Common problems in the magnesium oxide sintering process include incomplete sintering, excessively rapid heating or cooling rates, insufficient protective atmosphere, insufficient holding time, and inaccurate temperature control. These problems directly lead to decreased insulation performance, shell cracking, or failure of hot-state testing.
1. Incomplete Sintering (The Most Critical Problem)
Symptoms: Magnesium oxide grains have not recrystallized and remain in a loose powder state; hot-state insulation resistance <200 MΩ.
Causes: Actual sintering temperature is below 800℃ (e.g., set at 900℃ but with a large furnace temperature deviation); Holding time is less than 1 hour, resulting in insufficient grain growth; Low filling density (<2.8 g/cm³), affecting heat conduction uniformity.
Solution: Use an intelligent sintering furnace with automatic recording function to ensure a complete and traceable thermal control curve, and extend the holding time to 1.5 hours.
2. Excessively Rapid Heating or Cooling Rate
Symptoms: Cracks, bulges, or even bursts appear in the tube shell, especially during the cooling phase.
Causes: Heating rate > 5℃/min, leading to uneven expansion of the metal tube and magnesium oxide, generating thermal stress; Forced air cooling or water cooling causes sudden cooling cracking; Failure to allow the furnace to cool naturally to <200℃.
Risk: Even if the cold-state test passes, moisture seeping in and vaporizing at high temperatures during operation can easily cause tube bursts.
3. Insufficient Protective Atmosphere
Symptoms: Lead wire oxidation, magnesium oxide carbonization, unstable insulation resistance.
Causes: Failure to introduce high-purity nitrogen or a vacuum environment; oxygen content in the furnace > 100ppm; Insufficient gas flow or poor sealing leads to residual moisture and impurities.
Recommendation: Use ≥99.99% high-purity nitrogen for protection, and continuously ventilate to ensure an inert environment inside the furnace.
4. Insufficient Holding Time
Symptoms: Cold insulation resistance is qualified (≥500 MΩ), but the resistance drops sharply during hot testing.
Causes: Holding time of only 30 minutes is insufficient to activate grain recrystallization; The process prioritizes meeting deadlines, sacrificing material stability.
Data Support: Holding time of 1.5 hours improves the hot insulation pass rate by more than 15% compared to 1 hour.
5. Inaccurate Temperature Control
Symptoms: Large performance fluctuations within the same batch of products; some are qualified, some are unqualified.
Causes: The sintering furnace temperature control system is not calibrated, with a deviation of ±50℃ or more; PID segmented temperature control is not used, resulting in drastic temperature fluctuations.
Improvement Measures: Regularly calibrate the furnace temperature sensor and use intelligent sintering equipment with PID control.
