Engineered to withstand extreme environments in refrigeration, air conditioning, and automotive systems.
An in-depth industrial perspective on why double-wall brazed steel tubing remains the global benchmark for thermal transfer and high-pressure fluid control systems.
Bundy tubes, originally patented by Bundy Tubing Company and standardized globally, are manufactured through a highly complex, continuous cold-rolling process. A single copper-coated low-carbon steel strip is precisely formed and wrapped 720 degrees around a central axis to form a double-walled pipe. This raw structure then passes through a controlled-atmosphere induction furnace at temperatures exceeding 1120°C (2048°F).
During this thermal phase, the internal and external copper interfaces fuse at the molecular level, creating a completely seamless metallurgical bond. This double-wall wrapping design delivers outstanding mechanical integrity, high pressure resilience, and superior resistance to vibrations, making 4mm Bundy tubes the standard specification for modern refrigeration systems and automotive brake circuits.
"The primary mechanical advantage of the 4mm double-wall structure is its high hydrostatic burst pressure limit, often exceeding 120 MPa, combined with exceptional ductile fatigue limits. This balance of strength and flexibility is critical in dynamic automotive brake lines and high-velocity refrigerant loops."
Ningbo Taojun Refrigeration Equipment Co., Ltd. integrates decades of technical collaboration with premier academic institutions and advanced equipment.
Founded in 1988 as the Xiangshan Refrigeration Accessories Factory under the technical guidance of Zhejiang University, our journey has been defined by technological and process innovation. Over the past three decades, we have evolved into a national high-tech enterprise integrating design, development, high-precision production, and global logistics support.
Our facility in Xiangshan, Ningbo, implements an integrated Manufacturing Execution System (MES) to guarantee real-time tracing of raw material coil batches, temperature histories, and pressure leak parameters. We maintain close engineering partnerships with global brands including Haier, Midea, Gree, Whirlpool, and Electrolux, matching our processes directly with their rigorous supply chain audits.
Standardized specifications for refrigeration condensers, evaporator circuits, and high-pressure automotive line designs.
Our double-wall steel tubes comply with international specifications including ASTM A254, SAE J527, and DIN 74234. Below is the technical data profile for our 4.00mm outer diameter lines:
| Parameter Description | Refrigeration Grade Profile | Automotive High-Pressure Profile | Measurement/Standard Method |
|---|---|---|---|
| Outer Diameter (OD) | 4.00 mm ± 0.05 mm | 4.00 mm ± 0.05 mm | Laser Micrometer Micrometry |
| Wall Thickness | 0.50 mm - 0.70 mm | 0.70 mm ± 0.05 mm | Ultrasonic Wall Thickness Gauging |
| Tensile Strength (Rm) | ≥ 290 MPa | ≥ 340 MPa | ASTM E8 Mechanical Testing |
| Yield Strength (Rp0.2) | ≥ 180 MPa | ≥ 220 MPa | Tension Elongation Limits |
| Elongation at Break (A5) | ≥ 25% | ≥ 25% | ISO 6892-1 Verification |
| Internal Cleanliness Limit | ≤ 0.15 mg/m² residue | ≤ 0.20 mg/m² residue | Solvent Extraction & Gravimetry |
| Corrosion Resistance (SST) | 100h - 300h to White Rust | 1000h+ to Red Rust (PVF Coating) | ASTM B117 Salt Spray Chamber |
Low-carbon steel requires robust barrier protection to survive decades in harsh, moisture-laden environments. Our factories offer three primary coating configurations for 4mm Bundy tubing:
How the structural design of Taojun refrigeration tubes enhances thermal cycle performance and minimizes field failures.
Our core production machinery is imported from German specialists, ensuring high precision in forming, induction welding, and dimension straightening.
Collaborations with Zhejiang University and the University of Science and Technology of China keep our manufacturing at the industry forefront.
We supply custom tubing configurations, pre-bent coils, manifolds, and end-form configurations tailored to clients' physical schematics.
Our components undergo 500-hour environmental aging tests (-35°C to 75°C) and continuous 100V high-voltage insulation and pressure breakdown checks.
Our raw copper, premium desiccant molecular sieves, and steel strips are sourced from certified global partners to ensure long-term stability.
Advanced machinery ensures foil and tube thickness tolerances stay within ±0.02mm, providing robust fatigue and burst safety margins.
Deploying specialized micro-diameter tubes to address critical cooling and thermal challenges.
In domestic refrigerators and commercial freezers, 4mm Bundy tubing is widely used in static condensers and cooling loops. Bending the tube into serpentine shapes and welding it to low-carbon steel wires creates a wire-tube condenser with high heat dissipation capability.
The 4.00mm outer diameter provides an optimal balance: a high internal surface-area-to-volume ratio increases refrigerant turbulence, while the thin 0.50mm - 0.70mm walls maintain high thermal efficiency.
Automotive braking systems require high hydraulic pressure and reliability under harsh road conditions. Double-wall brazed steel 4mm lines serve as capillary links between master cylinders, ABS control actuators, and wheel calipers. Their ability to withstand dynamic vibrations and resist impact makes them ideal for demanding automotive fluid control applications.
A timeline of technical innovation and global expansion over 38 years.
Origins: Founded as Xiangshan Refrigeration Accessories Factory, working with Zhejiang University to manufacture early refrigeration components.
Brand Scaling: Established the "Taojun" brand, focusing on high-efficiency condensers, access valves, and filter drier assemblies.
Smart Industry: Implemented fully automated production, smart CCD defect scanning, and MES traceability systems.
We believe global brands are built on corporate culture. At Taojun, our core values of Honesty, Innovation, Responsibility, and Cooperation shape every partnership. By utilizing advanced production equipment and maintaining strict quality control, we ensure our systems meet international standards. We collaborate with clients to optimize design footprints, reduce manufacturing costs, and ensure reliable lead times.
We verify, audit, and document every stage of manufacturing to comply with regulatory standards and client specifications.
Our manufacturing facilities comply with GB/T19001-2016/ISO9001:2015 standards (Registration No.: 41325Q00065R0S). This quality system covers design, procurement, cold drawing, copper fusing, zinc coating, and final leakage verification of refrigeration products.
Every shipment includes Mill Test Certificates (MTC), chemical composition analysis, mechanical properties reports, and hydrostatic validation charts. Additionally, we conform to RoHS, REACH, and UL standards, helping clients integrate our products into environmentally conscious systems.
ISO 9001 Certificate Document
Scope of Certification Details
Engineering clarifications regarding design parameters, compatibility, and custom applications.
Complete components portfolio designed to optimize system reliability and thermal control.
Taojun