Square steel tube forming method

Square steel tubes are formed using specific bending techniques that shape the tube according to desired structural requirements. These methods ensure precise forming and play a crucial role in the final mechanical properties of the tube. The two primary methods used are solid bending and air bending, each with its own set of advantages and challenges. Below is a detailed explanation of both techniques.

1. Solid Bend

Solid bending, as the name suggests, involves compact bending. In this process, the inner and outer rollers compact the inner and outer walls of the tube blank in two directions.

- Advantages:

Solid bending offers small rebound, ensuring accurate forming. With precise roll shaping, the inner angle radius (r) is more accurately formed.

- Disadvantages:

Solid bending causes a stretching/thinning effect. The bend stretches the material, which shortens the longitudinal length of the bending line. Additionally, the metal at the bend becomes thinner due to the stretching effect.

2. Empty Bend (Air Bend)

Air bending is achieved by allowing the outer roller to contact only the outer wall of the tube blank, resulting in a one-way bending process. This causes the bending line to compress, which leads to longitudinal elongation and accumulation of metal, making the bend thicker—a process known as compression/thickening.

- Advantages:

Air bending can bend sections that solid bending cannot, such as simultaneously bending and finishing the top and side walls of a square tube. It can also bend inner angles with a radius (r) of less than 0.2t without breaking the tube wall.

- Disadvantages:

During top and side synchronous air bending, the pressure from both the upper and lower rollers may exceed the critical point, causing instability. This can result in edge concavity and negatively affect the unit’s stable operation and molding quality. This behavior is different from the air bending of round tubes, where such instability is less common.

Both methods play significant roles in the production of square steel tubes, and the choice of technique depends on the specific design and performance requirements.