As for the shed on the other side, it is used for coal washing.

Mainly through the impact of water flow, raw coal with different specific gravity is separated into different grades, and dust and waste rock are removed to reduce the ash and sulfur content.

However, the clean coal obtained in this way is not used directly, but is sent to the earth kiln behind the greenhouse for smoldering.

On the ground, there were rows of earthen kilns that looked like tombs, and from the brick chimneys, yellowish-brown smoke was slowly coming out.

The smoke was very choking, and it made people cry and cough from a distance.

Secretary Ma immediately put on a mask and goggles for the young master. Then she and the guards also protected themselves, which surprised Wang Yu.

Zhao Hao asked the guard to give him a set as well. Wang Yu put it on like him and immediately felt that his breathing was much smoother and his eyes stopped crying. He couldn't help but admire him again... He didn't like coming to the steel mill, largely because the smoke was too irritating.

Unexpectedly, Master Zhao already had a solution for this.

Wearing a mask, Uncle Wang was finally able to continue explaining to Mr. Zhao that the production of coke relies on the heat of the bituminous coal burning in the kiln. The coal is heated layer by layer, and after eight to ten days of smoldering, the coke is mature. Then water is injected to quench the coke, the furnace is cooled and the ash is removed, and the unburned part is the coke.

Although in Zhao Hao's opinion, this method is not only time-consuming and has a low coking rate, but the most fatal flaw is that the ash content is too high, which greatly reduces the effectiveness of coke. However, before the 01 Institute has developed a practical coking furnace, this is already the world's leading level.

It took more than 150 years for Europe to learn how to use coke to make steel.

He couldn't wait for the coke to come out of the kiln today, but Zhao Hao still went to the iron smelting furnace and saw a pile of dull, grayish-white fuel... That was the coke that had been refined before.

The cylindrical iron smelting furnace, which was more than one meter tall, had an inner wall made of clay mixed with salt that was more than a foot thick. It was fixed on the outside with a circle of solid logs driven into the wall, and then the entire furnace was tightly clamped with a wrought iron ring like a barrel hoop.

Wang Yu told Zhao Hao that it would take at least a month to build such a furnace, and he could not rush it. Otherwise, once cracks appeared in the salt mud, all the previous efforts would be wasted and it might even cause danger.

Such an iron smelting furnace can hold more than 2,000 kilograms of iron ore. Before ignition, a layer of coke is first spread in the furnace, followed by a layer of a mixture of ore sand and coal powder. After each layer is filled, ignition is started from the bottom to start smelting.

Next to the iron smelting furnace, there is a huge blower with two men wearing only calf-nose pants at each end, pushing and pulling it rhythmically to supply air to the iron smelting furnace.

The iron smelting master told Zhao Hao that after the ore inside was melted into molten iron, it would flow out from the waist hole of the iron smelting furnace. This hole was plugged with mud in advance. Every hour during the day, the mud plug would be poked open to let the molten iron flow out.

After the molten iron has flowed out, use a fork to pry the mud out immediately, plug the hole again, and continue blast smelting. After an hour, open the hole again to release the molten iron.

This method may seem less sophisticated than the crucible method, but in the crucible method, the ore and coke are not in contact, which makes the coke only act as a fuel, but not as a carburizing agent, reducing agent and material column.

On the contrary, this method of direct mixed calcination can bring out the four major functions of coke, and the quality of the steel produced will naturally be higher.

Zhao Hao stood far away, out of reach of the blazing fire, waiting for the next hole to be drilled.

Fortunately, although only a small number of Wang's steel mill's ironmaking furnaces were working, there were still a full ten of them. After a while, a hole was opened in one of the furnaces.

Although Zhao Hao was far away, he could still feel the burning heat of the fiery red molten iron. He watched the molten iron flow along the stone diversion channel into a square pond nearby.

Wang Yu told Mr. Zhao that the molten iron was pig iron. If pig iron was to be used for smelting, it could be poured into a mold and used directly after cooling. However, the quality of this pig ironware was too poor and not valuable, so Wang Ji never bothered to make it.

They also need to smelt pig iron into wrought iron in that pond.

The square pond was made in the same way as the iron smelting furnace, but it was only about one and a half feet high. A slightly higher platform was built with bricks next to it, and the iron smelting master and apprentice stood on the platform to operate, so as to prevent the molten iron from overflowing due to too much molten iron.

When the molten iron flows into the pond, the ironmaking master quickly sprinkles the prepared fine mud powder evenly on the surface of the molten iron.

"saute!"

When the master gave the order, several apprentices used willow sticks to stir the raw iron vigorously, frying it into wrought iron. Each time the willow stick was scorched, two or three inches would be burned off, and a new one had to be replaced when frying again.

This is the famous "steel frying method", which can oxidize the silicon, manganese and carbon in pig iron and reduce the carbon content to the level of steel or wrought iron. If the temperature can be raised by 200 to 300 degrees, the moment of witnessing miracles will come... Unfortunately, it is not possible at present.

"It's really worthy of its name to use latte as a dish." Mr. Zhao couldn't help but secretly admire it.

He knew that according to this method, the product would most likely be steel, and low-carbon steel at that. But in the eyes of the craftsmen at that time, the product of this step could only be called wrought iron.

In fact, it is the difference in definitions that causes this disagreement.

In Zhao Hao's concept, pig iron, steel, and wrought iron are all iron-carbon alloys. Pig iron is when the carbon content is over 2.11%, and wrought iron is when the carbon content is less than 0.02%. Steel is in between. Therefore, steel can also be divided into high carbon steel, medium carbon steel, and low carbon steel according to the carbon content... Anyway, as long as the carbon content is between pig iron and wrought iron, it is all steel.

But the craftsmen of the Ming Dynasty would never agree with Mr. Zhao’s hasty classification.

Yes, in the eyes of craftsmen in this era, "steel" is absolutely sacred. Only a small part of steel with few impurities and high hardness will be called "steel" and used on the blade. Anything that has not been tempered, whether it is low-carbon steel, medium-carbon steel, or even high-carbon steel, is all classified as wrought iron...

Therefore, Zhao Hao's First Five-Year Plan required an annual output of one ton of tool steel, which was not an easy goal.

Even for a large iron smelter like Wangji, more than 90% of its products are wrought iron products... Some are cast into various tools, weapons and armor. Some are directly cut into squares in the pond, and after cooling, they are taken out and hammered into round blocks and sold directly.

The 01 Institute purchased a large number of wrought iron billets produced by Wangji. The quality is naturally excellent, but it is still far from enough to make guns and cannons. However, it must be repeatedly forged and remelted to remove impurities before it can be used... It can be used to make guns, but the cost is too high to use it to make cannons.

Ultimately, less than 10% of high-quality wrought iron will be used to make "steel".