 |
 |
Hard Chrome Plating Training Course
Appendix 7. Troubleshooting Summary
(See Section 5 for details.)
| Problems | Causes | Solutions |
| Poor chrome appearance (dull, hazy, milky, or burnt deposit) | Incorrect relationship between current density and bath temperature. | A bright chromium deposit is desirable. Change bath temperature and/or current density to bright range settings. |
| Burnt deposit | Extremely high current density areas may cause localized burnt deposits. | Shield high current density areas. Increase solution circulation. |
| Burnt deposit | High chrome to catalyst ratio. | Analyze the plating bath for chromium and catalyst (e.g., sulfate). Make adjustments, as necessary to correct concentrations and the chromium to catalyst ratio. |
| Burnt deposit on large parts | Inadequate part warm up before plating. | Before initiating the plating cycle, allow parts to warm up in the plating bath until they reach bath temperature. This can take 20 min. or more for large parts. |
| Hazy deposits, etching and/or burning in high current density areas | Chloride contamination of bath. | Analyze the bath for chlorides; the concentration should be kept below 25 mg/L Cl and preferably near 0 mg/L. Dummy the bath or use a porous pot to reduce the chloride concentration. Chloride can also be removed by precipitation using silver oxide. Employ preventative measures to minimize future chloride buildup (e.g., use deionized water for bath evaporation make-up). |
| Hazy, dull or milky deposits | Current interruptions during plating. | Prevent current interruptions. |
| Dull deposits | Poor brightness of the base metal. | Polish the part prior to plating. |
| Partial chromium coverage | Low chromium concentration and/or low chromium to catalyst ratio. | Analyze the plating bath for chromium and catalyst (e.g., sulfate). Make adjustments, as necessary to correct concentrations and the chromium to catalyst ratio. |
| Partial chromium coverage | Bath temperature is too high for current density used. | Change bath temperature and/or current density to bright range settings. |
| Partial chromium coverage | Poor or intermittent electrical contact (e.g., between rack and tank busing). | Check connections for voltage drops. Make certain that all connections are clean and tight. |
| Partial chromium coverage | Inadequate current carrying capacity of racks/fixtures. | Check for overheating of rack/fixture. Increase size of rack/fixture leads. |
| Partial chromium coverage | Excessive high current density areas are present. | Shield high current density areas to limit electrical communication with these areas. |
| Partial chromium coverage/pitting | Certain part configurations (e.g., shoulders) will trap hydrogen gas bubbles and prevent plating in these areas and/or result in pitting. | Orient the part so that gas bubbles can flow freely to the surface of the plating tank. |
| Roughness/pitting | Inadequate cleaning prior to plating. | Improve cleaning techniques. Remove all foreign material from the base metal prior to plating. |
| Roughness/pitting | Inadequate mechanical surface preparation of base metal (e.g., slivers produced during polishing can appear as roughness in the deposit). | Implement good mechanical surface preparation procedures, which may vary from part to part. This includes pre-plate operations such as grinding/polishing, grit blast and pumice scrub. |
| Roughness/nodules/pitting | Suspended particles in the plating bath. | Filter the bath to remove suspended particles. Decrease bath agitation to avoid stirring up tank sludge. Improve cleaning and housekeeping practices to minimize bath contamination with suspended particles. |
| Roughness/nodules/pitting | Magnetic particles in the plating bath. | Use magnets to remove magnetic particles. |
| Roughness | High trivalent chromium (Cr+3) concentration. | Analyze the plating bath for trivalent chromium. The concentration should not exceed 1 oz/gal (7.5 g/L). Dummy the bath or use a porous pot to lower the Cr+3 concentration. Avoid organic contamination (e.g., oil) of the bath and exclusive ID plating to prevent excessive Cr+3 buildup. |
| Roughness | High tramp metal (e.g., iron and copper) concentration. |
Analyze the plating bath for iron, copper and other suspected tramp metals. The combined concentration should not exceed 1 oz/gal (7.5 g/L). Remove the tramp metal with ion exchange or other suitable technology. Avoid tramp metal contamination of the bath (e.g., dedicated etch tank, retrieve fallen fixtures from bath). |
| Roughness/incomplete coverage/ dull deposits | Excessive reverse etching will roughen the surface and can create a smut coating. Chromium plating will exaggerate the roughness and smut may leave a salt and pepper effect. | Check the part during reverse etch (e.g., at 50% of expected etch requirement) to avoid over etching. Most parts are adequately etched when the base metal first starts to turn a dull grey color. Use of conforming anodes will reduce etch time by 50% or more. |
| Pitting | Pitting is sometimes attributed to older types of fume suppressants. Modern fume suppressants are generally thought to be benign. | Check with your fume suppressant manufacturer for alternative fume suppressants. |
| Poor adhesion (peeling or blistering) | Inadequate cleaning. | Improve cleaning procedures. Parts must pass the water break test prior to plating. |
| Poor adhesion (peeling or blistering) | Inadequate reverse etch time. | Check the part during reverse etch (e.g., at 50% of expected etch requirement) to avoid over/under etching. Most parts are adequately etched when the base metal first starts to turn a dull grey color. |
| Poor adhesion (peeling or blistering) | Inadequate reverse etch due to passive anodes. | Yellow anodes are passive and may not provide sufficient activity during the etch cycle. Clean the anodes prior to use or activate them by dummy plating. Prevent anode passivation by removing anodes from the tank when not in use. |
| Trees/Beaded edge chromium buildup | Localized high current density areas. | Use masking materials such as PVC that discourage tree formation and encourage smooth run-outs. |
| Trees | High chromium to catalyst ratio (e.g., 125 to 1). | Adjust bath chemistry to reduce the chromium to catalyst ratio. A 100 to 1 ratio is considered optimal for most applications. |
| Excessive/inadequate micro-cracking | Lower chrome to sulfate ratios and higher temperatures increase the degree of cracking. | Microcracking is frequently considered a desirable property since cracking retains lubricants and reduces friction between parts. Select the ratio and temperature that produces the desired degree of cracking and then keep close control of these factors. |
| Macro-cracking (also called chicken-wire cracking) | Use of inappropriate grinding materials and techniques after plating. | Require grinders to use correct wheel, fluid, speed, and grinding techniques (no over cutting). |
| Slow plating rate | Inaccurate rectifier control readout causing to plate at lower than expected amperage/voltage. | Use a handheld volt/amp meter and check the actual amperage and voltage at the tank (fixtures, anodes, cables, etc.). Have maintenance performed on rectifier controls if necessary. |
| Slow plating rate | Voltage drop caused by bad connections. | Any electrical problems with busing, connections, racks, or cables may cause voltage drops. Use a handheld volt/amp meter and check for voltage drops. Have maintenance performed if necessary. |
| Slow plating rate/Uneven chromium distribution | Anode to cathode distance. | The anode to cathode distance should be uniform and as close as possible to within to 1 inch or less). Use conforming anodes whenever possible. Avoid having anodes too close to high current density areas (e.g., use shields). |
| Slow plating rate | Unmasked racks and fixtures connected to the part steal current. | Plastisol coat or mask off the bare metal surfaces of racks and fixtures. |
| Slow plating rate | Low current density and related bath temperature considerations. | Faster chromium deposition is attained at higher current densities. However, plating at higher current densities requires that the bath temperature be set in the upper end of the normal range. Maximum plating rates for acceptable deposits (bright range) are attained at approximately 4 to 5 APSI with a bath temperature of 140 to 145 °F. However, many parts and set-ups can not be operated at these maximum settings without producing roughness or other unwanted conditions. |
| Slow plating rate | Low chromium concentration and/or low chromium to catalyst ratio. | Analyze the plating bath for chromium and catalyst (e.g., sulfate). Make adjustments, as necessary to correct concentrations and the chromium to catalyst ratio. |
| Poor throwing power (thin or no chromium in low current density areas) | Chrome to sulfate ratio is too low. | Increase the chromium to sulfate ratio. Although a bath with 100 to 1 chromium to sulfate ratio is considered ideal for most applications, a bath with a 115 to 1 ratio will throw better than a bath with a 75 to 1 ratio. |
| Poor throwing power (thin no chromium in low current density areas) | Conventional chrome plating bath has limited abilities. | Switch from a conventional bath to a proprietary high-speed fluoride bath. |
| Uneven chromium distribution along long plated surfaces (e.g., piston) | Inadequate cathode connections for carrying current. | The voltage drop in long thin-walled parts can be dramatic, especially for some aerospace steels. Use current insertion points at both ends, and other points, if needed to achieve uniformity. |
| Poor corrosion resistance | Thin deposit or poor deposit crack structure. | Increase chromium deposit thickness. |
| Poor corrosion resistance | High tramp metal (e.g., iron and copper) concentration. |
Analyze the plating bath for iron, copper and other suspected tramp metals. The combined concentration should not exceed 1 oz/gal (7.5 g/L). Remove the tramp metal with ion exchange or other suitable technology. Avoid tramp metal contamination of the bath (e.g., dedicated etch tank, retrieve fallen fixtures from bath). |
| Poor corrosion resistance | Inadequate mechanical surface preparation of base metal. | Polish the part prior to plating. A smooth substrate that is chromium plated will generally have better corrosion resistance than a rougher surface. |
| Wild chrome (chromium deposited in unwanted areas) |
Inappropriate masking materials and/or poor masking techniques that lead to the lifting or loss of maskants during plating. | Maskants such as metal or plastic tapes, lacquers, and waxes have a tendency to be removed during plating, especially with a long plating cycles (>4 hours) and higher bath temperatures. Use no-mask conforming anodes, where economically warranted. Otherwise, optimize and standardize masking techniques. Reduce bath temperature, if necessary. |
 |
 |
 |
The information contained in this site is provided for your review and convenience. It is not intended to provide legal advice with respect to any federal, state, or local regulation.
You should consult with legal counsel and appropriate authorities before interpreting any regulations or undertaking any specific course of action.
Please note that many of the regulatory discussions on STERC refer to federal regulations. In many cases, states or local governments have promulgated relevant rules and standards
that are different and/or more stringent than the federal regulations. Therefore, to assure full compliance, you should investigate and comply with all applicable federal, state and local regulations.