Solder paste problems

Hi there

I have regularly used the large syringes of solder paste without any problems. However, I recently bought new torches and small syringes of solder paste for the class I teach - hard, med and easy - and it doesn't seem to work well at all, quite often the clay part just burns black but doesn't burn off and the solder doesn't melt. We've had numerous problems with it in class which has been frustrating, especially for nervous students. I've tested the same solder paste myself and sometimes it works and sometimes it doesn't, and seems to work best when the area is fluxed with Auflux before and on top of the paste. But the whole point surely is not to have to do that! I am wondering of the mix has changed, or if the torches have, or something else... However, Cooksons say not! Any ideas as to what the problem could be? Thank you.

I am sympathetic to a point, but paste solder can vary in age and quality. Beginners find the idea seductive, but it creates as many problems as it solves.

As you have spent good money on this, I would pass around the Auflux for now, but use strip solder in future. Dennis

I wonder if it might be the torches - if the mix is less oxygen rich than you've used previously, you may find you're burning the solder before the metal reaches a high enough temperature. What type are they?

How odd, I actually find that using Auflux with the solder paste prevents it flowing but not had any issues such as you describe.
I don't use it for much now but some things are certainly easier so I do still use it now and again and currently have several from Cooksons without any issues.

It's probably the new torches and not the paste. The only time I've ever had a problem with paste solder is if I applied too much heat and I end up with a lump of solder. Why don't you try the new torches with strip solder and flux to see if you notice a difference?

Solder from a syringe has a life of its own, if you go back into the archives of this forum you will have hours of fun catching up, things to watch for.

● The fumes rising from the paste when applying heat is the flux evaporating
● The longer you heat the paste without reaching melting temperature the more the flux will perish.
● No flux means the solder will not melt,
● Always heat the metal first and keep the flame off your solder (or paste)
● If you're having problems experiment on a small piece of metal 10 mm x 10 mm x 1mm
● Apply heat to the metal, the end of the flame should always be on the metal not 25 mm above
● Your solder or paste should run unless you're using candle power.

Good luck

Carlton

Thanks everyone. I've used the class solder paste and torches this morning to test them out ready for Saturday and they have worked fine for me! Same with my own lately. It doesn't sound form what you've all said that the paste is the main problem, so I will carefully check the students' use of the torches and see if their technique can be improved re: distance of flame, heating etc. I do recommend all the right techniques, but people have to learn to get it right... Thanks again.