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ImanCarrot
08-06-2008, 10:39 AM
What would you use to glue an acrylic lens to an acrylic cylinder? It's got to stand up to water pressure typical that a diver would experience.

I was thinking straight superglue. Would this work or are there better alternatives?

Any help appreciated!

karl1
08-06-2008, 11:10 AM
I use M.E.K. (A.K.A. Methyl Ethyl Ketone) - this will soften the plastic of the two surfaces and cement them together; use it sparingly since it could also "fog" the lens surface. The term glue wouldn't apply here since both surfaces are softened by the solvent and bonded by the evaporation of the M.E.K.

lovebugjunkie
08-06-2008, 01:21 PM
I use Weld-on 4, it is what the the place where I bought my acrylic from suggested.

http://www.ipscorp.com/industrial/acrylics.html

gandalf1
08-06-2008, 01:41 PM
Super glue may not withstand water and soften,
I always use Di-Chloromethane which dissolves the surface and 'welds' the pieces together.
John.

ImanCarrot
08-07-2008, 05:10 AM
Many thanks for the replies. I'll try the different methods on some scrap components and see what happens!

Geof
08-07-2008, 07:43 AM
What would you use to glue an acrylic lens to an acrylic cylinder? It's got to stand up to water pressure typical that a diver would experience.

I was thinking straight superglue. Would this work or are there better alternatives?

Any help appreciated!

Will the cylinder be empty or full? In other words same pressure inside and out; that is what a diver experiences, the pressure differential across the interior and exterior of the diver is zero. It will be easy to glue something together to withstand this pressure differential.:D

cam1
08-07-2008, 08:12 AM
Geof:
Perhaps I'm misunderstanding you (my cup of coffee is 1/2 full)
When the container is shut/sealed at atmospheric pressure, and then submersed there will be a pressure differential accross the walls directly proportial to the depth. This is no different than a submarine. I'm not sure as to what the maximum safe depth is for a diver.

regards

ImanCarrot
08-07-2008, 09:24 AM
Nope, the internal pressure will be different. ie: air on the inside, 100m (or so) of water on the outside (whatever divers go down to). I had toyed with the idea of filling the cavity with an index matching oil and having a thinner front dome since liquid is (fairly) incompressible I woldn't need as thick a dome- here's a rough sketch of what I'm gonna glue/ cement.

Behind the cylinder is going to be a PCB, some circuitry and a housing for the power supply.

cam1
08-07-2008, 01:08 PM
Hi:The presure adds up.....
at 100m the pressure = 9.91kN/m^3 X 100m
= 991kN/m^2 x 1m^2/ (1000mm)^2
= .991Mpa or 143.7 PSIg

regards

Geof
08-07-2008, 03:36 PM
Geof:
Perhaps I'm misunderstanding you (my cup of coffee is 1/2 full)....

I was being obtuse; if you have seen some of my previous posts in reply to queries from Mr Carrot you will see we both take the micky a bit.

You are correct, seal the container and submerge it and you do get a pressure differential; that is if the container is rigid and strong enough to sustain the pressure.

Humans are very floppy containers and cannot sustain any differential so a diver breathes air at the same ambient pressure as the surrounding water so there is no differential.

The sealed container mimics a submarine with a pressure differential across the wall.

The oil-filled container, if it included a flexible membrane between the oil and the water, would mimic the human body with no pressure differential between inside and outside. In my not humble at all opinion this is the preferred method.

Just make sure the acrylic cylinder is CAST acrylic not extruded.

bloefeld
08-07-2008, 04:30 PM
I would think hard about using PMMA in this application. Have you thought about perhaps using polycarbonate instead. It is much tougher over a wider temperature range. It is more difficult to bond and it is very hard to get an optically clear joint when you do bond them. However difficult and impossible are not the same thing.

I have some expertise in adhesion science and the key to getting good bond to acrylic (well actually anything) is good surface preparation. In your case it is important to make sure your two jointing surfaces are flat and square with each other. Mask off the area you do not intend to bond and sand the area you do want to bond with 80 or 100 grit sand-paper. Blow it down with clean, oil and water free air. I would suggest using one of those cans of cleaner for computers. They are very pure and will not put anything you don't want on the surfaces.

I use methylene chloride as the solvent for adhesion. Melt-Melt bonds are the strongest adhesive bonds you can get. Basically the MDC melts a bit of both surfaces, they flow together and when the solvent evaporates the two pieces become chemically identical.

If you do not want to use a chlorinated solvent (be really careful in handling it if you do) then the prior suggestion of MEK is an excellent alternative. MEK is rarely high purity though, so your joint may not look as pretty.

In either case, use one of those little polyethylene dispensers with a needle attached to apply the solvent. You only need a few drops to form a thin film to get the desired results

Do not use 'super-glue' for anything you are going to put into water. cyanoacrylites are great in anaerobic environments but they de-polymerize when exposed to moisture. In fact if you are not using it as loc-tite don't use it for anything.

