Once you have properly brazed the assembly, you will need to clean the brazed joint. Cleaning a braze joint is a two step process. The first step is to remove all flux residues. Second, pickle the joint to remove any oxide scale formed during the brazing process.
Because of tolerances, aesthetics or joint design, you sometimes need the flow of braze alloy to be restricted-to stop its flow or keep it off a surface. Capillary dams are often designed into these parts to limit braze alloy flow. A capillary dam is when the clearance is increased to a point where capillary action no longer exists. Ideal clearances for the best capillary strengths are .000"-.002" in furnace, and .002"-.005" in open air. Anything over .012" is preferred as a capillary dam. When the assembly cannot be designed to naturally prevent braze alloy flow, a brazing aid called Stop-Off can help you prevent or guide the flow of braze allow on your assembly.
Depending on your brazing process, you may need to perform post-braze joint cleaning to remove residual flux. This step can be crucial since most fluxes are corrosive. Post-braze cleaning is one of the Six Fundamentals of Brazing*.
Radiographic Examination - Discontinuity Images on Film
Examining finished joints may be the final step in the brazing process, but inspection procedures should be incorporated into the design stage. Your methodology will depend on the application, service and end-user requirements plus regulatory codes and standards.
Brazing methods range from torch brazing in open air to vacuum furnace brazing. Torch and induction brazing are the most common, using an Ag-Cu-Zn alloy to form joints. Oxides form on surfaces of base metals in open air, prohibiting the filler metal from wetting the assembly properly. Flux, applied before brazing, prevents oxidation from occurring and dissolves the oxides present on the base metal surfaces. Flux also allows the braze alloy to wet the base metal and flow into the joint interface. Fluxes come in forms including pastes, slurries, liquids, and powders. Typically, these require a separate application when brazing with solid wire. Manual fluxing increases cycle time and introduces a variable which can affect joint consistency and quality, increase post-braze clean-up time, and pose safety concerns.
What is Handy One®?
Handy One® flux-cored products offer flux inside a braze alloy wire, so no external flux application is required. This condenses the two steps of applying flux and alloy into one step, with the product being either applied during heating or placed in the joint region prior to brazing. Use of Handy One® helps limit inconsistencies in flux application, reduce brazing process times and safety/environmental concerns, plus improve braze joint quality.
Figure 1 shows the states of brazing with Handy One®. After a flux-cored braze ring is placed on the assembly (1), heat is applied and the flux inside the wire becomes molten, flowing out of the wire into the joint interface (2). The flux that flows into the joint interface prevents and removes oxide formation during heating, allowing the molten braze alloy to wet the base material and capillary into the joint (3). Capillary attraction pulls the alloy through the joint, forcing the flux out of the joint interface, and completes the braze (4).
Handy One® is available with several filler metal options. Click here to determine the correct product for your operation.