Standard Non-magnetic Passivation Process Specification For SUS304 Stainless Press-fit Parts, Compatible With Medical & Imaging Sheet Metal Equipment

Standard Non-magnetic Passivation Process Specification For SUS304 Stainless Press-fit Parts, Compatible With Medical & Imaging Sheet Metal Equipment

SUS stainless press-fit parts matched with NMR and diagnostic imaging equipment mandate low non-magnetic indicators. Grain deformation after ordinary stainless cold heading generates magnetism, which cannot be eliminated by conventional passivation and interferes with instrument imaging accuracy. Medical-grade non-magnetic passivation dissolves surface martensite grains via special acidic chemicals and simultaneously improves salt spray durability, serving as mandatory surface process for press-fit parts of medical sheet metal exported overseas. This article fully divides three-level passivation process parameters, clarifies magnetic limit values for different terminal equipment, and sorts out rectification procedures for batch magnetism defects on production lines.

1. Core Parameter Comparison Table For Three Grades Of Stainless Press Part Passivation Process

2. Four-step Standardized Non-magnetic Passivation Production Line Process

1. Pre-stress Relief Cleaning: Press-fit finished products undergo low-temperature stress relief tempering at 400℃ first to eliminate cold heading grain magnetism inducement; ultrasonic pure water removes residual cold heading oil on surface. 2. Graded Passivation Soaking: Select corresponding non-magnetic chemical solution for constant-temperature soaking according to terminal demand, circulate and stir chemicals regularly to ensure uniform surface reaction of workpieces. 3. Multi-stage Pure Water Rinsing: Three-stage counter-flow pure water cleaning to avoid residual passivation chemicals causing gray surface finish and local unqualified salt spray. 4. Low-temperature Hot Air Drying: 80℃ traceless drying; high-temperature baking is forbidden to prevent cracking of surface passivation film. Sampling test magnetic permeability and salt spray after drying.

3. Three Passivation Process Defect Causes & Production Line Rectification Plans

1. Excessive finished magnetism with permeability＞1.05: Missing low-temperature stress relief tempering, insufficient non-magnetic passivation soaking time; Rectify: Add tempering process, extend medical-grade soaking to 40min, replenish special non-magnetic activator regularly. 2. Early white rust in NSS test: Incomplete rinsing, attenuated chemical concentration; Rectify: Extend three-stage pure water rinsing time, test chemical concentration weekly and replace new chemicals as required. 3. Large-area dull gray surface of workpiece: Excessive drying temperature, shifted chemical PH value; Rectify: Lower drying temperature to 80℃, monitor chemical PH range 2.2~2.8 in real time and neutralize timely if exceeding limit.

4. Mandatory Acceptance Red Line For Press-fit Parts Purchased For Medical Imaging Equipment

1. Medical non-magnetic grade passivation is mandatory for press-fit parts matched with NMR cabinets; low-magnetism and ordinary industrial passivation products are rejected directly; 2. Measured magnetic permeability data sheet and 500-hour NSS test report attached to each batch, goods rejected before assembly if indexes exceed limit; 3. No gray spots or local film loss on passivated surface; surface defects will shorten anti-corrosion service life of equipment in outdoor environment; 4. MSDS chemical safety sheet must be provided for non-magnetic passivation chemicals to prove free of hexavalent chromium and heavy hazardous metals, meeting EU medical MDR environmental requirements.