ASTM B177 PDF

This produces a corrosive environment of dense salt water fog also referred to as a mist or spray in the chamber, so that test samples exposed to this environment are subjected to severely corrosive conditions. Chamber volumes vary from supplier to supplier. If there is a minimum volume required by a particular salt spray test standard, this will be clearly stated and should be complied with. There is a general historical consensus that larger chambers can provide a more homogeneous testing environment.

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You are on page 1of 6 Search inside document Designation: B 01 Reapproved e1 Electroplaters Society Endorsed by National Standard Guide for Engineering Chromium Electroplating1 This standard is issued under the fixed 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. Scope B Practice for Preparation of and Electroplating on 1. This is sometimes B Practice for Preparation of Copper and Copper-Base called functional or hard chromium and is usually applied Alloys for Electroplating and Conversion Coatings directly to the basis metal and is usually thicker than decorative B Practice for Preparation of Iron Castings for Electro- deposits.

Cross Section 1. It is the nesses by the Magnetic Method: Nonmagnetic Coatings on responsibility of the user of this standard to establish appro- Magnetic Basis Metals priate safety and health practices and determine the applica- B Test Method for Measurement of Thickness of Me- bility of regulatory limitations prior to use. Referenced Documents Racks 2.

Current edition approved April 1, Published April Originally of Electrodeposited Metallic and Inorganic Coatings approved in Last previous edition approved in as B Shorter B Specification for Automated Controlled Shot Peening times at higher temperatures may be used, if the resulting loss of Metallic Articles Prior to Nickel, Autocatalytic Nickel, in surface hardness is acceptable.

Materials such as aluminum and 2. When conditions are especially 3. Substrates unfavorable, definite steps must be taken to meet this important 3. The bond strengths of the chro- 4. Racks and Anodes mium varies with metallic substrate. Nevertheless, if the 4. Aluminum, titanium, and certain nickel alloys may need to 3. Chromium electrodeposits do not rack which can result in adhesion failures due to seepage exhibit leveling, and consequently the surface roughness of the during chromium electroplating.

The required surface smoothness may be obtained by current densities and the desirability of securing coatings of suitable chemical, mechanical, or electrochemical procedures. If this is a design be electroplated, to the anodes, and to the tank contact bus bars. This often requires anodes of special the fatigue strength. This should be done after any stress- shapes conforming to the shape of the part or area to be relieving heat treatment.

In all 4. This stress relief is essential if hydrogen embrittlement stop-offs, which are especially compounded nonconductive from subsequent operations is to be avoided.

Lead and aluminum tapes will provide a sharp line an unacceptable reduction in hardness by baking in accordance of demarcation between coated and uncoated areas with a minimum of buildup. Practice B offers many ways to prepare titanium nation of the solutions used in subsequent operations, or both.

The main difficulty with these materials when 4. In general, only deoxidizing satisfactory. Chemical lead is also satisfactory where hardness of the copper or copper alloy surface is necessary for chro- and rigidity are not important. However, it tends to form great mium electroplating. Lead wire used for small anodes should activating procedures for the preparation of stainless steel prior contain 0.

Some stainless steels benefit from tween rigidity and ductility in close tolerance areas. Lead- a Woods nickel strike prior to chromium electroplating.

Polar- sheathed steel, copper, or silver may be used when indicated by ized surfaces in high-nickel stainless steels can cause skip requirements for strength or conductivity. Platinum, platinum- plating if not properly activated.

If the anode contains little or no ing. In general, anodic etching in the chromium plating lead, the reoxidation of trivalent chromium to the hexavalent solution is not recommended. Due to the high carbon content in state will not take place or will be seriously impaired, which iron castings, anodic etching leaves a carbon smut on the will lead to trivalent buildup in the plating solution and poor surface of the metal which results in poor adhesion of the results.

Unique activation pro- cedures for steel exist with chromium plating that merit a 5. Cleaning separate discussion for successful plating as follows. To reduce the increase in roughness resulting from 5. If parts have been shot-peened to develop a compres- highly finished surfaces. There should not be any special preparation in order to achieve maximum adhesion of sulfuric acid present.

