The hazards of brazing include health hazards and safety hazards. Health hazards arise from exposures to metal fumes and ultraviolet (UV) radiation. Metal fumes can be released during the brazing process, especially if the base metals or brazing filler metals contain elements such as cadmium, zinc, or lead. These elements can give off gases when heated, which can contaminate the brazing furnace and extraction system. In addition, the outgassing of these volatile elements can increase the void content of the brazed joint.
Safety hazards include burns, eye damage, electrical shock, cuts, and crushed toes and fingers. Burns can occur due to the high temperatures involved in brazing. Eye damage can result from exposure to UV radiation, sparks, or hot metal particles. Electrical shock can occur if proper electrical safety precautions are not followed. Cuts can happen if sharp tools or equipment are mishandled. Finally, crushed toes and fingers can occur if heavy objects or equipment are dropped or improperly handled.
Other hazards related to brazing include splatter of the braze alloy, quench cracking, and distortion. These problems can be prevented by controlling the cleanliness of the parts, using proper setup techniques, designing a proper brazing recipe, and operating the furnace correctly. It is also important to avoid the use of screws or bolts, as they can sinter together at high temperatures and be difficult to remove. If springs or clamps are required, they must be able to withstand the temperatures of brazing. Metallic fixtures should have all points of contact with the brazed assembly masked with stop-off paints to prevent unwanted braze flow. Finally, fixtures should be cleaned and vacuum baked before use to remove any sources of contamination.
In terms of process hazards, brazing manually with a torch in an open-air atmosphere can lead to overheating, weakening, and oxidizing of the base metal. This can result in weak joints and unsightly cosmetic appearance. When flux is used to prevent oxidation, residue and flux voids can be a possibility. Controlled atmosphere furnace brazing is a preferred method as it prevents localized overheating and damage to the metal, allows the filler material to melt correctly and flow into the joints, and eliminates the need for flux. Brazing in a controlled atmosphere is typically done in a furnace, either inside a vacuum chamber with sealed doors or in a continuous-belt furnace without doors.
To ensure a successful brazing process, it is important to have an atmosphere devoid of oxidants, oxygen, and water. This helps prevent the reformation of oxide layers and corrosive hydrofluoric acid on the brazed assembly. The atmosphere should meet certain conditions, such as being a neutral gas (pure nitrogen), having an oxygen content less than 100 ppm, and having low humidity.
Overall, the hazards of brazing can be mitigated by following proper safety precautions, controlling the brazing environment, and using appropriate equipment and materials.
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