Technical & Reference Section > Tech and Restoration

Adventures in Anodising

<< < (7/14) > >>

griff:
Speak to Steve Animal about re-riveting calipers, he's done a bunch of 'em

Chris123:
Use titanium wire for connecting parts, it doesn't erode, doesn't need stripping after every use and makes a far better connection.

A much better way of doing it to to use constant voltage rather than constant current, you don't need to **** about working out surface area then. Although you would likely need a better setup with a pump to circulate the electrolyte.

What ratio of acid are you using and what temperature is the electrolyte at?

Avro:
Moving house today so my anodising should recommence soon.
Thank you for the input Chris. I read up quite extensively before beginning these experiments and found a concensus that constant amps was the best way? Using constant volts would be easier, and require a more simple set up, but would it be any better? As I have said I am finding my way as best I can and very happy to make mistakes and look stupid!

The electrolyte is at around 20 degrees C. I bought a fishtank heater, thinking I would need one, but this has not been required yet. A fishtank pump was also on my list to buy but I don't think I need it, at least not for my little tank. When I set up the bigger tank then I think I may get a pump. I Suspect that larger parts my harbour more bubbles so agitation will be required, it certainly will do no harm.

I am using 20% acid solution.

Avro:
*waves* Right, back in the game.
A few well earned days off work and back into the lab, or as it is now called 'The Man Cave'.
I had planned to ease myself back into the anodising with small parts again. I picked up a Hatta MX100 head set, for my Laserlite, off the Museum recently which was raw with the remnants of gold anodising visible. My plan was to anodise the cups and top nut black. However this will not be possible as the cups have steel inserts to form the bearing surfaces. I will have to paint the headset, never mind.

So, I had to tackle one of the larger items on the list and set up a bigger tank. This is a journey into the unknown as I do not know what difference the larger tank volume and distance between cathodes will make. Anyway, only one way to find out. One fun thing was making the acid solution. Into a 10 litre bucket I put around 7.2 litres of de-ionised water and then, very carefully, added 1.8 litres of 96% sulphuric acid. When you do this you get a scarey roar when the acid hits the water, quite alarming really! My set up is just as before, no changes there.

The first victim was a raw Sugino chainwheel for my Laserlite. As the Laserlite should have a black finished chainwheel with machined finished teeth I had a go at masking. This is done with polyester sticky tape. Here is said chainwheel, sanded, polished and masked, ready to be cleaned and etched.
[ Attachment: You are not allowed to view attachments ]

In it went into the caustic soda solution for around 5 minutes. If fizzed immediately and very aggressively, I think I have made a stronger solution than before. All was well and the wheel took on a grey-gun metal finish. I forgot to get the nitric acid solution (it can be tricky as nitric acid is for restricted use only) so I had to desmut as best I could by hand in de-ionised water. This is fine but dipping in nitric acid is far, far better, that much I have now learned. Here is the wheel just out of caustic soda solution. The colour change is the imputities sitting on the surface.
[ Attachment: You are not allowed to view attachments ]

Then into the anodising tank. This is where things were very different from my previous attempts. My acid solution is 3-4% stronger than before and the part started to fizz instantly. I had not observed that before. Also, when the power was turned on, the voltage did not ramp up in the same way at all. I had very accurately worked out the surface area, quite easy this time given the shapes, so set the amps accordingly. The voltage slowly ramped up to 5.3v and stayed there. Before I was seeing voltages typically between 12 and 15v. I do not know why such a low voltage. Something to do with volume of acid or distances between the part and the cathodes I guess. Anyway I let the experiment run for the allotted time. Then into the dye. Then to fix or seal the anodised layer. Before I was using the temperature method where you hold the part in water at around 90 degrees C for 20 minutes or so. This obviously impacted on my electricity bill and is terribly inefficient. So, I tried a chemical that allows fixing at room temperature and it worked fine. It adds a complication as it is partially consumed each time it is used. This alters the ph of the solution and the efficacy of the process. You have to add more chemical to maintain the correct ph, I think this in turn keeps the concentration within parameters but I am no scientist!

Here is the chainwheel out of the dye.
[ Attachment: You are not allowed to view attachments ]

As you can see the masking failed. Next time I will spend much more time on this element. Not to worry as removed the anodising on the teeth using a fine paint brush and caustic soda solution and, voila, a black Sugino chainwheel with machined teeth detail. I am pleased with it and the job is done.
[ Attachment: You are not allowed to view attachments ]

In2bmx:
Nice work  :4_17_5:

Navigation

[0] Message Index

[#] Next page

[*] Previous page