This technical information has been contributed by
Electrolizing, Inc.

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Dense Chrome Plating for Cosmetic and Functional Purposes

Chromium plating is used for both cosmetic and functional purposes. "Dense Chrome Plating," as described here, is a functional application of chrome which does not require heavy build-ups to achieve desired results. It provides lubricity and a surface hardness of 70-72 Rc.

In this review, the electro-deposition of chromium is referred to as "Electrolizing." Electrodeposited chromium is an alloy of chromium, oxygen and hydrogen. As normally deposited in a conventional bath, the oxygen is thought to account for its hardness. The Electrolized coating uniformity deposits a dense, high-chromium, non-magnetic alloy onto the host material. The special alloys used in the Electrolizing process provide the unusual combination of superior bearing properties, extreme wear resistance, high hardness, a very low coefficient of friction and excellent anti-seizure qualities, along with surface adhesion/cohesion properties.

Metals Which Can Be Coated

The Electrolized coating maintains all of its unique properties, as applied, regardless of the material treated. Materials which can be considered for coating are: all ferrous steels, stainless steels (300 and 400 series), 17-4ph, 15-5ph, inconels, monels, brass, bronze, copper, beryllium copper and others. Hardness condition of metal is not a factor. It can not be applied to plastics, fiberoptics, ceramics, lead, pure beryllium or magnesium. Metals which have been previously nitrided, carburized, or otherwise heat treated, welded or shot peened can be coated with no detrimental effects to the integrity of the base material.

It is important that all metals and their treatments, prior to Electrolizing, be identified prior to processing. The Electrolized coating, as applied, takes on the basic physical characteristics of the processed material. The coating will maintain the same rate of expansions as the metal, and will maintain the basic tensile/fatigue strengths of the metal being treated. Thus, the coating will not separate from the substrate, unless the physical limitations of the substrate have been exceeded. The coating can maintain its integrity up to maximum operating temperatures of 1600F (710C), approximate.

However, the time length under operating temperature should also be reviewed with a coating engineer prior to applying coatings to insure desired results can be obtained. This coating has the unique ability to be applied to both internal and external surfaces, on nearly all shapes and configurations. In general, slots or grooves greater than 0.200" wide, having a depth greater than their width (threads and splines included) and bores or holes greater than 0.87" in diameter can be coated.

Recommended Coating Thickness
Considering the extreme hardness and density of this coating, and its ability to be applied very uniformity, savings can be attained by applying a selected minimum thickness of coating alloy. By reducing the operational sequences of "Plate Heavy and Grind," further economies can be realized. Recommended coating thickness ranges from 0.000050" per surface to 0.001" per surface. Precision tolerance levels can be controlled and maintained in this thickness range, thereby eliminating the need for secondary grinding or machining operations. Special needs sometimes call for a heavier coating. The maximum thickness at which this coating can be applied, under present state-of-the-art, is approximately 0.012" per surface. However, this thickness requires final sizing, usually by grinding, to guarantee configuration and tolerances. The characteristic of the coating, however, will not be altered.

Electrolyzing Aluminum

..."Peanut butter and jelly"..."Aluminum and anodized Aluminum and hard-coat"..."Electrolized Aluminum!!" It is now possible to selectively apply a 70/72Rc surface coating on aluminum to gain all the advantages of a bearing surface coating. These include: oxidation protection, enhancement of appearance, excellent lubricity, dimensional repair capability, and elimination of static electricity build-up. However, hardness testing of treated aluminum surfaces, if penetration of the test probe exceeds coating thickness, will reflect the hardness value of the base material. This holds true with all materials.

Electrolizing is adaptable to most aluminum alloys, including: 2014, 2017, 2024, 6061, 7075 and most cast alloys.

Application Considerations

The reader may have an incomplete understanding of when, where, and HOW chromium deposition should be applied. Some will consider it applicable only for two reasons: to repair worn parts, or to build up undersized diameters or reduce oversized bores on new parts. These are common applications. However, when parts call for coating at the outset, the "coat-heavy-and grind-to-size" approach often used may be unnecessary and costly. Today's technology in precision applications, such as plastic injection molds, rubber compression molds, special tooling, machine components, gears, splines, gages, and aircraft and nuclear equipment and bearings, allows for precision deposits to be made and controlled to 0.000050" per surface. This means parts can be designed, manufactured and inspected to a plating-allowance size and precision plated to produce a finished part, ready for assembly after plating. A chromium plating specialist can help you insure proper specifications are included for precision plating work.

Fixturing/Tooling

Each part being processed is engineered and coated with requirements in mind. Unlike some conventional plating methods, the Electrolized coating necessitates specific fixturing to be fabricated for the parts being processed. The fixturing made is designed to meet the coating requirements as specified. Fixturing is fabricated using a variety of materials. It will usually take only 2 to 3 days to build.

General Operational Processing

Electrolizing coating and operational facilities are capable of meeting rigid plating specifications, such as Federal Specification QQ-C-320, AMS 2406, Mil-C-23422 and FDA, nuclear, aircraft and military demands. To insure adherence to specification, at least six quality control reviews are required, sometimes more, during processing of parts.

Electrolizing has the flexibility to economically process any number of parts. Small-lot processing normally requires 3 to 8 days. This, naturally, is dependent upon such considerations as part complexity and coating thickness specified.

Persons not expert in chromium deposition are usually not aware of the complexities involved in producing good results. Specifications for chrome depositions are often set without prior consultation with professional chromium engineers. Such contact will provide current information on types of chromium, deposit thickness, coverage requirements, surface finish needed, restricted areas and other data essential to properly engineering a plating requirement. Such information is readily available from plating specialists and can be obtained with the ease of a phone call or letter. It is important that companies utilize the wealth of information available to insure the performance of their plated components.

This technical information has been contributed by
Electrolizing, Inc.

Click here to find suppliers

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