An Overview from a Cable Industry Manufacturer

Today, we will explore copper, the most widely used core material in the wire and cable industry.

I. Fundamentals of Copper

Copper is one of the earliest metals used by mankind. As far back as prehistoric times, people were mining open-pit copper deposits to produce weapons, tools, and vessels. The use of copper had a profound impact on the advancement of early human civilization.

Copper exists naturally in the Earth's crust and oceans. Its average crustal abundance is about 0.01%, while in some copper ore deposits, concentrations can reach 3–5%. In nature, copper mostly occurs in compound form as copper ores. These ores are aggregated with other minerals, then mined and concentrated into copper concentrates​ with high copper content.

1. Properties

Copper possesses excellent physical and chemical properties, including high electrical conductivity, thermal conductivity, corrosion resistance, and ductility.

Pure copper ranks second only to silver in electrical and thermal conductivity. It can be drawn into extremely fine wires or rolled into thin foils. Freshly fractured pure copper appears rose-red, but forms a reddish-purple oxide film on its surface, hence it is commonly called red copper​ (purple copper).

Beyond pure copper, copper can be alloyed with tin, zinc, or nickel to create alloys with distinct characteristics:

Alloying significantly enhances strength and corrosion resistance compared to pure copper. Some alloys also offer superior wear resistance or casting performance.

2. Applications

Due to its outstanding properties, copper is extensively used across industries, including electrical, machinery, transportation, and construction.

• Electrical & Electronics (≈ 50% of industrial demand):​

  Manufacturing of power cables, communication cables, motors, generators, rotors, electronic instruments, and meters. Copper and copper alloys play a vital role in computer chips, ICs, transistors, and PCBs. For example, chromium-zirconium copper alloys are used for transistor leads due to high conductivity and heat resistance. IBM’s adoption of copper instead of aluminum in silicon chips marked a major breakthrough in semiconductor metallization.

• Construction:​

  In the U.S., Japan, and Western Europe since the mid-1980s, the electrical sector has been the largest consumer of refined copper—China followed a similar trend. However, after the 1990s, overseas consumption shifted significantly toward building services. According to the Copper Development Association (CDA), construction remained the largest end-use market for copper products in the U.S. in 1997. Copper’s corrosion resistance makes it ideal for water pipes, roofing, and drainage systems, while its aesthetic appeal supports architectural decoration. Construction accounts for the largest share of copper consumption in the U.S.

• Emerging Fields:​

  With technological progress, copper applications now extend to medicine, biology, superconductivity, and environmental protection. For instance, polyurethane foam containing copper or copper oxide drastically reduces the release of toxic hydrogen cyanide (HCN) during combustion. Numerous studies confirm that copper’s bactericidal properties help reduce the spread of pneumonia-causing bacteria, inhibit bacterial growth, and maintain drinking water cleanliness. Consequently, the prospects for copper piping in domestic construction remain highly promising.

II. Global Copper Reserves

Copper resources are abundant worldwide. According to the U.S. Bureau of Mines (1995), global copper reserves stood at 310 million tons, with a reserve base of 590 million tons. Chile and the United States hold the largest reserves, accounting for 23.7%​ and 15.3%​ of the world’s reserve base respectively, followed by Poland, Zambia, Russia, Zaire, Peru, Canada, and Australia.

There are nine major industrial types of copper deposits:

1. Porphyry

2. Sandstone/shale-hosted

3. Cu-Ni sulfide

4. Pyrite-type

5. Cu-U-Au type

6. Native copper

7. Vein-type

8. Carbonate-type

9. Skarn-type

The first four types dominate, representing 96%​ of global reserves, with porphyry and sandstone/shale deposits accounting for 55%​ and 29%​ respectively. Approximately 60 giant copper mines​ (each >5 million tons Cu) exist globally, including 38 porphyry and 15 shale types, together making up 88%​ of giant deposits.

China’s recoverable copper concentrate resources are relatively limited. Major domestic mines include:

• Dexing Copper Mine (Jiangxi)

• Yulong Copper Mine (Tibet)

• Ashele Copper Mine (Xinjiang)

III. Copper Smelting Processes

Copper ores mined from the earth are concentrated into copper concentrates​ or high-grade ores before being smelted into refined copper and downstream products.

Two primary smelting methods dominate globally:

1. Pyrometallurgy (Fire Refining)

• Produces cathode copper​ (electrolytic copper) via smelting and electrolytic refining.

• Suitable for high-grade sulfide ores.

• Scrap copper is another key feedstock, categorized as:

  • Old scrap:​ From obsolete equipment, buildings, underground pipelines.

  • New scrap:​ From manufacturing waste (~50% of copper production yield).

• Scrap classification:

  • Bare mixed copper:​ >90% purity

  • Brass / wire scrap:​ Contains copper materials (motors, PCBs)

  • Secondary copper:​ Produced from scrap and similar materials

2. Hydrometallurgy (SX-EW)

• Suitable for low-grade oxidized ores.

• Produces electrowon copper​ (cathode copper via solvent extraction–electrowinning).

3. Comparison of Pyro- and Hydrometallurgy

Hydrometallurgy offers significant cost advantages but is application-limited. Not all copper ores are suitable. However, technological improvements since the 1990s have enabled broader adoption in the U.S., Chile, Canada, Australia, Mexico, and Peru. This expansion increased global copper supply, contributing to a price decline from a 1996 peak of 2,600/t∗∗toaround∗∗1,600/t​ in late 1998.

