Cold Rolling of Flat Product: History and Evolution

The Aluminium Foil Manufacturing History in the last 20 years*

by Massimo Moschini, Ciro Sinagra (Laminazione Sottile Spa); Nicola Gioachin (Mino Spa)

The manufacture of aluminium foil dates back to the beginning of the 20th century. Prior to 1900 small quantities of aluminium foil had been produced by hammering, a laborious and costly process, it wasn’t until 1908 that the production of aluminium sheet in thicknesses down to 0.05 mm really began with so-called pack rolling, based on a patent taken out by Swiss entrepreneur Alfred Gautschi in 1908. The process involved cutting a thin sheet of aluminium foil into pieces placing one on top of the other and re-rolling several times. But it wasn’t until 1910 that the process began to make giant strides when Robert Victor Neher and his partner Dr. Edwin Lauber patented a method to produce strip and foil continuously using automatic coiling in a similar way to that used for tin. They produced usable aluminium foil strip in quantities of about 200 kg/month in thicknesses of 0.03-0.04 mm. Aluminium foil quickly found an application for chocolate wraps and by the middle of the decade coloured, embossed and printed aluminium foil was being produced. Between 1910 and 1920 a series of process-related problems associated with aluminium foil manufacturing were solved including slitting using rotary shears instead of a band saw, annealing of the ready-cut coils of foil, and grinding of the rolling rolls. One of the pioneers of modern aluminium foil technology was Rheinische Blattmetall (Rebag) based in Grevenbroich, Germany. Founded in 1922, Rebag established methods capable of rolling aluminium foil 320 mm wide at speeds of 12-24 m/min with an average thickness of 0.012 mm. After the end of the Second World War, productivity increased to a rolling width of 510 mm and rolling speeds of 80-90 m/min. During the 1950s and 1960s, foil production underwent dynamic growth, with new investment in technology leading to the development of two-high, then three-high and subsequently four-high rolling mills. This resulted in further improvements to auxiliary machinery and special equipment such as coilers and straighteners, exit devices, strip and slitting shears, coil transport units and ingot saws. By the second half of the 1950s, rolling widths of 1100 mm and speeds of 500 m/min were reached. Aluminium foil’s triumphant march as a barrier material in flexible packaging began in 1963 when thicknesses of less than 0.009 mm became possible. The rolling mills used high-purity steels for the rollers, which avoided the formation of rolling holes, while it also became possible to successively reduce rolling oil viscosity, thus increasing rolling speeds still further and also improving the annealing quality. At the end of the 1960s, it was possible to produce thin foils of 0.0065 mm, similar in thickness to the foils used today for aseptic packaging of liquids. At the beginning of the 1970s, the first rolling line with integrated transport and high bay warehouse technology for strip and coils was commissioned. And by the mid-1970s, rolling speeds reached 1500 meters/minute and the rolling width rose to 1500 mm. Roll roughness is increased step-by-step and electro-slag refined roll materials are used. The electro-slag process is used for remelting and refining steels and special alloys to create high-purity product. During this period, a strip thickness control with fully hydraulic adjustment was incorporated into a roll stand for the first time. It replaced the electro-mechanical adjustment that was used previously and allowed a high degree of dynamic control based on roll-gap measurement. Significant developments in rolling-mill technology were made during the 1980s with improvements to process engineering, drive technology, control and instrumentation. Ever greater rolling speeds led to a considerable increase in the requirements for strip flatness and strip thickness necessitating fully automatic measurement, display and control of the strip flatness. Six-high rolling mills and CVC (Continuous Variable Crown) technology were developed. In 1987, the rolling speed of new units reached 2200 m/min and a rolling width of 1800 mm; aluminium foil for flexible packaging was rolled down to a thickness of 0.00635 mm. In the 1990s, the emphasis was on the optimization and automation of the complete foil-rolling plant. This included plant optimization to provide environmental protection (exhaust air purification) and occupational health and safety. Today, foil-rolling plants with rolling widths of up to 2500 mm are commercially available and can produce aluminium foil as thin as 0.006 mm at rolling speeds of 2500 m/min.

Aluminium Rolled Product: Applications

Rigid Packaging
In the last 40 years, rigid packaging has shown a weight reduction of about 40% (Figure 1). Beverage cans have seen a thickness reduction from 0.30 to 0.25 mm and a speed increase from 1200 to 2500 cans/min. The augmentation of magnesium content from 0.9% to 1.1% and copper content from 0.06% to 0.15% allowed a considerable strength increase. For food cans, thickness has been reduced from 0.24 to 0.17 mm with a speed increase from 150 to 250 strokes/min. Regarding the production of pharmaceutical capsules, the newest progressive tools can reach speeds up to 550 strokes/min; thickness has been reduced from 0.24 to 0.19 mm.

Flexible Packaging
In the last 40 years, flexible packaging has shown a thickness reduction of about 35-40% (Figure 2). Lids have seen a weight reduction of about 40%, with a thickness reduction from 0.050 to 0.029 mm. Use of induction heat-sealing equipment instead of conduction heat-sealing has allowed considerable improvements in the production technology. For polylaminate, thickness has been reduced from 0.009 to 0.006 mm, with a weight reduction up to 35%. The production process has seen the development of advanced digital controls in printing and of appearance techniques to authenticate the source of packaged goods. Use of flexographic continuous-tone printers has allowed the production technology to improve and has extended the range of possible applications.

Heat Exchangers
As early as 1950, aluminium heat exchangers made moderate inroads into the automotive industry. With the introduction of the vacuum brazing technique, large scale production of aluminium-based heat exchangers began to flourish. Significant growth in the use of aluminium heat exchangers resulted from advantages of the controlled atmosphere brazing process (Nocolok® brazing process introduced by ALCAN).
Introduction of “long life” (highly corrosion resistant) alloys further improved performance of aluminium heat exchangers. Additional demands for aluminium heat exchangers resulted primarily from the growth of automobile air-conditioning systems and new applications due to the increasing engine performance. Over the years, extensive alloy development activities and product-specific process optimization efforts have allowed a significant downgauging of the aluminium heat exchanger materials, enabling a considerable reduction of weight and cost (Figure 3). Heat exchangers with copper tube and aluminium fins saw a thickness reduction from 0.15 to 0.09 mm; those with clad aluminium tube and aluminium fins up to 50% (fins from 0.15 to 0.08 mm, tube from 0.40 to 0.22 mm).