Zinc Applications

zinc applications

Zinc Coatings
Zinc coatings for iron and steel provide excellent corrosion resistance in most atmospheres, in hard fresh waters, and in contact with many natural and synthetic substances. Zinc coatings are widely used to protect finished products ranging from structural steelwork for buildings and bridges, to nuts, bolts, strip, sheet, wire and tube. The electrochemical relationship between zinc and steel enables zinc coatings also to protect steel at cut edges and at breaks in the coating by a sacrificial action. (See also Zinc anodes: cathodic protection)

The following are the seven principal methods of applying zinc coatings:

Batch (or 'General') hot dip galvanizing
Individual steel components or fabrications are chemically cleaned by acid to remove rust and millscale before being immersed in a bath of molten zinc at about 450°C. In the galvanizing bath a series of zinc-iron alloy layers are formed by a metallurgical reaction between the iron and zinc. As the steel is withdrawn, a layer of molten zinc remains on the surface.

The metallurgical bond between the base steel and the coating means that in addition to excellent corrosion resistance hot dip galvanized coatings are much less susceptible to handling damage than other coatings such as paint systems. Applications include structural steelwork, lampposts, crash barriers, power transmission towers, railway electrification supports, security fencing, trailers and many others.
Galvanizing offers duel protection against rust. Firstly, the coating covers the whole surface, reaching into even the most awkward corners of complicated structures, and provides an impermeable barrier between the basis material and the atmosphere which corrodes at a much slower rate than steel. Secondly, because of its electrochemical properties, zinc will sacrificially protect any small areas of damage and the coating may even self heal. Even when the exposed area is too wide to allow self-healing, these properties prevent the sideways creep of rust beneath the zinc coating.

Continuous hot dip galvanizing
After several preparatory stages, clean, non-oxidised steel strip is passed at high speed through a molten zinc alloy bath, wiped to control the coating thickness and cooled to form a thin, continuous zinc (or zinc alloy) coating. Depending on the final use, various thermal or chemical treatments may be applied. Continuous paint or plastic coatings may also be applied at the production plant to provide additional protection and/or a coloured finish. Applications include roofing and cladding for industrial and commercial buildings, domestic appliances and automotive bodies. All car manufacturers now use steel strip that has either been continuously hot dip galvanized or zinc plated.

Zinc Spraying
Atomised particles of molten zinc are projected on to a grit-blasted steel surface from a special flame or arc pistol fed with zinc or zinc alloy wire. The process is often applied to structural components too large to be dipped in a galvanizing bath, and to structures which are likely to distort during hot dip galvanizing.

Zinc plating (Electrogalvanizing)
The zinc coating is electrodeposited onto prepared steel from a solution of zinc salts. The process is used to protect smaller articles - such as nuts, bolts and other fasteners and small pressings – which require a finer finish than galvanizing can normally provide, although the coating is thinner. The process has also been adapted to provide thin coatings on steel strip and wire.

Prepared iron or steel articles are heated with zinc dust and sand in a slowly rotating drum at a temperature just below the melting point of zinc until the zinc has formed a zinc-iron alloy coating over their surfaces. The coating is very even, matt-grey in appearance and is mainly used for fairly small articles because of the difficulty of heating the contents of large drums evenly.

Zinc-rich paints
These are paints in which very high levels of fine zinc dust have been incorporated. Because of the very high pigmentation with zinc particles , the dry film is electrically conductive and so acts to some degree as a metallic coating. Zinc dust paints can be applied to any rust and scale-free steel surface by brushing, spraying or dipping. They are mainly used to protect factory steel work, ship’s hulls and parts of car bodies and also to repair damage to other types of zinc coatings.

Automatic grit blasting and zinc dust paint spraying equipment are widely used in steel workshops and shipyards to protect steel plates during storage before fabrication and until application of the final coating system.

Mechanical plating
Steel articles are cleaned and then given a very thin coating of copper by immersion in a copper sulphate solution. Zinc is then impacted onto the surface by tumbling with a mixture of zinc dust and ballotini (the tiny glass beads that are used in reflective paints) in an aqueous medium. A thin even coating is formed. The treatments are carried out at room temperature so there is no risk of softening tempered steel articles such as springs

Zinc alloy die castings

Pressure die casting, is a fast economical process for mass producing accurate parts. Molten metal is forced under pressure into permanent steel dies which are opened mechanically to allow the casting to be ejected. When specially developed zinc alloys - based on zinc of at least 99.99% purity, with additions of aluminium, magnesium and sometimes copper - are cast using the hot chamber variant of this process, the resulting parts can be not only uniquely accurate but also strong and with excellent corrosion resistance. When required for functional or aesthetic reasons, zinc die castings can accept a wide range of surface finishes including plating, painting and plastic coating.
Given this combination of strength, accuracy, consistency and finishability, it is not surprising that zinc alloy die castings are used in a vast range of applications: in car manufacture for handles, locks, carburettors, fuel pumps, etc.; in domestic appliances; for locks, door handles, bathroom fittings and other items of builder’s hardware; and in a variety of other products including scale model toys and zip fasteners.


