The core method for checking if sintering is complete after magnesium oxide refilling is through performance testing and physical characteristic analysis to confirm that insulation resistance, withstand voltage performance, and microstructure meet the standards. The specific testing methods are as follows:
1. Key Performance Testing Verification
|
Test Item |
Acceptance Standard |
Description |
|
Cold Insulation Resistance |
≥500 MΩ (500V DC) |
Measured using a calibrated 2500V megohmmeter, excluding surface leakage interference. |
|
Cold Withstand Voltage Test |
AC 2000V, no breakdown in 1 minute |
Must be performed after insulation resistance is qualified to prevent equipment damage. |
|
Hot Insulation Resistance |
≥200 MΩ (within 2 seconds after power failure after 30 minutes of operation) |
Verifies structural stability at high temperatures. |
|
Hydraulic Test |
≥200 MΩ after 48 hours at 40℃ and 95% RH |
Simulates high humidity conditions to test moisture absorption resistance. |
All test data must be traceable and reported by a qualified laboratory.
2. Physical and Microscopic Characteristics of Complete Sintering
Good Grain Recrystallization: Metallographic analysis shows that magnesium oxide grains are significantly grown, densely packed, and free of looseness or porosity;
Uniform Filling Density: Measured density is between 2.8–3.2 g/cm³, and X-ray inspection shows no off-center cores or voids;
No Thermal Stress Cracks: The metal casing shows no deformation or cracks, and the outlet terminals are well-sealed;
Strong Sealing: Ceramic sealing adhesive or metal sealing is used, achieving an IP65 or higher protection rating.
If large fluctuations in insulation resistance, flashover during withstand voltage testing, or a sudden drop in resistance after exposure to moisture are observed, it indicates incomplete sintering.
3. Process Traceability Verification
A complete thermal control curve (temperature-time graph) must be provided, confirming a holding time of 800–1000℃ for 1–2 hours; Atmosphere records must show the use of high-purity nitrogen (oxygen content <100ppm); The repair manufacturer should possess compliance qualifications according to HG/T 6445-2025 and JB/T 2379-2016.
In practice, fully sintered heating elements can operate stably for over 15,000 hours in demanding applications such as injection molding and medical applications.
