Surface Treatment

Electrolytic Zinc Plating

Zinc plating is the most common of the electrolytic deposits of steel. The coating made with this method results in a moderate corrosion protection and pleasant appearance with low cost. The coating is also frequently used under painting to improve the corrosion properties and paint adherence.

Zinc, as a less precious metal, gives cathodic protection to steel. Therefore small scratches in the coating do not cause immediate rusting of the steel. In modelling the corrosion durability, the coating is given a time limit it has to keep the object free of red rust. The most common model is neutral salt spray test according to standard ISO 9227:2006.

Hot Dip Galvanizing

Hot dip galvanizing (HDG) is a common surface coating for steel. It provides a very solid and durable corrosion protection. Hot dip galvanizing for steel parts is standardized in ISO 1461. The process of hot dip galvanizing is quite simple: the steel parts are dipped in a bath of molten zinc with normal temperatures between 460°C and 480°C. Next, the parts are spun to remove the excess zinc, and then they are cooled in water to solidify the zinc. What remains is a layer of zinc (40 to 70 microns) on the surface of the products. This layer is relatively thick compared to zinc electroplating (3 to 20 microns).

The large amount of zinc provides excellent corrosion resistance in normal outdoor environments, but with the downside that its layer thickness is significantly above the tolerances of precisely machined areas of the parts. Therefore, one should be careful when choosing hot dip galvanizing for precision parts.

Zinc Flaking

Zinc flake coatings are non-electrolytically applied coatings, which provide good protection against corrosion. These coatings consist of a mixture of zinc and aluminium flakes, which are bonded together by an inorganic matrix. The specifications for zinc flake coatings are defined in international standard ISO 10683 and also in European standard EN 13858. The coating thickness is often between 5 μm and 15 μm, with thicker layers also possible in case there are special requirements. This technique is more expensive than electroplating but gives also a better protection because of the better mechanical properties of the coating.

Shot Blasting

Shot blasting is a resurfacing process used to remove debris and irregularities from metal surfaces. While similar to the sand blasting process, shot blasting is different in both execution and effectiveness.

The shot blasting process utilizes a centrifugal blast wheel that shoots media, like steel shot, onto a surface at high velocity. This knocks the surface free of debris and other material. The shot media, which varies from steel shot to cut wire to nut shells, loads into a hopper that feeds the blast wheel. The media can “blast” off almost anything, from rust to epoxy.

Polishing

Metal polishing is a finishing method that uses an abrasive material to smooth surfaces. When polished, the surfaces of metallic objects are freed of defects and become more reflective and shiny, enhancing their appearance. Metal polishing can be complemented by buffing, a less harsh method that results in a brighter finish. Aside from its cosmetic value, metal polishing also serves a practical purpose. Beneath the surface, it removes oxidation from and prevents further corrosion of a metal, significantly prolonging its working life. Metal polishing can be performed with several varieties of abrasive. The best abrasive for it largely depends on the condition of the material that will be polished. If the material is unfinished, polishing will consist of several stages. During the first stage, a rougher abrasive that removes imperfections from the material is used. Finer abrasives that leave the material relatively unmarked are used in subsequent stages.

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Anodising

Anodising is an electrolytic process for producing thick oxide coatings, usually on aluminium and its alloys. The oxide layer is typically 5 to 30 µm in thickness and is used to give improved surface resistance to wear and corrosion, or as a decorative layer. For Aluminium casted parts, the layer will be unsuitable for decorative purposes because it will be inhomogeneous. On machined or extruded Aluminium, the anodisation layer is visually very smooth and homogeneous in colour.

In the electrolytic process, the components to be treated are made an anode in a dilute acid solution. Oxidation occurs at the component surface, resulting in the formation of a coherent oxide film that is very adherent to the underlying metal substrate. The majority of anodising is done on aluminium and its alloys. Other materials which can be anodised include magnesium and titanium alloys.

Powder Coating

Powder coating is a dry coating process used as a metal finish mostly on industrial equipment. Powder coating is applied as dry powder through an electrostatic process, then cured with heat. It is well known for providing high-quality finishes in terms of both functionality and overall look. The powder coating finishes are not only sturdy but flexible as well. It can be used on both metal and plastic surfaces. It’s suitable for both indoor and outdoor applications, and it’s one of the most cost-effective finish options.

There are two types of powder coating: thermosets and thermoplastics.

Thermoplastic powder coating finishes become liquid and very soft when heated. This eliminates chemical bonding. This process makes the powder coating both reversible and reusable. Thermoplastic coatings tend to be thicker, and hence more durable compared to thermoset coatings. For this reason, they can be used for a plethora of things from metal, auto parts, and even refrigerators.

On the other hand, thermoset powder is quite different in the fact that it forms chemical bonds once cured, making it impossible to recycle it. It is suitable for high heat areas because the bonds prevent it from melting away. This type is much cheaper compared to thermoplastic.

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Blackening

Metal blacking refers to the process of chemically altering the surface of metal objects to create a black oxide layer. The process improves corrosion resistance but is also favorable for the durability.

There are two ways in which metal blacking process can be performed: cold chemical blackening and hot chemical blackening. As their names would suggest, the first is performed at room temperature while the second is performed at high temperatures, with each yielding slightly different results in terms of durability and appearance.

The process of metal blackening itself involves several steps:

Surface preparation – The metal surface is thoroughly cleaned to remove any dirt, grease, or rust. This step is crucial to ensure good adhesion and an even coating.
Immersion in blackening solution – The metal object is then immersed in a blackening solution formed of various chemicals such as sodium hydroxide, nitrates, and selenium compounds. The exact composition of the solution may vary depending on the desired finish and the type of metal being treated.
Formation of black oxide coating – Once it’s been immersed, the metal will react with the chemicals in the blackening solution, resulting in the formation of a black oxide layer on the surface.
Rinsing, drying, and oiling – After the desired metal blacking layer has been formed, the object is thoroughly rinsed to remove any residual chemicals. It is then dried and sealed with a light oil to complete the process.

Many industries make use of chemical and steel blackening, including automotive industries, hardware manufacturers, and decorative arts. Some common uses of metal blackening include:

Aesthetics – Metal blacking can improve the look of an object by providing a sleek, black finish, either in matte or gloss depending on the exact chemical blacking process .These qualities are often used in architectural elements.
Corrosion resistance – The black oxide layer formed through chemical blacking acts as a protective shield, reducing the susceptibility of metal objects to corrosion. This makes blackened metals suitable for outdoor applications or environments prone to moisture and humidity.
Reduced light reflection – Blackened metal surfaces, especially those with a matte finish, exhibit low light reflectivity. This makes them ideal for optical and photographic equipment, where minimizing unwanted reflections is essential.

Materials

There are many different surface treatments for different materials. In most cases, the aim of a surface treatment is to improve the corrosion resistance, the smoothness or the look of the parts. Our material scientists can advise you on the most suitable technique for your application.