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A Brief Introduction to Cast Iron

 Cast Iron Mill

When someone calls us asking for a table base for a stone table top, we usually default to the same response: we recommend something made from cast iron. Many of you ask us why, and we are left trying to explain the somewhat complicated properties of cast iron versus steel. Thus, we thought it would be both fun and useful to give you a brief history of cast iron, highlighting the important bits that have brought us to that beautiful base under your table.

Firstly, what is cast iron? Simply put, it is a composite material made from a mixture of different metallic and stone elements. The process begins by taking pig iron and melting it down with other materials such as carbon, scrap iron, limestone and silicon. Iron ore is very rarely found in it's pure form; pig iron is formed form iron ores that are rich in carbon and other substances that occur organically with iron in nature. The materials are then heated and refined to remove impurities such as phosphorus and sulfur, which dramatically alter the structure and usefullness of the finished metal. After the correct proportions have been achieved, the material is poured into a cast (mold) and shaped for it's respective use. There are a few different types of cast iron, produced by varying the proportions of these different metals, as well as variations in the melting, casting and cooling processes. The most commonly used type of cast iron is known as grey iron, which has added graphite to increase it's strength. This is the type of cast iron used to make our table bases.

There are two main measures of strength we want to talk about in relation to cast iron table bases. The first, where cast iron excels, is known as compressive strength. This "is the capacity of a material or structure to withstand loads tending to reduce size" (Wikipedia). Think of the load as your table top, exerting pressure directly on top of your table base. This compressive strength is the reason why cast iron table bases work so well with heavy table top materials such as cement and granite, because the columns do not compress or bend when supporting a heavy load throughout the length of the structure. Steel columns, while also very strong, are more prone to flexing or bending when compressed near their limit.

The second measure of strength is known as tensile strength, and is the measure of "the force required to pull something such as rope, wire or a structural beam to the point where it breaks" (Wikipedia). Imagine the wooden beams in the ceiling of a building. Wood is able to flex and bend without breaking, and so is steel to a certain degree, whereas cast iron tends to be very brittle in comparison, causing it to crack or shatter when it exceeds it's tensile strength. So although cast iron is perfect for table bases, it does not work quite so well as a building material.

Cast iron has been used to make a wide variety of things throughout history, ranging from weapons, to cook wear, pianos, plumbing and even architecture. The first evidence of the use of cast iron comes from China in the 5th century BC, where it was used to make weapons, agricultural tools and for use in some structures. Cast iron's use was mostly limited to smaller endeavors in China until the 15th century, when we begin to see the material crop up in the construction of western European artillery, such as cannons.

Due to major improvements in the production of cast iron in the late 1700s, at the beginning of the industrial revolution, cast iron started to gain traction as a building material throughout most of western Europe. Cast iron was more economical and less labor intensive to produce than wrought iron. While suitable as a replacement for wrought iron in many cases, there were incidents where improper engineering meant the tensile strength of the cast iron was exceeded. A series of bridge collapses occurred in England in the 1700s and 1800s, and engineers began to rethink the use of cast iron. The most catastrophic occurred when the Tay Bridge in England collapsed as a result of failed cast iron lugs, killing 75 people.

The availability of cast and wrought iron dramatically changed the way buildings were constructed. Many sky scrapers and buildings through the industrial revolution in Europe and America were produced using cast iron. Cast iron columns and supports could be made much thinner than masonry buildings, which required thick columns and walls to support ever larger structures. Massive skyscrapers, warehouses and factories with huge interior spaces began to appear in major cities. However, beginning in the late 1800s, cast iron had almost completely been replaced by steel, which is much more adept at supporting large structures and which can now be made much more economically than in the past.

Cast iron still has it's place, though it may not be the best for our buildings and bridges of the future. Many cast iron projects are still standing, such as a historical five miles of cast iron plumbing laid in 1664, still in use in Versailles, France; the world's first cast iron arch bridge, known simply as the Iron Bridge in Shropshire, England constructed in 1781; and the Pontcysyllte Aqueduct in Wales, Britain built in 1805 (Wikipedia). Considering your cast iron table base is under considerably less stress than are the supports of a bridge, it should last you several lifetimes!