Common Bending Forms of Mild Steel Tubes

Mild steel pipe is a type of carbon steel pipe. ‌Mild steel pipe has a carbon content of less than 0.25%. It is also called soft steel because of its low strength, low hardness and softness. Common bending forms of mild steel tube mainly include four types: pressing, rolling, return bending and extrusion bending. These methods have their own characteristics and are suitable for different bending requirements and material properties.

Pipe Pressing

This bending method does not require special molds and can be completed on a press.

The pipe pressing method is simple and suitable for situations where the curvature radius does not need to be precisely controlled.

The bending radius is typically 3 to 5 times the mild steel pipe's outer diameter (R ≈ 3D to 5D).

A disadvantage is that the bend is prone to elliptical deformation or wall thinning, requiring a support mandrel to improve forming quality.

Rolling

On a plate rolling machine or a steel bending machine, a grooved roller is used for bending to obtain a bending effect with uniform curvature.

Rolling is suitable for occasions where a larger radius bending is required or where precise curvature requirements are required.

Highly precise control of bend angles and radii.

Commonly used in the manufacture of curved structural components, heat exchanger coils, and building steel structures.

Key Process Points: To prevent mild steel pipe wall instability, sand filling or support core rods are typically placed inside the mild steel pipe. Multiple, step-by-step rolling processes are employed to ensure uniform wall thickness and prevent cross-sectional deformation.

Return Bending

It includes rolling return bending and drawing return bending.

The former is bent on a vertical or horizontal pipe bending machine, and the latter is also bent on a vertical or horizontal pipe bending machine, but the clamping should be tighter to generate longitudinal tension.

Return bending is suitable for bending requirements that require a larger curvature change or a specific shape.

Can bend pipes with multiple curvatures, continuous arcs, or curved shapes.

It is suitable for automotive exhaust systems, hydraulic circuits, heat exchanger coils, and more.

It requires high equipment requirements but significantly reduces deformation and springback.

Extrusion Bending

Including mold extrusion bending and mandrel extrusion bending.

The former has a regular cross-sectional shape of the mild steel pipe and is generally cold extruded; the latter is generally hot extruded and is suitable for bending that requires higher precision and specific shapes.

High bending precision, with virtually no elliptical cross-section deformation after forming.

Bending radius can be as small as 1.5D to 2D.

Commonly used in high-pressure fluid pipes, aerospace piping, precision hydraulic systems, and other fields.

Deformation Properties and Basics of Low Carbon Steel

Low carbon steel (carbon content ≤ 0.25%) is widely used in construction, automotive, and machinery manufacturing due to its high plasticity, low strength, and easy machinability. Its deformability is closely related to the following properties:

1. Yield Strength

Typically ranges from 210-550 MPa; exceeding this value results in permanent deformation.

2. Elongation

Can reach 20%-40%, indicating resistance to fracture under tension.

3. Anisotropy

Rolling direction affects deformation uniformity, and fiber flow direction must be considered during processing.

Bending Process and Parameters for Low Carbon Steel

1. Minimum Bending Radius

(Refer to ISO 12126 to avoid lateral cracking)

2. Springback Compensation

The springback angle of low carbon steel is typically 2°-5°, which must be compensated through overbending or die correction.

How to Choose a Bending Method for Mild Steel Pipes

Low-carbon steel pipes, due to their excellent ductility and weldability, can be bent in a variety of ways.

1. For low cost and simple processing, press bending is an option.

2. For large radii and high finish, roll bending is an option.

3. For complex shapes, return bending is an option.

4. For high precision and minimal deformation, extrusion bending is the best option.

Summary

The choice of these methods for mild steel pipe depends on the specific engineering requirements, including factors such as bending radius, material type, and whether precise control of curvature is required. In actual applications, different bending methods may be used according to specific circumstances, or several methods may be combined to achieve the best bending effect.

Read more: Difference Between Mild Steel Pipe and Carbon Steel Pipe or Welding Process of Mild Steel Tube