Frequently Asked Questions
Aluminum Anodizing Tips and starting
Anodize World Aluminum Anodizing. Tips and Tricks!
We have better perfected the anodize process and are using better quality dyes from US Specialty and Brite Dyes
We are currently not doing outside anodizing since we don't have production capabilities and our anodizing time is taken up by other processes. Anodizing aluminum is a complicated process and the tank here is set up for smaller hardware runs.
The Anodizing Process:
Anodizing aluminum can be difficult. I will start a blog here about the process because many people try to anodize but run into problems. There is little real information on the internet as well. Many sites give amperage formulas and the like but can be difficult to follow. Over time I have better perfected the process and am always learning as well.
This type of anodize is done in a sulfuric acid bath, battery acid and water. Around 10 - 20% of acid to water. It's easier to start with a thinner mix and add more acid rather than take it away. This step is really important as it will have an effect on the current and it's density. In my experience the tank also needs a bit of aluminum, after a few runs the tank will break in and anodize will become more steady in it's formation.
A good variable power supply is needed. I've hear of a car charger being used but have never tried it. I use a variable supply with 3 amps maximum. This is enough to anodize 2 or 3 160mm rotors at a time. I usually set the voltage to be constant around 14.5v and let stay in the tank for about 80 minutes. Sometimes I will leave in a bit longer because some colors need a bit more anodize. Sometimes I anodize Less Time
The metal things going into the tank are anodes. They should be much greater in surface size than the parts you are anodizing. Titanium is the best solution. I use old titanium rotors and titanium wire to connect to the tank. They need to be cleaned occasionally but will last for years.
The dyes need to be heated to 140 degrees (generally). PH needs to be low as well. Pet stores sell electronic testers and ph down which does the job. Some colors like reds and purples wont take well unless the ph is lower. US Specialty dyes will boost the ph and this in combination with water will require careful checking.
Time in tank
The parts will need to be in the tank for as long as it needs to anodize. Start with scrap and learn before doing expensive parts. The parts should have a grayish look when done. Wash very well after the acid before dye. Time can usually cut down by increasing voltage but can form a poor coating. Temperatures should be around 68 degrees.
Boiling water alone will work. If the dye flushes out at this point the anodize is no good. A hard boil or steam for 30 minutes will lock the dye in. I use nickel acetate seal from US Specialty. The nickel molecule gets trapped in the pores and requires less heat and shorter time to seal properly.
Boiling will make a tougher surface. The nickel will have a bit nicer look and a bit more shine as an end result. For me it make sense to use a good sealant.
Your finished job should look nice. If it looks nice its basically ok. You should have deep color and wont be able to wash the color off with bleach (Bleach will strip the dye out of parts not sealed properly). Patience and experience will really help.
1. Pitting parts: Acid too strong also new tank without aluminum seeding.
2. Burnt parts: voltage too high
3. Wont take full color: Not fully anodized. Needs more time or more power.
4. Parts loose color in seal: Temperature of tank too high, Anodizing pores too large. Too low voltage.
5. Parts loose color over time: Bad sealing
6. Some dyes take color and some don't: Some colors need different temperatures in the acid bath. Play with the temps and try different colors to find the correct tank temperatures. Dye PH wrong.
If you have any tips to add or questions please leave a comment.
How to set a new dyebath
1. A cleaned tank is filled with di-water to about 75% of final volume and raise to dyeing temperature.
2. The necessary amount of dye is weighed out and dissolved with one to two times the amount of hot
di-water (160°-190°F) in a mixing bucket, drum, small tank, etc., until a paste is formed.
3. Continue adding more hot di-water while stirring until all the dye goes into solution. This is your stock solution.
4. With agitation turned on in tank, pour stock solution into tank.
5. Top off the tank to final working solution volume with more hot di-water.
6. The dyebath should then be agitated for 15 minutes.
7. Finally, the pH is checked and if necessary adjusted.
8. The dyebath is brought to dyeing temperature
Mixing 2 part dyes (Greens and some blues like blue 4a)
The procedure is the same as above but sometimes the blue pigment will not fully break and release into the water. Rather, the blue will remain as a solid in the bottom of the tank. This caused greens to come out gold...not good.
WE resolve this by "panning" the stock solution and crushing the blue grit with a spoon. This is like panning for gold except the original dye is recycled.
Also boiling the stock solution will make the blues release.
If you email or call on advice please have all parameters ready because I will ask.
Tank Temp, Voltage, time, dye temp, type of alloy ect....Need to know!
The photo on the left shows the open pores vs. the closed pores.
To seal anodizing means to convert the aluminum oxide in the pores to hydrated aluminum oxide which is a larger molecule and literally "clogs" or fills up the pore with hydrated aluminum oxide.