The other glue alternative is two part methacrylate adhesives. The will cross-link to the two surfaces, but are not as good as a solvent-melt joint.

Hope this helps,

Cheers,

Bloefeld

cam1
08-07-2008, 04:40 PM
Hi:
Geof, I missed the "interaction", my wife tells me I'm a bit too focused and that I miss the nuances.
Also came accross some Loctite products: any one tried this product?
I have a project coming up where we'll have to fabrcate some 12 X 16 ducting from 1/4 ploycarbonate.

cheers

bloefeld
08-07-2008, 04:56 PM
I have not tried these Loctite products but have experimented a lot with UV cure adhesives.

Is there a reason you wish to use UV?

A good UV lamp will cost you about $4000.00. The cheap ones do not have enough intensity of UV B and C to get good cure. The sun works OK, but gives unpredictable results.

The glue joint itself will need to be exposed to the light source because the polycarb will absorb a lot of the available UV.

You are on the right path though. I would recommend speaking with a Loc-tite technical person about the requirements of your joint; they will want to know what are the strength requirements, what are the exposure conditions, and what types of stresses will the joint see.

If you are doing a butt joint, it is important to tell them, because there is not much surface area to adhere to at .125"

Loc-tite has a wide range of excellent products. I would also recommend contacting 3M, they have a great deal of expertise in gluing these sorts of resins.

If you can attach a sketch of the part and to what else it is going to be attached, I may be able to shorten your search for the right adhesive.

Cheers,

Bloefeld

cam1
08-07-2008, 05:59 PM
Thanks, I'll do that.
I may elect to bond 1.5"X 1.5" architectural angle along the edges to increase the glue area. We're going to pull 25lbm/s air through these ducts, and there will be an appreciable amount of delta p.

regards

bloefeld
08-07-2008, 06:14 PM
Hi,

Why does it need to be clear? To see if it is plugged?

Cheers,

Bloefeld

Geof
08-07-2008, 06:16 PM
bloefeld describes a technique for acrylic (PMMA) that relies on capillary action to draw the swolvent into the joint. In my experience it works like a hot d**n on acrylic but does not work as well on polycarbonate. The polycarb onate seems to swell and stops the solvent flow.

If you can figure out how to do it what you may try is soaking one edge of the joint in a trough of solvent then when it is nicely softened bring it into contact with the other edge of the joint. This works extremely well and can give a joint as strong as the parent material.

And if my explanation is not understandable enough I can expand on it in a couple of days; at the moment I am on vacation and am about to go out for a good dinner.

cam1
08-07-2008, 08:50 PM
Bloefeld:
It's a tunnel for observing the buildup of ice on a gas turbine engine LP compressor blade.The reason the ducting needs to be clear is to allow for cameras and "laser" scanners to measure the buildup over time. If possible I may elect to go with Acrylic (depends on the buckling stresses) as it appears to be "easier" to bond.

regards

judleroy
08-08-2008, 03:45 AM
Polycarbonate can be welded if strength is needed. The process does take practice to acheive an attractive and permanent weld.
Polycarbonate solvent is also available and works very well. THF
Used to bond PVC is the best alternative to bond polcarb if a true
polycarbonate solvent is not available. Acrylic does not handle cold
weather very well if vibration or impact is an issue as it gets brittle when its cold. Transparent PVC tubing is also a good alternative.

Judleroy

ImanCarrot
08-08-2008, 06:40 AM
cyanoacrylites are great in anaerobic environments but they de-polymerize when exposed to moisture

Didn't know that! thanks!

I can't go with anything that melts the surface- the evaporating solvent will outgass onto the optical surfaces and the melted surfaces will no longer be opticaly square. ie: the dome will be at a slight angle I think.

I'll speak to Loctite and dump the problem on them.

UV curing stuff- I have benchtop and handheld UV sources and opticaly clear UV curing adhesive from Norland Products- woks perfectly for glass, unfortunately Acrylic don't transmit in the UV (well it does a bit, but not enough). I tried it and it don't work :(

And Geof is spot on about Cast Acrylic instead of Extruded. Don't go near Extruded.

Polycarb- I've machined this before and the finish is no where near as good (opticaly) as Acrylic- it's horrible stuff to machine, I won't even quote on any optics in polycarb!

Or! another thing I might do- machine the two parts and give them to the customer to glue! :)

Geof
08-08-2008, 08:07 AM
..... the evaporating solvent will outgass onto the optical surfaces and the melted surfaces will no longer be opticaly square. ie: the dome will be at a slight angle I think....

If you have an optical shape subjected to a pressure differential how do you expect it to maintain the correct shape?

I think you need to redesign the optics so you can have an oil filled chamber with the membrane I describe and no pressure differential across the lens, or you need to put the optics behind a window that holds the pressure.

ImanCarrot
08-08-2008, 08:35 AM
Exactly my own ideal solution, Geof- fill the bugger with and index matching liquid. No pressure problems.

