Fig. 20 Axial and Radial Clearance

　

An aid to judging the dynamic behaviour of the rings is offered by the computer programs developed in recent years by Goetze [6]. Such theoretical investigations cannot cover all the factors that affect ring dynamics and tribology. but they do provide an initial overview of the possible behaviour of the ring pack and contribute to reducing the development time of the engine.

　

5. SUMMARY OF RING PACKAPPLICATIONS

　

The development aspects discussed above have, to a great extent, been incorporated in the ring packs specified for 'state-of-the-art' medium speed engines.

A typical example of the way in which pistons have changed in recent years is given in (Fig 21). The number of rings has been drastically reduced in accordance with the latest level of knowledge in tribology and wear research. The more exacting the engine demands, the more it is necessary to specify advanced piston ring designs. The rings in the top groove are chromium plated or thermalsprayed coated and, for operation in heavy fuel engines, the same applies to the second and the third and fourth rings. The compression rings have asymmetrical barrelled peripheral surfaces and are, if necessary, pressure relieved. The taper faced rings in the second groove are replaced in most of todays engines by asymmetrical barrel shaped rings, as in the first groove to ensure a good lubrication of the first ring.

　

Fig. 21 Ring Packs for Four-Stroke Medium Speed Diesel Engines

　

The chromium coating has been upgraded by the introduction of the CKS 36 treatment developed by Goetze. It is now the best coating to interact with all existing liner materials and treatments with the exception of chromium plated cylinder bores.

The rings in the top groove in heavy fuel application are more and more chromium plated on the side faces and additionally run in hardened or chromium plated grooves to counter axial wear. Alternatively, axial as well as radial wear may be minimized by specifying high alloy, heat treated cast iron ring materials (eg F14).

Conformable oil control rings are incorporated, mainly with coil spring backing, which have the advantage of high flexibility, a flat spring characteristic and a broad spectrum of variation in wall pressure.

Finally a typical ring pack used today in a heavy fuel high performance engine is shown in (Fig 22).

　

Fig. 22 Piston Ring Proposal (230 mm)

　

6. ANTIPOLISHING RING (Fig. 23)

　

By lookink to the piston ring system today it is evident to keep in mind the importance of the antipolishing ring. This element which is already known since many years became a standard solution in most medium speed engines today. Besides the effect of avoiding bore polishing problems the ring has the great advantage to reduce the oil consumption up to 50%.

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