New process I'm playing with

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BradG

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Very much a test of a new process to me, and rather pleased with the first run.

This is Electropolishing of Aluminium. The first picture shows a rather rough piece of machined aluminium. As you can see, machining marks can still be seen on it.

The second picture shows after a 7 minute process. the reflection is as good as chrome, albeit mottled due to the machining marks. Id imagine if pushed for longer, and tweaking the process this would smooth out quite nicely, though most probably more practical to give it a light sanding while still on the lathe so it's at least smooth to begin with, and of course improve the process with better agitation and even cathodes rather than being one sided.

Quite a learning curve with regards to temperature, agitation, current density, and time frame, but looking good!

My next tests will be on an etched piece to see how well it cleans the base layer of the etch
 

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campzeke

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I was working in the lab late one night when .....

Pretty cool what you can do with water or chemicals and electricity.
 

Terredax

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Is there a benefit to polishing aluminum with this process?
It's fairly easy to sand and polish aluminum the traditional way, so does it save time? Polishing is pretty fast with aluminum. Maybe it would be beneficial for something intricate as not to ruin the detail.
Are the chemicals costly? It would seem there would be specialized equipment necessary for the process and I'm guessing that would be costly?

I would be interested in the complete process.
 

BradG

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take a look at my gallery. The work I do is quite intricate and sanding how you're thinking is not possible. That would only work on the surface. If you're intending on doing further processing such as plating or anodising, then the last thing you would want to do is go near the aluminium with a polishing compound with a buffer wheel.

I wouldn't recommend this to anyone not comfortable with working with strong acids, as this is 85% Phosphoric acid, heated to 167F
 

BradG

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Tonight's test:

The left side has been electropolished, right side mechanically. Note the brightness of the cut lines on the left side. That's exactly what im after.. polishing the hard to reach parts normally the sandpaper skips over.

This still wasn't a perfect run as I only electropolished it for 3 minutes instead of 7. Mainly due to putting my thumb on the 240 degree hotplate! soaked my thumb in a jug of cold water for the three minutes before deciding to stop the process and go get a bag of frozen veg to take the pain away

Made a note not to touch the hot plate again. Stupid man.

I need to build a jig to suspend the piece accurately in the middle, that's tomorrows joy. On a plus side, I made a bubble diffuser out of a section of LDPE pipe which the acid won;t dissolve so im getting much better agitation. Better than dissolving fish tank airstones anyway!

I will persevere
 

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Dale Allen

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Brad, this looks like a process similar to what is referred to as a 'bright-dip' pre-process. I have been heavily involved in getting some 6061 machined tools bright dip anodized in various colors.
It seems there are not as many places in the US doing this since apparently the EPA has cracked down on the disposal of the chemicals.
What little I know is that it uses a very strong acid, phosphoric usually, and it cleans or polishes the surface at the molecular level. Like what you are doing here. I just got some samples in today of a green that is a very nice shiny color.
I know it is not necessary to tell you but, be careful with that stuff!
 

BradG

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Brad, this looks like a process similar to what is referred to as a 'bright-dip' pre-process. I have been heavily involved in getting some 6061 machined tools bright dip anodized in various colors.
It seems there are not as many places in the US doing this since apparently the EPA has cracked down on the disposal of the chemicals.
What little I know is that it uses a very strong acid, phosphoric usually, and it cleans or polishes the surface at the molecular level. Like what you are doing here. I just got some samples in today of a green that is a very nice shiny color.
I know it is not necessary to tell you but, be careful with that stuff!

Hi Dale. Just to clarify, Electropolishing is NOT bright dipping.

Bright dipping is nasty stuff. A blend of Phosphoric, sulphuric, and nitric acid, which is heated to near boiling. It has to be kept in a double walled 316 stainless tank, and cannot be vented to the outside without first being treated with an air scrubber. the fumes being put out are highly corrosive. The baths are also difficult to regulate and maintain as the Nitric will absorb moisture from the air increasing the volume. If the concentration of Nitric falls by a small fraction the parts will come out etched instead of polished.

Electropolishing uses much calmer chemicals which can be used at lower temperatures without giving out plumes of nasty fumes. in some instances they can be used at room temperature when using recipes consisting of water, phosphoric, and Ethanol (Caution: flammable though) voltage on this one is a little higher at 30v to 40v , though many recipes voltage range is less than 10v. Environmental restrictions on Electropolishing are much lower, and the air does not need scrubbing, mainly due to no Nitrogen Dioxide being produced in the process
 

Dale Allen

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[/quote]

Hi Dale. Just to clarify, Electropolishing is NOT bright dipping.

Bright dipping is nasty stuff. A blend of Phosphoric, sulphuric, and nitric acid, which is heated to near boiling. It has to be kept in a double walled 316 stainless tank, and cannot be vented to the outside without first being treated with an air scrubber. the fumes being put out are highly corrosive. The baths are also difficult to regulate and maintain as the Nitric will absorb moisture from the air increasing the volume. If the concentration of Nitric falls by a small fraction the parts will come out etched instead of polished.

[/quote]

Yikes!
I had no idea there was that much involved.
It's a wonder anyone still does it.:eek:
Now I know the EPA would give them fits!
 
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