Manufacturing Process of Seamless Tubes
- Billet Preparation
A solid steel billet is heated to a high temperature (typically 1200–1300°C) to enhance malleability for subsequent forming processes.
- Piercing Mill Process
The heated billet is fed into a piercing mill, where it is gripped by skewed-axis main driving rolls and forced over a piercing point to create an initial hollow cavity.
Key Components:
Control rolls (upper and lower) stabilize the billet’s movement with axes parallel to the feed direction.
Internal cooling systems prevent overheating of critical components like the piercing point and control rolls.
Outcome: The solid billet transforms into a rough hollow tube, marking the first structural shift in seamless tube production.
- Elongation and Sizing
The pierced tube undergoes progressive stretching through dies and rollers, elongating the material to over 20 times its original length. This step refines wall thickness and diameter uniformity.
- Hot Rolling vs. Cold Rolling
Hot Rolling:
Conducted at high temperatures to maintain ductility.
Cost-effective but produces a scaled, oxidized surface (black finish).
Suitable for applications with looser dimensional tolerances.
Cold Rolling:
Performed at room temperature for tighter dimensional accuracy.
Enhances mechanical properties (e.g., tensile strength, surface finish).
Ideal for precision engineering and high-performance uses. - Final Treatment
Post-rolling, tubes may undergo heat treatment (e.g., annealing) or surface treatments (e.g., pickling) to meet specific industry standards.
Key Advantages by Process:
Method Benefits Limitations
Hot Rolling Lower cost, faster production Surface scaling, lower precision
Cold Rolling Superior strength, smooth finish Higher production cost
This streamlined process ensures seamless tubes meet rigorous industrial demands, balancing cost, strength, and precision.