Holding pipe when anodising??

Hi All,

Hope this query finds you all well.

Another question about anodising sorry but here goes. Want to anodise the outside dia of some 38mm tube only about 175mm long but stuck on how I'm going to attach the power? Thought about inserting a 'bung' down the inside but surely theres gotta be an easier better way to do it? Your suggestions would be gratefully accepted ladies and gents. TIA

Bend a piece of heavy aluminium (or titanium!) wire into a 'J' shape such that the bend jams into the tube, and attach your cable to that.

Dave

Hi Bevel, use a nut and bolt with washers to span over the ends, or if your not bothered about the inside getting anodized, use Dave's idea.

Regards Nick.

Both stirling ideas thanks chaps

I have always used Davids method.

My only query with Davids method is, wouldn't you have to take the inside surface area of tube into consideration when it comes to time, current etc?

Sure. Personally I have never done just the outside. Either it hasn't mattered or I have wanted everything coated. It's quite doable to seal off the inside, but it's more work and adds challenges like buoyancy.

Yeah I get that, I'm not bothered tbh I only care about the outside but its not as simple as that is it lol, if only eh.

Bit late for this one but when anidising or plating something like that I use bulldog or market stall clips . Fit the handles inside the pipe and let them expand to grip the pipe . Fasten the power supply to the clip and away you go. Simple and effective.

Yep that'll do it, another great idea thx Fred

I would be a little hesitant with putting any foreign metal into the anodizing bath, even if it wasn't connected to the power. This is another place where a 3D printer might come in handy. IIRC ABS can handle weak sulfuric acid fairly well.

I think Dave’s method would be how I’d do it as well.

Anodising, if I remember correctly, will not work on the full inside of a pipe anyway.

Cheers Will

I presumed Fred's method involved using bulldog clips or the like made of aluminium rather than regular galvanised steel.

Peculiar that it doesn't work so well on the inside tho but its an amazing process and one I'm still trying to master. Its taking me an age mind you and I still get occasional 'white' spots on components where the dye hasn't quite taken.

Has me pulling my hair out, well it would have if I had any lol, frequently and I still have my fingers crossed every time I do it

But what about the spring? Any metal (other than Al and Ti) connected to the anode will dissolve rapidly, it's a well known secret for removing broken taps from aluminum.

As for white spots, it's usually caused by dirt/grease or air bubbles stuck to the part. Cleanliness is extremely important.

Ah yes the spring didn't think of that.

I wash the parts with washing liquid, dry them with kitchen towel, then in between each step I give them a brush off with individual brushes using de-io water. But after the anodise step I wash off with de-io which is slightly ph+ or ph- can't remember which as I read thats better. I also have water aerator set up in anodise bath to hopefully erradicate any sticking bubbles. I never handle components with bare hands either after washing

Anodising will work perfectly well on all surfaces in contact with the liquid, including the inside of a tube. (It's unlike electroplating in this respect.). One just needs to ensure that the bubbles generated during the process don't get trapped anywhere, as this will prevent those areas being anodised.

I wouldn't put anything other than aluminium, titanium or lead in the anodising bath - definitely not steel.

White spots will be where something has shielded the part from the bath for all or part of the process - a bubble, dirt, the point where the part is held, grease spots, etc.

For a tube, provided I wasn't bothered about marks on the inside, I'd just bend some titanium / aluminium wire into a 'J' as above. For more stability, you can add multiple up/down bends to the tail of the J so there are several contact points inside the tube.

"I still have my fingers crossed every time I do it" - do you work out the current required for each part to a consistent current density (amps per square inch / foot / mm / cm)? Do you use a constant current powersupply?

Hi Andy,

I used to calculate area and use the 720 rule, back then I used a controllable power supply but my results were rubbish. I went back to my trusty old Wilko 5 amp battery charger and have much more success tbh.

Obviously I was doing something wrong and got confused with exactly how much surface area needed to be calculated. Say for instance we take the tube I mentioned, do I need to calculate the whole surface area for outer and inner dia's? Also when doing multiple parts do I say calculate whole area for one then times by number I intend to do in one hit? All got a bit confusing so I trialled and error and recorded results of Ines that can eout ok and used them as bench marks if that makes sense. Like I say crossing fingers lol

Anodising will work perfectly well on all surfaces in contact with the liquid, including the inside of a tube. (It's unlike electroplating in this respect.). One just needs to ensure that the bubbles generated during the process don't get trapped anywhere, as this will prevent those areas being anodised.

That’s good to know Andy.

I thought it was more difficult than that - I’m sure I recall an industrial supplier making jigs with internal cathodes running the length of the bore to get full coverage and an even thickness, as well as clever agitation.

But, I’ve never tried at home, and I wouldn’t put it past a supplier to rip us off and tie us in with special tooling 😂😂

Cheers Will

I have never had any problems getting a full coat on the inside of the tube, but then again I have never measured the coating thickness. So I wouldn't be surprised if the internal coating ends up thinner. After all the current density will be far less on the inside. At first that doesn't matter much as the coating increases the resistance, distributing the current to any low resistance areas. But after a while the resistance stops increasing, at least in my setup it quickly stabilizes to a constant current at 20-25V.

And while a constant current setup is the best I have gotten very good results by simply using 12V constant voltage.

Fulmen, surely you mean depth as anodising is not adding to the material but changing it!