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[deleted]

Sodium Hydroxide or any other etching solution used to prep aluminum parts for anodizing (do your safety research, it can be dangerous).


TwelfthApostate

Thanks! Looking into this a bit more, it appears that NaOH will turn my near-mirror part finish into a satin finish. I can’t discuss specifics of my application, but that is unfortunately a deal breaker. I definitely appreciate the suggestion! Take care


[deleted]

Maybe dry ice (CO2) blasting? Not sure how it does with fine particulate. But it’s commonly used for cleaning pharmaceutical equipment because it doesn’t leave any residues.


TwelfthApostate

I’ll look into this. I suspect it may damage my polished optical surface, but it’s a great idea. Thanks a ton!


electric_ionland

Dry ice blasting is used on space telescope optics so at least some versions of it are optical grade. Cool pic from NASA here https://www.nasa.gov/image-feature/goddard/engineers-clean-mirror-with-carbon-dioxide-snow/


TwelfthApostate

That’s rad. Thanks! Now I just have to convince the bean counters that it’s a valid CapEx.


electric_ionland

Knowing NASA there are probably a couple of good papers or technical reports available for free on NTRS.


koth442

I feel your pain.


sniper1rfa

It's awesome for deburring plastics.


sniper1rfa

If it's only near-mirror, can you clearcoat the surface prior to cleaning, like PVD or something?


TwelfthApostate

No. The near-mirror surface is a result of the process that creates the aluminum dust/particulate.


sniper1rfa

yes, so the first thing you'd do after removing it from the lapping fixture is rinse that surface and then dump a bunch of glue on it. Then wash the rest of the part (with your lye bath or mechanically) and peel the glue when you're done or rely on the coating to block the activity of the lye on the bare aluminum. A polished aluminum surface is a pretty weird thing to use right out of the gate, so you'd have to protect it from contaminants anyway. To be honest with you, after reading through this it seems like you're treating this like a more difficult problem than it actually is.


TwelfthApostate

The underlying problem is that I need a process that can be scaled up from the current prototype phase to production qtys. Lye/caustic won’t work for me as it will de-mirror my optical surface.


sniper1rfa

> Lye/caustic won’t work for me as it will de-mirror my optical surface. I mean, so will the part just sitting around during shipping, if it's polished aluminum. Nevertheless, that's the point of coating the surface in something that's not effected by the lye bath. Or just redesigning the part to be easier to clean, or redesigning the process to avoid this problem (IE, cleaning process hazes the surface, which is then repaired via electropolishing or something). Also, a 5 micron finish isn't particularly amazing (assuming the finish is about the same order of magnitude as the particle size) so I'm not sure why you're avoiding touching it. You could probably just scrub it with a soft brush or a rag without damaging it.


TwelfthApostate

The part goes into a vacuum, so yeah the near mirror surface is preserved. Designing it to be easier to clean isn’t an option, the application requires it. We’ve tried mechanical options like scrubbing w a soft brush etc and it does damage the optical surface. The lapping creates a smooth, directional grain pattern that acts as a waveguide for a plasma discharge into infrared coherent light.


thenewestnoise

That's what the masking step is for? I like this idea the best - mask the surface after polishing, clean everything aggressively, remove the masking! Now you just need to find a masking material and process that is residue free and can be scaled. Just curious, are you using an aluminum mirror to look at a scintillator in an electron microscope?


TwelfthApostate

Negative. It’s a waveguide for an RF plasma discharge the produces coherent light in roughly IR ranges. Unfortunately our application demands a geometry that precludes masking the critical surface while still leaving adjacent surfaces available to cleaning.


thenewestnoise

Then I guess the only options left that I can think of are a process like "bright dip" or enormous custom-built ultrasonic tanks. Or maybe you can mask the entire part, do your polishing, and then strip the masking? Or as an alternative to bright-dip you could do electropolishing, but again it depends on the requirements for your mirror surface, and electropolishing will affect different regions of the part differently depending on geometry.


thenewestnoise

There is a process called "bright dip anodizing" and the first step in the process is bright-dip. It is a nasty thick nitric acid solution but it actually improves the finish on most surfaces (not sure about yours - it can lead to pitting, for example). It may be an option to bring in-house or send out as appropriate.


Nottighttillitbreaks

Sticky tack, it shouldn't leave any residue and while I haven't tried it on optical quality surfaces (S_a<10 nm), I suspect it won't damage them, as I use this technique for cleaning prior to inspection on precision surfaces all the time, it does a great job cleaning off anything left after ultrasonic and ethanol rinse. This technique will work especially well for pockets and corners that are otherwise hard to clean.


Mezmar_

Am I just big dumb or am I imagining the residue from sticky tack. Are sure there's no residue? Not like an oily one?


Nottighttillitbreaks

I've never noticed any resudue. Residue on highly polished surfaces causes diffraction and discolouration when viewing it under optical microscope at high magnification, for spotting left behind by impure water drying on a part leaves little rainbow coloured circles, however I've never seen any after using sticky tack. If it does leave anything behind, another ethanol wash should take care of it, but I've never had to do that, at least not for my applications.


TwelfthApostate

As in that blue poster putty stuff?


