Copper Coiled Tube (Coiltube) — Casting and Rolling Process

Product Overview

The Copper Coiled Tube (Coiltube) is a continuous-length tubular product manufactured through advanced casting and rolling (cast-rolling) technology. Unlike conventionally drawn tubes, coiled tubes are produced as continuous coils, eliminating joints, seams, and mechanical fasteners along the tube length. This product is supplied by Wenzhou Jixing Metal Materials Co., Ltd., a manufacturer specializing in non-ferrous metal tube products with deep expertise in the casting and rolling metallurgy of copper alloys.

The cast-rolling process combines semi-continuous casting with hot or warm rolling to produce tubes in a coil configuration. This method offers significant advantages in production efficiency, material utilization, dimensional consistency, and cost-effectiveness compared to traditional seamless or welded tube manufacturing routes. The resulting product exhibits a homogeneous microstructure with superior mechanical properties and surface finish.

Material & Properties

Available Copper Alloy Grades

• T2 Copper (C11000) — High-purity electrolytic tough-pitch copper; excellent electrical and thermal conductivity
• H62 Copper (C26800) — Copper-zinc alloy; good mechanical strength with moderate corrosion resistance
• H65 Copper (C27200) — Brass alloy with enhanced formability and corrosion resistance
• H90 Copper (C28000) — High-brass alloy; superior strength and corrosion resistance for demanding applications
• TU1 Copper (C12200) — High-conductivity copper for electrical applications

Typical Mechanical Properties (Annealed Condition)

• Tensile Strength (UTS): 200–320 MPa (depending on alloy grade)
• Yield Strength (0.2%): 70–180 MPa
• Elongation at Break: 30%–55%
• Hardness (HBW): 45–110 (annealed); 100–180 (cold-worked/hard-drawn)
• Density: 8.89–8.94 g/cm³

Physical Properties

• Electrical Conductivity: 55%–60% IACS (T2); 25%–30% IACS (brass alloys)
• Thermal Conductivity: 380–401 W/(m·K) (T2 copper)
• Linear Thermal Expansion Coefficient: 16.5–18.6 × 10⁻⁶ /K
• Melting Range: 900–1050 °C (depending on alloy composition)

Specifications

Parameter	Specification / Range	Standard Reference
Outer Diameter (OD)	Φ6.0 mm – Φ50.0 mm	GB/T 18033; ISO 14422
Wall Thickness	0.3 mm – 3.0 mm	GB/T 18033
OD Tolerance	±0.05 mm to ±0.15 mm (depending on size)	GB/T 18033
Wall Thickness Tolerance	±0.03 mm to ±0.10 mm	GB/T 18033
Coil Weight	200 kg – 2,000 kg	Manufacturer Specification
Coil Length	50 m – 500 m per coil	Manufacturer Specification
Surface Finish	Mill finish, bright annealed, or polished	GB/T 18033
Delivery Condition	Annealed (M), Half-Hard (Y2), Hard (Y4)	GB/T 18033
Roundness (Out-of-Roundness)	≤ 0.10% of OD	GB/T 18033
Coil Flatness	≤ 2 mm per 1,000 mm of tube length	Manufacturer Specification
Minimum Bend Radius	≥ 3× OD (annealed); ≥ 5× OD (hard-drawn)	GB/T 18033

Manufacturing Process

The production of copper coiled tubes via the casting and rolling (cast-rolling) route is a metallurgically sophisticated process that integrates multiple unit operations to achieve high-quality, continuous tubular products. The process flow is described below:

Step 1: Raw Material Preparation and Melting

Copper or copper alloy ingots (typically T2 cathode copper or brass alloy stock) are charged into an electric resistance furnace or induction furnace. The melt is heated to a temperature 150–200 °C above the liquidus temperature (typically 1,150–1,250 °C) to ensure complete dissolution of alloying elements and homogeneity. Fluxing and degassing operations are performed to remove dissolved gases (hydrogen, oxygen) and non-metallic inclusions, which are critical for preventing porosity and defects in the final tube product.

Step 2: Semi-Continuous Casting (Preform Production)

The refined molten copper is cast into a semi-continuous casting machine equipped with a water-cooled copper mold (crucible). The cast product is a solid or semi-solid cylindrical billet (preform) with a central hollow core. Key process parameters include:

• Casting temperature: 1,150–1,250 °C
• Pull speed: 20–80 mm/min (adjusted for alloy grade and preform dimensions)
• Mold cooling water flow rate: 5–15 L/min
• Preform outer diameter: Typically 1.5×–2.5× the final tube OD

The resulting preform exhibits a fine, equiaxed grain structure near the surface with a columnar grain structure toward the center, providing a favorable microstructure for subsequent rolling deformation.

Step 3: Preform Homogenization Heat Treatment

The cast preforms undergo a homogenization anneal at 700–850 °C for 2–8 hours, followed by controlled cooling. This step eliminates casting segregation, relieves residual stresses, and ensures uniform grain size throughout the cross-section, which is essential for achieving consistent mechanical properties and dimensional accuracy during rolling.

Step 4: Hot or Warm Rolling (Tube Formation)

The homogenized preform is fed into a multi-pass rolling mill (typically a 2-high or 4-high rolling mill configured for tube rolling). The preform is progressively deformed through multiple passes, reducing the wall thickness and outer diameter while maintaining the hollow cross-section. Key considerations include:

• Rolling temperature: 600–850 °C (warm rolling) or 900–1,050 °C (hot rolling)
• Total reduction ratio: 40%–70% (distributed across 4–8 passes)
• Roll gap control: ±0.02 mm precision hydraulic gap control
• Roll material: High-speed steel or cemented carbide rolls with precision ground surfaces

During rolling, the preform undergoes significant plastic deformation, leading to dynamic recrystallization and grain refinement. The rolling direction imparts a fibrous (elongated) grain structure along the tube axis, enhancing longitudinal mechanical properties.

