Plastic tops?

[|kbn|]

My recent attempt at a copper top failed, so now Im trying plastic.
The idea of this thread is to find out as much as possible about different plastics and ways to make tops, which seems simple but there is not many good threads on it.

I have lots of polyethylene atm. Im intending to use plastic 1/2" 90 degree barbs.Which glue would be bet to join them to avoid leaks? I also have a body filler/resin which says on the packet that it bonds metal plastic and lots other stuff, it smells a lot too, and its still in the sealed bag!

What Id like to know is what plastics youve used, how good they were, thickness, price/quantity, good places to get it. Glue to seal it/bond to the base/barbs.

Also what about the plastic that you melt and mold to the right shape. Ive forgot what its called but would this be any good for water cooling? It would mean one-piece tops with barbs at any angle - might be too weak for that though...
I got the body filler for making tops on its own, but Ive got the polyethylene now instead which should be a lot better.

Also the polyethylene I have is designed for cutting boards for vegetables and such, so it has an annoying textured surface. How could I remove it while keeping it flat? Sanding it might take ages as its the sort of plastic that slides around and compleatly water resistant, that said it cuts very easly with a hacksaw.

[bigben2k]

Polyethylene is one of the toughest plastics to deal with, because it doesn't bond well to anything (Cyanoacrylate works OK). Consider Lexan (aka polycarbonate), or acrylic.

I use polycarbonate myself. You can purchase a 1/4" thick "sample" sheet from McMaster Carr ( www.mcmaster.com ) pretty cheap.

Both of these will tend to crack, so I also picked up a 4 oz jar of IPS Weld-On #4, which contains methylene chloride (nasty stuff!!!) and should seal the mirco-cracks quite easily, which should prevent crack propagation (just dab some in the holes you'll be drilling).

For a seal, the best recomendation I've seen, aside from an o-ring (which is hard to do properly) is using an RTV silicone, to make your own gasket. JayDee116, among others, can tell you all about it.

Supplier of IPS Weld-On #4:
http://www.delviesplastics.com/
(I've purchased from them, they're good)

[|kbn|]

Cyanoacrylate is super glue isnt it?
McMaster Carr doesnt ship to UK? I couldnt ifnd anywhere that sells polycarbonate in the UK, closest I found was on US ebay site, there wasnt any on the UK ebay site.
I dont htink this plastic will crack very easly. Im using plastic barbs, and they are not threaded so I dont think I will have a problem with that.
Ive got some sillicone so Ill try that. For testing I just used bluetack which seems to work very well, the only leaks were from the barbs not fitting properly, and not from the base/top seal.

[hikke]

Is polycarbonate reactive with those anti-corrosion fluids? I'm making my blocks (~7mm copper plate+plastic top) and many people seem to use polycarbonate and it should be pretty easy to get here in Finland so I'm most likely going to use it. And what do you think about using polycarbonate varnish (stuff that my brother uses to coat his hand made lures etc) which should be methanol and polycarbonate?
So it shoud melt the plastic and when it dries it should form a piece that looks like it would be made from a single piece. (this needs testing, but I haven't bought any plastic yet)
For sealing the copper-plastic contact I will most likely use silicone and two or four M10 bolts, because my scrap copper pieces have those holes already. I will post pictures when I'm done, but it will take a while because i have only a dremel clone and I need to buy tap's and plastic etc.

[|kbn|]

M10 bolts would be a bit big? For my gpu block I only have space for 2 M3 bolts, which will be enough, as it doesnt leak without bolts.
A dremel can stil make good blocks with a good design
Taps are expensive (about £25 each in UK iirc) so Im not using them. For the barbs plastic ones are best so that they wont crack the top if they get overtightened. Im going to glue the barbs to the top, instead of tapping holes and using ptfe to stop them leaking.
Also in plastic you might not even need taps. For the mounting holes Ive done I used a 2.5mm bit, for 2.9mm screw. In the plastic the screw bites into the side and taps its own thread. Just tryed this with the silver and it was easy, just use the screw like a tap, 1/2 turn forward, 1/4 back...

[bigben2k]

Yes, it's superglue!

I'd go with M4 if you can: they're easier to tap. I've also been tipped that using more than 4 bolts is preferable, for a level, uniform seal, but I haven't verified it. I'm going for an 8 bolt pattern for my block.

Check for Lexan. McMaster I believe does ship to the UK, but you have to contact them. 1/4" is the thickness of the sample, and it's fine, but if I can, I'll stack a couple of them for a 1/2" thick top plate.

