The Locomotive - Lighthouse Survival Blog

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PUBLISHED BY THE HARTFORD STEAM BOILER INSPECTION AND INSURA COMPANY.
Vol. XXII. HARTFORD, CONN., JULY, 1901. /, No. Tf
Concerning' Pressed Steel Braces.
In the May issue of The Locomotive we printed an article entitled "A Common
Defect in Bracing," in which we drew attention to the fact that it is by no means uncommon
for boiler makers to provide adequate strength in the body of a brace, while
leaving the blade, or part by which the brace is secured to the shell, altogether too
weak across the line where the first rivet hole comes.
The article in question aroused a great deal of interest, if we may judge by the
considerable correspondence that it has called out ; and for this reason we desire to
supplement it by a few more remarks on the same subject. In the previous article, we
discussed only the solid type of brace, which is forged up out of round iron. The so-
called " formed braces," which are stamped or pressed into shape out of sheet metal, are
coming more and more into favor, in place of the forged kind, both because they are
cheaper, and because they have no weld. We desire to call attention, however, to the
fact that the formed braces are also liable to the same defect that we have already indi-
cated in connection with the solid ones.
Fig. 1.
—
D
B
The Shell End of a Pressed Steel Brace.
Fig. 1, for example, represents the shell end of a formed brace, with two rivet holes
to secure the brace to the shell. Such braces are almost invariably made strong enough
along the section CD, but are often too weak along AB, owing to the removal of metal
at this point, in making the rivet hole. It is common to find the brace 2f in. wide at
AB, over all ; and the usual thicknesses of material are §", T 7
5 ", and J". Taking the
|" brace as an example, we see that the sectional area of the solid part of the blade
(aloug CD) is |" x 2f " = 1.03 sq. in. The error that we wish to call attention to consists
in counting a brace of this sort as though it had a full square inch of sectional area, just
because it has such an area in the solid part. For the weakest section of the brace is
plainly that along the line AB, where the rivet hole is punched. Assuming that the
rivet hole is f§" i Q diameter, or (expressed decimally) 0.8125", it is evident that the
effective section, across AB, has a width of only
2.75"-0.8125" = 1.9375".
The effective sectional area at this point is therefore