×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Helicoil into Quartz?

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.

V

RE: Helicoil into Quartz?

Why don't you go to the mfr of Heli-Coil. They have a wealth of applications data.

RE: Helicoil into Quartz?

I suppose it could be done...

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?

Can't imagine that there would be anything for the helicoil to engage against.  Wouldn't it be sitting in a smooth-walled hole, as opposed to a threaded hole in metal?

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

FAQ731-376: Eng-Tips.com Forum Policies

RE: Helicoil into Quartz?

I think you'd have more luck cementing a threaded insert in place, using a nut and a bolt (preferred) or filling the hole with something solid that will take a thread and then drilling and tapping that, or using an expanding nut.

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?

Maybe you should consider  using a "Hilti" anchoring system.
With an adhesive there would be no "abuse" of the quartz.

RE: Helicoil into Quartz?

Potting with epoxy or other adhesive is the normal way to put in caulking anchors or thread inserts in stone products, as several others have mentioned in this thread.

RE: Helicoil into Quartz?

(OP)
Hmmm. All good suggestions.

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?

(OP)
KENAT-

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?

Wiki   "invar"   -  good stuff

RE: Helicoil into Quartz?

(OP)
Another perceived problem (news to me), is that the coefficient of friction between the helicoil and the quartz will be larger than that of the helicoil and the screw, so even if slight galling occurs, the helicoil will be screwed out of the hole.

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?

Re: IRstuff

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?

Actually, I believe that table is for the fused silica mount, and not the screws, per se.  Not that the number is right, it's just not about the Invar screws.

TTFN

FAQ731-376: Eng-Tips.com Forum Policies

RE: Helicoil into Quartz?

How about a custom metal insert, perhaps invar as mentioned, of a shape that's fairly easy to machine into the quartz but resists turn out so the adhesive is just stopping it from falling out?.

Also, am I being dumb or do you have your coefficients of friction back to front?

KENAT,

Have you reminded yourself of FAQ731-376: Eng-Tips.com Forum Policies recently, or taken a look at posting policies: http://eng-tips.com/market.cfm?
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?

RE: Helicoil into Quartz?

(OP)
You're right, KENAT. I had 'em mixed up.

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?

I'm not saying it's cheap but we use quite a bit of it, for instance a 50lb or so casting.  In fact, when we had one of our many draw-downs of stock I think we basically gave a bunch away.

Plus I'm sure those Malaysians can knock it out cheapwinky smile.

KENAT,

Have you reminded yourself of FAQ731-376: Eng-Tips.com Forum Policies recently, or taken a look at posting policies: http://eng-tips.com/market.cfm?
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?

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. "

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?

(OP)
Yea, they would, but I imagine it would be Invir or Invor, or the like. Yay, outsourcing. 2thumbsup

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?

>Thanks all, for the help, and if there are any other comments, suggestions, etc. keep them coming.

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?

(OP)
gwolf2-

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?

Are there limitations on thread pitch, diameter, etc?  Why not just have a somewhat looser thread and screw the Invar directly into the quartz?  If the diameters are sufficiently loose, you might not have much CTE worries as well.  This is all predicated on the fastener not having to support much load, though.

TTFN

FAQ731-376: Eng-Tips.com Forum Policies

RE: Helicoil into Quartz?

(OP)
IRstuff-

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?

Darn, IRstuff beat me too it.  I too was thinking if you believed you could tap the quartz for the helicoils why not tap it directly for a screw.

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,

Have you reminded yourself of FAQ731-376: Eng-Tips.com Forum Policies recently, or taken a look at posting policies: http://eng-tips.com/market.cfm?
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?

RE: Helicoil into Quartz?

Enlighten me, folks who keep talking about this:  how the $^&%& do you propose to thread a small, blind hole in vitreous quartz?  I suppose where there's a will, and sufficient diamond, there's a way- but from my armchair I'm not seeing an easy way to do that!

RE: Helicoil into Quartz?

Hellma, eh?  Lab stuff- you wouldn't want to pay for it out of your own pocket, that's for sure...

All the same, very cool!

RE: Helicoil into Quartz?

your quartz supplier should be able to answer these questions for you.  (if not get a better one)

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?

Would it be possible to use clips around the periphery?  Those are often used to hold wafers in their positions for some evaporation systems.

TTFN

FAQ731-376: Eng-Tips.com Forum Policies

RE: Helicoil into Quartz?

Or a 1/4-turn bayonet mount.

RE: Helicoil into Quartz?

interesting.

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?

Might it not be easier to simply epoxy or otherwise bond a metal shaft in place in a blind hole in the quartz "base", with a through hole in the 2nd piece of quartz, use that as your stud? You could then use a nut, circlip, or any other type of connector you wish.  you still need to deal with CTE, of course, but you had that problem before anyway!

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?

I did not see why you needed Quartz for your application.

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.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources