Metal Service Center Glossary: Slitting and Coil Terms

A metal service center runs on a vocabulary of its own, and most of it comes from the slitting line and the planning desk behind it. These are the working definitions, written the way schedulers and operators use the words, grouped by where you run into them.

The coil

Coil weight. The weight of a coil in pounds or tonnes, either as received from the mill or as calculated for a mult after slitting. Mult weight is derived from the master's weight in proportion to width, less trim and any material lost to defects.

Edge condition. How the strip edges are finished: mill edge (as rolled, untrimmed), slit edge (sheared on the slitter), or deburred, rounded or squared edges made with extra tooling. Tube mills and roll formers specify it explicitly, and a required edge can force a pattern you would not otherwise choose.

Gauge. Material thickness, quoted in decimal inches (0.030", 0.125") or in millimeters outside North America. Older gauge-number scales still show up on drawings, but they differ by metal and do not convert one to one. Coils of different gauge cannot run in the same setup, which makes gauge the hardest compatibility rule in planning.

Grade. The metal's chemistry and mechanical properties, such as CS Type B, HSLA 50, 304 stainless or 3003-H14 aluminum. One grade cannot stand in for another without customer approval, even when the dimensions match.

ID and OD. ID is the inside diameter of the coil eye, the hole the mandrel goes through, typically 16, 20 or 24 inches. OD is the outside diameter of the wound coil. Both are set by the equipment at each end (your recoiler and the customer's uncoiler), and an OD too large for the customer's uncoiler means a rewind.

Master coil. The full-width, full-weight coil as it arrives from the mill, before any processing. Flat-rolled masters commonly run between 36 and 72 inches wide and weigh tens of thousands of pounds, though both vary by mill and product. The master is the unit that gets bought, inventoried and certified, and scrap is measured against it.

PIW (pounds per inch of width). Coil weight divided by coil width: a 20,000-pound coil 40 inches wide is 500 PIW. It lets coils of different widths be compared directly. Customers order to a PIW range because it sets how long a coil runs on their press between changeovers, so a mult outside the range is a reject even at the right width and gauge. Rolled Metal Products has a PIW calculator.

The slitter

Arbor. The shaft that carries the knives and spacers through the slitter head, one above the strip and one below. Its usable length caps the total width of material and tooling you can run, and its diameter and material set the heaviest gauge the head can cut.

Cut-to-length (CTL). A line that uncoils material, levels it and shears it crosswise into sheets or blanks of a set length. Many service centers run both slitting and CTL, sometimes on the same master, so the two lines draw on the same inventory.

Edge trim. The narrow ribbon taken off each side of the master so the outer mults have clean, accurate slit edges instead of mill edge. A quarter inch to an inch per side is typical, depending on the mill's width tolerance and the condition of the incoming edge. It is lost on every coil, so it belongs in the yield math from the first calculation.

Knife change. Tearing down the tooling stack and building a new one when the next coil needs a different set of widths. Depending on the line and the setup it takes anywhere from a few tens of minutes to well over an hour, and the line produces nothing in the meantime. Running similar setups back to back is often worth more than the last half point of yield.

Knife setup. The arrangement of circular knives, spacers and rubber stripper rings on the arbors that produces a given set of widths. Spacers are ground to precise thicknesses, and the stack has to fill the arbor's usable length. Building one is skilled manual work.

Line speed. How fast material runs through the slitter, in feet per minute. It drops with heavier gauge, harder grades, more knives in the stack and tighter tolerances. Real throughput is line speed minus the setup and threading time between coils.

Mult. Short for "multiple": one of the narrower coils produced when a master is slit. A pass across a 60-inch master might give four 14-inch mults plus edge trim. Also called strips or slits, mults are what ship to the customer or feed the next process.

Multi-pass. Running the same material through a line more than once, for example slitting a wide master into intermediate widths and then re-slitting those into final mults. It is used when the final widths are too narrow to run stably in one pass, or when the arbor will not hold the stack. Each extra pass adds handling and line hours, and another chance to put camber into the strip.

Remnant (drop). Usable width left over after the ordered mults are cut, wound and put back into inventory. It carries a tag and a weight and may match a future order. Remnants that never find a home slowly turn working capital into scrap value.

Skidding. Banding, wrapping and mounting finished mults on skids or coil cradles for shipment. When one master produces many narrow mults, the packaging crew at the exit end is often the bottleneck.

Slitting. Cutting a coil lengthwise into narrower coils with rotating circular knives. The coil is uncoiled, passed through the knife stand, separated, tensioned and rewound as several mults on one recoiler shaft. It is the highest-volume first-stage process at most service centers, and the point where width decisions become permanent.

