CYLINDER LINER
(i) Abrasion, and (ii) Corrosion
Abrasion depends on the atmospheric con- dition and the efficiency of the air filter and oil filter. Dusty atmospheric air is more harm- ful as it increases abrasion in the cylinder.
Corrosion of the cylinder is caused due the corrosive products of combustion, which are formed after burning of fuel with air. Cor- rosion is accelerated at low cylinder tempera- ture due to acid bearing moisture on the cyl- inder walls,
The use of separate barrels or sleeves, which are known as cylinder liners, provides a long life to the cylinder. These cylinder liners are made of superior material and are fitted in the cylinder block. The liners are removable and can be replaced when worn or damaged. The liners should have good wear resistance and the ability to retain oil to lubricate the surface between the walls and the piston rings.
Materials for Cylinder Liners:
For cylinder liners nickel-chromium iron has been popularly used. The nickel-chromium iron used contains carbon 3.5%; manganese 0.6%: phosphorous 1.5%; sulphur (0.05%; silicon 2%; nickel 2%; and chromium 0.7%.
To increase the wear resistance, the liners are hardened by heating to 855°C-865°C for 30 to 40 minutes and then quenched in oil. By such heat treatment, the life of the liners is increased to three times as compared with grey iron or cast iron cylinders.
Types of Liners
The cylinder liners or sleeves are of two types:
1. Dry liners.
2. Wet liners
1. Dry Liners:
Dry liners are made in the shape of a barrel having a flange the top as shown the Fig. 3.3.
The flange keeps the liner in position in the cylinder block. The liner fits accurately in the cylinder. The perfect contact of the liner with the cylinder block is necessary for the effective cooling liner. Also, the gas pressure, piston thrust and impact load- ing during combustion are resisted by the combined thickness of liner and the cyl- inder. Therefore, dry liners are thinner having wall thickness varying from 1.5 mm to 3 mm and are used mostly for reconditioning worn liners. The dry liners are not in direct contact with cooling water.
2. Wet Liners :
Figure 3.4 shows a wet liner. A wet liner is so called because the cooling water comes in contact with the liner. This liner is provided with a flange at the top, which fits into the groove made in the cylin- der block. To stop leakage of cooling water in the crankcase, the lower end of wet liner is sealed with the help of sealing rings or packing rings.
As the wet liner has to withstand gas pressure, thrust and impact loading, the wall thickness of the liner is increased and is made more than that of the dry liner. Generally, the wall thickness of the wet liner ranges from 3 mm to 6 mm. The outside of the liner is coated with aluminium so that it is protected from rust. The wet liner is better cooled than the dry liner. It is easily removable when it is worn-out or damaged.
Comparison of Dry and Wet Liners:
1. A wet liner can be easily replaced whereas a dry liner requires special tools because it is tight-fitted in the cylinder block.
2. A wet liner is properly cooled as it comes in direct contact with the cooling water, whereas a dry liner does not come in direct contact with the cooling water. Hence the working temperature of a dry liner is more than a wet liner.
3. A wet liner needs leak proof joints, so that the cooling water does not leak into the crankcase, whereas a dry liner has no such requirement.
4. A wet liner does not require accurate finishing on the outside, whereas a dry liner needs accurate finishing.
5. Finishing may be completed in a wet liner before assembly, whereas a dry liner needs finishing after assembly.
