Technical Information

Galvanising is the process of applying a protective zinc coating to iron or steel, to prevent rusting. The most common method is hot dip galvanising, in which steel sections are submerged in a bath of molten zinc.

Steel is being dipped into a bath of molten zinc means that hot dip Galvanising provides protection to external and internal surfaces of the steel component.

The long-term durability provided by galvanising is achieved at relatively low environmental burden in terms of energy and other globally relevant impacts.

Several studies have demonstrated the high economic and environmental costs associated with the repeated maintenance painting of steel structures. These burdens can be significantly reduced by an initial investment in long-term protection. Lack of attention to optimal corrosion protection can leave a damaging economic legacy of repeated maintenance costs.

In social housing projects, future maintenance costs will be borne by the local authorities. In public infrastructure projects, use of galvanised steel leads to lower maintenance budgets, releasing public funds for other purposes.

Hot-dip galvanising is the process of immersing iron or steel in a bath of molten zinc to produce a corrosion resistant, multi-layered coating of zinc-iron alloy and zinc metal.

While the steel is immersed in the zinc, a metallurgical reaction occurs between the iron in the steel and the molten zinc.

The unique nature of the galvanising process – formation of a series of zinc-iron alloy layers – provides a tough and abrasion resistant coating.

This means less site damage and speedy erection of structures.

Zinc corrodes in preference to steel and sacrifices itself to protect the steel, hence hot dip galvanising will provide this sacrificial protection. The corrosion products from the zinc are deposited on the steel resealing it from the atmosphere and therefore stopping corrosion.

We are aware that not all material fabricated will be uniform size, at NK Coatings LTD we put our all into processing any size of material brought to us by our clients. We are only restricted by the size of our bath. If you are planning to galvanise a oversized or awkwardly shaped piece of material, we can accommodate the following sizes.

Providing

2 out of 3 of the dimensions fit within these parameters we can process

your material for Galvanising. For information on any extra costs for

these services please Contact Us.

Any material which is fabricated with black steel and galvanised steel that requires to be galvanised must be stripped back to base material.

This is to ensure that when the material is processed through the galvanising bath the metallurgical reaction between base material and zinc occurs thus ensuring your material is processed to BS ISO 1461.

Sound galvanised steel with many years of corrosion-free life ahead can sometimes be rust stained or discoloured. This may give an incorrect impression that the coating has failed and is, in some cases, visually unacceptable. Below illustrates the main causes of staining and discolouration and indicates how the problems can be avoided or the effects remedied. The staining and discolouration of galvanised coatings by rust may occur as a result of one or more factors:

1. Direct contact of galvanised parts with unprotected or inadequately steel (e.g. galvanised steel sections fastened with unprotected, electroplated or painted steel bolts).

2. Deposits of iron dust and swarf from other operations or sources onto the galvanised surface.

3. Water draining from unprotected or poorly protected steelwork, e.g. from damaged areas on painted steelwork.

4. During pickling, hydrochloric acid may penetrate into the weld area via pin holes or if the welding is intermittent. Residual salts can sometimes pick up water and cause ‘weeping’ from the weld areas. This effect is normally limited to a small area, ceases after a short time and is not detrimental to the coating.

5. Rusting of areas welded after galvanising and subsequently left unprotected or inadequately protected.

6. Staining of galvanising can occur when water runs off other materials notably metals such as copper, certain hardwoods, e.g. oak, an indeed whenever water can dissolve materials from one surface and redeposit on the galvanised steel.

The galvanisers association has advised that a standard galvanised coating may now achieve a coating life of 50 years in most environments, although urban / marine are up to 25 years.

For further information see https://www.galvanizing.org.uk...

Polyester powder coating is a type of coating that is applied with a spray gun as a free-flowing, dried powder which is electrostatically charged and sprayed onto a material. The process involves coating metal in powder form and baked to a fluid state to bond it to the product's surface, creating a protective layer

Sales can advise how to specify NK Coatings – Approved finish.

You can view colour charts via the links below:

• HMG Colour Chart
• Dupont Colour Chart
• Akzo Nobel / Interpon Colour Chart

Booth Size: 4 m long

Maximum Working Envelope: 0.500 wide x 3m high

Paint, oil and grease have to be removed before the powder coating process to provide a clean surface to ensure a good quality finish. If you require any material to be powdered only without being galvanised beforehand the material is required to be clean, fresh steel with no rust, oil, paint or grease on the surface.

Every sealed section of a fabricated structure must be vented for reasons of safety and to allow access and drainage of chemicals at the pre-treatment stage. Holes should be as close as possible to the sealed end and on opposite sides of the section. The larger the hole size the better the drainage.

Zinc Flow is the key to top quality.

Good design requires:

1. Means for the access and drainage of molten zinc

2. Means for escape of gases from internal compartments (venting)

It is important to bear in mind that the steelwork is immersed into and withdrawn from a bath of molten zinc at about 450°C.

Any features which aid the access and drainage of molten zinc will improve the quality of the coating.

With certain fabrications, holes which are present for other purposes may fulfil the requirements for venting and draining; in other cases it may be necessary to provide extra holes for this purpose.

