Metal cans are what we often call cans. The lid and body are produced separately and then assembled together. There are two kinds of materials for making cans: aluminum and tinplate. Because aluminum has a high recycling value, for environmental protection considerations, cans began to use aluminum in large quantities. The strong opponent of aluminum in the packaging industry comes from PET materials. PET materials can be made into strange shapes through injection molds, while aluminum is more difficult. But there is a big difference in price between the two. PET is affected by the price of oil, while aluminum can be recycled and reused, thereby reducing material costs. In recent years, Europe and the United States and other regions with active cans consumption have continuously increased the recovery of aluminum cans and aluminum packaging materials, which has also made aluminum cans rampant.
The advantages of this kind of metal can are obvious. It has very good airtightness and can withstand high internal pressure. It is very suitable for loading carbonated beverages, which only have a little requirement for pressure, air and acid resistance. For fruit and vegetable juice, organic acid is an important component that determines its taste, and it can show the unique aroma of fruit. The ratio of sugar to acid content in fruit and vegetable juice is an important factor affecting the taste, but organic acids are corrosive to a certain extent. In addition, the enzymes, vitamin C, pigments and other important ingredients in fruit and vegetable juices have certain requirements for light and temperature. However, the cans are made of tinplate three-piece cans and aluminum two-piece cans, and are also coated with epoxy phenolic paint (sometimes it is necessary to apply a layer of vinyl paint on the epoxy phenolic inner coating). In this way, The organic acids in fruit and vegetable juices are not a threat at all.
Metal cans are classified according to the manufacturing method; there are mainly three-piece cans and two-piece cans:
(1) Three-piece can
The application history of three-piece cans has been nearly 200 years. Although it has been improved many times, its basic composition is still made of three metal sheets (mostly tinplate) of the can body, bottom and lid, hence the name "three-piece can". The shape, size and manufacturing method of the bottom and lid of the ordinary three-piece can are exactly the same, and they are collectively referred to as the lid. There are two main sealing forms for the longitudinal seam of the can body: soldering and fusion welding. The former was used earlier, but due to the lead in the solder, it has been eliminated; the latter can avoid lead pollution, low energy consumption, and low material consumption. , But the production equipment is complicated.
The three-piece can has good rigidity, can produce cans of various shapes, high material utilization rate, easy to change size, mature production technology, and many types of packaging products.
(2) Two-piece can
The two-piece jar was introduced in the middle of the 20th century. The whole packaging can is composed of two pieces, namely the can body and the can lid, so it is called a two-piece can. The can body of the two-piece can is made of a thin metal plate, which is stretched and deformed by a punch through a stretch forming die, so that the can bottom and can body are connected into one body.
There are many types of can bodies for two-piece cans: according to the height of the can, it is divided into shallow cans and deep-drawn cans; according to canning materials, divided into aluminum cans and iron cans; according to manufacturing technology, divided into DWI cans and DR cans. Compared with the three-piece can, the two-piece can has the following advantages:
①Good airtightness. The can body is directly formed by the punching process, no leakage, and the leak detection process can be avoided.
②Ensure product quality. The two-piece cans do not need to be welded and sealed to avoid lead contamination of the solder cans, and are resistant to high temperature sterilization, which can ensure product hygiene.
③Beautiful and generous. The can body has no joints, beautiful appearance, and the can body can be continuously decorated and printed with good effect.
④High production efficiency. The two-piece can has only two parts, and the can body manufacturing process is simple, which is of great benefit to simplifying the process and improving the production capacity.
⑤Save raw materials. The body of the two-piece can is stretched and deformed when it is formed, and the wall thickness is thinner than that of the three-piece can; in addition, the body of the two-piece can is integrally formed without the can body longitudinal seam and the seam with the can bottom, which also saves material.
However, two-piece cans have higher requirements on material performance, can-making technology, can-making equipment, etc., and there are fewer types of filling materials.
The metal cans currently used for packaging are mainly aluminum two-piece cans. Aluminum two-piece cans use aluminum alloy thin plates as materials, and a thinning and stretching process is used in the manufacturing process, so the thickness of the can wall is significantly thinner than the bottom of the can. When used in beer packaging, strong internal pressure will compensate for the rigidity of the thin tank wall. However, the high gas barrier, light-shielding and sealing properties of metal cans will keep the quality of beer in the cans stable.
It is also the existence of these metal characteristics that make the metal cans can be filled at high speed even with the time-consuming filling method of equal pressure filling.