Step 5: Coiling and Controlled Cooling

The rolled tube is wound onto a coiling reel at controlled tension to maintain dimensional stability and prevent springback or distortion. The coiling speed and tension are precisely managed to ensure uniform coil winding without overlaps or gaps. The coil is then allowed to cool at a controlled rate to avoid thermal stresses and residual deformations.

Step 6: Final Annealing and Stress Relief

To achieve the desired delivery condition (annealed, half-hard, or hard), the coiled tube may undergo a final batch annealing in a protective atmosphere furnace (hydrogen or nitrogen) at 600–700 °C for 1–4 hours. This relieves cold-work hardening from rolling, restores ductility, and produces a uniform, equiaxed recrystallized microstructure. The annealing cycle is carefully controlled to prevent over-grain growth and surface oxidation.

Step 7: Quality Inspection and Coiling

Final quality control includes dimensional measurement (OD, wall thickness, roundness), mechanical property testing (tensile, hardness), surface inspection (visual and eddy current), and hydrostatic pressure testing. Approved coils are labeled, protected, and packaged for shipment.

Applications

Copper coiled tubes manufactured through the casting and rolling process find extensive application across multiple industries:

• Refrigeration and Air Conditioning (HVAC): Heat exchanger tubes, evaporator coils, condenser coils, and refrigerant piping due to excellent thermal conductivity and corrosion resistance
• Automotive Industry: Radiator tubes, intercooler coils, oil coolers, and automotive heat management systems requiring high thermal performance and lightweight construction
• Heat Exchangers and Boilers: Shell-and-tube heat exchangers, plate-fin heat exchangers, and industrial boiler tubes where continuous tube length eliminates leak-prone joints
• Electrical Applications: Busbar tubes, electrical conduit, and current-carrying components leveraging high electrical conductivity
• Plumbing and Water Supply: Domestic and industrial water supply piping, hydronic heating systems, and solar thermal collectors
• Process Industries: Chemical processing, pharmaceutical manufacturing, and food processing where sanitary-grade copper tubes are required for fluid conveyance
• Specialty Applications: Cryogenic systems, nuclear cooling loops, and high-purity fluid transfer systems

Quality Certifications and Standards Compliance

Wenzhou Jixing Metal Materials Co., Ltd. adheres to internationally recognized quality management systems and product standards:

• ISO 9001:2015 — Quality Management System certification ensuring consistent product quality and process control
• GB/T 18033 — Chinese national standard for copper and copper alloy tubes
• ISO 14422 — International standard for copper and copper alloy tubes and pipes
• ASTM B152 — Standard specification for seamless copper and copper alloy tubes (where applicable)
• EN 12735 — European standard for copper and copper alloy tubes (where applicable)
• RoHS Compliance — Restriction of Hazardous Substances directive compliance
• REACH Compliance — Registration, Evaluation, Authorization, and Restriction of Chemicals compliance

In-Process Quality Control Measures

• Spectroscopic Analysis: Optical emission spectrometry (OES) for alloy composition verification at each heat batch
• Hydrostatic Pressure Testing: 100% inspection at 1.5× working pressure for minimum 15 seconds hold time
• Eddy Current Testing: Non-destructive testing (NDT) for surface and near-surface defect detection
• Dimensional Inspection: Automated laser or ultrasonic measurement of OD and wall thickness at defined intervals
• Mechanical Testing: Tensile testing, hardness testing, and bend testing per lot
• Metallographic Examination: Periodic microstructural evaluation for grain size, texture, and inclusion assessment

Unique Selling Points

1. Joint-Free Continuous Length: The coiled tube format eliminates welded or brazed joints, significantly reducing leak risk and improving system reliability in critical applications such as refrigeration and automotive cooling systems.

2. Superior Microstructure: The cast-rolling process produces a fine, uniform microstructure with reduced segregation compared to traditional casting or welding methods, resulting in consistent mechanical properties along the entire tube length.

3. High Production Efficiency: Continuous casting and rolling enable high-throughput production with minimal material waste, offering cost advantages over drawn seamless tubes while maintaining comparable performance.

4. Excellent Dimensional Consistency: Precision hydraulic roll gap control and automated dimensional monitoring ensure tight tolerances on OD and wall thickness, facilitating automated downstream forming and installation.

5. Versatile Alloy Selection: Availability across multiple copper and brass alloy grades (T2, H62, H65, H90, TU1) allows customers to optimize the material selection for specific application requirements regarding conductivity, strength, and corrosion resistance.

6. Multiple Delivery Conditions: Supply in annealed (M), half-hard (Y2), or hard (Y4) conditions provides flexibility for downstream processing and end-use performance requirements.

7. Environmental Responsibility: The cast-rolling process consumes less energy than traditional seamless tube manufacturing, and copper's 100% recyclability supports sustainable manufacturing practices.

Technical Summary

The Copper Coiled Tube (Coiltube) produced by Wenzhou Jixing Metal Materials Co., Ltd. represents a state-of-the-art product combining the metallurgical advantages of casting with the dimensional precision of rolling. The cast-rolling process yields continuous, joint-free copper tubes with homogeneous microstructures, excellent mechanical properties, and tight dimensional tolerances. This product serves as an ideal solution for applications demanding high thermal performance, corrosion resistance, and system reliability in refrigeration, automotive, heat exchange, electrical, and industrial processing sectors. The company's commitment to ISO-certified quality management, rigorous in-process controls, and adherence to international standards ensures that every coil meets the highest performance benchmarks.