The nitrogen used in nitrogen ovens must meet the following key requirements to ensure the safety and reliability of equipment performance and application scenarios:
1. Purity requirements
- Core indicators: Nitrogen purity usually needs to be ≥99.9% (i.e. "three nines"), and some high-precision scenarios (such as medicine and semiconductors) may require ≥99.99% (four nines) or higher.
- Reasons:
- The oxygen, moisture, impurities, etc. contained in low-purity nitrogen may cause oxidation, moisture or contamination of the baked items (such as deterioration of pharmaceutical raw materials and rusting of electronic components).
- When the purity is insufficient, the inert protection effect of nitrogen is weakened and it cannot effectively isolate the active ingredients in the air.
2. Dryness (dew point)
- Indicator: The dew point of nitrogen needs to be ≤-40℃ (even ≤-70℃), that is, the water content is extremely low.
- Reasons:
- High-humidity nitrogen may condense water vapor in the high-temperature environment of the oven, causing the items to become damp (such as moisture absorption of pharmaceutical packaging materials and rusting of precision instruments), affecting the baking effect.
- Dry nitrogen can prevent water vapor from chemically reacting with items at high temperatures (such as some materials decomposing in water).
3. Impurity control
- Oil-free, dust-free, and odor-free:
- If the nitrogen contains oil (such as compressor lubricant residue) or dust, it may contaminate the baked items (such as pharmaceutical products that do not meet the cleanliness standards).
- Odors or harmful gases (such as sulfides and nitrogen oxides) must be strictly controlled to ensure compliance with industry safety regulations (such as the pharmaceutical industry must comply with GMP standards).
4. Pressure and flow stability
- Pressure: According to the design requirements of the oven, it is usually necessary to maintain a stable gas supply pressure of 0.1-0.5MPa to ensure that the nitrogen circulates evenly and exhausts the air in the box.
- Flow: It needs to match the oven volume and baking requirements. Insufficient flow may cause oxygen residue in the box, affecting the inert atmosphere effect; excessive flow wastes resources.
5. Special requirements of the industry
- Pharmaceutical/food industry: Nitrogen must comply with the provisions of the "Chinese Pharmacopoeia" or FDA on "pharmaceutical gas", ensure non-toxicity and no residue, and can be used in scenarios where direct contact with medicines or food is required.
- Electronic/semiconductor industry: In addition to high purity, metal ions and particle contaminants in nitrogen (such as ≥0.1μm particles ≤1/cubic foot) must also be controlled to avoid affecting component performance.
In conclusion, the selection of nitrogen for nitrogen ovens should be based on "high purity, low moisture, and no impurities", and the gas supply conditions should be adjusted in combination with industry standards (such as pharmaceutical GMP, electronic ISO standards) and equipment parameters. In actual use, the demand can be met by a nitrogen generator (on-site nitrogen production) or by purchasing bottled high-purity nitrogen, but the gas indicators need to be tested regularly to ensure reliability.
