Rolling

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Reducing or changing the cross-sectional area of a workpiece by the compressive forces exerted by rotating rolls. The original material fed into the rolls is usually an ingot from a foundry. The largest product in hot rolling is called a bloom; by successive hot- and then cold-rolling operations the bloom is reduced to a billet, slab, plate, sheet, strip, and foil, in decreasing order of thickness and size. The initial breakdown of the ingot by rolling changes the coarse-grained, brittle, and porous structure into a wrought structure with greater ductility and finer grain size.

A schematic presentation of the rolling process, in which the thickness of the metal is reduced as it passes through the rolls, is shown in illus. a. The speed at which the metal moves during rolling changes, as shown in illus. b, to keep the volume rate of flow constant throughout the roll gap. Hence, as the thickness decreases, the velocity increases; however, the surface speed of a point on the roll is constant, and there is therefore relative sliding between the roll and the strip. The normal pressure distribution on the roll and hence on the strip is of the form shown in illus. c. Because of its particular shape this pressure distribution is known as the friction hill.

The rolling process, (a) Direction of friction forces in the roll gap. (b) Velocity distribution, (c) Normal pressure acting on the strip in the roll gap. V_i = initial velocity, V_f = final velocity, V_roll = velocity during rolling operation.

A great variety of roll arrangements and equipment are used in rolling. The proper reduction per pass in rolling depends on the type of material and other factors; for soft, nonferrous metals, reductions are usually high, while for high-strength alloys they are small. Requirements for roll materials are mainly strength and resistance to wear. Common roll materials are cast iron, cast steel, and forged steel.

The use of heavy metal or stone rollers on terrazzo topping to extract excess matrix.

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Involuntary rolling in animals; an important sign of abdominal pain or of disease of the vestibular apparatus. In the latter it is accompanied by persistent head rotation. Passive rolling is a therapeutic manipulation for the correction of torsion of the uterus in mares and cows. The animal is cast, laid on its back and swung sharply from side to side, sometimes with one hand in the rectum attempting to retard any movement of the fetus. The objective is to rotate the dam's body around an immobilized fetus and uterus.

• r. average — see moving average.
• r. disease — a nervous system disease of mice caused by Mycoplasma neurolyticum.
• r. mean — see moving average.
• r. skin syndrome — see idiopathic hyperesthesia syndrome.

• Cinematography Tools and Techniques - rolling: (adj) indication that cameras are shooting scene

For other uses, see Rolling (disambiguation).

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Rolling is a type of motion that combines rotation (commonly, of an axially symmetric object) and translation of that object with respect to a surface (either one or the other moves), such that, if ideal conditions exist, the two are in contact with each other without sliding. This is achieved by a rotational speed at the line or point of contact which is equal to the translational speed. When no sliding takes place the rolling motion is referred to as 'pure rolling'. In practice, due to small deformations at the contact area, some sliding does occur. Nevertheless, rolling friction is much lower than sliding friction, and thus, rolling objects, typically require much less energy to be moved than sliding ones. As a result, such objects will more easily move, if they experience a force with a component along the surface, for instance gravity on a tilted surface; wind; pushing; pulling; an engine. Unlike most axially symmetrical objects, the rolling motion of a cone is such that while rolling on a flat surface, its center of gravity performs a circular motion, rather than a linear one. Rolling objects are not necessarily axially-symmetrical. Two well known non-axially-symmetrical rollers are the Reuleaux triangle and the Meissner bodies. Objects with corners, such as dice, roll by successive rotations about the edge or corner which is in contact with the surface.

One of the most practical applications of rolling objects is the use of Rolling-element bearings, such as ball bearings, in rotating devices. Made of a smooth metal substance, the rolling elements are usually encased between two rings that can rotate independently of each other. In most mechanisms, the inner ring is attached to a stationary shaft (or axle). Thus, while the inner ring is stationary, the outer ring is free to move with very little friction. This is the basis for which almost all motors (such as those found in ceiling fans, cars, drills, etc.) rely on to operate. The amount of friction on the mechanism's parts depends on the quality of the ball bearings and how much lubrication is in the mechanism.

Rolling objects are also frequently used as tools for transportation. One of the most basic ways is by placing a (usually flat) object on a series of lined-up rollers, or wheels. The object on the wheels can be moved along them in a straight line, as long as the wheels are continuously replaced in the front (see history of bearings). This method of primitive transportation is efficient when no other machinery is available. Today, the most practical application of objects on wheels are cars, trains, and other human transportation vehicles.

The velocity of a particle in the rolling object is given by: , where is the distance between the particle and the rolling objest's contact point (or line), and is the rolling objest's angular velocity.

Rolling is also a metal forming process.

See also

• Contact mechanics
• Rolling friction
• Frictional contact mechanics: Rolling contact
• Terrestrial locomotion in animals: Rolling
• Tumbling (gymnastics)

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