Brazing is a process of joining metals. This process involves a filler metal being heated and apportioned between two or more close-fitting parts using a capillary action. During this process, the filler metal is heated to reach slightly above its melting point, and a flux is normally used to protect the filler metal from oxidation. With the filler metal as liquid, it is allowed to flow over the base metal, and then it is cooled, and this joins the work pieces together.
Although brazing is comparable to soldering, the main difference is that during brazing, the temperatures used to melt the filler metal are above 650 °C.
If you want to have top quality brazed tools, the base metals must be thoroughly cleaned; they must be free of oxides, and the parts must be closely fitted. It is very important to have clean brazing surfaces because if the surfaces are contaminated, this can cause poor wetting. There are two main approaches that can be used to clean the parts prior to brazing, and these are mechanical or abrasive cleaning, and chemical cleaning. In mechanical cleaning, it is important to maintain the appropriate surface roughness because wetting can be easily done on a rough surface compared to smooth surface.
Temperate has a great influence on the quality of brazed joints. The alloying and wetting action of the filler metal increases as the temperate of the braze alloy is raised. Generally, it is important for the brazing temperature to be slightly above the filler metal’s melting point. The ideal temperature that can be used must keep any heat effects on the assembly to a minimum and must keep interaction between the filler metal and base metal to a minimum.
The importance of using flux
Flux is used to avoid oxides from forming when the metal is being heated. A flux is used in situations where the brazing operation is not carried out in an inert environment. Further cleaning of any contamination remaining on the brazing surfaces is also achieved with the flux. Flux can be in liquid, paste or powder form when it is applied. A flux core, or brazing rod with a coating of flux can be used to apply the flux. When applied to the heated joint, the flux flows into the joint, and is displaced by the liquefied or molten filler metal flowing at the joint.
Filler materials that can be used
During the brazing process, a wide range of alloys can be used as filler metals. The choice of the alloy is subject to application approach to be used, and the intended use of the piece. A braze alloy is made up of about three or more metals, which form an alloy with necessary and important properties.
Ability to wet the base metals; melt at a lower temperate than the base metal, and endure the necessary service conditions are the main factors which influence the selection of a filler metal for a particular application.
The main types of filler metals that are normally used are copper and its alloys, aluminium-silicon, copper-phosphorus, nickel alloy, silver, gold-silver and silver, among others. In order for the flux to be effective, it must be compatible, chemically, with both the filler metal and base metal being used.
Single point brazed cutting tools are very essential in today’s industry, and demand is expected to continue increasing.
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