Thread: Corrosion protection question

A work problem that members may have suggestions for -

We laser cut small coupons from steel sheet, linish the edges to remove the oxide and the grind top and bottom to size them. However, the edges with the oxide removed seem to rust where the clean up is not perfect (I only realised the clean up was not 100% when I saw it through a microscope, so to the naked eye it is good)
The edge eventually gets painted but before then Inspection complains about the rust, and - because edges are used for location of calibration equipment at intermediate stages - it is important.

I'm trying to think of a way to prevent those edges from rusting once cleaned up that won't take a large amount of time to do or cost a lot. I think the problem is that the grinding coolant is wicking into those fine pits and when the parts are dried post grinding, not all the moisture is removed. Any coating needs to be thin and uniform so it does not interfere with measurement. I wondered about

• a phosphoric acid dip to give a thin phosphate coating before grinding, or
• a quick drying laquer of some sort.
• a burst of hot air to drive any moisture off after grinding before it can rust, but as the parts need to be at 20 degrees C for accurate dimensional measurement, that spins the process out. They would need to be dried and then put in a very low humidity environment to cool down for say 24 hours

Something like WD40 could possibly fix the problem but that causes extra work downstream as the parts then need to be cleaned before measuring (otherwise it causes problems with the gear being used). Inspection are also saying that they should not have to spend extra time to clean parts just because production can't get the process right. (The inspection team are under a lot of pressure at the moment and are normally pretty good, so this is not them being difficult just for the sake of it)

Any other thoughts?

Michael

Hi Michael,

Depending upon how large the parts are if they could be warmed and then placed in a tin with a desiccant that would remove the moisture and keep them dry till needed. I keep small Items that might corrode in a small tin with a bag of silica gel in it.

Maybe a spray with a quick drying solvent, use something like xylene of brake cleaner to carry the moisture away? Nasty stuff though.

Sent from my SM-G973F using Tapatalk

Hi Michael,
Instead of the current material could you use a magnetic stainless? You could still grind it on a mag chuck and maybe no need for paint.
https://www.metalsupermarkets.com/is...teel-magnetic/

cheers, shed

Originally Posted by Michael G

a burst of hot air to drive any moisture off after grinding before it can rust, but as the parts need to be at 20 degrees C for accurate dimensional measurement, that spins the process out. They would need to be dried and then put in a very low humidity environment to cool down for say 24 hours

The simplest would be a burst of dry (don't worry about hot) compressed air. You might need an inline air drier but that would be handy anyway, and immediately put the parts in a sealable container together with a few bags of desiccant. If you wanted extra protection fill the container with TIG Ar.

Dunking in a volatile solvent bath (acetone or similar) post grinding might be an option but this is an additional process step and will have WHS implications due to fumes and flamability.
Air blast might do the job also but again, additional process.
Better to to eliminate the root cause than add steps if possible.
Improve edge cleanup process to eliminate location of rust occurance.
If grinding coolant is causing the oxidation, look into different coolant options.
Cheers,
Greg.

Would it not be appropriate to change the coolant to an oil

Any chance you could change the cutting process to one that doesn't heat the pieces? Water jet for example.

Pete

I never get rust on parts or machinery after machining using coolant,.
It is a possibility that the coolant in the grinder needs to changed if the corrosion inhibitor is not working. The other possibility is that the water has been added to the coolant, the coolant needs to be added to the water otherwise it will not mix properly and some or many of the additives in the coolant wont perform as required.

*Water mixes very well with metho/alcohol..a quick dip may be all it needs...very little residue left behind.

*Hair drier/hot airgun?

If your coolant is in good condition you shouldn't get rust on the parts. What coolant are you using? how old is it? how well is it maintained? if the coolant is old and has been topped up may times with tap water you can get a build up of salts which will cause corrosion problems, i have had this issue at work. might be better to treat the problem and not just slap a bandaid on it.

Originally Posted by Michael G

A work problem that members may have suggestions for -

We laser cut small coupons from steel sheet, linish the edges to remove the oxide and the grind top and bottom to size them. However, the edges with the oxide removed seem to rust where the clean up is not perfect (I only realised the clean up was not 100% when I saw it through a microscope, so to the naked eye it is good)
The edge eventually gets painted but before then Inspection complains about the rust, and - because edges are used for location of calibration equipment at intermediate stages - it is important.

*Clip*

Michael

What gas do you use? i use 4kw fibre laser and pure (medical) nitrogen for 0.5mm-6.0mm steel and pure oxygen (again, same or better than what you get at hospital) for 6mm-15mm+ steel... i don't remember that rust would have been a problem in our products... nitrogen is inert, it just removes the molten metal, and PURE oxygen leaves this glass like layer behind, that protects the cut surface (although its hard to weld on... or so i'm told, i'm not a welder)

But yeah... my first attempt would be a change to the cutting gas

Edit:
i cut off part of the original post, since [spoiler] tag doesn't work on this forum