Seamless Internally Threaded Coil Tube (Coiltube) for Air Conditioners
Product Overview
The Seamless Internally Threaded Coil Tube (Coiltube) is a specialized refrigerant heat-exchange tubing engineered for use in air conditioning systems, refrigeration units, and HVAC (Heating, Ventilation, and Air Conditioning) applications. This product represents an advanced evolution of traditional coil tubing, incorporating internal micro-fin threading technology that significantly enhances heat transfer efficiency while maintaining the structural integrity and pressure resistance required for high-performance refrigerant circuits.
Developed through systematic research and iterative process optimization, this coil tube addresses the critical industry demand for compact, high-efficiency heat exchangers that minimize refrigerant charge while maximizing thermal exchange performance. The product is manufactured by Wenzhou Jixing Metal Materials Co., Ltd., a recognized supplier in the metal coil tube segment.
Material & Properties
Base Material
The coil tube is fabricated from seamless copper tube stock, conforming to international standards including ASTM B88 (Standard Specification for Copper Tube, Seamless), GB/T 17791 (Chinese National Standard for copper tubes), and EN 1057 (European Standard for copper and copper alloys). The primary alloy used is C12200 copper (T2 grade), characterized by a minimum copper content of 99.90%, ensuring superior thermal conductivity and corrosion resistance.
Key Material Properties
- Thermal Conductivity: 398 W/(m·K) at 20°C, providing exceptional heat transfer capability
- Density: 8,940 kg/m³
- Electrical Resistivity: 1.724 × 10⁻⁸ Ω·m at 20°C
- Melting Point: 1,083°C
- Corrosion Resistance: Excellent resistance to atmospheric corrosion, with proven performance in humid and mildly aggressive environments
- Mechanical Properties (Annealed Condition): Tensile strength ≥ 210 MPa; elongation ≥ 45%
- Workability: High ductility enabling deep coil winding without cracking or deformation
Internal Thread Characteristics
The internal threading is formed through precision mechanical or hydrodynamic processes, creating micro-fin structures along the inner wall surface. These internal threads increase the effective heat transfer surface area by up to 60–80% compared to smooth-bore tubing of identical outer diameter, while simultaneously enhancing turbulence of the flowing refrigerant, thereby improving the convective heat transfer coefficient.
Specifications
| Parameter | Specification | Unit | Standard Reference |
|---|---|---|---|
| Outer Diameter (OD) | 3.0 / 3.5 / 4.0 / 4.5 / 5.0 / 6.0 | mm | ASTM B88 / GB/T 17791 |
| Wall Thickness | 0.35 / 0.40 / 0.45 / 0.50 / 0.60 / 0.70 | mm | ASTM B88 |
| Coil Winding Diameter | 150 – 600 (customizable) | mm | Customer Specification |
| Coil Length | 3 – 50 (standard); up to 100 (special order) | m | — |
| Working Pressure | ≥ 3.5 (low pressure side); ≥ 4.5 (high pressure side) | MPa | EN 12828 |
| Internal Thread Pitch | 0.2 – 0.5 | mm | Proprietary Design |
| Internal Thread Depth | 0.05 – 0.15 | mm | Proprietary Design |
| Heat Transfer Enhancement Factor | 1.6 – 2.0 (vs. smooth tube) | Dimensionless | Experimental Validation |
| Refrigerant Compatibility | R-134a, R-410A, R-32, R-1234yf | — | ASHRAE 34 |
| Operating Temperature Range | −40 to +120 | °C | — |
| Surface Finish (External) | Smooth, oxide-free, clean | — | GB/T 1804-m |
| Surface Finish (Internal) | Machined thread, burr-free, contaminant-free | — | ISO 8785-2 |
| Dimensional Tolerance | ±0.05 mm (OD); ±0.03 mm (wall thickness) | mm | ASTM B88 Class B |
| Packaging | Coiled on spool, moisture-proof wrapping, wooden crate | — | ISO 4180 |
Manufacturing Process
The production of seamless internally threaded coil tubes follows a multi-stage precision manufacturing workflow designed to ensure dimensional accuracy, surface quality, and mechanical reliability:
- Raw Material Selection & Inspection: Seamless copper tube billets are procured from certified suppliers. Incoming material undergoes spectroscopic analysis (OES — Optical Emission Spectroscopy) to verify chemical composition, along with ultrasonic testing (UT) for internal defect detection.
