Rolling practice — kinematics of a two-high mill A two-high rolling mill has two counter-rotating work rolls. In conventional (non-reversing at the instant), how do these two rolls rotate to bite and pull the strip through?

Introduction / Context:
Understanding roll kinematics is essential for predicting neutral points, frictional traction, and strip transport through the bite. Two-high mills are basic configurations used for roughing or laboratory practice, and their motion principles underpin more complex mill stands.

Given Data / Assumptions:

• Two-high mill with one strip pass through the roll gap.
• No intentional speed mismatch (i.e., no differential speed rolling).
• Friction provides grip to pull and deform the strip.

Concept / Approach:
For the strip to be drawn in, the roll surfaces must move toward the roll gap from both sides, which requires opposite directions of rotation. Typically, both rolls rotate at the same angular speed in opposite directions so that their surface velocities at the nip oppose each other, compressing and transporting the strip through the bite. Any intentional speed difference is a specialized process (e.g., skin-pass with tension control), not the default two-high arrangement.

Step-by-Step Solution:

Verification / Alternative check:
Standard rolling schematics show counter-rotation with matched speeds in two-high mills; reversing mills change direction between passes but retain opposite directions during a given pass.

Why Other Options Are Wrong:

• Same direction: would eject the strip rather than pull it in.
• Different speeds: not typical for basic two-high operation.
• One roll stationary: cannot transport material.

Common Pitfalls:
Confusing reversing mill sequence with instantaneous rotation directions; overlooking the role of friction and forward slip.

Final Answer: