friction coefficient of Loctite 620 5

[kirstant]

I have been trying to work out the correct torque for a 12.9 socket cap screw. I have written a spread sheet based on the formula in MIL-HDBK-60, it works well with the friction coefficients supplied in MIL-HDBK-60. The problem is there are no friction coefficients given for any kind of Loctite.
The loctite data sheets don't supply this information. I have contacted loctite directly and have been supplied with nut K factors, this is a very simplistic way of working out the correct bolt torque and does not allow for lubrication under the bolt washer face.
Does any have actual friction coefficients for loctite products.

 

[unclesyd]

mog69,

If you omit the spaces when referencing a previous thread it becomes a link with no typing required.

thread404-161524

 

[mog69]

unclesyd
Thanks - I'd exhausted about every permutation of cutting /pasting/ dragging etc, so I went for the "stick with what you know" option !

 

[dimjim]

http://www.nord-lock.com/video/nl_uk.wmv

I saw this nord-lock video and am not certain
that the strait line that they show is simply
separation of the parts? The video shows the
vibration loosening the nut which means that
the clamping load was in turn decreasing.
After you loose the preload who cares which
type of nut stays on the stud. The video was
impressive but not certain that what you are
concluding is correct.

 

[kirstant]

dimjim,
I think you need to watch the video in full. Nord lock seemed to have the last say on the other thread mentioned. I have a sample of a Nord Lock washer, even finger tight it works incredibly well, with 45Nm I would be more than confident.
As for the dowels, they have been added after the fact, we have yet to see their worth.
Regards
Anton

 

[dimjim]

After a review, I have to agree that the demonstration
is impressive. Let us know how this works out for you.
I do think the dowels make the most sense but will be
curious to see what they look like after 100 hours in
the field. From viewing the video, I too would try those
Nord-lock washers.

 

[MintJulep]

Note that Nord-lock imposes a maximum hardness requirement on the faying surfaces of the joint material next to the washer.

 

[unclesyd]

You might want to give these people a call. This is a little different approach that may help alleviate your failure by aligning the bolt without the extra holes. It may be possible to use the Nord-Lock alone with the open dowel.

http://www.spirol.com/apps/internet/spirol/website.nsf/DowelsBushings!OpenForm

 

[BillPSU]

We were experiencing fatigue failures in a spindle attachment bolts on a planetary drive axle. The solution in that application was counterboring the thread to allow the bolt to flex.

 

[kirstant]

unclesyd,
That is another very good approach which would no doubt help.

BillPSU,
Counter boring the holes also increases the effective bolt length which is also a good thing, using the dowels above would also do that. One of the repairs includes counter boring with far side tapped holes.

I have been talking to a local engineer associate, we are both unconvinced that separate dowels was a good idea as they reduce the bearing surface but don't address the problem of clamp pressure and fretting. We think correct bolt tension is a better place to start.

I don't want to modify the existing components to much as we will then be in a very experimental phase, certainly this thread has come up with some very sound ideas.

No one has used or seen loctite on the mating surfaces (a la Metalguy's post) but can't say why it shouldn't work, the only concern is what would happen if the product broke down, would it then form a low friction area with reduced clamp pressure.

Regards to all,
Anton

 

[unclesyd]

Could you comeback with the hardness of the flywheel proper and the mating crank surface?

Also how thick is the flywheel?

What is the radius under the head of the SHCS?

What is the hole clearance in the flywheel?

What is the call out on the relative surfaces between the flywheel and crank? Things like flatness, surface finish, etc.


I need some food for for thought.

Actually this reverts to several problems that I've encountered in using high strength fasteners and things mentioned in previous posts.

 

[unclesyd]

One more question, does the flywheel drive the starter as a generator?

You might want to look at this approach as time permits.

http://www.spiralock.com/

 

[kirstant]

unclesyd,
Unfortunatly I don't have all the answers to tour questions, but here are some.
The radius of SHCS's is approximatly 1.5 X the diameter of the bolt.
The surface of the crank and flywheel have been blued and found to be perfect.
I don't have the exact hole clearance but I imagine it would be the standard size ie 5/16th in this case.
The overall grip length is 3/4" prox.
I have no idea what the hardness is.
No the flywheel does not drive the starter.
Regards
Anton

 

[unclesyd]

Here is what I was eluding to in respect to the bolt failures in short form general terms.


Hardness:
The hardness of the mating pieces can be concern due several reasons, some of which have been mentioned above like the loss of integrity due say asperities on the mating surface under the fastener head. Another would be that the head of the fastener tends to embed in the mating material. This causes all types of problems like putting a bending moment on the head of the fastener. While embedding there is usually a gall therefore the contact stress and point loading to the head of the fastener, and friction coefficient under the head can be altered. Another problem if the mating part, crankshaft, has a much lower hardness than the hardened fastener it can actually reform some internal threads corrupting the thread geometry and throwing the friction values off.

Thin Disks.
I had some problems with flywheels flexing while running if they were too thin. My first encounter with this was in my hot rod days when we attempted to shave the flywheels. This was solved by leaving a hub in the center for mounting the flywheel. The bolts broke in a similar manner as yours. In my high speed machinery days we had the same problem with the additional problem with exciting the high speed disks with the resultant vibrations wrecking several machines. I have seen problems where the flywheel was driving a generator and the gears were causing the flywheel to flex. Displacement transducers and strobe lights reveal strange things.

Radius:
The radius I was referring to is the small radius between the shank of the fastener and head. On some fasteners this radius can be enough to interfere if the hole clearance for the fastener is to close. This happened to me when we had to use hardened ground washers on some H11 SHCS and the forgot the chamfer.

Clearance:
The clearance between the bolt and mating part can become a factor in critical applications. For an application such as yours the tighter the clearance without interference the better. Make sure the under head clearance doesn't interfere, use just enough chamfer to clear. Too much clearance will exasperate any possible relative movement between the 3 components.

 

[Tmoose]

Loctite to fortify an interference metal-to-metal fit - In the semi modern era Harley factory recommendation for crankshaft assembly was to use high temp, high strength, slow curing loctite (620 ?)on the tapered joints used to lock the mainshafts and crankpin to the flywheels. Previously nut torque alone was used to lock the tapered shafts to the flywheels.
General description here on page 4 -

http://www.nightrider.com/biketech/...pdf#search="harley flywheel assembly loctite"

 

[EdDanzer]

You may want to consider using a body fit studs and tapered washers similar to larger truck axles. Your flywheel should not require much clamping force, but may require a lot of torque holding. Another advantage to studs is you can measure elongation with a dial indicator as you tighten them.
Loctite is a plastic, when cured it has a low yield strength, and can be brittle so torque induced impact will turn the material to dust.

 

[kirstant]

EdDanzer,
Regarding Loctite, that's what I thought also.