[|kbn|]

You said its one of the worst plastics because it doesnt bond to anything, thats only a problem though if using glue to hold the barbs on? With my next blocks I intend to drill and tap the holes so that I can use normal barbs, couldnt do that with this block as I cant get 90 degree 1/2 bspt barbs here. Instead I used a very restrictive 90 degree elbow with part of it cut off.
I think bluetack or silicone aka plumbers goop should definatly seal this properly, and two screws should be more than enough, theres not going to be much pressure (whats the cheapest easyest way I can pressure test my blocks?). With the next blocks I will deinfaly use 4 or more screws, I couldnt with this as the base wasnt wide enough.
If McMaster do ship to the UK postage will cost a lot and take ages, Ill contact them anyway but I doubt it would be worth the cost to import.

[bigben2k]

Polyethylene can be bonded, but it's not easy, because you probably have a nylon barb, and the cyano acrylate won't bond to it very well. I spent countless hours Googling over glue specs... You don't want to know what would actually bond both nicely.

The Goop is a sealer, and not so much a glue, so keep that in mind! It's not going to hold the two pieces well at all.

In your position, I'd pick up the polycarb top, and a short section of polycarb pipe (also from McMaster) and use IPS' Weld-On #4. Nice, clean, elegant, and rock solid. If it leaks, then seal it with Goop.

I believe I have some left over polycarb piping, but I'd have to check: I think it's 5/8" OD though (gotta check!) but 1/2" flexible tubing can be made to fit over it.

[|kbn|]

The barbs im using are blue, and probably nylon. THey fit resonably well and to remove them i have to twist them, the wont move just pulling unless i use plyers and grip it quite tight. So do you think it needs bonding, or do you think sealing would be enough.
I will try hot glue, not sure how well it will work. If the glue that arrives witht he glue gun dosnt work well, then i will try using the polyethelene in the gun, which bond slightly to nylon ifapplyed quickly while hot. or i could just insert the barb and melt them together with something hot, soldering iron? dunno how well that could work though. The problem is as my dad says, the barbs are not mechanicly held on well, like the base to polyethelene is. I coudl always add another layer of plastic to hold them on better? woudl there be any point?

[|kbn|]

bigben2k would you know what polypropelene (I think ive spelt it right) is like for bonding. Ive been looking for a container to use for a res instead of a coffee jar, and today I found an old free, broken thermal flask sitting in its box on my shelf. The inside of it was just a moulded 2mm thick wall polypropelene container surrounded by polystyrene foam (which will be usefull if I ever stick ice in the res to get lower temps just for a test).
If that wont work then Im going to build one out of copper and stick an acrylic window on the side

[Gooserider]

1. Cautionary note - some cyanoacrylics (at least the retail store variety) will soften and fail under long term water exposure, espec. hot water.

2. THREADED fittings work well with sealants, but press in fittings are marginal at best for use with sealants, you need some sort of mechanical bonding as well.

3. Melting different types of plastics together is generally NOT a good idea, especially since some plastics are not even intended to be melted (not sure if polyethelene is one or not) Hot glue is also not a good idea. Plastics should generally be bonded with a solvent type adhesive appropriate to the plastic type. The fun part comes when attempting to bond different types of plastic, as it becomes necessary to find a solvent that works on both types.

Hope this helps,

Gooserider

[bigben2k]

Polypropylene is just as bad. Just like Polyethylene and Teflon, it falls under a category dubbed "soft plastics".

Like I said, it's possible, just not easy. The polycarb or acrylic solution is much easier. With the Weld-On#4, these plastics pieces actually melt and chemically bond together: that's why they're so strong, but it still doesn't mean that it's sealed, hence the Goop.

If you still want to go your way, I'd recomend that you test what you have handy, and see how they bond, before commiting them to a water cooling loop. As Gooserider pointed out, some CA (CyanoAcrylate) adhesives don't resist water all that well, but you'll have to look up that specification, or contact the manufacturer and ask them about leaving the dry adhesive submerged in water. IF that doesn't work, consider using Goop on top of it, but then you're getting into some pretty iffy joints.

[|kbn|]

Thanks. Im going to try with threaded conenctions for all my stuff now, which means £17 for a 1/2" BSPT tap, £5 for 1/2 drill, and then guess what.... Ill neeed a new drill too....
Im going to need to sell some blocks to make up for these costs!

[|kbn|]

Decided to use a brass barb to cut a thread and use that instead of 90o's. The barbs ended up being too close together, so I adjustted them at an angle. I attached the bottom and ran it at full mains tap pressure and the barbs didnt leak, the bottom was shooting water about 3' into the air though - It wasnt screwed down tight, let alone sealed. prev tests with blue tac for sealing bottom workd very well without leaks... will use sillicone instead this time though..

[Gooserider]

As an economy measure, if you are just tapping into plastic, try getting a steel fitting of the appopriate thread (perhaps an air line fitting?) and filing a groove or two along the length of the threads. This will make a very good 'poor man's tap' for soft materials (brass might work, but is probably not going to take a good edge the way steel will.) This will also work with a regular bolt for cleaning up buggered threads in many materials.

