Tin-plated steel

A reversal of potential of the tin—iron couple occurs when tin-coated steel (tin-plate) is in contact with acid solutions in the absence of air. The tin coating acts as an anode it is the tin that is slowly attacked and not the steel. This unique property is the keystone of the canning industry because dissolved iron affects the flavor and appearance of the product. Thus, the presence of tin protects the appearance and flavor of the product. 

In many cases there will be a need to test metal-coated specimens, e.g. galvanised steel, tin-plated copper, nickel-plated zinc, etc. It will then be necessary to test specimens in the completely coated condition and also with the coating damaged so that the basis metal is exposed. The latter condition will provide the conditions for galvanic action between the coating and the basis metal. With sheet specimens this condition is most readily achieved by leaving cut edges exposed to the test environment. 

The metals used to manufacture cans, ends and closures are either steel (tin plated or chromium passivated) or aluminium. In most cases they are coated on the food contact surface with a resinous or polymeric protective coating to avoid interaction between the foodstuff and the metal. However, there is a well defined sector of the tinplate food packaging market where no protective organic coating is needed or used. 

Tin fin( extensive use as a protective layer for mild steel. Tin plating is done by dipping clean sheets of mild steel into molten tin, or by electrolytic deposition. Copper and other metals are sometimes also coated with tin. 

Coatings for Sheet-Metal Cans and Containers. By far the most important area of use is the coating of sheet-metal containers and cans for the storage and preservation of food and other products. Thin sheets of galvanised steel (tin plate), nickel-plated steel (tin-free steel), or aluminum alloys are generally used as substrate. Untreated steel sheet may, however, also be used (e.g., to produce containers and drums for chemicals), and are usually coated with pigmented or nonpigmented paint systems (varnishes). 

Provides good adhesion to a variety of substances including aluminum, stainless steel, tin plated steel, and polyethylene (general Properties ... 

Containers. Aerosol containers, made to withstand a certain amount of pressure, vary in both size and materials of constmction. They are manufactured from tin-plated steel, aluminum, and glass. The most popular aerosol container is the three-piece tin-plated steel container. Glass containers, which are usually plastic coated, generally have thicker walls than conventional glass jars. They are limited to a maximum size of 120 mL and are used for pharmaceutical and cosmetic aerosols. 

The mounting cup (ferrule for botde valves) mechanically joins the valve to the container. The mounting cup may be made from a variety of materials, but is typically tin-plated steel coated on the underside. It contains the gasket which provides the seal. Soft gasketing material is appHed wet and bonded in place or, more frequently in larger cans, cut mbber, polyethylene, or polypropylene gaskets are used. 

Three-Piece Cans. Most steel cans, whether or not tin-plated, are three-piece, ie, a body and two ends. In the past, solder was used to bond the longitudinal seam, but solder has been replaced by welded side seams. 

The composition of the builders in an alkaline cleaner is dependent on the metal substrate from which the soil is to be removed. For steel (qv) or stainless steel aggressive, ie, high pH, alkaline salts such as sodium or potassium hydroxide can be used as the main alkaline builder. For aluminum, zinc, brass, or tin plate, less aggressive (lower pH) builders such as sodium or potassium siUcates, mono- and diphosphates, borates, and bicarbonates are used. 

Tin. Apphcation of tin on strip steel for can stock has decreased. Nevertheless, tin plating is still done in large volume, and tin plate for can stock was estimated at 11,750 t in 1990 (11). Additionally, 603 t of tin anodes were used for electroplating in electronic apphcations in the United States in 1990. The use of tin in solder manufacture is reported to exceed that used in can stock (12). The cost of tin in early 1993 was 7.50/kg (see Tin and tin alloys). 

In this chapter, we are not concerned with establishing the thickness of a uniform sample that is, we shall not deal with thickness gaging, which has already been discussed (3.2), but with determining the thickness of a film that rests upon a substrate of different composition for example, tin plate upon steel. 

An interesting description of a commercial tin-plate installation appears in a special issue of the Norelco Reporter Each side of the coated steel strip can be traversed continuously by a separate measuring head, and the results appear on a two-pen strip-chart recorder located near the 4 x 2 x 9-foot dual electronic rack that energizes and regulates the two measuring heads some 100 feet away. 

Here, as in the thickness gaging of steel (3.2) and in the blending of tetraethyllead fluid and gasoline (3.15), one may look forward to automation. In the present instance, if the tin plating is too thick or too thin, an error signal from the x-ray detector could be fed back into the system to produce an automatic adjustment, perhaps by changing the plating current. 

The continuous tin-plate thickness gage utilizing Method I (6.2) has a counterpart in the Applied Research Laboratories Quantrol,16 which makes the same measurement by Method II (modified) on electrolytic tin plate at the Kaiser Steel Company, Fontana, California, and elsewhere. 

Materials used for various pharmaceutical drug-delivery systems include tin-plated steel, mild steel, stainless steel, tin-free steel, and aluminum and its various alloys. 

One of the most important uses of tin is in the coating of thin steel sheets to make tin plate, which in turn is used to make what is known as the tin can. The tin coating is thin, inexpensive to apply, and resistant to most foods for extended periods of time. Other inert coatings are sometimes used on the inside of the can to further protect the foods for longer periods of time. 

Materials. Reagent grade materials were used as received. The hexakis(methoxymethyl)melamine (HMMM) resin was Cymel 303 (American Cyanamid). Bonderite 1000 pretreated cold-rolled 3"x9"x2AGA steel panels (Parker) were used for enamel testing. Q-Panel Type DT 3"x6" 0.010" tin-plated steel panels were used for preparation of free films. 

Known to the ancients Soft metal mined from the ore cassiterite highly malleable and useful as an alloy to form pewter and bronze and as tin plate to protect steel from corroding. 

One of the most important direct uses for nitromethane is in the stabilization of halo-genated hydrocarbons. For example, small amounts of nitromethane are widely used in industry to form stable non-corrosive mixtures with 1,1,1-trichloroethane for vapour degreasing, dry cleaning and for cleaning semiconductors and lenses. It is also used to stabilize the halogenated propellants for aerosols and to inhibit corrosion on the interiors of tin-plated steel cans containing water-based aerosol formulations (Markofsky, 1991 Angus Chemical Co., 1998). 

Aluminum is used as the material of construction for some aerosol drug products. Also a three-piece tin-plated steel container finds use in topical pharmaceutical aerosols, and to decrease the compatibility problems, an internal organic coating is often used [90]. 

Quality assurance. Tin is leached (dissolved) into canned foods from the tin-plated steel can.24 For analysis by inductively coupled plasma atomic emission, food is digested by microwave heating in a Teflon bomb (Figure 28-8) in three steps with HN03, H202, and HC1. 

---