Silver brazing process

Brazing process enables to join two metal parts. There are different steps involved for brazing an alloy. In brazing process, the metals are heated and join with a filler metal which is heated above 800°F. The filler is either pre-fixed or place over the metal after heating. Again the metal is either coated with brass or can be of brass like finishing. Except for the higher heating temperature; the brazing process is pretty similar to soldering.

Depending on the material, the brazing process and the heating temperature also differs. For silver brazing; the filler used is not pure silver but an alloy which contains nonferrous metal. The silver alloy as a filler for brazing provides a long lasting metal bonding. Refer the below elaborated silver brazing steps which you can try yourself.

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Brazing process : Silver brazing at home

How to Choose Right Brazing Alloy?

Choice of the right form of brazing alloy is one of the most important issues which affects the integrity of any joint assembly- other factors being joint design and proper fit; cleaning procedure to prepare surface; fluxing practice; proper cooling and flux removal; and method of heating. So, how to choose just the right form of brazing alloy? Let's know about it.

Some Criteria to Choose Brazing Alloy!

A brazing alloy is the metal which is added during the brazing process in order to complete a joint. Melting range for a brazing alloy has been defined by the minimum temperature at which the alloy starts melting (“solidus”) and the temperature at which the alloy becomes liquid (“liquidus”). For most purposes, the actual brazing temperature lies within 50°F to 200°F (30°C to 110°C) above the liquidus. While the melting range depends upon the chemical composition of alloy, it is also important to note that individual batch characteristics may differ slightly. Some alloys have a very narrow melting range and others have a relatively wider range. Those having narrow melting range are used for filling very narrow gaps while others with wider range are better used for filling larger gaps.

There are many forms of brazing alloys. Different alloy combinations change the melting temperatures as well as other properties of brazing alloy. However, a brazing alloy should fulfill the following basic criteria.

• It should flow evenly across the surfaces of the base metal, and through capillaries even if they are as small as 0.001-inch;
• It should resist alloy separation into solid and liquid phase during brazing.
• It should provide a strong bond by partially alloying with the base metals.
• It should meet conditions of corrosion resistance, ductility, thermal and electrical conductivity, or other desired properties.

High temperature brazing alloys like gold, nickel and copper can be used for brazing multiple joints at a time but care must be taken with the joint design and joint clearance. In such cases, heating time should be minimized to the time needed to bring all components to the heating temperature and for the molten alloy to flow quickly. high temperature brazing should be used for joining cobalt or nickel-based superalloys.

Comparison of Popular Brazing Alloys

Although copper, nickel and silver are the most frequently-used base metals for brazing alloys; aluminum and gold are also used for some brazing applications.

Brazing Alloy	Brazing Temperature	Joint Clearance	Benefit
Copper	2000° F	interference to 0.002”	Joint Strength, Low Cost
Silver	1300° F	0.002-0.005”	Low Temperature
Silver with Lithium	1300° F	0.002-0.005”	Low Temperature, Self-Fluxing
Nickel	1900° F	0.002-0.008”	Joint Strength, Resistance to Corrosion
Aluminum	Column 21080° F	0.002-0.01”	Only braze for aluminum
Gold	1800° F	0.002-0.008”	Resistance to oxidation and corrosion

Most of the above mentioned brazing alloys are generally available in various forms like wire, foil, tape, powder and paste. Know about all such forms of brazing alloys.

How is Brazing Done?

Brazing, as people dealing with metals would know, is a process of joining metals (and non metals too.) There are different techniques for joining metals through brazing which are known as brazing processes but there is a common basic working principle for all these processes.

Basic Brazing Process

For brazing, a Braze Filler Metal (BFM) is used. Most brazing filler metals are alloys, or combinations of pure elements or materials. The filler metal must have a melting temperature above 840°F (450°C) but below the melting point of the base metals or the metals that need to be joined.

In brazing process, the base metals are heated, generally to a point that is slightly above the liquidus (liquidus is the temperature above which an alloy is completely molten. When an alloy exceeds the liquidus temperature, there are no solid phases present.) of the filler metal, causing it to melt. As a result, the filler metal flows into the parallel joint clearance between the two base materials by capillary attraction and bonds to their surfaces through atomic attraction and diffusion.

Thus, the basic principle through which brazing works is by joining the base metals by creating a metallurgical bond between the filler metal and the surfaces of the two metals being joined. However, there are certain differences in this basic technique of joining metals when we refer to different types of brazing processes.

Brazing Procedure

For an effective brazing, some conditions have to necessarily fulfilled. If not then problems associated with brazing occurs. Thus, the following conditions should be there:

• Good fit and proper clearance
• Clean base metals
• Proper fixturing
• Proper fluxing and atmosphere
• Heating the assembly
• Cleaning the brazed assembly

All these can be attained by following proper brazing procedure. To get step by step instructions about how to do brazing, read Basic Brazing Procedures