It should be remembered that the outer
flame of the oxy-acetylene torch may be depended on for a certain amount of
preheating, as this flame gives a very large volume of heat, but a heat
that is not so intense nor so localized as the welding flame itself. The
heat of this part of the flame should be fully utilized during the
operation of melting the metal and it should be so directed, when possible,
that it will bring the parts next to be joined to as high a temperature as
possible.
When the work has been brought to the desired temperature, all parts except
the break and the surface immediately surrounding it on both sides should
be covered with heavy sheet asbestos. This protecting cover should remain
in place throughout the operation and should only be moved a distance
sufficient to allow the torch flame to travel in the path of the weld. The
use of asbestos in this way serves a twofold purpose. It retains the heat
in the work and prevents the breakage that would follow if a draught of air
were to strike the heated metal, and it also prevents such a radiation of
heat through the surrounding air as would make it almost impossible for the
operator to perform his work, especially in the case of large and heavy
castings when the amount of heat utilized is large.
_Cleaning and Champfering._--A perfect weld can never be made unless
the surfaces to be joined have been properly prepared to receive the new
metal.
Pages:
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115