Rodillos

Experiment (3)

Rolling Operations
Dr. Mohammad Al-tahat Department of Industrial Engineering. University of Jordan. Lab. Of Manufacturing Processes. Course No: 906412, 0906412

1. Objective: The main objective of this experiment is to study the process of rolling of metals and to examine the deferent factors influence the process. 2. Background: For more information about the subject of theexperiments, it is recommended for the student to review section 6.3 of chapter six of the text. 3. Theory It is the first process in converting a cast material (ingot) into a finished wrought product, rolling process can be defined as: the Bulk deformation process of reducing the thickness or changing the cross-section of a long work-piece by compressive forces applied through a set of rolls(mills) similar to rolling dough with a rolling pin to reduce its thickness as demonstrated in figure 5.1.

Figure 5.1: Rolling process description.

Rolling accounts for about 90% of all metals produced by metal forming. The process first developed in the late 1500s the basic operation is flat rolling (simply) where the rolled products are flat plate and sheet. Plates: having greater than 6mm –0.3 m thickness. Sheets: having less than 0.6 mm. A schematic outline of various flat and shape rolling process are shown in figure 5.2 the figure implies the sequence of operations needed to convert an ingot or a continues casting into a useful product like strip, plate, bar etc.

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Figure 5.2 Schematic Outline Of various flat-and shape rolling processes

1. Mechanics ofRolling
Strip Sliding. Schematic illustration for flat rolling is shown in figure [5.3]. Because of volume constancy, the velocity of the workpiece (strip) must increase as it moves through the roll gap. At the exit of the roll gap, the velocity of the strip is Vf. because Vr is constant along the roll gap, sliding occurs between the roll and the strip.

FIGURE [5.3]: Schematic illustration of theflat rolling process. A greater volume of metal is formed by rolling than by any other metalworking process.

Neutral point. At a certain point a long the arc of contact strip velocity and roll velocity are the same. It is known as neutral point, or no slip point to the left of the neutral point, roll moves faster than the workpiece, and to right the workpiece moves faster than the roll.

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FIGURE [5.4]: Relative velocity distribution between rolls and strip surfaces. Note the difference in the direction of frictional forces. The arrows represent the frictional forces acting on the strip.

Forward slip. In rolling is defined in terms of the exit velocity of the strip Vf and the surface speed of the roll Vr as: Forward slip = (Vf –Vr)/Vr State of Stress in Rolling andRoll Pressure The calculation of forces and stress distribution in flat rolling is more involved than in upsetting because of the curved surface of contact. In addition, the material at the exit is strain hardened, so the flow stress at the exit is higher than that at the entry.

FIGURE [5.5]: Stresses on an element in rolling: (a) entry zone and (b) exit zone.

The stresses on an element in theentry and exit zones are shown in figure [5.5]. Using the slab method of analysis for plane strain.

Figure [5.6]: Forces on the element.

From the equilibrium of the horizontal forces on the element in figure 5.6,
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(σ x + dσ x )(h + dh) w − (2 pRdφ sin φ ) w − σ x hw ± (2µpRdφ cos φ ) w = 0 (σ x + dσ x )(h + dh) − 2 pRdφ sin φ − σ x h ± 2µpRdφ cos φ = 0
σ x h + σ x dh + dσ xh + dσ x dh − σ x h = 2 pRdφ (sin φ m µ cos φ ) σ x dh + dσ x h = 2 pRdφ (sin φ m µ cos φ )

for unit width (w = 1)

FIGURE [5.7]: Stresses on an element in plane-strain compression (Rolling) between two rolls.

1 [σ 1 − υ (σ 2 + σ 3 )] E 1 In general ε z = E [σ 2 − υ (σ 1 + σ 3 )] 1 ε y = [σ 3 − υ (σ 1 + σ 2 )] E The maximum value for v (or that value for which volume change is zero) is...