How is bonded flux made?

• A. Dry mixing flux ingredients with a binder such as sodium silicate or potassium silicate, followed by wet mixing, drying, and pelletizing in a rotary kiln; pellets sized and packaged
• B. Direct melting of flux and pouring into water
• C. Using a ceramic binder with high curing temperatures
• D. Mixing flux with oil binder

Answer: (A)

Bonded flux is made by binding the powdery flux ingredients into solid pellets using a binder, then forming and sizing those pellets for use. The typical process starts with mixing the flux powders with a binder such as a silicate (for example sodium or potassium silicate). This is followed by a wet mix to ensure the binder coats and binds the particles evenly, then drying to remove moisture. The material is then pelletized, commonly in a rotary kiln, to produce uniform pellets. Finally, the pellets are sized to the desired diameter and packaged for shipment.

This approach gives pellets that flow well, reduce dust, and dissolve predictably in the weld, while maintaining consistent chemical composition. Other methods described would not produce the same practical product: melting flux and pouring into water creates a frit or glassy material rather than discrete, durable pellets; using a ceramic binder with high curing temperatures adds unnecessary heat processing and can alter flux properties; and mixing with an oil binder would introduce hydrocarbons and contamination that are undesirable in welding flux.