Select Committee on Welsh Affairs Minutes of Evidence

Annex 2


Sinter  An iron rich clinker formed by heating iron ore fines and coke in a sinter line.

Ironmaking  Production of molten iron in a blast furnace from iron ore, sinter, coke and limestone. The furnace generates great heat using blasts of super heated air. The molten metal is about 95 per cent pure iron with 5 per cent carbon and other elements and is known as hot metal.

Steelmaking  The conversion of hot metal to steel in a converter using a process known as basic oxygen steel making (BOS). A water-cooled lance is lowered into the vessel and high purity oxygen is blown onto the metal to remove carbon and other unwanted elements. Fluxing agents are added during the blow and alloying elements are added, in various forms of secondary treatment, to adjust the chemistry of the steel.

Slab Casting  The production of slabs from liquid steel by a continuous casting process. Continuous casting is a technique in which the molten steel is channelled through a water-cooled mould. The metal that has begun to solidify on the outside is led through water sprays and between rolls to be cut into lengths of slabs. Generally a slab thickness of 250 mm is used.

Hot Rolling  The hot mill comprises four stages:

    (i)   a slab re-heating furnace is used to bring the slabs up to about 1300 degrees C.

    (ii)   the slabs are descaled and passed through a roughing mill to reduce the thickness to about 25 mm.

    (iii)  the partially finished strip goes straight onto the finishing section of the hot mill where it passes through series of rolls (seven sets in tandem) for further reduction in thickness generally between two and 12 mm although greater thicknesses are produced for some applications

    (iv)  the strip then passes through water sprays and onto a coiler.

Pickling  Before coils can be further processed, the scale formed during hot rolling is removed by treatment with dilute sulphuric or hydrochloric acid. This is done in a continuous line with the hot rolled strip being uncoiled and then passed in succession through acid baths, water tanks and drying ovens.

Cold Rolling  The pickled coil passes into a cold rolling mill where the gauge is further reduced to generally between 0.15-2.0 mm. The cold mills typically have five stands in tandem.

Annealing  Cold rolling makes the metal hard and springing and this hardness must be removed. Annealing is carried out by heating the coils to about 700 degrees C, keeping them at this temperature for a prescribed time and then slow cooling. To prevent oxidation control of the atmosphere in the annealing furnaces is necessary. Two types of annealing are common—continuous annealing and batch annealing.

Temper Rolling  A small reduction of up to 1 per cent is necessary to impart mechanical properties on the final cold roll strip. Using rolls of appropriate surface roughness also give the required surface finish at this point.

Metallic Coating  A metallic coating is put onto steel to improve corrosion resistance. Two processes are involved; either hot dipped coatings which are generally zinc or aluminium, or electrolytic coatings which are usually tin, zinc or a nickel zinc alloy.

Hot Dipped Galvanised (HDG) Coating  The hot dipped process involves a continuous line which processes cold rolled unannealed strip by heating it to about 700 degrees C, passing it through a bath of liquid zinc followed by a controlled cooling process. An induction heating process after coating can be employed to produce a galvannealed or iron zinc (IZ) product used principally in the automotive sector.

Aluminised Strip  Similar to HDG strip but using a bath of liquid aluminium.

Tinplate  Low carbon cold rolled and annealed strip coated with a thin layer of tin by electrolytic deposition in a tinning line.

Electro Chrome Coated Steel (ECCS)  Also called TFS (Tin Free Steel), low carbon mild steel coated on both surfaces with metallic chromium and chromium oxide applied by electrolytic deposition.

Ferrolite  Very thin cold rolled strip (usually ECCS) laminated with an organic film coating.

Electrogalvanised Coating  Annealed cold rolled strip is coated by electrolytic deposition on a continuous line which cleans the strip, coats it by passing through a number of electrolytic cells before the final strip is dried and coiled. Electrogalvanised coatings are either pure zinc or can involve an alloy of nickel and zinc.

Prepainted or Prefinished Strip  Two principal products are available. Colorcoat coatings are applied in liquid paint form whereas Stelvetite is a film coating laminated to the steel using an adhesive. A variety of coatings are available using different paint types and are generally applied to HDG coils but can also be applied to uncoated CR or electrogalvanised coils.

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