51 101 ME 4563 Fall ’05 Dr. S. Haran • • Advantages Advantages – – Deformations of ~ 50 to 80% Deformations of ~ 50 to 80% – – Work hardening increases strength Work hardening increases strength – – Excellent surface finish Excellent surface finish – – Excellent tolerance on thickness and shape Excellent tolerance on thickness and shape • • Disadvantages Disadvantages – – High forces High forces – – Small reductions give rise to surface stresses and Small reductions give rise to surface stresses and non non - - uniform stress distributions uniform stress distributions – – ? ? Cold Rolling Cold Rolling 102 ME 4563 Fall ’05 Dr. S. Haran • • Input and output coils with tensioning control Input and output coils with tensioning control • • Shape meters consisting of segmented coils Shape meters consisting of segmented coils measuring force measuring force • • Tandem mills allow multiple reductions in one Tandem mills allow multiple reductions in one operation operation • • Laser inspection systems for surface finish inspection Laser inspection systems for surface finish inspection becoming popular (especially for canstock) becoming popular (especially for canstock) • • Surface condition of rolls critical to maintain surface Surface condition of rolls critical to maintain surface finish finish • • Roll bending almost essential to provide crown Roll bending almost essential to provide crown control control Cold Rolling Mill Design Cold Rolling Mill Design 52 103 ME 4563 Fall ’05 Dr. S. Haran Cold Rolling Cold Rolling - - Schematic Schematic Cold Rolling Cold Rolling 104 ME 4563 Fall ’05 Dr. S. Haran   Cold rolled sheet can be produced in various conditions Cold rolled sheet can be produced in various conditions such as such as skin skin - - rolled rolled , quarter hard, half hard, full hard , quarter hard, half hard, full hard depending on how much cold work has been performed. depending on how much cold work has been performed.   This cold working (hardness) is often called This cold working (hardness) is often called temper temper   In In Skin Rolling Skin Rolling , the metal is reduced by 0.5 to 1% and , the metal is reduced by 0.5 to 1% and results in a surface that is smooth and the yield point results in a surface that is smooth and the yield point phenomenon phenomenon excessive stretching and wrinkling in excessive stretching and wrinkling in subsequent operations, is eliminated. subsequent operations, is eliminated.   This makes the metal more ductile for further forming This makes the metal more ductile for further forming and stretching operations and stretching operations Cold Rolling Cold Rolling 53 105 ME 4563 Fall ’05 Dr. S. Haran   Quarter Hard, Half Hard, Full Hard Quarter Hard, Half Hard, Full Hard stock have higher stock have higher amounts of reduction, amounts of reduction, upto upto 50%. 50%.   This increases the yield point; grain orientation and This increases the yield point; grain orientation and material properties assume different properties along the material properties assume different properties along the grain orientation. grain orientation.   However, while the yield point increases, ductility However, while the yield point increases, ductility decreases decreases   Quarter Hard Quarter Hard material can be bent (perpendicular to the material can be bent (perpendicular to the direction of rolling) on itself without fracturing. direction of rolling) on itself without fracturing. Half hard Half hard material can be bent 90 material can be bent 90 º º ; ; Full hard Full hard can be bent 45 can be bent 45 º º . .   