Galling with Stainless Fasteners 1

[MrGearhead]

Design will use Stainless Steel Helical Inserts paired with SHCS. If Stainless Steel SHCS were specified, there would need to be some Moly Lube, etc to lubricate the stainless on stainless pair which would be an issue... BUT... Design cannot use lube. How about a Steel Alloy cap screw? Assumption is zero galling worry and pick up about 20 ksi tensile on the fastener... Only disadvantage is not as corrosion resistant as Stainless...

Please give comments on galling... Thanks.

 

[MikeHalloran]

Okay, no lubricant.
Can you use sealant, like Loctite Pipe Sealant with Teflon?
It lubricates screws during assembly, then cures in place and doesn't migrate. It locks the screw in place, but doesn't require heat for removal. Works great with alloy SHCS, and protects them from corrosion if you use a lot. Downsides to using that much; you get to wipe off a lot of excess, and the smell can get annoying.

Failing that, you have a universe of materials available other than stainless for whichever part is not stainless, subject to environmental and other factors not stated.

Mike Halloran
Pembroke Pines, FL, USA

 

[KENAT]

You don't give much information on the application be it pre-load on fasteners, environment...

There have been lots of threads on galling, maybe one of them will give you what you're after.

http://www.eng-tips.com/search.cfm?...lling&t=&h=&searchSite=2&searchArea=1&d=1&s=1

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[desertfox]

What kind of environment are the fasteners in? You might find that you create electrolytic corrosion between the alloy steel and stainless steel.

 

[btrueblood]

We have had better luck (not galling) with stainless cap screws, in steel and cast iron female threads, since we started specifying strain-hardened screws per ASTM F837 condition CW or CW1. Dunno if that will help with the helical-coil inserts or not (they too might be fairly hard materials).

 

[Tmoose]

Helicoil offers inserts made of the fancy Nitronic alloys. The claim is "Compatible with stainless steel screws," with a few other benefits thrown in.

http://www.stanleyengineeredfastening.com/sites/

http://www.emhartamericas.com/files/downloads/Gall Resistant Data Sht HC1020 rev.5.pdf

 

[CoryPad]

There is much lower concern with galling when the mating part is made from hardened low alloy carbon steel. To reduce risk more, you can use an integral lubricant in a coating on the bolt, e.g. ASTM F2833 or F3019.

 

[drawoh]

MrGearhead,

We use helical thread inserts and stainless steel screws almost systematically. We have no problems with galling.

--
JHG

 

[tbuelna]

If you can use an alloy steel SHCS, why can't you also use an alloy steel thread insert? If there is a galvanic compatibility issue between the thread insert and substrate materials, you can always install the thread insert using some type of primer or sealant.

If you want a readily available cres material for the thread insert and SHCS that will minimize galling, I'd suggest A286. If it is not permitted to use an anti-seize paste/grease, a dry film or silver plating applied to the threads of one part would work quite well.

 

[DAVIDSTECKER]

Have you thought about switching from stainless steel to silicon-bronze?

 

[geesamand]

1) Confirm whether assembly and maintenance will use impact tools or manual wrenches. Impacts tend to cause galling.
2) Consider using larger screws and reducing torque to achieve the same clamping pressure. We use stainless on stainless (304 on 304, 316 on 316) without galling but our torque values are not very high.
3) Consider using another grade of stainless screw. 17-4PH or NAS A286 grade fasteners will be less likely to gall on 300 series base metal. 400 series and Nitronic 60 have their place also - if you can get the inserts in Nitronic 60 you may have solved your problem.

David