Aluminium foil is produced first by rolling heated direct chill (DC) cast ingots called hot rolling down to thicknesses around 4mm. This coiled product is then cold rolled in a sheet rolling operation to foil stock. This reroll stock which is a semi-finished rolled product of rectangular cross section is
coiled form is suitable for further cold rolling at the Foil Mill. Another method of production developed in the last number of years for production of high quality sheet and foil products is by continuous casting. This process bypasses the ingot stage and directly converts the molten aluminium into thick strip which is then immediately rolled into coil from which foil can be produced.
To obtain foil in final thickness below 0.040mm two layers from the coils are rolled simultaneously. The rolling of the doubled foil results in one of the rolled surfaces on the outside of the doubled coil being bright and the inside being matt or mill finish. After the doubled coil is rolled to gauge it is sent to a separating machine and the two layers are separated into two single layers of foil material for sending to the customer.
After the completion of rolling the metal may be heated in a large industrial furnace to obtain an annealed 0 temper or partial annealed temper such -H22. The particular temperature used for annealing or partial annealing will be dependent on the aluminium alloy and if any special quality features are required such as improved wettability on the surface for subsequent laminating and/or printing at the customers.
In the case of foil that will be used for containers a special food grade approved lubricant (texturing) is applied during the slitting operation to facilitate the container forming operation at the customer's plant
In some instances that foil may be supplied as rolled example -H18 temper condition for a particular end use. This is the case for instance in blister packaging for pharmaceutical application.
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