Posts Tagged ‘low current density’

There were some questions raised awhile back concerning home anodizing and exactly how it is accomplished. I thought I would share my procedures (good and bad) and show how I have been able to achieve, what I would consider to be, successful Type II home anodizing.

However before I begin I think I need to say the following (I think because I don’t really know). It’s the almighty disclaimer. What I am claiming to dis is I am not a professional and I try things at home. Anodizing involves certain chemicals that can cause good things to go BAD…namely you. Sulphuric acid is used in the anodizing process and as we all know acid can be BAD. I do not want BAD things to happen. So please note the following. This blog posting is not a step by step guide. This blog posting is simply showing how I do my anodizing. I am not going to litter the posting with safety information. Gloves, safety glasses, and respirators are all no brainers. If you don’t know when to use these things then please turn your tools in at the door and find a comfy seat in front of the television. Now on with the show.

These are a set of sport bike race stand spools that I machined for a friend and then anodized.

The type of anodizing I do in my garage is known as Type II, Low Current Density (LCD) , Controlled Current (CC) anodizing. I am not going to explain all this since this is not an instruction guide. There is lots of information out there that can assist in defining the process. If you have specific questions then send them my way, I will do my best to answer them. I will, however, clarify one misconception. Anodizing does not give a piece of metal a cool funky color. The color comes from the dying process after the part has been anodized. Anodizing is the process of building up the exterior layer of oxide on aluminum in order to give it a more durable finish. When the part is anodized this oxide layer is comprised of many small pores. It is these pores that are what absorbs the dye color in the dying phase. The dye provides no benefit other then looks.

Different types of metal can be anodized however the most common home anodizing deals with aluminum. In my case it revolves mostly around 6061 grade. The process can be broken down into 5 stages and they are;

  1. Surface preparation
  2. Cleaning of the part
  3. Anodizing
  4. Dyeing
  5. Sealing

I will attempt to address each step and try to explain how I deal with the challenges of each stage.  As a demostration piece I am going to use a rubber band gun reciever and trigger mechanism that are fabricated from 6061 aluminum. A cyber friend of mine, Jason, sent me one of the trigger assemblies that he engineered, designed, and built to fit into a custom wooden stock to create a dual action rubber band rifle. Very cool set up and mechanism. If you are interested in learning more about Jason’s project you should check out his blog. He has lots of pictures, drawings, and explainations.

1. Surface preparation

This is the trigger and receiver assembly that Jason sent me. The purpose of this picture is to demonstrate the finish I was starting with.

Anodizing hides nothing; I mean nothing (ok maybe it hides a little bit). It is best to assume that any surface imperfections that were present before anodizing will be visible afterwards. Anodizing is not like paint, powder coating, or chroming where the surface gets covered with a different material. Any scratches, nicks, or gouges will be visible afterwards. Therefore part preparation is crucial in order to achieve satisfactory results. In my case I am still experimenting with surface preparation. Some of my aluminum is finished with a 400 grit brushed finish, sometimes it is sandblasted (careful with the blasting, there are things to consider when anodizing blasted parts) and sometimes I polish the part. I have found my best success has come from polishing. Success being defined as the colored dye really “pops” on the polished parts. Since most of my anodizing involves parts I machine on my lathe I use the following to obtain my desired surface prep.

When I am not using my lathe to spin the part while I buff it I am using a 1/2 hp 8 inch buffing motor bolted to my drill press.

  1. With the part mounted in the lathe and spun at 1620rpm I sand with 100 grit sandpaper
  2. Then I move to 220 grit
  3. Step it up to 320 grit
  4. Move onto a fine grade aluminum oxide Scotchbrite pad
  5. 0000 grade steel wool
  6. Then I remove the part from the lathe and put it through some buffing wheel abuse starting with a 8” sisal wheel lathered with black buffing compound
  7. Onto the spiral wheel with a brown compound bar
  8. And I finalize it with a loose buffing wheel coupled with white compound

By this time the part has a mirror finish and any more surface prep would be a waste of time

This is showing the 3 differnt buffing wheels I use along with the compund I use on each wheel. I dedicate wheels to only one compound so that I prevent any cross contamination.

This is the surface prepped trigger and receiver after I performed 3 stage polishing on them. Almost too pretty to anodize at this point.

2. Cleaning of the part

The first 2 stages of the cleaning process is done with acetone first and then the parts gets a good wipe down using wax/grease/oil remover (acetone based).

In my uneducated opinion I would say that out of all the stages to anodizing the cleaning phase is the most crucial. The cleaning process will determine the success of how well the part will dye to the desired color. The parts can have NO grease, oil, wax, or buffing compound on them. There are multiple ways to ensure the part is clean. Again I am going to tell you how I do it, there are other options. The process starts by using a clean cloth and wiping the entire part down with acetone to take the initial grime off. Next I move onto a professional body shop wax/grease/oil remover solution. I use another clean cloth and, again, wipe down the entire part.

This is the SP Degreaser in powder form. The stuff I order is 2 lbs. worth which is enough for 4 gallons of distilled water. The package states to heat to 190 deg F however I find that 160 deg F works.

Now it’s time to start the serious cleaning. I use a product called SP Cleaner/Degreaser. It is a biodegradable product that is used in cleaning food processing equipment. I heat the cleaner to 160 degrees F and then submerge the part in it for 5 minutes. It’s now time for me to peek inside the back door of the house and perform a quick visual to see if the wife is anywhere in sight. No? Good! Now I take the part and quickly move to the kitchen sink. It is here where the next phase of cleaning takes place. I need to move fast because the wife could be lurking and end up silently standing behind me while I contaminate her kitchen with  my “disgusting garage dirt”. It is here where a pair of nitrile gloves are put on and then washed with hot soapy water. It is at this point where the part no longer gets touched with ungloved hands. I use dishwashing soap and a nylon brush (and sometimes a toothbrush) to scrub and scrub the part. After cleaning with dishwashing liquid the part then needs to pass the water break test.

