Metal Finishes

Many every day metal fittings and parts are available in such a wide range of finishes; it can be confusing when deciding which one is best suited to your needs. . Skill rating : Beginner

Introduction...

Many every day metal fittings and parts are available in such a wide range of finishes; it can be confusing when deciding which one is best suited to your needs. These different finishes are not only designed to give greater colour choice, but to provide corrosion resistance and improved wear qualities, depending upon the prevailing environmental conditions and usage. Listed below are a few of the more common metallic finishes you may come across;

1: Sheradising

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Discovered around the turn of the twentieth century, sheradising is a method of providing steel or cast iron products with a hardwearing, corrosion resistant coating. The diffusion bonding zinc process of ferrous metals involves placing the components inside a retort chamber, together with zinc powder, and heating to around 400ºC. The durability and toughness of sheradising lends itself to a wide range of applications, from simple nuts, bolts, hinges, and woodscrews, to major use and applications within the mining, Railway, and automotive industries.

Sheradising

2: Zinc Plating

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Zinc plating, a process of galvanisation, is a technique for depositing a protective zinc coating on the surface of another metal, by immersing the object in a plating bath and applying an electrical current. The zinc disperses through the electrolytic bath from a zinc anode and attaches to the metal surface. The thickness of zinc plating is dependent on the time immersed in the plating bath, the volume of current, and the chemical composition of the alkaline bath solution. Zinc plated components are corrosion resistant, attractive, and exhibit a silvery bright, smooth surface

Zinc Plating

3: Galvanised

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Another technique for applying a protective zinc layer to a metal part is the hot dip galvanisation method. The part is dipped into a vat of molten zinc, is then removed from the bath, and the adhered zinc layer allowed to dry. A hot dip galvanised coating is dull and does not provide such a smooth surface. The duller, galvanised surface finish generally has a thicker zinc coating, and usually lasts longer than the bright, shiny finish of zinc plated products.

Galvanised

4: Self Colour Steel

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Self colour steel is uncoated mild steel generally more suited for use in internal joinery applications, or other situations around the house that do not require corrosion resistant properties. Self colour steel has no definitive colour; and can vary with the effects of natural oxidisation and weathering, from a bright steel finish, to almost black. Self colour steel can be used for external purposes if painted, or otherwise suitably treated.

Self Colour Steel

5: Stainless Steel

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The main difference between plain carbon steel, and stainless steel (a steel alloy), is the amount of chromium present. Carbon steel with a minimum of 11.5 % chromium content is classified as Stainless steel. This superior metal does not stain, corrode or rust as easily as ordinary carbon steel; nor is it magnetic. There are different grades and surface finishes of stainless steel, to suit both the environment and conditions to which the material will be subjected during use.

Stainless Steel

6: Black Powder Coated

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This is an attractive black decorative finish, used both indoors and outdoors.

When used outside the corrosion protection is provided by the applied black powdered coating only, and so any damage or breakdown of the surface will allow contamination from oxygen and moisture. Once corrosion has set in it is hard to eradicate completely. Black powder coated finishes are popular and suited perfectly to antique effect door furniture and external gates and doors.

Black Powder Coated

7: Chrome Plated

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Chrome (or chromium to use the correct term), does not corrode and is completely impervious to the weather, but the tiniest of cracks or flaw in chrome plating will allow the onset of oxidisation and rapid corrosion to the metal to which it is applied. Chrome plating, is the method of electroplating a thin layer of chromium onto another metal. Decorative chrome plating (sometimes called nickel-chrome plating) has many uses around the home, including the manufacture of furniture, bathroom fittings, and a multitude of other decorative objects. A chromed plated finish is highly decorative, provides a bright, silvery sheen, offers a degree of corrosion resistance, and is easy to keep looking bright and clean.

Chrome Plated

8: Anodised

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Anodising is an electrolytic passivation process (formation of a hard non-reactive surface film that inhibits corrosion) used to increase the thickness of the natural oxide layer on the surface of metal parts, and is usually used mainly on aluminium substrates. The process of anodising increases the corrosion and wear resistance of the host metal, and provides better adhesion for paint systems, than bare metal. Aluminium double glazing is a good example of an anodised metal finish.