Fig. 1 Overhauled cylinder liner of Mitsui-ADD engine

Fig. 2 Overhauled piston of Mitsui-ADD engine

Table 2 Comparison of Sliding Condition between Mitsui-ADD 4 Stroke Engine and Mitsui-MAN B&W 2 Stroke Engine

　

2.2 Test experience of MAN B&W 2 stroke engines

MAN B&W Diesel A/S has been testing coated liners of various kinds (25 pieces) since 1990. The liners have been installed on various bores from 35MC to 90MC. The service condition of these liners has been good. The bonding strength between the coating and the liner has proven to be excellent as no peeling off has occurred, even on the highest loaded engines.

　

3. SELECTION OF COATING MATERIAL

　

3.1 Coating Method

Cylinder liner of Mitsui-ADD engine is applied with coating by low-pressure plasma spray with extremely low wear performance, which was required by greatly severe sliding condition shown in Table 2. On the other hand, the sliding condition of 2 stroke engine is much lower than it as shown in Table 2. Thus, we have adopted the method of atmospheric plasma spray, which is also practical for coating large size of cylinder liners.

3.2 Characteristics of the Coating Layers

We adopted 2 kinds of coating layers as the candidates. One is Cr₃C₂ based NHM-1, and another is Cr₂O₃ based CMZ15. NHM-1 is similar to the layer tested on MAN B&W engines, and CMZ15 is similar to the layer on Mitsui-ADD engines. The micro structure of the layers are shown on Fig. 3 and 4.

　

Fig. 3 Micro structure of NHM-1 (x70)

Fig. 4 Micro structure of CMZ15 (x70)

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