How Much Coil Weight Can an NC Straightener Feeder Handle?

Three Numbers Set the Real Capacity

A decoiler's usable capacity is determined by three quantities working together: coil weight, coil outer diameter, and coil inner diameter. Change any one of them and the load on the mandrel, the bearings and the frame changes.

Coil weight creates the bending moment on the mandrel and the vertical load on the main bearing. Outer diameter sets the torque arm — a coil of the same weight but larger diameter produces more torque at the mandrel and more centrifugal effect at speed. Inner diameter determines how much mandrel expansion is available and how concentrated the contact pressure becomes at the segments.

This is why the same machine can be perfectly safe with a 6-ton coil at 1,250 mm outer diameter and marginal with a 6-ton coil at 1,500 mm. The weight is identical; the loading is not.

How to Read a Capacity Rating Without Getting Fooled

Manufacturers quote capacity in different ways, and the differences are not cosmetic. Ask which of the following the number refers to before you compare machines.

Two machines both described as "8-ton" can differ by a factor of nearly two in usable capacity once you resolve these six lines. Ask for the reference coil OD, the safety factor and the brake torque curve. A supplier who cannot answer in one email has not engineered the rating carefully.

Mandrel Design Decides Where the Limit Sits

Two decoilers with the same nominal capacity behave very differently depending on mandrel construction. The choice is not about quality tiers; it is about matching the design to how your coils arrive.

Segment or wedge mandrels

Four or six expanding segments driven by a hydraulic or mechanical wedge. These grip the coil ID evenly and handle the widest range of inner diameters. They are the standard choice for mixed coil supply, and they tolerate coil ID variation well. The trade-off is that contact pressure concentrates at the segment edges, so very thin-wall or soft-material coils can mark if expansion pressure is set too high.

Scroll or scroll-type mandrels

Continuous wrap expansion rather than discrete segments. Contact is more uniform around the circumference, which suits thin-gauge and surface-critical material. Inner diameter range is narrower, so a scroll mandrel sized for 508 mm coils will not accept 610 mm coils without a change of the expansion assembly.

Cone or wedge-lock mandrels

Simplest and most robust, but they rely on friction over a smaller area and need higher expansion force for the same grip. On heavy coils at high pay-off speed they are more prone to slip than a segmented design.

What Overloading Actually Does to the Machine

Overload rarely produces a dramatic failure. It produces a slow, expensive degradation that shows up as quality problems long before it shows up as a breakdown.

• Mandrel deflection increases, so the coil centre of rotation moves off axis. The strip leaves the decoiler at a varying angle, which the straightener then has to absorb
• Main bearing life falls sharply. Bearing life scales roughly with the cube of load, so a 25 percent overload can cut service life by more than half
• Coil slip becomes intermittent. The mandrel cannot hold grip under the higher inertia, so the coil rotates ahead of the pay-off command and the loop collapses
• Frame and baseplate fatigue appears at weld toes and anchor points. This is the failure mode that becomes a safety issue rather than a maintenance cost
• Brake fade under sustained pay-off, because the brake is dissipating more energy per coil than it was sized for

Bigger Coils Are Not Automatically Cheaper

Heavier coils reduce the number of changeovers per shift, which is a real saving. They also raise crane requirements, floor loading, foundation cost and the consequence of a mistake.

Work the trade honestly. A line running 900 kg coils at 4 tonnes per shift needs roughly five changeovers. Moving to 2,500 kg coils cuts that to two. If a changeover costs twelve minutes of lost output and you run two shifts, the heavier coil returns about 72 minutes a day — meaningful, but only if the decoiler, the crane and the floor can take it without added maintenance.

Where the calculation usually goes wrong is on the maintenance side. A decoiler running at 90 percent of its rated capacity will need bearing attention far sooner than one running at 60 percent. Over a five-year horizon that difference can exceed the value of the changeover saving.

Check the Floor Before You Check the Catalogue

A loaded decoiler concentrates a lot of mass into a small footprint, and the dynamic load during acceleration is higher than the static weight. Two checks belong in the specification process.

First, point load. Ask the supplier for the load per mounting pad, then compare it against your slab capacity. Second, vibration isolation. Heavy coils at pay-off speed generate a rotating imbalance that transfers into the floor and into neighbouring equipment. If your press sits on the same slab, that energy can show up as a periodic variation in feed accuracy — the kind that is very hard to trace once it is buried in a scrap report.

FANTY builds decoilers and 3-in-1 decoiler straightener feeder systems in a 45,000 m² facility with a 370-person production team, and we supply the foundation loading drawing as part of the standard documentation package. If a supplier cannot give you that drawing before shipment, you are going to be guessing at civil work on installation day.

Common Questions About Coil Weight Capacity