Copper Wire Testing

Copper wire inspection mainly conducts scientific testing and analysis on the electrical conductivity and resistivity, mechanical properties, dimension and structure, chemical composition analysis, surface quality and defects and insulation and sheath properties, objectively assessing the product quality grade and issuing a detailed test report, providing a basis for manufacturers' quality control and downstream users' product acceptance.

Testing Items

Electrical conductivity and resistivity: This is the core indicator of measuring the conductive properties of the copper wires, directly related to the losses of the electrical energy during the transmission. The testing is usually carried out according to the standards such as GB/T 3048.2 or ASTM B193. Through the measurement of the DC resistance per unit length and unit cross-sectional area, the electrical conductivities or resistivities are calculated. The electrical conductivity of the high-purity oxygen-free copper can reach more than 101% IACS (International Annealed Copper Standard).

Mechanical properties (tensile strength and elongation): The tensile strength reflects the maximum tensile stress that the copper wires can withstand before the fracture, and the elongation characterizes their plastic deformation ability. This is crucial for judging the mechanical reliability of the copper wires during the drawing, stranding, laying and long-term operation. The testing is carried out according to GB/T 4909.3 or ISO 6892-1, using the universal material testing machines.

Dimension and structure: Including the conductor diameters (or cross-sectional areas), out-of-roundness, insulation layer/sheath layer thicknesses and concentricity, etc. The precise dimensions are the basis of ensuring the consistent electrical properties, meeting the current carrying capacity requirements and installation compatibility. Usually measured with the micrometers, optical projectors or laser diameter gauges.

Chemical composition analysis: The purity of the copper and the contents of the trace impurity elements (such as the oxygen, phosphorus, arsenic and bismuth) are detected. The impurities will significantly reduce the electrical conductivities and affect the processing properties. The analysis methods include the spark direct-reading spectrometry (OES), inductively coupled plasma optical emission spectrometry (ICP-OES), as well as the coulometric method for the oxygen content measurement, etc.

Surface quality and defects: Whether the copper wire surfaces have the defects such as the oxidation, burrs, scratches, cracks, peeling or oil stains is checked. The surface defects may become the starting points of the electrical breakdown or corrosion, affecting the long-term use safety and lives. The testing is mostly completed through the visual inspection or automatic optical inspection equipment.

Insulation and sheath properties: For the insulated copper wires and cables, the insulation resistance, withstand voltage strength, dielectric loss tangent, as well as the mechanical properties and environmental stress cracking resistance of the sheaths need to be tested. These items are the keys of evaluating their insulation reliability and safety.

Solderability and plating quality: For the copper wires requiring the soldering (such as the electronic leads), their solderability needs to be evaluated. For the tinned copper wires, the plating thicknesses, continuity and adhesion also need to be tested, to ensure the good soldering properties and anti-oxidation abilities.

Testing Scope

Electrical copper wires: Mainly including the bare copper wires, hard copper wires, soft copper wires (annealed copper wires) and copper stranded wires used for the power transmission and distribution. The testing emphases are the electrical conductivities, mechanical strengths and dimension tolerances, ensuring that they meet the requirements of the large current carrying and overhead laying mechanical stresses.

Winding wires (magnet wires): Used to manufacture the windings such as the motors, transformers and inductance coils. In addition to the basic properties, the heat resistance grades, scrape resistance, solvent resistance and breakdown voltages of their paint films or fiber insulation layers are emphatically tested, to ensure the long-term insulation stability in the complex electromagnetic environments.

Copper conductors for the communication cables: Including the copper core wires for the data cables, coaxial cables and telephone cables. The testing focuses on the structural consistency of the conductors (such as the star-quad structures), transmission properties (such as the characteristic impedance and attenuation), as well as the high-frequency properties related to the signal integrity.

Electronic component leads and wiring harnesses: Referring to the fine copper wires or tinned copper wires used in the fields such as the integrated circuits, connectors and automotive wiring harnesses. The testing scope covers the micro dimension precision, solderability, plating qualities, bending fatigue lives and corrosion resistance.

Special copper alloy wires: Such as the copper-silver alloy, copper-tin alloy and copper-magnesium alloy wires, used for the special occasions requiring the higher strengths, wear resistance or heat resistance. The testing needs to take into account the alloy composition control, unique mechanical and physical properties, as well as the corresponding functional indicators.

Copper wire production raw materials and semi-finished products: Including the testing of the electrolytic copper plates and copper rods, controlling the quality from the sources. For the semi-finished products such as the copper wires after the intermediate annealing, their softening degrees and grain sizes need to be tested, providing the basis for the subsequent processing.

Testing Methods

DC resistance method (bridge method): The standard method of measuring the conductive properties of the copper wires. The double-arm bridges or micro-ohmmeters are used. At the standard temperatures (such as 20°C), a tiny DC current is applied to the specimens of the specified lengths, the resistance values are precisely measured, and the resistivities or electrical conductivities are further calculated. This method has the high precision and is the mandatory item of the type testing.

