Surface treatment determines a piston ring’s wear resistance, sealing and corrosion protection. This article covers phosphating, sandblasting, chrome plating, nitriding and C.T.I.’s in-house DLC coating and patents.
Surface treatment of piston rings is mainly aimed at reducing wear and improving durability, enhancing sealing, improving lubrication and preventing corrosion — ensuring long-term reliable engine operation, raising performance and fuel efficiency, and lowering energy use and emissions. Common methods include phosphating, sandblasting, chrome plating, nitriding and DLC coating.
Usually applied by chemical immersion, forming a dense black oxide film on the surface. This treatment not only improves wear and heat resistance but also improves compatibility with lubricating oil, enhancing sealing. Phosphating is a simple, economical and effective surface treatment, widely used on piston rings for all kinds of engines.
High-speed sand is blasted onto the ring surface, producing a uniform rough texture with a matte metallic finish. This increases surface area and oil adhesion, improving sealing; it also removes the oxide layer and tiny defects, raising wear resistance and fatigue strength.
Piston rings are often chrome-plated, forming a dense chromium-alloy film with excellent hardness, wear resistance and corrosion resistance. Plating both strengthens mechanical properties and improves appearance. Compared with phosphating, plating is more complex and costly, but delivers better surface performance.
The ring is placed in an ammonia atmosphere; at high temperature the ammonia breaks down and nitrogen atoms diffuse into the surface, forming a nitride layer that greatly raises surface hardness and wear resistance. Compared with plating, the nitride film is denser and more uniform, with advantages in wear and corrosion resistance; its appearance is a yellowish-brown metallic shade. The nitride film also has good lubricity and thermal stability, and is often used on higher-performance piston rings such as those for high-power racing or heavy engineering machinery.
This technology deposits an amorphous carbon film on the ring surface whose hardness, wear resistance and low friction rival or even exceed nitriding. Unlike the matte black of phosphating, DLC has a glossy, deeper black. It greatly extends service life and effectively reduces the rise in oil consumption and emissions caused by wear, making it especially suitable for high-power, high-speed engines where it maintains good sealing under extreme operating conditions.
Compared with other methods, DLC technology is relatively more complex and expensive, but delivers outstanding mechanical performance. C.T.I. has researched DLC coatings for many years and, through persistent exploration and innovation, has successfully obtained two new DLC patents (US: 905744B2; Taiwan: M300746). These patents are innovative in both material composition and structure, and their performance is industry-leading. We will continue to deepen our fundamental research while advancing these patented technologies.
Each of the surface treatments above has its own characteristics; in practice the most suitable approach must be chosen according to each engine’s operating conditions and performance needs. As technology advances, we may yet see more innovative surface-treatment methods applied to piston rings to meet ever-stricter performance demands.
