Removing sharp perforation edges on stators with ferric chloride - Page 4 - diyAudio
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Old 9th July 2007, 11:59 PM   #31
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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.
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Old 10th July 2007, 09:50 AM   #32
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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
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Old 14th July 2007, 08:19 PM   #33
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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?

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Old 15th July 2007, 02:56 AM   #34
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Quote:
Originally posted by bear
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...

John L.
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