However... I have to have an air (or gas) filled compartment in there for the batteries- they will inevitably have to be replaced. I thought of presurising this bit, but thought "Lawsuit!" if the thing exploded on land.

The problem is that the strongest interface between gas and water will be the spherical lens surface. Think like compartments in a submarine. The next bulkead in this submarine is a 1mm thick PCB that needs power from the battery cells (in the next compartment). There has to be wires from the battery cells to the PCB and no hole sealant will withstand that pressure.

I may just chuck the bloody problem back at the designer and say "you realise this has got to withstand the equivalent of 140PSI? I can make it, but you can assemble it."

Bloody designers, I swear they have a club where they sit all day and think "hehe, let's try this one" :)

[Edit]Or! thinking about it! I could fill the battery compartment with the same liquid and state categoricaly "Batteries only to be replaced by [MY COMPANY]" that is a money maker!

Geof
08-08-2008, 09:03 AM
....However... I have to have an air (or gas) filled compartment in there for the batteries- they will inevitably have to be replaced. I thought of presurising this bit, but thought "Lawsuit!" if the thing exploded on land....

Make the battery pack separate in its own housing with a pressure tight connector. This is also handier for recharging because you can have several battery packs available and switch in a full charged one in a few seconds.

I used to make things like this when I worked for DAFS in Aberdeen (Dept of Agriculture and Fisheries for Scotland). I was involved in instrumentation used on deep trawl nets. My fanciest device was a 2000 psi electrically triggered water pistol shooting a formalin solution out to stun fish. It was used on a deep diving submersible where the ambient was around 1800 psi so really it was only a 200 psi pistol. But on the surface it was a potentially lethal weapon.

ImanCarrot
08-08-2008, 09:38 AM
Can't do it mate, the customer specificaly wants a self contained unit- he's adamant on this, dunno why, but there it is.

Spookily enough, this project is for Scotland too, but not for DAFS. Small world innit!

bloefeld
08-10-2008, 03:26 PM
Hi,

I think I have the correct answer, the only issue is that the adhesive cures to a light yellow colour.

The adhesive is DP-8010 or DP-8010NS (no sag).

Lap shear on Lexan 1250 psi with cohesive failure and on PMMA 1075 with substrate failure.

It comes in 35 ml and 250 ml cartridge sizes.

This glue bonds low-surface energy plastics very well

Contact sales at 800-362-3550, ask nice and they may even send you some free samples.

Cheers,

Bloefeld

bloefeld
08-10-2008, 03:44 PM
The problem is that the strongest interface between gas and water will be the spherical lens surface. Think like compartments in a submarine. The next bulkead in this submarine is a 1mm thick PCB that needs power from the battery cells (in the next compartment). There has to be wires from the battery cells to the PCB and no hole sealant will withstand that pressure.

Somewhere along the line I have lost track of the pressure differential. I think it was around 145 psi. I am assuming you mean PVC and not PCB.

The materials sound sort of goofy to me, the designers are not leaving a whole lot of room for error if everything has to be optically clear and you have a battery pack to boot.

This would be a cinch with braided carbon fibre with a glass lens.

Anyway, why don't you simply pot the battery pack with potting epoxy or urethane. No issues with sealing it, and no problems with pressure. I have about 10,000 lithium C cell batteries potted, with a transmitter all over Johannesburg SA that have been in service for more than 10 years. We have never had a failure.

I'm with you though, get some bikers to go talk to the designers and see if maybe they can think of something that can actually be built out of real stuff instead of the cheese and Popsicle sticks approach they have now.

Cheers,

Bloefeld

Geof
08-10-2008, 04:06 PM
...The materials sound sort of goofy to me, the designers are not leaving a whole lot of room for error if everything has to be optically clear and you have a battery pack to boot.....Cheers,

Bloefeld

Materials are okay, design is goofy having the optical element also holding pressure. Acrylic is fine for this, after all you could, maybe still can, get acrylic housings for using regular cameras underwater, but these have a glass window set in an O-ring for the optics to 'see' through. The deflection in the glass is negligible over a small diameter.

bloefeld
08-10-2008, 04:43 PM
You make a very good point. The problem I have is the absence of the o-ring. Getting everything to seal up with the adhesive joints is not all that trivial. The compressive forces and thermal expansion issues on both sides of the cylinder seem to me to make everything that much more complicated.

Because the materials are somewhat difficult to adhere the choices of adhesives are few. They tend to be too rigid and I foresee some environmental stress cracking as the result.

However I am also inexperienced with compressive pressure issues; I can make you a really nice pressure vessel that can handle giant pressure made of composites, but I am out of my league with the experience of you guys in building underwater components.

I hope though that at least I have given some insight on the adhesive issues.

Cheers,

Bloefeld

cpcp
08-22-2008, 09:13 PM
It may be too late but had you thought of changing the design to allow inductive charging of the batteries?

ImanCarrot
08-25-2008, 06:01 AM
Thanks, the customer's put the project on the back burner, but the induction charging is a great idea! I'll definately use it, if not on this project, then certainly in the future.