Helicoil into Quartz?
Helicoil into Quartz?
(OP)
Hi All-
I have a higher temperature (200-300 °C) application where I need to use a helicoil.
I've never tried to use a helicoil in quartz before, and I'm wondering if anyone has experience with it (holding power, strength, etc.). It's not holding a great deal of weight, but I'm getting some push back about using it. I've looked online, and in these fora, but haven't found any info.
Most likely I would be using an Nitronic Helicoil to prevent galling.
Any experiences or advice is welcome.
I have a higher temperature (200-300 °C) application where I need to use a helicoil.
I've never tried to use a helicoil in quartz before, and I'm wondering if anyone has experience with it (holding power, strength, etc.). It's not holding a great deal of weight, but I'm getting some push back about using it. I've looked online, and in these fora, but haven't found any info.
Most likely I would be using an Nitronic Helicoil to prevent galling.
Any experiences or advice is welcome.
V





RE: Helicoil into Quartz?
RE: Helicoil into Quartz?
Caveats which you probably well know - brittle materials are tough to thread, and don't hold threads well, the usual failure mode is for the first thread to fail in shear, and then the next thread, and the next, unzipping down the line. Using a helicoil may help to spread the load out, if for no other reason than the thread is size or so larger where the coil engages the quartz. Differential expansion will be an issue, but again adding a helicoil will help by adding some tolerance "slop".
No way you can make it a through bolt/fastener?
RE: Helicoil into Quartz?
Is it molded in place? The thermal expansion of steel is something like 30 times that of quartz. That means that whatever you've threaded into the helicoil would be under huge compression at operating temperature, possibly enough to cause some cracking?
TTFN
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RE: Helicoil into Quartz?
I like IRStuff's point about thermal expansion.
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Helicoil into Quartz?
With an adhesive there would be no "abuse" of the quartz.
RE: Helicoil into Quartz?
KENAT,
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What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Helicoil into Quartz?
RE: Helicoil into Quartz?
Use of a nut is not possible, as we're trying to assemble/disassemble from one particular side.
I would be tapping into the quartz for the helicoil. So the hole would not be smooth.
My main perceived problem, as was mentioned, is thermal expansion.
Anything that I try to press, epoxy, thread, etc. into the quartz is most likely going to expand a lot more than the quartz.
The situation is that I have two pieces of quartz, surface to surface that I need to hold together. Attached is a cross-section of what I mean. Also, this will be in vacuum.
V
RE: Helicoil into Quartz?
KENAT,
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RE: Helicoil into Quartz?
TTFN
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RE: Helicoil into Quartz?
The material behind the quartz is aluminum (no good for electrical isolation POV). Sorry should've mentioned that before.
IRstuff-
I suppose if they make 'em, we can get 'em. Does Invar have a low CTE?
V
RE: Helicoil into Quartz?
RE: Helicoil into Quartz?
http://www.meteng.com/ceramnt.html
http:
TTFN
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RE: Helicoil into Quartz?
Another reason why I was thinking of using either Inconel or Nitronic helicoils.
Any thoughts?
Thanks for all the help so far.
V
RE: Helicoil into Quartz?
Your first recommended site meteng.com says the "strength" of invar is 30 million psi.
Does NASA know about this stuff ? (;<))
RE: Helicoil into Quartz?
TTFN
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RE: Helicoil into Quartz?
TTFN
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RE: Helicoil into Quartz?
Also, am I being dumb or do you have your coefficients of friction back to front?
KENAT,
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RE: Helicoil into Quartz?
That's what I was thinking, but I have a feeling that will be shot down, as I imagine Invar is fairly expensive.
V
RE: Helicoil into Quartz?
Plus I'm sure those Malaysians can knock it out cheap
KENAT,
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RE: Helicoil into Quartz?
Not half as expensive as the quartz, I'd think. A reverse-tapered sleeve with a tapped hole thru it, and some silicone or other high-temp. adhesive to help cushion along the interface b/n metal and quartz...
RE: Helicoil into Quartz?
I'm being told to go in a different direction by my fearless leader (read as knob of a boss), so I believe we'll have to end this discussion for now. Thanks all, for the help, and if there are any other comments, suggestions, etc. keep them coming.
V
RE: Helicoil into Quartz?
Quartz isn't that strong in tension or bending compared to metal. The limiting factor on this design for shear pull-out or plate bending will be the quartz and not the metal fastener by quite a large margin. So why use a metal fastener?
Just eyeballing it makes me think that there is plenty of shear area for pull-out for an adhesive to work well although the temperatures are higher than I have experience of.
Have fun.
gwolf
RE: Helicoil into Quartz?
If I didn't have to disassemble the parts at all, I'd completely agree; however, it's necessary to disassemble every 2 weeks or so for cleaning.
V
RE: Helicoil into Quartz?
TTFN
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RE: Helicoil into Quartz?
The only weight it's supporting is its own. Six screws around a bolt circle (can be more). Number 10's (can be bigger). That's a very good idea.
Maybe I'll try to convince the powers that be to test that theory.
V
RE: Helicoil into Quartz?
I'd guess you'd want a fairly coarse thread and you'd maybe want to be carefull not to over torque it.
Maybe these guys can help.
http://www.hellma.co.uk/precision.htm#6
Their US office is just round the corner from you I believe http://www.hellmausa.com/
KENAT,
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RE: Helicoil into Quartz?
RE: Helicoil into Quartz?
RE: Helicoil into Quartz?
http://www.hellma.co.uk/precision.htm#6
KENAT,
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RE: Helicoil into Quartz?
All the same, very cool!
RE: Helicoil into Quartz?
KENAT,
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RE: Helicoil into Quartz?
If you are in a vacuum be carefull with your adhesive selection because of outgasing. Try a retaining ring or other design change instead if you are still unsure.
RE: Helicoil into Quartz?
TTFN
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RE: Helicoil into Quartz?
RE: Helicoil into Quartz?
In your cross section, the blind threaded hole is in vacuum? Isn't this not allowed, creating a pocket at ambient within a vacuum?
Can a threaded compression ring be included in the assembly/disassembly side, assuming your quartz pieces are located within a bore or housing can be changed to an internal bore detail. Or ring with bolt circle into other housing pieces compressing quartz pieces? Apologies if these are old ideas.
RE: Helicoil into Quartz?
I would imagine that assembling the part once with a thread wouldn't be a big problem, but repeated removal and rereassembly is bound to have somebody overtorque, cross thread, or otherwise abuse the helicoil and quartz beneath.
One other thing to consider is the holding force of the screws as they expand, since they'll expand axially much more than the quartz will. If the temperature is being cycled, they could actually start to back out some, which would be bad.
RE: Helicoil into Quartz?
You might consider using MACOR, a glass ceramic which can be machined, is excellent for high temperature and is strong.
It is used in high vac systems and is clean.