Quality Finishing: Troubleshooting Hexavalent Chromium Plating Even though many are not using hexavalent chromium baths or phasing them out of production, there are still finishers who use them and will continue to plate from them…   Identifying the origin of a plating deficiency is the first step toward solving the problem. The source of poor plating can be divided into three categories: 1) Defective bath chemistry; 2) Improper temperature and/or current density; and 3) Poorly finished and/or cleaned substrates. An experienced plater can often identify the source of a problem without having to do much detective work; however, chemical analysis, Hull cell tests and reliable supplier recommendations are the best troubleshooting sources. The most common defects for hexavalent chromium plating deposits are listed here, along with some suggested solutions. Despite the simplicity of their formulations, chromium plating baths are more complicated to operate than most plating baths and require more rigorous controls. TROUBLESHOOTING HEXAVALENT CHROMIUM PLATING Problem Possible Cause Solution Milky Deposit High chromic acid/sulfuric ratio increase sulfate Chloride contamination remove chloride with silver carbonate Iron contamination dilute bath Excess trivalent chromium clean anodes; reoxidize trivalent chromium Poor nickel surface carbon treat nickel, improve rinsing of nickel, use nickel activator High temperature reduce to normal, check controller Hazy Deposit High chromic acid/sulfate ratio increase sulfate High chloride contamination remove chloride with silver carbonate Iron contamination dilute bath Excess trivalent chromium clean anodes; reoxidize trivalent chromium Low temperature increase to normal Current density too high adjust anode-to-cathode ratio Intermittent current flow check electrical contacts Poor nickel surface improve rinsing and use nickel activator Gray, Dull but Smooth Deposit High chromic acid/sulfate ratio increase sulfate Current surge when contact made reduce current High temperature check temperature controllers Dull Spots in High-Current Density Areas High chromic acid/sulfate ratio increase sulfate Passive nickel improve rinsing; use nickel activator Bipolar condition Use live entry to chromium bath Blue Deposits High temperature reduce temperature to normal Rough Deposits Low sulfate add sulfuric acid Low temperature adjust temperature to normal Surface preparation improve cleaning/rinsing Suspended particles in bath filter bath/eliminate source Burned Deposits High chromic acid/sulfate ratio increase sulfate Low chromic acid add chromium salts Excess trivalent chromium clean anodes/reoxidize trivalent chromium Too high current density reduce current density or increase temperature Low temperature increase temperature/preheat large, cold parts Brown Spots or Rainbows Low sulfate or catalyst increase sulfate concentration/submit samples for analysis Inefficient contacts check racks for buildup on hooks/tip, check for proper contacts on buss bars Poor Adhesion Insufficient etch increase etch time/check etch bath Surface contamination improve rinsing and/or cleaning cycle Intermittent contact clean/check contacts and put work in the chromium bath live Poor nickel deposit check surface prep before nickel plating and nickel bath Poor Coverage Low chromic acid content Add chromium salts Low chromic acid/sulfate ratio precipitate excess sulfate with barium carbonate Plating current too low raise current density Oxidized contact clean contacts Scaled anodes clean anodes High temperature reduce to normal Passive nickel activate nickel surface Slow Deposition Rates High chromic acid/sulfate ratio Add sulfuric acid Too low current density Increase voltage; check part distribution and for current leaks Scaled anodes clean anodes Oxidized contacts clean contacts Insufficient power supply increase rectifier size Iron contamination dilute bath Excess trivalent chromium follow procedure for reoxidation of trivalent chromium Too high temperature reduce to normal Partial Deposition Rates Too low current density increase voltage; clean rack contacts and anodes Uneven current density Improve part arrangement on racks Passive nickel activate cathodically or immerse in 50% hydrochloric acid Gas pockets Suspend parts so gas escapes No Deposit Reverse polarity make proper connections Defective contacts clean contacts Excess sulfate check ratio and correct Chloride contamination remove chloride with silver carbonate Pitted Deposits Pitted nickel deposit filter nickel bath Pitting in base metal Improve preparation Solution contamination from magnetic particles on ground surfaces improves grinding andcleaning procedure Gas pitting reposition work on racks Serving the Finishing Industries. Since 1936. PF Online and all contents are properties of Gardner Publications, Inc. All Rights Reserved.