What is anodizing?
What is anodizing? Anodizing is the electrochemical process that uniformly accelerates the naturally occurring protective coating of aluminum. although it sounds complicated, it’s really not.
Everyone has seen rust. Rust is the oxidation of steel or iron, called ferrous oxide. Aluminum also “rusts” or “oxidizes.” All aluminum has a microscopic layer of aluminum oxide on it.
There are two interesting things about aluminum oxide. First, when an aluminum oxide coating forms on the surface, the reaction ceases. Rust on a car will continue to grow and will devour the car, however, “rust” on aluminum forms a protective barrier and stops the reaction. This means that aluminum oxide has excellent weather resistance.
Secondly, aluminum oxide is extremely hard, second only to a diamond. This means it is very difficult to scratch relative to raw aluminum. Most sandpaper is made of aluminum oxide.
What does this mean to you? In the anodizing process, aluminum is intentionally rusted. Electricity, sulfuric acid and water are used to convert the top layer of aluminum into a controlled layer of aluminum oxide. The aluminum oxide coating is part of the extrusion, not a coating which could fall off. This hard aluminum oxide provides an extremely long lasting, durable finish.
The Anodizing Process
- Racking Material: This process creates the electrical contact for the electrochemical process.
- Cleaning Material: Cleaning is necessary to remove grease, oils and any other surface contamination.
- Etching Material: The surface of the aluminum has many imperfections. To hide the imperfections, we use caustic to give the material a “matte” finish. No coating is found in the etch tank.
- Deoxidation: Etching does not remove all the impurities that are in aluminum. Any surface smut must be removed by deoxidation.
- Anodizing: Electricity is used to form the aluminum oxide coating. The coating thickness is dependent in the amps per square feet and the amount of time in the tank.
- Coloring: The anodizing process forms a porous surface that can be colored. Electricity is used to plate tin into the bottom of the pores. The amount of tin deposited determines the color. A small amount of tin plus a short time in the tank results in a light champagne color, while a large amount of tin and an expanded period in the tank results in a dark bronze, or black.
- Sealing: Not all material is colored, but all material is sealed. The pores that allow for the coloring of the material also allow the colors to run back out and cause the coating to degrade. So, the color and the coating are sealed in by closing the top of the pore.
- Inspection: If material is within color range, has the proper coating and thickness and has the required seal, it is ready for use.
Anodizing is not quite this simple, but then again, it is. And the results? It is still the most durable and long lasting finish available.
Original specifications for anodizing were all proprietary with each company having their own specifications. The first attempt to unify the anodized specifications was made by the Aluminum Association publication 46. The concept is still used today where mechanical, chemical and anodic coatings are all defined in a single specification. Below are the basics of this specification:
Mechanical (M), designates how the surface of the aluminum should be sanded or polished. Vistawall and all other similar manufacturers produce material as fabricated or as extruded, in our case, with no mechanical finish. Therefore, M10 or M12 would be appropriate specifications.
- M10: Unspecified as fabricated
- M12: Non-specular as fabricated
- M22: Specular buffed
- M32: Medium satin, directionally textured
Chemical (C), determines how the surface of the aluminum should be etched or brightened chemically. The typical specification is C22.
- C12: Inhibited chemical cleaned
- C22: Medium matte etch
- C31: Highly specular – brite dip
- C32: Diffuse brite dip
Anodic coatings (A), determine the thickness of the anodic film and the process used to color the coating. Today, the traditional bronze and black finishes are created using electrolytically deposited color. This process became prevalent in the early 1980’s and replaced the previous integral color method. Currently, the availability of integral color is limited. The typical anodic coatings to be specified are A31 and A44.
- A31: Class II (.4 mil) clear
- A32: Class II (.4 mil) integral color
- A34: Class II (.4 mil) electrolytically deposited color
- A41: Class I (.7 mil) clear
- A42: Class I (.7 mil) integral color
- A43: Class I (.7 mil) dyed color
- A44: Class I (.7 mil) electrolytically deposited color
A standard spec would be AA-M12CCA31. This is a simple Class II clear finish. For a standard bronze specification, use AA-M10C22A44.
What is a Pinnacle ?
Sentinel is Wasco’s OSHA compliant skylight. It’s domes are formed from virtually unbreakable copolyester or impact modified acrylic. The domes are fastened into thermal break aluminum such that they will not break or disengage from the frames under 775 foot-pound impacts.
Why 775 ft-pounds? OSHA cites a 200 lb. load but doesn’t specify what type of load. Impact?…point?…uniform?…sustained? etc. So, Wasco calculated 775 ft pounds as being a conservative model of a 200 pound man falling onto a skylight. Though OSHA is not in the business of approving products, they have agreed that this meets the intent of the regulations.
Vertex — OSHA compliant skylights…without unsightly fall protection screens!
What is a Drop Out?
A “drop out” or “melt out” is a term used to describe a unit skylight/smoke vent that has passed the UL 793 fire test. To pass the test, the skylight domes must drop out of their frames in less than 5 minutes when subjected to heat from below of less than 500° F. In case of a building fire, this would allow heat and smoke to vent from the building.
Though sometimes referred to as “melt outs,” the plastic doesn’t actually melt but rather shrinks back and drops out. Wasco uses only premium grade acrylic for their drop outs. Some competitors use PVC which has severe negative consequences.
Wasco’s UL Rated Drop Out Heat & Smoke Vent is model PSO.
What is an Automatic Unit?
Automatic heat and smoke vents are typically spring powered doors that automatically open when a small fusible metal link breaks at a preset temperature. The doors, which are either skylight domes or opaque metal lids can be manually re-closed. The fusible links are available in 160,° 212° and 360° F. Automatic units can also be activated by electro-thermal links that are wired to a smoke alarm system or fire command panel.
Contact us for pricing on automatic heat and smoke vents.
Can you tell me about Failed PVC Skylights?
For decades, two manufacturers have marketed an FM rated drop-out smoke vent made with PVC instead of acrylic. Though cheaper than acrylic, PVC will discolor and physically break down under prolonged exposure to the sun’s UV rays. After the lenses turn black, they absorb so much heat that the PVC deforms and no longer fits the frames. The result is a skylight that blocks out light and lets in water.
Wasco uses only premium grade acrylic in their standard skylights and smoke vents. Wasco offers a retro-fit frame mount smoke vent for failed PVC units.
PVC units are easy to identify. They have a lightweight aluminum frame over the lenses since the design could not pass the 10 PSF uniform dead load aspect of the test method without it. These aluminum frames should not be confused with OSHA fall protection screens. They do not comply with OSHA.
