In Fig. 7 is shown an illustration of a spring draft-gear and the method of its attachment to the car-frame. This is the recommended practice as adopted by the Master Car-builders' Association at their convention in 1896. By vote of the association it was decided, as their opinion of standard practice, that the draft-spring should be 6¬" in diameter, 8" long, and with a permissible motion of 2⅛". The capacity of the spring was placed at 19,000 pounds. These figures are given since they indicate the standard in accordance with which a large proportion of the freight-cars now in existence were built; but, as shown later, they are far from representing the present standard practice for future construction. It should be noted that the essential features of such a coupler consist of the yoke N which passes around the two followers BB which are separated by the heavy spiral springs R; the followers BB extend out beyond the yoke, where they press against the shoulders which are fastened into place by four heavy bolts. During compression the front follower presses against the spring which transmits the pressure to the rear follower, which, in turn, transmits the pressure to the shoulders and the car-body. During tension the yoke N is drawn forward, which draws forward the rear follower which transmits its pressure through the spring to the front follower, which, by pressing against these shoulders, draws the car forward. In either case the spring is compressed. Fig. 7 also gives in outline form the standard dimensions and shape as required for an M.C.B. coupler. No details are given, as they are left to the individual designer of the coupler. Any couplers which have those same outline dimensions may be operated with any other coupler with the same standard dimensions, regardless of their precise design. Spring-couplers are used on a very large majority of the cars now in service, and they answer their purpose as long as the total weight of the cars with their loads is not excessive, and provided that the handling of cars in freight-yards is done with care. The enormous freight business handled by railroads during recent years has resulted in a considerable increase in the cost of freight-car repairs, which has been due very largely to the fact that freight-yard men have been required and urged to do their work as quickly as possible. This has resulted in a far higher average velocity in freight-yard movements. The invariable consequence is a jerking of the cars when they are pulled forward and a severe compression of the cars when they run together. Considering that the effect of impact increases as the square of the velocity, an increase in the velocity of yard movement from one mile per hour to two or three miles per hour will mean that the destructive impact will be from four to nine times as great. The adoption of very heavy steel cars has had the incidental disadvantage of increasing the cost of repairs of the lighter wooden cars, since the heavy cars, with their greater weight and especially with the greater velocity of freight-yard movement, which is now so common, will crush lighter cars between them. The inevitable result has been that with the continued growth of weight of rolling-stock even the spring principle became inadequate. It became necessary to introduce some device which would be better capable of absorbing the very great shocks due to compression and also the jerks due to the sudden starting of a very heavy and powerful locomotive. This was accomplished by means of "friction" draft-gear. The committee on draft-rigging of the Western Railway Club reported to the club in May, 1902, on some tests of draft-rigging as follows:

"From the general results of the tests, it is believed that the tensile strains in draft-gears with careful handling will frequently reach 50,000 pounds, with ordinary handling 80,000 pounds, and with decidedly rough handling fully 100,000 pounds, while the buffing strains can be placed at 100,000, 150,000, and from 200,000 to 300,000 pounds respectively. In extreme cases the buffing strains will go considerably above the last-named figure. We think the figures show the necessity of something better and more effective than the spring draft-gear as commonly used. It would be reasonable, in view of the above figures, to require draft-gears and underframes to be capable of withstanding tensile strains of 150,000 pounds, and buffing strains of 500,000 pounds, and it is evident that the present spring resistance is inadequate. Whatever one may think of the details of the various friction draft-gears, it must be evident that in the character and amount of resistance they are superior to, the spring-gears".

98. Friction Draft-Gear

The principle underlying friction draft-gear is that of a device which shall harmlessly transform into heat the excessive energy produced by the shocks of the operation of trains. The frictional draft-gear constructed by the Westinghouse Air-brake will be here briefly described. This gear employs springs which have sufficient stiffness to act as ordinary spring-couplers for the ordinary pushing and pulling of train operations. Sections of the gear are shown in Figs. 8 and 9, while the method of its application to the framing of a car of the pressed steel type is shown in Fig. 10, a and 6. When the draft-gear is in tension the coupler, which is rigidly attached to B, is drawn to the left, drawing the follower Z with it. Compression is then exerted through the gear mechanism to the follower A which, being restrained by the shoulders RR, against which it presses, causes the gear to absorb the compression. The coil-spring C forces the eight wedges n against the eight corresponding segments E. The great compression of these surfaces against the outer shell produces a friction which retards the compression of the gear. The total possible movement of the gear, as determined by an official test, was 2.42 inches, when the maximum stress was 180,000 pounds. The work done in producing this stress amounted to 18,399 foot-pounds. Of this total energy 16,666 foot-pounds, or over 90%, represents the amount of energy absorbed and dissipated as heat by the frictional gear. The remaining 10% is given back by the recoil. The main release spring K is used for returning the segments and friction strips to their normal position after the force to close them has been removed. It also gives additional capacity to the entire mechanism. The auxiliary spring L releases the wedge D, while the release pin M releases the pressure of the auxiliary spring L against the wedge during frictional operation. If we omit from the above design the frictional features and consider only the two followers A and Z, separated by the springs C and K, acting as one spring, we have the essential elements of a spring draft-gear. In fact this gear acts exactly like a spring draft-gear for all ordinary service, the frictional device only acting during severe tension and compression.

Application of the Westinghouse friction draft gear to freight cars of the pressed steel type.

Fig. 10. Application of the Westinghouse friction draft-gear to freight-cars of the pressed-steel type.