A method of continuously casting thin strip by controlling roll crown comprising the steps of: a. assembling a caster having a pair of counter rotating casting rolls with a nip there between capable of delivering cast strip downwardly from the nip, each casting roll having a casting surface formed by a cylindrical tube having thickness of no more than 80 millimeters of a material selected from the group consisting of copper and copper alloy, optionally with a metal or metal alloy coating thereon, and having a plurality of longitudinal water flow passages extending through the cylindrical tube; b. positioning at least two expansion rings within and adjacent the cylindrical tube and spaced within 450 mm of edge portions of the cast strip formed on opposite end portions of the casting rolls during a casting campaign, and/or positioning at least one expansion ring within the cylindrical tube corresponding to center portions of the cast strip formed on the casting rolls during casting, each expansion ring having at least one heating element and an insulating coating of at least 0.25mm (0.010 inches), with the insulating coating being such that when the cylindrical tube is cooled with the longitudinal water flow passages and the heating element operated, one said expansion ring with an insulating coating of 0.64mm (0.025 inches) is capable of achieving a temperature difference relative to the cylindrical tube at least 67% greater than a temperature difference that a similar but uncoated expansion ring could achieve under similar operating conditions; c. assembling a metal delivery system capable of forming a casting pool supported on the casting surfaces of the casting rolls above the nip with side dams adjacent to the ends of the nip to confine the casting pool; and d. controlling the radial dimension of the expansion rings responsive to at least one of digital or analogous signal received from at least one sensor to control the roll crown of the casting surfaces of the casting rolls during the casting campaign. a. assembling a caster having a pair of counter rotating casting rolls with a nip there between capable of delivering cast strip downwardly from the nip, each casting roll having a casting surface formed by a cylindrical tube having thickness of no more than 80 millimeters of a material selected from the group consisting of copper and copper alloy, optionally with a metal or metal alloy coating thereon, and having a plurality of longitudinal water flow passages extending through the cylindrical tube; b. positioning at least two expansion rings within and adjacent the cylindrical tube and spaced within 450 mm of edge portions of the cast strip formed on opposite end portions of the casting rolls during a casting campaign, and/or positioning at least one expansion ring within the cylindrical tube corresponding to center portions of the cast strip formed on the casting rolls during casting, each expansion ring having at least one heating element and an insulating coating of at least 0.25mm (0.010 inches), with the insulating coating being such that when the cylindrical tube is cooled with the longitudinal water flow passages and the heating element operated, one said expansion ring with an insulating coating of 0.64mm (0.025 inches) is capable of achieving a temperature difference relative to the cylindrical tube at least 67% greater than a temperature difference that a similar but uncoated expansion ring could achieve under similar operating conditions; c. assembling a metal delivery system capable of forming a casting pool supported on the casting surfaces of the casting rolls above the nip with side dams adjacent to the ends of the nip to confine the casting pool; and d. controlling the radial dimension of the expansion rings responsive to at least one of digital or analogous signal received from at least one sensor to control the roll crown of the casting surfaces of the casting rolls during the casting campaign.