Thus, these materials can be used for in applications Thus, these materials can be used for in applications involving great amounts of bending and deformation, involving great amounts of bending and deformation, without fracturing without fracturing Cold Rolling Cold Rolling 106 ME 4563 Fall ’05 Dr. S. Haran   Another form of cold processing is cold drawing Another form of cold processing is cold drawing   Steel rod is dragged at pressure (drawn) through a series Steel rod is dragged at pressure (drawn) through a series of dies which progressively reduce the rod's circumference to of dies which progressively reduce the rod's circumference to produce wire produce wire   The drawing process substantially increases the steel's The drawing process substantially increases the steel's tensile strength tensile strength   Steel wires can be spun into huge ropes strong enough to Steel wires can be spun into huge ropes strong enough to support the world's largest suspension bridges support the world's largest suspension bridges Cold Drawing Cold Drawing Cold Rolling Cold Rolling 54 107 ME 4563 Fall ’05 Dr. S. Haran Cold rolling Mill Cold rolling Mill Cold Rolling Cold Rolling 108 ME 4563 Fall ’05 Dr. S. Haran Cold rolling Mill Cold rolling Mill Cold Rolling Cold Rolling 55 109 ME 4563 Fall ’05 Dr. S. Haran Cold Rolling Cold Rolling Cold Rolling Cold Rolling 110 ME 4563 Fall ’05 Dr. S. Haran Cold rolled coil being Cold rolled coil being split into narrow strips split into narrow strips Cold rolled coils Cold rolled coils Cold Rolling Cold Rolling 56 111 ME 4563 Fall ’05 Dr. S. Haran Al Sheet being rolled out Rolling Aluminum Rolling Aluminum 112 ME 4563 Fall ’05 Dr. S. Haran Al Foil Roll Al Foil Roll Rolling Aluminum Rolling Aluminum 57 113 ME 4563 Fall ’05 Dr. S. Haran Independent Variables for Rolling Independent Variables for Rolling For a given rolling set For a given rolling set - - up: up: • • Roll speed Roll speed • • Draft (amount of thickness reduction) or roll gap Draft (amount of thickness reduction) or roll gap • • Billet thickness Billet thickness • • Billet width Billet width • • Billet material (not always allowed to select) Billet material (not always allowed to select) • • Billet temperature Billet temperature • • Lubricant Lubricant 114 ME 4563 Fall ’05 Dr. S. Haran For a given rolling set For a given rolling set - - up: up: • • Roll force Roll force • • Power Power • • Speed of exiting strip Speed of exiting strip • • Final strip temperature Final strip temperature • • Maximum draft Maximum draft • • Roll strip contact length Roll strip contact length • • Sheet or plate shape Sheet or plate shape Dependent Variables for Rolling Dependent Variables for Rolling 58 115 ME 4563 Fall ’05 Dr. S. Haran Control of Overall Properties Control of Overall Properties • • Thickness Thickness – – Roll gap which impacts roll force and hence the dimensions Roll gap which impacts roll force and hence the dimensions of the mill frame of the mill frame • • Width Width (due to spreading of slab) (due to spreading of slab) – – Edge rollers (push material back) Edge rollers (push material back) – – Edge shears (cut material off) Edge shears (cut material off) • • Length Length – – End shears End shears • • Mechanical Properties Mechanical Properties – – Controlled by the microstructures which is controlled by the Controlled by the microstructures which is controlled by the rolling parameters (reduction, temperature, etc) rolling parameters (reduction, temperature, etc) 116 ME 4563 Fall ’05 Dr. S. Haran • • Tolerance Tolerance – – Thickness Thickness • • Operator skill/automation Operator skill/automation – – Gauges measure thickness Gauges measure thickness of input and output of input and output – – Computers control roll gap Computers control roll gap – – Camber Camber • • Roll bending/automation Roll bending/automation – – Special segmented tension Special segmented tension meters measure "shape" meters measure "shape" – – Computers bend the rolls Computers bend the rolls • • Surface finish Surface finish – – Roll finish Roll finish Bearing reaction forces Applied forces Control of Overall Properties Control of Overall Properties . coils Cold rolled coils Cold Rolling Cold Rolling 56 111 ME 4 563 Fall ’05 Dr. S. Haran Al Sheet being rolled out Rolling Aluminum Rolling Aluminum 112 ME 4 563 Fall ’05 Dr. S. Haran Al Foil Roll Al Foil. bending and deformation, without fracturing without fracturing Cold Rolling Cold Rolling 1 06 ME 4 563 Fall ’05 Dr. S. Haran   Another form of cold processing is cold drawing Another form of. Drawing Cold Drawing Cold Rolling Cold Rolling 54 107 ME 4 563 Fall ’05 Dr. S. Haran Cold rolling Mill Cold rolling Mill Cold Rolling Cold Rolling 108 ME 4 563 Fall ’05 Dr. S. Haran Cold rolling Mill Cold