. The railroad and engineering journal . e bars Question 182. Is there any form of construction which ob-viates the difficulty of staying crown-sheets -which has been pointedout? .-Ins-uier. Yes. In what is l<nowci as the Helpaire fire-boxboth the crown-sheet and the shell of the boiler over it are madeflat, as shown in figs. 97 and 98. which show longitudinal andtransverse sections of this form of fire-box. These plates arestayed with screw-bolts, b, b, b, at right angles to the sides, which are also flat, are stayed with rods, r r, r r,which pass through both the sides. Questio
. The railroad and engineering journal . e bars Question 182. Is there any form of construction which ob-viates the difficulty of staying crown-sheets -which has been pointedout? .-Ins-uier. Yes. In what is l<nowci as the Helpaire fire-boxboth the crown-sheet and the shell of the boiler over it are madeflat, as shown in figs. 97 and 98. which show longitudinal andtransverse sections of this form of fire-box. These plates arestayed with screw-bolts, b, b, b, at right angles to the sides, which are also flat, are stayed with rods, r r, r r,which pass through both the sides. Question 183. How are the ends or heads of boilers strength-ened? Answer. Usually diagonal stays or braces, s s s, figs. 90 and95, are arranged with one end attached to the end or head ofthe boiler, and the other is fastened to its outside shell. Question 184. What precaution should be tai-en in the designand construction of stays or braces like those -vhich are used forstrengthening the ends or heads of boilers and supporting the crown-bars ?. Fig. 95bear on the fire-box only at each end, as shown in fig. 91, andare usually made with projections, 7/, which rest on the edgesof the side plates. Iron rings or washers are interposed be-tween the plate and the bars at the points where the bolts orrivets which secure the rivets pass through. This permits the Fig. 96Answer. Great care should be taken to make the parts bywhich the stays are fastened as strong as the main part of thebar which forms the brace. The principle that the greateststrength of any part of a structure is only tTiat of its weakestpart applies with especial force to boiler-stays. Often the
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