Analysis and Solutions for Common Issues in Stainless Steel Electrolytic Polishing Liquids
Importance and Principle of Aging Treatment for Electrolytic Solution
Newly formulated electrolytic polishing liquids (including chromium anhydride systems and environmentally friendly non-chromium systems) must undergo "aging" treatment before practical production applications. This process is crucial for achieving the desired polishing effect. From the perspective of electrochemical mechanisms, the valence state balance of chromium ions in the electrolytic solution is a core factor affecting polishing quality.
In traditional phosphoric-sulfuric-chromium anhydride systems, hexavalent chromium (Cr6+) acts as an oxidant with dual roles: on one hand, it forms a passivation protective layer on the stainless steel surface through oxidation; on the other hand, it partially converts to trivalent chromium (Cr3+) during cathodic reduction reactions. The presence of trivalent chromium ions significantly regulates current distribution, effectively improving uniformity in current density. Newly prepared electrolytic solutions lack sufficient trivalent chromium ions, resulting in disordered current distribution that leads to uneven metal surface dissolution and difficulty forming a smooth mirror-like finish.
For environmentally friendly non-chromium electrolyte systems, trivalent chromium ions need to be obtained by anodically dissolving chromatic elements from the stainless steel substrate. This process requires adequate electrolysis time to achieve equilibrium concentration of chrome ions. Experimental data indicate that when the concentration of trivalent chrome ions reaches 0.5-1.2g/L within the electrolytic solution, optimal polishing results are achieved. Therefore, it is recommended that new bath liquids undergo pre-electrolysis aging treatment lasting 8-12 hours prior to formal production; during this period waste parts can be added for activation until parameters stabilize before commencing official production.
Impact Mechanism of Phosphoric Acid Content Adjustment on Polishing Quality
In electrolytic polishing processes, phosphoric acid serves as a core component whose concentration control directly affects final product quality. According to membrane theory, phosphoric acid reacts with metal ions generating viscous membrane layers which are key substances enabling selective dissolution and surface leveling. When processing low-nickel stainless steels such as SUS201 or SUS301 or iron products, it is advisable to increase phosphoric acid concentration by 5-8%. This adjustment stems from two reasons: firstly low-nickel materials are more prone to over-corrosion; increasing phosphoric acid concentration enhances membrane protection; secondly these materials contain higher manganese content requiring additional phosphoric acid for complexing dissolved manganese ions. However care should be taken not exceeding a maximum limit of 65% phosphoric acid concentration otherwise leading:
- Excessively high solution viscosity (>25cP) affecting ion diffusion; 2 Increased resistance causing energy consumption rise; 3 Low metal dissolution rate impacting production efficiency. Practical operations may utilize hydrometers monitoring liquid specific gravity maintaining at best between 1.72-1.78g/cm³ (20℃). When treating high-manganese stainless steels supplementation every 100kg processed product with 2-3L phosphoric acid helps maintain stable concentrations.
Research on Pre-treatment Processes Affecting Special Materials
Stainless steel products subjected mechanical grinding or heat treatments exhibit significant changes in surface conditions posing unique challenges towards subsequent electrolytic polishing processes.The work-hardened layer present upon ground products’ surfaces (depth approximately ranging from 20-50μm) possesses distinct electrochemical characteristics differing from substrates while oxide scales formed via heat treatment primarily composed Fe3O4 & Cr2O3 display dense structures firmly bonded onto substrates . nTo address such cases scientifically established pre-treatment workflows must be developed: nInitially employing mixed acidic cleaning solutions(recommended ratio :15%HNO3+5%HF+80%H2O , temperature range maintained at40 -50℃ )for duration spanning around five-to-eight minutes efficiently removes superficial oxides without damaging base material.For high-carbon martensitic stainless steels(like420 series), strict adherence limiting cleaning times under three minutes along adding0 .5 % corrosion inhibitors becomes necessary.Post-preparation thorough rinsing(demonstrating conductivity <50 μS/cm )is essential avoiding residual acids interfering throughout electropolishing procedures.Needless caution dictates concerning lower-end materials likeSUS201 recommending abolishment altogether regarding acidic washing opting instead utilizing two-step electropolish method initially applying lower current densities(8 -10A/dm² )over span two minutes transitioning into standard polish protocols.This approach mitigates risks associated intergranular corrosion stemming acidity washings effects . n### Detailed Maintenance Techniques And Regeneration Technologies For Electrolites nAs ongoing electrolysis progresses metallic ion concentrations within solutions(mainlyFe^3+, Cr^3+, Ni^2+) gradually elevate surpassing total metals threshold levels exceeding35 g/L prompts ensuing complications including: n• Viscosity increases resulting bubble retention issues ; n• Deterioration electrical conductance performance ; n• Declining overall polish quality output . To combat accumulation problems related specifically toward metallic constituents adopting tiered maintenance strategies remains advisable :Primary upkeep :Post-every eight-hour shift using hundred mesh sieves filtering out suspended particulates simultaneously per cubic meter batch introducing five-to-eight kilograms activated carbon adsorbing organic impurities.Mid-level management :Once density exceeds1 .82 g/cm³ calculations utilized determining dilution water volumes required following formulae:m={m0×(1−ρ2/ρ1)}÷(ρ2 −1) nm0 representing mass initial tank fluid whilst values denoting respective densities targeted versus existing states.Additional hydration necessitates reintroducing specialized additives restoring activity levels post-dilution efforts.Deep regeneration occurs whenever ionic saturation breaches eighty grams/liter whereupon utilizing ion-exchange resins alongside partial replacements(mixing30%-40%) proves beneficial retaining twenty-five percent older fluids ensuring tri-valent chromate concentrations remain intact.. ... ...