Do you remember Pogo? Bogo is a little opossum and a great philosopher -- in a Sunday newspaper cartoon! He once said, "We have met the enemy, and they are us!" Well, sometimes we're our own enemy -- because at any stage of coil processing, shape defects can be induced, and we're all part of it.
Torsion is also an edge-to-edge length difference defect.
How many metal buyers want to specify coils instead of coil sets? The problem is that the coils are coils. Most coils have a 20-24 inch ID. In most cases, unless the metal is very thin or very hard, the coil processor collects the coil back into the material during recoil. Leveling equipment in the production shop can make the material completely flat, but the metal will be transported back to you by recoil, which puts the coil back in place.
Where did the coil equipment come from? It's in the coil!
The coil set should be more visibly wrapped on the inside of the coil and less on the outside, because the inner bending radius is smaller. In fact, it may have the remaining reverse coil set on the outer wrapping from the original main coil to swap head to tail in some previous operation. We can also induce the reverse coil setup in our own uncoiling process by backcrushing the material through a miniature circuit breaker or channel roller.
How many coil processors can use the 60,000-pound main coil obtained directly from the mill? Someone's got to pickle it, anneal it, coat it, cut it open, maybe cut the outer diameter a little bit smaller. Flatness problems can occur anywhere along the line. Here are some examples of how this might happen.
Crown is a kind of surface - surface thickness difference defect, is a common problem of slitting machine. Straighteners or straighteners do not significantly reduce the crown because their work rolls are offset.
I once inspected a new steel tension straightener on the hot-dip galvanizing line. The metal comes out of the zinc tank and into the level looks terrible. It's like a bright, shiny mirror coming out of a tension straightener. It is then put into a 40-year-old, misaligned battery, which is then rewound or cut to the right length for customers to use. The battery destroys the shape and mass. The rolls and sheets shipped are not smooth. Line operators are frustrated because they know about the problem but can do nothing about it. My heart goes out to them.
The tension leveling coil is on a new production line at the aluminum factory. When it came out of the grader, it was completely flat, and then they retracted it under a lot of pressure. The coil is coronated, which means the strip is thicker at the center, so there is a larger od at the center of the coil on the rewind rack. Big surprise! The operator is winding the coil around the barrel. That's pulling the middle buckle back!
Check the flatness after leveling and before rewinding. QC insists that the material is perfectly smooth. The customer said he got caught when he opened it. Engineering wants to know the material's "memory" or trapped stress.
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