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Tube Bending Terminology

An understanding of the terminology used within the tube and pipe bending industry will help you to better comprehend the basics:

Compression bending is a method of bending pipes or tubes when the die in place remains stationary, while a counter die is used to bend the material round the stationary die. Also called compression forming, this technique is the original method of bending tubes. It involves the tube being clamped in place, while a pressure die moves around the radius to create a bend. It does not involve the use of a mandrel.

Mandrel bending is carried out by placing a mandrel inside the pipe or tube that’s being bent. It is used in particular with thinner wall materials, as it helps to prevent defects – such as flattening, rippling or collapse – in the bend. It is the most commonly-used form of bending.

Roll bending is used when large radius bends or curves are needed. A piece of tube or pipe is passed through a series of three rollers in a pyramid formation. This allows it be shaped to a large centre line radius. The metal is formed into the bend design by the lower rollers pushing against the feed path.

The outside diameter (O/D) is the distance across the widest area of the tube or pipe.

The inside diameter (I/D) is the distance measured across the widest part of the inside opening of the tube or pipe.

The wall thickness (W/T) is the measurement between the exterior and interior surfaces of the tube or pipe. This can also be called the schedule in a pipe or the gauge in a tube.

The degree of bend is the angle of the bend – measured on the outside.

Straights between bends refers to a part that requires multiple bends. A minimum straight length is needed between each bend. This is also called a clamp length.

The centre line radius (CLR) refers to the radius along the tube or pipe’s neutral axis.

An S-curve is the term used when bends occur in opposite directions in the same plane.

The yield point is the point at which the tube or pipe will deform permanently during the bending process.

If you require any professional advice or if you have a project in mind, please do not hesitate to contact Pipecraft – the metal fabrication experts.

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