Zinc, Cadmium, or other?

CLEMTOG said:
I am using them for bolting most things up, on TOG, but I have found that when removing discs from the wheels that all the bolts appear to be barely finger tight, when they where Loctited, torqued correctly and lock tabbed as well, those locktabbs may well be much more useful than you think,
CLEM
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An interesting point you make there Clem: i recently noticed the same phenomenon on my Mirage and was wondering whether the fault lay in the bolts or a lack of locktite. Either way I need new locktabs as the current ones have shredded themselves
Am pretty sure stainless bolts don?t stretch too well and so, if mated with a nut of similar metal can loosen through either vibration or heat cycles.
 
Yep, the stainless bolts have usually min. twicefold the amount of friction in threads and under bolt head than zinc plated ones, which means they are prestressed to only half the clamping force (at best) compared to a zinc plated bolt, when the same torque is applied. With that lack of pretension force, actually no wonder the stainless bolts are working loose. :LOL: You might use some specific lubricant to overcome the friction issue of stainless bolts to a certain extent, but you will be still worse than zinc plated ones, and use of Loctite isn't possible anymore. When talking about bolts on engine, suspensions, wheels and brakes, I'd consider replacing zinc plated bolts by stainless ones w/o reculating the bolted connection simply as bad practice, usually done by people who have not the slightest clue how bolted connections are actually designed.
As a rule of the thumb, you might use stainless bolts to connect fenders, tail light brackets, tool trays and the like to the frame, but never on structurally stressed connections. 







 
Be careful with the term 'Stainless'!
There are at least five basic types of stainless bolts/studs and surprisingly most are magnetic and can be high-tensile.

The most common type is for the most part non-magnetic (304/316 Austenitic etc.), these are the ones I bet you are referring to.

The problem with Austenitic is that there are hard oxides on the mating surfaces of the metal, the oxides can cause galling and cold welding of the fastener. Once seized up, usually the only cure is to cut the fastener.
The good thing about them is that they are great at resisting corrosion.
Yes! They don't like cyclic-loading with heat cycles perhaps and tend to snap after extended service.
I haven't had issues with torquing up stainless verses carbon steel, although galvanised is especially slippery.

We use Omega 99N Nickel Grease at the Power Station to prevent seizure, it isn't cheap and it is horrible stuff as once it is on your hands or body it tends to spread grey streaks everywhere to infinity.
 
From my understanding, stainless bolts can't be stretched much before they yield. Hence, they just fall off unless you use locknuts and/or threadlock. Something to do with Young's modulus of elasticity where by comparison a good quality HT steel bolt will stretch nicely, maintain its strength, and stay tight.
 
Yes, the stainless type you may be referring to does tend to work harden if pushed to extremes, if they aren't stretched past the 'elastic limit' they are pretty durable though to a limit.
This applies to carbon steel too, although a bit more forgiving.

I have previously worked in the Pharmaceutical industry, we had 304/316 stainless bolts all over the place.
They didn't snap a lot, tended to seize rather than snap.
The only ones that snapped were the ones that were subjected to heating and cooling cycles on a constant basis.
 
Interesting comments about the limits of stainless. I rebuilt a Royal Enfield 700 meteor with 9.5:1 about 30 years ago. I used stainless for the barrel/head studs. I was later told that was stupid as the heat would make them brittle and they would snap.

Never saw the outcome, had to sell the bike for the demands of life.

I used a lot of stainless when I put the Dog back together, even on disks, engine mounts ect, but I'm starting to feel really unsettled about stainless. This why I'm looking at getting the oem bolts recoated. (that, and also for the bean counters...)

Regards, Greg
 
Readed a little bit what do the standards say about bolts.

According to ISO 898/2 (should be correct standard to specify strenght properties for standard metric bolts) 8.8 bolts has nominal tensile strenght 800 N/mm2 and nominal yield strenght* 540 N/mm2.

According to EN ISO 3506 (specifies stainless steel fasteners A1 to A5) that A1-70 to A5-70 bolts has nominal tensile strenght 700 N/mm2 and nominal yield strenght* 450 N/mm2.

