Repair Methods for The Dry Cylinder Liner of Diesel Generator Sets

The working environment of the cylinder of a diesel generator set is extremely harsh. Specifically, it has the following characteristics:

(1)The inner surface is directly affected by high-temperature and high-pressure combustion gases.

(2)During the working process, the temperature changes drastically. During the combustion process, the upper limit temperature of the combustion gas can reach about 2000°C, while the temperature of the cold air during the intake process is only in the dozens of degrees Celsius.

(3)The outer wall of the cylinder is affected by the cooling water, resulting in severe corrosion.

(4)The reciprocating movement of the piston generates alternating stress, causing severe wear of the cylinder.

Due to the extremely harsh conditions under which the cylinder operates, it can be said that the cylinder is truly in a "harsh situation" during operation. The degree of cylinder wear is the main basis for the major overhaul of the diesel engine and determines the service life of the diesel engine. Therefore, generator set manufacturers believe that it is very important to find ways to reduce cylinder wear.

Generally speaking, the repair steps for the cylinder of a diesel generator set are: boring and grinding the cylinder. When the cylinder cannot be bored any further or when there are no boring conditions, the cylinder liner is replaced or fitted. In most cases, there are no boring and grinding conditions. Therefore, when the degree of cylinder wear exceeds the service technical requirements, the cylinder is usually repaired by directly replacing or fitting the cylinder liner. The process of replacing a dry cylinder liner is as follows:

When fitting the cylinder liner for the first time, a standard-size cylinder liner should be selected to facilitate multiple liner-fitting repairs in the future. The surface roughness of the outer surface of the cylinder liner should not exceed 0.8μm; the cylindricity tolerance should not exceed 0.02mm, and the outer edge of the lower end of the cylinder liner should have an appropriate taper or chamfer.

According to the outer diameter of the selected cylinder liner, bore the cylinder to the required repair size and the appropriate surface roughness. The surface roughness of the bore for the liner should not exceed 1.60μm, and the cylindricity tolerance should not be greater than 0.01mm. If the original cylinder is equipped with a liner, a special tool can be used to pull out the old liner or a boring machine can be used to bore it out. The commonly used tools for pulling and pressing the cylinder liner are of two types: hydraulic and mechanical. After removing the old liner, check whether the bore for the cylinder liner meets the requirements. There should be an appropriate interference fit between the cylinder liner and the bore. Generally, for a cylinder liner with a flange at the upper end, the interference fit is 0.05 - 0.07mm; for a cylinder liner without a flange, the interference fit is 0.07 - 0.10mm. The clearance fit between the flange and the bore is 0.25 - 0.40mm for a cast iron cylinder liner. If the fit between the old bore and the newly selected cylinder liner does not meet the requirements, the bore should be rebored to the required size.

After cleaning the cylinder and the cylinder liner, apply an appropriate amount of engine oil on the outer wall of the liner. Insert the cylinder liner into the cylinder partway, align it with a square. Place a flat pad of hardwood or soft metal on the upper port of the cylinder liner, and then press it in with a 5 - 10t press. During the pressing process, always keep the cylinder liner perpendicular to the upper plane of the cylinder block, and increase the pressure gradually. After pressing in 30 - 50mm, release the pressure to allow the liner to adjust its position naturally. If the resistance suddenly increases during the pressing process, stop immediately and find out the cause to prevent damaging the cylinder wall. To prevent the cylinder block from deforming, when pressing in the dry cylinder liner, the method of pressing in cylinders in an alternating order should be adopted.

When the bore for the cylinder liner is enlarged and a suitable cylinder liner cannot be selected, the method of brush plating the outer wall of the cylinder liner can be used for repair. During brush plating, nickel plating solution and copper plating solution can be used. When multi-layer plating is used, a plating thickness of 0.20mm can meet the requirements of the interference fit between the cylinder liner and the cylinder wall.

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