The importance of correct procedures
The real skill lies in the engineering of the joint, however even with the best planning in the world it can go wrong if procedures aren’t followed. Using an example of brazing with a hand-held torch and hand-fed filler metal we’ll discuss core steps that apply not only to hand held, but across mass production brazing, even if they are performed in a different manner.
Step 1: Allow proper clearances.
Ensure that during the brazing operation you have a decent clearance between the base metals to allow the capillary action to work effectively.
Step 2: Clean the metals
I know it seems obvious however to make sure the capillary action will work you must ensure the surfaces of the metals are clean. Even a little bit of dirt can create a barrier between the base metal surfaces and the brazing materials. Once you’ve cleaned the parts it’s advisable to flux and braze as soon as possible (especially in repair brazing).
Step 3: Fluxing the parts
Flux, which is derived from the Latin word “flow”, is essentially a cleaning agent. Typically, you apply flux just before brazing if possible so it has the least amount of time to dry out and flake off or get knocked off the parts in handling. Choose a flux that’s formulated for the specific metals, temperatures, and conditions of your brazing application.
The only exception is that you can join copper to copper without flux.
Step 4: Assemble for brazing
You’re getting there, as now you have parts of the assembly cleaned and fluxed. Now you must ensure they are kept in a correct position, essentially gravity is your friend. Adding to much weight your clearances may be affected and as a result, the brazing filler metal may be forced out of the joint area.
Step 5: Braze the Assembly
Keep an eye on your flux, if the appearance changes in a consistent manner then the parts are being heated evenly. Keeping to the example of manual brazing, you’re ready to deposit the filler metal so carefully hold the wire against the joint area. It might be worth considering adding flux to the end of the filler metal to improve flow.
Step 6: Cleaning the brazed joint
After you have brazed the assembly, it must be cleaned. There is a widely known two step process:
- Remove the flux residues.
- Remove any oxide scale formed during the brazing process by pickling.
Most brazing fluxes are water soluble therefore on this basis quenching the assembly in hot water (120°F/50°C or hotter). Just ensure that the filler metal has solidified prior to quenching. Unfortunately you might hit a stumbling block if you A. haven’t used enough flux to begin with or B. you overheated the parts during brazing.
Once you’ve dealt with the flux, use a pickling solution to remove any oxides. Normally, the best pickle to use will be recommended by the supplier of the brazing materials you’re using.