The quality testing methods for black tungsten wire (unpolished, alkali-washed tungsten wire) production cover physical properties, chemical composition, surface quality, and dimensional accuracy to ensure the product meets industrial standards (e.g., for applications in electronics, lighting, and vacuum devices). Below are the common quality testing methods:
1. Dimensional Testing
- Method: Use high-precision tools (e.g., laser diameter gauges, microscopes, or micrometers) to measure the diameter and roundness of black tungsten wire.
- Purpose: Ensure consistent wire diameter within tolerance limits and check for ovality or deviations.
- Tools: Laser diameter gauges, profile projectors, scanning electron microscopes (SEM).
2. Surface Quality Testing
- Method:
- Visual Inspection: Observe the surface for cracks, scratches, oxides, or other defects.
- Microscopic Examination: Use optical microscopes or SEM to inspect microscopic surface defects.
- Surface Roughness Testing: Measure the Ra value (surface roughness parameter) using a surface roughness tester.
- Purpose: Ensure the black tungsten wire has a smooth surface without significant defects to guarantee performance in subsequent processing or use.
3. Chemical Composition Analysis
- Method:
- Spectral Analysis: Use X-ray fluorescence (XRF), inductively coupled plasma optical emission spectroscopy (ICP-OES), or atomic absorption spectroscopy (AAS) to detect impurity elements (e.g., iron, nickel, carbon).
- Gas Analysis: Measure oxygen, nitrogen, and hydrogen content using gas analyzers.
- Purpose: Confirm tungsten purity (typically 99.95% or higher) and ensure impurity levels are within standard limits.
4. Mechanical Property Testing
- Tensile Testing:
- Use a universal material testing machine to measure tensile strength, elongation, and fracture toughness.
- Purpose: Ensure the wire has sufficient strength and ductility for high-temperature or high-stress environments.
- Hardness Testing:
- Use Vickers or microhardness testers to measure wire hardness.
- Purpose: Evaluate material hardness and processability.
- Bending Testing:
- Test the wire’s flexibility and resistance to brittleness to check for susceptibility to fracture.
5. Microstructure Analysis
- Method:
- Metallographic Microscopy: Observe grain size and microstructure.
- X-ray Diffraction (XRD): Analyze crystal structure and internal stresses.
- Electron Backscatter Diffraction (EBSD): Provide precise analysis of grain orientation and microstructure.
- Purpose: Ensure uniform internal structure without abnormal grains or defects.
6. Density Testing
- Method: Use the Archimedes principle (water displacement method) or a densitometer to measure wire density.
- Purpose: Confirm the wire’s density is close to the theoretical value (19.25 g/cm³) to rule out internal voids or inclusions.
7. Electrical Performance Testing
- Method: Use a resistance tester to measure the wire’s resistivity or conductivity.
- Purpose: Ensure stable electrical performance for applications such as filaments in heating elements.
8. High-Temperature Performance Testing
- Method:
- Test oxidation resistance, high-temperature deformation, and volatility in a high-temperature furnace.
- Use thermogravimetric analysis (TGA) or differential scanning calorimetry (DSC) to evaluate high-temperature stability.
- Purpose: Verify the wire’s performance in high-temperature environments, such as vacuum or inert gas conditions.
9. Defect Testing
- Ultrasonic Testing: Detect internal cracks or inclusions.
- Eddy Current Testing: Non-contact detection of surface and near-surface defects.
- X-ray Nondestructive Testing: Inspect internal defects or inconsistencies.
10. In-Process Monitoring
- Method: Use online inspection equipment (e.g., CCD cameras, laser scanners) during drawing or annealing to monitor wire diameter, surface quality, and tension in real time.
- Purpose: Identify production anomalies promptly to reduce defect rates.
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