For complete protection, molten zinc must be able to flow freely to all surfaces of a fabrication. With hollow sections or where there are internal compartments, the galvanising of the internal surfaces eliminates any danger of hidden corrosion during service.

External stiffeners, welded gussets, webs on columns, beams and gussets in channel sections should have their corners cropped. This will aid access and drainage of molten zinc and a cleaner coating will be obtained.

Stiffeners, welded gussets and webs on columns and beams, and gussets in channel sections should have their corners cropped. Stiffeners, welded gussets and webs on columns and beams, and gussets in channel sections should have their corners cropped.

Angle bracings should, if possible, be stopped short of the main boom flange. This will allow the free flow of molten zinc across the surface of the flange, enhancing drainage from the structure. This will assist the development of a smoother galvanised coating, reduce the potential for retention of ash on the surface of the flange and help to avoid air traps within the structure, which could lead to uncoated areas.

Internal diaphragms in large box sections should have cropped corners and a ‘manhole’. Internal diaphragms on small box sections should have cropped corners. Where any hollow section is vented internally it is essential, for safety reasons, that the galvaniser is able to view such venting.

Alternative designs for venting sections fixed to base plates:

Please visit link:

https://www.galvanizing.org.uk...

When undergoing the galvanising process, steel is slowly lowered into a 450°C 'Bath' of molten zinc. Due to the immense heat of the bath, steel will expand with the heat, potentially causing the material to distort or warp as it is galvanised. Adequate venting can help prevent distortion.

When bringing steel mesh panels in for galvanising, to lower the chance of distortion you are required to weld every other wire in the mesh before they are processed.

Design structures to avoid run-off water from other metals on to galvanised steel. In particular avoid run-off from inadequately protected steel and from copper.

Welds should be continuous and slag-free wherever possible to minimise the retention of pickle residues.

NK Coatings Limited powder application is recognised as being in the forefront for quality and finish. However, in order to preserve the aesthetic finish it is recommended to regularly clean the coating.

Regular cleaning, on a maximum 3 month interval or to a mutually agreed timescale, using warm water and mild detergent. Abrasive cleaners including strong solvent must not be used to remove any heavy soiling. Where spirit should only be considered if the mild detergent is not strong enough.

In areas where the coating may come in contact with concentrated atmospheric pollutants [marine, chemical] it would be prudent to clean more frequently, E.G monthly.

Full documentation of the cleaning schedule must be maintained.

If damage occurs to the coating, repairs must be carried out immediately, contact N.K. Coatings Limited

Discolouration and staining have no effect on the life of the coating. However, affected areas may be cleaned to improve the appearance of the structure. Generally, wire brushing or the use of a scouring powder will remove the stain and leave a sound galvanised coating

Small areas of galvanising may be damaged by operations such as cutting or welding after galvanising. Because of the sacrificial action of zinc, small localised flaws (typically up to 5mm diameter) tend to be self-healing and have little effect on the life of the coating. Nevertheless, it is often aesthetically desirable to renew the coating over small areas as well as larger areas using one of the following techniques:

a) Thoroughly wire brush the affected areas and apply several coats of zinc rich paint to give a coating thickness at least equivalent to the original galvanising.

b) Thoroughly wire brush, heat the bare area with a blow torch to 300C and apply a special zinc alloy rod.

Painting with zinc rich paint is usually simplest but if a colour match is important, the zinc alloy rods are usually most suitable.

Contact the sales team for technical queries.

If welding after galvanising is necessary, welded areas should be thoroughly cleaned and the zinc coating restored either with an appropriate thickness of zinc rich paint or with a proprietary repair compound, in accordance with section 6.3 of BS/IS EN ISO 1461.

Dark grey or light grey – it’s all galvanised.

Protection is equal – and often better – with dark grey coatings than with light grey coatings.

Variation in colour is generally due to variations in the chemical make up of the steel being galvanised. Due to these variations steels can be much more reactive with zinc resulting in very different appearances E.G. Silicon content of steel is particularly important. A dull, dark grey finish is usually a much tougher and more corrosion resistant coating than a shiny finish. Each of these finishes are entirely acceptable according the British standard EN 1461. resistance as zinc, thickness for thickness can have better intrinsic corrosion resistance in acid industrial environments. These thick coatings can be more susceptible to mechanical damage particularly if handled roughly, and appropriate care must be taken.

The dark grey coating surface may develop iron oxide staining on atmosphere exposure, even in mild conditions when moist. This is only a surface effect and does not develop into nodular or flaking rust: the galvanised coating remains intact to protect the steel.

What is BS EN ISO 1461?

BS EN ISO 1461 is the internationally recognised standard that governs the hot dip galvanising of fabricated iron and steel. It outlines the minimum requirements for coating thickness, finish, testing, and acceptable repairs to ensure long-term corrosion protection and structural durability.

At NK Coatings, all galvanised items are processed in full compliance with BS EN ISO 1461.

For more technical details, see the Galvanising Association's guide to BS EN ISO 1461.

https://galvanizing.org.uk/gal...

For those fast – track jobs that just can’t wait, the ‘NK Express Service’ offers a 24 hour turnaround on request.

Contact our sales team for more information