From Blank to Foil: The Rolling Process
Aluminium foil production starts with blanks, which are cold-rolled aluminium coils with a thickness of about 0.4-0.7 mm and a high rate of multiple deformation. The blanks are first pre-quenched at temperatures around 240-480 degrees Celsius, then fed into roll presses. Rolling proceeds through roughing, intermediate, and finishing stages using high-hardness, high-finish steel rolls, and the material is finally formed into foil after quenching. This multistage reduction is what allows an ingot of several millimeters to become foil measured in microns.
Controlling Foil Thickness
Thickness control is one of the most critical parts of foil production. In rough rolling, operators adjust the rolling force and strip tension, and in finishing, the rolling speed becomes the main control variable. As a rule, thickness decreases as rolling speed increases in the finishing stage, and higher tension produces thinner foil. Modern mills combine automatic gauge control with operator adjustments to hold thickness tolerances across the full coil width and length. With the strip production method, the minimum thickness can reach about 0.0025 mm, and widths can extend to 1800 mm.
Common Alloys, Tempers, and Dimensions
A typical specification for foil blanks used in applications such as air-conditioning fins is alloy 8011 or 3012, in O, H22, or H24 tempers, with thickness from 0.09 to 0.16 mm and widths from 100 to 1200 mm, supplied with a double-sided bright surface. The O temper is fully annealed for maximum formability, while H22 and H24 are strain-hardened and partially annealed to add strength while retaining the ability to be formed, folded, and laminated without cracking.
From Plain Foil to Finished Products
Foil that receives no additional processing is called light foil or plain foil. Because plain foil has limited load-bearing capacity, it is seldom used alone. Depending on the application, it is deep-processed into more advanced packaging materials. A common downstream step is embossing, which improves the surface properties of the foil: raised patterns add rigidity, reduce sticking between layers, and improve the appearance of household and decorative foil. Other conversions include lamination with paper or plastic film, coating, printing, and slitting to customer widths.
Choosing the Right Foil Specification
When specifying foil for a converting project, define the alloy, temper, thickness, width, and surface finish against the end use. Food packaging favors alloys such as 8011 and 1235 with controlled pinhole counts; industrial applications may accept wider tolerances; and decorative uses may require embossed or coated surfaces. Because foil properties interact, it is wise to confirm elongation, tensile strength, and sealability with the supplier and run a production trial before committing to large volumes.
FAQ
How thin can aluminium foil be rolled?
With the strip production method, foil can be rolled to about 0.0025 mm. Most commercial packaging foil is between 6 and 30 microns, with household foil commonly around 10-24 microns.
What is the difference between O, H22, and H24 foil tempers?
O is fully annealed and soft; H22 and H24 are strain-hardened then partially annealed, giving progressively higher strength and stiffness while keeping useful formability for converting.
Why is plain foil rarely used alone?
Very thin plain foil has low load-bearing capacity and tears easily, so it is usually laminated, coated, or embossed to gain the strength, sealability, and appearance needed for packaging.
What is embossed foil used for?
Embossing adds patterns that increase rigidity, prevent layer sticking, and improve appearance. It is common in household foil, decorative wrapping, and some industrial applications.
How is thickness controlled during rolling?
By adjusting rolling tension and force in roughing and rolling speed in finishing: higher finishing speed and higher tension both reduce final thickness. Automatic gauge control holds consistency across the coil.
Q: What is the production sequence for aluminium foil?
The sequence is: cast slab, hot roll to strip, cold roll to about 0.4-0.7 mm coil, then foil rolling in roughing, intermediate and finishing passes down to 6-100 micrometres, followed by annealing, slitting and re-coiling to finished rolls.
Q: What is rolling oil and why is it used?
Rolling oil (a low-viscosity mineral oil with additives) lubricates the roll gap, cools the strip and controls friction during foil rolling; it must be filtered and evenly applied because trapped oil causes stains and defects, and it is removed by annealing.
Q: Why is annealing done after foil rolling?
Annealing softens the work-hardened foil to the O temper, removes rolling oil residues, and stabilises the microstructure so the foil folds, seals and dead-folds correctly; without annealing the foil would be too stiff and brittle for wrapping.
Q: What is slitting in foil finishing?
Slitting cuts the wide jumbo foil roll into narrow rolls with clean, burr-free edges using rotary knives; the slitting operation sets the final roll width, tension, and edge quality that packaging machines depend on.
Q: What are common foil defects and how are they prevented?
Common defects are pinholes, edge cracks, scratches, oil stains, streaks and gauge variation; they are prevented by clean rolling environment, filtered oil, polished rolls, controlled tension, on-line gauge measurement and final inspection by light table.