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Full text of "Metallurgy Of Cast Iron"

SUMMARY OF   RESULTS OF THE A. F. A.   TESTS.        573
1.69 diameter finished bars (Table 126, page 570). some casts having a difference of only .01 diameter, show 5,380 ..pounds or 5.25 per cent, less tensile strength than the unfinished bars. Carrying this to transverse tests, in calculating the difference of fifty tests of each class in similar sizes of bars, we find that the finished bars were 212,000 pounds or 16.2 per cent, weaker than the unfinished bars. The hard grades show a greater difference than the soft grades in this respect. Of all the transverse tests in Tables 115 to 126 there are only about six finished bars that show a greater strength than their mates in the unfinished bars. The j^-inch bars are ignored in all the computations because of their unreliability, as proven by the series of A. F. A. and other tests.
The adaptability of different size bars for compara= live testing is well demonstrated by the A. F. A. series of tests. They strongly endorse the author's contention against the use of bars as small as % inch square or round, and also show that bars can be too large as well as too small. The committee's report recommends bars to be no smaller than i% inches diameter and not larger than 2^ inches, and all bars to be cast on end, which is another point originally and strongly advocated by the author. These recommendations are seen on pages 575 and 583. For several years the author has realized from experience in testing that a i y% -inch diameter bar was about as small as should be used where the best records are desired in gray irons, but he accepted the i^-inch diameter bar shown in other parts of this work for testing, on account of its being of an area the most used in the past to meet the general conditions of founders whod on page 555.SlolrlciiKc .i! : •,»   l'fjii]-.y!v,iu;.i M.ii!« ,«!.'..   <•*'•, t«.Mii«! i v, I'it l:,l.ui>;, P,i,ll. The chilland j^reen sand  showedast on end, us such will tfive truer results than the [J4™inch round bar in general practice, especially in making comparison <>i; the widest ranges in grades.temper '' or damp-              ,| |