Disc Blades Spurred Steel Processes
Let's Talk Rusty Iron
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The author's 1946 Minneapolis-Moline ZTS and Roderick Lean disc harrow.
Sam Moore
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Not long ago, someone asked about the early history of disc harrows and, particularly, disc blades.
I’d never thought much about it but, upon reflection, it was obvious that disc harrow blades, along with rolling coulter blades, could hardly have been hammered out of wrought iron on a blacksmith’s anvil, nor could they have been cast from pig iron, the two most popular materials for making early implement parts. These circular blades had to be sharp enough to cut through trash and soil, which meant they had to be thin, and they had to be tough so they could withstand rocks, roots and other obstructions in the field. In other words, they had to be made from steel — and pretty good steel at that.
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Making steel affordable
In the early to mid-1800s, the problem faced by inventors and manufacturers of disc harrows and rolling coulters (and many other products) was the scarcity of such steel and, consequently, its high cost. An American, William Kelly (in about 1850), and an Englishman, Henry Bessemer (in 1856), discovered independently of each other a steel making process. The process (named for Bessemer because Kelly went broke in the panic of 1857) entailed making steel by blowing a steady blast of air through molten iron. The oxygen in that air caused the impurities in the iron (such as silicon, manganese and carbon) to burst into flame and burn away, leaving steel behind. By controlling the amount of carbon burned away, different grades of steel could be produced, although that wasn’t discovered until later.
In the 1860s, American steel makers produced less than 17,000 tons of steel per year. By 1880, after the Bessemer and other processes were developed, U.S. production was 10 times that, and continued to grow at an average of more than one million tons every year. Steel became plentiful and cheap, a factor that contributed greatly to the Industrial Revolution and to the fortunes of farm equipment manufacturers as well.
Evolution of the disc
Rolling coulters for plows seem to have been introduced in about 1840 and the few early patents I’ve found specify that the blade should be made of “steel saw plate” or “thin steel.” The dished blades found on disc harrows are tougher to pin down, but seem to have appeared toward the end of the Civil War. In his 1894 book, American Agricultural Implements, Robert Ardrey claims the Japanese used a tillage implement “from time immemorial” that had a row of straight, undished discs in a framework, but in those days Japan didn’t export its technology as the country does today.
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