(* or 0.2% proof stress)

I have found that most bolts sold to consumers at the moment in Finland as "stainless steel" are A2-70 and most bolts sold here as "withstands acid" are A4-70. Both tensile and yield strenghts are then lower on these stainless ones than on normal zinced 8.8 bolts. Of course these standards doesn't prohibit some manufacturers to make much more durable bolts, it sets the minimum.



 
SimonR501 said:
I have previously worked in the Pharmaceutical industry, we had 304/316 stainless bolts all over the place.
They didn't snap a lot, tended to seize rather than snap.
The only ones that snapped were the ones that were subjected to heating and cooling cycles on a constant basis.
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Re: Stainless. I supply machines into food mfg and pharma industries.
I have one machine that uses stainless spindles and bolts that hold a heat element running at 320C 24 hours a day, 5 days a week, never had one snap or come loose.

Much to AnyW's distaste ('cause he's a mentalurgist), I use them in my bikes, and have never had any issues. Yep, the occasional nut has locked up on threading, but a socket and long handled breaker bar makes them (the bolts) snap, but even a rattle gun couldn't do that to an M12 304 stainless.

On one of my Lavs, I had almost every nut bold and lots of other parts cad plated, from some crowd in Sydney ......... finish was great.
 
MotoJouni said:
Readed a little bit what do the standards say about bolts.

According to ISO 898/2 (should be correct standard to specify strength properties for standard metric bolts) 8.8 bolts has nominal tensile strength 800 N/mm2 and nominal yield strength* 540 N/mm2.

According to EN ISO 3506 (specifies stainless steel fasteners A1 to A5) that A1-70 to A5-70 bolts has nominal tensile strength 700 N/mm2 and nominal yield strength* 450 N/mm2.

(* or 0.2% proof stress)

I have found that most bolts sold to consumers at the moment in Finland as "stainless steel" are A2-70 and most bolts sold here as "withstands acid" are A4-70. Both tensile and yield strengths are then lower on these stainless ones than on normal zinced 8.8 bolts. Of course these standards doesn't prohibit some manufacturers to make much more durable bolts, it sets the minimum.
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8.8 is high tensile! No wonder they have have higher nominal tensile strength and yield.
I think zinc-plated 8.8 are reasonably standard in the steel construction industry.

Normal standard bolts for industry have a strength around 400-420 N/mm, so the stainless bolts you mentioned are actually stronger than standard bolts.

The downside of stronger bolts is that they generally snap rather than elongate when over-torqued.
 
SimonR501 said:
8.8 is high tensile! No wonder they have have higher nominal tensile strength and yield. <snip>. Normal standard bolts for industry have a strength around 400-420 N/mm ...
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(Hmmm.  Not sure 8.8 can really be called 'high' tensile  ??? - see below*; but ...)

The important thing is that 8.8 is the norm on bikes, including our old clunkers - and certainly in any critical applications.  Which is why, if you fit stainless replacements, you risk ending up with lower tensile and yield strengths.

* Here's the table for steel fasteners from the current ISO.  As you can see. there are 2 grades with higher tensile strengths than 8.8: 
Bolts2.jpg
 
This is fun.

Much chat about material mech properties, but please also take into account the geometry of any joint. A huge amount of 'strength' can be achieved by just getting those basics right.

A caliper mounting bolt is a great example.... If you really want to use stainless there, at least make sure the shear plane (in this case the caliper to fork mounting plane) goes through an unthreaded section of your bolt [i.e. is plain diameter]. In this example, many square mm of material are gained and many stress focus points (thread roots) are eliminated.

'Common' sense I know, but looking at DPOs efforts and replacing fixings, not that common, with thread-to-head screws seeming to be used willy-nilly.

 
Okay, assumimg the 10mm bolts clamping the calliper to the fork leg are made of A2-70 grade and with thread up to head, you'll need a force comparable to 5 tons(roundabout) to shear a single one of those bolts off. Some impressive strenght in your right hand required to provide that force at the calliper, I'd assume :D.

