Deleted gearcase thread issue 8

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On Mike's suggestion, I have asked admin of the forum to delete the thread. But we can discuss that here

Desert forx post
"What grade of bolt is it ie whats its proof load? img511 and 514 don't work.
I assume the bolts are in tapped holes?
Could be a number of things like you have already mentioned
vibration;cyclic loading.
If the bolt pre-load is not high enough the bolts can loosen
off under vibration and subsquently fail in fatigue.
Have you any of the failed screws? if so post a pic.
In addition if your truely getting 80% - 90% of proof load on all bolts it doesn't give you much room for increasing
bolt tension unless you use a higher strength material.
Finally the bolts will not see equal tension , shear etc
for a given engine position: but depending on engine position and external force position at a particular point in time the bolts will share the load unequally.
"

Yes the bolts are in tapped holes and the holes are blind. Bolts dont break, they just come loose or missing.

6 Bolts,joint and proof load info

4 perimeter bolts (Bolt 1-4) – 3/8-16 (1.75 in) unc-2A stainless steel plated(tq spec – 27 ft-lb target)-min proof load - 8370 lbs
1 bolt in center- 3/8-16 (3.5 in) unc-2A stainless steel(tq spec – 27 ft-lb target)-min proof load -8716
1 bolt in center– 7/16-14 (3.5 in) unc-2A stainless steel(tq spec – 47 ft-lb target)-min proof load - 9567


Desertfox you saw one of the pic which is been deleted now right.Did that give u an idea about the joint?

 

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Desertfox,

yield stress of joint materials is 19ksi and tensile strength is 42ksi

 

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MintJulep,

Could you please explain how does a hard plastic mechanical lock patch will be ineffective if the cutting lube oil in the tapped hole is not cleaned?

and also could you please help me understand how wool grease effects this lock patch?

 

[MikeHalloran]

Uh, "wool grease"? I thought that was a misprint for "well greased". I had to look it up. It means 'lanolin'. I haven't seen that used in ages.

Loctite forms a chemical bond, on clean parts. On oily parts, it forms a weak bond, or none.

The plastic lock patch wedges the male threads to one side of the female threads, relying on friction between the threads (and some retention of strain energy in the plastic) to prevent loosening. Anything greasy, e.g. lanolin, is going to interfere with that locking to an even greater extent than the leftover cutting oil would.

I'm guessing the engineering dept. specified the lanolin because of excessive torque levels required to deform the plastic inserts without it. It's not sounding like a winner of an idea right now.







Mike Halloran
Pembroke Pines, FL, USA

 

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Mike,

Great explanation. Thanks a lot.The hard plastic kind of lock patch we are using is called epoxy-lock.

Anyway, the other way of decribing this kind of behaviour is " There isn't enough friction in the joint to make the joint immune to vibration loosening" right????

so how low of a friction coefficient or K value should be minimum for a joint to not to loose under vibration?

 

[MikeHalloran]

Ah. That's a horse of a different color. Not a friction lock.

I think that ND brand "epoxy-lock" smears epoxy on the bolt during assembly, in hope of forming a chemical bond. I can't see that happening in a greased joint, unless the lanolin has some special property such that it doesn't interfere with an epoxy bond.

I couldn't get into the ND website, which doesn't seem to have a non "Flash!" entry point.





Mike Halloran
Pembroke Pines, FL, USA

 

[MintJulep]

As usual, Mike has it right.

ND epoxy-lock is a pre-applied adhesive thread locker.

(non-flash PDF of the sales sheet here mike:

http://www.electronicfasteners.com/pdfs/ndindustries/ND_Epoxylock.pdf)

Adhesives do not adhere to lanolin, cutting oil, grease or other lubricants.

I still think a proper plastic lock patch (MIL-DTL-18240, Type L) would be effective here. The plastic tends to work as a squeegee to clean out any lubricant from the female threads.

 

[MikeHalloran]

<blush> Thanks for the compliment, and the link.

The epoxy-lock looks like it would work great, _if_ you clean out the cutting oil and don't grease the bolts, or limit the grease to the shanks and under the head.

I agree with Mint that the friction type plastic locks would probably hold the bolts well enough; my only concern with them is that they do nothing to exclude corrodents, e.g. seawater. Maybe _that's_ what the lanolin was intended to do. I'm real curious about the design intent, and any history the stuff may have at your outfit.



