Galvanized steel coatings

Domestic appliances (e.g., refrigerators, deepfreezers, dishwashers, washing machines, and laundry dryers) are mainly made from blank sheet iron, or electrolytically or hot dip galvanized steel. Coatings must protect these construction materials against corrosion caused by food ingredients, household chemicals, and the humid atmosphere in a kitchen or laundry. 

Fig. 2.44 Galvanized steel coating weight versus life to 1% rust 100 g/m = 14 Jim (ASTM, 1954).

In the future, pre-coated metal sheets could probably be used, but then the spot weld bonding would be no more possible. In addition, one has to keep in mind that the adhesive strength on such coatings is lower than that of high strength structural adhesives. Even the adhesion quality of a hot dip galvanized steel coating has to be tested since with some structural adhesive the zinc layer debonds from the metal surface. 

Therefore, this type of coating is not sensitive to defects, pinlroles or mechanical damage during service. A typical example is galvanized steel (Zn layer on steel). 

Steel coated with tin (tinplate) is used to make food containers. Tin is more noble than steel therefore, well-aerated solutions will galvanically accelerate attack of the steel at exposed areas. The comparative absence of air within food containers aids in preserving the tin as well as the food. Also the reversible potential which the tin-iron couple undergoes in organic acids serves to protect exposed steel in food containers. 

Cell formation can easily be detected by measuring potential if coated surfaces with no pores have a more positive potential than uncoated material. Usually this is the case with coated steel in solutions containing oxygen. More negative potentials can only arise with galvanized steel surfaces. Figure 5-4 shows examples of measured cell currents [9,10,16]. 

Fig. 5-4 Cell currents between a coated specimen (5 = 300 cm ) and uncoated steel electrode (5 =1.2 cm ) in NaCl solutions at 25°C. Left shot-peened steel sheet, 150 pva EP-tar. Right hot-dipped galvanized steel sheet, 150 jim EP-tar.

Fig. 13-7 Potential of a cathodically protected special cable with galvanized steel armoring (zinc coating already eorroded).

Fitzpatrick et al. [41] used small-spot XPS to determine the failure mechanism of adhesively bonded, phosphated hot-dipped galvanized steel (HDGS) upon exposure to a humid environment. Substrates were prepared by applying a phosphate conversion coating and then a chromate rinse to HDGS. Lap joints were prepared from substrates having dimensions of 110 x 20 x 1.2 mm using a polybutadiene (PBD) adhesive with a bond line thickness of 250 p,m. The Joints were exposed to 95% RH at 35 C for 12 months and then pulled to failure. 

Organic coatings are applied mainly to mild steel structures and equipment. They are also used on aluminum, zinc-sprayed and galvanized steel, but to a lesser extent. The applications for organic coatings can be divided into three areas corrosion by atmospheric pollution, protection from splash by process liquors, and linings for immersion in process liquors [70-74]. 

Galvanized steel A zinc-coated steel sheet or plate with good corrosion resistance properties used for ductwork and other applications. 

The interior surface finish, to comply with EEC and other health standards, must be rustproof, cleanable, and free from any crevices which can hold dirt. Bare timber in any form is not permitted. Most liners are now aluminium or galvanized steel sheet, finished white with a synthetic enamel or plastic coating. GRP liners are also in use. Floors are of hard concrete or tiles. Very heavy working floors may have metal grids let into the concrete surface. Floor concrete is coved up at the base of the walls to form a protective curb. 

The solution was applied to the surface of cold-rolled steel, dip-galvanized steel sheet, and aluminum strip for degreasing and passivating in a single operation at 40°C for 90 s. The surfaces were then lacquered (85-100 pm thickness) and tested in a salt-spray test for 480 h without showing subsurface migration and blistering. The method is especially useful in the automobile industry for coated sheet [191]. 

Galvanizing steel or iron parts involves dipping them into molten zinc. The zinc coats the steel or iron object, providing a barrier... 

Steel that has been hot-rolled and pickled may be cold-rolled immediately at ambient temperatures before further oxidation can occur. This is done to impart the desired mechanical and surface properties in the steel, and for cold working of the pipe and tube. The two main types of cold mill products are cold-rolled sheets/coils for sale or for further processing in galvanizing and coatings lines, and cold-rolled coils for subsequent tinning.1... 

Plant A Coating Cold Rolled Steel and Galvanized Steel. 277... 

Coil Coating on Zinc Coated Steel (Galvanized Steel) Subcategory... 

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