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　　Cold rolling of cold rolled strip, instead of smooth rolling, is a method of producing thinner and higher strength tin plated (plate) strip. The two cold rolling is a kind of process with cold rolling and leveling. It has a larger deformation degree, and the reduction rate is generally in the range of 30% ~ 50%.
　　Two cold rolling thickness than the conventional production of thin (up to 0.14mm), due to work hardening, improve the strength but still maintain sufficient ductility, can save metal materials can be used, so it is called material economy. The properties of the two cold rolled strip are obviously directional, so the products are marked with grain orientation. The tin plate (called DR tin plate) made by this type of film should be paid attention to in the process of drawing. The two cold rolled plate mainly has the following two varieties: tensile strength of 750MPa, mainly used as beverage cans box body; tensile strength of 680MPa, usually used as the bottom and cover of tin cans.
　　In the past, in order to produce a thinner tin plate with higher strength and proper formability, the two cold rolling was first used in industry and promoted gradually. The mills used are single frame, double frame, three frame, even five rack, and the most universal is double rack.
　　Double frame two times cold rolling mill, usually the first main deformation, take the total reduction of 90%, second main smooth function, take 10%. In this way, the deformation is guaranteed and the shape and surface quality are guaranteed. The total reduction shall be based on the requirements of the product standards and hardness (strength). When the required hardness is high, the amount shall be lowered accordingly (i.e., a larger part of the initial cold rolling). But as a tin box body material, the maximum amount of press shall not be greater than 32%; and as the bottom material of tin cans, the maximum shall not be greater than 38%. Otherwise, the hardness is too high and the plasticity decreases. The most effective lubricant must be used in the two roll mill when the ratio of working roll diameter to strip thickness is large. The rolling and cooling water is used only for the first frame, while the second is for dry operation. The two time cold rolling mill sometimes adopts prestressed frame, adopts tension measuring instrument, rolling force load sensor, thickness gauge and thickness automatic control system, and shape monitoring and control system.