Because many of the parts I work with are fairly small I am able to work using just a 1500watt electric kettle. Here I heat the SP Degreaser to 160 deg F and suspend the part in it for 5 minutes. I keep the used degreaser and just pour it back into my jug. The sediment that has been cleaned from the part is visible at the bottom of the kettle.

The water break test is a test which involves holding the part underneath a stream of water and inspecting how the water runs off the surface. If you have ever washed a newly waxed car you will notice that the water beads. Waxed car = beaded water, this is good. Cleaned anodizing part = beaded water, this is BAD! The water needs to cover the part in almost a mirror type finish; it needs to flow off the part in one continuous sheet. This is the indication that the part is free from wax, oil, and grease. This is good.

Here I head into the house to clean the parts with dishwashing soap and hot water. At this point I put on a pair of nitrile gloves and wash them first with soap and water. I scrub until the parts pass the water break test. After this cleaning stage the parts never get touched with bare hands. Only things that come into contact with them are gloves and clean aluminum hanging wire.

If you have choosen to clean parts in the house and have been caught by the wife in the kitchen then you are probably in one of two positions. First one is she is mad and kicks you into the garage cause she thinks that is punishment in which case give me a cyber high five. The second case is she now makes you do all the things you should have been doing other then anodizing in which case I did warn you to scope the place out ahead of time. And no…there is not a 3rd option here cause there is no way she is happy.

I buy the De-ox and De-smut in liquid concentrate form and mix it with distilled water.

So now that I am back in the garage I sprits the part down with distilled water from a spray bottle I keep close by. The part now gets dunked into a container filled with aluminum de-oxidizer/de-smut solution. The part gets a 5 minute soaking in the bath at 72 degrees F. Oxidation is known as rust on ferrous metals. In the case of aluminum it too oxidizes however its absence of iron makes the “rust” harder to see. De-oxidizing the part in the solution helps minimize the oxidation layer on the aluminum. Some aluminum contains copper, silicone & magnesium which, when anodized, would produce smut therefore the de-smut solution helps rid the aluminum of these unwanted metals. The de-oxidizing and de-smutting is done at the same time in one chemical solution.

I pour my De-ox and De-smut into a clean container. I store the liquid inside the house therefore it has a temperature of around 72 deg F. I soak the parts at this temperature for 5 minutes.

It is at this point that I deem the part to be free from demons. I do not know if my cleaning process is under kill or overdone however I appear to be achieving success therefore there’s no need for change at this point. The process of prepping the part and cleaning it is by far the most time consuming aspect of the whole anodizing process however it pays off in the end. I often say that is you spend 5 minutes completing a project then it will look like you spent 5 minutes completing the project.

So this completes the first 2 processes of the anodizing procedure. To view the remaining steps you can check out The Full Monty: Part 2

I figured it was about time to set up my anodizing line so that it would be more useable. I had played with anodizing awhile back and really struggled. I was able to succeed at it however it was a result of more luck then chemistry. Anyway…I decided it was time to revisit the project and hammer some knowledge into my head. I am pleased to say that with the anodizing process I have gained a solid understanding of the chemistry, and factors involved, and therefore have been able to reproduce consistent results using proper set up and calculations.

The type of anodizing I have been doing is considered LCD (low current density) CC (constant current) Type II anodizing. I want to be able to anodize some of my machining projects and since the size of my lathe determines the size of project I don’t need a huge tank to perform the process. Right know I have set myself up a 4 gallon bucket which is plenty of room to perform the current (pun intended) tasks.

For those of you who are new to home anodizing the process is probably unknown. For myself I separate the process into 2 sections. First one is the process of anodizing, the second is the process of dyeing which is what gives the aluminum its color. For now I have directed my attention to the anodizing portion.

I have been practicing my aluminum TIG welding on scrap metal and decided it was time to put my practice to use. Using some 6061 aluminum flat bar and round bar I welded up a hoop to sit on top of my 4 gallon bucket. The hoop allows me suspend my parts into the anodizing solution as well as holds my agitation lines. I welded up a bracket in order to clip a 150 watt aquarium heater onto the side of the tank. Then I built some 6061 aluminum cathodes to aid with the “negative” side of things.

I was able to track down a used power supply which was in great shape. The unit I am using is an Astron VS-50M which is a 50 amp 15 volt variable DC power supply. It has plenty of jam to perform the smaller projects I am anodizing.

Sample dye colors on aluminum knobs

With the tank set up coupled with the massive amounts of research I had done I started turning out great consistent, well controlled results. Since I run small parts through the system I rely on a DVOM to monitor my current draw which allows me to dial in the power supply.

Once the part is anodized it can then be dyed to any color. I have 6 dyes, some of which I have sampled and some that still are waiting discovery. The process of dyeing is nothing more then soaking the part in the dye tank, at the right temperature, for anywhere between 1 to 15 minutes depending on the shade of color desired. Once dyed the aluminum can then be sealed. I have experienced some blotches with some colors which I believe is a result of poor cleaning of the part. The cleaning process is incredibly important to the success of the entire operation. I have a cleaning sequence I perform however it needs some tweaking.

Overall I am pleased with my results. The setup is compact and performs its function. Overtime I hope to build up a sample library of anodized finished, colors, and dye techniques to be able to reference to.