Metal cans for canned food
Metal containers can be tin, aluminum, from chrome and aluminized tin.
Metal cans for canning are manufactured in two types: I - failures and II - solid ones. Type I banks come in a round and rectangular section, and Type II banks come in a round and shape section (rectangular, oval, elliptical). The list and characteristics of the most commonly used metal cans of circular cross section are given in Table.
The material for the production of tin cans is white tin, which is a thin-rolled steel with a thickness of 0.18–0.36 mm, covered on both sides with a protective layer of tin. Depending on the method of applying a protective tin coating, the tinplate is available in two types: hot and electrolytic tinning.
In hot-dip tinning, a suitably prepared tin is passed through a molten tin bath. In this case, it is not possible to obtain a thin (less than 1.5 μm), adjustable and uniformly over the entire surface of the sheet a layer of tin.The loss of tin during the hot tinning process is significant. Put tin in the hot way on rather unproductive units.
Electrolytic tin plating is carried out on highly mechanized, high-speed units of high productivity. The thickness of the tin coating with this method of tinning can be drastically reduced to 0.6 μm, thus achieving significant savings of tin (2.5 times compared with hot tinning).
Many canned foods have a strong aggressive effect on the tin coating, especially if it is applied electrolytically. Therefore, the tinplate has to be varnished internally. To protect the outer side of the metal container from atmospheric corrosion and to give the container a good tovaya look, its walls are coated with varnishes and paints.
Crash cylindrical can consists of three parts: the lid, body and bottom. The lid and bottom, which are exactly the same in construction and are called ends, are attached to the flanged (i.e. with bent edges) cylindrical body by means of a seam sealing. As can be seen from the figure (Fig.6), the seam consists of five layers of tin, two of which give a flanged body, and three - a cover.
The tightness of the seaming seam is ensured not only by a tight compression of the said layers of tin, but also by the presence of a sealing material - water-ammonia paste with various fillers, which is in the form of a thin elastic film on the channel of the twisted flange and tightly filling the gap between the layers of tin. Without a sealing material, even with a very strong compression of the layers of tin, the seam is permeable to air.
The can body is formed after rolling a rectangular tin plate into the cylinder, on which the edges are pre-bent, and then riveting them “into the lock”. The resulting seam, called the longitudinal one, is sealed with tin-lead solder. Thus, the longitudinal seam consists of four layers of tin (except for the edges, where there are only two layers, which also give four layers when bent). Consequently, the junction of the longitudinal seam with the seam (a hook called Ugloshov) consists of seven layers of tin: four gives a body and three covers.
The ends of the cans are stamped, and to give them elasticity,facilitate swelling during sterilization and landing in the original position after cooling, they make a special relief in the form of concentric circles.
Connect the case with the ends of the seamers. The seam is formed in two steps with seaming rollers. First, the zakatochny roller of the first operation preliminarily bends the ends of the ends under the bent flange of the body, and then the roller of the second operation presses together all 5 (or 7) layers of tin and finally forms a double zakatochny seam.
Along with the tinning of electrolytic tinning, new materials for canning metal containers have recently been introduced. These include chrome lacquered sheet metal, aluminum and its alloys, aluminized varnished tin.
Especially promising is the use for the manufacture of aluminum canning in combination with lacquer coating. Aluminum is characterized by high plasticity, lightness, harmless to the body. Also has the prospect of aluminized tin. It is obtained by depositing an aluminum layer with a thickness of 1–5 microns for rolling steel strip.
Tubes are made of 4–5 mm thick aluminum sheet for filling pasty canned products, mainly for feeding children, as well as cosmonauts.Tubes are filled from the side of the tail, which is then sealed. The tightness of the tail seams is ensured by sealing gaskets, and the tip of the tube is sealed with a metal film. The inner surface of the aluminum tubes is lacquered with food lacquers, colorful labels are printed on the outside.
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