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Technical Articles Electroless Black Oxide
Of Aluminum Alloys – A New, Simpler And Faster Process Eden Prairie, Minnesota: Black anodize finishes have long been favored by general industry for their thick, hard coating properties. Ironically, it is these very same characteristics that often make the anodizing unusable for many military and aerospace applications. Consider critical military components, such as inertial guidance systems, ordnance trigger mechanisms, vacuum pumps and piston/cylinder assemblies. Many of these components may sit idle in a desert or winter cold warehouse for years, and are then expected to work perfectly when put into service. Many require a uniform, non-dimensional finish (under 2 microns) that will not reduce hole diameters, change critical dimensions or interfere with critical clearances. Many also require a finish with enough inherent lubricity to prevent galling and allow for smooth initial operation, without chattering, in assemblies that do not receive added lubricants. Or, they may require a coating that can withstand elevated temperatures of 500° F and higher. These requirements often eliminate black anodizing as a process option and open the door for a new process development that meets all of the above requirements and more. The process is called LUMICLAD® electroless black oxide for aluminum alloys. (Photo One)
Process Is Durable, Scratch Resistant And Attractive This new LUMICLAD process develops a coating thickness of just .000060 inches (1.5 micron) and is smooth and durable. The finish has a slightly porous crystal structure that absorbs an optional topcoat, such as a clear polymer, light oil or dry-to-touch sealant. The resulting finish is an attractive satin-gloss black surface that is well suited for many machine components, tooling and a wide range of decorative aluminum applications requiring scratch resistance and sales appeal. (Photo Two)
LUMICLAD Process Is Much Simpler Than Black Anodizing Prior to the development of this new blackening process, black anodizing had been the only viable blackening option for manufacturers of aluminum components. While the anodized finish is extremely durable, the process is so complex that only those who specialize in it can operate it properly and consistently. And, though the protective properties of a black anodized finish are quite high, they are often higher than the application requires, and at significant cost. Conventional black anodizing is a long and complicated electrolytic process requiring experienced operators for consistent quality. Parts must be manually clamped onto spring-clip racks to ensure electrical contact. For this reason, small parts cannot be processed economically. Because the LUMICLAD process requires no electrical current, small parts can be economically bulk-processed in baskets or rotating polypro barrels. This opens the door to economical blackening of low-value parts, such as stampings, screw machine parts, fasteners and other parts that require lubricity or galling resistance, but are not good candidates for anodizing. The LUMICLAD process utilizes a conventional immersion tank process line. It is easy and safe to operate so that manufacturers can operate it themselves, thereby eliminating the need for outside processing. (Photo Three)
LUMICLAD Process Cycle
For most aluminum alloys, the LUMICLAD process takes about 30 minutes from start to finish. Aluminum extrusions and heavily corroded parts may require etching or bead blasting prior to finishing. Discharge Considerations The LUMICLAD coating reaction utilizes zinc/molybdenum chemistry to form the black finish. Process rinse waters will contain minor concentrations of these metals and must be disposed of properly. Many process lines are configured to utilize Ion Exchange technology to purify and re-use the rinsewaters. In this manner, the process line operates as a self-contained, closed-loop system, with no discharge to the drain. Ion exchange systems and services are available in most localities for this type of process line. Birchwood Casey, the manufacturer of LUMICLAD, offers an Ion Exchange system for purchase. In addition, Birchwood Casey has coordinated with Siemens Water, the industry leader in Ion Exchange technology, to supply water purification on a lease basis. Comparison Of Type II Anodizing With LUMICLAD® Black Oxide
The LUMICLAD process can be designed to handle any part size and volume requirement at modest cost. Options for installing an in-house aluminum blackening system include retrofitting an existing tank line, installing a new manual tank line or implementing an automated finishing system. The process can be automated through the use of a CNC programmable hoist system. Whatever design is chosen, the new process offers savings in finished part cost and part turnaround time while providing a high quality black finish to most grades of aluminum. (Photo Four)
The LUMICLAD® Black Oxide process (patent applied for) is the first and only high quality method for blackening aluminum that doesn’t involve the complexities and high costs of electrolytic black anodizing. It is supplied by the originator of the unique and widely used TRU TEMP® low temperature black oxide process for ferrous metals.
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