A cylinder liner is a cylindrical portion that is fitted into an engine block to form a cylinder. While some may know this as the cylinder sleeve, this is actually a cylinder liner.
What does a Cylinder Liner do?
Cylinder liners are one of the most important parts in an engine block. The cylinder liner serves as the inner surface or wall of the cylinder where it forms a sliding surface for the pistons and piston rings while containing the lubricant within it. Cylinder liners are expected to fulfill four very important characteristics in order to be efficient. They have to have good anti-galling properties, should be less susceptible to wear on the cylinder liner itself, should produce less wear on the piston rings and should consume less lubricant.
The cylinder liner absorbs the heat of the combustion through the piston and transfers this to the coolant in order to keep the engine block from overheating. Since the cylinder also acts a barrier that prevents the leakage of combustion fuel and other gases, it is necessary that the cylinder liner be able to withstand high temperature as well as high-pressure conditions.
The cylinder lining experiences a tantamount number of varying kinds of stress.
- Circumferential or hoop stress: This is a normal kind of stress that is experienced in the tangential direction over a cylinder liner. A very common example of hoop stress is the tension that is applied to the iron bands on a wooden barrel. In the case of a cylinder liner, the force applied on it by the difference in pressure will give rise to hoop stress.
- Axial stress: Here, the stress is produced along the axis of the cylinder and cylindrical lining.
- Radial Stress: This the type of stress that is produced along the same plane of the axis but at ninety degrees to it.
Another factor that contributes to stress is the great difference in temperature between the outside and inside of the cylindrical liner due to it being in close contact with the combustion chamber.
Given the fact that the requirements of a cylinder liner in terms of strength and resistance is high, the most commonly used material to make cylinder liners is cast iron. Cast iron also has lubricating properties that stem from the presence of micro amounts of graphite being present in it. Since cast iron is non-porous, this material can prevent the risk of seizure and extensive galling that can result from the rubbing of the piston against the liner. However, since cast iron is not a very strong metal in its original form, it is often used as an alloy that contains chromium, copper or nickel apart from cast iron.
Cylinder liners are generally cast in two ways depending on the kind of engines they are designed for – a centrifugal casting method or the sand casting method. The sand casting method is generally used for the manufacturing of large and slow speed engines whereas the centrifugal casting method is used for in the case of high and medium speed engines.
Hence, a cylinder wall in an engine of a truck or high power vehicle is subjected to high temperature and high pressure which makes it necessary that they are excellently resistant to wear and tear. With the current trend of light motor vehicles, the use of cast iron has given way to the use of aluminum alloys that are more durable. However, aluminum alloys also have their faults when it comes to operation and wear resistance which is much less in the case of cast iron.
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