Holding pipe when anodising??

It actually does both. It's an electrolytic oxidation, forming an porous oxide coating. IIRC the coating thickness for the typical type II anodizing is less than 30um (1mil) where 1/3 to 1/2 will be buildup.

Buldog clips are nade of steel arnt they ? When anodising the only metals in the bath should be aluminium, titanium or lead . Steel will ruin the bath. Ok for plating but not Anodising.

Yes and yes

I calculate based on 6mA per square cm which is near as dammit the same as 6A / square foot. I then use a constant current power supply to maintain this. For a protective coating, I find that 1 hour is enough, or 2 hours if the anodising will by dyed. (I think that this is the same basis as the '720' rule with 13µm or 25µm thickness respectively).

I have a simple spreadsheet that I use to calculate simple parts as a combination of blocks, cylinders and discs, but it the part is drawn in CAD, I can get the surface area reported from it.

Note that I quite often require >20 volts to maintain the required current. (This is with sodium bisulphate rather than sulphuric acid, but I don't think that should make any difference - the chemistry is the same.). A warmer bath needs less volts, but I've had rough looking coatings if the bath warms up too much. I don't bother with agitation, but then I'm not chasing any sort of specification.

I clean the parts using fairy liquid and Scotchbrite under running tap water. I avoid them drying out between final cleaning and anodising by keeping them submerged in tap water. They have a quick dip in dilute sodium hydroxide (2% solution for 1-2 minutes - long enough for them to be covered in fine, white bubbles), then a rinse with DI water from a spray bottle, and into the anodising bath. They get another spray rinse when they come out, and I seal in almost boiling tap water for ~20 minutes.

I have been pleasantly surprised by the predictability and consistency of the results. It's a lovely way to tidy up aluminium parts.

This is a very important aspect that is seldom mentioned. Some sort of temperature control is required for best results. I've had baths heat up so much it just ate the part without forming any coating.

Brilliant guys, Andy's method very similar to mine but more technical. I have a fish tank heater set at 20 when it's cold and monitor the anodise bath with a thermometer to make sure it doesn't get too warm. I have ice on hand to introduce to an outer bath if it starts heating up. My dye is heated via an old electric camping stove which again I control with thermometer but I know where to set dials for a particular temp. Like Andy I seal in 90 degree water for ½ hour. Looks like I'm almost there but I will start using scotchbrite with detergent soap instead of my normal brush. Thanks chaps I learned a lot from this thread

For degreasing try some non caustic truck wash neat or the Tesco kitchen degreaser , it smells nicer comes in a trigger spray and you d9nt have to buy gallons at a time. A good scrub with an old tooth brush shouldnt damage any polished parts or scotchbright pad if your not worried about the finish then a dip into some hot water and the grease is gone. Its strong stuff so make sure no holes in glove or dry skin will occur. Also a prewash before degreasing in some cellulose thinners also works well on very oily messy parts.

Nobody has mentioned using a de-smut dip prior to anodising bath. Not sure of acid content but it disolves any traces of other metals present in the surface of the alloy that will affect the finish .

Edited By Engine Doctor ( Phil ) on 21/05/2023 10:54:29

I use 10% nitric acid for the desmut / bright dip, but it's getting hard to get hold of these days. I'll have to try HCl and nitrates one of these days.

Why do you think these chemicals are getting harder to purchase fellas? The cynic in me thinks its partly down to all these crazies living amongst us hell bent on earths destruction and another part thinks its possibly the snowflake elf + safety dominated society we live in. Be good to know what others think??

That is something I am interested in, but have never used. What problem does it solve?

I have had a couple of odd results:

Some sheet that displays a streaked pattern when anodised, but confined to the original surface - if you machine the surface, it disappears (this is dyed a pale yellow):

One of the chunks of alloy I have comes out a brassy yellow after anodising, despite the rest of the stuff being OK (From memory, the pieces on the left are H30/6082. The ring on the right is scrapbinium - all anodised together and not dyed.)

I this the sort of thing that de-smutting would address?

(For 'known' alloys, the resuts are consistent).

Edited By Andy_G on 21/05/2023 19:56:08