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Flame Head Design
Quenching (Continued)
Flame head design is another important consideration
severe a cooling rate. Water is a severe quenchant,
and brine is even more so. They produce high
in successful flame hardening. MAPP gas flame heads
hardness but must be used carefully to prevent surface
differ from flame heads used for other fuel gases.
cracking. Water gives a higher hardness than oil and
MAPP gas flame heads usually have No. 69 drill-size
can be used where surface cracking is not likely to be a
flame ports counterbored 1/16 in. deep with No. 56
problem (as it is in very high-carbon steels). Most
drills. The rows and ports are on 1/8 in. centers and
flame hardening is done with water-cooled or
the rows are offset 1/1 6 in. Acetylene flame heads
water-quenching flame heads because of the extreme
usually have No. 56 drill-size flame ports with the
heat reflected from the workpiece.
ports and rows on 1/4 in. centers; the ports are offset
1/8 inch, row to row.
Flame Hardenable Materials
Plain carbon steels for flame hardening should have at
least 0.30 percent carbon. Lower carbon-steel grades
Quality cuts are readily obtained with MAPP gas. But
can be hardened if they have first been carburized.
quality cuts require a proper balance between preheat
flame adjustment, oxygen pressure, coupling distance,
Cast iron can be flame hardened if it has a
torch angle, travel speed, plate quality, and tip size.
combined-carbon content of 0.35 percent -0.80
Fortunately, this balance is easy to achieve with the
percent. It responds much the same way as steel of
following simple operating procedures:
equivalent total carbon content. However, cast iron
also has a lower melting point than most steels, so care
must be exercised to prevent surface melting during
flame hardening.


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