1. Classification and performance characteristics of copper tubes
1. According to material composition:
Copper tubes can be divided into red copper tubes (TP2), brass tubes (H62/H65/H68), bronze tubes (QSn6.5-0.1), nickel silver tubes (Ni-Cu alloy), etc. Among them, red copper tubes have the best thermal conductivity, but are more expensive; brass tubes have high strength but low thermal conductivity; bronze tubes and nickel silver tubes have good corrosion resistance but poor processing performance[1].
2. According to production process:
Copper tubes can be divided into oxygen-free copper tubes, oxygen-containing copper tubes, internally threaded copper tubes, etc. Oxygen-free copper tubes have high purity and are generally used to make precision parts such as capillaries; oxygen-containing copper tubes have moderate strength and hardness, good weldability, and are mostly used as connecting tubes; internally threaded copper tubes have threads on the inner wall, which has a good enhanced heat transfer effect[2].
3. According to hardness:
Copper tubes can be divided into three categories: soft state (O state), semi-hard state (1/2H), and hard state (H state). O-state copper tubes are soft, with good plasticity and ductility, but low strength; H-state copper tubes have high strength and hardness, but poor plasticity; 1/2H copper tubes have moderate strength and plasticity, good processing performance, and are the first choice for refrigeration pipelines [3].
2. Technical requirements for copper tubes for refrigeration systems
1. Material requirements
Refrigeration systems mostly use 1/2H-state copper tubes (TP2M), and their chemical composition should comply with the provisions of GB/T 17505-2010 [4]:
Cu+Ag≥99.90%
0.015%≤P≤0.040%
The content of impurity elements should meet the following requirements: Bi≤0.001%, Sb≤0.002%, As≤0.002%, Fe≤0.005%, Pb≤0.005%, S≤0.005%, Zn≤0.005%, Ni≤0.002%, Sn≤0.002%.
2. Mechanical properties
The mechanical properties of 1/2H copper tubes should meet the following requirements [4]:
Tensile strength Rm ≥ 295MPa
Yield strength Rp0.2 ≥ 255MPa
Elongation after fracture A ≥ 3%
