Sheet metal

Lore & Background

Hand-hammered metal sheets have been used since ancient times for architectural purposes. Water-powered rolling mills replaced the manual process in the late 17th century. The process of flattening metal sheets required large rotating iron cylinders which pressed metal pieces into sheets. The metals suited for this were lead, copper, zinc, iron and later steel. Tin was often used to coat iron and steel sheets to prevent rust, and this tin-coated sheet metal was called 'tinplate'. Sheet metals appeared in the United States in the 1870s, being used for shingle roofing, stamped ornamental ceilings, and exterior façades. Sheet metal ceilings were only popularly known as 'tin ceilings' later, as manufacturers of the period did not use the term. The popularity of both shingles and ceilings encouraged widespread production. With further advances of steel sheet metal production in the 1890s, the promise of being cheap, durable, easy to install, lightweight and fireproof gave the middle-class a significant appetite for sheet metal products. It was not until the 1930s and World War Two that metals became scarce and the sheet metal industry began to collapse. However, some American companies, such as the W.F. Norman Corporation, were able to stay in business by making other products until historic preservation projects aided the revival of ornamental sheet metal.

Reader's Guide

Sheet metal is a foundational material in modern manufacturing, used across industries from transportation to construction. Its significance lies in its versatility: it can be formed into complex shapes through bending, stamping, and hydroforming, while maintaining uniform thickness for ideal results. Historically, sheet metal enabled the mass production of affordable, durable, and fireproof building materials in the late 19th century, such as shingles and ornamental ceilings. Its legacy includes both practical and decorative uses, from tin cans to plate armor. The industry faced decline during the 1930s and World War Two due to metal scarcity, but later revived through historic preservation. Today, sheet metal remains critical for transformers and electric machines, where laminated steel cores exploit high magnetic permeability. The use of gauge numbers to designate thickness is discouraged by international standards, as gauge definitions vary between ferrous and non-ferrous metals and lack universal agreement.

Did You Know?

• In the US, the thickness of sheet metal is commonly specified by a traditional, non-linear measure known as its gauge; the larger the gauge number, the thinner the metal.
• Copper thickness is traditionally measured in ounces in the US, representing the weight of copper contained in an area of one square foot.
• Sheet metal workers are also known as 'tin bashers' (or 'tin knockers'), a name derived from the hammering of panel seams when installing tin roofs.
• The use of gauge number to designate sheet metal thickness is discouraged by numerous international standards organizations, including ASTM.