RING COATINGS


It is not possible to use rings made of cast iron or steel materials immediately after production. Corrosion tendency due to the difficulty of working conditions and the natural structure of the material creates serious problems in terms of life. In order to overcome these problems and prolong the life of the rings, a number of coatings are applied to the piston surfaces.

The most common type of coating used to eliminate these disadvantages is chrome plating. However, under these harsh conditions, chrome plating is not enough. Some other common coatings used after chrome plating are tin, molybdenum, nickel, phosphate and nitrate.

Generally, molybdenum coatings are preferred in America due to their relatively inexpensive and porous structure, as they can hold oil. While this preference is made for gas nitriding in Japan, chromium and chrome ceramics are preferred in Europe. However, with the developing technology, the transition to PVD and DLC coatings, which have higher efficiency, started. These coating types are becoming more common day by day due to their higher thermal and abrasion resistance and long life.

While this PVD coating, which has just been used in piston coatings, can achieve much higher output powers and stability, DLC coating ensures that very low friction and vibration are reduced to the lowest levels possible.

RING COATING AND SURFACE TREATMENTS

Cr= Chrome Plating

Mo= Molybdenum Coating

P= Phosphate Coating

Fe= Ferroxide Coating

Cu= Copper Plating

Nt= Nitrite Coating

Sn= Tin Coating

Ck= Chrome Ceramic

Pvd= Physical Vapor Deposition

Cdc= Chrome Diamond Coating

Dlc= Diamond Coated Carbon Coating

Cr= Chrome Plating

The method commonly used in increasing the durability of the rings is hard chrome plating. The purpose of coating with chromium is to reduce the wear and extend the service life of the ring and cylinder liner. Reducing the ring and roller wall wear is possible by chrome plating of the top ring. 

Today, there is a tendency not only to top rings, but also two or more rings to be plated with chrome.

It is clear that, as the chrome coating creates a hard surface, it will reduce wear on the rings itself.

Chromium plating is mainly applied in two ways:

- hard

- Porous chrome plated

In hard chrome plating, the rings get their final shape by grinding their surfaces after they are covered with chrome. Rings acquire an oil-retaining feature due to their porous chrome plating. Thus, they minimize the wear on both themselves and the liner surfaces they will work with.

Mo= Molybdenum Coating

The circumference of the ring is covered with molybdenum to prevent abrasion. In order to avoid burn marks, the working surface of the rings can be filled with molybdenum or the entire surface can be covered. Coating can be done both by flame spraying and plasma spraying. Molybdenum, high melting point (2620 C0), porous structure and lubricant effect, makes piston ring work surface more durable. It has high thermal conductivity and abrasion resistance.

Ck (Chrome-Ceramic Coating)

Chrome-Ceramic Coatings (CK) is a composite coating type obtained by the mesh structure formed by chrome and aluminum oxide elements. 

These coatings are mainly used for coating the first seat rings of the pistons of diesel engine vehicles. CKS coating brings high quality and performance due to the difference in electrolysis method.

Differences of Ck coating from hard chrome coating;

- higher abrasion resistance

- higher melting point 

- higher hardness and crack density

Due to these advantages, CK coatings in the vehicles it is used to extend the engine life and form low emission exhaust gases.

Pvd (Physical Vapor Deposition)

A method formed as a result of the deposition of hard coatings from the vapor phase on the ring surface is called PVD method. The evaporation and ionization of the metal is provided by this method by electric arc or ion bombardment.

Separated and regulated metal ions are advanced towards the surface of the component. As a result, metal atoms react with reactive gases and form nitrite, carbide, and oxide. After the reaction, a thin coating is formed on the ring working surface. It shows high resistance against wear and tear thanks to the ceramic character in the coating.

Nt= Nitrite Coating

The entire ring surface is hardened with nitrite coating. With this coating, the surface's resistance to friction is increased. In this way, the ring service life is extended. It is environmentally friendly with nitrite coating production and emission properties. With nitrite coating, it was seen that more effective working results were obtained from the critical performance surfaces. Reduces oil losses from the sensitive points of the rings. Reduces the fragility of cast iron rings. Extends engine life.

Cdc= Chrome Diamond Coating

This coating type is used in Euro 4 and top rings of diesel engines. It can be applied to flexible and alloy cast irons, carbon steel. The diamond particle was used in place of the ceramic particle. In this way, wear resistance and performance against friction are increased.

Dlc (Diamond Like Carbon) (Diamond Coated Carbon Coating)

Thanks to this coating, friction is reduced and resistance to wear is increased. DLC coating is environmentally friendly due to its features. It has strong chemical bonds and does not break under mechanical tension. They are not crystalline, they are amorphous. This material is a very strong material due to its structure. Compared to other coatings, it is more resistant to friction.



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