The Fabricator - Sample Issue

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 ^wasStraightening, flattening, and leveling ^mild ^steel, ^new ^steels ^have ^yieldmachines are very sensitive to their ^strengths ^from ³⁰ ^kilopounds ^perupper capacity limits. One plant had ^square ^inch ^(KSI) ^to ¹⁸⁰ ^KSI. ^Steelbeen leveling ³⁄8-inch hot-rolled plate ^and ^aluminum ^are ^processed ^on ^theon a machine built for ¹⁄4-in. material. same machine, and they all require _The _frames _were _sprung _out _of _linevery 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
operator said.

operators. Today, operators cannot be expected to just “figure it out.” ^At ^another ^plant, ^operators ^com-

_Each _range _of _yield _strength _andplained that they could not remove _material _type _needs _a _different _gapedge 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 _andle control. Their unsupported straight-reduced scrap loss, you cannot rely on ^ener ^rolls ^were ^deflecting, ^and ^theytrial-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 ^supplyplate. 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 machine settings.

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 the machine.

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
straightener.

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 way!” ■

Eric Theis is with Consultants to The Industry, 603 Maple Lane, Sewickley, PA 15143, 412-741-2111, etheis@comcast.net.

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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