Tinplate cans

In most of its uses, e.g. the external surfaces of tinplate cans, tinned steel has only to resist condensed moisture. In the absence of pollution of the atmosphere by unusually large amounts of sulphur dioxide or chlorides, or of several days of continuous wetting, tinned steel remains unrusted even the thin porous coatings on the common grades of tinplate remain bright and unmarked over the periods involved in the commercial handling and domestic storage of cans, and the domestic use of kitchenware. When... 

The oil film present on both types of tinplate and on newly hot-dipped tinware has a slight protective value. The passivation processes have much more effect but this is unlikely to compensate for a substantial reduction in coating weight. The effects of oil and passivation on the outside of tinplate cans may be reduced during can manufacture, filling and sterilisation. 

In plain tinplate cans for acid foods, tin provides cathodic protection to steel (3,4). The slow dissolution of tin prevents steel corrosion. Many investigators (5-1I) have defined this mechanism in detail and have shown that the tin dissolution rate is a function of the cathodic activity of the base steel, the steel area exposed through the tin and the tin-iron alloy layers, and the stannous ion concentration. Kamm et al. showed that control of the growth of the tin—iron alloy layer provides a nearly continuous tin-iron alloy layer and improves the corrosion resistance of heavily coated (over 45 X 10"6 in. tin) ETP for mildly acid food products in which tin provides cathodic protection to steel (12). The controlled tin-iron alloy layer reduces the area of steel exposed to the product. ETP with the controlled alloy is designated type K, and since 1964, 75 type K ETP has been used to provide the same protection as 100 ETP provided previously (13). 

Tinplate can be purchased in a wide range of tempers and thicknesses. Currently 17 different basis weights are available commercially, from 55 /BB (pounds per base box or 217.78 ft2) to 135 /BB. These weights range in nominal thickness from 6.1 to 14.9 mils. 

While each container manufacturer has developed proprietary tests, most are based on electrochemical techniques. Corrosion in enameled ETP or TFS cans can be evaluated using one of the available procedures (28, 29, 30). Corrosion performance of plain tinplate cans can be estimated using the Progressive ATC Test developed by Kamm (6, 7). These tests should speed the development of new containers. 

Drawn and Ironed Steel Cans. Drawing and ironing grew out of the drawing process. Figure 7 depicts D I cans for foods. The drawn and ironed tinplate can is usually produced by drawing a cup from a coil of lubricated matte tinplate. 

At first, the program which investigated the packaging of irradiation-- processed foods, concentrated on the most advanced type of container, the tinplate can. It had performed successfully for a century as a container for thermoprocessed foods. However, as a container for the irradiation-processed foods, its physical, chemical, and protective characteristics had to be evaluated, including the effects of radiation on enamels and end-sealing compounds. This container was satisfactory for packaging foods that were irradiation sterilized while unfrozen (1, 2). 

Meat Products. Laboratory investigations as well as practical experience have shown that aluminum containers do not cause the objectionable darkening of meat that occurs with other metals. Wunsche (13) found that luncheon meat stored in lacquered aluminum cans retained its normal color after more than one year, while a slight surface discoloration was observed on the same product packed in lacquered tinplate cans. 

Foods such as meat, fish, and some vegetables contain sulfur-bearing amino acids that form volatile sulfur compounds during processing and storage. When these compounds react with iron, a black precipitate forms on the container and in most instances darkens the food. A small piece of aluminum welded to the tinplate can has been used to prevent container corrosion and sulfide staining in commercially canned hams. In this case, the aluminum acts as a sacrificial anode and stops the reaction with tin and iron that otherwise could occur at the small exposed tinplate areas (14). 

Beer. Laboratory results obtained by Jimenez and Gauldin (19) as well as commercial experience have shown that beer in aluminum cans is superior in flavor, color, and clarity to beer packed in tinplate cans. Table V summarizes the effect of aluminum and iron on beer stored for six months in the two types of metal containers. Aluminum ends used in conjunction with tinplate or tin-free-steel can bodies increases the shelf... 

