Removing sharp perforation edges on stators with ferric chloride

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Regardless of what we call the abrasive, the important point is to use liberal amounts of water to keep the abrasive from clogging up. A soft backing for the abrasive system, such as a heavy sponge or a soft grout float will allow you to break down the edges without the use of chemicals.
 
Electropolishing AL

Using NaOH (lye) will usually leave a grey or black smut on the aluminum... it will etch but not polish the edges... maybe not the effect you want...:xeye:

Commercial epolish uses decidedly unfriendly acids and high current density for the desired effect... typically Sulfuric/HF solutions:bigeyes: ... or phosphoric-chromic-sulfuric-nitric mixes at 100 - 200 asf... not gonna post any formulas as someone will get hurt...

Brite dipping would also work... but again... find an anodizer and let them deal with the hazards...

Lye won't form an oxide, it'll keep etching till all the OH is exhausted and will leave the aforementioned smut.

Best to either find a commercial plating/finishing shop and see if they'll do it... or live with a crappy half-baked NaOH etch and then sand the results... <- would not be my choice.

Why not pour lye down the drain? That's what Drano is... and most other drain cleaners (excepting the sulfuric acid or enzyme types)... won't hurt pvc or copper plumbing... and it'll clean out all the hair and organic crud from years of mis-use...

btw... emery IS aluminum oxide....:D http://en.wikipedia.org/wiki/Emery_(mineral)

Emory is a university in Atlanta Ga.

I'd leave the chemistry to chemists..

John L
 
Yeah, I'm now thinking of just countersinking every hole and sanding it with very fine whatever-paper.

However, I performed an experiment in which I dipped an aluminium candle holder in lye. The black smut readily washes off and the resulting surface does not look corroded.. In fact it looks pretty good.
 
etching

If it works, and gives you what you want.. go for it...

The smut problem depends on the alloy... low alloy Al (6061, 2000 series) aren't too big of a problem, especially if you can wipe the smut off and no further finishing is required. You can also polish up the surface afterwards with Softscrub (w/o the bleach) or even Ajax or Comet.. (or a pumice slurry)

John L.
 
bigwill said:
Isn't Al just Al? What is it alloyed with?


Not at all... pure aluminum is almost never found... most is 6061, alloyed with copper, silicon, and magnesium to make it heat treatable...

http://www.suppliersonline.com/propertypages/6061.asp#Spec

other alloys include 202x copper-magnesium series, 7xxx series, etc... pure Al is extremely soft and of limited use... I believe spec'd 1199... 1000 series is the purest

http://mdmetric.com/tech/alumcomp.htm

All these alloys behave very differentluy and have dramatic differences in tensile stregth, heat treatability, surface properties, etc.

most of the black smut left is copper, iron, silicon and other insoluble crud... it plays havoc in the metal finishing industry w/o the proper post treatments (hence the nitric, HF, etc. ) post-etch rinses

FWIW

John L.
 
Auplater knows his stuff in this department.

Although I have never seen a "smut" build up on aluminum, that doesn't mean that it wouldn't happen.

As far as pouring lye down the drain, it could simply etch right through copper or brass sink traps. Probably wouldn't, and just leave it bright and shiny?

Guess it depends somewhat on the amount and concentration...

Ok, flush liberally with water when ur done...

:cool:

_-_-bear
 
Those of you brave enough to try the lye method should heed bear's warnings about safety religiously. His suggestion of having a mild acid such as vinegar on hand to neutralize the lye is sound advice indeed. Add the acid slowly, however, as the solution will froth up violently if you add the vinegar too quickly. Keep adding the vinegar a little at a time, until the solution stops bubbling, then add a bit more. The result will be a slightly acidic (but safe) solution of Sodiun Acetate.

You can obtain lye (sodium hydroxide) in most home improvement centers as drain cleaner. Red Devil brand is the purest. READ THE LABEL before you buy it! If there is anything in there besides Sodium Hydroxide, keep looking. Newer drain cleaning products such as Drano often incorporate additives (even aluminum shavings) to make them evolve gas to "blow" the obstruction down the pipe.

Those of you considering HCl or pool acid for etching should immediately lose that thought. When aluminum is dissolved in HCl, the gas evolved is hydrogen, which is explosive. The fumes from HCl will rust every tool in your shop, not to mention tearing your lungs out.

Most importantly, if you choose chemical etching, work in an open, well ventilated area. Preferably outside. I for one am sticking with wet sanding, and orienting the sharp side away from the membrane.
 
Hi Folks,

anything you do without the assistance of current is etching, which won't round sharp edges as required.

Only electropolishing will do, since it will remove material especially at sections of highest field densitiy and those sections are edges and burrs.

If you cant electropolish the better compromise is sand blasting with fine grid.

Capaciti
 
Probably a very fine grit glass bead is best...

as far as etching for this process.
seems to me etching will work equally on all surfaces, so areas with greater surface area, and that are thinner will be removed by etching before a significant reduction of overall thickness occurs. that would be the burr... thin, and with higher surface area than the flat?

_-_-bear
 
bear said:
Probably a very fine grit glass bead is best...

as far as etching for this process.
seems to me etching will work equally on all surfaces, so areas with greater surface area, and that are thinner will be removed by etching before a significant reduction of overall thickness occurs. that would be the burr... thin, and with higher surface area than the flat?

_-_-bear


Not exactly... etching is purely geometrically driven... so to a linmited extent, what you say CAN happen. BUT, as the higher relative etching rate (due to surface area) occurs, you also deplete the etchant more rapidly, and it slows back down to the diffusion limited rate of fresh etchant to the surface.

Electropolishing, OTOH, drives the reaction with a differential between the etching process (dissolution) and the diffusion of the active material being etched away from the surface.... the boundary layer of reactants is thinner over projections than it is over depressions in the surface, thereby creating a higher current density on the projections and thus resulting in a differntial etch rate in favor of removing burrs and projections faster than smooth continuous regions....

in case anyone wants to know...:D

John L.
 
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