Mike Halloran
Pembroke Pines, FL, USA

 

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Mike and Mint,

One of our lube doc says,

All IFI124 (non-metallic lock patch fasteners) shall be coated with wool grease heated to 200 F. But the mating parts, holes, nuts should be oil and residue free.

All IFI125 (chemical lock fasteners) shall be free of oil and residue and wool grease.

If epoxy lock is a non-metallic lock patch, it says we can use wool grease, is this wrong?

 

[MintJulep]

Yes, that is wrong.

Epoxy-lock is a chemical adhesive lock, not a mechanical lock.

The patch that you see contains tiny capsules of liquid epoxy harder and resin. These capsules are embedded in the patch that you see.

When the fastener is threaded into a mating thread, the capsules are broken, the epoxy parts get mixed and are supposed to form a chemical expoxy bond between the male and female threads.

Epoxy does not adhere to oil, wax, lanolin and the like.

 

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Mint Julep.

Thanks for explanation. Just for my knowledge, In case if the lock patch is not chemical patch and if it is a non-metallic mechanical lock patch, then does the wool grease effects the patch effectiveness? if yes why and how?

Thanks in advance

 

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Initial clamp load results on production line on 3 joints ranges from 4300lbs to 9400lbs and avg being 7500 lbs.

min proof load for this bolt is 8370 lbs. Other two bolts has the same avg.

So, this shows we are following our 80-90% of proof load.

for vibration looseining the extrenal loads should be more than our avg clamp load in the joint right?

I requested for field test and gotta see how much time its gonna take.

 

[MintJulep]

Preload,

Take a look at the Handbook available for download here:

http://www.longlok.com/

You can also download the MIL-DTL-18240 spec there.

 

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Mint, Thanks for the handbook and MIL spec.

 

[desertfox]

Hi preload

Your clamp load figures off 3 joints show a scatter of 4300lbs which is only about 51% of proof load and 9400lbs
which is 112% of proof load so if your tolerance is 80%-90%
of proof load your outside the spec.
In the thread where you pasted a torque fastening spec which you asked people to comment on there was mention of a formula for the constant K (friction constant) can you tell us what that formula is and what friction constant you are using in this case.

regards
desertfox

 

[desertfox]

Hi preload

No the loads don't have too exceed your clamping force to come loose just the friction force between the two clamped joint surfaces.

regards

desertfox

 

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Here is the formula

http://img477.imageshack.us/img477/7749/untitlednb4.png

M – Assembly torque - 333 in-lbs
Fv – 90% of the proof load
P = pitch
d2 = PITCH DIA
DKM = DW+DH divided by 2


When I calculated K for our application, using our torque and collected clamp load data, It came up to 0.11 (this low friction is because of cad plating and also wool grease on the bolt)

Regarding vibration loosening theory, I thought if the external load exceeds the preload in the joint, then the joint comes loose. So am I wrong?

And also I wanna let you guys know that I observed the l/d ratio of the bolts is les than 8. It is actually 4.6. I read some where that of the l/d ratio is less than 8 then the bolt is susceptible for vibration looseining.

 

[desertfox]

Hi preload

I can't see the file you have posted till friday evening.

Imagine two plates clamped together the bolt axis vertical,now if you try and push the plates at 90 degrees to the bolt axis relative to each other you only need to exceed the friction force generated by the bolt pre-load.
Roughly speaking lets say your clamp load is 100lbs now to slide one plate over the other you only need:-

mu * 100lb = .25*100lb = 25lb

mu= coefficient of friction and not to be confused with K the friction factor for bolt torque calcs.

Not sure about your l/d ratio I have never heard of that.

regards

desertfox

 

[dimjim]

Preload,

l/d ratio = 3.50/.375 = 9.333 ?????

or

l/d ratio = (3.50 - .81)/.375 = 7.173 ?????

 

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Oh alright, then I can type it here in words.

Over all friction Mu = numerator/denominator
Numerator = M/F – 0.159 * Pitch
Denominator = 0.578 * pitch dia + (Dkm/2)
Where DKM = DW+DH divided by 2 = effective bearing dia of bolt

 

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And formula for K = numerator/denominator

Numerator = [0.16* Pitch + O.58*Pitch dia* Mu + (Dkm*Mu/2)]
Denominator = D = nominal dia of bolt