Aluminum disc circle is often used as one of the primary materials for high pressure cookers due to its lightness, corrosion resistance and excellent thermal conductivity. The production process for aluminum disc circles typically includes casting, rolling, cutting, and stamping. These aluminum discs undergo rigorous quality testing to ensure their safety and durability under high-pressure environments. The aluminum disc circle for high pressure cookers (typically serving as lid components, heating plates, or sealing support components) are directly impacting the safety, sealing, and durability of the high pressure cooker, and must adhere to strict food contact safety, mechanical properties and structural precision requirements.
1. Core Material Requirements: Food-Grade Safety + High-Temperature and High-Pressure Resistance
The aluminum disc circle's material is fundamental, requiring it to meet the dual requirements of being "safe in contact with food" and "resistant to deformation under high pressure and high temperature."
Material Grade: Food-grade aluminum alloy preferred.
Pure aluminum (low strength and prone to deformation) must not be used. A 3000 series (such as 3003 aluminum alloy) or 5000 series (such as 5052 aluminum alloy) food-grade aluminum alloy must be used:
- 3003 aluminum discs: Contains manganese, offers high tensile strength (≥110 MPa), strong corrosion resistance, and uniform heat conduction, making it suitable for use as a lid support or heating base.
5052 aluminum discs: Contains magnesium, offering excellent ductility and fatigue resistance. It can withstand the repeated heat (120-130°C) and pressure (0.12-0.18 MPa) of a pressure cooker without cracking.
Hazardous Substance Limits: Meets food contact standards.
- Heavy Metal Migration Limits:
Lead (≤1.0mg/kg), Cadmium (≤0.01mg/kg), Arsenic (≤0.05mg/kg), etc., to prevent leaching and food contamination at high temperatures.
- No Harmful Additives:
Impurities such as lead and mercury are prohibited, and the impurity content must be controlled during the smelting process (e.g., iron ≤0.7%, copper ≤0.2%) to prevent material embrittlement.
2. Structural and Dimensional Accuracy: Ensuring Sealing and Pressure Resistance
The sealing of a high pressure cooker relies on the precise fit of the aluminum disc circle, lid, and body. Dimensional deviations can lead to air leaks and uncontrolled pressure, so extremely high precision is required.
- Flatness: Preventing seal failure.
The aluminum disc surface must be absolutely flat, with a flatness tolerance of ≤0.1mm/100mm (i.e., the deviation within 100mm of the aluminum disc length should not exceed 0.1mm). Warping or denting can prevent the silicone seal from fitting properly, resulting in air leaks or even popping out under high pressure.
- Thickness uniformity: Avoid localized strength deficiencies.
Thickness deviation must be controlled within ±0.05mm:
Excessively thin areas: Long-term pressure can easily cause plastic deformation (such as bulging), reducing the pressure resistance limit.
Excessively thick areas: Uneven heat conduction can lead to uneven heating of the food inside the pot and increase the weight of the lid.
- Fitting tolerance: Ensure a precise fit with the lid/pot.
If the aluminum disc is the "inner support plate" of the pot lid, its outer diameter must strictly match the inner ring of the pot lid, with a clearance tolerance of ≤0.03mm. If it is the heating base, the positional tolerance of the mounting holes (such as screw holes) must be ≤0.02mm to ensure precise alignment with components such as the heating tube and pressure valve, avoiding stress concentration after assembly.
- Edge treatment: No burrs or sharp corners.
Edges must be chamfered (R ≥ 0.5mm) and polished to prevent:
Scratching the silicone sealing ring (causing it to break and leak);
Scratching the operator during installation.
3. Mechanical Properties: Deformation Resistance, Fatigue Resistance, and Impact Resistance
When operating, the aluminum disc for pressure cooker must withstand high temperatures (130°C) + high pressure (approximately 0.15 MPa, equivalent to 1.5 times atmospheric pressure) + repeated hot and cold cycles. Mechanical properties must meet the following standards:
- Tensile Strength and Yield Strength
Tensile Strength: ≥110 MPa (to ensure resistance to cracking under high pressure);
Yield Strength: ≥70 MPa (to prevent permanent deformation, such as disc dents, after long-term use).
- Pressure Test: Simulates extreme operating conditions.
The disc must pass a hydraulic pressure test: maintaining pressure at 1.5 times the rated working pressure (typically 0.225 MPa) for 30 minutes, with no leakage or deformation (such as bulging or cracking). Some high-end products also undergo fatigue testing (repeated pressurization and depressurization 1000 times) to ensure long-term durability. - Hardness: Avoid scratches and wear.
The Brinell hardness (HB) must be ≥30 to prevent scratches from spatulas and ingredients during use, as well as surface wear caused by friction with the sealing ring (impairing sealing).
4. Surface Treatment: Corrosion Resistance + No Migration
Aluminum is easily oxidized and comes in direct contact with food and water, requiring surface treatment to enhance safety and durability. Common, compliant treatments include:
- Anodizing (Mainstream Process)
A 5-10μm thick oxide film (Al₂O₃) is formed on the surface of the aluminum disc.
Features:
High Corrosion Resistance: Insulates the aluminum substrate from water and acidic foods (such as tomatoes), preventing oxidation and rust.
No Harmful Substance Migration: The oxide film is stable and does not flake or dissolve at high temperatures, making it safe for food contact.
Smooth Surface: Reduces dirt adhesion and facilitates cleaning.
- Passivation (Auxiliary Process)
Some products undergo an additional "chromate passivation" after anodizing to further enhance surface stability and prevent corrosion of the substrate if the oxide film is partially damaged.
5. Safety Certification and Labeling: Compliance Assurance
International Certifications (Export Products)
EU: Requires CE certification (in compliance with EU Regulation No. 10/2011 on Food Contact Materials);
US: Requires FDA certification (verification that the material does not migrate harmful substances).
Only aluminum disc circles that meet the requirements can be used in high pressure cookers. This is a core prerequisite for ensuring the safety, durability, and compliance of pressure cookers. Qualified aluminum discs must meet multiple standards: They must be made from food-grade aluminum alloys; their flatness, thickness deviation, and fit tolerances must be precisely controlled, with no burrs on the edges; they must pass tensile strength, pressure resistance, and fatigue tests; and their surfaces must utilize safety processes such as anodizing, and they must be certified. These requirements together constitute the bottom line for the safe use of high pressure cookers, ensuring that they can achieve stable sealing and avoid safety risks under long-term high temperature and high pressure conditions, truly meeting the use needs of household high pressure cookers.