Brazing Alloys
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Brazing alloys are also known as brazing filler metals. They are used
to be added in making a brazed joint. They have a lower melting point than
the metal members being joined. There are many types of brazing alloys,
which are used in different industries. For joining different pairs of
metals, the brazing alloys can be different. The selection of brazing alloys
depend on the metals being joined and their physical and chemical
characteristics.
The brazing alloys when heated liquefy and melt to flow onto the space
between the closed metal surfaces thus creating a brazed joint. The brazing
alloys should have adequate melting and flow properties to allow proper
distribution by capillary attraction in the prepared joints.
Temperature Range
The melting temperature range for a particular brazing alloy is determined
by the minimum temperature at which that alloy will start melting (solidus)
and the temperature at which the alloy is totally liquid (liquidus). All of
the brazing alloys have the actual brazing temperature above the liquidus,
almost 50°F to 200°F (30°C to 110°C).
The melting range of an alloy is primarily determined by its chemical
composition. But the individual batch characteristics also have a slight
effect. Some brazing alloys have wide melting range while others have a
comparatively very narrow range. Alloys having wide melting ranges are used
for filling larger gaps while narrow range alloys are better for filling
narrow gaps. Wide range alloys, if heated too slowly, tend to decompose into
their basic components. So it is always better to heat rapidly through the
melting range to attain the brazing temperature.
Properties
- The brazing alloys should be non ferrous.
- The melting point of the brazing alloys are lower than the metals to
be joined.
- The brazing alloy must wet the abutting metal surfaces or adhere to
them.
- Usually the melting point of the brazing alloys are more than 800°
F.
- Most of the brazing alloys have less shear strength than the metals
they join.
Types of Brazing Alloys
Forms of Brazing Alloys
Brazing alloys are mainly found in solid forms.
- Brazing Rings
- Brazing Wire
- Brazing Slugs
- Brazing Washers
- Brazing Powder
- Brazing Paste
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Selection of Brazing Alloys
Different types of metals have different physical and chemical
characteristics, so they require different brazing alloys for brazing. The
selection of brazing alloys depends on a number of criteria. Some of the
important points are:
- Nature and state of treatment of the base materials
- Dimensions and manufacturing tolerances of the workpieces
- The equipment available for carrying out the brazing work
- Applicable regulations relating to the technique
- Media attacking the brazed connections
- Economic production
- Operating temperature
- Operating pressure
- Work safety
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