“This great increase of strength, stiffness, elasticity, and resilience is obtained at the expense of some ductility, which diminishes as the tenacity increases. The modulus of ultimate resilience of the cold-rolled iron is, however, above 50 per cent. of that of the untreated iron.
“Cold-rolled iron thus greatly excels common iron in all cases where the metal is to sustain maximum loads without permanent set or distortion.”
From this it appears that cold-rolled iron is peculiarly adapted for line shafting. Suppose, for example, a given quantity of power to transmit, and that a length of cold-rolled and a length of hot-rolled iron be connected together to form the line. Then the diameters of the two being such as to have equal torsional strength, we have—
1st. That the weight of the cold rolled will be the least, and it will, therefore, produce less friction in the hanger bearings.
2nd. That the cold rolled will be harder, and will therefore suffer less from abrasion of the journals.
3rd. That being of smaller diameter the journals are more easily and perfectly lubricated.
The resistance to transverse stress (say) 50 per cent.; but the elastic limit under transverse stress is increased from 80 to 125 per cent., accepting the lesser amount we have in the case of the two shafts.
4th. That the resistance to permanent set or bend will be 30 per cent. more in the cold rolled.
5th. The accuracy to gauge diameter enables the employment of a coupling having a continuous sleeve, and gives an equal bearing along the entire coupling bore.
6th. The reduction of shaft diameter enables the employment of a smaller and lighter coupling; and