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Aluminum coating of piston rings

2020-03-25

The outer surface of the piston ring is often coated to improve the performance characteristics of the ring, such as by changing the frictional or abrasion characteristics of the surface. Some coatings, such as deposition coatings such as physical or chemical vapor deposition coatings, often improve the insertion characteristics of the ring.

Alu-coat is an insoluble copper-based coating based on alumina, which was developed in the late 1990s to reduce uptime of the new MAN B & W MC engines.

MAN Diesel has introduced an aluminum coating based on the effective running-in characteristics of its running-in and semi-wearing linings. Extensive experience and 100% success rate make alu-coat stand out. 1 running-in coating option. Alu-coat reduces trial time and creates a safe and reliable break-in period. Today, aluminum-coated rings are used in new engines and in older engines with honing and semi-honing bushings. The aluminum coating also reduces cylinder oil consumption during break-in.

Alu-coat is a semi-soft thermal spray coating with a thickness of approximately 0.25 mm. It was "painted" and looked a bit rough, but quickly formed a smooth contoured running surface.

The soft matrix on the coating causes hard insoluble matter to protrude onto the running surface of the ring and acts on the running surface of the liner in a slightly abrasive manner. The matrix can also be used as a safety buffer to prevent initial abrasion problems before break-in is complete.

The benefits of retrofitting are multiple. When installed in previously used bushings, the aluminum coating not only eliminates the running-in time of the piston ring. This coating also provides extra safety margin when dealing with operational issues. This process usually takes 500 to 2,000 hours. The slightly abrasive effect of aluminum-coated piston rings makes them ideal for replacing worn piston rings in connection with overhaul of the piston. Linings with wear rings often show signs of paint blemishes and / or blow-outs that are partially perforated and polished. Alu-coat causes some wear-out lining wear on the microscopic scale, which is usually enough to reconstruct the important opening structure of the lining, which is crucial for the tribology of the lining / oil / piston ring system.