The plan

Cutting-stock problem. The classic operations research problem of cutting ordered pieces from larger stock with the least waste. Gilmore and Gomory formalized it in 1961 and introduced column generation to solve it. Coil slitting is the one-dimensional version, made harder by real inventory, compatibility rules and due dates.

Must-ship order. An order the plan cannot leave behind, such as a contract commitment, a customer whose line is down, or a due date at the edge. Planners flag these before optimizing, and the plan has to cover them even at a cost in yield.

Nesting. Choosing which patterns to cut across which coils. A full order book generates millions of feasible patterns, so nesting is a search problem, and it is where most scrap gets decided.

Partial coverage. Filling part of an ordered quantity now and leaving the balance for a later run. Orders rarely divide neatly into coils, so it is normal, but the remainder has to be tracked or it turns into double shipments and phantom shortages.

Pattern. One arrangement of ordered widths across a coil, such as 14 + 14 + 14 + 14 inches plus trim across a 60-inch master.

Slitting plan. The instructions for a period of production: which coils to pull, which patterns to cut from each, which orders each mult fills, and in what sequence. It is the output of nesting, put in order for the line. Software such as LineSight AI builds these from live order and inventory data and hands them back to the ERP as work orders. From PO to release shows where the plan sits in the wider flow.

Work order. The shop-floor instruction to process a specific coil a specific way: coil tag, pattern, resulting mults, line and target date. Production is reported back against it.

Yield and scrap

Scrap rate. The share of consumed material, by weight, sold at scrap value instead of product value. It has two parts with different fixes: planned scrap, the trim you knew you would take, and unplanned scrap from defects, mis-slits and short runs. Reporting them as one number hides which problem you have.

Trim loss. Material that leaves the line as unusable width: the edge trim off each side, plus any width left over because the ordered mults did not add up to the coil width. It is expressed as a percentage of master coil weight, and reducing it is the main goal of slitting optimization. How to reduce scrap on a slitting line covers the levers that move it.

Yield. The share of input material that leaves as saleable product, by weight: pounds shipped divided by pounds consumed. Trim, scrap, defect rejections and unsold remnants all pull it down.

Quality and traceability

Camber. Sideways curve along the length of the strip. One edge is longer than the other, so a length laid flat bows away from straight. It comes from the mill or is introduced in slitting when knife clearance differs across the arbor, and cambered mults wander in the customer's press and come back as claims. Ulbrich explains how it is measured.

Coil genealogy. The recorded lineage of every piece of material: which master it came from, which heat and mill cert stand behind it, which mults were slit from it and which remnants remain. A tag number on each coil anchors that chain in the ERP. Without it you cannot answer a customer claim or a recall question.

Crown. A thickness profile across the strip width, thicker in the center than at the edges, as rolled. Some crown is normal and intended. Too much means mults slit from the center run heavier than mults from the edges, so two mults of the same ordered width are not quite the same product.

Mill test report (MTR). The mill's certificate of a coil's chemistry and mechanical properties against the ordered specification, tied to a heat number. Also called a mill cert. EN 10204) defines the certificate types, and type 3.1 is standard in steel. The cert follows the material to every mult, and a mult without one cannot be sold into certified work.

Width tolerance. The allowed deviation from ordered width, written as a plus and minus band such as +0.010" / -0.000". The customer's application sets it, and it governs how the knife setup is built and how mults are gauged during the run. Tight tolerances limit which widths can run together.

Orders and the business

ERP. The system of record for orders, inventory, tags, work orders, shipments and invoices. It answers questions that have one true answer. Choosing patterns is a search ERPs were never built to run, so planning usually happens in a separate tool or spreadsheet that reads from the ERP.

Metal service center. A company that buys metal from mills in bulk, holds inventory, does first-stage processing such as slitting and cut-to-length, and sells to manufacturers in the sizes and quantities they need. MSCI, the industry's trade association, represents several hundred member companies across North America. The business is buying wide and selling narrow, and the margin lives in that conversion.

Release. Authorization to ship a set quantity against a larger standing order or blanket contract. Customers on annual agreements release material in weekly or monthly increments, so planning against the contract total instead of the releases builds inventory nobody has asked for yet.

RFQ (request for quotation). A customer's request for pricing on specified material: grade, gauge, width, quantity, tolerance, packaging and delivery. A good quote depends on what the job will really cost to produce, and that depends on what else is being cut the same week.

Toll processing. Processing material the customer owns, for a fee, as opposed to selling from your own inventory. Outside processing is the same arrangement from the other side: sending your material to a shop with equipment you lack. Toll coils take up tags, floor space and line hours but carry no material margin, so they are planned and costed differently. Worthington Steel's definition matches common trade usage.