High-frequency welded spiral finned tube production process
As a high-efficiency heat transfer element, high-frequency welded spiral finned tubes are widely used in petrochemical, electric power, metallurgy, air conditioning and refrigeration and other fields. Its core process uses the skin effect and proximity effect of high-frequency current to quickly weld spiral fins on the surface of the steel pipe to form an enhanced heat transfer structure.
Raw material selection and pretreatment of high-frequency welded spiral finned tubes
The production process of high-frequency welded spiral finned tubes begins with raw material screening. The base tube usually uses low-carbon steel such as 20#, Q235 or ND steel, stainless steel, with a diameter range of 20-159mm and a wall thickness of 2-5mm; the fin strip is mostly made of cold-rolled steel strips such as 08Al and SPCC, with a thickness of 0.5-1.5mm.
The pretreatment of high-frequency spiral welded finned tubes includes three key processes:
1. Straightening of base tube: Eliminate the curvature of the steel tube through a seven-roll straightening machine, and the straightness must be controlled at ≤1mm/m
2. Surface treatment: Use sandblasting or pickling to remove the oxide layer, and the surface roughness Ra must reach 12.5μm or more to enhance the welding bond
3. Steel strip cutting: The longitudinal shearing and slitting equipment cuts the coil into the designed width, and the error is controlled within ±0.1mm
The quality of pretreatment directly affects the welding qualification rate of the finished tube, and standardized treatment can reduce the defect rate by 40%.
High-frequency welding core process
The welding process uses a solid-state high-frequency power supply (frequency 200-400kHz), and the edge of the steel strip is instantly heated to a plastic state of 1200-1400℃ through electromagnetic induction.
The key technical parameters of high-frequency spiral welded finned tubes include:
– Power control: adjusted in the range of 80-200kW according to the tube diameter, the typical parameter of φ32mm tube is 120kW/15m/min
– Pressure system: The hydraulic device applies 0.8-1.5MPa upsetting pressure to ensure the diffusion and bonding of the metal lattice
– Cooling method: The atomized water cooling system performs gradient cooling at a flow rate of 5-8L/min
Industry innovation is reflected in the application of composite welding technology, such as the “high frequency + laser” dual heat source process developed by a Jiangsu enterprise. While the welding speed is increased to 25m/min, the tensile strength of the fin reaches more than 350MPa.
High-frequency welding spiral welded fin tube forming and post-processing technology
Fin forming adopts multi-station progressive rolling, and the key equipment includes:
1. Spiral lead mechanism: servo motor drive, lead accuracy ±0.05mm
2. Dynamic straightening module: online correction of fin inclination deviation
3. Online detection system: CCD visual detection of weld continuity
The post-processing process chain of high-frequency welding spiral welded fin tube includes:
– Stress relief: 580-620℃ tempering treatment, insulation time ≥30min
– Surface treatment: hot-dip galvanizing layer thickness 80-120μm or aluminizing treatment
– Airtightness test: 3.5MPa water pressure holding test, leakage rate <0.01%
High-frequency welding spiral welded fin tube quality control system
The industry implements GB/T 28713-2012 standard, and the key inspection items include:
| Inspection items | Method | Index requirements |
| Weld strength | Tensile test | ≥90% substrate strength |
| Fin height | Laser ranging | Tolerance ±0.15mm |
| Thermal resistance | Transient test | ≤1.25×10⁻⁴m²·K/W |
A nuclear power project case shows that the use of X-ray real-time imaging detection can increase the internal defect detection rate to 99.7%.
Development trend of high-frequency spiral welded finned tube technology
1. Intelligent upgrade: A factory introduced a digital twin system to achieve dynamic optimization of welding parameters and reduce energy consumption by 18%
2. Application of new materials: The penetration rate of titanium alloy finned tubes in the field of seawater desalination increased by 15% annually
3. Composite structure innovation: The heat transfer coefficient of three-dimensional inner rib-outer fin composite tubes reached 6800W/(m²·K)
4. Green manufacturing: Electromagnetic induction heating replaces gas furnaces, and the carbon emissions of production lines are reduced by 35%
The main challenges facing the current industry are the control of welding deformation of large diameter (>φ89mm) and thin wall (<1.5mm) tubes, and the improvement of anti-ashing performance under extreme working conditions.
It is expected that in the next five years, with the development of ultra-high frequency power supply (>600kHz) and nano-coating technology, the heat transfer efficiency of the new generation of finned tubes is expected to exceed the existing theoretical limit by more than 30%.