Upstream of the fabrication shop
A fabrication shop begins with plate, bar, sheet and sections. Someone else made those. The plants that did are the primary metal industry, and they are some of the largest and most energy-intensive industrial sites there are. This article stays at a conceptual level: it describes what each stage does and the kind of equipment involved, not how to run or design it.
The main path has four stages: making liquid metal, refining it, casting it into a solid shape, and rolling or otherwise working it into a product. Details differ between plants and between metals, so treat this as a general outline rather than a description of any specific facility.
Making liquid metal
Steel is typically made by one of two broad routes.
From iron ore. Iron ore is first processed and then reduced to iron in a large furnace, using coke or another reducing agent as fuel and chemical partner. The resulting molten iron has more carbon than steel should, so it goes on for refining. Plants of this type are integrated sites with raw-material yards, conveyors, preparation plants and extensive gas handling.
From scrap. Scrap steel can be melted in an electric arc furnace, where electric current passing through electrodes produces intense heat. These furnaces are charged with scrap and sometimes other iron sources, then tapped when the melt is ready. They are often described as more flexible in output, though they use large amounts of electricity and need strong power supplies, switchgear and transformers.
Other metals follow their own routes. Aluminum, for example, is typically made by electrolysis from an intermediate material, then melted and cast. Copper and others have their own smelting and refining steps. The industrial furnaces involved share a common theme: they contain extreme temperatures, so their linings, cooling and combustion or power systems are major design concerns.
Refining and adjusting the melt
Raw melt from the first stage is rarely the final composition. Refining removes unwanted elements, adjusts carbon and adds alloying elements to reach a target grade. This happens in ladles and refining vessels, where gases may be blown through the metal, additives are dosed in and samples are taken for chemical analysis. The goal is a consistent, known composition before casting. Sampling and process control sensors play a big role, since temperature and chemistry both need monitoring.
Casting
Liquid metal has to be turned into a solid shape that can be worked.
- Continuous casting. In modern steelmaking, molten steel is poured from a ladle into a tundish, a reservoir that feeds a water-cooled mold. A solid shell forms at the mold wall, and the strand is drawn downward, cooled further by water sprays and cut into lengths. The results are typically called slabs, blooms or billets, depending on the cross-section. Continuous casting largely replaced older ingot casting in many plants because it is more efficient, though ingot casting still exists for some products.
- Foundry casting. Foundries pour metal into molds to make finished or near-finished shapes, such as engine blocks, valve bodies and pump casings. The molds can be sand, metal or other materials, depending on the part.
Casting depends on heat removal as much as on heat input. Industrial cooling systems supplying mold and spray water are therefore an essential part of the equipment.
Rolling and working
Cast slabs and billets are reheated in furnaces and passed through rolling mills.
- Hot rolling squeezes heated metal between large rolls to reduce thickness or change its shape. Different mill arrangements produce plate, coiled strip, bar, rod and structural sections such as beams.
- Cold rolling works the metal at or near room temperature after hot rolling, producing thinner, smoother sheet with tighter thickness control.
- Forging, drawing and extrusion are other ways of shaping metal. Forging presses and hammers produce strong shaped parts, drawing pulls wire and tube through dies, and metal extrusion pushes heated metal through a die to form profiles.
Rolling mills are enormous machines with powerful motors, gearboxes and hydraulic systems. Because strip moves fast and thickness tolerances are tight, rolling relies heavily on measurement and automatic control.
Heat treatment and finishing at the mill
Some products leave the mill after further processing. Heat treatment furnaces adjust hardness and toughness through controlled heating and cooling cycles. Coating lines may apply zinc or other layers for corrosion protection, and cutting lines slice coils into sheets or lengths. Final inspection checks dimensions, surface and, where applicable, chemical and mechanical properties.
Supporting equipment
Behind the main process sits a large support system:
- Material handling. Overhead cranes carry ladles and coils, and conveyors and rail systems move raw materials and products. Ladle handling in particular uses cranes designed and rated specifically for hot metal.
- Energy and heat recovery. Hot exhaust gases represent a lot of energy, and many plants use waste heat recovery to capture some of it. Combustion systems rely on burner and flame control equipment.
- Environmental control. Dust, fume and gas collection equipment cleans furnace exhaust, and water treatment handles cooling and process water.
- Electrical and automation systems. Large electrical supplies, drives and control systems run the line, with metalworking automation increasingly used to keep quality consistent.
How this connects to downstream shops
Fabricators and manufacturers receive product from these plants, often via service centers that cut and store stock. The grade and form chosen upstream affects how easily a shop can cut, bend or weld later, which is why drawings and purchase orders specify material grade. The hazards and upkeep demands of such plants are covered in a companion article on handling hot, heavy metal equipment.