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Stripped Thread on Brass Nut

02/23/2017 11:07 AM

Good afternoon,

Failure mode: 3/8" brass nut threads are stripping

I have inherited a machine where by 3/8" brass nuts are secured to a 3/8" 316 st/st. The purpose is to clamps an arrangement. The operating temperature ~280degC. Currently Torqued to 42Nm.

1. How to calculate maximum torque? Taking into consideration operating temperature (change to yield strength)

2. Alternative materials - Any guidance of using a different material for the nut? Concerned with galling and corrosion resistant.

Any help would be much appreciated,

Mark

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Pathfinder Tags: bolt stripping torque
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#1

Re: Stripped thread on Brass nut

02/23/2017 11:19 AM
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#2

Re: Stripped thread on Brass nut

02/23/2017 11:27 AM

Way back in the 90's when I went to tech college we had a class demonstration on such things.

The professor was a old school machinist with 40+ years in the field experience and nearing 10 more as a educator.

One day for a lab class we learned about torque limits for fasteners the old fashioned way by doing sacrificial testing methods namely using a graduated torque wrench (bending bar type) and several combinations of odd nuts and bolts.

The test was simple. Just torque the nut and bolt combination until they either stripped out or sheared off and record the measurement then calculate out what ~75 - 80% of that number was.

Wouldn't you know it, that calculated number fell right at the upper limits of what the manufactures own torque ratings were based on their published charts for each fastener!

The moral is, if you don't know exactly what your torque limits for a unknown fastener is do a sacrificial test and find out then try to not torque them beyond 75 - 80% of that failure value.

Now if that level of torque does not hold thing then you probably need to consider going to a higher strength fastener which depending on the application will make things more complicated.

If they don't have to be brass for a specific reason going to a common grade 5 or grade 8 or metric equivalent will probably be sufficient. However if they do then the only option may be to redesign the device to use a larger diameter fastener with a finer thread pitch if it can be done.

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#4
In reply to #2

Re: Stripped thread on Brass nut

02/23/2017 2:04 PM

great post,good story too

Del

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#6
In reply to #4

Re: Stripped thread on Brass nut

02/23/2017 4:04 PM

Thanks!

It's nice to know that a educational story of how things were done the old school common sense way can be appreciated. It's getting rare these days.

On a farming forum, I got run off from this week no less for repeatedly trying to educate idiots (and embarrassing a bunch of 'know it all' fools too with bonehead obvious and simple solutions to a few problems), I did one on how to make very nice custom gaskets for odd components (because someone said that making a large gasket for a tractor rear end was a all all day project when it's not if you actually know what you are doing) of any size, only to be attacked and trolled to shreds by every suposed experienced farm machinery service tech on the forum, plus several old farmers, to who claimed that gasket making is never ever done in service shops regardless of what the situation is and if they ever caught someone hand cutting a gasket for a tractor they brought in they would sue the company for gross negligence on their repairs.

One hell of butthurt bulshyte storm exploded all over me having showing how making a gasket of most any size that is neat, clean and accurate even for a large complex part can be done quickly and easily using little more than a utility knife and the fasteners related to the components at hand.

BTW, according to them, engineers and technicians should never ever be allowed to work on machinery because they are all stupid and don't know anything aobut how to properly fix stuff and any shop mechanic or person who has ever met one knows that. (Never mind the fact that those are the types of people who both design the machines and develop those actual service procedures that every shop mechanic uses.)

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#7
In reply to #6

Re: Stripped thread on Brass nut

02/23/2017 5:54 PM

Yeah, I can remember making gaskets for a Lambretta out of cornflake boxes when I couldn't get a replacement! And a plumbing gaskets from an old wellington boot.
They guys who made the first engines couldn't buy gaskets so they must have made 'em.
I get all sorts of BS on archery forums from people with all the gear and no idea.
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#12
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Re: Stripped thread on Brass nut

02/23/2017 8:30 PM

Yep. The old school professor I had for that class even told us about how boiling different papers and thinner cardboards stock in various natural and petroleum based waxes was how many non leather based gaskets were first made.

Same concepts for making waxed rope type shaft seals.

I've never purposely boiled any paper in wax to make a gasket but I did make a gasket for a antique brass gear pump out of a wax kitchen paper once. Worked perfect!

As for the farmers forum I rather got the impression that most felt that just throwing money at things until it was someone else problem then complaining about how poor they are was best.

It always bewildered me to hear guys complain about $200+K a year repair bills and have zero personal shop or mechanic of their own in place because they don't feel it worth it to do their repair work at home on their own time.

I don't get it. That's not how the farmers I grew up with and still associate with work.

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#8
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Re: Stripped thread on Brass nut

02/23/2017 6:20 PM

Jeez, don't those guys know how use a ball peen hammer and a crochet hook?

.

.

.

.

(To fish the punchings out from the bolt holes.)

