Sherardizing

The most environmentally friendly surface treatment, minimum carbon footprint, sustainable technology

How to ensure maximum protection for your steel?

Do you prefer the most environmentally friendly method of surface treatment?
Try the unrivalled method of thermal diffusion galvanizing – Sherardizing, offered by our company ERLEN

Benefits of Sherardising

Superior

It surpasses all other methods of anti-corrosion coating in many respects.

Hardest

The hardest of all zinc coatings, able to withstand significant industrial pollution.

Even

Uniform coating, ideal for smaller and irregularly shaped objects without adverse changes in the thickness of the protective layer.

Lower temperature

Lower process temperature range that prevents loss of mechanical properties and shapes of the parts.

Long lasting

Long-term durability, tested in salt chamber for 2500 hours.

Hydrogen free

Total elimination of hydrogen embrittlement.

Enironmental

Environmentally friendly – approaching a zero-emission process with no toxic substances.

Lower costs

Cost-effective in terms of initial protection costs, follow-up treatment and maintenance costs over the entire life cycle.

Sherardizing – Thermal diffusion galvanizing

Technology Description

The process of thermal diffusion galvanizing, also known as Sherarding, consists of diffusion filling steel objects with zinc. The reaction takes place in a rotating electric furnace filled with zinc powder at temperatures of 360-430 °C. The process results in the formation of an outer layer of zinc-impregnated steel on the surface of the protected steel objects. The surface layer thus formed is characterised by exceptional corrosion protection. The thermal diffusion method is also characterised by unrivalled abrasion resistance due to the absence of a deposited and therefore peelable layer. Due to the lower temperatures, there is no change in the internal steel structure and therefore this method is also suitable, for example, for the protection of springs and similar heat-treated elements.

The galvanising process is carried out in closed chambers in which the zinc diffuses into the steel structure. For this reason, the size of the chambers limits the maximum dimensions of the parts to be thermo-diffusion galvanised. We are able to offer our customers thermal diffusion galvanizing of parts with a maximum length of 300 mm. A special type of parts are bars, which we are able to galvanise up to 1000 mm in length and up to 10 mm in diameter. The maximum weight of the input is 250 kg. The structure of the surface layer resulting from thermal diffusion galvanizing consists of various intercrystalline compounds of zinc and iron.”

The resulting layer has a matt grey colour. Machine components can be realized with a guarantee of reciprocal mobility.

Corrosion Tests of the ERLEN Company

ERLEN, in cooperation with Accredited Testing Laboratory No. 1053, has demonstrated through pre-production and continuous corrosion tests that:

the thickness of the thermodiffusion layer at a level of approx. 35 µm is equivalent to the corrosion resistance of a layer 85 µm deep in the hot-dip galvanizing version; valid for corrosion aggressiveness class C5 (according to ISO 14713-1 – very high corrosive activity)

tensile tests according to ISO 6892-1 do not adversely affect the strength characteristics of thermal diffusion coated steels

metallographic analyses did not confirm a detectable effect on the microstructure both qualitatively and quantitatively (grain size, phase morphology, etc.)

the rolling abrasion test (calotest method) shows measurably better results in resistance to breakage compared to hot-dip galvanizing

Presentation & Test Results

Technical Support

Quality standards

ISO 17668:2016 – Zinc diffusion coatings on ferrous products – Sherardizing

American Standard Testing: ASTM B633, ASTM B695

Russian Federation Standard: GOST R 51163-98

Coating classes

In accordance with EN ISO 17668:2016, the thickness of the thermal diffusion coating is determined according to the following classes:

Class	Coating Thickness Min. (µm)	Application Fields
Class 15	15	Normal indoor and outdoor environments
Class 30	30	Outdoor applications in more severe environments, or where there is a requirement for extended service life
Class 45	45	Highly corrosive and or abrasive environments, e.g. industrial or marine

FAQ – Questions & Answers

Why should we sherardize our products?

Sherardizing is the most effective, reliable and uniform method of protecting steel from corrosion. It provides a long-term solution that completely prevents hydrogen embrittlement. It is an environmentally friendly process that is highly cost effective compared to other applications such as hot dip galvanizing.

How does sherardizing or diffusion galvanizing work?

In closed rotating drums, the metal products are heated together with the zinc powder. The temperature rises to around 380 °C. At this temperature, the zinc powder is converted into zinc vapour. This vapour reacts with the product to form a uniform layer of zinc and the zinc is bonded to the base material by diffusion. This creates a protective layer that prevents corrosion.

Is sherardizing a sustainable application?

Sherardizing is a sustainable solution because the products have a longer service life thanks to the diffusion galvanizing process. The service life is extended. In addition, it is an environmentally friendly solution. It does not require any chemical treatment and therefore no chemical waste is generated. Because sherarding is a so-called closed galvanizing process, no toxic zinc fumes are released.

Is sherardizing better than other paint protection applications?

Yes, sherardizing is much more reliable and cost effective than other coatings. If the surface is damaged by other methods such as paint or plastic coatings, the steel will become exposed and corrosion may occur. By cathodically protecting the zinc, the coating will continue to protect the exposed steel.

Which products can be sherardized?

Sherardizing can be applied to many steel products, systems and shapes. So much that it can be said that almost anything is possible.

How does sherardizing affect the appearance of my product?

Sherardized products have a matt grey appearance, which is often considered an advantage.

