Question

In rolling, the point on the surface of contact between roll and sheet where surface velocity of the roll is equal to velocity of the sheet is referred as

• A. no-slip point
• B. no-stick point
• C. maximum slip point
• D. maximum stick point

Hint:

Remember that the friction in rolling acts in two directions. Before the no-slip point, friction pulls the sheet in. After the no-slip point, friction opposes the faster-moving sheet. The no-slip point is where the direction of the friction force on the sheet reverses.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
The rolling process involves passing a sheet of metal between two rotating rolls to reduce its thickness. The friction between the rolls and the sheet is essential to pull the material through. This friction causes relative motion, or "slip," between the roll surface and the sheet surface.
Step 2: Detailed Explanation:
- At the entry point of the roll gap, the peripheral velocity of the roll (\(v_r\)) is greater than the entry velocity of the sheet (\(v_i\)). The rolls are moving faster than the sheet.
- As the sheet passes through the roll gap, its thickness decreases, and to conserve mass, its velocity must increase. The sheet accelerates.
- At the exit point, the exit velocity of the sheet (\(v_f\)) is greater than the peripheral velocity of the roll (\(v_r\)). The sheet is now moving faster than the rolls.
Since the sheet's velocity starts lower than the roll's velocity and ends higher, there must be a single point along the arc of contact where the sheet's velocity is exactly equal to the roll's peripheral velocity (\(v_{sheet} = v_r\)). At this specific point, there is no relative slipping between the two surfaces.
This point is known as the no-slip point or the neutral point.
Step 3: Why This is Correct:
The term "no-slip point" directly describes the condition where the relative velocity between the roll and the sheet is zero. The other terms are not standard terminology for this specific point in the rolling process.