Tensile testing method: The main method of evaluating the mechanical properties of the copper wires. The specimens are clamped on the material testing machines, and the axial tensile forces are applied at the constant rates, recording their stress-strain curves, thereby obtaining the key data such as the tensile strengths, yield strengths and elongations after fracture, judging the toughness and strengths of the material.

Metallographic analysis method: Used to observe and analyse the micro-structures of the copper wires. Through the sampling, mounting, grinding, polishing and etching, the grain sizes, morphologies and distributions are observed under the metallographic microscopes, as well as whether the internal defects such as the inclusions, cracks and oxidation exist, relating them to the properties.

Spectroscopic analysis method: The efficient means of the qualitative and quantitative chemical composition analysis. The spark direct-reading spectrometers (OES) are suitable for the fast composition screening of the solid samples such as the copper rods and copper blocks; the ICP-OES can more precisely determine the trace element contents in the solutions, with the extremely high sensitivity.

Eddy current conductivity instrument method: A fast and non-destructive electrical conductivity testing method. Based on the electromagnetic induction principle, the high-frequency magnetic fields generated by the probes induce the eddy currents in the copper wires. Through the measurement of the probe impedance changes caused by the eddy current effects, the electrical conductivities of the material are indirectly calculated, often used for the 100% online testing on the production lines.

Withstand voltage testing and insulation resistance testing: The key safety property testing for the insulated copper wires. The withstand voltage testing applies the AC or DC high voltages far higher than the working voltages between the conductors and insulation layers for a certain time, checking whether the breakdown occurs. The insulation resistance testing measures the leakage currents after applying the DC voltages, calculating the resistance values and evaluating the qualities of the insulation materials.

Testing Standards

Domestic Standards:

1. GB/T 3953, Copper wires for electrical purposes

2. GB/T 3048.2, Test methods for electrical properties of electric wires and cables — Part 2: Test of metallic material resistivity

3. GB/T 4909, Test methods for bare wires

4. GB/T 228.1-2021, Metallic materials — Tensile testing — Part 1: Method of test at room temperature

International Standards:

1. IEC 60228, Conductors of insulated cables

2. ASTM B193, Standard test method for resistivity of electrical conductor materials

3. ISO 6892-1, Metallic materials — Tensile testing — Part 1: Method of test at room temperature

Note: The applicable standard can be selected according to the product use and customer trade requirements; standards agreed in the contract take precedence over general standards.

Testing Instruments and Equipment

DC resistance tester/double-arm bridge: The core equipment of the precise measurement of the conductor DC resistances. The modern digital DC resistance testers have the automatic range switching, temperature compensation and data analysis functions, with the wide measurement ranges and high precision, meeting the requirements of the standards such as GB/T 3048.2 and IEC 60247.

Universal material testing machine: The key equipment of carrying out the mechanical property testing such as the tensile, compression and bending. Equipped with the high-precision load transducers and extensometers, it can precisely control the test rates and collect the force and deformation data in real time, outputting the complete stress-strain curves and test reports.

Digital micrometer and laser diameter gauge: The basic tools of the dimension measurement. The digital micrometers are used for the manual sampling inspection, with the precision up to 1 micrometre; the laser diameter gauges are used for the non-contact and high-speed online measurement, which can monitor the copper wire diameters and ellipticity in real time and feed back to control the production lines, ensuring the dimension stability.

Spark direct-reading spectrometer (OES): The precision instrument for the fast composition analysis of the metal materials. Through the spark discharge excitation of the samples, the intensities of the characteristic spectral lines of the various elements are measured. Compared with the standard sample calibration curves, the percentage contents of the multiple impurity elements in the copper matrix can be simultaneously given within tens of seconds.

Eddy current conductivity instrument: The dedicated equipment realizing the non-destructive and fast electrical conductivity testing of the copper wires. The instruments are usually equipped with the probes of the different sizes to adapt to the different wire diameters, can directly display the electrical conductivity values (%IACS) or resistivities, widely applied to the production site quality control and incoming material inspection of the copper rods and copper wires.

High-voltage breakdown tester and insulation resistance tester: The dedicated safety testing equipment of evaluating the insulation properties. The high-voltage breakdown testers can output the adjustable high voltages from thousands to tens of thousands of volts, and automatically detect the breakdown points. The insulation resistance testers (megohmmeters) can apply the DC voltages from hundreds to thousands of volts, measuring the insulation resistances up to the tera-ohm (TΩ) levels.

Metallographic microscope and image analysis system: Used for the micro-structure observation and analysis of the material. The system includes the optical microscopes, digital cameras and computer analysis software, which can carry out the quantitative measurement and statistics of the grain sizes and second phase distributions of the copper wires, providing the micro basis for the process improvements.