. Railroad construction. Theory and practice . s a break in one main rail (or both)at the switch-block. In both methods the wheels are led to oneside by means of the ^4ead rails, and finally one line of wheelspasses through the main rail on that side by means of a are some designs by which even this break in the mainrail is avoided, the wheels being led over the main rail by meansof a short ynovahle rail which is on occasion placed across themain rail, but such designs have not come into general use. 255. Frogs. Frogs are provided with two channel-ways orflange spaces through which
. Railroad construction. Theory and practice . s a break in one main rail (or both)at the switch-block. In both methods the wheels are led to oneside by means of the ^4ead rails, and finally one line of wheelspasses through the main rail on that side by means of a are some designs by which even this break in the mainrail is avoided, the wheels being led over the main rail by meansof a short ynovahle rail which is on occasion placed across themain rail, but such designs have not come into general use. 255. Frogs. Frogs are provided with two channel-ways orflange spaces through which the flanges of the wheels move, 265 266 RAILROAD CONSTRUCTION. § 255. Each channel cuts out a parallelogram from the tread the wheel-tread is always wider than the rail, the wingrails will support the wheel not only across the space cut out bythe channel, but also until the tread has passed the point of thefrog and can obtain a broad area of contact on the tongue of thefrog. This is the theoretical idea, but it is very imperfectly. •♦—TOWARD SWITCH Fig. 130.—Diagrammatic Design of Frog. realized. The wing rails are sometimes subjected to excessivewear owing to ^hollow treads^ on the wheels—owing also tothe frog being so flexible that the point ^ducks when the wheelapproaches it. On the other hand the sharp point of the frogwill sometimes cause destructive wear on the tread of the the tongue of the frog is not carried out to the sharptheoretical point, but is purposely somewhat blunted. Butthe break which these channels make in the continuity of thetread area becomes extremely objectionable at high speeds,being mutually destructive to the rolling stock and to the jarring has been materially reduced by the device of ^ springfrogs—to be described later. Frogs were originally made ofcast iron—then of cast iron with wearing parts of cast steel,which were fitted into suitable notches in the cast iron. Thisform proved extremely heavy
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