A common way to create brazing filler metal (BFM) powder is by melting the raw metallic ingredients for the BFM in a large melting pot using induction heating and then pouring that alloyed liquid metal through a specialized atomization nozzle (Fig. 1). 

As the molten metal stream exits the tundish (a funnel-like refractory device that channels the molten metal into a single stream pouring out of its base), it passes through an atomizing nozzle through which a very high-pressure gas is flowing. The nozzle will literally blast the molten metal stream into millions of tiny particles inside an atomization chamber. The tiny particles will fall by gravity to the bot-tom of the chamber, solidifying along the way into solid powder particles of various sizes (Fig. 2). 


Fig. 1. A typical atomization process, in which a metal is melted using induction heating and is then poured through a specialized atomization nozzle to create tiny metal droplets. These droplets solidify into metal powder particles as they fall to the bottom of the tank. 

Because of the wide range of sizes of these metal powder particles, the powder needs to be run through a size-separation-process known as powder screening. In powder screening, the powder is poured through a series of screen sieves, starting with screens with large openings and proceeding sequentially through screens with smaller and smaller openings in them. The purpose of this “screening” process is to create a controlled range of BFM particle sizes for use in various brazing applications.    

Please note that the mesh size of a particular BFM powder is related to the size of the openings in the sieve screens used for these powders. The mesh-size number itself relates to the number of openings per linear inch of the screen, which is the same as the number of wires per linear inch blocking the flow of powder through that screen (per the U.S. Std. Sieve series).

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Fig. 2. Wide range of metal-powder particle sizes resulting from production of powder from a molten metal via an atomization process.