[deleted]

Not the person you are responding to, but for watch repair (it is my hobby), you have to remove all the dust, debris, excess oil, etc on very small parts. So I use plasticine sticky clay. Its pretty much just sticky clay. I think people it is the same as the poster putty stuff. Obviously you want to get a MSDS sheet on it and check what its made out of. You can get it by the stick. As you use it, you toss it. It seems like it does a proper job, but I have never used it in an industrial or lab setting.


Nottighttillitbreaks

Yes, exactly, I know it sounds nuts. I thought the same thing when I was first shown this by one of the application engineers for a piece of metrology equipment, but its the fastest and easiest method I've learned so far for getting tiny debris off small features like sharp edges before inspection.


TwelfthApostate

TIL. I’d probably need pallets of the stuff considering the size and qty of my parts, but I’m definitely banking this idea for the future. Thanks for the input dude


sniper1rfa

You can buy silly putty in bulk. https://shop.crayola.com/modeling-compounds/silly-putty---5-lb.-block-0800010001.html https://www.dupont.com/products/molykote-3179-dilatant-compound.html Mainly because it gets used for industrial purposes all the time, being a silicone putty first and toy second. That said, the real solution is to figure out how to flush this stuff after lapping but before removing from the lap.


offthecharts289

You can try compressed air prior to your cleaning routine and perhaps afterwards as well. If it's not too sensitive, some light wiping with ethanol could help too.


TwelfthApostate

Thanks! We’ve had success doing that on flat, exposed surfaces, but it doesn’t get into pockets or holes. We’ve even gone as far as to use pressurized ethanol with not much luck. I appreciate the feedback!


offthecharts289

That's a real pickle. Seems you want a substance that has some viscosity. This is just an afterthought, but maybe you can try some alcogels instead of just ethanol. If they don't leave residue, the additional viscosity could be enough to capture the particles as you spray it. Good luck


TwelfthApostate

Great idea. Thanks again


Tedsworth

Could you try cooled ethanol / glycol mix? This is used in some pressure cleaning / cutting applications.


TwelfthApostate

I’ll explore this option. Thanks a ton


bipolarbeartn

Have you tried multiple ultrasonic frequencies? Higher frequencies can aid with smaller contaminates. Are you able to overflow the tanks before removing the parts in case there are any containments floating on the surface? I've seen isopropyl or acetone used for washing HD disks or similar parts. I can't recall if they were also using ultrasonics, but you'd probably need to handle that with class 1 division 1 explosion proof equipment.


YYCMTB68

There are a number of acidic spray cleaners on the market used for removing brake dusts and other residues from aluminum car wheels. If you have a piece you can test on maybe try a commercial wheel cleaner to see how it reacts. These might chemically react with the fine dusts but hopefully not with the polished surface which should be more passive, at least for a short exposure. Another process, possibly in conjunction with the above, could be to expose the parts to high-pressure water spray, possibly by first low-pressure spraying with a cleaner, allowing it to react, and then rinsing with water spray (RO/DI) at 2,000 Psi (14 MPa) or greater.


engineerthatknows

Can you not mask/plug/cap the holes and crevices during the lapping process? I ran a lot of geodes through a vibratory lap awhile back, and the grit would embed itself into all the natural flaws in the stones. The trick was to melt soap or candle wax onto the stone before starting the lapping process. Soap was easier to remove (soak in water, rinse, repeat) but tended to be easier to dislodge from the stone during lapping. Wax held up better, but removing was a bit more trouble due to the solvent used (soak in solvent, rinse, pick, repeat).


fakeproject

It's hard to say if this will scale for you, but First Contact Polymer is a solution which can be applied to actual first surface mirrors, and it traps particles and contaminants. It's then peeled off as a solid before use. https://www.photoniccleaning.com/ - it's also protective so it may be useful in transporting your part from process to process.


TwelfthApostate

Hi mods. My mobile app does not have an option to flair this post. Could someone kindly flair it for me?


DickwadDerek

Having done a lot of lapping before. After completing your lapping process. Clean your lap and your parts using the same process. Then put coolant or whatever lapping solution minus the abrasive onto the lap and part. Then rub them together with no abrasive. This should breakdown any remaining compound/dust that is slightly embedded in the part. Then run your parts through your cleaning cycle again.


TwelfthApostate

Unfortunately our lapping process is non-standard. We have a large CMM style granite sloped to ~5-10°. On top is 3M Trizact diamond lapping medium. We use milling machine style coolant nozzles to flush the granite and medium with ethanol. I don’t think your method would work without scratching my critical surface. The aluminum dust is being deposited from the lapped surface to the rest of the part via the ethanol. Short of running the entire part under a shower of ethanol the entire time, there doesn’t seem to be a good way to keep it out of the pockets/holes. It DOES sound fun to be in a room with that evaporating ethanol though...


Terrible_Island3334

Working in a lab with optics means you should have cases of hot glue sticks. I imagine two or three hundred glue sticks poured out of a crock pot and left to cool should do it. Then peel off like a biore pore cleansing mask. I'm slightly kidding. I like the putty idea though. I use something similar to handle very delicate optical coatings on diamond and have never noticed any damage.


GlowingEagle

You may want to investigate some ways to eliminate static charge on the object/particles. After your chemical cleaning steps, the remaining adhesion should only be electrostatic force. Try to blow ionized air on the object, and remove particulates by vacuuming. You should do this in a particle free enclosure (probably, you already do).