Page 23 - MetalForming May 2009

Safe coil containment requires the use the proper holddown and containment arms, particularly given the growing use of higher-strength steels. Holddown and containment arms are needed on reels and cradles to prevent the coil from dangerously unraveling or clock- springing. For higher-strength materi- als, use a holddown arm with a powered wheel on its end to help peel the mate- rial off of the coil and onto the thread- er/peeler table.
Head Designs
With the method of decoiling select- ed, let’s focus on the feeder/straightener- head features. Metalformers select from two basic straightener-head designs— one uses individual roll adjustment for bending the material between two opposing rolls, the other employs a bank-adjustable setup.
A bank-adjustable straightener head yields optimum flatness results. With a bank adjustment versus an individual- roll-adjusted straightener, the rolls can have a smaller diameter and be spaced more closely together. This setup bends the material more tightly around the roll radius. Also, a bank-adjustment design requires only two adjustments to the straightener-roll settings—for entry and exit gap.
Typically, the feeder/straightener head performs more work to the mate- rial at the entry side then at the exit, with the exit-side gap set at or near the material thickness. As the capacity of the straightener increases, metalformers look to add backup or support rolls to the straightener to prevent the smaller- diameter rolls from deflecting, much like the design of a precision leveler. Also, the more rolls in the bank the better the straightening results. Typical straighteners with individual roll adjust will only include only five or seven rolls. With nine or more rolls, flatness toler- ance will improve and, in many cases, material defects such as crossbow can be reduced or eliminated.
To ensure sufficient power to pull the material through the straightener head, the rolls must be driven—ideally all of them, although this greatly increases
the cost and complexity of the machine. Therefore, in most cases stampers can get by with a machine with driven bot- tom rolls.
Other Straightener-Head Features to Consider
1) Straightener-head opening option. With this important option, the head can be opened for easy access to the rolls for cleaning. This proves particu-
larly useful to stampers that switch from forming hot-rolled scaly material to cold-rolled steel or aluminum on the same machine. This feature also eases the task of threading the start of the coil into the straightener-feeder head.
2) An effective peeler/threading table promotes hands-free and safe coil threading into the straightener-feeder head. An extendable peeler tongue will reach the leading edge of the coil to
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