You should also use some sort of teflon tape, plumbers dope, or other sealant on the threads, this will greatly reduce the odds of getting slow leaks.

Gooserider

[|kbn|]

What do you mean? getting a steel tap or using a 1/2 tappered steel BSPT barb?
I think brass works well enough for that. Im happy with the brss for my own blocks but it appears I might be able to make some for selling, in which case I would get a proper tap.

I think polyethelene is definatly a v good material for the tops of blocks, the only downside is that it is translucent and doesnt bond well. Its good points are it is not at all brittle, cuts like butter,non absorbant, self lubricating, and strong.

[RazielWard]

I see this thread seems to mostly be about plastics so I'll post my question here. I'm looking to make my own resivour. What would be the best substance to bond two pieces of plexi. I was thinking epoxy, but then I thought that it might also be slowly washed away. I'm looking for a permanant solution for bonding these two pieces without any leaks.

[Zogthetroll]

there are definately better solutions than epoxy, as BB2K mentioned, IPS weld-on is great for that sort of thing, either plexi or lexan. that stuff is about as permanent as you can get. to be safe, you'll still want to use some sort of silicon goop to seal any small spots you may have missed. check out the clear cube thread in my sig to see an example of a project using IPS. or look Here for another example. also, IPS is probably easier to apply than epoxy. hope that helps.

[Pureh20]

make an O-ring in the block, buy rubber O-ring and use some polycarbonate, its rigidy stuff, im using some 10mm (4/10) polycarb for my next block as its thick enough for me to add 8 leds in there

[Butcher]

epoxy won't wash away, but it's not the best glue for bonding plastics, it's hard to get enough adhesion to the surfaces.

[Pears0]

the easist wat is clear silicon sealant and bolting. The silicon sealant alon is probly enough to hold the top on, but i would still use bolts as this would increas the pressur on the seleant, making the sels tighters, and an exra bit of security incase the selan isnt quite up to the job. And as the selant drys clear, u wont even know its there!

[Gooserider]

Bonding plastics is a nasty and difficult issue to deal with, as there are so many different sorts, and each has it's own set of properties, including what adhesives will work, and which ones won't.

Plastics tend to be difficult to bond to, so most 'generic' adhesives are going to be iffy at best. A few random thoughts that might be of use...

1. Generic names like 'polycarbonate' or 'polyethylene' can encompass several different sorts of plastic, try to get a more specific name, preferably one that identifies the particular plastic as narrowly as possible.

2. Look at manufacturer's websites or spec sheets for the plastic you are considering to find out what the reccomended adhesive's and / or glueing techniques are.

3. Mixing different sorts of plastic is very problematic, as it is necessary to find a glue that will work with BOTH materials. It is better to avoid this as much as possible.

4. In addition to glues, it might be worth considering 'welding' the plastic together if that is an appropriate technique for that type of plastic. (Harbor Freight, and presumably other places, sells plastic welding units for fairly short money although they also need an air compressor)

5. Glues that work by fusing the parts together by making a 'solvent weld' are usually better than those that just make a glue bond. (example - PVC pipe and fittings)

6. I would reccomend AGAINST the comments above about using silicon sealant on top of a glued seam "in case you missed a spot" . A properly done glueup should not leak, if it does, re-do or fix the leak properly. Silicone seal on top of a leak is a kludge at best, and a leak waiting to happen later more likely.

7. It might be worth making some practice joins with scrap material if using a technique that is new to you, especially if there are considerations about needing to work quickly, or use other special tricks. Test gluing is also reccomended when using material that is salvaged or purchased without a manufacturers spec in order to verify that the material has actually been identified properly, and the glue being used will work.

8. When designing, keep in mind that glue plus a mechanical backup is better than glue alone (such as threaded fittings, use of screws and bolts, or even just a mechanicaly sound joint like a PVC pipe and it's fitting)

Hope this helps,

Gooserider

[bigben2k]

Originally Posted by Gooserider

...
6. I would reccomend AGAINST the comments above about using silicon sealant on top of a glued seam "in case you missed a spot" . A properly done glueup should not leak, if it does, re-do or fix the leak properly. Silicone seal on top of a leak is a kludge at best, and a leak waiting to happen later more likely.

...
Gooserider

Yeah, that was a bad tip . I had to revert to this method for my second prototype airtrap. What I didn't mention is that the glue was used for structure, involving an irregular surface, and the silicone sealer was applied, not on top of the glue but on the edge of the joint, for a firm seal.

Yeah, it's ghetto, but it works for me.

The final product is all screw-in, schedule 80, PVC parts: no glue required, just a thread sealer.