The world runs on steel. As a key element in transportation, construction, appliances, and many types of infrastructure, we all rely on steel’s strength and security under pressure. That’s why it’s vital that all steel products are, to the greatest extent possible, defect-free.
Whether you’re dealing with steel on the supply or buy-side, it’s important to be able to spot product defects, identify them with proper terminology, and understand how to resolve them. At Pacesetter, where we are heavily involved in both steel processing and distribution, understanding defects helps to fix and resolve them.
In a perfect world, there would be zero defects in steel. In the real world, however, with the myriad of steelmaking processes, raw material inputs, numerous finishing lines, and various grades and thicknesses, some imperfections are bound to occur.
Finding, quarantining, and reporting defects helps assure that products are up to the standard our customers and partners expect from us, and keeps the manufacturing world running smoothly. For this reason, quality assurance is a top priority for Pacesetter.
So what are steel defects, how do they occur, and what’s the proper way to address them? When you work with steel day-in and day-out, this information is a necessity. Our associates are incredibly well trained in this regard, so our customers can be confident in the product quality and the many minds and hands that ensure it.
Here are some common flat-roll steel defects we watch out for.
Bare Spots (Galvanized/Coated)
Bare spots result when coating fails to adhere, leaving the substrate exposed. They can be caused by carbon, smut, or grease deposits on the strip being coated, or by roll pickup of foreign material.
Roll marks and/or bruises are typically indented (occasionally raised), and often have a repeating pattern. Handling damage bruises repeat at ID or OD, then fade out and change slightly in repeat distance as the coil pays off. The repeat distance and pattern gives clues about the defect’s root cause. On repeating roll marks, the distance from mark to mark gives a clue as to which roll (at the mill or processing line) induced the mark.
A buckle is a series of waves, usually transverse to rolling direction, varying in severity and frequency. A buckle can be called a “center buckle” on the middle of strip, a “quarter buckle” on the quarters, or a “side buckle” when it is located near edge. The sides can be relatively flat (not an edge wave, which we’ll get to in a moment).
Dross (on Galvanized Strip)
Dross is signified by zinc streaks on a hot dip strip, and dross pick-up can result from contaminants picked up in the zinc pot. Dross is a raised type defect.
Edge wave is a shape phenomenon caused by the coils’ edges being longer (in the rolling direction) than the center section of coil. Due to the crown in flat-roll coil, if the edges are longer lineally than the center of the strip, that extra length manifests itself as edge wave.
Pinchers are fern-like or feathery looking ripples or creases that are diagonal to rolling direction.
Most often, pinchers are light and cannot be felt.
These are just a few common defects to look for when inspecting flat steel products for quality assurance. The more we know about defects, the better at reporting and preventing them we become, meaning better quality—and a more smoothly-run world—all around.