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THE EFFECT OF EXPANSION ON SHRINKAGE AND CONTRACTION IN • IRON CASTINGS.*
The fact that iron expands, when heated, until fusion takes place, and that molten iron occupies more space than cold, solid iron of the same grade, is now universally admitted. It was proved by the extensive experiments of Mr. Thomas Wrightson, reported in the first volume of the Journal of the Iron and Steel Institute (1890 and 1891), and, in a manner, is illustrated in heavy founding by the shrinkage of the molten metal, which must be '' fed'' in order to obtain solid castings.
This decrease in volume requiring " feeding " while the metal is still liquid I call " shrinkage " (see pages 394 and 395), applying the term " contraction " to the decrease in volume which takes place after solidification, while the iron is cooling to atmospheric temperature. The light-work founder, not having the opportunity to make heavy castings, in which shrinkage can be observed, is apt to confound the two; but they are in fact distinct, and are separated by an act of expansion, which takes place at the moment of solidification.
^(Contribution by the author to the Discussion of the Physics of Cast Iron, at the Pittsburgh Meeting, February, 1896.)in Chapter LII,,pa^r jMi, Thru a^isiin, I)y referring to (liaptcr L1V,, paja* ,\<).\ tbc cj'fc-cts of expansion in causing* shrink holes in castings arc j'tillv outlined. broken and contraction had begun.