The core method for determining if a magnesium oxide insulation layer has failed is to measure its insulation resistance, combined with a comprehensive evaluation of its appearance and operating status. Under normal circumstances, the insulation resistance of the magnesium oxide insulation layer in the hot runner or heating element should be ≥ 100 MΩ. If it is below 10 MΩ, it is considered failed.
1. Main Detection Methods
Insulation Resistance Test (Most Direct and Effective)
Use a 2500V megohmmeter to measure the insulation resistance between the heating element and the metal casing with the power off.
The insulation resistance of new equipment or newly filled magnesium oxide elements is typically > 500 MΩ.
≥ 100 MΩ: Normal;
10–100 MΩ: Potential problems exist; the trend needs to be monitored;
< 10 MΩ: Failed; must be replaced.
It is recommended to perform a monthly test and record the changes in value. If it drops rapidly from 50 MΩ to 2 MΩ, it indicates that the insulation layer is deteriorating.
Power-on Observation Method (Auxiliary Judgment): The following phenomena during equipment operation may indicate insulation failure: Frequent leakage protection alarms or grounding faults reported by the controller; Slower heating speed or inability to heat up; Power indicator light is normal but no heat output (potential short circuit in the heating element).
Visual Inspection: Check for blackening, rust, water stains, or crystals on the wiring terminals; Check for bulges, cracks, or severe oxidation in the metal casing; If the sealing adhesive is aged and cracked, moisture can easily penetrate, causing the magnesium oxide to absorb moisture and fail.
2. Common Causes of Failure
|
Cause |
Explanation |
|
Moisture Absorption |
Magnesium oxide is a porous material; exposure to humid environments causes it to absorb moisture, leading to a sharp decline in insulation performance. |
|
High-Temperature Aging |
Long-term operation at excessively high temperatures loosens the structure of magnesium oxide powder, degrading its insulation performance. |
|
Mechanical Damage |
Bending or impacts can cause micro-cracks in the tube shell, allowing moisture to seep into the interior. |
|
Impurities |
Ordinary magnesium oxide contains impurities such as Fe₂O₃ and CaO, which can easily form conductive pathways. |
High-purity magnesium oxide (99.9% or higher) has stronger resistance to moisture absorption and aging, significantly extending its service life.
3. Handling Recommendations
Situation Recommendation
Insulation resistance < 10 MΩ Replace the heating element immediately; it cannot be repaired.
Insulation resistance 10–100 MΩ and continuously decreasing Plan replacement to avoid sudden failure.
Only the wiring terminals are damp and the length allows The damp section can be cut off and re-crimped, but a waterproof seal must be ensured.
Industry Standard: In critical processes such as injection molding and pharmaceutical sterilization, insulation resistance < 10 MΩ is considered a failure and must be replaced.
