(a) What is the difference between sheet and strip? (b) What are the characteristics of cold rolled sheets ?
(c) What do you understand, by (i) orange-peel effect, (ii) stretcher strains or Luders' lines ?
(d) Define (i) temper rolling, and (ii) aging in steel.
(a) The difference between sheet and strip is based on width and is arbitrary.
(b) Cold working produces a better surface finish, improves the mechanical properties, and permits the rolling of thinner gauge material than hot rolling.
(c) (i) Sheets for deep-drawing applications must be dead soft to have maximum amount of plasticity. These must also have a relatively fine grain size, because a large grain size causes a rough finish, an "orangepeel" effect, on the deep drawn components,
(ii) Usually low-carbon steel has sharp yield point characteristic which results in sudden local elongation in sheet during forming, which results in strain markings called stretcher strains of Luders' lines. This characteristic must be eliminated.
(d) (i) The sharp yield point characteristic of low carbon steel can be eliminated by cold rolling (resulting in 1% reduction of thickness), known as temper rolling, followed by alternate bending and reverse bending in a roller leveller.
(ii) An important phenomenon of the temper-rolled low-carbon sheets is the return of the sharp yield point after a period of time, known as aging in steel.