- Tube Straightening & Cutting: The raw seamless tube is straightened to achieve the required straightness tolerance (≤ 0.5 mm/m) and cut to predetermined lengths using precision shearing equipment.
-
Internal Threading (Micro-Fin Formation): Internal threads are created through one of the following methods:
- Mechanical Threading: Precision-cut inserts or rotating mandrels are passed through the tube to form uniform internal thread profiles.
- Hydrodynamic Threading: High-pressure fluid jets are directed through the tube interior to create controlled surface roughness and thread patterns.
- Electrochemical Threading: Selective anodic dissolution is used to form thread geometries with high dimensional precision.
- Surface Cleaning & Degreasing: The internally threaded tube is subjected to alkaline cleaning, acid pickling, and rinsing cycles to remove all machining residues, oils, and contaminants. Final cleanliness is verified through visual inspection and particle count analysis.
- Coil Winding: The prepared tube is wound into coils of specified diameter using automated winding machinery. Winding tension is precisely controlled to prevent tube deformation, ovality, or kinking. The minimum bend radius is maintained at ≥ 5× tube OD to ensure structural integrity.
- Heat Treatment (Annealing): Where required, the coiled tube undergoes controlled annealing (typically at 400–500°C for 30–60 minutes) to relieve residual stresses introduced during winding and threading, restoring full ductility.
-
Final Inspection & Testing: Each coil undergoes comprehensive quality verification including:
- Dimensional measurement (OD, wall thickness, coil diameter)
- Hydrostatic pressure testing (typically at 2.5× working pressure for 5 minutes)
- Internal bore inspection (endoscope or optical measurement)
- Surface defect inspection (visual and magnetic particle testing where applicable)
- Chemical cleanliness verification
- Packaging & Storage: Qualified coils are wrapped in moisture-barrier film, placed in ventilated wooden crates or steel drums, and labeled with batch traceability information for shipment.
Applications
Primary Applications
- Residential & Commercial Air Conditioners: Evaporator and condenser coil assemblies in split-system, window, and central air conditioning units
- Heat Pump Systems: Air-source and ground-source heat pump evaporators and condensers
- Refrigeration Equipment: Commercial refrigerators, freezers, and cold storage units
- Automotive Air Conditioning: Compact evaporator coils for vehicle climate control systems
- Industrial Process Cooling: Precision temperature control in manufacturing and pharmaceutical applications
System Integration Advantages
The internally threaded design enables significant system-level performance improvements:
- Reduction in coil length by 20–35% for equivalent heat transfer capacity, resulting in more compact heat exchanger designs
- Decreased refrigerant charge volume by up to 30%, contributing to environmental sustainability and compliance with GWP (Global Warming Potential) regulations
- Improved COP (Coefficient of Performance) by 5–12% in installed systems
- Enhanced performance under partial load conditions due to improved flow distribution within the threaded bore
Quality Certifications
The production system and final products conform to the following quality management and industry standards:
- ISO 9001:2015 — Quality Management Systems certification for manufacturing operations
- ISO 14001:2015 — Environmental Management Systems certification
- ISO/TS 16949:2009 — Automotive Quality Management (where applicable for automotive AC components)
- CE Marking — Conformity with European Machinery Directive and Pressure Equipment Directive (PED 2014/68/EU)
- RoHS 2011/65/EU — Restriction of Hazardous Substances compliance
- REACH Regulation — Registration, Evaluation, Authorisation and Restriction of Chemicals compliance
- UL 484A — Safety standard for air-conditioning and heat pump equipment (material compliance)
- GB/T 19001 — Chinese National Standard for Quality Management Systems
Unique Selling Points:
- Proprietary internal thread geometry optimized through CFD (Computational Fluid Dynamics) simulation for maximum heat transfer enhancement with minimal pressure drop penalty
- Full-process traceability from raw material to finished coil, ensuring consistent quality and rapid root-cause analysis
- Capability for customized coil winding diameters and lengths to accommodate OEM (Original Equipment Manufacturer) design requirements
- Environmentally responsible manufacturing with closed-loop wastewater treatment and energy-efficient production processes
- Extensive R&D (Research and Development) heritage in coil tube technology for HVAC applications, supported by academic-industrial collaboration