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A New Blackening Process for Aluminum

The LUMICLAD® Black Oxide process (patent applied for) is a new blackening method by which aluminum alloys can be coated with a durable and attractive black oxide finish. Utilizing a simple immersion tank process line, the LUMICLAD solutions carry out a two-stage chemical reaction to form an attractive, satin-gloss black finish that is tightly adherent to the aluminum surface.

The LUMICLAD Finish is Attractive & Durable

With a coating thickness of only 1.5 microns, the LUMICLAD finish is quite smooth and durable, and has a smooth crystal structure that absorbs an optional topcoat, such as a dry-to-touch sealant or clear polymer. The result is an attractive satin-gloss black surface that is well-suited for many machine/tool or decorative applications requiring good sales appeal and scratch resistance. On many surfaces, such as castings, the LUMICLAD finish improves the overall smoothness of the base metal, thereby enhancing the appearance and handling properties.

An Attractive, In-House Blackening Option

Until today, black anodizing has been the only viable option for manufacturers of many aluminum components. While the anodized finish is extremely durable, the process itself is so complex that only those who specialize in it can operate it properly. In addition, the anodized coating is thick enough to cause a measurable dimensional change and close down critical hole diameters. While the protective properties are very high, they are often far higher than the application demands. Similarly, the cost of the anodizing is often prohibitively high, as well.

Most manufacturers send their work to an outside shop - a practice that often involves excessively long turnaround times that do not fit with today’s "just-in-time" manufacturing. Though the corrosion resistance of the LUMICLAD finish will not match that of black anodizing, it is durable enough for many indoor industrial applications. Its simple process cycle allows manufacturers to do their own blackening, in-house, without the long turnaround times of outside finishing. This feature creates opportunities for the user to streamline workflow patterns, reduce inventory levels, speed shipment of finished product and reduce costs.

The LUMICLAD Process is Simple

For most aluminum alloys, the LUMICLAD process takes about 30 minutes and utilizes the following steps:

Step 1: SAFE SCRUB® ETCH Cleaner: Cleans and micro-etches the metal surface.
Immerse parts for 8 minutes at room temperature.

Step 2: Water Rinse: Clean water; 20 seconds.

Step 3: LUMIPRIME® Primer/Prep: Deposits a primer coating to prep for blackening.
Immerse parts for 8 minutes at room temperature.

Step 4: Water Rinse: Clean water; 20 seconds.

Step 5: LUMICLAD® Black Oxide: Blackens the metal surface.
Immerse parts for 10 minutes at 200° F.

Step 6: Water Rinse: Clean water; 20 seconds.

Step 7: DRI TOUCH® DS Dewatering Sealant: Displaces water & seals the black finish.

The finished black surface has a very smooth, semi-gloss appearance, with no ruboff.

Note: Extrusions and heavily corroded parts may require bead blasting or more extensive etching in order to properly prepare the surface for blackening.

What About the EPA?

The LUMICLAD process utilizes zinc/molybdenum chemistry to form the black finish. In short, the LUMIPRIME step deposits a very thin layer of metallic zinc on the aluminum surface that serves as a primer for the LUMICLAD molybdenum black oxide finish. Consequently, the rinse waters in the process line will contain very low concentrations of zinc and molybdenum. There are two options for handling these metal-bearing rinses:

A. Small process lines usually do not exceed the regulated limit of 5 ppm.
Rinse tanks under 10 gallons can usually be discharged to the drain without treatment.

B. Larger process lines use Ion Exchange to purify and recycle the rinse waters.
For process lines utilizing tanks of 40 gallons or more, Ion Exchange is a proven, cost-effective method for purifying rinse waters in a completely closed-loop manner, with no discharge of any kind to the sewer. No discharge permit would be needed. In this scenario, all the rinse water is collected and cycled through the Ion Exchange system that purifies it so it can be re-used in the rinse tanks. No water goes to the drain.

Ion Exchange Systems are available for purchase offer on request:

For LUMICLAD process lines of up to 200 gallon tank size,BIRCHWOOD CASEY supplies a complete, skid-mounted Ion Exchange System, for purchase by the customer. This unit incorporates the following components:

A sump tank to collect the rinse waters, ¾ hp centrifugal pump, 20” particle filter, 14” x 48” carbon filter chamber, two mixed-bed resin tanks (each tank contains 3.5 cu. Ft. of mixed cation/anion resin), conductivity light and hose connections. The system can generate a total flow rate of about 10 gpm and has a central control panel for straightforward water and power connections.

LUMICLAD® Process Lines Are Available, from BIRCHWOOD CASEY, at Low Cost

For example, a standard LUMICLAD BC40 Tank Line can process up to 1,500 pounds of work per shift and would utilize a series of 40-gallon tanks, each measuring 16" x 24" x 24" deep. When supplied with the necessary chemical products and Ion Exchange System, the BC40 tank line sells for about $22,000.

The BC100 Tank Line is rated for up to 4,000 pounds of work per shift, utilizing a series of 100-gallon tanks, each measuring 24" x 40" x 28.5" deep. When supplied with the necessary chemical products and Ion Exchange System, the cost is about $37,000.

Details of these process lines are available in our price proposals.