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A roll bender is a mechanical jig having three rollers used to bend a metal bar into a circular arc. The rollers freely rotate about three parallel axes, which are arranged with uniform horizontal spacing. Two outer rollers, usually immobile, cradle the bottom of the material while the inner roller, whose position is adjustable, presses on the topside of the material.
Roll bending may be done to both sheet metal and bars of metal. If a bar is used, it is assumed to have a uniform
A roll bender is a mechanical jig having three rollers used to bend a metal bar into a circular arc. The rollers freely rotate about three parallel axes, which are arranged with uniform horizontal spacing. Two outer rollers, usually immobile, cradle the bottom of the material while the inner roller, whose position is adjustable, presses on the topside of the material.
Roll bending may be done to both sheet metal and bars of metal. If a bar is used, it is assumed to have a uniform cross-section
Cross section may refer to:
* Cross section (geometry)
** Cross-sectional views in architecture & engineering 3D
*Cross section (geology)
* Cross section (electronics)
* Radar cross section, measure of detectability
* Cross section (physics)
**Abs ...
, but not necessarily rectangular, as long as there are no overhanging contours, i.e. positive draft
Draft, The Draft, or Draught may refer to:
Watercraft dimensions
* Draft (hull), the distance from waterline to keel of a vessel
* Draft (sail), degree of curvature in a sail
* Air draft, distance from waterline to the highest point on a vesse ...
. Such bars are often formed by extrusion
Extrusion is a process used to create objects of a fixed cross-sectional profile by pushing material through a die of the desired cross-section. Its two main advantages over other manufacturing processes are its ability to create very complex c ...
. The material to be shaped is suspended between the rollers. The end rollers support the bottomside of the bar and have a matching contour (inverse shape) to it in order to maintain the cross-sectional shape. Likewise, the middle roller is forced against the topside of the bar and has a matching contour to it.
Operation
After the bar is initially inserted into the jig, the middle roller is manually lowered and forced against the bar with a screw arrangement. This causes the bar to undergo bothplastic
Plastics are a wide range of synthetic or semi-synthetic materials that use polymers as a main ingredient. Their plasticity makes it possible for plastics to be moulded, extruded or pressed into solid objects of various shapes. This adapta ...
and elastic
Elastic is a word often used to describe or identify certain types of elastomer, elastic used in garments or stretchable fabrics.
Elastic may also refer to:
Alternative name
* Rubber band, ring-shaped band of rubber used to hold objects togethe ...
deformation. The portion of the bar between the rollers will take on the shape of a cubic polynomial
In mathematics, a polynomial is an expression consisting of indeterminates (also called variables) and coefficients, that involves only the operations of addition, subtraction, multiplication, and positive-integer powers of variables. An exampl ...
, which approximates a circular arc
Circular may refer to:
* The shape of a circle
* ''Circular'' (album), a 2006 album by Spanish singer Vega
* Circular letter (disambiguation)
** Flyer (pamphlet), a form of advertisement
* Circular reasoning, a type of logical fallacy
* Circular ...
. The rollers are then rotated moving the bar along with them. For each new position, the portion of the bar between the rollers takes on the shape of a cubic modified by the end conditions imposed by the adjacent sections of the bar. When either end of the bar is reached, the force applied to the center roller is incrementally increased, the roller rotation is reversed and as the rolling process proceeds, the bar shape becomes a better approximation to a circular arc. During the rolling process, the force applied to the center roller is incrementally increased to gradually bring the arc of the bar to the desired radius.
Plastic and elastic deformation
The plastic deformation of the bar is retained throughout the process. However, the elastic deformation is reversed as a section of bar leaves the area between the rollers. This spring-back needs to be compensated in adjusting the middle roller to achieve a desired radius. The amount of spring back depends upon the elastic compliance (inverse ofstiffness
Stiffness is the extent to which an object resists deformation in response to an applied force.
The complementary concept is flexibility or pliability: the more flexible an object is, the less stiff it is.
Calculations
The stiffness, k, of a ...
) of the material relative to its ductility
Ductility is a mechanical property commonly described as a material's amenability to drawing (e.g. into wire). In materials science, ductility is defined by the degree to which a material can sustain plastic deformation under tensile str ...
. Aluminum alloys, for example, tend to have high ductility relative to their elastic compliance, whereas steel tends to be the other way around. Therefore aluminum bars are more amenable to bending into an arc than are steel bars.
See also
* Tube bending * Roll forming *Rolling (metalworking)
In metalworking, rolling is a metal forming process in which metal stock is passed through one or more pairs of rolls to reduce the thickness, to make the thickness uniform, and/or to impart a desired mechanical property. The concept is simi ...
*Metalworking
Metalworking is the process of shaping and reshaping metals to create useful objects, parts, assemblies, and large scale structures. As a term it covers a wide and diverse range of processes, skills, and tools for producing objects on every scale ...
*Plate rolling machine {{Orphan, date=February 2018
A plate rolling machine is a machine that will roll different kinds of sheet metal into a round or conical shape.
It can be also called a “roll bending machine”, “ plate bending machine” or “rolling machine ...
References
{{reflist Metalworking tools Metal forming