Silver solder flux

[Bill DawesParticipant @billdawes]

[Bill DawesParticipant @billdawes]

Hi all, I have in my workshop both EF & HT5 flux.

My question is, is it detrimental to use HT5 on a lower melting point solder such as 455.

Bearing in mind also that as a relative novice at silver soldering I get the impression (maybe wrongly) my heating times may be longer than an expert achieves so I have tended to use HT5 flux which as I understand it, can tolerate a longer heating cycle.

I am ok on small components but when it comes to something with a bit of mass to it I am still struggling to get the flux nicely melted and metal up to temperature to get the solder to melt in that lovely textbook fashion I have read about.

I think I understand the theory but find it difficult to achieve, a particular problem I seem to have is keeping the flame away from the flux. On a lot of assemblies it is all but impossible. Having said that I have seen video demos where the flame is played on the joint, is there a critical time where this can be done?

I know this has all been answered before and I am sure I will get there in the end but I find it incredibly frustrating that I take great care in preparation, cleanliness etc and it still all goes wrong. Is this just a normal painful learning curve.

I think perhaps I should do a few sample joints to see if I can improve (I did actually do this a while ago but when it comes to solder 'in anger' it is always a disappointing exercise.)

Bill D.

[shaun meakinParticipant @shaunmeakin78815]

Good morning Bill. Taking your questions in order;
HT5 has a working temperature of 500 – 1000 degrees C and therefore is suitable for use will the lower melting point alloys such as our 455 (630 – 660 degree C).
If you feel you are taking time to get to temperature then it is even more important to use HT5, although it is best brazing practice to get the joint up to brazing temperature as quickly as possible. Are you using a big enough burmer?
Don't worry about playing the flame on the flux, it is the rod you want to keep the flame away from, using the flame to 'attract' the solder to where you want it. The solder will always run to the hottest point.
Mix the flux with water and a drop of washing up liquid and apply all around and in the joint. Then heat the whole joint area where you have fluxed until the paste goes like water. You are now almost at brazing temperature. continue heating the area for a few more seconds then move the flame to one side of the joint and apply the rod at the other. Continue heating until the rod melts and it will run to the flame. It is a skilful process, but also simple if you stick to the principles. As with most things in life, practice makes perfect!
I don't like to advertise on the forum but hopefully I will be forgiven by saying there are lots of helpful advice and tips including a brief video demo on http://www.cupalloys.co.uk check out the dropdown menu from 'introduction to brazing' on the top navigation bar.
Just a final note, HT5 is a more aggressive flux than say EF. That is why it is recommended for stainless steel, as chromium oxides are difficult to remove. It follows therefore tat HT5 residues are more corrosive so please clean after as much as possible.
Hope this helps,
Shaun..

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