In reality, that connection is designed to provide a clamping force that is high enough to avoid slipping at the mating surfaces between fork legs and caliper under load. If they start to slip, the bolts will inevitably shake loose in the end, with probablly dire consequences for the rider. If you put in a stainless A2-70 bolt instead of the original 8.8 one, you will not achieve the same clamping force with the stainless ones at the same torque settings as with the 8.8 bolt, which eventually could cause slipping at the mating surfaces and the bolts comming loose. Does not make a difference if the bolt has threads up to head or plain shaft.
 
Paul H said:
'Common' sense I know, but looking at DPOs efforts and replacing fixings, not that common, with thread-to-head screws seeming to be used willy-nilly.
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If there is not a bolt available with correct length for unthreaded part, I have bought a too long one with correct unthreaded section. Then cutted it to correct length on my lathe and applied some zink paint (if zinced bolt) to the end of it.
 
On 2nd thoughts, the caliper joint wasn't a great example to pluck from the air, as one part is threaded. But my point still stands -> where possible have non-threaded portions of a fixing at the joint shear plane.
 
Bolts shouldn't be loaded in shear mode. If a bolt is subject to shear, the joint is either too loose, over-loaded or poorly designed in the first place, and you could end up with bent bolts and other damage. Nearly all bolted joints are designed so that the bolts carry tensile load only.

With the caliper mount example, the shear force between the caliper and fork leg is held by the friction between the mating surfaces, not the bolts. So it shouldn't matter if the threaded part or the un-threaded shank of the bolt passes through the joint plane.

There are some instances where a bolt is loaded in shear (shackle pin for example) but such applications are the exception rather than the rule.
 
Myself and my workmate were pondering torque values and bolting techniques one day while sitting at a top of a boiler.
We had spent days renewing joints and bolts/studs due to steam leaks.

We realised that after decades of bolting, we had never had a definitive answer as to how tight steam flange studs/bolts should be,
Certainly very rare to torque them up on pipe systems rather than machines.

So got hold of some professor on one of those Bolting Science websites and asked him the question?

The answer from the professor left us rather crestfallen:
'Just flog the bolts up as hard and evenly as you can' was the verdict!!!!!!!!!!!!!


As far as stainless(A2-A4) verses 8.8 carbon steel is concerned, chances are the 8.8 was not near the hairy edge of failure when used, so as long as stainless is torqued correctly then why should that fail? There is surely quite a generous safety factor?

This website highlights that Stainless (A2-A4) needs to be done up tighter to get the same stretch:
https://mdmetric.com/fastindx/TI-168.pdf


I have not heard of generic failure of the the stainless (A2-A4) bolts on motorcycles, although I am selective where I put it on my bike.
 
blab said:
When I worked on boilers, we just did the bolts/nuts up bloody tight and used copious amounts of coppercoat on the gaskets,never had a leak.
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Coppercoat or Copperslip is now strictly forbidden in our industry!
It has been found to cause 'stress corrosion cracking'.

Now we have to use Nickel or Aluminium grease!

After we had scientifically assessed why our flanges were leaking steam on the aforementioned boiler (insufficient pipe support), we tightened up the bolts at the bottom slightly harder and they never leaked again - Yes! they were flogged up until they squealed.

The bloke that designed the pipe supports should have got shot!!!!!!!!!!!!!!
 
I did boiler shutdowns every Christmas, we used copper coat not only on the bolts, but also on the pipe flange gasket faces. Gaskets almost fell off when unbolted, great stuff in the day. Pressure release valves were also copper coated at the gaskets and nuts, never had a steam leak? Lagging for valve stems was copper coated as well, so smooth you could spin the hand wheels on the battery with two fingers.

As for tensions of the bolts, as tight as we could.

 
"As tight as possible" still has a some sort of value depending on tools and person etc. The value should be correct.

Take a torque multiplier and a 10 meter long shank. That system was used here to open rusty 100 mm nuts. :D Guess then if the torque is correct.
 
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