"Cold Weld" for u/c joints

[Matt Carlton]

Hello,

I stumbled across this the other day;

 

Permatex Cold Weld

 

If the description is to be believed, this could be potentially used for metal joints like piano wire undercarriages. Obviously the joints would still need wrapping with wire, but it might be neater than my terrible soldering.

 

Has anyone used this or a similar product for that purpose with any success? 

 

I personally suspect that the bond would be weak when subjected to a landing shock. 

 

Thanks

 

[Basil]

This reminds me of something we used back in the 60/70's when I worked in an oil refinery, was it called 'Bellsona' or something that sounded a bit like this. Shows my age.

Bas

[Cuban8]

Matt, you say that your soldering is "terrible", but this is almost certainly due to either using the wrong materials or having the wrong or unsuitable tools. To produce a mechanical joint to a standard that is pleasing to the eye and is sufficiently strong for our purposes is not a 'black art' but does require a degree of practice although nowhere near that required for welding or brazing.

Cleanliness and a physically big enough iron or gas torch (not just wattage that counts)are the main points to get right before anything else along with some basic techniques that do need to be followed. YouTube is your friend for all that! Good luck.

Edited February 21, 2021 by Cuban8

[Matt Carlton]

That's probably true. My soldering iron is a bit small, but I'm nervous of using a torch as I don't want to detemper the wire. Practice makes perfect of course, but it's always useful to have an alternative up one's sleeve. 

My joints are 'ok' (or they were when I was an off the rails youth...) but some models need more than ok, so perhaps I'm just getting lazy. 

 

[Andy Stephenson]

18 minutes ago, Matt Carlton said:

... I don't want to de-temper the wire. ...

 

This is why I would never use a flame to solder piano wire. Piano wire is medium carbon steel which is supplied in a hardened state which is what gives it's spring. Once heated above a certain temperature which can easily be reached with a flame, it softens the metal when it cools and therefore looses its spring and is subject to easy bending. The only way to get the correct hardness back is to quench it from red heat in the correct medium (not water as this cools it too quickly and renders it glass hard and very brittle). Alternatively quench from red heat in water then temper it back by heating to a precise temperature and letting it cool slowly.

 

[Matt Carlton]

On that subject, is it my imagination or is the piano wire we get these days a fair bit softer than it used to be? I remember it being almost black in colour, maybe higher carbon content? The latest stuff I got was silvery with a distinct mottled pattern.

[Cuban8]

I take your points about overheating the material with a flame, but with care I've not caused any problems when getting the wire only hot enough for soft solder to flow. It is interesting to experiment with heating and quenching piano wire to get some idea of the various effects on its properties. I recall heating a  length of 1/4" diameter to as hot as I could get it with a propane torch and then cooling in water. Afterwards, I could snap it between my fingers like balsa!

[Martin Harris - Moderator]

I understand that it isn't possible to temper piano wire with heat treatment.  It gets its spring properties during manufacture from being drawn so once overheated, it is useless for undercarriages.

[Andy Stephenson]

It's not impossible to temper carbon steel but you need the appropriate equipment or technique. We used to do it all the time as engineering apprentices.

 

The black colour has nothing to do with the carbon content. It is almost certainly due to an oil quench in the heat treatment process.

 

I read about modellers saying that piano wire is not a hard as it used to be because it's much easier to cut. I don't think this is the case because cutting tools have improved greatly over the decades.