How to Determine if a Hot Runner Channel is Moisturized During Baking

I. Dynamic Method of Resistance to Insulation

Determination Procedure: Measure insulation resistance between the heating element, sensor core wire and housing of the hot runner channel with 500V digital megohmmeter per hour during baking.

Moisture Absorption Characteristics: The initial insulation resistance is <5MΩ and the insulation resistance has a continuous and stable increasing trend with the increase of the baking temperature, which indicates that there is moisture inside the hot runner channel and it is progressively being dried.

How to know the drying is finished? If the insulation resistance is≥20MΩ and the value does not increase considerably after two consecutive tests with 1 hour interval, it means the moisture is totally evaporated, and the hot runner channel is not damp any more.

II. Method Appearance and Physical Characteristics

Determination Procedure: During the baking process periodically monitor the condition of the hot runner sealing surface, junction box gaps and exposed metal surfaces.

Moisture absorption characteristics: When baking in the early stage, a fine water fog will soon appear on the surface of the hot runner channel, and obvious hot air will escape from the gaps of the junction box, indicating that a large amount of moisture has been absorbed inside, showing a significant moisture absorption state.

Drying Completion Criteria: After 2 hours of continuous baking, surface water vapor is fully eliminated, no more hot air exits, and no condensation lines on the metal surface indicating that surface moisture has been fully removed.

III. Criteria for Heating Lag Characteristic

Criteria Operation: Record the rate of heating of the hot runner in baking, and compare it with the standard heating curve of a similar type of drying hot runner.

Moisture absorption requirements : Hot runner temperature stays at a low temperature for long time ( without reaching 100C ) before it raises . The moisture inside is evaporated and removed by a huge amount of heat. This means that there is a large amount of free moisture, indicating a very damp state.

Drying Completion Criteria: When the temperature exceeds 100℃, the heating rate of the hot runner will tend to revert to the standard level of a similar model of drying hot runner, and there is no evident temperature plateau, indicating that the internal moisture has been entirely evaporated and gone.

IV. auxiliary criteria for special scenario:

Slightly Moist Hot Runner: Insulation resistance is just slightly below 5MΩ, no apparent water vapor, no heating stagnation, dehumidification may be done in 8 hours of normal baking. Severely Moist Hot Runner: If all of the following three characteristics are present – insulation resistance <1MΩ, significant surface condensation and prolonged temperature hold at 100℃ – the total baking time must be extended to 20-24 hours to prevent insulation breakdown in subsequent heaters caused by residual moisture.

No Moisture Criterion: If the insulation resistance is ≥20MΩ during the baking process, there is no water vapor overflow, and the temperature rise curve is totally normal, then the hot runner is not moist, and the baking can be instantly stopped and entered into the installation stage.