Philadelphia Correspondence Schools of Foundry Practice

Annotation

Whilst the greatest effort has been made to ensure the quality of this text, due to the historical nature of this content, in some rare cases there may be minor issues with legibility. Semi-steel is a mixture of cast iron and steel scrap melted together in a cupola furnace, in contact with the melting fuel. A true semi-steel is composed of 50 per cent cast iron and 50 per cent. Steel, but these proportions are seldom used in mak ing mixtures, as it has been found that a smaller per cent. Of steel gives equally as good results and with more certainty of an even grade of semi-steel than the larger per cent. For castings desired to be soft and strong. But it is the common practice to call all cast iron containing steel a semi-steel. Steel is melted with cast iron for the purpose of increasing the strength of the iron, reducing the size of the crystalline structure of the iron and making a denser and closer metal that finishes and polishes similar to steel and gives a better wearing surface. Also to reduce the porousness of the iron and prevent leakage or sweating of the metal in fittings, valves, etc. Owing to the wide difference in the characteristics in foun dry pig, made from different ores, or smelted with different fuels, pig from the different furnaces frequently give different results when melted with steel and cast iron, even when showing the same analysis of the four elements commonly analyzed for in pig. For this reason no definite per cent, of steel that gives the best results can be stated that will apply to all iron.