Steel cleanliness standards for medical injection molds
The steel cleanliness of medical injection molds is directly related to the safety and compliance of medical products, and is the core prerequisite for ensuring impurity-free and pollution-free injection parts. This specification focuses on the core cleanliness requirements for medical injection mold steel, covering material selection, inclusion control, surface standards, testing methods and full-process control points, in line with the stringent quality standards of the medical industry.
1. Basic Requirements for Steel Materials
Medical injection molds prefer high-purity stainless steel, with the following core material specifications: Preferred steels: High-purity martensitic stainless steels such as S136 ESR/ESR+VAR, STAVAX, 1.2083 ESR, and 316L medical-grade austenitic stainless steel Purity index: Steel purity ≥99.95%, carbon content ≤0.03% (316L), impurity elements such as sulfur and phosphorus ≤0.01% Special requirements: Nickel-free stainless steel (e.g., Cr18Mn14Mo3 N) shall be used for molds of implantable products to avoid allergy risks Process selection: Electroslag remelting (ESR) or vacuum arc remelting (VAR) must be adopted to reduce non-metallic inclusions.
2. Control Standards for Non-Metallic Inclusions
Non-metallic inclusions are key factors affecting cleanliness and must meet the following control indicators:
| Type of Inclusions | Control Standard | Testing Method |
|---|---|---|
| Sulfides | ≤0.001% (Grade A) | GB/T 10561, ASTM E45 |
| Oxides | ≤0.002% (Grade A) | GB/T 10561, ASTM E45 |
| Silicates | ≤0.002% (Grade A) | GB/T 10561, ASTM E45 |
| Nitrides | ≤0.001% | GB/T 10561, ASTM E45 |
Key requirement: No single inclusion ≥5μm is allowed, and the total number of inclusions ≤5μm in any 100mm² area shall not exceed 10.3. Surface Cleanliness and Roughness Specifications
Surface roughness: Cavity surface Ra ≤0.05μm (optical grade), non-cavity surface Ra ≤0.4μm Particle residue: Surface particulate contaminants ≤10 particles/cm² (≥0.5μm), no particles ≥5μm Oil content: Total carbon residue ≤5μg/cm², no visible oil stains, fingerprints or processing residues Surface condition: No scratches, pits, scale, burrs and other defects, polished with 12000-grit abrasive + diamond paste Passivation requirement: The surface shall be passivated with nitric acid to form a uniform oxide film, improving corrosion resistance and cleanliness
4. Cleanliness Testing Methods
The cleanliness of medical mold steel shall comply with regulations through the following combined tests: Inclusion testing: Rated according to GB/T 10561-2019 or ASTM E45, observed with metallographic microscope (500×) Surface testing: Roughness measured by white light interferometer (ISO 4287); surface particles detected by laser particle counting (ISO 16232); organic residues analyzed by gas chromatography-mass spectrometry (GC-MS) Biological testing: ATP fluorescence detection (≤10RLU/cm²), settling bacteria count ≤10CFU/plate (ISO 14698) Ionic contamination: After extraction with deionized water, detected by ion chromatography, chloride ions ≤0.1μg/cm², heavy metals ≤0.1μg/mL (ISO 10993-18)
5. Cleanliness Classification and Application Guidelines
According to the risk level of medical products, the cleanliness of mold steel is divided into three grades:
| Cleanliness Grade | Applicable Products | Core Requirements |
|---|---|---|
| Grade 1 (Implantable) | Orthopedic implants, cardiac stents, etc. | Manufactured in ISO Class 5 cleanroom, ESR+VAR steel, Ra ≤0.025μm, qualified sterility test |
| Grade 2 (Invasive) | Syringes, infusion sets, etc. | ISO Class 7 cleanroom, ESR steel, Ra ≤0.05μm, bioburden ≤10CFU/cm² |
| Grade 3 (Non-invasive) | Medical catheters, reagent bottles, etc. | ISO Class 8 cleanroom, high-quality stainless steel, Ra ≤0.1μm, no visible contaminants |
6. Key Points for Manufacturing and Maintenance Control
Processing environment: Molds shall be manufactured in ISO Class 7 (10,000-class) or higher cleanroom, temperature and humidity controlled at 22±2℃, 45±5%RH Cleaning process: Mechanical cleaning (ultrasonic cleaning, 40kHz, 10-15min); chemical cleaning (medical-grade neutral cleaner, avoid chloride ion residue); final rinsing (18.2MΩ ultrapure water, ensure no cleaner residue) Antirust protection: Use NSF H1-grade antirust agent, avoid residue on product-contacting surfaces Process traceability: Record steel batch, heat treatment parameters and cleaning process throughout to ensure traceability
7. Reference to International Standards
Core reference standards: ISO 10430 (Steel Cleanliness), ISO 14644 (Cleanrooms), ISO 16232 (Cleanliness Testing), ASTM F86 (Surface Standards for Surgical Instruments), ASTM F2847 (Cleanliness Reporting for Implants)
