Any experiences with Araldite epoxy?

[Stealth]

A local reseller for tape, resin, gasket and car repair materiel has Araldite epoxies listed in their inventory. Has anyone had good experiences with those for either pickup cover manufacturing or pickup potting?

Edit: Did a search beforehand, didn't come up with any info on such a use.

[Steve Conner]

Araldite is a popular brand of epoxy glue in the UK. It's meant for sticking broken things together and would probably be too thick and viscous for potting.

[jonson]

Spot on Steve. Although it's been around for probably 40 years and well respected it's old hat now and never was the best. 24 hour setting Araldite is the better one but way to thick. Araldite rapid with a short setting time just stays rubbery and Araldite 2004 is the expensive larger quantity one and good as a filler but all of them not pourable and way too expensive. Look at the West systems instead.

[David King]

Epoxies.com has a lot of different specialized formulations to meet all the potting needs you might have. They are USA based but they may have European distribution.
Araldite has it's own set of formulations for potting. Have you checked their website? Potting Resin | Epoxy Electrical Potting Compound | Resins Online
If you do decide to go with West Systems for potting I'd get their slow hardener (209) to avoid any exothermic internal stresses that could do damage.

[Stealth]

Thank you all for the input. I never even though of just entering epoxies.com as a viable address. I'll have to look around. I assume potting epoxy is supposed to be less viscous (more freely flowing) than casting epoxy - am I correct?

[David King]

Stealth,
Potting epoxies come in different viscosities for different types of potting. In some cases you just want to put a thin black layer over all the components and the circuit board. In that example you would want a higher viscosity. In other cases you want to build a 3D cube where a lower viscosity will expel air and fill in completely around all the components. Some potting epoxies are formulated to conduct heat away from the circuit.

[Stealth]

Thanks for the clarification. Much obliged.

[Stevenson]

Potting epoxies set very slowly so that they don't get extremely hot and so that air bubbles can escape before it cures. Try mixing up some West systems epoxy in a small container and see how hot it gets.

[Mick Bailey]

Potting epoxies set very slowly so that they don't get extremely hot and so that air bubbles can escape before it cures. Try mixing up some West systems epoxy in a small container and see how hot it gets.

I tried potting with Araldite rapid and it got so hot it smoked. It has a critical mass and is clearly intended just as an adhesive. Afterwards it still wasn't hard as I expected and had a permanently sticky finish.

Standard epoxies leave lots of voids and don't penetrate at all well they also mix up with lots of trapped air. There's a chance of increased failure rate in using an incorrect formulation; the mix can set up stresses as it cures and place a strain on wires and joints. Additionally, thicker adhesive formulations are more difficult to mix correctly and in exact proportions, leaving an excess of either resin or hardner.

There are also issues with corrosive by-products that are marginally water-soluble. These become active in atmospheric moisture. I test new materials on a piece of clean PCB - apply a drop of the product (can be resin, flux, paint etc) and leave it in the bathroom for a few weeks to see what happens. A green ring around the spot is a bad sign.

A final consideration is that epoxy potting is pretty much a one-way ticket.

[jonson]

All resins and potting compounds can be played with to acheive what you want. Nowdays I use a black hot melt designed for the job using a good quality glue gun and gives the appearance of the gibson potted humbuckers and posted a link to this on a thread about a year ago. As to playing with the stuff, then back in the early 80s when I started doing pick-ups ala Kent Armstrong style there wasn't that many resins and expoxies available so I used ordinary fibre glass resin. Before somebody jumps about that's no good it will overheat I played with it. My first coats in the mold were gel coats in black which contain no wax so as polyester resin will not dry exposed to the air then the poly against the mold side dried (no air) and the inner shell remained tacky. As my coils were waxed the the remainding fill with standard waxed type didn't have to quite so runny so I added Penrhyn slate powder to to resin to thicken it up but also to slow it down and drop the temperature considerably. It was still pourable so did get where I wanted and the result was a sealed block that looked the part and never caused any problems. Most filler powder will have a cooling affect but so will pouring in smaller quantities as there isn't really the need to fill your mold or just pot your cover in one big hit. You can search till you find a compound that works for you but also get inventive and play around to achieve the same results. When I first started using polyester resins in the late 60s and early 70s they came as a 3 part mix as the resin didn't contain cobalt to accelerate the process so that was mixed in first then the peroxide hardener but, mix just the cobalt and hardener together and say goodbye to a large area of your workshop..

[David King]

It doesn't pay to take shortcuts. Mix in one container and then pour that into a second container and continue mixing with a new stick. The last thing you want is a sticky spot right on the top of a cast pickup.
If you plan to pot using a vacuum to de-gas the epoxy. Know that you need a very strong vacuum, as close to 29"Hg as you can get. Rotary vane type pumps that only get to 26"Hg won't help you at all.

As Jonson points out polyester resin is wonderful stuff aside from the styrene smell that lingers for months. It's easy to subtract hardener to control the exothermic output. You want to look for top-coating/finishing resin with the wax added as opposed to the more common laminating resin which stays tacky. Polyester used to be much cheaper than epoxy but that no longer appears to be the case. Polyester is harder but more brittle than epoxy.

[jonson]

I've sprayed gallons of wax addative poly in my life David and yes as you point out the wax coming to the surface as it dries does cause a complete cure but with the normal 2% cobalt accelerator and 2% hardener a half inch left in the bottom of a measuring cup can get hot and to the point of smoking which I end up filling with water to be on the safe side. One that I do use a lot is polyester basecoat which doesn't have the wax addative but is packed out with I believe sterate powder. Same mix but a lot cooler and I'm talking about the polyester used in the furniture trade not the car basecoat polyester which is a different animal alltogether.
Has anybody tried the famous fullerplast (fuller obrien plastic) still available but known now as Fuller Obrien varnish. 15 mins drying and not sure about the heat buildup.

[paggerman]

Not really relevant to potting pickups, but a piece of knowledge that my old man passed on to me was that the Supermarine Spitfire, the classic WWII fighter, was assembled using Araldite.

[jonson]

Don't want to doubt your dad Paggerman but the spit was aluminium riveted panels but Araldite which was a formaldahyde glue back then called aerolite was used to glue the spruce and pre stressed ply skin of the mosquito together. They used a microwave system to cure the glue but maybe could have used it to seal joints on the spitfire. Whichever it still goes back a long way.. The Hurricane was canvas skinned which is not a lot to have between you and a load of bullets.

[the great waldo]

They might have used a drop or two to glue the propeller laminations together on the earlier variants ?

Cheers

Andrew

Don't want to doubt your dad Paggerman but the spit was aluminium riveted panels but Araldite which was a formaldahyde glue back then called aerolite was used to glue the spruce and pre stressed ply skin of the mosquito together. They used a microwave system to cure the glue but maybe could have used it to seal joints on the spitfire. Whichever it still goes back a long way.. The Hurricane was canvas skinned which is not a lot to have between you and a load of bullets.