Conventional hard chrome deposits are highly stressed and exhibit a pattern of cracks on a microscopic level. These cracks vary in size, width and density due to differences in bath chemistry and the plating parameters used. These cracks can be detrimental in certain situations. Corrosion occurs when service conditions expose the deposit to an environment that is aggressive to the substrate. The cracks serve as passageways for the atmosphere to gain access to the base metal. In fact, corrosion cells are formed at the bottom of these cracks, which accelerates the corrosion. It is common for these corrosion cells to form at two nearby cracks which actually undermine the deposit. The resulting flaking off of the coating is sometimes mistaken for poor adhesion when it is actually a corrosion problem associated with the natural crack structure.
Ideally a chromium deposit would have a hard and Crackless structure nearest the substrate and a traditional microcracked structure on top to assist with lubrication.
Until now, such a coating was not available. Early attempts to create a chromium deposit that was free of cracks centered on conventional bath chemistry; the deposits were dull in color and very soft. The old style crack-free deposits were, therefore, not well suited to high wear applications. The Durachrome Pulse Process solves this problem by being able to obtain chromium deposits that are both bright and hard. The trade name “Crackless” has been adopted to differentiate it from the old style crack-free chrome. The trade name “Multi-Phase” has also been adopted as a special variation of the application.
Following are the benefits of using the Dura Pulsed Crackless process.
|● Ability to plate micro-cracked, crackless and multi-phase deposits in the same tank.|
|● Deposit thicknesses up to 0.100" per side are possible.|
|● Hardness of 70 RC with excellent brightness and wearability.|
|● Corrosion resistance of 500 hours of salt spray with less than 0.002" deposit.|
|● Extremely low deposit stress and high rates of deposition.|
|● Excellent adhesion, no boundary lines with Multi-Phase deposits.|
This unique process offers the ability to obtain the following hard chrome deposits in the same tank and at the same bath temperature.
100 % Crackless
100 % Micro-Cracked
The Multi-Phase deposit can be any combination of Crackless or micro-cracked. Typically, the Multi-Phase deposit has a Crackless base and a micro-cracked surface. A boundary does not exist between these two deposit types. They are not deposited in layers as a two step process would. Instead the Crackless base merely transforms into the micro-cracked surface. A division line is not visible even at 1,000 magnification. The adhesion between these two deposit types is excellent.
Detailed process operation data is provided upon execution of a confidentiality agreement. The following, however, outlines the basic process conditions that will be used.
|Chromic Acid||30.0 oz/gal.|
|Dura-100 Pulse Catalyst||3 % Vol.|
|Dura-76-F Additive||2.5 oz/gal.|
|Trivalent Cr||1 % of Hex.|
|Metallic Contaminants||< 5.0 g/l|
|Chloride||< 20 ppm|
The process uses special bath chemistry and operating conditions in conjunction with a unique pulse rectifier. The waveform provided is a special type of modified pseudo sine wave which is significantly less expensive than a true square wave. Plating Resources, Inc. can assist with the optimum design and specifications, as well as provide this unit.
Regulations & Fume Suppressants:
All chrome plating baths produce misting and this can be reduced if lower chrome levels are used. This mist contains Cr(VI) which is regulated by the EPA for environmental and OSHA for worker safety issues. Be sure to follow all federal, state and local regulations for safe operation and hazardous disposal.
The plating bath contains chromic acid, sulfuric acid and the Dura additive outlined above. These are all industrial chemicals and must be handled carefully and in accordance with the directives provided in the individual MSDS forms.
Read and understand the MSDS on all of these chemicals before handling or using. Ensure that all regulatory standards are followed and limit personal exposure as required for Cr(VI) by OSHA.
Avoid personal contact with these chemicals, avoid splashing and avoid breathing any fumes released during operation. Do not inhale any dust, mist or vapors from these chemicals. Do not allow these products to contact the skin or eyes. In case of contact, flush immediately with large amounts of fresh water and seek immediate medical attention.
Wear protective clothing such as aprons, gloves, face masks and respirators. Be sure that adequate eyewashes and emergency showers are available nearby before handling or using any of these chemicals.
Designated work clothing should be worn while using these chemicals and the worker(s) should thoroughly shower and change into fresh-clean street clothing before going home. Decontaminate all work clothing before reuse.The user is responsible for providing adequate work clothing, personal protection, and limiting personal exposure and providing any required clean-up, decontamination as well as any needed medical attention.