The manufacturing process of gilled tubes varies depending on the fin location (internal/external), fin geometry (straight/spiral), and base tube material (carbon steel, copper, stainless steel, etc.). The following four primary industrial methods are widely used:
1. External Gilled Tube Manufacturing
Roll Forming
- Suitable for carbon steel and copper alloys under medium to low-pressure conditions.
- Process: A metal strip (fin material) is fed together with the base tube into a roll forming unit, where multiple sets of forming rolls apply pressure to mechanically interlock the fin and tube.
- Advantages: No weld seam or heat-affected zone; excellent corrosion resistance, suitable for high-temperature and high-pressure environments.
- Technical requirements: Bond strength must pass pull-off tests (≥200 MPa); fin pitch tolerance controlled within ±0.2 mm.
High-Frequency Resistance Welding (HF Welding)
- Most widely used for carbon steel and stainless steel finned tubes.
- Process: After pre-assembly of the base tube and fin strip, the joint interface is heated to melting point via high-frequency induction coil, then pressed to achieve metallurgical bonding.
- Key parameters: Welding speed up to 150 m/min; weld width must exceed fin thickness; weld penetration rate ≥99%.
- Quality control: Hammer test (no cracking), bending test (±20° without cracks), and heat-affected zone depth inspection (≤0.5 mm).
Mechanical Expansion
- Commonly used for copper and aluminum tubes, especially in air conditioning and refrigeration systems.
- Process: Pre-formed fins are placed over the base tube, then a hydraulic or mechanical expander is used to radially expand the inner tube, creating tight contact between fin and tube.
- Features: No heating required, avoids material annealing, suitable for thin-walled tubes.
2. Internal Gilled Tube Manufacturing
Cold Rolling with Custom Mandrel
- Used to produce straight or arc-shaped internal ribs, commonly applied in evaporators and condensers.
- Process:
- Select tube billet with appropriate outer diameter and wall thickness;
- Acid pickling to remove oxide layer;
- Use a mandrel matching the target internal rib profile, and cold-roll the tube in an LD tube mill to form the internal fins in one pass;
- Cut ends, inspect, apply anti-rust oil, and package.
- Advantages: Integrated fin-tube structure eliminates risk of fin detachment; significantly improves heat transfer efficiency.
Heated Mold Continuous Casting
- Used for high-precision mass production of copper alloy internal finned tubes.
- Principle: By controlling the solid-liquid interface position in the crystallizer, friction between the tube wall and mold is reduced, enabling near-net shaping.
- Outcome: Smooth surface, free of periodic scars; capable of producing complex internal fin profiles, suitable for high-purity refrigeration systems.
3. Spiral Finned Tube Manufacturing
Integral Helical Rolling
- Used to produce seamless spiral finned tubes, widely applied in boiler economizers and air preheaters.
- Process: The base tube is heated to a plastic state and fed into a set of helical rolling rolls, where continuous rotary compression causes the metal to extend axially and form a continuous spiral fin.
- Advantages:
- Seamless structure increases pressure resistance by over 30%;
- Resistant to vibration, corrosion, and ash accumulation;
- Heat transfer area can be 5–10 times that of a bare tube.
- Certification: Complies with ISO 9001 standards; has been widely used in coal-fired power plants in China since the 1980s.
4. Material and Process Compatibility Table
| Base Material | Recommended Process | Typical Applications | Key Technical Requirements |
|---|---|---|---|
| Carbon Steel | HF Welding, Roll Forming | Power plant boilers, economizers | Weld penetration >99%, HAZ ≤0.5 mm |
| Copper Alloy | Cold Rolling (internal fin), Continuous Casting | AC condensers, refrigeration systems | Surface roughness Ra ≤1.6 μm, no cracks |
| Stainless Steel | HF Welding, Mechanical Expansion | Chemical heat exchangers, seawater desalination | Corrosion resistance met, no porosity in weld |
| Aluminum Alloy | Extrusion, Roll Forming | Automotive radiators, air coolers | Uniform fin thickness, no delamination |
5. Industrial Standards and Quality Control Points
Although ASME or GB/T standards are not directly cited, the technical parameters provided align with Chinese industrial norms. Key control indicators include:
- Weld strength: Pull-off force ≥200 MPa, or base tube rupture;
- Weld width: ≥ fin thickness;
- Fin pitch: Tolerance ±0.2 mm;
- Fin perpendicularity: ±1°;
- Heat-affected zone depth: ≤0.5 mm (measured by microhardness);
- Length consistency: Minimal length variation across welded tubes in the same batch.