Hey Toby -
In interesting point about helicoils is their ability to maintain
preload even after they are stripped out. They are a spring and as the
bolt threads are loaded against it, they expand out and the sharp edges
of the helicoil grab the hole sides. Keenserts don't have this ability
because they are a rigid structure.
Loctite - oh, Loctite. At this point Loctite has been banned by JSC
Engineering for any critical application on Space Station due to recent
failures. We all know it works but through extensive testing can not
iron out the sensitivities of this system. Our data is all over the
place. Big pow-wow next week at LaRC to figure this mess out.
-----Original Message-----
From: owner-datsun-roadsters@autox.team.net
[mailto:owner-datsun-roadsters@autox.team.net] On Behalf Of
RacerY@comcast.net
Sent: Tuesday, August 15, 2006 2:31 PM
Cc: datsun-roadsters@autox.team.net
Subject: Re: ARP, the result - K factors
Well, Phil,
then don't use Helicoils, use Keenserts/tineserts/timeserts, etc- they
uprate your stud threads to at least the next fastener size up!
And yes, loctite is your friend...
And one of the cool things about head studs- if you REALLY care about
stud preload and stretch, you can set up a dial indicator and tension
the fastener to an exact preload.
With rod bolts it can really matter in a race engine.
On head fasteners, it's overkill. Until you boost it to 50 psi, then
everything starts to really apply!
heh heh
Toby
-------------- Original message ----------------------
From: "Hall, Phillip" <Phillip.B.Hall@nasa.gov>
> Hey List, and Roadster nuts.....
>
> Interesting discussion on torque values. We (the NESC/NASA) have been
> working these issues for a few months now. I am the lead on a Team of
> experts to find a resolution to the application of dry film lubricants
> on the bolts that hold the cap on motors on the Power Drive Unit (PDU)
> that drives the body flaps and rudder/speed brake actuators on the
> Space Shuttle. The problem is with the DFL applied to the bolts, the
> K factor decreases which (by analysis) shows we are under negative
> margins at the helicoil insert (the insert can be pulled out). By the
> relationship of T=KFD (T=torque, K=K factor, F=force or preload, and
> D=diameter of the
> bolt) one can see by using torque values for a non-DFL bolt on a DFL
> bolt (lower K factor), the preload can really increase. Through test
> we demonstrated we have enough margins (system is robust) to handle
> the increase in preload without pulling the insert which would result
> in lose of hydraulic pressure and vehicle. The important thing to
> remember, as you all have been discussing, the K factor is a key
> component in the system. It can vary dramatically depending on if you
> use a lubricant and which lubricant you use - as Fred found out. Oh
> yea, the K factor is the amount of friction produced in the thread and
> bolt head interfaces.
>
> The short of it. Like you guys are talking about - use the basic
> principles of a better lubricant will increase your preload so you
> must decrease your torque values. To really know what is going on in
> a system you have to use load washers to measure preload.
>
> Happy Roadstering!
>
> Phil
> SEROC
>
> PS: Next subject - the application of Loctite....
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