.
3Levelers are just expensive
straighteners.
To say a leveler is an expensive
straightener or flattener is like saying a
pair of binoculars is an expensive
hammer. They are two entirely different tools for entirely different purposes. The question should be, “What is
the right tool for the job?”
Truthfully, I seldom actually hear a
stamper put it this way. What I have
heard is “We cannot afford better
equipment.” The last time I heard that
I was standing next to a 250-ton
straight-side press processing millions
of dollars’ worth of product. The cost
of a proper leveler would have been
less than the cost of monthly rejects.
The cost of a leveler is high compared with a spread-center straightener or flattener. The cost of a leveler is
very high if you don’t need it. But the
cost is probably not high relative to the
cost of a good press and its die sets, and
if it can significantly reduce rejects or
tinker time.
4The builder taught us how to
run the straightener, flatten-
er, or leveler.
You and the equipment builder really
speak a different language. The equipment builder probably sees his job as
teaching you how to operate the
equipment, and you want to understand how to get flat material. These
are not the same goals.
The builder’s serviceperson generally is a great mechanic who has never
run one of these machines in production. He may or may not be a good
teacher. He probably never had any
formal training in straightener, flattener, or leveler operation himself.
5Our senior operator does all
the training.
Last year I met a man who claimed 38
years of experience running the same
two leveling lines. The plant superintendent stood behind me as we
watched. After a few minutes and several questions, the superintendent
turned to me and whispered in horror,
“He hasn’t a clue. And he trained
every operator we have.”
Another senior operator assigned
to train new hires told me that the
machine’s exit roll gap is adjusted for
hot-rolled and the entry roll gap for
cold-rolled. Nonsense.
The same operator said he doesn’t
use the leveler’s manually adjustable
backup rollers because he doesn’t need
them. The truth was that they were
very hard to adjust and he simply did
not know how to adjust the machine.
6The operators already know
how to run our equipment.
Another operating manager actually
said, “The factory trained our people
when we bought the machine.” The
equipment is 15 years old. Even if the
same operators were still running the
line, some ongoing training should
have been in place.
One well-respected shop has established a best practices program. Each
crew has certain tasks that they do
better than other crews. The production team identified these skills. Once
a month production crews from all
shifts get together to trade ideas.
There is no finger-pointing. Managers
sit on the sidelines and are there only
to support the good ideas and approve
process corrections. The improvement
in productivity and quality has been
astounding.
The FABRICATOR | An FMA Publication
www.thefabricator.com | March 2007