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#9
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Re: Stripped thread on Brass nut

02/23/2017 7:32 PM

We used to make all our own gaskets....we had sheets of various materials for whatever the application was...just cut the material to size and go around the profile with a ball peen hammer, or trace it out on paper....Working in the field on critical systems you don't have time to order or wait for gaskets all the time....

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#11
In reply to #9

Re: Stripped thread on Brass nut

02/23/2017 8:06 PM

And People look at you as if you were joking about making a gasket.

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#13
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Re: Stripped thread on Brass nut

02/23/2017 8:32 PM

Wish I would have had you guys in my corner in that discussion.

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#15
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Re: Stripped thread on Brass nut

02/23/2017 9:52 PM
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#31
In reply to #15

Re: Stripped thread on Brass nut

02/24/2017 9:54 AM

I always get my 'techincal link on' when proving someone is wrong. Outrightly buried some people on some subjects

You've seen me and a few others go after fools and idiots here with that approach. I do the same with topics I know well and have first hand working knowledge and experience in every forum.

The problem is some people are just too proud, stupid or trollish for it to have any effect. You can outrightly burry them in proof they are wrong to the point it's clear they are so god awful dumb it's embarrassing to everyone to watch yet it doesn't phase them.

In fact with too many now all it does is get you attacked personally with slander and false accusations about you and everything about who you are and what you have done in your life to gain the knowledge and experience you have to no end in every thread on every post you make from then on. You can't have a civilized conversation in any thread about anything from then on without getting attacked by the village idiot and his buddies from then on.

The stupider you make them look the more they make up about personal life and too many will gravitate towards believing that nonsense over any factual information or proof you can ever provide.

Once they figure out who you are in real life and who your neighbors are then start making outrageous lies claiming they know you or them and that you are not who you are in real life how do counteract that? You can't.

Well enough off to not have to work for a living anymore becomes deadbeat bum,

Having all your own equipment and whatnot to work for yourself becomes you get paid a pathetic rent rate to keep it on your property for someone else or you don't have any of it to begin with.

A story about a bad experience at work or something that just happened locally with a bad boss or badly manage business become they have a suposed brother or whatever who worked the and it was you who screwed everything up or the event and general public view of said place are not what you claim they are.

And that's the nicer things they come up with to discredit you with all because you link bombed some fool and made them look as stupid and petty as they turned out to be.

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#33
In reply to #31

Re: Stripped thread on Brass nut

02/24/2017 10:30 AM

Well a lot of people in these online forums have an agenda....and sometimes all their 'friends' are just them posting with different identities, so all you can do is make your point and move on....I wouldn't take it personally....You may get some satisfaction out of thrashing them, but you make it look like you then have an agenda, most people will just ignore these type people that argue endlessly back and forth...and if somebody is getting paid to promote or discredit some product or service, you are wasting your time trying to convince them you are right, they already know that....In any case, getting emotionally involved is a newbie mistake....it causes you to lose your focus....

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#34
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Re: Stripped thread on Brass nut

02/24/2017 1:06 PM

I figured out a few were likely the same guy with some perverse agenda. Even called them/him out on it and had others do the same and got one or two f them to come over here if you remember, Bypass oil filter system design questions. That moron or two like him in that thread is what I was dealing with nearly every day in every thread on those sites. Stupid proud to be stupid and nothing less.

ignoring them made it worse (remember how long that idiot followed me around CR4 attacking me on every thread I posted? 2 - 3 weeks and CR4 was not even his home forum?) to the point that's where posting anything drew immediate flaming from them and their proxies flooding threads to point of shutdown because any post I made drew several direct attacks on whatever I said or whatever credibility they could equate me to not having by nonsensical association then gleefully patting each other on the back over it in triumph.

Mostly it just gave me the impression that site ownership didn't care or even found it good because it drove up the posting counts for a bit and thus their 'clickbait' payment value even if all it was dragging the overall credibility, feel and honest participation of the forum down in the end.

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#35
In reply to #34

Re: Stripped thread on Brass nut

02/24/2017 1:23 PM

, I should poke around Cr4 more deeply... or maybe not.

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#10
In reply to #6

Re: Stripped thread on Brass nut

02/23/2017 8:05 PM

On a farm you had to be resourceful... gaskets from cereal boxes. And that was the minor task... you may have to Mae, it twice, because the first try failed.

the other thing is when you still have 10 acres of hay down and thunderstorms on the horizon. The knotter in the baler is out of adjustment. Neighbor never could figure that out, and they'd call the implement dealer and wait as their hay got rained on.

And the experience served me well, was never afraid to try anything... twice.

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#19
In reply to #2

Re: Stripped thread on Brass nut

02/24/2017 3:09 AM

Thanks for the feedback. I will look to set up a trial, but will have some difficulty simulating the operating temperature.

