Why Are Different Coatings Used For Piston Rings?

Piston rings have evolved in recent years. Until recently they were heavier, thicker, and made of cast iron. Modern rings are thinner, come in many widths, and must be precisely configured to suit the needs of the user.

Coatings play an ever more important role when it comes to extending the lifespan of sealing rings too. Choose the wrong type and the reverse effect could be achieved – with wear and tear accelerating instead of decreasing.

In this guide we’ll look at:

1.     why coatings are important

2.     types of wear and tear

3.     why lubrication matters

4.     different types of coatings

If you have any questions at the end, get in touch to ask one of our experts a question.

Piston ring coating compatibility is extremely important. Choose the wrong type and it could adversely affect the lifespan of your sealing rings – costing you money and wasted time in the process.

To understand the pivotal role coatings play it’s important to think about the top piston ring, which is arguably the most important component in an engine. It must transfer considerable volumes of heat at speeds of up to 5000 feet per minute through a minimally sized contact zone.

As you can imagine, this places incredible pressure on the top sealing ring which could fall prey to many issues – including adhesive and corrosive wear – if its thin line of contact is inadequately protected. This is something that should be avoided at all costs.

The four types of wear and tear are:

1. Corrosive – for example, oxidation or thermo-chemical wear

2. Adhesive – which could give rise to scuffing or galling

3. Fatigue – evidenced by spitting, flaking, or spalling

4. Abrasive – resulting in grinding or ploughing

Abrasive wear affects the durability of the top ring most acutely. That’s because, as friction levels increase, hydrodynamic lubrication ends, and boundary lubrication becomes more important.

This event occurs when the soft graphite lining in the top piston ring starts to erode and becomes softer – making it softer and more malleable.

The graphite lining – itself a form of coating – becomes more lubricious, preventing wear and tear to preserve the piston ring for longer.

As established, coatings extend the lifespan and efficiency of piston rings – preventing undesirable issues like corrosion or scuffing. Select the wrong coating and you could accelerate wear and tear instead and reduce performance.

Here is a breakdown of the different coating types to guide your decision making:

1. Molybdenum stops scuffing, is plasma sprayed, and used most with 4 stroke piston rings

2. Ceramic chrome minimises friction and high temperatures because it’s thermally stable

3. Copper assists with piston bed-in but is thin and disintegrates within a matter of hours

4. Hard chrome is durable, used in 2 and 4 stroke engines, and stops issues like galling

5. Nickel graphite is often combined with other coatings and is used universally

Which of these industrial and marine piston coatings is best? Why not contact us for guidance. As recognised leaders in the manufacture of high-quality piston rings, we’re perfectly positioned to answer your questions.