Three-piece canisters have been used for nearly 200 years. Although it has been improved for many times, its basic composition is still the tank body, the bottom of the tank, the lid of the three metal plate (mostly for tinplate), so it is named “three-piece can”. The bottom and lid of a common three-piece can are identical in shape, size and manufacturing method, and are collectively referred to as the lid. There are two main sealing forms for the longitudinal seam of tank body: brazing and fusion welding. The former was used earlier but has been phased out due to lead in solder. The latter can avoid lead pollution, low energy consumption, less material consumption, but complex production equipment.
Three-piece can has the characteristics of good rigidity, can produce various shapes of cans, high material utilization rate, easy size change, mature production technology, packaging products variety and so on.
Two cans were introduced in the mid-20th century. The whole package can is composed of two parts: the tank body and the lid, so it is called the two-piece can. The tank body of the two pieces of cans is stretched and deformed by a metal sheet with a punch through a drawing die, so that the bottom and the tank body are integrated.
There are many kinds of two-piece tanks: depending on the height of the tank, there are shallow impact tanks and deep impact tanks; According to the canning material is divided into aluminum cans and iron cans; According to the manufacturing process can be divided into thin drawing pot and deep drawing cupping. Compared with three-piece cans, two-piece cans have the following advantages:
① Good sealing performance. The tank body is directly formed by stamping and drawing process, so there is no air leakage, and the leak detection process can be omitted.
② Ensure product quality. The two cans do not need to be sealed by welding, can avoid lead pollution of solder, high temperature sterilization resistance, can ensure product health.
③ Beautiful and generous. Tank body without seam, beautiful appearance, tank body can be continuously decorated printing, good effect.
High production efficiency. There are only two parts of the two pieces of tank. The simple manufacturing process of the tank is of great benefit to simplify the process and improve the production capacity.
⑤ Save raw materials. The wall thickness of the two-piece tank is thinner than that of the three-piece tank when the tank body is stretched and deformed during forming. In addition, the body of the two-piece tank is formed in one piece, without the longitudinal seam of the tank and the seam with the bottom of the tank, which also saves material.
However, the requirements for the material properties, canning technology and canning equipment are higher, and the types of filling materials are less.