Shop Problems Plating and Anodizing Use the Shop Problem Card in this issue for free expert advice.

Nickel Acetate Seal

Q . Can you provide a formulation . for a nickel acetate seal for an-

odized aluminum? C.S.

A . The following formulation is . reported in “The Surface Treat-

ment and Finishing of Aluminum and Its Alloys” by S. Wernick, Pinner, and Sheasby. Nickel acetate 6 to 6.8 g/L and boric acid 8 to 8.4 g/L with opti- mum pH 5 to 6. Use distilled water for making up the seal. Operate at 70 to 90°C for 15 to 20 minutes.

Poor Adhesion of Hard Chromium Deposits

Q We would appreciate your : help in solving a peeling prob-

lem in our hard chromium plating. In the past we have successfully plated a variety of exotic alloys including Stellite, Inconel, and Hastelloy. In addition 400 series stainless steel has been handled without problems; how- ever, recently a job for plating 316 stainless steel has caused severe problems.

The parts vary greatly in diameter and length. They are screen baskets used for reducing wood pulp into paper products. Some of the baskets have many holes drilled into the sides and others slots milled along the sides.

We have used a mixture based on

muriatic acid for preparation (with cur- on hydrogen peroxide and sulfuric rent) with success, but it does not work acid would be one possibility. For- with these baskets. There does not ap- mulations are available from several pear to be any pattern to the rejects. suppliers. Other processes to investi- Please provide any advice on a simple gate include mechanical finishing or way to solve this problem. electropolishing.

D.P.

A . You do not clearly indicate the . nature of the preparation with

Gold Plate Fails Hydrogen Sulfide Test

muriatic acid. For plating onto 316 stainless steel a Wood’s nickel strike should be used to obtain good adhe- sion. Details for preparation and oper- ation of the Wood’s nickel strike are provided in the Metal Finishing Guide- book.

Q . Our selectively gold-plated . printed circuit connector con-

Alternatives for Bright Dipping Brass

3

We bright dip brass using a : mixture of sulfuric, nitric, and

hy rochloric acids. Is there a method for recycling the drag-out, which con- tains the diluted acids as well as cop- per, lead, and zinc? Off-site disposal is expensive. Please provide any infor- mation on options for dealing with this headache.

tacts are turning black after a hydrogen sulfide test. The base material is punched phosphor bronze. An under- coat up to 4 microns of nickel is plated from a sulfamate bath, followed by 1.2+ microns of gold selectively and 6 to 7 microns of tin-lead selectively on the tail portion. Proprietary baths are used for all formulations. Your com- ments would be appreciated.

J.S.

S.M.

A . I’m not aware of a suitable . method for recycling your

mixed acid waste. You might wish to consider changing the bright dip composition to one that is more readily handled. A bright dip based

A . A sulfide test is unusual for . testing of gold over nickel.

Normally, a nitric acid vapor test would be specified. You don’t indicate the point of failure. If it is on the connector surface then the problem is in the plating; however, if failure is at a cut edge there may be a base metal problem. A thickness of 4 microns of nickel may be too high leading to a high stress in the deposit, especially if the bath is not operated within range. Limit the nickel thickness in the range of 1.25 to 2.5 microns. MF

No longer a need to put up with the hazards environmental problems of nitric acid. Citri

??Highly Effective + Environmentally Friendly

Circle 104 on reader information card

88 METAL FINISHING . SEPTEMBER 1997