ASTM Standards: B Practice for Operating Salt Spray (Fog) Apparatus2. B Guide for Engineering Chromium Electroplating3. B Practice for. Endorsed by AmericanDesignation: B – 01 (Reapproved )e1. ASTM B/BM() Standard Guide for Engineering Chromium Electroplating Scope
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B — 01 Endorsed by American Electroplaters’ Society Endorsed by National Association of Metal Finishers Standard Guide for Engineering Chromium Electroplating1 This standard is issued under the xed designation B ; the number immediately following the designation indicates the year of original adoption or, in the case of revision, the year of last revision.
A number in parentheses indicates the year of last reapproval. A superscript epsilon e indicates an editorial change since the last revision or reapproval. This is sometimes called “functional” or “hard” chromium and is usually applied directly to the basis metal and is usually thicker than decorative deposits.
Specied chromium electrodeposits on ferrous surfaces are dened in Specication B It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. Current edition approved Nov. Originally published as B — Last previous edition B — The bond strengths of the chromium varies with metallic substrate.
Nevertheless, if the procedures cited in the appropriate references are followed, the bond strength is such that grinding and honing can be conducted without delamination of the coating. Chromium electrodeposits do not exhibit leveling, and consequently the surface roughness of the electrodeposit will always be greater than that of the substrate. Any mechanical operations that can result in grinding checks or glazing of the metal are detrimental and should be eliminated.
The required surface smoothness may be obtained by suitable chemical, mechanical, or electrochemical procedures. Depending upon the thickness of the electrodeposit and the smoothness required of the electrodeposit, grinding of the electrodeposit may be required. If this is a design consideration, the use of mechanical methods such as shot peening see Specication B or MIL-SC, or both or autofrettage to compressively stress the surface can increase the fatigue strength.
This should be done adtm any stressrelieving heat treatment. In all cases, the duration of the bake shall commence from the time at which the whole of each part attains the specied temperature.
This stress relief is essential if hydrogen embrittlement from subsequent operations is to be avoided. Shorter times at higher temperatures may be used, if the resulting loss in surface hardness is acceptable.
Materials such as xstm and titanium have an inherent oxide lm on the surface that can only be removed or minimized just prior to the electroplating process see 6.
When conditions are especially unfavorable, denite steps must be taken to meet this important requirement, including storage in a noncorrosive environment, or the use of a suitable coating to exclude air and moisture.
Racks and Anodes 4. Aluminum, titanium, and certain nickel alloys may need to have cleaning and etching operations done before racking due to entrapment of cleaning and etching solutions in the plating rack which can result in adhesion failures due to seepage during chromium electroplating. The design of racks for chromium electroplating on the various base metals previously mentioned for functional use should provide for the following to the greatest possible extent.
This often requires anodes of special shapes conforming to the shape of the part or area to be electroplated. Lead and aluminum tapes will provide a sharp line of demarcation between coated and uncoated areas with a minimum of buildup. B on areas that should be electroplated. Chemical lead is also satisfactory where hardness and rigidity are not important. However, it tends to form great quantities of scale that may fall off on the work and cause pitting or roughness.
Lead wire used for small anodes should contain 0. Leadsheathed steel, copper, or silver may be used when indicated by requirements for strength or conductivity. Platinum, platinumclad niobium, or even steel rods or wire may be used for internal electroplating of small holes, but the latter will contaminate the bath with iron. If the anode contains little or no lead, the reoxidation of trivalent chromium to the hexavalent state will not take place or will be seriously impaired, which will lead to trivalent buildup in the plating solution and poor results.
If parts have been shot-peened to develop a compressively stressed surface, it is important to avoid removing that surface by excessive grinding. Deoxidizing and Etching 6. Depending on the type and nature of the metal and prior surface preparation steps, various deoxidation and etching methods may be used to activate the substrate prior to chromium electroplating.
Guide B offers many useful methods for preparing aluminum prior to chromium electroplating. The removal of the ever-present, tenacious oxide lm on the surface of aluminum is what makes electroplating difficult. When using test methods in which a zinc immersion lm is applied to the aluminum surface for protection against oxide formation, the article to be plated must enter the chromiumplating solution under live current. Practice B offers many ways to prepare titanium prior to chromium electroplating.
The main difficulty with these materials when chromium plating is polarization of the nickel alloy surface prior to plating which results in deactivation of the material and skip plating. In general, only deoxidizing of the copper or copper alloy surface is necessary for chromium electroplating.
Some stainless steels benet from a Woods nickel strike prior to chromium electroplating. Polarized surfaces in high-nickel stainless steels can cause skip plating if not properly activated.
In general, anodic etching in the chromium plating solution is not recommended. Due to the high carbon content in iron castings, anodic etching leaves a carbon smut on the surface of the metal which results in poor adhesion of the chromium. Unique activation procedures for steel exist with chromium plating that merit a separate discussion for successful plating as follows.
