Design Engineering

Steve Koelzer Vice President, Research & Development K & K Products & Consulting 709 W. Remington Drive Sunnyvale, CA 94087 E-mail: [email protected]

Cleaning & Pretreatment & How They Concern Design Engineers

he focus this month is cleaning range is the work of separation plus coating formulation contaminates Tand pretreatment. The following the interface restructuring work. The the cleaning bath. Concern for will entertain that portion of this restructuring work of the interface is human health originally got us into subject that is of particular concern to influenced by many adsorbates this “pickle.” design engineers. Others who read (sulfate, chloride, benzotriazole, The best cleaner for carbon this column should benefit as well. , nitrogen, etc.). Therefore, was perchloroethylene, creosote and The principal idea behind clean- cleaning and rinsing conditions ortho-dichlorobenzene. The best ing before plating or finishing is to become very important for adhesion alternatives were addressed in prepare for subsequent adhesion. bond strength. This also applies to P&SF’s “Branch News” (July 1997, The finish may receive another the constituents in the plating bath. p. 79) from the Santa Clara Valley layer, such as paint or Teflon®, and Bond strength is also affected by Branch. will still benefit from a particular surface oxide reduction (application Platers like to have some of their microstructured surface, cleaned for of initial high current) or “striking,” cleaning woes alleviated by the adherence of the applied coating. which also initiates many growth design engineers. So here’s what The microrough surface sturcture centers. Brush plating owes its you can do from the field of metal- may be obtained by etching, as in success to both close anode and lurgy for “green” design engineer- the case of “inhibited” acids or cathode proximity (more efficient ing. Consider your sources of pickles, or if the material is not of current conduction, so less bulk material, their quality of composi- the right grain size and relatively solution resistance) and high tion and heat treatment. “Contami- impervious to physical or chemical nucleation rates for growth, also nation” introduced for ease of treatment, such as with hardened from the use of pulsed rectification machining (e.g., lead, , steel, an inorganic crystalline (equal times, on and off), where sulfur, etc.) might be reconsidered. surface can be grown. Such surfaces each “time on” renucleates growth To ensure the best paradigm for (Parkerizing at 200 °F in centers. cooling, quenching chemistry, phosphate baths) are Other methods of increasing subsurface scale often has to be used for holding oil during “break- adhesion include anodically remov- removed from alloy. Poor annealing in” of camshafts, molysulfide onto ing basis material for a short time will enrich surface composition pistons for friction reduction by before going forward cathodically, compared to cores of bulk material. electrocoating of solids from using an ammonia-containing Specify compatible machining solution, and trisodium phosphate solution to reduce oxidation and tie coolant-lubricants and pickles (TSP), which degreases as well as up hard metals (such as calcium), (protective coatings used for leaves sodium phosphate surface laser cleaning of surface volatiles, storage). crystals for binding paint. plasma etching, etc. Just because a Specify alloys that will better An adherent but evanescent surface is clean, doesn’t mean retain tempers; don’t allow the least coating is zincating. It protects plating will adhere. expensive raw material type or aluminum surfaces from oxidation Carbon steel is a common engi- source of material to enter the until the coating dissolves and/or neering material. Unfortunately, if picture, and maintain a quality of codeposits during plating. Most over-etched in hydrochloric, a engineering standard for manufac- cleaning is for hydrocarbon, burr surface rich in graphite becomes ture. P&SF and debris removal. exposed. This happens when A previous “Design Engineering” cleaners aren’t perfectly maintained, column (May 1998, p. 91) dealt with or the brand of anti-oxidant used in adhesion. The adhesion working the machining oil or protective

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