Average production costs in the late 1990s were 1,400–1,600/t​ (64–73 ¢/lb). The lowest recorded hydrometallurgical cost was 20 ¢/lb​ (450/t),withanaveragebelow∗∗50¢/lb∗∗(1,100/t). Costs rise above 50 ¢/lb when processing sulfide ores, high-grade ores, or operating in cold climates.

China’s Hydrometallurgical Development

Since the 1970s, China has researched copper extraction from low-grade ores. The first hydrometallurgical plant (120 t/year) was built in 1983. In recent decades, dozens of small plants (capacity: hundreds to 2,000 tons) have emerged, yet total output remains only ~15,000 t/year—insufficient compared to China’s ~1 million t/year refined copper production. Domestic copper production costs (~¥18,500/t) far exceed the global average (~$1,477/t or 67 ¢/lb). During the Ninth Five-Year Plan, hydrometallurgy was designated a national priority, with demonstration plants constructed at Dexing, Yulong, and Tonglüshan mines. By 2000, China’s hydrometallurgical capacity was expected to exceed 50,000 t/year.

Globally, hydrometallurgical refined copper rose from 2.5%​ (1980) to 10%​ (1994) and 18%​ (1997), with projections suggesting eventual shares of 25–35%.

IV. Differences Between Oxygen-Free Copper Rod and Low-Oxygen Copper Rod

1. Oxygen Absorption/Desorption and Existence State

• Cathode copper typically contains 10–50 ppm oxygen; solid solubility at room temperature is ~2 ppm.

• Low-oxygen copper rod:​ 200–400 ppm oxygen (sometimes up to 450 ppm), absorbed in liquid state.

• Upward-cast oxygen-free copper rod:​ Usually <10–50 ppm oxygen, sometimes as low as 1–2 ppm.

Oxygen precipitates as Cu₂O​ at grain boundaries in low-oxygen copper, negatively affecting toughness. Oxygen-free copper exhibits a homogeneous single-phase structure with fewer inclusions and almost no pores, whereas porosity is common in low-oxygen rods.

2. Microstructure: Hot-Rolled vs. Cast

• Low-oxygen rod: Hot-rolled → recrystallized structure (8 mm), broken cast dendrites.

• Oxygen-free rod: Coarse cast grains, sometimes several mm in size → smaller grain boundary area → requires higher annealing temperatures.

For successful annealing, the first anneal after drawing must be 10–15% higher​ in power than for low-oxygen rod under equivalent conditions. Subsequent continuous drawing demands sufficient annealing margin to ensure final product softness.

3. Inclusions, Oxygen Variability, Surface Oxides, and Rolling Defects

Oxygen-free copper generally shows:

• Fewer inclusions

• Stable oxygen content

• No hot-rolling defects

• Surface oxide films as thin as ≤15 Å

In contrast, low-oxygen rods may suffer from subsurface oxides formed during casting and rolling, leading to wire breakage. To mitigate this, some producers resort to peeling​ or even double-peeling​ the rod.

4. Toughness

Both rods can be drawn to 0.015 mm, but ultra-fine superconducting wire inter-filament spacing may reach 0.001 mm, where oxygen-free copper excels.

5. Economic Considerations

Oxygen-free copper requires higher-grade raw materials. For wire diameters >1 mm, low-oxygen rod is more economical; for finer wire, oxygen-free rod holds the advantage.

6. Processing Differences

Drawing and annealing processes cannot be identical. Wire softness depends on composition, rod manufacturing, drawing, and annealing parameters—neither type is universally “softer.”

V. Identification of Copper Materials for Cables

The cable market faces challenges distinguishing genuine copper from counterfeit products, especially copper-clad aluminum (CCA)​ and copper-clad aluminum-magnesium (CCAM), which have emerged in recent years.

Price comparison (approx.):

• Oxygen-free copper: ¥50,000/t​

• CCA: ¥25,000/t​

  (Specific gravities: Cu = 8.9, Al = 2.7)

Five Identification Methods

1. Visual Inspection

Genuine copper cores appear purple-red, glossy, and soft. Fake cores look dark purple, yellowish, or whitish, with poor mechanical strength. Rubbing the exposed core on white paper may leave black marks if impurities are present.

2. Cross-Section Examination

CCA and CCAM are usually stranded fine wires. Cutting the cross-section reveals white aluminum cores​ beneath a thin copper layer.

3. Flame Test

• CCA / CCAM: Conductor sags, does not ignite easily; after burning, turns gray/dark; brittle and breaks into segments when twisted.

• Oxygen-free copper: Forms molten beads; behavior varies with wire diameter (fine wire melts, thick wire retains shape).

4. Scratch Test

• Tinned copper: Yellow scratch mark

• Bare oxygen-free copper: Reddish scratch

• CCA / CCAM: Snowflake-white scratch pattern

• Copper-clad steel: Magnetic attraction confirms steel core

5. Instrument Testing

Conductors must comply with GB/T 3953-2009​ (Round Copper Wire for Electrical Purposes). Key metric: DC resistivity at 20 °C.

Test standard: GB/T 3048.2-2007​ (modifies IEC 60468:1974)

Resistivity limits (max):

• Hard round copper wire (Ty3.0 mm): ≤ 0.01777 Ω·mm²/m​

• Soft round copper wire (TR): ≤ 0.017241 Ω·mm²/m

Measurement is typically performed using a Kelvin bridge or similar precision instrument, converting resistance to resistivity based on cross-sectional area.

Provided by Minfeng Cable Group, a direct factory and one-stop solution provider for the wire and cable industry.