Cold Bending Technology of Mild Steel Pipe

As a common material widely used, mild steel pipe is often used to manufacture various parts, components, etc. Cold bending of mild steel pipe is a processing method that directly processes steel at room temperature and bends it into the desired shape or curve

What is cold bending

Cold bending refers to applying external force to the steel pipe at room temperature to make it plastically deformed, so as to achieve a predetermined bending angle and curvature. This method mainly relies on mechanical equipment such as pipe bending machines, rolling machines, and stretch bending machines. In the processing of seamless steel pipes, the cold bending process can form it into a specific pipe shape for different scenes such as construction and machinery

Process characteristics of cold bending

1. Advantages:

High processing efficiency: no heating is required, the equipment is simple to operate, and it is suitable for mass production.

Low cost: no additional energy heating is required, reducing energy consumption.

High dimensional accuracy: after cold bending, the surface of the bent pipe is smooth and the dimensional accuracy is high.

Low environmental impact: no oxide scale will be produced, and the anti-corrosion layer on the surface of the pipe will not be affected.

2. Disadvantages:

Bending angle is limited: Due to the elastic recovery of the material, a large bending angle will cause rebound problems.

High risk of fracture: For high-strength steel or steel pipes with thick walls, cold bending is prone to cracks or even fractures.

Large residual stress: After cold bending, large residual stress may be generated inside the material, affecting the long-term performance of the steel pipe.

Cold bending method

1. Manual cold bending method

Manual cold bending method refers to bending steel pipes with hand tools, such as pipe bender, elbow, etc. This method is suitable for small batch production, but the accuracy is low, and the bending angle and radius are difficult to control.

2. Mold cold bending method

Mold cold bending method refers to bending steel pipes with molds. This method is suitable for mass production, can control the bending angle and radius, and has high accuracy. It is very suitable for large-scale steel pipe manufacturers, especially manufacturers of precision tubes.

3. Hydraulic cold bending method

Hydraulic cold bending method refers to bending steel pipes with hydraulic presses. This method is suitable for large-scale production, can control the bending angle and radius, and has high accuracy, but the equipment cost is high.

Factors affecting cold bending of mild steel pipes

1. Material composition

Mild steel pipes usually have high ductility and plasticity, and are easy to cold-bend.

2. Hardness and strength

The higher the hardness and strength of the steel, the more difficult it is to cold-bend, and more cold-bending strength or adjustment of the cold-bending angle is required. For occasions such as drill pipes that have special requirements for the strength and hardness of steel pipes, fine adjustments and optimizations are often required in the cold-bending process.

3. Cold-bending radius

If the cold-bending radius is smaller than the curvature radius of the material itself, it will cause the material to bend or shear, thereby affecting the accuracy and quality of the shape after cold bending.

4. Cold-bending temperature

Some mild steel pipes have strong low-temperature brittleness. If the cold-bending temperature is too low, it may cause cracks, fractures and other failures in the material, and even cause material damage. During the installation and manufacturing of pipelines in cold areas or low-temperature environments, such as some outdoor casing pipe installation operations, attention should be paid to the control of cold-bending temperature.

5. Number of cold bending times

The more times the material is cold bent, the easier it is to form cracks and fissures at the bends, affecting the shape and surface quality.

Cold bending processing standards for mild steel pipes

1. Roundness tolerance standard

The steel pipe after cold bending should maintain its original roundness, and no eccentricity, distortion, etc. should occur. Under normal circumstances, the roundness deviation of the steel pipe after cold bending should not exceed 3% of its diameter.

2. Shape tolerance standard

The shape of the steel pipe after cold bending should meet the national standard requirements for steel pipes. The size, angle, bending radius, etc. should meet the requirements, and no dents, deformation, etc. should occur. In the large-scale production of carbon steel pipes, the shape tolerance standard is the basis for ensuring qualified product quality

3. Wall thickness tolerance standard

The wall thickness of the steel pipe before cold bending should meet the design requirements, and the wall thickness should not be thin or thick after cold bending. Under normal circumstances, the wall thickness of the steel pipe after cold bending should meet the error range of the original wall thickness.

4. Bending strength standard

The steel pipe after cold bending should maintain good bending strength, and no cracking or breaking should occur. Under normal circumstances, the bending strength of the steel pipe after cold bending should be at least 85% of the original.

5. Dimension tolerance standard

The dimensional error of the steel pipe after cold bending should meet the requirements of national standards.

Cold bending process recommendations for mild steel pipes

1. Select appropriate cold bending equipment and process parameters, and select appropriate cold bending force and angle parameters according to material composition, hardness and strength.

2. Ensure that the cold bending radius of the material is large enough, and the bending angle of the material should not be less than 3 times the radius of curvature to prevent the influence of material bending and shear deformation.

3. Control the cold bending temperature, heat up slowly, try to avoid excessive material temperature, and avoid the influence of low-temperature brittleness.

4. Control the number of cold bending to avoid excessive bending that causes material failure such as cracking and cracking.

5. Pay attention to the changes on the surface of the material during the cold bending process. Once damage, cracks, etc. are found, the cold bending process should be stopped in time.

Conclusion

Cold bending is a very practical processing method, which is not only low-cost but also widely applicable. In practical applications, attention should be paid to selecting the appropriate processing method and paying attention to safety and quality control during processing. For the cold bending processing of mild steel pipes, it is necessary to control the cold bending radius, temperature and number of times to ensure the accuracy and quality of the cold bending shape, and pay attention to observing the changes on the material surface to ensure the safety of the cold bending process.

Read more: Thermal conductivity of carbon steel pipe or  Difference between mild steel pipe and carbon steel pipe