Enter the tank with the current off and the chromium to the substrate. Tank voltage is normally 4 deoxidation and etching methods may be used to activate the to 5 V. There does not have to be rinsing before transfer to the substrate prior to chromium electroplating. Guide B offers many useful meth- same times and current density described in 6. A reversing switch should The removal of the ever-present, tenacious oxide film on the be provided to make the part anodic.

This process is much surface of aluminum is what makes electroplating difficult. The temperature should be kept below gloves, and other safety equipment should be used when 30C and preferably below 25C. The time of treatment is 10 handling sulfuric acid and when making this addition. Lead cathodes should be used and the tank before handling sulfuric acid or chromic acid! Two difficulties that may be encountered that Sulfate SO 2. With 6. As the electrochemical efficiency there is a danger of rusting of the surfaces before the part can decreases somewhat with increasing current density and bath temperature, be introduced into the chromium electroplating bath.

This is concentrations give increased efficiency but the throwing power, which is normally used on highly finished steel requiring only a thin always poor, gets worse. The higher concentration bath gives slightly improved other procedures and in hydrogen embrittlement of the steel.

Chromium Electroplating 7. The addition of fluoride or 7. Any auxiliary anodes more masking may be required than is necessary with the integrated with the rack are connected to the anode bus bar. Analytical control of the silicofluoride is more Steel or ferrous parts to be plated are allowed to reach the bath difficult than the other components, but ion selective methods temperature and electroplating is then commenced. If the parts are satisfactory. This bath will deposit chromium at an appro- were etched in the plating solution, plating is initiated when the priate rate of WarningThe silicofluoride sometimes shown as the reversing switch.

This acid also requires great care in handling. Consult baths, there are various proprietary baths offered that may be safety references or personnel before using. Most proprietary chromium plating Silicofluoride SiF , see Warning 2. These co-catalysts may use organic based or inorganic based compounds to achieve higher plating efficiencies and are 7. The deposits are throwing and covering power are needed.

The most recent dull gray in color and can be buffed, if desired. The efficiency baths do not use fluoride co-catalysts and do not etch unpro- is very high and the chromium evidentially deposits in a tected low current density areas. These baths produce micro- different crystal structure than is obtained in other baths.

There cracked deposits which may be an advantage in some deposits. WarningLiterature which will also produce micro-cracked deposits. This is a very chromium at the approximate rate of 25 m 0. WarningThe sulfate anion of course, be handled with all the caution required of standard SO42 is added to the bath as sulfuric acid. The calculated chromium plating baths. There are also proprietary solutions available. These deposits are frequently used on solar collectors and for 9.

Repair of Chromium Electrodeposits on Steel applications on steels and other alloys where a more wear- Substrates resistant coating than black oxide types is desired. In operating 9. All baths of this type include barium salts or other 9. As the deposit is nonconductive, the areas originally electroplated, it may be prepared for electro- maximum thickness that can be expected is 3 to 5 m which plating in accordance with Practice B Mild steel anodes are usually employed.

Either solution 8. Treatments of Chromium Coatings should be kept below 25C during operation using cooling, if 8. There are also proprietary solutions available which chromium plating is apt to embrittle steel, and the potential for should be operated according to the suppliers instructions.

Test Methods steels. Baking appropriate for the tensile strength of the Guide B lists bakes appropriate the following test methods. In all cases, the duration of the bake shall commence part being measured instead.

When direct measurement of the from the time at which the whole part attains the specified thickness of the coating is desired and the part can be temperature. The bake should be performed as soon as possible sacrificed, it should be done in accordance with Test Method after the parts are removed from the plating bath, rinsed, and B If a nondestructive method is required, magnetic dried in order to reduce the risk of hydrogen embrittlement.

Test methods between plating and baking operations. Test discussed with the purchaser to ensure that the bake selected does not Method B may be used accurately for chromium up to cause distortion in the part or adversely affect its mechanical properties.

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More B This is sometimes called "functional" or "hard" chromium and is usually applied directly to the basis metal and is usually thicker than decorative deposits. This guide is not intended as a standardized procedure, but as a guide for obtaining smooth, adherent coatings of a desired thickness while retaining the required physical and mechanical properties of the base metals. Engineering chromium may be plated directly to the surface of a commonly used engineering metals such as aluminum, nickel alloys, cast iron, steels, copper, copper alloys, and titanium. Substrate requirements including smoothness, fatigue, high-strength steel stress relief, and oxidation are specified.

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