Photo credit: Applied Nano Surface
In this article, we’ll discuss in detail which materials compose high-quality Cylinder Liners used in your car’s IC engines. If you own a car, you’d know cylinder liners don’t come cheap. These are precisely manufactured engine components you can buy from auto parts shops.
Cylinder liners are usually made from Cast Iron alloyed with Nickel, Chromium, Molybdenum, Vanadium or other elements. These are important engine components found in cars, vans, trucks, refrigeration systems on wheels, earthmover engines, tractors, and lots of other automotive vehicles. It’s also popularly used in marine diesel engines and diesel power plants to efficiently facilitate good combustion.
Curious how this piece of metal component is engineered to perform its duties? Let’s find out!
Cylinder Liner End-Product Requirements
A Cylinder Liner is a thin and hollow metal cylinder installed in an engine block to receive the traveling piston. The cylinder liner is there for many reasons.
1. Provide a Well-Lubricated, Anti-Corrosive Sliding Surface for Piston
First, it should form an effective sliding surface for the reciprocating piston while maintaining the lubricant on its walls. In order to do that, the liner should be made of anti-galling and anti-corrosive materials, which can naturally handle lubricants and induce lesser wear on contact parts.
Solution: This is one of the reasons cast iron is often used as it contains graphite, a natural lubricant. Its alloying elements also resist corrosion and improve the wear resistance at high temperatures.
2. Conduct High Temperature Heat to Coolant to Avoid High Thermal Stresses
Next, the cylinder sleeve should be made of a material which can facilitate efficient transfer of heat between its inner wall and water jacket/coolant. During combustion, the cylinder and piston is subjected to a high pressure and high temperature. The cylinder liner should be able to conduct the heat to the coolant to prevent wearing of engine parts.
The liner is fitted into the coolant section/water jacket to allow water to circulate it and help lower the temperature during combustion. To prevent leakage of water to the liner ports, O-rings seal the passage above the scavenge and ports.
3. Withstand Hoop & Radial Stresses from the High Pressure System
As mentioned earlier, during combustion, the cylinder liner becomes hotter than the water jacket. Since hotter objects tend to expand, so does the liner at working temperature. Its tendency is to grow in diameter or in length.
Imagine if the engine block is cast in one piece as the liner. This will definitely put the engine block at large thermal stresses which will lead to fracture.
To prevent fracturing the engine block, the liner is manufactured separately from the block. They are also made with different materials, with the liner made from a more superior range of elements. While the engine block can be manufactured from grey cast iron, the liner is made from cast iron alloyed with vanadium, molybdenum, chromium or other alloyants.
The cylinder liner is also made to be removable for replacements when it does experience wear.
Materials for Cylinder Liner Manufacturing
Now, different Cylinder Liner Manufacturers use different materials which they will usually specify in their manuals. The reason is that different vehicle engine blocks are made from various types of material which the liner should be compatible with.
Cylinder liners are manufactured from the old and known metallurgy process of Centrifugal Casting. Foundries often use pig iron or remelted pig iron to make cylinder liners in a blast furnace or induction furnace. Mild steel and other scrap metals can also be used for raw materials depending on the requirements.
But cast iron alone cannot sustain all the needs for a cylinder liner properties mentioned above, so alloying elements are added to increase its strength, hardness and overall properties.
Furthermore, Sulphur, Phosphorus and contaminants are kept in under the right levels.
Cast iron is usually the main material used in the manufacture of engine liners. It contains graphite which is great at making a natural lubricant for the piston traveling across it. Cast iron also has a porous surface which serves as a natural damper whenever the engine goes through vibrations.
Chromium is alloyed with cast iron providing it with texture hardness and anti-corrosive properties. Moreover, chromium improves the wear resistance of the cylinder liner.
Molybdenum stabilizes the carbide in cast iron boosting its strength without sacrificing machinability. Hence adding molybdenum as an alloying element in cast iron boosts its wear resistance against high pressure and temperature effects.
Nickel is added in small amounts in cast iron to improve its machinability and ensure uniform strength across the casting. It also boosts the mechanical properties of cast iron.
Copper hardens the ferrite and pearlite of cast iron thereby increasing its strength and hardness and improves its viscosity and machinability. It also improves its corrosion resistance, wear resistance and lowers its friction coefficient to enhance its sliding surface for the traveling piston.
Vanadium improves the microstructure of cast iron, refining its grain formation and thereby improving its metallic base structure. It makes cast iron less fragile and harder.
Titanium is added to combine with nitrogen to form titanium nitride (TiN). It prevents forming compacted graphite iron, which becomes an undesirable thick and short formation. Titanium lessens impurities and prevents blow-hole formation, but a higher quantity may pose undesirable properties for the cast iron.
Phosphorus improves the cast iron’s liquidity which further improves its grain structure.
Silicon helps reduce cast iron’s shrinkage rate and strengthens its structure.
2.5 to 4%
1.6 to 2.7%
What are the Different Types of Cylinder Liners Made Of?
There are 3 types of cylinder liners, namely, dry, wet and finned cylinder liners. Dry cylinder liners are the most common type available. These may have slight differences in material compositions depending on what you use for your engine.
Dry Cylinder Liners
Dry cylinder liners have no contact with the engine’s coolant, instead, have extremely close fit with the jacket to perform effective heat transfer for the piston ring. Hence, they have thinner walls than wet liners. To satisfy design requirements, they are constructed from high-grade cast iron and ceramic-nickel plating.
Dry liners are often honed for finishing with a transition fit (minimum clearance). Finished dry cylinder liners need not to be removed from the engine block and can be seamlessly installed with basic tools. Dry cylinder liners can also be supplied semi-finished with pressfit. This means you’d have to professionally fit it inside a cylinder block with effort and the engine block be removed before installing the liner.
Wet Cylinder Liners
Wet cylinder liners are subjected to direct contact with the coolant. The liner is manufactured with a flange at its top that fits in the groove on the cylinder block.
To prevent water ingress inside the crankcase, the wet liner is sealed at the bottom with packing rings. Furthermore, to withstand high pressure, impact loading and thrust, its wall thickness is larger than the dry liner ranging from 3 to 6mm.
Wet cylinder liners are often finished with aluminum to protect it from corrosion and rust.
Finned Cylinder Liners
Finned cylinder liners are also made with an impurity resistant metal but with an extra fin set at the top to provide efficient cooling. These are used for air-cooled engines and work like a dry liner. The only difference is it uses air as its cooling medium. To increase its corrosion resistance, finned cylinder liners are often phosphated.
Cylinder liners are usually made from cast iron alloyed with special elements to increase its hardness, toughness, resistance to corrosion and abrasion and provide a sliding surface. We hope you learned from this article on how each function of the cylinder liner in a diesel engine is combated with its proper material construction.