How long has sherardizing been on the market?

Sherarding is a reliable and proven application that was developed as early as 1900. Since then, the technology has been further refined and improved. The name sherarding refers to the creator of the technique: Sherard Cowpler-Coles.

What are the different classes of sherardizing and which do I need?

Class 10 minimum layer 10 µm – corresponds to corrosion aggressiveness C1 very low
Class 15 minimum layer 15 µm – corresponds to corrosion aggressiveness C2 low
Class 30 minimum layer 30 µm – corresponds to corrosion aggressiveness C3 medium
Class 45 minimum layer 45 µm – corresponds to corrosion aggressiveness C4 high
Class 60 minimum layer 60 µm – corresponds to corrosion aggressiveness C5 very high
Class 75 minimum layer 75 µm – corresponds to corrosion aggressiveness CX extreme
If necessary, we can advise you on the thickness of the coating. Please contact our technical team for specifications and application recommendations.

Is it necessary to leave space on the threads or tolerance on the connected parts?

As with all plating systems, deposition increases the external dimensions and reduces the dimensions of holes and threads. As always, our technical team can advise you on specific drawings and requirements.

Is it possible to sherardize over another plating, e.g. zinc or zinc plating?

This option is not recommended. To ensure optimum conditions for the application of a quality sherarded zinc layer, we recommend removing the plating down to bare metal.
With any original existing plating, we would not be sure of the quality of adhesion of the base metal. We can easily remove most original coatings with a few exceptions. Galvanizing and powder coating are relatively thick and soft coatings that cannot be easily removed by mechanical methods, but it is still possible.
However, some we cannot remove for environmental reasons, such as cadmium and hexavalent chromium, these would require professional removal prior to the application of sherarding.

What is the largest size of parts you can sherardize?

The size is limited by the diameter of the galvanizing container. Maximum part size is 300 mm, larger parts can be galvanized only after consultation.

What weight will my material gain after sherardizing?

Sherardizing adds 70 grams per square meter of surface per 10 microns of layer thickness.

How should I prepare the material for sherardizing?

Ideally, all parts should be clean and dry of cutting, oil, paint, grease and rust. However, we have the equipment to ensure that all of these activities are done in-house. Preparation by you will speed up the actual implementation.

What quality standards do you meet?

We meet the standards according to ČSN EN ISO17668:2016.

What is hydrogen embrittlement and why does sherardizing prevent it?

Hydrogen embrittlement is caused by the rapid diffusion of atomic hydrogen in iron and is the cause of unpredictable failures. However, the sherardization process is hydrogen-free and completely dry, which means that the risk of hydrogen embrittlement is completely eliminated, which is important for safety components and products made of spring steel, hardened or high-strength steel.

To what temperatures are sherardized products temperature resistant?

Unlike other zinc-based coatings, zinc-iron alloys are resistant to temperatures in excess of 600 °C. In addition, the sherardized products are cold resistant up to -40 °C.

Can the zinc layer just scrape or peel off?

Thermal diffusion galvanizing (sherardizing) creates a solid alloy with the base metal material. It cannot just peel off.

What is the layer hardness after sherardizing?

The hardness of this coating is approximately 400 HV (41 HRC) and exceeds that of other zinc coatings or varnishes. This property makes sherardizing popular in harsh or rugged applications where corrosion protection and wear resistance are important.

Why do sherardized products have a reliable and durable rubber-to-metal joint?

Sherardized products have a microcrystalline rough surface. This allows the adhesive coating to be applied to the sherarded surface without pre-treatment and results in excellent adhesion of the rubber to the metal. The result is a reliable and durable rubber-to-metal bond protected against corrosion.

Haven’t found the answer to your question?

If you haven’t found the answer to your question, ask us using the form in the Contacts section or call us on +420 775 110 868 and we’ll be happy to help.

References

Parts of trailers

Production of truck trailers

Parts of pumps

BBA Pumps

Components and parts of chains

pewag

Sherardizing

The most environmentally friendly surface treatment, minimum carbon footprint, sustainable technology

How to ensure maximum protection for your steel?

Benefits of Sherardising

Superior

Hardest

Even

Lower temperature

Long lasting

Hydrogen free

Enironmental

Lower costs

Sherardizing – Thermal diffusion galvanizing

Technology Description

Corrosion Tests of the ERLEN Company

Technical Support

Quality standards

Coating classes

FAQ – Questions & Answers

Why should we sherardize our products?

How does sherardizing or diffusion galvanizing work?

Is sherardizing a sustainable application?

Is sherardizing better than other paint protection applications?

Which products can be sherardized?

How does sherardizing affect the appearance of my product?

How long has sherardizing been on the market?

What are the different classes of sherardizing and which do I need?

Is it necessary to leave space on the threads or tolerance on the connected parts?

Is it possible to sherardize over another plating, e.g. zinc or zinc plating?

What is the largest size of parts you can sherardize?

What weight will my material gain after sherardizing?

How should I prepare the material for sherardizing?

What quality standards do you meet?

What is hydrogen embrittlement and why does sherardizing prevent it?

To what temperatures are sherardized products temperature resistant?

Can the zinc layer just scrape or peel off?

What is the layer hardness after sherardizing?

Why do sherardized products have a reliable and durable rubber-to-metal joint?

Haven’t found the answer to your question?

References

Parts of trailers

Parts of pumps

Components and parts of chains

Gallery