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I have an interlocking set of parts (1 and 2) which are used under vacuum. The last time I used it, the interface was wet with a mixture of water and ethanol. When the vacuum was removed, the two parts stayed firmly fused and no amount of force that I can apply can pull them apart. I suspect I will break the glass neck before I break the connection.

Can anyone suggest some tricks I could try to use to unstick them? I have tried heating the interface, which had no effect, and I have tried lubricating it, but the connection is too tight to allow the lubricant to penetrate.

Here is a crudely drawn picture of the fused pieces: enter image description here

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  • $\begingroup$ have you tried putting the parts into the vacuum again? Perhaps some form of vacuum bagging which would allow you to apply force in opposite directions (sliding) until they are fully separated. It would be necessary to perform multiple iterations, vacuum, slide a bit, release, reposition the bagging, repeat. $\endgroup$
    – fred_dot_u
    Jun 26, 2018 at 14:29
  • $\begingroup$ @fred_dot_u interesting suggestion, I will look into how I can make that happen. I'm having a hard time picturing the setup $\endgroup$
    – KBriggs
    Jun 26, 2018 at 14:33
  • $\begingroup$ Can you post a picture or drawing of the parts so we understand the interface itself? $\endgroup$
    – Carl Witthoft
    Jun 26, 2018 at 17:15
  • $\begingroup$ @CarlWitthoft I have edited the OP with a really bad drawing $\endgroup$
    – KBriggs
    Jun 26, 2018 at 20:22
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    $\begingroup$ "Stop cock grease" is normally used to prevent this and improve the seal. $\endgroup$
    – blacksmith37
    Jun 27, 2018 at 16:35

3 Answers 3

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Perhaps, depending on the materials, you could try gently heating one piece while cooling (or at least heat-sinking) the other piece, and hoping that the expansion mismatch will separate them.

You haven't identified the glass types nor their surface quality-- if the interface areas are porous, your contaminants may well have formed physical bonds which are stronger than the glass. In which case, you're stuck (pun intended)

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  • $\begingroup$ The links in the OP show the two elements - the interface has a frosty finish which is slightly rough to the touch, which seems to form a vacuum-tight seal with only contact between the two parts. I can't imagine water and ethanol forming physical bonds to glass beyond Van Der Waal's. Heating/cooling is a good idea, if I can get the heatsinking right. $\endgroup$
    – KBriggs
    Jun 26, 2018 at 17:53
  • $\begingroup$ oh, dear.... my experience with frosted glass is it ain't never coming apart no matter what. $\endgroup$
    – Carl Witthoft
    Jun 26, 2018 at 18:56
  • $\begingroup$ Well, the thing broke while I was playing with pressure fittings anyway, so I guess I need to buy a new one anyway! Any idea what causes it to fuse? I've used it in exactly the same way about 50 times already, why this time in particular? $\endgroup$
    – KBriggs
    Jun 26, 2018 at 20:18
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    $\begingroup$ My personal theory is that gremlins comprise a sizable percentage of dark matter. And O-rings are cool. $\endgroup$
    – Phil Sweet
    Jun 26, 2018 at 23:09
  • $\begingroup$ That does indeed seem like a more intelligent setup. $\endgroup$
    – KBriggs
    Jun 27, 2018 at 13:00
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Vacuum bagging is used in the creation of various items, including and especially amateur built aircraft. A suitably strong surface holds the item being bagged. Plastic film is placed over the item and taped to the surface, along with a port for the vacuum source.

Typically, a layer of dacron material is placed over the fiberglass, as it does not adhere to epoxy resin, but also serves as a porous space for air to be removed. You won't be applying resin, but you would want the spacer. In your case, the material would be useful below the item as well.

There are many resources when using "vacuum bagging composites" as a search term. One source I've used in the past is fiberglast.com for supplies.

The following image is from their site:

bagging image

But most of it would not apply to your application.

I think the tricky part would be moving it after the vacuum is in force. Two opposing strings? It would slip under the sealing tape and yet be more easily applied than trying to slide the two parts with hands through the bagging film.

If possible, bunch up the film where you need movement.

Even if the film tears, you would not be breaking glass!

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  • $\begingroup$ I could seal the two inlet holes, and apply vacuum to the top part, which would leave 1 atm of pressure inside the jar and effectively push them apart, is this the right idea? I could also hook up a compressed air line to the interior, applying vacuum to the top part while pressurizing the interior for even more force. Thanks, I'll give it a shot. $\endgroup$
    – KBriggs
    Jun 26, 2018 at 15:00
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    $\begingroup$ Actually it might be easier to do this in reverse - simply seal the holes and pressurize the interior. I can easily get about 20-30 psi of pressure inside it with a compressed air line, which should be an equivalent force to the vacuum but would be much simpler to implement. $\endgroup$
    – KBriggs
    Jun 26, 2018 at 15:04
  • $\begingroup$ I envisioned flat panels of glass, which will also bond if clean. I wasn't aware you had access to the internal volume. That definitely changes the picture. Atmospheric pressure is 14.7 psi. You would not need much more than that, I suspect. $\endgroup$
    – fred_dot_u
    Jun 26, 2018 at 15:59
  • $\begingroup$ Thanks for the tips. I'll need to dig up some appropriately pressure-reinforced tubing and fittings to seal everything. If it works I'll let you know. $\endgroup$
    – KBriggs
    Jun 26, 2018 at 16:22
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    $\begingroup$ You'll want to constrain things appropriately so that if the two parts -are- 'disassembled' under pressure that the obvious projectile problem doesn't occur... Perhaps wrapping the whole assembly in a foam pillow? $\endgroup$
    – BobT
    Jun 26, 2018 at 16:46
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Sorry for late reply, but may be this will help. I usually separate such stuck glass joints in ultrasonic cleaner with water. Cleaner should not have very large power to not crack the glass. In severe case may be couple drops of kerosene before sonication will help, but i haven't tried this.

To avoid such stuck in the future it is good to use vacuum grease, for example, silicone-based high-vacuum grease, it is quite clean, inert and inexpensive.

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