Chemistry Reference
In-Depth Information
techniques are usually distinguished:
soft soldering
and
hard soldering
,
also known as
brazing
). The two techniques are differentiated by the tem-
perature at which the solder melts: solders used for soft soldering, obvi-
ously known as
soft solders
, melt at temperatures below 425°C; those used
for hard soldering and known as
hard solders
or
brazing metals
, melt at
higher temperatures. Soft soldered joints are generally weaker than
brazed joints (Peter 2006).
All soft solders are alloys composed mainly of lead and tin mixed in
proportions that vary from as little as 30% lead (and 70% tin), to as much
as 98% lead (and only 2% tin). The brazing metals are mostly alloys of
copper or silver; their composition, as well as that of other alloys used since
antiquity for soldering, are listed in Table 48 (Zhadkevich 2004).
TABLE 48
Solders and Brazing Alloys
Composition (%)
Melting range
Alloy
(°C)
Copper
Tin
Lead
Silver
Solder
Ordinary
above 250
13-65
87-35
Plumber's
above 215
50
50
Tertiarium
a
above 190
66.6
33.3
Brazing bronze
above 800
50
50
50
Brazing silver
above 650
15-50
5-40
33.3
80-10
a
Latin name for a solder used in anciet Rome, where it was also known as argentarium.
Welding
Two welding techniques were practiced in antiquity:
forge welding
and
fusion welding
. In
forge welding
adjacent parts become joined when sub-
jected to heat and pressure (the pressure was applied exclusively by ham-
mering). As early as the tenth century
B
.
C
.
E
. around the Mediterranean Sea,
metal parts, mainly iron, were joined using the forge welding technique.
For
fusion welding
, the parts to be joined are heated until they reach
a temperature at which their contiguous edges melt and form a homoge-
neous piece. Fusion welding was used for producing
granulation
and
fili-
gree
work. The finished objects produced by either technique show no
visible evidence of the joining operation.
Fusion welding is possible because copper, a component of most gold
and silver alloys, easily forms
eutectics
, alloys that melt at a temperature
lower than any of the metals composing them (Duval et al. 1989; Wolters
1983, 1981). To attach granules or wires to a surface of gold or silver alloy
