Mi;-,TURKS FOR HEAVY GRAY IRON CASTINGS. 277
not a modern or patentable idea. There is no fad or physic necessary, although a *' secret '' dope is sometimes used by so-called inventors, chiefly in order to throw a veil of mystery over a quite simple process. An analysis of one of these expensive " medicines, " which, however, possibly serves a useful purpose by agitating or mixing the metal in the ladle and perhaps reducing its sulphur contents, is given in the preceding paragraph.
"The phenomenal tensile strength (49,000 pounds and above) claimed for certain gun iron and semi-steel castings is also misleading, if the size and treatment of the attached test coupons is not stated, as we shall see later. Tests have been and are frequently reported as correct — i.e., as fairly representing the pieces the physical qualities of which they are intended to determine— when in reality they are from 3,000 to 10,000 pounds per square inch too high. This is due to the fact that the coupons cast on are only i to i% inches round instead of 3 inches, on castings 3 inches in section, and therefore chill and harden more rapidly and show a correspondingly higher strength than the castings. " In conclusion Mr. Ulke says: "The depth to which the ' chill ' penetrates, as determined by special chill-blocks 6x4x1^ inches in size, cast in special moulds in the same heat as the pieces, is a good indication of the tensile strength of the semi-steel cast, and serves the foundryman as a simple and convenient guide for grading his metal."
rielting gun iron mixtures in cupolas has given some exceptional results, as will be seen by the excellent strengths shown in Tables 52 to 55. These Salisbury irons have been used by large concerns, and are spoken of in the Iron Trade Review of December 15, 1898, asp or of similar material in a cupola, or in a ladle isap ...... 15 x ro x 1.50 i. So 22.50 iS.oo