Henry Bessemer's Bessemer converter is generally understood to be the technology that created the concept of industrial-scale steelmaking, but what constitutes "industrial-scale"? The Wikipedia page says that a Bessemer converter could process batches of 5 to 30 tons at a time, and that one stage of the process lasts 20 minutes, but that's as far as the information goes.

If I was a steelsmith in the 1860s with a single Bessemer converter (original model) and access to an unlimited amount of raw materials, how much steel could I make each day at a sustainable pace?

  • Skill mattered - cf. Capt. Bill Jones and John Fritz' mastery. Nov 3 '15 at 2:27
  • 1
    How much steel could a steel maker steal if a steel maker could steal steel?
    – Schwern
    Nov 5 '15 at 6:04

According to "Iron And Steel In 19th Century America: An Economic Inquiry" by Peter Temin, in 1867 a pamphlet claimed...

The cost of a plant with 2 three‑ton converters was given as $80,000; of a "five‑ton plant" with steam power, $125,000; and of first‑class apparatus with fireproof buildings and duplicate machinery making 50 tons of ingots in twenty‑four hours, $200,000. It cost only two‑thirds as much for a Bessemer plant as for a crucible steel, charcoal bloom, or puddled bar plant of the same capacity, the trustees asserted, and it took only 30 men to run a five‑ton Bessemer plant.

"The Albany and Rensselaer Iron and Steel Works, Troy, New York" by A. L. Holley is an excellent source. Holley licensed the technology from Bessemer and set up the Troy mill. His book, published in 1881, has extensive detail about the plant. It used three 7-ton vessels.

As the departments grew gradually and experimentally, and were not expected to exceed 60 tons of product per day, the buildings are not the size and arrangement that would now be made; but by means of convenient transporting apparatus, 400 tons of hot ingots per 24 hours are delivered by power into the blooming furnaces, and are rolled, cut up, and chipped, under a 7-ton hammer, and loaded hot on the rail mill cars with reasonable facility.


Two copulas running together can melt 500 tons per 24 hours.

I'm no steel maker, but from reading Holley's accounts it seems the limiting factor was not the size of the converter but many, many others. He spends very little time on the converters and much more on blowing engines, pressure pumps, boilers, blooming trains (whatever that is), power feeding tables...

Troy had three 7-ton vessels in a mill able to deliver (not just melt) 400 tons per day. A single vessel would likely be less efficient. For example, with three one could be melting, one pouring, and one being cleaned.

  • I think a bloom is a piece of iron or steel in the process of being rolled through a mill to make it longer with smaller cross-sectional area. If you process it through a series of machines to do this (rather than just moving it backwards and forwards through the same machine many times) then you have a blooming train.
    – Henry
    Jun 24 at 23:54

The use of the converter did not really ramp up until about 1867. In 1868, the best performing mill had two 5-ton converters that produced 500 tons per month combined. By 1876 various improvements and mastery of the process resulted in typical production for a single 5-ton converter at a good mill averaging around 3800 tons per month. The best mills are reputed to have done as much as 4200 tons per month in a single 5-ton converter.

Thus, by the mid-1870s good mills were doing 750 to 800 heats a month, or perhaps about 32 heats every work day. Note that the nominal 5-ton capacity of a converter could be exceeded by a good crew, so they might be doing heats of 5.5 tons or more.

At that time 5-ton converters were the norm. Giant 30-ton converters did not come until later. In 1877 there were two converters as large as 10 tons in Britain, and there were numerous 2 and 3 ton converters.


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