Silver soldering small components

[thehomeengineer]

Excellent craftmanship!

I have three questions on your technique:
Q1) How do you preheat the metal parts? Would a butane torch work in this case?
Q2) How do you measure the correct temperature range for soldering? Would Tempil Sticks (temperature-measuring crayons) work for this application?, or a thermocouple?, or a temperature gun?
Q3) At what point does brazing become necessary (in lieu of silver soldering)? Presumably the stresses on your parts during operation aren't high enough to cause the silver solder joints to fail?

Gary Kingsep (kngtek)

Hi Gary

Thank you for the comment.

I use a Mapp gas and Bernzomatic torch https://www.screwfix.com/p/bernzomat...ng-torch/71976 for small fabrications which quickly gets most smaller materials up to temperature. On the bigger fabrications like copper boilers I use a Sievert propane gas torch off a large propane bottle. The reason for this you have the option to change the torch burner size. On my Sweetpea Loco boiler I had two large Sievert torches to maintain the heat need. Practical Engineering Some people use the propane for main heat and a Oxy/Propane for localised heat.

To measure the temperature is a combination of things. The first being experience (please don't think I am blowing my own trumpet, believe me I had a lot of items end up in the scrap bin when I first started silver soldering) But the best advise I could give is the flux.

The flux goes through four changes as you heat it.

1st: when heating the water is evaporated off so the flux bubbles up white.

2nd Once the bubbling stops it settles down to a smoother white almost like back to powder.

3rd: As the temperature increases the flux changes state again and looks like glass (at this point very close to the soldering temperature 600 degrees)

4th: the flux then goes into a almost water/clear state and this is when the temperature has been reached to apply the rod (650/700 degrees).

Another couple of tips for anyone starting out silver soldering is:

The job has to be spotlessly clean to allow the solder to flow.
You can never apply to much flux. But you can apply to much solder which can be expensive, unsightly and difficult to clean up.
Do not put the solder stick to close to the flame as the end will melt and drop off. Remember it is the heat from the job that melts the solder NOT the flame. So you must get the heat correct in the job for the solder to flow.
Try and heat from one side of the job and apply the solder opposite as the solders capillary action will be drawn to the heat source and the solder will flow nicely into the joint.

Brazing is another level up in temperature.

I hope this information has answered your questions
Many thanks again
The Home Engineer