Spring frog assembly

Below is a diagram of a typical spring-frog assembly from the book Elements of Rairoad Track Construction, which is available on Google Books.

Defective spring-frog assemblies were the cause of the derailments at Dassel, Minn. and Fero, ND in 1948.

Spring Frogs.—In stiff frogs there is a break in the continuity of both the main track and the turnout rails at the point of frog, there being a space over which the wheels must pass, the wheels being supported over this opening by a partial bearing on the wing rails of the frog, consequently a blow is struck by each wheel as it passes this point. These blows loosen and wear out the frog rapidly, besides necessitating a slow rate of speed. In the case of a turnout from the main track in which the main track is used considerably more than the turnout, a spring frog is used, the spring frog giving practically a continuous rail for the main track. In Fig. 95 is shown the arrangement of the rails in a spring frog. The spring in the case S holds the movable wing rail A B firmly against the adjoining part of the frog so that the main rail A C is practically unbroken. When a train is passing from the turnout to the main track, the wheel flanges enter the heel of the frog at 6 and force the wing rail over, the spring not being stiff enough to prevent this action, but being stiff enough to force the wing rail back after the flanges have passed. In the same manner the wing rail is forced over when a train enters the turnout from the main track, the guard rails which are always placed on both the turnout and main track opposite the frog assisting in this action. A spring frog is more complicated in design than a stiff frog, not only on account of the movable parts and the spring, but also on account of the special tie plates and braces necessary for the proper working of the frog. frog

The section through A B is shown in Fig. 96a.

The fixed wing rail D E is bolted to the frog point rails through rolled steel fillers shown in the figure. In Figs. 96a and 96b is shown the reinforcing bar which is riveted to the web of the movable wing rail A B. The bar is not shown in Fig. 95, as the additional lines necessary to show it would add confusion to the figure. For the same reason the spikes, the bolts, and some of the rivets are not shown. The movable wing rail A B slides over the tie plates and is braced when pushed over by the flanges by the braces f f, shown in Figs. 95 and 96c, the braces being riveted to the tie plate and shaped so that they fit snugly against the web of the rail or the reinforcing bar. The wing rail is further controlled by the arm G, which is riveted to the rail and moves through a socket riveted to the tie plate. In Fig. 96b is shown a section through C D.

Below is a more detailed spring frog drawing from the book Track Standards, also available on Google Books.

spring frog