Sealing is done by 3 methods.
1. Boiling Water / Steam
Boiling will close the pores in about a half hour. During this process some dye will leach out so is best to boil hard before moving the part out of dye. We have used steam in the past but uses much energy and can become blotchy if not hot enough.
From what I have heard the boiling method produces the hardest surface but not the best finish in my opinion. I always do silver in boiling water
2. Mid Temperature Sealant - Nickel Acetate
This is what we sell and use for all our sealing. The nickel will clog the pores but requires less time and heat. Thus this has a bit less leaching of dye color. The corrosion resistance is generally not as good as boiling water or steam seal, unless the nickel acetate process is done at boiling temp. We Boil.
When sealing with nickel acetate alone, a smutty deposit may form on the work. This can be prevented by the addition of a Dispersant. Nickel acetate is suitable for sealing dyed or clear anodized aluminum. Nickel acetate offers the advantage of increased weather and light fastness on coatings dyed with organic dyes.
3. Cold Sealing
This is done with flouride. We don't have much knowledge on the process and is not used in standard production.
Without a high quality seal the anodized coating feels sticky and is absorbent to all kinds of dirt, grease, oil and will also leach dye. The sealing gives a maximum corrosion resistance but minimizes the wear resistance of the anodized oxide layer.
How much dye should be used ? The amount of dye required will vary and the mixes on our dyes are posted and prepackaged for 2 gallons. Black Dye is the heaviest concentration.
Can more or less dye be used than the recommended concentration? Yes, the user can vary the concentration to fit specific needs.
What is the best way to store unused dye? Dye is best kept in a closed container in a cool, dry place, away from sunlight.
How long will unused dye last before it expires? When stored per the recommended method, the dye has an indefinite shelf life.
What dye is for Matt "Flat" Black? Flat black is not in the dye but the surface treatment. a blasted surface will be matt.
Can non-deionized water be used for the dye bath? Yes it can but deionized, reverse osmosis, or distilled water is recommended. Regular tap water can be hard and contain high levels of calcium and chlorine, resulting in white spots after a part is sealed and has dried.
How critical is the dye bath pH and/or temperature? The recommended ranges vary by color but are important in achieving consistent results . If reds are too high of a ph they will not soak dye properly.
How should a dyed part be sealed? The sealant we offer is used to seal faster than just boiling water. Nickel / Acetate causes the seal in a shorter time. This method causes a bit less dye loss. Boiling water works fine but takes 30-40 minutes. Boiling will give a bit tougher finish but seems like a bit less luster.
Why is the color uneven across or in different areas of the part? The part may not have been cleaned well prior to anodizing. Thoroughly cleaning and rinsing between steps are both critical to achieving a uniform color. Dye bath agitation is recommended to maintain a consistent bath temperature.
Why do small white spots appear? White spots are often caused by foreign contaminants attaching themselves to parts and preventing dye penetration. They can also be the result of sulfuric acid from the anodizing bath being carried into the dye bath which can be prevented by steps such as a neutralization rinse before dyeing.
More Internet Anodizing Basics:
The great majority of aluminum anodizing is done with room temperature (20 °C 68 °F) sulfuric acid (approximately 15% by weight, 10% by volume) at 10-20 volts. Depending on for how long the work is processed, and the specific aluminum alloy being anodized, this produces an anodizing thickness from about .0001" to .0008" thickness. Thicknesses greater than this are difficult to achieve in conventional sulfuric acid anodizing for two reasons: first, as the coating gets thicker, the dissolution by the acid can limit additional build; second, the coating is non-conductive, with its resistance being roughly proportional to the thickness of the coating. As the coating gets thicker, the conventional 10-20 volts applied will no longer drive sufficient current to cause further buildup.
The anodized film is somewhat, but not completely, transparent/translucent so the thin end of the range is used for aluminum mirrors and reflectors. The thicker end of the range is used where greater corrosion resistance is required.
Conventional sulfuric acid anodized coatings are often dyed to attractive decorative colors. Although "white" is problematic, virtually every other color of the rainbow is readily achieved. The pores in the coating absorb the dye, and then the coating is subsequently "sealed", locking the dye in. The degree of saturation of the color will depend on how thick the coating is and consequently how much dye it can absorb. While light pastel colors can be obtained with an anodizing thickness of perhaps .0002", to get a saturated dark black color may require a thickness of .0006" or more.
Most of the dyes used in anodizing are organic dyes, with various degree of color-fastness; but metallic (inorganic) dyes are often used in architectural applications where continuous resistance to strong sunlight is required. These inorganic dyes tend to produce colors ranging from champagne to bronze, which is why those colors are so popular on aluminum roofs, awnings, and building features.
How to Anodize, What is anodizing, Sealing anodized aluminum,
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