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Cylinder-wear Research Summarized

18th November 1938
Page 84
Page 84, 18th November 1938 — Cylinder-wear Research Summarized
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Which of the following most accurately describes the problem?

T"past few years have seen intensive research carried out on the many aspects of the problem of cylinder wear in internal-combustion enginas. The results of these researches are summarized and discussed in an interesting booklet entitled " Cylinder Wear, with Special Reference to Liner Materials," by Gwilym Williams, A.M.I.A.E., M.S.A.E., which has recently been issued by the Bureau of Information on Nickel, Thames House, London, S.W.1.

An easily digested summary' of the interim report of the Research Department of the Institution of Automobile Engineers, concerning its investigation of corrosion in cylinder bores, is included, and the conclusions reached in these researches are, says the author,

amply supported in practice. Wellestablished facts concerning the mechanical side of cylinder wear are also summarized, and a section is included giving consideration to the physico-chemical aspect of the problem.

Oil-absorption Data.

A section on lubrication contains useful facts on the subject of absorption, and it is noteworthy that in " boundary" lubrication the metal surface, whether it be iron, alloy steel, non-ferrous or metalloid, makes only about 5 per cent. difference to the coefficient of friction. The metal of the cylinder bore or cylinder liner does not, therefore, contribute niuch to the " oiliness " of the oil.

There is reason to believe, says the author, that " oiliness" depends partly upon the power of the oil to adhere to or saturate • the surface of a4S the metal molecules, and partly upon the end group of the chain atoms in the oil molecules. The effect of the temperature of the cylinder walls on lubrication is also described and the question of " boundary " lubrication discussed.

Photomicrographs of the surfaces of cylinder bores made from various metals and at different stages of their life add interest to a section dealing with the bore " skin." It is demonstrated that the " skin " which is formed on a cast-iron cylinder block by running-in an engine for a considerable period is identical in composition with the east iron beneath it. There is, however., a physical effect, in that the surface of the cast iron is, to a greater or lesser extent, work hardened.

Before dealing with the problem of liners and liner materials, there is included a useful classification of cylinder wear showing the types of wear that may be expected under various conditions. .

Some notes on the design of both wet and dry liners form a useful introduction to the subject of liner materials, and the advantages and disadvantages of sand and spun casting are described.

A discussion on the general com position of bearing metals which, in the majority of cases, consist of a material with a hard, relatively brittle constituent embedded in a soft and relatively tough matrix, leads the author to draw a parallel between the functioning of bearings and cylinder liners. The composition 'of various • liner materials are described, and photomicrographs clearly illustrate the hard constituent embedded in a softer but tough matrix.

To meet corrosive and abrasive wear and to combat the slight wear under " boundary " lubrication conditions, the author has come to the conclusion, after considerable research, that the most effective material is a nickel-copper-chromium austenitic cast iron; the chemical composition, as used for spun-cast cylinder liners, is as follows :—Total carbon, 3.0 per cent. approx.; silicon, 2.0 per cent. approx.; manganese, 1.0 per cent. approx.; sulphur, 0.1 per cent. Max.; phosphorous, .0.2 per cent, to 0.5 per cent.; nickel, 13.0 per cent, to 15.0 per cent.; copper, 5.0 per cent. to 7.0 per cent.; chromium, 1.5 per cent. to 4.0 per cent.

Combating Corrosive Wear.

The high resistance to corrosion of this material is of special benefit in combating the corrosive wear during starting, moreover, its work-hardening properties, its toughness and embedded cementite are invaluable in resisting the slight wear that takes place under " boundary " lubrication and even under undesirable dry-wear conditions.

Some informative wear figures obtained in actual service are given, and the examples quoted have been obtained from vehicles running under varied conditions of operation.

This booklet, which is the first of a series to be written by leading authori ties, and of special interest to automobile engineers., may be obtained free of charge from the Bureau of Information on Nickel, at the address given in the first paragraph,


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