Coated Aluminum Coil Production Process: Five Stages From Alloy and Chromizing to Curing and Packing

Inside the Coated Aluminum Coil Production Line: Five Stages That Decide Service Life

Coated aluminum coil begins long before paint. It starts with molten alloy cast into ingot, hot rolled, cold rolled down to gauge, then annealed to the temper the customer's forming operation actually needs. Whether the line runs 1050, 1060, 1100, 3003, 3004 or 5052 determines the final tensile strength of 50 to 260 MPa and elongation of 8 to 25 percent. Thickness at this stage runs 0.25 to 1.2 mm and width 600 to 1250 mm — and strip flatness here sets the ceiling for everything that follows.

Stage 1 — Degreasing and Chromizing

Alkaline cleaning strips rolling oil, emulsion residue and dust. A chromate or chromium-free conversion coating then etches a micro-porous layer that the paint can physically grip and chemically bond to. A coil that passes this stage poorly will peel at the bend six months later, and no premium resin will rescue it.

Stage 2 — Precision Roller Coating

Rollers lay down primer and topcoat on the face, plus a protective back coat. Front film builds to 10–25 µm and back film to 5–10 µm, adjusted by resin type. Choosing the right chemistry is a specification decision, not a marketing one:

Inorganic ceramic pigments keep colour stable under sunlight instead of chalking within two summers — a detail that matters more than the initial gloss reading.

Stage 3 — Curing

The wet strip crosses a multi-zone oven and must reach a narrow peak metal temperature window. Under-cure leaves the film soft and poorly bonded, so it blocks on the rewinder; over-cure makes it brittle, so it cracks when the customer runs it through a roll former. Pencil hardness of 1H–3H on the finished coil is only reachable with correct cure combined with correct film build.

Stage 4 — Verification

After cooling and protective film lamination, each coil is checked for coating thickness, T-bend adhesion, gloss, colour difference against RAL or the approved sample, and mechanical properties under GB/T 17748, ASTM A924 or EN 12526. Surface effects — high gloss, matte, metallic texture, imitation wood grain and imitation stone grain — are confirmed against the approved sample at the same time.

Stage 5 — Slitting and Export Packing

The coil is slit to final width and packed with moisture-proof paper inside, iron sheet and wooden pallet outside. That packaging sequence is what keeps coil edges intact through ocean freight and monsoon humidity.

Why the Line Itself Matters

Hangxi Metal runs a colour-coating line designed specifically for aluminum rather than a converted colour-steel line, which keeps film thickness and cure repeatable across a 15,000-ton monthly programme. Coils are ISO certified and shipped from Qingdao or Tianjin within 20–40 days on a 25-ton minimum order.

The lesson for buyers: ask what the mill monitors at chromizing and at cure, not only what film thickness it prints. Those two invisible stages separate a fifteen-year façade from an early repaint.