Herald of Steel

Chapter 301 Bessemer Converter

The blast furnace was responsible for transforming iron ores into merchant iron, i.e- iron with 4% - 4.5% carbon, which was also called pig iron because the originally, the cooled large, central, and adjoining smaller ingots resembled a sow and suckling piglets

This pig iron had too much carbon content to be made into anything useful and so had to have its carbon content and other impurities reduced.

In the current timeline, this was done by repeatedly hammering the iron and thus literally beating the impurities out of it in the form of slag.

While in Alexander's previous time, the first industrial process of carbon removal was done by the puddling process, where workers called puddlers would use long oar-shaped tools to stir the molten iron like one would stir a pot of curry.

The molten liquid would thus slowly combine with oxygen and fly away as carbon dioxide, and carbon monoxide over many hours of slow cooking, while, as the carbon content decreased, the iron's melting point would increase, and so masses of iron would start to agglomerate and float to the surface.

These masses of iron would be removed such as one would remove scum from the side of pots when cooking some dishes, and this iron would finally be strong enough to be forged with hammers by blacksmiths into shapes such as swords and structural rods, or for making less loading structures such as manhole covers or decorative wrought gates.

In this way, usable iron was first mass-produced.

But though it was much faster than the traditional method, it was still very fuel and time-consuming, not to mention the toxic environment around the workplace it created.

In fact, it could be argued the toxicity of the environment around the pudding process was comparable to that of near Chornobyl.

This might sound excessive but the puddlers that worked in these factories were enormous men, fit, hale, and hearty, as very high strength was needed to stir molten iron, but these strapping men, all in their early twenties only lived on an average of three to five years after they started working in these puddle furnaces.

This was because every day they breathed in enormous amounts of toxic gases like carbon dioxide, carbon monoxide, and sulfur dioxide and it destroyed their lungs.

And that was where the Bessemer process came in, which did not make wrought iron, per se, but steel, otherwise known as mild steel. with a carbon content between 0.02 to 0.2%.

And this was what Alexander had also built.

Alexander's Bessemer converter was directly charged with molten iron from the blast furnace using a sloping channel that was covered on the top by a wooden shed to keep out the rain and snow, while also allowing workers access to it so that they would be able to fix problems such as the iron solidifying midway through the flowing process quickly.

Though this was never too big a problem as the flowing distance from the furnace to the converted was quite short and the 4 to 4.5% carbon in the pig iron helped to lower the melting temperature and make the molten iron quite runny.

He had designed the Bessemer converter in the traditional shape, as a pear-shaped furnace about 6m in height and 3m in diameter, made of concrete, with an inner lining of clay bricks to resist heat.

There were numerous small air holes at the base of the structure that allowed entry of hot blasts of air into the furnace by two giant blowers manually operated by strong men.

The reason for using human muscles was because there was no space to build the waterwheel and the accompanying aqueducts.

As soon as the molten iron would enter the converter, crushed limestone would be added using cranes to allow the removal of phosphorus.

This step was critical, as even amounts as small as 0.04% would increase the tendency of steel to become cold-short, that is, brittle at reduced temperatures, making weapons such as swords much weaker at room temperature.

Once the Bessemer converted had the two ingredients, hot continuous blasts of air, rich in oxygen would be pumped into the mixture and this would oxidize the impurities present in the pig iron, such as manganese silicate and silicon into their respective oxides, and form a thin layer of slag atop the iron.

The more volatile oxides such as carbon monoxide formed from carbon would get expelled out of the furnace in the form of a gas which would burn with a blue flame at the mouth of the converter.

At this point, as the blue flame would die down, signaling the end of that particular reaction, a measured mixture of iron craps, carbon, and manganese called spiegeleisen was supposed to be theoretically added to the mixture.

The reason why iron and carbon would need to be added was because the Bessemer process would eject too much carbon from the iron through the hot blasts of air, and thus some was needed to be added back.

This was because it was the carbon that gave iron its strength and without it, just pure iron would be a very soft, weak metal, one that could be bent just by bare hands and hence pretty useless.

And Alexander would add some molten pig iron right at the end to achieve this.

But while this could be easily added, the critical manganese could not.

The addition of manganese was critical to making steel because it reacted with the leftover oxygen in the molten steel to form an oxide that separated itself in the form of slag.

And unfortunately for Alexander, he was unable to find manganese, which looked very similar to iron ores but was quite brittle.

And this meant that his steel, once cooled, would have small, micro-voids of air bubbles, comprising the metal's strength and making it more brittle.

Of course, this was not as big a deal as one might make it up to be.

Such micro defects would only really matter once one started making huge structures like skyscrapers and ocean liners, while for small steel products such as swords, armor, and pots and pans, the things Alexander planned to make for the time being, it was negligible.

And thus Alexander had decided not to lose much sleep over it.

"Oh, finally we can see the final product," Menes impatiently called out as the group had waited for more than an hour to see this, from waiting for the blast furnace to be tapped, to finally the Bessemer process to be finished.

As soon as Menes pointed this out, the slag tapping hole at the top was first opened by the same process as in the blast furnace, and all the waste was let out into a large ladle, after which the lower tapping hole would be opened, letting the molten steel flow out to the sand ingot molds below.

Such a sequence was necessary because unlike in the blast furnace, the Bessemer converter was not kept full all the time, and as the converter had to be drained of all the products, if done the other way, the slag would come out mixed the steel and basically render the whole process moot.

It was also why Alexander had designed the large furnace with a bit of tilt, kind of like the leaning tower of Pisa, so that so molten iron or slag would remain there as leftovers.

Once the steel cooled a bit, these molds would be broken, the small strips of steel connecting the ingot cut out using chisels, loaded into horse carts to be then transported to workshops to be made into all kinds of weapons, armor, and tools.

"How much can we make in a day?" Menicus had a hard time keeping his emotion in place as he watched the enormous quantity of pure steel solidifying right in front of him.

Though he had heard it from Alexander himself, still, the amount of steel that was produced right before him was truly mind-boggling to him.

"About thirty-five tons a day. Give or take," Harun subconsciously produced a very smug look as he said so.

He too had a similar feeling of incredulity as Menicus, and in conjunction with the others, when he had first seen the volumes produced.

"*Shoooo*," Many of the people audibly sucked in air at this huge number.

"And how much does it cost?" Heliptos's very eagerly asked as his eyes seemed to have turned into gold coins and he was literally drooling at the thought these ingots could fetch, spraying small bubbles of spittle everywhere.

A kilogram of raw iron ingot cost one hundred to hundred fifty (100 - 150 ropals) ropals, while a slag-free ingot went for five hundred.

And if that iron ingot was worked on and transformed into a usable product like a sword, the price would literally jump ten times, as a good steel sword could cost anywhere from twelve hundred to fifteen hundred ropals (1,200 - 1,500 ropals).

This meant that the steel in a sword weighing 700 -800g, went for 2 ropals per gram, or the equivalent of one kg of wheat.

Harun felt numerous curious gazes as Heliptos made his inquiry and the mining chief then directed this gaze to Alexander because he himself had no idea of the price.

And fortunately for him, Alexander did.

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