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Galvanized Steel

Fall 2010 | Volume 25 |  Issue 3

At the age of 24, Polish-born mechanical engineer Tadeusz Sendzimir found himself in Shanghai, China, after escaping his homeland to avoid the draft for World War I. In 1918 he opened China’s first nail and screw factory, using jury-rigged drill presses. He spent his spare time walking along Shanghai’s canals and riverfronts, visiting machine shops and scrap iron dealers. He’d bargain in pidgin English with the shop’s assistant while the owner snoozed peacefully in the back, clutching an opium pipe.

In the postwar years Sendzimir decided to diversify and make fences in addition to nails. Fences, like many steel products, were usually made from zinc-coated—galvanized—steel. If applied correctly, the zinc bonds chemically with the steel in a thin but hard layer. Such a coating not only shields the underlying steel but draws corrosion away from it if it cracks or develops a hole.

All galvanizing, whether in the modern factories of Europe or in the antiquated shops of Shanghai, was done in small batches by hand, usually by dipping. First the steel was pickled in acid to remove scale, oxides, and corrosion; then it was rinsed with water and placed in a flux bath of zinc ammonium chloride to further remove oxides. After that it was carefully dipped by hand into molten zinc at around 850 degrees and set to dry on a spike-studded cylindrical rack known as a porcupine.

Besides being hellish for the workers, the process was hard to control and only moderately effective. All galvanized products of the day would begin to oxidize at the first bump or scratch, when their silvery skin would flake away and leave an open wound. Sendzimir realized that the zinc was bonding not with pure iron but with a thin layer of iron hydroxide on the surface, which was produced by air and humidity. The key was finding a way to keep the iron’s surface pure. Sendzimir began conducting experiments and hit on an idea.

At the end of 1929, Sendzimir visited the United States and then Poland in search of investors to develop the concept, finally attracting the interest of Zygmunt Inwald, who was interested in competing in the roofing business. Sendzimir proposed sending cleaned steel through a box that was sealed so that oxygen could not get in. In addition, he would use a continuous strip, not individual sheets. A reducing atmosphere of hydrogen gas in the box would suck off the oxygen from the iron oxide on the steel’s surface, leaving pure steel. Then the strip would cool partially and pass down a long enclosed chute to be dipped in the molten zinc bath. From the bath the strip would be pulled up four stories high; the zinc would crystallize before it reached the pulley on top. When finally in operation, Sendzimir’s process would prove faster, cleaner, and cheaper than the old way—and create a far superior galvanized sheet. The steel could be bent, tacked onto roofs, or formed into buckets or mailboxes or manure spreaders; the zinc stayed on it like fleas on a dog.

But a problem still remained: galvanizing had always been done on large individual sheets of steel. Inwald couldn’t use sheets in the roofing business; he needed long strips in coils of thin gauge and wide width. No one in Europe made steel in coils to the fine one-third-millimeter gauge. So Sendzimir decided to make it himself, launching his second great innovation: the Sendzimir cold-rolling mill that could turn out a strip of steel half the thickness of a human hair.

Cold rolling became an increasingly important part of the steel industry in the 1930s and 1940s. Its rise was induced by, and contributed to, a boom in the automobile and appliance industries, which needed strong, good-looking sheet steel ductile enough to be stamped into auto bodies, refrigerators, toasters, and washing machines. His rolling mills made airborne radar possible in World War II and produced the material that formed the outer shell of the Apollo spacecraft. Today more than 90 percent of the world’s stainless steel is rolled on his mills.

We hope you enjoyed this essay.

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