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#3

Re: Stripped thread on Brass nut

02/23/2017 12:02 PM

Here is a torque chart for bolts and different materials. (Torque is in foot pounds)

You need to have more information about clamping force... more than likely, brass may be sufficient, but it was just over torqued.

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#5

Re: Stripped Thread on Brass Nut

02/23/2017 2:29 PM

The brass nuts are used to prevent galling which would occur if stainless nuts were used. If you know the grade of the stainless studs, you might get away with using a different grade for the nuts. Alternatively, you could re-tap the nuts to take Nitronic 60 Helicoils which are made to prevent galling on stainless at high temperatures.

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#20
In reply to #5

Re: Stripped Thread on Brass Nut

02/24/2017 3:16 AM

Yer I agree I am looking into using a 304grade nut but didn't consider a helicoil, Thanks

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#25
In reply to #5

Re: Stripped Thread on Brass Nut

02/24/2017 4:10 AM

Concerned about SS galling?

Bostik, Loktite and others have a plethora of anti sieze formulations that solve that problem, Bostik Never Seez pure Nickel is a likely candidate, and it will easily handle the temperature.

It has an added advantage of reducing required tightening torque for the same or better clamping force and you get a more consistent and accurate torque, but be a bit careful you don't exceed the fastener's proof load when using this stuff. You can also use a simple Graphite powder such as lock/key lube if you're stuck.

Also be cognizant of health regs if this is a food environment.

Another trick is to use different grades of SS for the bolt and nut as this can reduce galling tendency, and do turn the nuts down by hand first so that heat build up doesn't destroy the passive layer as this is where the galling begins.

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#14

Re: Stripped Thread on Brass Nut

02/23/2017 8:57 PM

How are the threads formed? It looks like the threaded rod, they are roll formed, as the threads major diameter is larger then the rod. Assuming it has not been turned down. As for the brass nut, how are the threads cut? Was a thread forming tap used. Also torque specs for 3/8-16 is 192 inch-lbs= 22 Nm, possible you are over torquing?

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#16
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Re: Stripped Thread on Brass Nut

02/23/2017 10:38 PM

The 192 in lb is for brass, 316 stainless is 247 in lb.

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#21
In reply to #14

Re: Stripped Thread on Brass Nut

02/24/2017 3:25 AM

The st/st stud is turned. And the brass nuts are made as per BS 1083:1965.

I think this may be the case and they are being torqued to high.

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#28
In reply to #21

Re: Stripped Thread on Brass Nut

02/24/2017 8:07 AM

Any nut will strip if the torque is <...to[o] high...>. The torque needed needs re-evaluation.

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#29
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Re: Stripped Thread on Brass Nut

02/24/2017 8:18 AM

It's the nut that's holding the other end of the spanner that needs controlling.

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#32
In reply to #29

Re: Stripped Thread on Brass Nut

02/24/2017 10:01 AM

Good point. Usually, one flogs it up until the stud breaks, then backs it off half a turn. Brass being softer than stainless, the nut goes first.

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#17

Re: Stripped Thread on Brass Nut

02/24/2017 1:10 AM

You show what appears to be brass studs [you say nuts] I am a little confused by your description.?

I do not know if it is practical but change your studs to stainless steel and use double diameter depth brass nuts.

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#22
In reply to #17

Re: Stripped Thread on Brass Nut

02/24/2017 3:30 AM

The studs are stst, they look the colour they do due to heat tint (temper) as the operating temps are high.

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#26
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Re: Stripped Thread on Brass Nut

02/24/2017 4:17 AM

Comment withdrawn.

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#27
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Re: Stripped Thread on Brass Nut

02/24/2017 7:34 AM

In that case use monel for your nuts it has a high toughness, certainly do not use stainless steel.

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#18

Re: Stripped Thread on Brass Nut

02/24/2017 2:48 AM

<...corrosion resistant...> to what fluid, please?

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#23
In reply to #18

Re: Stripped Thread on Brass Nut

02/24/2017 3:33 AM

The main concern being oxidation due to atmosphere, the environment is high humidity and temp.

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#24
In reply to #23

Re: Stripped Thread on Brass Nut

02/24/2017 3:34 AM

Brass is routinely used in water fittings, however, bronze might be better for elevated temperatures.

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#36
In reply to #24

Re: Stripped Thread on Brass Nut

02/24/2017 5:37 PM

A grade of silicon bronze is used in electrical connections, should be somewhat easy to find, bolts and nuts, not too much galvanic potential with stainless steel, and zinc, if memory serves. Used on outdoor substation fittings and connectors, but local supply houses were able to find them also.

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#30

Re: Stripped Thread on Brass Nut

02/24/2017 9:22 AM

I believe that your fastener failure is at least partially due to usage at high temperature. (you state 280C -- 536F)

Most codes and guidelines recommend that brass piping and bolting materials not be used above 250F

Brass materials should have never been originally specified for this high temperature application.

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