. Machine design. SAFE SPEED FOR WHEELS. 167 Wide, thin rims are usually fastened together byinternal flanges and bolts as shown in Fig. 77, whilethe stocky rims of the fly-wheels proper are joineddirectly by links or T— head prisoners as in Fig. 78. As will be shownlater, the former is aweak and unreliablejoint, especiallywhen located mid-way between thearms. The principalstresses in fly-wheelrims are caused by centrifugal force. Fig. 78. 82. Safe Speed for Wheels. The centrifugal forcedeveloped in a rapidly revolving pulley or gear pro-duces a certain tension on the rim, and also a bendingof
. Machine design. SAFE SPEED FOR WHEELS. 167 Wide, thin rims are usually fastened together byinternal flanges and bolts as shown in Fig. 77, whilethe stocky rims of the fly-wheels proper are joineddirectly by links or T— head prisoners as in Fig. 78. As will be shownlater, the former is aweak and unreliablejoint, especiallywhen located mid-way between thearms. The principalstresses in fly-wheelrims are caused by centrifugal force. Fig. 78. 82. Safe Speed for Wheels. The centrifugal forcedeveloped in a rapidly revolving pulley or gear pro-duces a certain tension on the rim, and also a bendingof the rim between the arms. We will first investigatethe case of a pulley having a rim of uniform crosssection. It is safe to assume that the rim should be capableof bearing its own centrifugal tension without assist-ance from the arms. Let D=mean diameter of pulley of of —weight of material per cu. in. = .26 lb. for cast-iron. = .28 lb. for wrought iron or —number of number rev. per of rim in ft. per sec. 108 MACHINE DESIGN. First let us consider the centrifugal tension centrifugal pressure per square inch of concavesurface is p= .... (a) where W is the weight of rim per square inch of con-cave surface =wt, and r=radius in feet =^-r* 24 The centrifugal tension produced in the rim by thisforce is by formula (13) 2tSubstituting the values of p, W
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