Araldite on Bakelite?

[alanworland]

I have acquired my first Bakelite set, a Murphy A574 in cracking order, except that it has suffered in transit. The transformer end of the chassis has broken the corner out of the case where I think it must have been dropped! Everything else inside looks to be intact and it still works and sounds a treat.

However I would like to repair the case, (and service the circuit) I have the pieces which have broken free so could put them back in position. There also is a crack which goes from front to back of the case in the corner which also needs repairing with possibly a piece of metal used internally for reinforcing.

Do bakelite and araldite like each other enough to make a long lasting repair? The case will unfortunately need painting after the repair to disguise the damage.

Alan

[Darren-UK]

Yes, Bakelite and Araldite do like each other.

Perhaps the best thing to do is Superglue the parts together and then reinforce from behind with Araldite or Milliput. Metal reinforcing shouldn't be necessary.

If you try using Araldite directly to repair cracks and broken-off frgaments it'll ooze onto the outside, leaving a mess to try and get off.

[paulsherwin]

Araldite adheres well to bakelite, but good quality superglue is usually better for most repairs.

[60 oldjohn]

Yes Araldite "Original" makes a stong bond. But it is soft so after the Araldite has set I Dremmel or scrape a groove 1mm deep and fill proud with Milliput fine "white" then smooth with wet and dry paper before painting. Milliput sets as hard as Bakelite.

John.

[alanworland]

Thanks for quick response guys!
Never heard of Milliput, but just googled it and seems useful stuff.
I would consider a superglue for the cracks which are still together with no chance of getting araldite in
The metal reinforcing piece would be bonded over the crack on the inside (not visible) which I feel would be needed as the weight of the chassis is supported right across this area.
Is it recommended to use an etch primer on the surface to be painted?

Alan

[Darren-UK]

If you really want the metal reinforcement, consider using a piece of an expanded metal grille or similar mesh. These cabinets are quite flimsy and not 100% rigid due to the thin section bakelite, so strength plus a little give is desirable.

[richrussell]

I've used aluminium mesh (available for car body/bumper repairs) embedded in Araldite very successfully on thin, brittle plastics like Bakelite a few times. I prefer the softer Araldite so it allows slight movement, and let the metal take make up the strength of the joint. If you use too much hardener, or the harder epoxy resins, they have a habit of cracking, because although it's pretty stiff, there is some flex still in Bakelite.

[alanworland]

That makes sense to allow a bit of 'flex' especially as the break across the base goes right between two of the chassis fixings.
Etch primer or just a good rub down and primer?

Alan

[Skywave]

Originally Posted by paulsherwin

Araldite adheres well to Bakelite, but good quality superglue is usually better for most repairs.

I'd certainly agree with the phrase "good quality superglue", since in my experience there are some really awful variants out there - usually the ones in the little tube: commonly found in petrol stations, corner shops, etc.

Al.

[G8UWM-MildMartin]

I've had more success with the slow-setting Araldite than the Rapid version, with some, sadly apparently discontinued, cheapo "151" with black resin and white hardener or vice-versa giving intermediate results but a good black colour that matches some bakelite very well.
Superglue from model shops seems to work as well as some more expensive but widely-available Loctite products, both being vastly superior to the cheap ones containing chloroform which are banned yet very widely available!

Good old slow set Araldite (called 'precision' now) can flow in small gaps if the thing is hot. Pop the case in an oven at 80°C for a bit and then apply the Araldite to the inside, flows a treat into the gap.

[alanworland]

Must admit I have always preferred the slow product it seems more fluid at room temperature anyway.
80°C sounds hot! The material is obviously ok up to this temp?

Alan

80°C sounds hot! The material is obviously ok up to this temp?

It's fine, and gets very runny, sets quite quickly too.

[Brased]

An Araldite representative told me years ago that the original product produces a better joint if allowed to set at a higher temperature. It will take far higher temperatures according to the instructions.

[emeritus]

The instruction leaflets for the original Araldite used to say that curing at high temperature gave a stronger joint. Where items such as porcelain or metal assemblies can stand it, once it has set sufficiently to be handled and the excess trimmed, I usually finish curing of the traditional sort in the oven, set to about 100 degrees C.

Back in the 1960's I mended a broken earthenware casserole dish lid that my mother had dropped and broken. It worked fine and withstood gas oven temperatures with no problems. Indeed, a few years after I mended it she dropped it again and it fractured at a different angle, the fracture crossing the original break. Exposure to high temperatures for extended periods does make it go brown.

When I was working in a lab at STC, they used to add titanium dioxide powder to Araldite to give a white finish to Araldite-encapsulated assemblies.