Artistic Plating Featured in Products Finishing Magazine for Expansion in Medical Industry
Artistic Plating to once again Exhibit at 2012 Medical Design and Manufacturing Show in Minneapolis, MN
Artistic Plating Launches Expansion of Precision Tin/Lead and Lead Plating Lines
Artistic Plating Expands with New Flagship Heavy Build Copper Plating Line
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Corrosion1. Corrosion:What causes metals to oxidize or “rust”? In addition to the surface oxidation that occurs on individual metals, any two dissimilar metals placed in contact with one another with an electrolyte (such as atmospheric moisture or water) will form a corrosion cell. This is the very basis of batteries used in everyday products. One of the two metals in contact will corrode in preference to the other and form that metal’s respective oxide. Which metal corrodes is based on what chemists call the electromotive series of metals. The selection of what plated layer to use is an important one since electroplating in its very essence is the process of placing two dissimilar metals in contact with one another. The plated layer (or layers) can either be an anodic coating (coating corrodes in preference to the substrate) or cathodic coating (substrate corrodes in preference to the plated layer). Whether a coating is an anodic or cathodic coating greatly impacts how the finishing system will perform once in service and there are advantages and disadvantages to each. Figure F.1 shows a cross section of a two-layer (duplex) nickel plated product as an example of a cathodic coating. The corrosion occurs between the two dissimilar nickel layers (bright nickel and semibright nickel) which forces the corrosion to propagate laterally. The use of two layers of dissimilar nickel helps prevent the galvanic attack from occurring between the basis steel and the plated layer. Figure F.1: Duplex Nickel System
What type of plating should be selected and how much plating thickness is required to prevent rusting or corrosion of my product? To stop the oxidation of substrates would seem to be a simple matter. However, several finishing decisions must be made. Coating selection: Coatings can also prevent substrate oxidation by encapsulating the basis metal and sealing it from the environment. This method is typical of nickel plating on steel. For this method to be successful the deposit must be "pore-free." Holes in the deposit become avenues for the entrance of oxygen and water to reach the underlying steel and start the corrosion process. Substrate Roughness: "Rule of Thumb": How do I stop post-plate tarnishing of my product? All metals with the exception of the precious group (gold, palladium, platinum, rhodium) are subject to tarnishing. The tarnishing is typically seen as a darkening or discoloration on the deposit. The occurrence of the tarnish is exacerbated by:
To minimize tarnishing, many products receive a post plate anti-tarnish conversion coating which will effectively seal off the plated surface from the precursors of oxidation. Typical of these coatings are chromates, triazoles, clear powder coatings and lacquers. Mechanical barriers are also used to minimize exposure to oxygen and moisture. Typical of these are desiccants and various types of protective wraps. Artistic Plating can provide many options to minimize the tarnishing of a plated deposit including nitrogen bagging. In nitrogen bagging the oxygen that is responsible for forming metal oxides is removed by filling the bag with pure nitrogen. APC will guarantee protection from tarnish for your product for up to one year if nitrogen bagging is specified. My passivated “stainless” steel product is exhibiting corrosion, how can this be prevented? Passivation of stainless steel on the surface would appear a simple matter – just dip it in the acid and ship it, right? In reality proper passivation of stainless steel is one of the most complex “simple” finishes in metal finishing. Unfortunately it is also one of the most incorrectly specified finishes by product design engineers and improperly employed finishes by finishing job shops. Often these two factors result in stainless parts which may have been passivated but are not truly passive which can result in field failures. To properly passivate stainless steel the passivation method must specified based upon the basis grade of stainless and the heat treatment that the stainless receives. Several specifications such as QQ-P-35 and ASTM A380 provide guidelines along this manner but they are often just that – guidelines! Some higher quality grades of stainless such as 316SS passivate very readily; other grades of stainless, especially free machining grades such as 303SS or 416SS, can be extremely difficult to passivate – especially if a high surface luster must be maintained such as with centerless ground shafts. F.2: Improperly Passivated 416SS Stainless Component Showing Red Rust After High Humidity Testing on Scaled Hex Head Portion of Product While Not on Ground Shaft Portion.
The other key point of passivation is that validation through testing is critical to ensure the process was successful. Artistic Plating offers a number of test methods including copper sulfate, potassium ferricynaide, high humidity and salt spray testing to test, validate and certify that stainless parts are indeed passive and “stainless” after processing. Artistic Plating has devoted a tremendous amount of research and development over our history in the proper methods and applications that are required to make the respective grades of stainless steel passive. We have a full range of room temperature and heated nitric and citric systems available both with or without inhibitors to proper passivate even the most difficult stainless steel grades. We welcome the opportunity to work with companies on problem parts that have failed in the field and in most cases can validate the problem and provide a process that will solve the issue. We also have a wide range of proprietary methods as well as exacting ultrasonic cleaning and rinsing systems available to “precision passivate” demanding stainless products such as implantables used within the medical and dental industries. |
FINISH SELECTOR Gold Plating CERTIFICATIONS
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