Other zinc alloys

In addition to the pressure die casting alloys there are three alloys containing approximately 8, 12 and 27% aluminium that are used for traditional sand castings or gravity die castings. With their relatively low melting points and competitive mechanical properties, they can be sometimes be used as alternatives to aluminium, cast iron or brass, thus saving energy and production time. Exceptional fluidity allows thin wall castings to be made when required. If needed, secondary finishing operations like machining are easy and heat treatments are rarely required.

A zinc alloy containing of 30% aluminium and 5% per cent copper (known in the United Kingdom as Alzen 305) can be used to replace phosphor bronze in some bearing applications, particularly for high loads and low speeds. This alloy can also be extruded.

Zinc alloys based on 22% aluminium display marked superplasticity at 260°C after preparatory heat treatment. In sheet form they can be vacuum of blow-moulded in cheap dies, taking advantage of the 1000 per cent elongation available. These alloys have found niche markets, particularly replacing other sheet metal in equipment housings.



Brasses are copper-zinc alloys with a zinc content ranging from about 20 to 40%, and sometimes containing additions of other metals. Alpha brasses with 28 to 37% zinc content are single-phase alloys suitable for cold working (i.e. rolling, pressing and drawing), and for small castings. The alpha-beta brasses with 40 to 45% zinc content consist of two phases and are suitable for casting, hot pressing and extrusion.

Brasses are easily recognised by their yellow colour and – because of their ease of working, high corrosion resistance and good electrical conductivity – are widely used in a wide range of engineering applications as well as for plumbing and electrical components. For further information on brass visit Copper Development Association on www.brass.org.


Zinc oxide

Zinc oxide is the most important compound of zinc. It is an indispensable raw material for a multitude of everyday products and is produced in a number of different 'grades' of purity and particle size depending where it is to be used.

Zinc oxide is made by heating zinc metal or residues containing metallic zinc to temperatures beyond the boiling point of 907°C. The zinc vaporises and is allowed contact with the air: it oxidises and is cooled, collected and graded.

Applications include:

Glass and ceramics: zinc oxide is a fluxing agent in the preparation of frits and enamels for ceramic wall and floor tiles.

Rubber and tyre products: zinc oxide is essential. It is an activator in the vulcanisation process, putting the 'bounce' into the rubber. Other benefits include improved physical properties and resistance to degradation.

Electronics: high purity grades of zinc oxide are used in specialised applications such as ferrites and in varistors to protect sensitive equipment from electrical power surges.

Pharmaceuticals and cosmetics: for example suntan lotions (to absorb ultraviolet radiation), baby creams and antiseptic healing creams.

Nutrition: zinc is an essential micronutrient for plants and animals and humans. Zinc oxide is a convenient form in which to add zinc to fertilisers and animal feeds to avoid deficiency. It is also used in the preparation of other zinc compounds used in the preparation of dietary supplements for humans


Zinc dust

As for zinc oxide, zinc dust is made by vaporising metallic zinc. However the vapour is in this case allowed to condense in the absence of air, when it forms a fine powder.

The principal uses of zinc dust are in paints and sherardising (See under Zinc Coatings). It is also used in alkaline batteries and as a chemical reducing agent


Zinc phosphate

Zinc phosphate is essentially produced by reacting zinc oxide with phosphoric acid, followed by precipitation, filtration and drying. It is available as a product in various states of hydration. Zinc phosphate is mainly used in solvent or water-borne anti-corrosive primer systems and paints.


Zinc sheet: roofing

The main use of rolled zinc sheet and strip is for roofing, cladding, flashings, and rainwater disposal applications. It has been used extensively for these purposes in continental Europe for many years. Now, with increased awareness of its technical and aesthetic qualities, its use is rapidly increasing in the UK.

The product is used today is a zinc–copper-titanium alloy. This conforms to a European standard – EN 988, which covers such factors as surface finish, dimensional tolerances, tensile and creep strength.

In addition to its technical qualities zinc sheet offers the advantages of excellent visual appearance, long life with minimal maintenance, cost effectiveness, and a versatility which enables it to be used confidently for innovative architectural designs.

Whilst the main tonnage of zinc sheet is used for architectural purposes it has a wide range of other applications, including electrical and engineering components, printing, organ pipes, coffin linings, gaskets, stencils, bar and table tops, with new uses continually being developed.

Cathodic Protection: Zinc Anodes

Because of their different positions in the electrochemical series, when zinc and iron or steel are joined together and placed in an electrolyte, a cell is formed in which the zinc becomes the anode and the steel the cathode. The zinc then dissolves preferentially ('sacrifices') and the steel does not rust. This is the process that enables zinc coatings to protect steel at damaged areas (See 'Zinc coatings')

Marine sacrificial zinc anodes, which are available in many shapes and sizes, are bolted onto ships’ hulls and ballast tanks, rigs and other installations to protect the steel structure from corrosion. High purity zinc and a range of special alloys are used for cathodic protection to ensure that the surface remains active.


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