Our advanced ERW Tube Mills are dedicated to produce high-quality steel pipes through HF induction solid state welding. In these mills, flat strips or coils of steel are formed into cylindrical shapes, and high-frequency electrical currents are used to bond the edges, creating robust and durable tubes.

In the forming & sizing section, roll forming, H.F induction longitudinal welding, sizing, cooling and turks head pre-straightening work cooperatively to process carbon steel strip into required shape.

The forming commences with a steel strip, being fed into the mill through a series of rollers. These driven and non-driven rollers, arranged in a precise configuration, progressively bend the strip into a circular cross-section. As the strip progresses, it gradually forms into a desired tube shape.

The welding section is comprised of seam guide stands, weld squeeze stands, external scarfing stands and ironing stand. Crucial to this process is the welding step, where the edges of the now-circular strip are brought into close proximity and fused together, often using high-frequency induction welding technique. This ensures a seamless joint, critical for maintaining structural integrity and fluid tightness in the final product.

After the welding section, the tube is cooled in the cooling section. It is a shower type consisting of water trough and water pipe. Then the outside diameter of the tube will be fined tuned at the sizing section of the mill line to the required dimensions. For the production of circular pipe, the outside of the tube is squeezed gradually by each stand to produce accurate OD. For the square/rectangular tube, the round-shaped tube is converted and fine-tuned into specified size in this section.

In addition to the sizing mill, a series of Turks Heads are provided to further fine tune the tube and pre-straighten the tube. For sizing and straightening, they not only size or reshape the tube (pipe, square, rectangles, and etc.), but also relieve stress at the same time so that the properties are normalized into the body of the material.

Throughout the entire process, tight control over temperature, speed and pressure are essential to achieve consistent quality and dimensional accuracy. Automation and advanced control systems have significantly enhanced the precision and efficiency of modern tube mills, enabling them to produce tubes with a wide range of diameters, wall thicknesses, and materials, catering to diverse industries such as construction, automotive, and oil & gas.

 Forming Methods

There are mainly three kinds of forming methods in the tube mill: W Forming, FF (Flexible Forming) and FFX (Flexible Forming Excellent). As for W Forming, the strip is gradually bent through multiple rolls (usually 8 to 12 passes), with a “W” shape (double radius bending) in the intermediate stages, and finally closed into a round tube.

As for FF, there is no forced bending phase in the conversion of the strip from flat plate to round tube and with less edge stretching due to the progressive & smooth C-shaped bending approach and optimized roll curve design, bring with reduced residual stress, high roundness, uniform wall thickness and smooth surface finish.

As for FFX, it is an advanced evolution of FF, which adopts high-precision rolls and dynamic control system, designed to produce ultra-high-precision welded tubes with even higher tolerance, better roundness and improved mechanical properties. It enhances traditional forming with pre-bending stage to reduce stress concentrations and minimize edge cracking, and multi-stage finishing to challenge high properties demanding.

For the FF and FFX, the rolls sharing in break down section is really fulfilled, which dramatically saves the costs of rolls material and rolls changeover time.

Value Highlight

• Accurate arc-curved design on rolls and scientific forming technology to guarantee high precision tube forming and high quality products
• Great quality of welding seam, significantly enhancing the performance and safety of pipe systems
• Advanced design of double closed-loop drive control for precise synchronization and stability
• Equipped with an alarm mechanism, prompts for machine failure can be made in advance, providing great convenience for the maintenance of the mill
• Featured with capability of individual and compound drive of forming and sizing mills, the corresponding drive mode can be chosen according to the actual needs on site
• For FF forming, unlike traditional W forming (which uses a wave-like bending pattern), ituses a smooth C-shaped bending approach with reduced residual stress, allows for the following significant benefits:

• Higher dimensional accuracy
• Reduced material waste thanks to the less edge cracking and distortion
• Suitable for high-strength and stainless steels due to controlled forming stress
  • Combining the benefits of FF with additional refinements to handle thicker materials, high-strength steels and demanding applications, FFX Technologyallows for the following significant benefits:
• All break down rolls in the forming section are sharable when producing certain range of round tubes and square tubes in one line without changing the rolls, saving about 50% of rolls material and change time
• FFX technology allows for quick mechanical adjustments, enabling the production of round, square and rectangular tubes without stopping the production line
• FFX system can accommodate a wide range of product designs and production volumes, making them adaptable for various industries.

Technical Data Sheet