The quality standards for reworked magnesium oxide must strictly adhere to the industry standard HG/T 3928-2012, and undergo triple verification through metallographic analysis, thermal testing, and X-ray inspection to ensure that the material purity, structural density, and insulation performance fully meet the standards.
1. Chemical Composition Standard (Based on HG/T 3928-2012)
|
Test Item |
Acceptance Standard |
Test Method |
|
Magnesium Oxide (MgO) Content |
≥ 95% |
Acid-Base Titration |
|
Active Magnesium Oxide Content |
≥ 60% |
Hydration Method |
|
Hydrochloric Acid Insoluble Matter |
≤ 0.5% |
Acid Dissolution, Filtration, and Weighing |
|
Chloride (Cl⁻) |
≤ 0.02% |
Silver Nitrate Titration |
|
Sulfate (SO₄²⁻) |
≤ 0.1% |
Barium Sulfate Turbidity Method |
|
Loss on Ignition |
≤ 5% |
950℃ Constant Weight Method |
All returned workpieces must be accompanied by a CNAS/CMA certified test report as the legal basis for quality release.
2. Physical and Structural Performance Standards
Table Item Acceptance Criteria Verification Method
Filling Density 2.8–3.2 g/cm³ Actual measurement after vibration and compaction
Grain Recrystallization Significantly grown grains, clear boundaries, and dense structure Metallographic analysis (gold standard)
Internal Structural Integrity No voids, off-center cores, or uneven density X-ray inspection (resolution ≥5μm) Any defect may lead to insulation failure or tube bursting at high temperatures.
3. Electrical and Sealing Performance Standards
Table Test Item Acceptance Standard Test Conditions
Cold Insulation Resistance ≥ 500 MΩ 500V DC, RH≤30%
Hot Insulation Resistance ≥ 200 MΩ Measured within 2 seconds of power failure after 30 minutes of operation
Withstand Voltage Performance AC 2000V, no breakdown after 1 minute Normal environment
Air Tightness No leakage after 30 minutes of 0.3MPa pressure testing Underwater pressure test
Hot testing is crucial and can effectively identify hidden defects such as "passing cold but failing hot".
4. Process Control Standards
|
Stage |
Control Parameters |
|
Sintering Temperature |
900±50℃, holding time 1.5 hours |
|
Heating Rate |
≤ 5℃/min, segmented temperature control |
|
Protective Atmosphere |
High-purity nitrogen (oxygen content <100ppm) |
|
Cooling Method |
Natural cooling with the furnace to <200℃, forced cooling is strictly prohibited |
It is recommended to use an intelligent sintering furnace to record the complete temperature curve to achieve process traceability.
