Anodizing Tips: Nitric Acid

   Nitric Acid is used in anodizing to remove heavy metals. Most notably Copper and Zinc but more so copper. Aluminum always has different elements alloyed with it to give strength and in anodizing we do not want these contaminants.
     Anodized metals that are alloyed with copper give a great anodize and also gives a hard glossy shell like appearance if done properly. The problem is too much copper is usually left after phosphoric de-smut. Too much copper left can give black streaks and spots. The parts to the right have copper content (Not the 6061). Note the glossy finish but no blackening on the gold part. The 7075 parts feel slick to the touch. this is assisted by a 10% nitric acid dip for about 5 minutes, followed by a hot water blast and re-dip. The hot water helps wash the surface.
    Nitric Acid is the only acid that will aggressively attack copper and the noble metals. It's not so aggressive on aluminum so can give a shine boost if done properly. It will also aggressively attack eyes, skin and clothes much worse that sulfuric. It also fumes badly if heated and is a requirement in brite dip. The fumes on reaction with copper is strong and produces Nitrogen Dioxide or Mustard Gas...not good. For this reason we only sell reduced to 35% and has to be shipped surface hazard material. At this level it wont fume out and greatly reduces risk.
    

Precision Billet Jockey Wheels

Precision Billet jockey wheels new for 2016.

These will fit vintage Proshift / Precision Billet / Paul and most other derailleurs including Shimano. These are all made in Canada and anodized in house. These have a metal shielded ball bearing for easier spinning.

ID is for 5mm bolts.

Total width including caps is 8mm.

Gold side caps only.

8 grams per pulley.

Currently for sale on Toronto Cycles website and will be added to Precision Billet site shortly.

Anodizing Tips: Setup Parameters

I've been asked many times about the basic parameters for type 2 anodizing. below I will list the voltages, temperatures and basic information that I use for anodizing. This tip page does not include dyes, dyes and de-smut will be a later topic).
   

Green AEN

Term used: Dissolution = When the acid eats back the anodized coating faster than the end current can produce.

Jet Black Anodizing

    Voltage: I run at 14.2 to 14.8 volts. This can vary a bit depending on the acid strength and tank temperature. Warmer tank = lower voltage. If the voltage is too high the parts will start to burn. If the parts burn at 14.0 volts then the acid is too strong. If the acid is too strong than pitting (Severe burning) will occur.
    Amps: Amps will self regulate. Amps must fall during the process. Amps will fall fastest at first then slow down. The final value to dissolution will be about 70 - 75% of the starting amps after 5 minutes). In other words if the starting amps after 5 minutes is 2.0 then will be anodized fully at 1.4 to 1.5 amps.
    Time: I go 1 hour 10 minutes. I go less on silver. Going longer time will hit dissolution. Really it's only necessary to go as much time as needed to take full dye and no burning.

Hot Pink

    Temperature: 70 degrees. Some dye wont take with cooler tanks (Grey BL, Pink, Reds I've had issues with cooler tanks). Warmer tank = lower voltage.
    Agitation: I use a wave maker. I don't like the bubble method but some feel is ok.
    Acid: Sulfuric acid at a 10-15% ratio. There is a 720 rule or formula but I don't use it. Really complicated and how to find the surface area of a bolt? Change the bolt and new formula...hmmm. Most rookies start with way too strong acid bath. I use a hydrometer value of 1.4 baume.
    This step is the hardest to get. My advice is a 10% bath and follow the above values. If it's too weak add a bit of acid. Remember its much easier to add acid then the split the tank to reduce.
     New acid tanks can burn parts easier. Adding some aluminum matures the tank and helps resist burn. I add phosphoric and oxalic acid in very small amounts but isn't needed. This can help burn and black tracks. Clean Tanks are very important...I will follow up on this later.
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