If the thickness is reduced from 0.22mm to 0.16mm and the same cold-rolled ordinary quenched and tempered material is still used, the strength will be significantly insufficient. A more reasonable approach is to use two-stage cold rolling (DR) and high-purity high-strength base material.
1. The secondary cold rolling DR series replaces thick with thin
Electrolytic tinplate is categorized based on its tempering degree into primary cold-rolled grades T1-T6 and secondary cold-rolled grades DR8, DR9, and DR9M. DR8 has a tensile strength of approximately 550MPa, while DR9 has a tensile strength of approximately 620MPa. They are suitable for round can bodies and bottom covers. DR9M, with even higher tensile strength, is commonly used for beer and carbonated beverage bottom covers. When substituting DR material for thick primary cold-rolled material in the same can type, it is possible to reduce the thickness of the base plate while maintaining its rigidity. For can bodies with a thickness of 0.16mm, DR8/DR9 are preferred over other grades, rather than following the misconception that "the harder, the better" - too hard can lead to cracking during deep drawing, while too soft can cause bulging during stacking after thinning.
2. High nitrogen, high purity, narrow composition substrate
Extremely thin tinplate is more sensitive to inclusions. In public cases, 0.17mm tinplate is supplied to TULC for further stretching and canning. Steel mills achieve stable forming of extremely thin plates by reducing inclusions. Domestic high-nitrogen tinplate adopts composition designs such as nitrogen enrichment and boron addition to improve strength while retaining deep drawing and extension, which is used for DRD can thinning. For mass production of 0.16mm tinplate, it is necessary to include steel purity, inclusion level, thickness tolerance, and hardness uniformity in the procurement specifications, rather than just writing "tinplate 0.16mm".
3. Thickness tolerance and hardness of the same coil
Any thickness fluctuation after thinning will be magnified. The iron hammer controls the tolerance of the entire coil according to the high-speed can-making requirements, to avoid hardness differences at the beginning and end of the same coil, which may lead to a batch of soft cans or a batch of cracked cans. For food cans, the control idea of adjusting the degree of fluctuation can be referenced, and incoming re-inspection can be conducted in accordance with GB/T 2520.
