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This model represents a part of the Altos Hornos de Vizcaya factory. These facilities were closest to Sestao, next to the Benedicta dock.
If we position ourselves on the side of the estuary, we find the area of solid bulk in the foreground on the left: ore and coal. Different cranes were used to unload them.
RAW MATERIALS:
IRON ORE, COAL, LIMESTONE AND HOT AIR
Three elements are necessary to feed the blast furnace: iron ore, fuel and flux.
The iron ore had to be prepared to get the maximum performance when it entered the furnace. To do this, the mineral that arrived in huge pieces had to be crushed, and the mineral that arrived in a very fine form had to be agglomerated, a process called sintering. The Sinter building is one of those we have in the part closest to the estuary.
The fuel (coal) also had to be prepared to achieve the highest calorific value. The mineral coal that arrived in ships had to be treated to obtain coke. First, it was ground, and then a homogeneous compact mass was formed that was placed in the batteries, subjected to a very high temperature, around 1,300ºC, and cooled with a jet of cold water. That water vapour made AHV look like a cloud factory when it was fully operational.
Coke was a molten mass, very hard and had a spongy appearance. As byproducts of this process, tar and ammonia were separated, which was obtained with ammonium sulfate and other solvents from the distillation of the tar. The Sefanitro company used these coke manufacturing byproducts as raw materials.
The flux, usually limestone, was responsible for the fusion of iron taking place at high temperatures. The flux reacted chemically with iron impurities called gangue, and slag was formed, which weighed less and floated on the molten iron.
The three products were lifted using carts up the skip (an inclined plane) to the highest part of the oven, the top, and from there, they were introduced into the blast oven.
In addition, hot air had to be injected at a specific pressure. This hot air was introduced into the oven from the external stoves through the nozzles.
PIG IRON AND SLAG
The crucible is the lowest part of the furnace. Two components arrived at the crucible: the liquid iron, called pig iron, and the slag (the non-metallic portion of the mineral, plus the flux and ashes). The pig iron weighed more than the slag, so it stayed in the bottom layer of the crucible, and the slag floated on top of the liquid iron.
Through a hole made in the lower part of the crucible of the furnace, called a cast iron spout, the liquid iron came out and was poured into tanks called spoons.
The slag was extracted through the slag pit and used to make cement and fertilizers.
The first smelted pig iron was collected in spoons, some of which were of large capacity called torpedoes due to their shape, which could carry more than two hundred and fifty tons and was taken to the steel mill.
If the pig iron was poured directly into ingot moulds and allowed to solidify, iron ingots were formed.
STEELWORKS
Liquid pig iron fresh from the furnace still had too much carbon and impurities, so it had to be refined into steel. It was taken to the converter or an electric arc furnace to be tuned. Its carbon content was adjusted, and impurities such as silicon or phosphorus were eliminated. In the converter, other alloying elements were added to obtain specific properties.
As for the impurities, the main ones were phosphorus and sulfur. Phosphorus gives steel hardness but makes it more brittle and, therefore, must be eliminated. Sulfur forms sulfides with iron and, if present in high quantities, produces defects when the steel is rolled.
The liquid mass contained in the converter was called the casting and was poured into a casting spoon.
TRANSFORMATION
The ingots were taken to the reheating ovens to begin rolling them. Once the ingot was heated, it received the shape following the rolling needs of the final product. The roughing mill was the one that made the sheets and plates.
The roughing was achieved by repeatedly passing the ingot in one direction and another between cylinders brought closer until they were flattened.
From there, all iron and steel manufactures are obtained.
- Single piece or welded profiles for railway tracks, rails, sleepers, sheets, bars, tubes and similar prepared for construction.
- Seamless hollow tubes and profiles used in oil pipelines for the extraction of oil or gas;
- welded or riveted tubes of circular section;
- cold rolled plates; construction materials, such as bridges, lock gates, towers, castles, pillars, columns, roofing frames, doors and windows.
- Cables, wires, metal fabrics, hardware, tanks, cisterns, vats, drums, cans, jars, boxes and containers of all types of products;
- chains, anchors, propellers; radiators, stoves, boilers;
- aircraft fuselage, ship hulls, car bodies, train cars, etc.
As a curiosity: It is estimated that blast furnaces were responsible for more than 4% of global greenhouse gas emissions between 1900 and 2015.
You can activate the screen on the left to get an idea of the steel manufacturing process. On the screen on the right, you can discover a joint work by the artist Alberto Salcedo and the filmmaker Itxaso Díaz that shows the dismantling of all these industries.
