How should flatness, camber and dimensional tolerances be specified for prepainted aluminium coil?

The short answer: specify geometry as a measurement agreement

A workable order does more than list nominal thickness and width. It identifies the product form, alloy and temper, bare-metal gauge basis, applicable standard and edition, width and edge condition, required length or coil dimensions, shape characteristics that matter to the fabrication route, how each characteristic is measured, where samples are taken and what happens when a result is disputed.

BS EN 1396:2023 is the European product specification for coil-coated aluminium sheet and strip for general applications. Its public information points shape and dimensional tolerances to EN 485-4. It also separates the uncoated substrate thickness from the organic coating thickness, so a buyer should not compare a coated overall-gauge reading directly with a bare-metal tolerance table without an agreed method.

Separate four questions that are often collapsed into one tolerance

The Aluminum Association defines lateral bow, commonly called camber, as the deviation from straight of a longitudinal edge. That is different from a local wave across the strip or a lengthwise curvature caused by the coil's wound state. Calling every shape complaint 'flatness' makes supplier and processor measurements difficult to compare.

ANSI H35.2/H35.2M-2024 covers dimensional tolerances for aluminium mill products, while EN 485-4 is the dimensional reference used by BS EN 1396. Their public descriptions show why the order must identify its chosen system: tolerances depend on product category and dimensions, and a value taken from one table should not be treated as a universal prepainted-coil promise.

Use a five-step receiving and release workflow

• Translate the fabrication risk first: slitting, blanking, panel lamination and roll forming may be sensitive to different combinations of width, camber, edge condition and flatness.
• Freeze the standard, edition, product form and measurement state in the purchase specification, then add only the order-specific limits that have a real process reason.
• At receipt, preserve coil identity and packaging evidence, then measure at the agreed locations with recorded equipment, support, tension, span and environmental or rest conditions where relevant.
• Compare like with like: bare-metal gauge with the substrate rule, coating thickness with its coating method, camber with the agreed gauge length and sheet flatness only in the specified state.
• Release, hold or run a representative first piece under the agreed rule. For a dispute, repeat the documented setup on retained material instead of trimming, levelling or forming the sample first and then comparing it with the original result.

Qihao perspective: tie shape evidence to the customer's feed path

From a prepainted-aluminium manufacturing and process-communication perspective, a shape limit is useful only when it protects a real downstream operation. A coil that feeds one levelling line acceptably may behave differently on another line with different tension, roll settings, width or blank length, so the most informative approval combines incoming geometry records with a representative first-piece check.

Qihao recommends sending the application, alloy/temper and bare-metal gauge, coating construction, required width and edge, coil inside diameter and weight range, feed direction, cut length, levelling or roll-forming route, critical shape characteristic, measurement basis and representative sample requirement for technical review.

This is a marked Qihao perspective based on public standards information and general manufacturing practice. It is not a claim that one tolerance class, levelling condition or process window suits every order; the confirmed specification and representative evidence remain controlling.