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Soldering |
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Soldering
is the process of joining metal parts by means of a molten
filler metal (solder) whose melting point is lower than that
of the metals to be joined. The latter are wetted by the molten
filler without themselves being melted (as in welding). The
solder is employed in the form of rods, wires, strips, sheets,
granules, powder or paste.
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In contrast with welding, different
metals can be joined by soldering. A distinction is made according
to the type of solder employed :
1. Soft solders usually a mixture of lead and tin
2. Hard solders, which comprise brass solders copper-zinc
alloys, silver solders, copper solders, nickel silver solders,
solders for light alloys, etc.
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The solder must be suitably chosen in relation to the
metals to be joined. In particular, the melting point of the
solder should be well below that of the metals. In soft soldering,
the heat may be supplied by a soldering iron (Fig.1) or a
blowpipe. Another method consists in placing the assembled
work on a plate along with a piece of solder and flux. The
work is then heated in a furnace, so that the solder melts,
and is then allowed to cool. The last-mentioned technique
may also be used in hard soldering. More usually the heat
to melt a hard solder is supplied by a blowpipe (Fig.2) or
torch.
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In
certain cases heat generated by electrical resistance is used.
The term brazing is applied more specifically to a form of
hard soldering using brass i.e., a copper-zinc alloy as the
jointing medium. A flux is generally employed in conjunction
with the latter. In brazing, borax is used as a flux; it serves
as a means of preventing the formation of an oxide coating
on the joint faces, as a cleaning agent, and as a wetting
agent to aid the flow of the molten metal. In some cases a
shielding gas may be used to prevent oxidation of the faces
of the joint. Dip brazing is a technique in which the assembled
parts to be joined are immersed in the molten jointing medium
(Fig.3). It is widely used in industrial mass-production processes.
In other industrial techniques the workpiece, provided with
solder at the joint, is heated to the appropriate soldering
temperature by immersion in a salt bath (Fig.5) or an oil
bath.
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In
another method, the molten solder is poured through the highly
heated joint until the metal cools and unites the two parts
(Fig.4). In electrical-resistance soldering (Fig.6), the solder,
flux and workpiece are heated between tungsten or copper electrodes.
Induction soldering (Fig.7) utilizes a high-frequency alternating
current to induce a heating current in the workpiece. A more
recent method is ultrasonic soldering, which is used, for
example, for the soldering of aluminum. The ultrasonic vibrations
are transmitted by a nickel rod through the solder on to the
surface of the workpiece, destroying the oxide film on the
aluminum. | |
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Soldering
is a process in which two or more metal items are joined together
by melting and flowing a filler metal into the joint, the
filler metal having a relatively low melting point. Soft soldering
is characterized by the melting point of the filler metal,
which is below 400 °C (800 °F). The filler metal used
in the process is called solder.
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Soldering
is distinguished from brazing by use of a lower melting-temperature
filler metal; it is distinguished from welding by the base
metals not being melted during the joining process. In a soldering
process, heat is applied to the parts to be joined, causing
the solder to melt and be drawn into the joint by capillary
action and to bond to the materials to be joined by wetting
action. After the metal cools, the resulting joints are not
as strong as the base metal, but have adequate strength, electrical
conductivity, and water-tightness for many uses. Soldering
is an ancient technique mentioned in the Bible and there is
evidence that it was employed up to 5000 years ago in Mesopotamia.
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