It is a technique suitable for automatic equipment since there is no contact between the heating device and the materials to be sealed, there are none of the problems of sticking that can arise with sealing dies or electrodes. On modern machines, even with relatively thick-walled sections, sealing times can be as little as a fraction of a second. The method is ideal for work in which thermoplastics and metal components have to be joined—as in the assembly of medical syringes and the sealing of tinplate cans. 

Mineral and carbonated drink bottles Caps for bottles and aerosols Carboys for industrial chemicals Coatings for tinplate cans Bottle crates Tote boxes... 

Both tinplate and aluminium sheet may be used to produce shallow drawn containers, the choice depending on cost versus product resistance. Dry products and nonaqueous creams are usually satisfactory in tinplate, whereas aqueous creams are better packed in aluminium. Alternatively, lacquered tinplate can be used for aqueous creams but there is always a chance of corrosion at any raw edges. Tinplate is stronger than aluminium for a given thickness. 

Three-piece aerosol cans are constructed by seaming a cone onto the body of a twopiece built-up tinplate can. The can itself is constructed in a similar way to an open top can but with a strengthened locked and lapped side seam so that it will withstand internal pressure. The base of the container is domed upwards for the same reason and is invariably compound-lined and double seamed onto the side wall. 

Built-up metal containers are used for the storage and transport of a wide range of bulk chemicals, e.g. dry powders and liquid. Although the heavier gauges of tinplate can be used for containers of up to about 5 gallons capacity, from this size upwards steel is invariably used. 

Aerosols differ from other packs partly because they are pressurised and partly because of the number of seals. For example, a tinplate can normally has about five seal areas. 

Full-cream milk powder has traditionally been packaged in tinplate cans evacuated before closure. The oxygen content of the headspace can increase to 5% over the first week of storage due to release of trapped air. Oxygen concentrations such as these can severely limit the shelf-life (Abbott et al., 1961). Milk powder is given heat treatment on spray-drying in order to increase the thiol concentration in the casein to provide the natural antioxidant. Heat treatment increases the chance of forming cooked milk flavour in the reconstituted product. 

In carbonated beverages the potential reversal does not take place therefore, the steel dissolves preferentially at the defects in the tin layer. Under such conditions pitting corrosion sometimes results in perforation. Consequently, except for fruit cans almost all tinplate cans are lacquered. 

Pournaras, A.V., Prodromidis, M.I., Katsoulidis, A.P, Badeka, A.V., Georgantelis, D., and Kontominas, M.G. (2008) Evaluation of lacquered tinplated cans containing octopus in brine by employing X-ray microanalysis and electrochemical impedance spectroscopy. J. EoodEng., 86,460-464. 

Tin occurs in all humans organs. Although a growth-promoting effect was detected in rats, it is disputed. The natural level of tin in food is very low, but it can be increased in the case of foods canned in tinplate cans. Very acidic foods can often dissolve substantial amounts of... 

D. Xia, S. Song, W. Gong, Y. Jiang, Z. Gao 2012. Detection of corrosion-induced metal release from tinplate cans using a novel electrochemical sensor and inductively coupled plasma mass spectrometer. Journal of Food Engineering 113,11-18. 

The internal coating is applied last by airless spray from static spray guns with an 80 millisecond burst of spray onto the inside of the spinning can. The can is then stoved, typically at 190-200°C for 60 seconds to 2 minutes peak metal temperature, upright in a flat bed conveyor oven. The tinplate can usually receives two coats of lacquer (wet on dry, i.e., each coat is stoved in turn), in contrast to the aluminium can which receives one coat of lacquer. 

R.L. Horst and G.C. English, Corrosion Evaluation of Aluminum Easy-Open Ends on Tinplate Cans, Mater. Perfem., Vol 16 (No. 3X 1977, p 23... 

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