Helicoil into Quartz?

[vc66]

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

 

[KENAT]

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 cheap;-).

KENAT,

Have you reminded yourself of faq731-376 recently, or taken a look at posting policies:

http://eng-tips.com/market.cfm?

What is Engineering anyway: faq1088-1484

 

[btrueblood]

"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...

 

[vc66]

Yea, they would, but I imagine it would be Invir or Invor, or the like. Yay, outsourcing.

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

 

[gwolf2]

>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

 

[vc66]

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

 

[IRstuff]

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

 

[vc66]

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

 

[KENAT]

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 recently, or taken a look at posting policies:

http://eng-tips.com/market.cfm?

What is Engineering anyway: faq1088-1484

 

[WH74]

Do you need the two quarts parts, can you use one and retain the center can a different way? see picture.

 

[moltenmetal]

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!

 

[KENAT]

moltenmetal take a look at the link I gave above. Apparantly someone appears to have managed it.

http://www.hellma.co.uk/precision.htm#6

KENAT,

Have you reminded yourself of faq731-376 recently, or taken a look at posting policies:

http://eng-tips.com/market.cfm?

What is Engineering anyway: faq1088-1484

 

[moltenmetal]

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!

 

[KENAT]

molten, that applies to a lot of stuff our company does, nanotechnology and all that aint always cheap.

KENAT,

Have you reminded yourself of faq731-376 recently, or taken a look at posting policies:

http://eng-tips.com/market.cfm?

What is Engineering anyway: faq1088-1484

 

[HDS]

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.

 

[IRstuff]

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

 

[btrueblood]

Or a 1/4-turn bayonet mount.

 

[pierdesign]

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.

 

[jmblur]

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.

 

[jedward]

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.