To reduce the increase in roughness resulting from etching, the etching times should be kept as short as is consistent with good adhesion, particularly in the case of highly nished surfaces.
B1777 should not be any sulfuric acid present. Tank voltage is normally 4 to 5 V. There does not have to be rinsing before transfer to the plating tank, but parts should be thoroughly drained to prevent spillage of the etching solution.
A reversing switch should be provided to make the part anodic.
ASTM B177/B177M – 11(2017)
This process is much simpler than that in 6. Lead cathodes should be used and the tank constructed of a material, such as lead or vinyl, that is resistant to sulfuric acid.
Two difficulties that may be encountered that make this process less attractive than those described in 6. This is normally used on highly nished steel requiring only a thin chromium deposit as its use may result in less adhesion than other procedures and in hydrogen embrittlement of the steel.
ASTM B/BM() – Standard Guide for Engineering Chromium Electroplating
Drag-over of either solution into the chromium electroplating bath because of poor rinsing will cause contamination problems. Any auxiliary anodes integrated with the rack are connected to the anode bus axtm. Steel or ferrous parts astk be plated are allowed to reach the bath temperature and electroplating is then commenced.
If the parts were etched in the plating solution, plating is initiated when the parts are made cathodic at the end of the etching period using the reversing switch. Most nonferrous metals enter the chromium plating solution under live current and are not placed in the chromium-plating solution for warming prior to electroplating.
ASTM B / BM – 11() Standard Guide for Engineering Chromium Electroplating
Most proprietary chromium plating baths are co-catalyzed plating solutions in which an additional catalyst is used in conjunction with the traditional sulfate anion catalyst.
These co-catalysts may use organic based asmt inorganic based compounds to achieve higher plating efficiencies and are often employed where higher rates of plating and better throwing and covering power are needed. The most recent baths do not use uoride co-catalysts and do not etch unprotected low current density areas. These baths produce microcracked deposits which may be an advantage in some deposits.
There are additives, such as selenium, in the patent-free art which will also produce micro-cracked deposits. The sulfate anion SO42— is added to the bath as aastm acid. The calculated amount should be diluted by adding it to deionized water prior to adding it to the bath. Face shield, chemical goggles, astj gloves, and other safety equipment should be used when handling sulfuric acid and when making this addition.
Consult with appropriate safety manuals or safety personnel, or both, before handling sulfuric acid or chromic acid!
The addition of uoride or silicouoride auxiliary catalysts increase the tendency of the bath to etch steel in unprotected low-current density areas, and more masking may be required than is necessary with the standard bath. Analytical control of zstm silicouoride is more difficult than the other components, but ion selective methods are satisfactory.
This bath will deposit chromium at zstm appropriate rate of This acid also requires great care in handling. Consult safety references or personnel before using. The deposits are dull gray in color and can be buffed, b1777 desired. The efficiency is very high and the chromium evidentially deposits in a different crystal structure than is obtained in other baths. There are many modications reported in the literature and some manufacturers offer proprietary baths. Literature references suggest preparing this bath by adding sodium hydroxide to a 4 Mol chromic acid solution.
This is a very wstm exothermic reaction. The preceding solution should, of course, be handled with all the caution required of standard chromium plating baths. NOTE 1—Many factors inuence the choice of current densities. With very great agitation, the highest current density shown is possible with a concomitant decrease in the plating time.
As the electrochemical efficiency decreases somewhat with increasing current density and bath temperature, the increase in the plating rate is not linear with the b77 in the current density.
The lower concentrations give increased efficiency but the throwing power, which is 7. There are also proprietary solutions available. These deposits are frequently used on solar collectors and for applications on steels and other alloys where a more wearresistant coating than black oxide types is desired.
In operating these baths, it is essential that no sulfate be introduced into the bath. All baths of this type include barium salts or other precipitants for sulfate. As the deposit is nonconductive, the maximum thickness that can be expected is 3 to 5 m which requires 4 to 8 min.
Mild steel anodes are usually employed. Treatments of Chromium Coatings 8. Baking appropriate for the tensile strength of the electroplated part must be performed to reduce the risk of hydrogen embrittlement. Guide B lists bakes appropriate for the tensile strength of the electroplated part and should be consulted for post-electroplating baking procedures and classes.
In all cases, the duration of the bake shall commence from the time at which the whole part attains the specied temperature. The bake should be performed as soon as possible after the parts are removed from the plating bath, rinsed, and dried in order to reduce the risk of hydrogen embrittlement. Consult Specication B for maximum length of time permitted between plating and baking operations.
NOTE 6—It is suggested that the selection of an appropriate bake be discussed with the purchaser to ensure that the bake selected does not cause distortion in the part or adversely affect its mechanical properties.