Lesson 1: Tinplate

Taught by Professor Timothy Cann

Students, welcome to Can Anatomy 101. For our first class, we're going to start with one of the most basic aspects of tin manufacturing, the most common material that composes the body of your metal packaging: tinplate.

As the name implies, tinplate is, in fact, partially made of tin, but mostly it's made of steel, with only a thin coating of tin. Though tinplate existed for many years prior, the first patent on tin-plated cans in the United States was taken out by Thomas Kensett, Sr. in 1825. Today, 90% of tinplate produced is used for packaging, but at that time it was mostly used for things such as trays and kettles for tea sets, and painted toys for children.

1.1 - Red hot steel rolls off the production line at a mill

If you've ever played with one of those antique wind-up toys, like the one in figure 2.1, you know that they're quite heavy. That's because not only didn't the technology exist to make the extremely thin steel sheets that we have today, but the tin coating was also applied by simply hot-dipping a sheet of steel into a vat of molten tin.

Obviously, the technology has come a long way since then. Today, tinplate can be as thin as one tenth of a millimeter, and the tin coating is applied by an electrolytic process. The steel is washed in a pickling solution, and then fed through tanks containing an electrolytic tin solution. With the use of induction coils, the steel is negatively charged, and the solution positively charged. The tin molecules in the solution are attracted and bound to the steel, creating a coating that can be less than a thousandth of a millimeter thick and actually meshes with the steel on an atomic level. As a result, exactly where the tin stops and the steel starts is almost indistinguishable, and no matter how the tin plate is worked, the coating won't separate from the steel. You can see this process in action by rolling your cursor over figure 1.3, below. I hear you snickering... yes, it's a somewhat crude animation, but we're waiting for the administration's approval to purchase a new video.

1.2 - An antique toy made of painted tinplate

Of course, the tin plating has all kinds of benefits for the can manufacturer. For starters, it lends a clean, attractive sheen to an otherwise dull metal, and if you don't like the natural look, tin is far better for painting, printing and varnishing than steel. From a fabrication standpoint, the steel is a strong, durable material, while the tin makes the metal far easier to seam and weld, and when subjected to the pressure of manufacturing, it acts as a built-in lubricant.

1.3 - Steel electroplated with tin molecules

Additionally, the steel plate and tin coating can be customized to create a number of different types of tinplate. Through different processes, tinplate manufacturers can control the thickness, the temper or hardness, and the brightness of the coating from matte to glossy. The tin coating can even be imbued with special textures that make for a particularly striking appearance, as illustrated in figure 1.4.

1.4 - A can manufactured with textured tinplate

Another side benefit to using tinplate as a packaging material is that it's quite environmentally friendly. For starters, on average, steel contains 28% recycled material, and used steel is recycled at a 68% rate, which is more than all other materials combined. Furthermore, even if a tin doesn't make it to the recycling plant, it is biodegradable. When exposed to the weather, a can made from tinplate will eventually rust and return to the environment. For more information, visit the Steel Recycling Institute's website.

1.5 - Bales of crushed cans ready to be recycled

So there you have it: a brief overview of tinplate right down to its return to the earth. No homework, but prepare for our next class: Basic Lids!