Cleaning metal parts
March 14, 2014 4:16 PM   Subscribe

I am beginning the manufacture of small stainless steel parts that I hope to sell. They are back from the machine shop with an oil or lubricant and grit that needs to be completely cleaned off prior to adding an injection molded santoprene (thermoplastic elastomer) part. I have an ultrasonic cleaner available - how do I get them clean before and after the injection molding?
posted by Northwest to Technology (11 answers total) 1 user marked this as a favorite
Our shop uses a water based lubricant. The best way to get it off is simple soap and water (like dish soap). Wash your parts by hand first to get the big bits off, then immerse them in soapy water in your ultrasonic cleaner for a few minutes. Try that before doing any more extensive degreasing.
posted by huckit at 4:30 PM on March 14, 2014

I knew a guy that used to work at a reputable high vacuum equipment manufacturer. He said they had a dedicated dishwasher in the lab for occasional cleaning of high vacuum parts (probably 10e-6 Torr base pressure). Unfortunately I don't recall the common, off the shelf detergent they preferred (I may see someone tomorrow that will know).
posted by tinker at 5:30 PM on March 14, 2014

Soap and water might be a good place to start. Then isopropyl alcohol, in higher concentrations than what is available from a drug store. More volatile organic solvents like acetone and so on are an aggressive last resort. Those are the big three used at my laboratory, but we are far from experts.
posted by Verg at 6:58 PM on March 14, 2014

Came in to also suggest a ordinary dishwasher. I would get a used one off Craigslist and just sit it next to a sink and there you go. Ordinary dishwasher soap is designed to cut grease/oil and not leave a residue (you would taste it). If the dry cycle doesn't dry them sufficiently use a toaster oven. I have used dishwashers for years to clean car parts and cosmoline off old guns, it works better than anything else I have tried.
posted by bartonlong at 7:09 PM on March 14, 2014

Yes for small runs a plain household dishwasher is an efficient parts washer and degreaser for things that aren't damaged by water. If you have lots of part to wash a commercial unit is faster.

Ideally you'd want to rinse the parts first to get as much grit off as you can as metal grit is going to be hard on impellers. A plain parts washer with water based solvent would be best for this step.
posted by Mitheral at 8:57 PM on March 14, 2014

I think the dish washing detergent used by the high vacuum manufacturer was Electrosol. They liked it because it didn't have extras like fragrance that might out gas and pollute the chamber. The right way to clean things there was to send them out to a place like Chemetal (now called _?_) or Persys but that cost tens of dollars per part.

For stainless parts I've cheated by having them electropolished at a plating shop. Expect a ~$80 lot charge for a small box of parts. They'll come back bright and shiny. btw, we cheat-cleaned aluminum parts by having the anodizer do just his acid etch step.

Back to diy, I know several machine shops that like Simple Green. Some even do an alcohol wipe.
posted by tinker at 9:13 PM on March 14, 2014 [1 favorite]

Please don't wash them yourself and dump this pollution down the drain. Sewage treatment cannot deal with machine oil and you'll just be dumping it into some waterway downstream.

Take them back to the machine shop and tell them you expect your parts to be degreased when they are delivered. In the future, Add this to your specifications so you can point to your prints and ask "show me we it says on the drawing covered in machine oil?"
posted by three blind mice at 6:54 AM on March 15, 2014 [2 favorites]

Seconding tbm. The machine shop almost certainly already has this capability. Tell them to do it.
posted by Kirth Gerson at 10:43 AM on March 15, 2014

Please don't wash them yourself and dump this pollution down the drain. Sewage treatment cannot deal with machine oil and you'll just be dumping it into some waterway downstream.

This is not true for the quantity and dilution of oil we are talking about here. Machine oil is actually pretty easy for the critters at the plant to digest (and yes we call the microbes that treat sewage critters). It isn't really any different from most cooking oils at a molecular level and the plants can handle that really , really well. In fact it is a lot cleaner than most oil residue from cooking (the biggest, nastiest costliest stuff to treat isn't car wash runoff or filling station runoff ((all hooked to the plant)) it is restaurant effluent, not due to any change in material going down the drain but the large volume of it without a lot of water to dilute it.

And I can pretty much guarantee the machine shop does have this capability and they are using something very close to a dishwasher hooked up to the sanitary drain-I permit these kind of things on a regular basis. It is cheaper and easier than using solvents.

For more intense degreasing and treating they use some kind of solvent-and this stuff is a nightmare-it is called Dense Non-Aqueous Phase Liquids (DNAPLs) dry cleaning fluid is offender #1-this stuff is toxic to the plant and you and contaminates aquifers/rivers in such a way that is impossible to clean. So you might actually be contributing to a more damaging waste stream by asking the machine shop to clean them.
posted by bartonlong at 12:44 PM on March 15, 2014 [2 favorites]

Does the ultrasonic cleaner have a temperature control? Hot (~50 C) water + 2% liquinox in an ultrasonic tank does a really good general purpose technical clean. If the parts have sharp corners or recessed areas that trap dirt it may require some q-tips/old toothbrush and acetone prior to cleaning. If there are too many parts that are too filthy to handle this way look into vapor degreasing. It is possible to jury rig your own vapor degreaser but I wouldn't recommend it due to safety concerns.

Heck, the hottest water you can manage + Ultra Dawn does a pretty fantastic job on its own.
posted by Dmenet at 6:22 PM on March 15, 2014

I recently had to machine parts in stainless steel that will be put under ultrahigh vacuum. The cleanliness requirement for that environment is very high - a small fingerprint in a large chamber produces enough gas raise the pressure by several order orders of magnitude. My cleaning process is based on recommendations from people with a lot of experience in the field:

Most of the rough work is done with hexane(s). Pure gasoline should do the same job (taken from a bottle, not from a gas station pump). Dip a lint-free clot in it and wipe off anything that you can see with the bare eye. Then let the part soak in it overnight and sonicate it for as long as you have patience for. The second step is a similar soak and sonication in acetone. I may also wipe the parts with isopropanol just before putting them together.

I don't think your requirements are as strict as these, so maybe the hexane/gasoline would be enough on its own? It seems to attack the cutting oil I use quite a bit better than acetone.
posted by Herr Zebrurka at 10:26 AM on March 17, 2014

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