Thread: Galling

When I started working in Chandleries (another of my incarnations) I was surprised to find out that the fastenings in that dinghy oriented chandlery were 304, so asked the boss.

In that place there was no attempt to mislead or overcharge people - long established knowledgeable customers would have sawn us up into little pieces.

He said that if we stocked the 316 at 316 prices we would have to charge more and someone would slot in underneath with 304 at 304 prices.

Those boaties don't like spending more than the minimum!

It is a similar position (but nowhere near as bad because the 304 is still acceptable in many small boat applications) to plywood where the quest for cheap gaboon ply has pushed the quality down and down and down, so until recently there was little available but unpredictable Chinese ply.

Not that all the chinese ply is bad either. Just inconsistent and because the only clear message coming from the consumer is "cheaper" everyone struggles to oblige.

304 is adequate for many small boat applications.

Best wishes
Michael

OK then, I guess I can tolerate half a lie.

Just a followup on my original post.

I was talking about this with the engineer who is making me my new fittings and he explained why it is that stainless steel is susceptible to this. He didn't call it galling, he referred to it as something else.

He explained that it was because stainless stell is a poor conductor of heat. The heat built up by the friction at the surface doesn't dissipate into the rest of the meterial, but is contained at the surface where it continues to build up to a point where the metal begins to deform and bond.

I was not aware of this property of stainless steel.

I remember from engineering that it happened because the two metals were the same and can be avoided by using two different metals - this is often not a good idea on boats!

But it makes the point that there are other mechanisms at play other than the heat. But the heat might explain why the stainless is susceptible.

MIK

Galling can be broken down into technical terms, well above what would interest most. With stainless steels and most other metals that have surface oxide formations, it's plastic deformation of these oxidizes during movement, that causes the problems.

In a nut shell the surface oxides get scrapped as the parts move against each other. They pile up in the threads, making a tighter fit and increasing friction. As the heat goes up the oxides break down, melt, attach, get sheered off again, then scrapped into a new location and the process repeats. It doesn't take much of this before you have sufficient material in the threads to do one of three things; fill the threads with broken and chewed up bits of oxides, clogging them tight or the oxides melt slightly and solder the one metal to the other or enough heat has been produced to physical weld both metals into each other. This is often called cold welding, but there's nothing cold about it.

Lubrication is the best method to prevent this from happening. Moly based lubricants work best, as does graphite. Dissimilar metals that will work harden at different rates also works, but can have draw backs in the marine environment.

Does graphite cause electrolysis problems? I remember from highschool that it was a good material to make the cathode of a battery from. Or I think i remember.

MIK

Yes graphite does cause electrolytic problems in boats.

There are documented mast failures where a lead pencil was used to mark off the attachment points. It was along these pencil lines that the mast failed......Texta pens are now the norm in mast fabrication shops.

Graphite is a great conductor.

However, used as a lubricant in 316 or 304 ss, it will not cause any consequences. The BEST lubricant for ss is lanoline.

316 (and 304 especially) are NOT good underwater materials for boatbuilding. 316L is better (L is simply low carbon).

The best fasteners are monel followed by silicon bronze, but of course subject to mechanical loadings required.

You've learned well grasshopper . . .

...trying master.......trying, sometimes more trying to others than myself, but at least I try.

Ta, John

Spoke to the fastener business next door and they recommend use of molybdenum paste as the lubricant.

Says more common with nylock nuts as the friction melts the fine particles left over from the threading of the nuts and in effect the nut welds to the bolts, as stated elsewhere on this forum.

And as PAR (and others?) said similar grades more common so use 316 bolt and 304 nut.

Is it called galling because its........ galling?