Three-high rolling mill — relative roll rotation directions In a three-high mill (three work rolls placed one above another), which statement correctly describes the rotation directions so that the strip can pass alternately up and down without reversing the motor?

Introduction / Context:
Three-high mills permit consecutive passes without stopping to reverse roll rotation. By arranging the rotation directions properly, material can be threaded back and forth between gaps to increase reduction efficiency.

Given Data / Assumptions:

• Three stacked rolls: top, middle, bottom.
• Strip is alternately fed through top–middle and middle–bottom gaps.
• No electrical reversing between passes is desired.

Concept / Approach:
To draw the strip into each gap, the rolls that form that gap must present opposing surface velocities at the nip. Therefore, the middle roll must rotate opposite to both top and bottom rolls, while the top and bottom rotate the same way. This allows the strip to pass upward through one gap and downward through the other simply by changing the vertical position.

Step-by-Step Solution:

Verification / Alternative check:
Milling schematics of three-high stands depict exactly this arrangement to avoid motor reversal while enabling multi-pass reductions.

Why Other Options Are Wrong:

• Top–middle same direction: one of the nips would not bite simultaneously.
• Bottom–middle same direction: same issue.
• “Any one of the above” or “all same direction”: physically incorrect for feeding.

Common Pitfalls:
Assuming speed differences can substitute for correct direction; the nip requires opposing tangential velocities.

Final Answer: