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  1. #1
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    Default HIGH TENSILE BOLTS Vs MILD BOLTS.

    I have a mate (mechanic by trade), we were chewing the fat one day when he mentioned that mild steel has the same sheer strength as high tensile ( referring to bolts for general use).
    I told him I didn't think that that was correct.....ensued an argument. He is also the same bloke who when doing some job some months ago used High Tensile bolts as well as high tensile washers. To my mind, flat washers would only be mild steel because they would always be in compression.
    Am I right in my thinking? If the sheer strength of mild and HT is the same, why do we use HT at all?
    Any way I thought I would bring up the subject here and tap into the combines census of opinion on the subject.
    Just do it!

    Kind regards Rod

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  3. #2
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  4. #3
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    Default

    Thanks Bob for that very informative information!!
    I knew that there would have to be a distinction between the 2. Do you have any info on flat washers? I can't see why there would be high tensile washers. Or am I showing my lack of knowledge/naivety.

    From what you have sent me there is quite a science in the bolting game.

    Just another case for the knowledge held in these Forums.
    Just do it!

    Kind regards Rod

  5. #4
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    Default

    Without getting into bolts shouldn't be used in sheer, certainly not single sheer Bolts are for clamping, not location. blah blah blah

    As I understand it, high tensile washers are needed if you are going to be doing high tensile bolts up to the correct torque.(hands up if you use a torque wrench every time?) sure they are always in compression, but how much? i.e. its no use having a bolt that can take the tensile load if the washer fails in compression there by loosing the preload on the bolt. For my use they seem to last longer in apps where the fastener used repeatedly(though thats hardly scientific testing). Though if you were really getting down to it you likely shouldn't be reusing washers anyway. There really is a lot to working out the right bolt to use when you are trying to save weight(or space). Happily its not often an issue for the things I make.

    Stuart

  6. #5
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    Default

    I use high tensile washers on the boilers as expansion and contraction ruins ordinary ones and the bolts can come loose and blow out the joint.

    Phil

  7. #6
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    Default

    It is not all what it seems.... Ask your mate if he knows what an IZOD measurement is...

    There is a reason why high tensile bolts snap when bent, while mild steel, being more ductile bends...
    Light red, the colour of choice for the discerning man.

  8. #7
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    Default Nuts?

    Hi chambezio,

    Interestingly, I've been told there are no such things as high tensile nuts. The reasoning being that nuts usually don't strip, rather the bolts shear first. The proof presented was any vehicle wrecking yard where you would see some sheared bolts but no stripped threads (at least from accidents).

    Cheers

    The Beryl Bloke
    Equipment er.... Projects I own

    Lathes - Sherline 4410 CNC
    Mills - Deckel FP2LB, Hardinge TM-UM, Sherline 2000 CNC.

  9. #8
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    Default

    Probably in a car wrecking yard the nuts are rusted on and the bolts give way first.

    Phil

  10. #9
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    Default

    Hi all,

    interesting subject. WRT washers, we have a 20M tower in our yard at work, It is made out of angle iron and bolted together in sections (assume HT bolts) and the washers are round with distinctive tabs on the outer, maybe 3 or 4 tabs. They are completely flat so can't see that they would be lock washers. Any ideas? Don't have a photo but can post one tomorrow night. Just read the thread and it reminded me of these washers.

    Simon
    Girl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.

  11. #10
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    Default

    Thanks to all for the contributions. The mate and I had a debate over the issue as I said on the outset. Its interesting just how the information that should be used is twisted to make the uneducated sound "intelligent".

    This discussion should be had around a campfire in winter(cos its flamin' hot here at the moment) while sipping on a good Muscat.
    Just do it!

    Kind regards Rod

  12. #11
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    Default

    While there are some high tensile bolts used in car manufacture, the majority would not be (cost).

    Typically, a bolt is designed to be stressed to roughly 65% it's yield strength (point of permanent deformation). This is judged to give a reasonable joint where loading won't take all tension off the bolt but at the same time allow for joint characteristics so that the bolt is not deformed in service (for example, a typical tension applied by a torque wrench can vary by 30%).

    By juggling fastener strengths, the designer can reach this 65% yield figure without necessarily over stressing other parts of the joint (for example, the female thread is die cast) or incurring unnecessary cost. While there is a temptation to put in stronger bolts when replacing worn fasteners on some occasions a designer may specify a particular grade of bolt to act as a sacrificial element - for example in a crash, particular bolts break (absorbing energy) while other joints stay intact, causing deformation in a "controlled" way.

    High tensile bolts and nuts are sometimes called "structural" bolts and nuts. While a normal nut may have a height of 80% of the thread OD, a structural nut will be greater than this. This is dictated by the distribution of stress within the fasteners once again to ensure that the failure (if it occurs) of the fastener occurs in a predictable manner. Things like coronet washers are used to indicate that a structural fastener set is tensioned to the right level. Other methods used are "torque-turn", where the fastener is torqued to a low level (nominally to ensure that the joint is bedded down) before being turned through a nominated angle to get the correct tension in the joint. In car plants joints made with this method are typically made with electronic wrenches that are data logged so that in the event of a failure of the joint information is on file and other affected vehicles can be traced.

    Michael

  13. #12
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    Default

    Quote Originally Posted by simonl View Post
    WRT washers, we have a 20M tower in our yard at work, It is made out of angle iron and bolted together in sections (assume HT bolts) and the washers are round with distinctive tabs on the outer, maybe 3 or 4 tabs. They are completely flat so can't see that they would be lock washers.
    Simon, these are likely to be coronet washers. They have several (3/4/?) dimples on them and when the joint is correctly torqued these dimples are crushed. These are of course a one time use device. The aim of a bolted joint is to have a particular tension in the bolt that then increases the friction between the two or more elements being fastened together.

    A spring washer is meant to do the same thing in a non structural joint but who knows?

    Michael

  14. #13
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    Default

    Washers - James Glen might be structural washers (2nd from bottom page)


    Quote Originally Posted by simonl View Post
    Hi all,

    interesting subject. WRT washers, we have a 20M tower in our yard at work, .......... the washers are round with distinctive tabs on the outer, maybe 3 or 4 tabs. ......... Any ideas?

    Simon

  15. #14
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    Default

    Quote Originally Posted by Theberylbloke View Post
    Hi chambezio,

    Interestingly, I've been told there are no such things as high tensile nuts. The reasoning being that nuts usually don't strip, rather the bolts shear first. The proof presented was any vehicle wrecking yard where you would see some sheared bolts but no stripped threads (at least from accidents).

    Cheers

    The Beryl Bloke
    Having collected many bolts and nuts over many years I sort them into sizes so I can find what I want. One way I pick HT nuts and bolts is by the way rust affects them. Both nuts and bolts appear to be affected the same. I assume it is the heat treatment that causes this.

    Dean

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