The Tinplate Production Process

All tinplate originates in the steelmaking furnace, where the proper chemistry for steel is obtained to meet the specific needs of the end user. All tin mill products start their production process in a Basic Oxygen Furnace. This highly productive process uses a mixture of recycled steel scrap (25 to 30 percent) and liquid iron (70 to 75 percent) to make high-quality, new steels, including tinplate.

Continuous Casting

Once the steel is produced, the continuous casting process transforms molten steel into slabs in one continuous operation. Continuous casting is a highly energy- and cost-efficient process that produces a slab of excellent quality and consistency. Next, the slab goes into the hot strip mill where its thickness is further reduced into a coil form. In the pickling process, the coil's surface is cleaned and oiled for further treatment in the cold reduction mill. At this stage, the coil gauge is further reduced and then must be annealed (softened) to obtain the desired strength and formability. Temper mills and double reduction cold mills are used to create the final desired strength and formability characteristics.

Blackplate

Blackplate is not actually black, but the surface qualities of blackplate steels are the same as cold-rolled steels that have not been coated. Blackplate is easily painted or plated for corrosion protection and appearance and can be easily bonded and welded. Blackplate is most commonly used for items such as toys, serving trays, building materials, household goods, closures and caps.

Electrolytic Tin Coating

The unique properties of tin provide a coating on the steel that protects the contents, while providing the steel with an attractive appearance, corrosion resistance and ease in bonding, welding and painting. Tin is applied to both sides of the blackplate coil through an electrolytic process at speeds up to 2,000 feet per minute. The thickness of the tin coating (called coating weight) is dependent upon the end-use application. Typical applications for electrolytic tinplate include food and beverage containers, paint trays, battery tops and paint, varnish and aerosol cans.

Continuous casting methods are now used in virtually all carbon steel production facilities to produce products of consistent, high quality.

Electrolytic Chrome Coated Steels (ECCS)

Unlike the multiplicity of coating weights with tin, only one standardized chromium-coated product is manufactured. The chromium coating process was developed in the 1960s as an alternative to tin coatings for packaging products cost-effectively, with desirable material properties. Chromium offers excellent lacquer adhesion, storage properties and strong resistance to food corrosion with proper applications of lacquer. Chromium-coated steels are most frequently used for can tops, screw and lug caps, snap and press-on closures and shallow-drawn food cans.

Packaging steels are coated with different protective and decorative coatings, depending on their intended use.

Other Coatings Used in Cans

Many additional internal coatings, such as polyester, vinyl and acrylic, are used to further protect the contents of steel cans. Because of the vast range of products packaged in steel cans, more than 25 lacquers and 30 types of tin coatings exist. These coatings may be applied to the steel either prior to forming the can or by spraying the can after fabrication. Cans have either an external paper label or decorative inks applied directly to the steel's outside surface. New techniques for decorating include film or shrink-wrap labeling that allow for vibrant, colorful decoration.