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19 A - METAL BULK DEFORMATION - ROLLING


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Bulk deformation processes
PROCESSES TO DEFORM BULKY PARTS, commercially and technologically important processes, achieving net shape or near net shape by deforming the workpiece in hot, warm, or cold temperature, strengthening the product when the operation is done at cold temperature, processes relying on operations such as: [1] Rolling, [2] Forging, [3] Extrusion, [4] Drawing. >>> RFED: ROLLING, FORGING, EXTRUSION, DRAWING.
ROLLING
A deformation process in which the thickness of the workpiece is reduced by compressive forces exerted by two opposing rolls. The rolls rotate, thus pulling and simultaneously squeezing the workpiece between them. Process requires expensive equipment and is good for big quantities >>> EXPENSIVE ROLLS SHAPE STURDY METAL.
Hot rolling
ROLLING OF HEATED STEEL, a process producing large amount of deformation without work hardening and residual stresses, yet producing rough surface finish due to oxidation and poor dimensional control due to shrinkage. The ingot, after soaking is rolled into an intermeadiate shape: bloom, slab, or billet. HOT AND SIMMERING METAL FORMS INTO INACCURATE AND ROUGH SHAPE
Soaking
HEATING THE STEEL TO HOT ROLLING TEMPERATURE - 1200[degC], using a furnace called a soaking pit, soaking the ingot for a few hours, until the temperature throughout it is uniform
Bloom
A 15cm x 15cm SQUARE PROFILE use to make structural shapes, such as rails for rail road tracks.
Slab
RELATIVELY FLAT SECTION OF METAL, rolled from ingot or bloom, used to make plates, sheets, and strips of metal used in sheet metal, ships or what ever.
Billet
A 4cm x 4cm SQUARE rolled from a bloom, a profile used to make bars and rods
Analysis of rolling
Force and power required in rolling can be reduced by following means: [1] Using hot rolling: more malleable material with lower K and n values, [2] Reduction of draft at each pass - pressing less at each pass, [3] Using smaller roll radius to reduce force, [4] Using lower rolling speed to reduce power. On the other hand the maximum draft depends on the friction coefficient and the roll radius $d_{max}=\mu^{2}R$ >>> HD SeeD: HEAT(+), DRAFT(-), SPEED(-), DIAMETER(-)
Draft
Reduction of work after one pass $d = t_0 - t_f$
Spreading
Increase of width in the rolled part, and since it's the same volume of matter being rolled, then the entering volume or volume rate equals to the exiting volume rate: $t_{0}w_{0}v_{0}=t_{f}w_{f}v_{f}$
Neutral point
POINT WHERE WORK VELOCITY EQUALS ROLL VELOCITY, a point on the ark where the roll contacts the work, a point before which the work's velocity is lower than roll velocity, and afterwards the work's velocity is higher than roll velocity, thus meaning that there is slip occurring everywhere besides the NO-SLIP POINT
Average flow stress in rolling
Obtain true stress in rolling by: $$\epsilon=ln\frac{t_{0}}{t_{f}}$$ Using this value of true strain to calculate average flow stress in rolling: $${\overline{Y_{f}}=\frac{K\epsilon^{n}}{1+n}=\frac{K\left(ln\frac{t_{0}}{t_{f}}\right)^{n}}{1+n}}$$
Maximum draft
Maximum draft in rolling depends on roll radius and coefficient of friction: $$d_{max}=\mu^{2}R$$
Rolling force
Rolling force required to achieve a certain separation between rolls depends on the flow stress($\bar{Y_f}$), width of the roll (w), and roll contact length (L): $$F=\intop_{0}^{L}pdL=\overline{Y_{f}}wL$$ $$L=\sqrt{R(t_{0}-t_{f})}$$ $$F=\frac{K\left(ln\frac{t_{0}}{t_{f}}\right)^{n}}{1+n}\cdot w\cdot\sqrt{R(t_{0}-t_{f})}$$
Rolling torque and power
The torque for rolling is the rolling force multiplied by its leverage, thus the torque for each roll: $$T_{one\, roll}=\frac{1}{2}FL$$ And the power required to operate the two rolls is the torque for each roles multiplied by angular velocity: $$P=2\pi NFL$$
*Shape rolling
SERIES OF ROLLS ROLL METAL INTO A SHAPE, an I-beam or an L-beam or a U-channel or a rail for a rail road track, a more complicated process than flat rolling, a process requiring roll-pass design, a design to achieve uniform deformation through the cross section at each reduction in order to avoid cracking or warping the rolled product.
*Rolling mills
Quite a few rolling arrangements exist for flat rolling, such as [1] Two-high rolling mill - two rolls rotate and flatten the workpiece, sometimes even reversing direction to flatten the slab time after time again. [2] Three-high configuration - slab moves between three rollers rotating in same direction with the aid of lifting mechanisms. [3] Four-high rolling mill - presses two small rolls with two bigger ones, thus preventing bending of small rolls that require less power to deform metal. [4] Cluster mill - two big rolls support a small roll from each side. [5] Tandem rolling mill - a set of consecutive rolls. >>> TiT FuCT: TWO, THREE,,, FOUR, CLUSTER, TANDEM
Two high configuration
TWO ROLLS FLATTEN SLAB, either rotating in the same direction or reversing direction to continuously flatten the slab in a reversing mill configuration.
Three high configuration
THREE ROLLS ROTATE IN SAME DIRECTION and slab moves between them with the use of lifting mechanisms.
Four high configuration
TWO BIG ROLLS SUPPORT TWO SMALL ROLLS, the big rolls preventing deformation of the thin roll, the thin rolls working more efficiently to deform metal.
Cluster mill
Two big supporting rolls support each small roll.
Tandem rolling mill
Consecutive rolls flatten continuous strip.
OTHER ROLLING DEFORMATION PROCESSES
Deformation processes that use rolling to form the work part, processes like: [1] Thread rolling, [2] Ring rolling, [3] Gear rolling, [4] Roll piercing. >>> TaR GaP: THREAD, RING, GEAR, PIERCING
Thread rolling
THREADED DIES FORM THREAD ON BOLT BLANK, pressing the metal and strain hardening it, creating a stronger and more fatigue resistant threads with a better surface finish due to strain hardening, a process that can produce parts and a blinding fast rate: up to eight parts per minute. >>> BLINDLY FAST DIES FORM STRONG AND RESISTANT THREADS
Ring rolling
ROLLING ROLLS FLATTEN THICK RING, producing any desired geometry of ring walls, be it a circle or an oval, creating roller bearing faces, steel tires for rail road wheels, or rings for pipes or pressure vessels, a processes that saves on raw material, strengthens the part through cold working while producing ideal grain orientation. STRONG AND ORIENTED GRAINS STRETCH ALONG DURABLE AND RESILIENT RING.
Gear rolling
ROLLING PLATES SHAPE GEARS LIKE BOLTS, producing a stronger part in a shorter amount of time.
Roll piercing
CREATES A SEAMLESS TUBE BY COMPRESSING AND PIERCING HOT ROUND BILLET, the rolls compressing the billet so hard that a crack forms at it's center, and the mandrel pushes through