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Hellbender
02-26-2004, 12:51 AM
I'm building a locking mechanism for a project and have a question....

Think of an old fashioned simple sliding door deadbolt with a sliding lock bar that will be UNlatching under a fairly heavy load. The total slide bolt travel is .400 inches. The load direction would be like a heavy door with sloppy hinges (i.e. downward on the end of the slide bolt)

Two parts... the lock slide bar (has to be stainless steel for shear strength issues) and part 2 is the bore it rides in (needs to be either aluminum or stainless steel for corrosion resistance, i.e. outdoor conditions, possibly some occasional salt water splashes.

The latch will only see intermittant use, i.e. 5-600 cycles over 5 years (maybe once or twice a week) and little maintenance.

I prefer NO wetlubrication (may not be possible, maybe use dry film lube?) as it will collect dirt and may cause friction problems if it gets on the lock/load end.

Any combination of common alloys (304SS, 316SS, 5052, 6061) that would work in this system w/o galling or galvanic corrosion issues?

Would 304SS on part 1 and 316SS on part 2 be different enough to not have a galling problem?

Would 304SS on part 1 and Aluminum for part 2 have galvanic action problems?

Thanks for any input.
HB

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NRA Lifetime Member

Evan
02-26-2004, 02:52 AM
Aluminum won't cut it in that application. Pure 1000 Al will not corrode much but is soft as butter. Use silicon bronze. The same stuff the the Little Mermaid in the harbor in Copenhagen is made of. It will make a nice match for the stainless steel. It develops a nice hard patina and won't interact with the SS significantly. The electrochemical difference is around .100 (max allowed should be under .250) and the metals are not similar so galling won't be an issue.

x39
02-26-2004, 08:56 AM
I think Evan has the right idea, but if it must be stainless, I'd suggest looking into what materials firearms manufacturers use in stainless semi-auto handguns.

NAMPeters
02-26-2004, 10:56 AM
Cres/Aluminum combination is a no go, galvanic corrosion will eat it up. This is a good application for the use of Nitronic 60 stainless steel. It is a nitrogen modified 300 series CRES designed for anti-galling properties. Works great dry, no lube. Designed a number of missle fin locking mechanisms with the stuff and had good results. Note you will have more motion in your devise than just using it, there will most likely be motion just from the vibrations from a shaking door etc. thus galling is a big issue. Dry lube will waer off over time under such conditions. JMHOBOE

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Neil Peters

Cass
02-26-2004, 11:55 AM
Any old stainless and brass you find will work fine. It is a waste of time and money to go find special types of these materials. Aluminum is a bad choice.

Evan
02-26-2004, 12:11 PM
I wouldn't use any old brass. Brass contains up to around 30% zinc and will corrode. High silicon bronze contains less than 1.5% zinc.

gunsmith
02-26-2004, 07:50 PM
Oil impreganated bronze bushing material is available at almost all bushing and bearing suppliers. I use it on a regular basis in conjunction with stainless and it has caused no problems I am aware of. Salt is a big issue for most of the applicatins as well and still no problems even under extreme loads. Because of the oil impregnation it never needs lubrication either.

ibewgypsie
02-26-2004, 07:59 PM
A little far off from what you are doing, Voit didn't specify the lubricant in the vari-pitch props on a hydro plant.

Service shop tried to put it together dry, they had about 100 tons of jacks trying to pull it back out. It pulled stainless balls out of the metal tolerance fit the size of my thumb.

Major screwup. All stainless needs lube.

David

wierdscience
02-26-2004, 09:22 PM
316 and Nitronic 60 is the choice material for salt water,304 will and does pit and frost in salt water,I always use stainless with 932 microcast bronze bushings,I never have problems with that combination.

Aluminum and stainless in salt water is a no-no unless the aluminum is hard anodized,even then I don't like it.

Cass
02-26-2004, 09:24 PM
You could make the bushing out of nylon if you make the shaft size large enough. If you use nylon or some plastic reinforced with glass you can use aluminum. One drop of oil on nylon goes a long way. With your proposed level of use "any old brass" will work fine in this not very high tech or heavy use application. Keep it simple ....is a good rule.

Hellbender
02-26-2004, 09:37 PM
All- Thanks for the replies, I've learned a lot.

I looked up the Nitronic 30/60 and silicon bronze 1.5% I think both would work very well. But the price is pretty bad on both, and I can only find the SS alloys in round bar stock (need 3/4x1" rect.).

What if I hard anodized the Alum block and/or hard chromed the latch?

First, would it work; and 2nd what would the cost be for small parts (2x4x1" and 3/4x1")on the 2 processes? Lot size would be 100-250 at a time.

Thank again for the help, the combined knowledge on this board never ceases to amaze me.

HB

wierdscience
02-26-2004, 10:28 PM
Cheapest I ever had a part hard anodized for was $1.15 each in 1500 quanities.

Try looking for the 316 stainless,cheaper by far than the nitonic.

NAMPeters
02-26-2004, 11:48 PM
A further thought is if you go the CRES route electropolish your parts when finished. This will definately increase the corrosion resistance by removing tramp iron and removing surface finish peaks. Nitronic 60 has better galling resistance than 316SS. JMHOBOE

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Neil Peters

[This message has been edited by NAMPeters (edited 02-26-2004).]

Evan
02-27-2004, 03:42 AM
Hard chrome won't do the job. Hard chrome is primarily for wear resistance, not corrosion resistance. It has microcracks down to the substrate and in wear applications this is a good thing as it holds oil. Without oil it will allow salt water to penetrate to the substrate material. Hard anodizing of aluminum will work pretty well but is expensive enough that you might as well use bronze. If you go the hard anodizing route you will want to specify the thickest layer possible. Of course that will raise the cost. Also, it will mean special attention to design. No sharp edges or corners, they must all be radiused. No small interior holes and the dimensions will grow up to .015" including the ID of holes becoming smaller.

lynnl
02-27-2004, 12:14 PM
When stationed on Guam I did a lot of scuba diving, and explored lots of underwater acft and a couple of ships from the WW II Marianas Turkey Shoot. Most were Japanese. I don't know if they were stainless or chrome plated, but when you brushed away all the sediment and crust from the landing gear struts on some of those planes what you saw looked as new and shiny as brand new. There was no corrosion or tarnishing whatsoever. None.

Hellbender
02-27-2004, 09:35 PM
I thick we'll bite the bullet and use the silicon bronze with the SS pin.

Thanks again for the help.

HB

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NRA Lifetime Member