may have been done to the metal affecting its
pattern should be used. Heavy drafts of air against the
properties. The metal may not melt and fuse readily.
spark pattern should be avoided as the air can change
the tail sparks. Such a change will lead to incorrect
The final weld may be unsatisfactory. The usual cause
identification.
of this condition is that there are impurities imbedded
in the metal. The impurities are usually slag and roller
dirt or excessive sulphur and phosphorus. For these
Oxyacetylene Torch Test
reasons, a welder should subject steel to the torch test.
Metals may sometimes be identified by their
Even if you know the physical composition and
characteristic reactions to being heated with an
oxyacetylene welding torch. Identifying factors
know whether the metal has good welding properties.
include the rate of melting, the appearance of the
For example, some cold rolled sheet steels may show
molten slag, and the color changes (if any) that occur
very good physical and chemical properties. However,
during the heating. Table 6-4 indicates the reactions
during some part of the manufacturing process,
impurities may have been added to it or certain work
of various metals to the torch test.
Table 6-4.--Identification of Metals by Oxyacetylene Torch Test
Reactions When Heated By Oxyacetylene Torch
Metals
White cast iron
Metal becomes dull red before melting. Melts at moderate rate. A medium tough film of slag develops. Molten
metal is watery, reddish white in color, and does not show sparks. When flame is removed, depression in
surface of metal under flame disappears.
Gray cast iron
Puddle of molten metal is quiet, rather watery, but with heavy, tough film forming on surface. When torch
flame is raised, depression in surface of metal disappears instantly. Molten puddle takes time to solidify, and
gives off no sparks.
Malleable iron
Metal becomes bright red before melting: melts at moderate rate. A medium tough film of slag develops, but
can be broken up. Molten puddle is straw colored, watery, and leaves blowholes when it boils. Center of
puddle does not give off sparks, but the bright outside portion does.
Wrought iron
Metal becomes bright red before it melts. Melting occurs quietly and rapidly, without sparking. There is a
characteristic slag coating, greasy or oily in appearance, with white lines. The straw-colored molten puddle
is not viscous, is usually quiet but may have a tendency to spark; is easily broken up.
Low-carbon and Melts quickly under the torch, becoming bright red before it melts. Molten puddle is liquid, straw colored,
cast steel
gives off sparks when melted, and solidifies almost instantly. Slag is similar to the molten metal and is quiet.
High-carbon
Metal becomes bright red before melting, melts rapidly. Melting surface has cellular appearance, and is
steel
brighter than molten metal of low-carbon steel; sparks more freely, and sparks are whiter. Slag is similar to
the molten metal and is quiet.
Stainless steels
Copper
Metal has high heat conductivity; therefore, larger flame is required to produce fusion than would be required
for same size piece of steel. Copper color may become intense before metal melts; metal melts slowly, and
may turn black and then red. There is little slag. Molten puddle shows mirror like surface directly under flame,
and tends to bubble. Copper that contains small amounts of other metals melts more easily, solidifies more
slowly, than pure copper.
These metals melt very rapidly, becoming noticeably red before melting. True brass gives off white fumes
Brass and
Bronze
when melting. Bronze flows very freely when melting, and may fume slightly.
Aluminum and
Melting is very rapid, with no apparent change in color of metal. Molten puddle is same color as unheated
aluminum alloys metal and is fluid; stiff black scum forms on surface, tends to mix with the metal, and is difficult to remove.
Monel
Melts more slowly than steel, becoming red before melting. Slag is gray scum, quiet and hard to break up.
Under the scum, molten puddle is fluid and quiet.
Nickel
Melts slowly (about like Monel), becoming red before melting. Slag is gray scum, quiet and hard to break up.
Under the scum, molten puddle is fluid and quiet.
Lead
Melts at very low temperature, with no apparent change in color. Molten metal is white and fluid under a thin
coating of dull gray slag. At higher temperature, puddle boils and gives off poisonous fumes.
6-17