One for the engineers. One of the suspension bolts on my Polo sheared off when I tried to remove it. It's the bolt which goes through the bottom of the rear shock absorber unit, and takes the weight of the car. I looked for a replacement today at a kit car show, but the only bolts I could find in the right size were stainless steel. Are stainless bolts strong enough to be used to locate crucial bits of suspension? If so, I'll fit them to all the suspension arms on my self-built sports car.
|
Stainless steel strong enough to replace what? Mild steel?
MUCH stronger. And don't rust.
(Do the Adam Hart-Davies bit - try it for yourself. Buy 2 6mm bolts in s/s and "ordinary". Compare hacksawing through and bending with hammer)
|
Trevor,
a blanket statement that a stainless bolt is much stronger than a mild steel one is a bit misleading.
Bolts are marked with a grade (SAE standards) or a property class (metric) that denotes the strength of the bolt.
When replacing a bolt, the replacement should be of equivalent grade irrespective of the material.
Kevin...
|
Make sure you replace with the same grade. If you use a different grade the stretch characteristics of the material will be different so the original torque figure will no longer be correct to achieve the required clamping force.
Personally, I'd use a new original bolt and protect it with some kind of coating method (waxoil, hammerite etc etc).
|
Ive tried this DONT DO IT if you are screwing into a captive thread .If you are using it as a nut and bolt its ok only if you use the same grade stainless nut
I dont know why it happens but if you screw stainless into mild steel once they get tight they weld themselves together and you will sheer it before you undo it again
numerous sheered off captive bolts on a previous car means ive got a pile of unused stainless bolts in my garage too expensive to throw away and too risky to use by the way it was A8 marine grade stainless apparently the best
Dave
|
|
|
It can be so hard that you can't saw it but it may break rather than bend.
|
|
|
In my work as the Chief Engineer for a brewery I use stainless bolts all of the time, but there are situations where you dont want to go with stainless, and on critical suspension fixings you have found one. There are so many types of stainless that can be used for fixings that trying to find the right one is almost impossible. Some of them are no better than the stainless used to make knives and forks, it won't corrode but look how easy it is to bend a fork. Another issue with stainless is that with only small amounts of dirt in the threads it can gaul up and be impossible to undo. We have to saw bolts off on all sorts of plant. If the bolt if subjected to heat there is almost no way to get them undone so don't fit stainless exhaust studs and nuts.
Do as Cyd suggests, new original bolt and Hammerite.
Bill
|
Bill Doodson wrote:
>
> In my work as the Chief Engineer for a brewery
Backroom Cultural Outing venue?
Some of them are
> no better than the stainless used to make knives and forks,
> it won't corrode but look how easy it is to bend a fork.
Another tip, if you are off to buy a new s/s sink, remember to take a magnet with you.
If its non magnetic (at worst very very faintly magnetic) that is good,
strongly magnetic reach for the barge pole, that means its ferritic stainless, it might be stainless ie it stains less. ;-(
|
|
|
No. The steel bolt is most likely grade 8.8, which is much stronger than virtually all grades of stainless steel.
However, if it's in a bottom shock mount, as opposed to a bottom strut mount, then they don't tend to be load bearing, as shock absorbers don't take the weight of the car. They are only there to damp the bouncing effect of the spring. Even so, just by the proper grade steel bolt and treat it before you put it in.
|
The shocker is part of the strut on a polo.
Use a grade 8.8 bolt with a nylock nut (as OEM) and put a bit of copper grease over the exposed threads.
Dont use stainless.
|
|
|
Whilst stainless has less sheer strength that the bolt you have removed, the margin for safety built into the original means that the difference is insignificant. You will never sheer the bolt in a month of Sundays. I should say use it if you want to, but do not go out and buy one specially.
Mike
|
|
I earn my living with stainless in one way or another.
The simplest answer Richard is to replace it with the original spec component.
Trevor is right s/s vs MILD steel. The reality is though that the ferritic bolt is most likely to be a mildly alloyed component, probably hardened by some form of heat treatment, in which case it is 99.9% certian to have higher yield and ultimate tensile strengths than the s/s.
If you really want s/s (which I guess is not the case) then if you know the markings on the original so we can work out the spec, I can probably advise you of a stainless which might meet the properties. Essentially though it won't be cheap, and it will be a lot easier and cheaper just to go down to the dealer/factor.
|
|
Flat-in-fifth
We do do brewery visits with a visit to the FREE bar after, I'm sure that they are booked up well in advance. If you want to try to arrange a backroom visit then I will see what I can do. The brewerys south of Manchester.
Bill
|
|
Thanks very much everyone, I knew I could count on the Back Room Boys to come up with the answer.
|
|
J Cronin - I wish that was true the day I spent 16 hours [1] trying to drill out a sheared bolt from the rear shock of my 414. ;-)
[1] And 30 quid on drills!
|
|
Just to get in before the old forum closes down, don't like these multiple subject fora.
Trying to put all the above in context.
Just to quote some typical properties. I?ll also quote steel grades in old money so as to include the old uns in the conversation ;-)
Grade of steel , 0.2%yield N/mm sq, Ultimate tensile N/mm sq, elongation% (measure of ductility), condition
En2 Low alloyed , 150min , 310 min, 25% min, as rolled
En8 C+ bit of Mn steel , 245 min, 510min, 17% min , normalised
En24 (higher C +1.2% Cr +1.5% Ni, 635 min, 850/1000, 13% min (quenched & tempered)
316L S/s, 205 min, 515/690, 40% min, annealed
SAF 2507 super duplex, 550 min, 800-1000, 25% min, annealed
Trevor's comment *was* right re the relative strengths, compare En2 vs 316L, please note En2 is actually stronger than true MILD steel. Out of politeness I did not mention that he was wrong in the way in which he suggested testing the relative strengths of the two materials, ie by sawing/bending. The problem with this is that stainless work hardens quite rapidly thus in hacksawing a s/s bolt if your technique is not good or, more likely the blade has seen better days and you are rubbing rather more than cutting work hardening occurs with a resulting false impression of the true hardness of the bolt in its as supplied form.
You?ll also notice that even a small amount of alloying elements, eg EN8 gets properties up to the region of s/s and further alloying additions eg En24 with heat treatment gets mechanical properties which are above ?standard? stainless, and comparable with stronger stainless material albeit with lower ductility. As the engineers will know I have just quoted the T properties for En24 its quite possible to heat treat up to yield strength >1000 N/mm sq and UTS about 1200, but the ductility is low at these levels.
Of course the alloy content of these carbon/low alloy grades is such that they are not resistant to corrosion in either wet or high temperature corrosion conditions. Which is where increasing the alloy content and such as stainless steels come into the frame.
Then the development of stainless has concentrated on increasing strength and increasing corrosion resistance, and tailoring alloys for particular applications. So for example the super duplex grade is often used, not only for good corrosion resistance, but due to its good strength it is possible to reduce component thickness and hence weight. It is now possible to obtain stainless tube which has better strength to weight ratio than titanium tubing. Likewise there are other alloys with high strength at elevated temperatures, but creep strength is perhaps not an appropriate discussion point here.
Pause for advert.
If you really want more info than this which is only very basic please visit our website, here is a link
Regards,
FiF
The Reliable Partner for Competitive Solutions :o)
|
|