# Glossary of common bending-rolling terms

Arc. Part of the circumference of a curve. The curved portion of a bend.

Arc length. The curved distance along a circumferential line. The length of the curved portion of a member.

Bend radius. The radius of curvature, measured to a reference point on the cross section.

Center-to-center. The distance between tangent points of two adjoining bends.

Chord. The straight distance between two points on a curve.

Cold bending. Any bending process where curvature is induced by load application at room temperature.

Compound bend. A curve made up of two or more arcs in the same plane, joined tangentially without reversal of curvature.

Degree of bend. The angle to which a bend is formed.

Distortion. A deviation from the original cross-sectional shape.

Ductility. The ability of the material to deform without fracture.

Easy way. The orientation of a member where bending occurs about the weak principal axis.

Gag pressing. A cold-bending method that uses hydraulic rams to simultaneously apply bending forces at discrete, widely-spaced, locations along the member. Also known as point bending.

Grip. An additional straight length at each end of a curved member required in the bending operation. Also known as “hold and tail” or “lead and tail” to emphasize the additional length is required at each end of the member.

Hard way. The orientation of a member where bending occurs about the strong principal axis.

Heat curving. A bending process that relies only on the application of heat in specific patterns to induce curvature.

Horizontally curved member. A member with curvature in the horizontal plane.

Hot bending. Any bending process where curvature is induced by load application at an elevated temperature.

In-plane flexure. Bending of a curved member where moment is applied about the axis of curvature. The primary flexural stresses and deflections are in the plane of curvature.

Incremental step bending. A cold-bending method that uses hydraulic rams to apply bending forces at several discrete, closely spaced locations along the member.

Induction bending. A hot-bending method that utilizes an electric induction coil to heat a short section of the member before it is curved by force.

Local buckling. A type of potential cross-sectional distortion that is caused by compression stresses in the member induced during the bending operation. Local buckling can be in the form of a single half-wave or a series of wrinkles along the entire bend length. Also known as waving or wrinkling.

Mandrel. A tool that can be inserted into a HSS member to support the walls and minimize cross-sectional distortion during the bending process.

Multi-axis bend. A bend with curvature about more than one axis. Also known as a multi-plane bend.

Normalizing. A thermal treatment where the member is heated to a suitable temperature above the upper transformation temperature, followed by cooling in still air at room temperature.

Off-axis bend. A bending orientation where the member is curved about a non-principal or non-geometric axis. Also known as conical rolling.

Oil-canning. A form of local buckling that can cause collapse of the cross section due to the combined effect of ovalization and local buckling in a single half-wave.

Out-of-plane flexure. Bending of a curved member where moment is applied in the plane of curvature. The primary flexural stresses and deflections are in perpendicular to the plane of curvature.

Ovality. The cross-sectional distortion of a round HSS where the deviation from the theoretical shape forms an oval.

Pyramid roll bending. A cold-bending operation where a member is bent progressively by repeatedly passing it through a set of three adjustable rolls in a pyramid arrangement.

Reverse-compound bend. A curve made up of two or more arcs in the same plane, joined tangentially with reversal of curvature. Also known as an S-curve or an offset bend.

Rise. The distance, perpendicular to the chord, between the mid-point of a chord and an arc. Also known as the mid-ordinate.

Rotary-draw bending. A bending method where the member is clamped to a form and bent by rotating it around a bend die.

Slope. The angle of an inclined member designated using the vertical (rise) and horizontal (run) distances between two points. Also known as bevel or pitch.

Snap-through buckling. A type of instability where the load-displacement diagram descends after reaching a limit point and the structure abruptly transforms from one equilibrium state to another remote equilibrium state on the ascending, stable portion of the curve.

Spiral. A three-dimensional curve with an arc in one plane and a constant slope in a perpendicular plane. Also known as a helix or helical curve. The curving process is often called sloped rolling or pitched rolling.

Springback. The deformation of a bent member immediately after a bending load is released, where a portion of the curvature is lost.

Strake. A protruding fin that can be connected to a structure to improve aerodynamic stability.

Synchronized incremental cold bending. A cold-bending process where synchronized forces are applied at several locations along the member.

Tangent. A straight line, perpendicular to the radius, that touches a curve at a single point. A straight member adjacent to a curved segment.

Tangent point. The start or end point of a curve.

Variable-radius bend. Parabolic, elliptical and other noncircular bends with variable radii. Also known as multiradius and a non-circular bends.

Vertically curved member. A member with curvature in the vertical plane.

Waving. See Local buckling.

Wrinkling. See Local buckling.

Yield point. The curvature at which a member will deform permanently during bending.