The function of a fly-wheel in a system with a rapidly fluctuating load is to equalize the power requirements, thus reducing the sudden shocks to the moving parts and thereby the strains on the machine frame and both the mechanical and electrical strains on the driving motor. For the fly-wheel to be effective the speed characteristic of the motor should be such that the motor will slow down as the load increases and will increase in speed as the load decreases. In the case of large shears the

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... ll working load is applied suddenly and the fly wheel is called upon to deliver energy through a very short space of time, varying from one-half a second to two seconds, according to the size of the machine and the size and condition of the material cut. Thus it is evident that the speed characteristics of the driving motor must be inherent, as the time is too short to depend upon a practical control means for changing the motor characteristics. The ideal working condition for motor-driven shears would be one in which the fly-wheel does all of the cutting work, leaving for the motor only the friction load and the work of accelerating the fly-wheel after the cutting and subsequent slowing down period. The results of a test made on a large bloom shears, which is referred to later, show that this ideal condition can be approximated very closely when the speed characteristics of the motor are properly chosen. Before outlining the exact conditions which the motor speed characteristics should meet, it would be well to analyze the speed curves of a shunt, a standard compound, a 50 per cent compound, and a series direct current motor. These. curves as shown in Fig.