What is the difference between coil and sheet?

Aluminium sheets, plates, and coils are widely used across various industries for their strength, corrosion resistance, and lightweight properties. At Aluminium Trading, we supply these products to numerous sectors throughout Southern Africa every month. Despite the widespread use of aluminium, many people still ask, "What sets aluminium sheets, plates, and coils apart?"

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The distinction between these aluminium forms primarily lies in their thickness: plates are the thickest, followed by sheets, with coils being the thinnest. The precise measurements that define these categories can vary based on factors such as the type of metal, the gauge, and the intended application.

Before advanced measurement tools and technology, 'gauges' were utilized to classify metal thickness, especially wires. Over time, different industries developed their own standards, leading to inconsistencies. For instance, 10-gauge aluminium is 0.259 cm thick, whereas 10-gauge standard steel is 0.341 cm, and 10-gauge galvanized steel is 0.351 cm, as catalogued in the Dictionary of Units of Measurement.

Due to the resulting confusion, the American Society for Testing and Materials (ASTM) advised against using gauge numbers in specification ASTM A480-10a, describing them as outdated and insufficiently clear.

Today, specifying exact thickness measurements for metal products has become more standard. Although gauges are still mentioned in the U.S., their use has decreased in South Africa and Europe.

In South Africa, the classification of aluminium by thickness is not strictly defined, with many distributors establishing their own categories. At Aluminium Trading, we consider aluminium plate to be thicker than 4.5 mm, aluminium sheet to range between 0.5 mm and 3 mm, and aluminium coil to be between 0.5 mm and 0.6 mm, with foil being around 0.29 mm thick.

We also reached out to Mr. Kent Bell, Market Manager at Hulamin South Africa, to provide insights into their classification standards for aluminium thickness. Hulamin specializes in precision-rolled aluminium products for high-tech applications and is among Africa's largest producers.

Businesses nationwide constantly search for ways to enhance their profit margins. They focus on improved marketing efforts and faster quoting processes while also investing in automation to cut labor costs.

For manufacturers looking to optimize raw material expenditure, bulk purchasing is often an effective method. In sheet metal fabrication, buying in bulk usually means acquiring material in coil form. On average, rolled carbon steel in coil form is 5 to 15 percent cheaper than the same material in sheet form.

However, switching to coil isn't universally applicable. Several factors must be considered before making this move.

Ultimately, the decision to use coil or sheet will depend on your product and material mix and the type of processing required. Some companies may benefit more from using coils, while others will find sheet more appropriate.

"Coil won't replace sheet in all scenarios," notes Sylvain Touboul, U.S. Managing Director for Dimeco, a producer of sheet metal coil production systems. "Certain products necessitate the use of coils, while others are better suited to sheets. For fabricators handling diverse materials and short production runs, coils might not be suitable. In contrast, manufacturers with longer runs of similar parts will find coil advantageous."

Manufacturers need to account for the equipment in their facilities. Coiled material must be cut to length for machines like flat-bed lasers or punching machines. A steel coil that is 60 inches wide and weighs 20,000 lbs. can yield about 270 sheets of 5' x 10' material.

"There will be an added cost for a cut-to-length line, but that cost will be offset by the savings from purchasing coil," Touboul explains. "The overall cost is influenced by the quality of the coil and the sheet needed. While laser-quality sheets may require an investment in a higher-quality leveler, manufacturers focusing on punching might not need a leveler at all."

Apart from cutting coils to length, coil-fed machines that incorporate punching, laser cutting, and forming are available. "A frequent question from customers is regarding the number of parts that can be produced from one coil," says Touboul. "Feeding material directly from the coil to a punch press or laser enhances material utilization, minimizing scrap."

This setup can reduce both material and labor costs. With automation, a single operator can handle the entire production process, loading the coil and managing material handling during setup.

Storage space is another advantage of using coils. If you opt to cut the coil to length, those sheets will need storage. Using coils can help save valuable floor space.

Whether you choose to cut the coil to length or use a fully coil-fed setup, transitioning to coil will depend on your material and product variations. It will also require careful consideration of the necessary equipment investments.

"The initial investment in coil-fed equipment may be higher, but the savings on material cost and utilization can accelerate ROI," says Touboul.

If businesses need help justifying the investment or estimating the time to ROI, consulting services are available. Dimeco offers free consultancy and continued support for their customers, providing training and assistance long after the initial purchase.

Ultimately, transitioning to coils requires the right candidate, appropriate coil usage method, and a realistic approach.

"Companies aiming for significant production increases have two options: replicate their current operations, which involves duplicating machinery and labor – a challenging task in regions with labor shortages – or transition to coil. While coils alone won't dramatically increase margins, combining them with automation can," Touboul concludes.