Rolling mill driving mechanism

A sizing mill operated under a common driving system, comprising:

• prime mover means;
• an upstream rolling mill and a downstream rolling mill driven by said prime mover means;
• a first power transmission device for transmitting power from said prime mover means to said downstream rolling mill;
• a second power transmission device for transmitting power from said prime mover means to said downstream rolling mill, said second power transmission device allowing said downstream rolling mill to develop a higher feed speed than said first power transmission device;
• a one-way clutch incorporated in said first power transmission device for disengaging a driven side from a driving side of said first power transmission device when power transmission from said prime mover means to said downstream rolling mill is effected through said second power transmission device;
• and
• switching means for engaging said downstream rolling mill with said first power transmission device when material lying in a space between said upstream and downstream rolling mills comes to undergo tensile force such that said tensile force divided by mean resistance to deformation of said material is in excess of 0.2 and engaging said downstream rolling mill with said second power transmission device when said material lying in said space comes to undergo compressive force such that said compressive force divided by mean resistance to deformation of said material is in excess of 0.1.