Sheared bolt supporting alternator

[mjcoon]

Like for like not as strong as a steel bolt, more prone to pinning/gauling and using dissamilar metals will/can cause electrolytic corrosion.

No doubt you are referring to galling Galling - Wikipedia, named after tree galls such as oak apples which look like the microscopic appearance.

 

[GH29]

My background is in ROV's, and every bolt on an ROV is stainless steel. In 45 years I've never seen a bolt sheer on an ROV, and that's with kit that has from 450hp down to 1hp motors.
How much is it usual for an alternator to be rated for? 1kW, which is a bit above an hp.
I'd suggest that if bolts are shearing, then it's because they weren't correctly installed. Ford probably don't use stainless because it costs more.

It isn't a Ford. And it is stainless steel. Lasted 24 years.

 

[JumbleDuck]

My background is in ROV's, and every bolt on an ROV is stainless steel. In 45 years I've never seen a bolt sheer on an ROV, and that's with kit that has from 450hp down to 1hp motors.
How much is it usual for an alternator to be rated for? 1kW, which is a bit above an hp.
I'd suggest that if bolts are shearing, then it's because they weren't correctly installed. Ford probably don't use stainless because it costs more.

Your ROVs are probably designed with bigger bolts in the first place, though. There's no reason why stainless bolts can't be used; they just have to be a bit chunkier than mild steel.

 

[GH29]

 

[vyv_cox]

At the risk of significant deviationm the keel bolts on my Moody are whopping big mild steel ones which are rusty in appearance, However when I saw the boat which lost its keel in the Scilly Isles there were two rows of what looked like very shiny neatly snapped stainless steel bolts.

I tried to obtain more photos of the failed bolts and offered metallurgical assistance but no reply was received. The only photos I have seen appear absolutely characteristic of fatigue fracture. The principal cause of fatigue in fastenings is undertightening and I also suspect this to be the case for the alternator bolt.

The fatigue resistance of 316 stainless steel and mild steel is very similar. However, the low yield strength of 316 means that it is easily stretched by exuberant use of spanners, which is equivalent to undertightening in practice and lowers the fatigue resistance.

 

[jamie N]

Your ROVs are probably designed with bigger bolts in the first place, though. There's no reason why stainless bolts can't be used; they just have to be a bit chunkier than mild steel.

Not really, no. An SM4 motor from any one of a variety of Seaeye ROV's, gives 22kgs of thrust, and is held by a couple M4 bolts in it's housing. As Vyv Cox has stated, I've seen a number of very 'distorted' ones through over exertion when tightening.
Always on the 'other shift' of course.