Process Details: Specialized equipment pre-machining a continuous spiral groove—typically 0.2 mm to 0.4 mm deep—into the outer wall of the base tube. The fin strip (aluminum or copper) is wound under high tension and embedded into the groove. The edge metal of the groove is then squeezed through plastic deformation, tightly “locking” the fin root into the groove.

Thermal Resistance Analysis: Relies on a pure mechanical interference fit. This creates an extremely tight metal-to-metal contact between the base tube and the fin. Even under high-temperature conditions with differential thermal expansion between the materials, the locked fin root will not loosen—ensuring that thermal contact resistance remains virtually unchanged over time or with rising temperatures.

Temperature Limits: By completely eliminating the issue of thermal loosening, the maximum operating temperature can reliably reach 350°C to 400°C, making it the premier choice for high-pressure, high-temperature operating conditions.

Process Details: An upgrade built upon the standard L-foot winding process. During manufacturing, the leading roller first presses dense spiral knurling (a mesh texture) onto the base tube’s surface. The L-shaped fin flange is then pressed into these knurled grooves, and the trailing roller firmly compacts it into place.

Thermal Resistance Analysis: The knurling increases the contact area, while the micro-teeth formed by the pattern “bite” into the L-shaped fin foot. This significantly improves resistance to shear forces and thermal expansion/contraction, keeping the thermal contact resistance noticeably lower than that of standard L-type fins.

Temperature Limits: The operating temperature is elevated to 250°C–260°C. This method retains the L-type tube’s key advantage—complete base tube coverage for superior corrosion resistance—while substantially increasing heat transfer stability and the upper temperature limit.

Process Details: An aluminum or copper strip is formed into an “L”-shaped cross-section using dies (with a base foot width of roughly $1.5\text{ mm}$–$2.0\text{ mm}$). It is then spirally wrapped around the outer surface of the base tube under high mechanical tension, using that tension to force the base foot flush against the tube wall.

Thermal Resistance Analysis: The mechanical bond relies entirely on the residual tensile stress of the material. Over repeated thermal cycles (heating and cooling), the difference in thermal expansion coefficients between aluminum/copper and steel causes the fins to lose tension and loosen. This creates microscopic air gaps between the tube wall and the fin root, leading to a sharp increase in thermal contact resistance over time.

Temperature Limits: Generally strictly limited to below 130°C–150°C. It is primarily used in standard HVAC or low-temperature heating equipment operating under lower ambient temperatures.