TM 55-2840-251-23
Section VIII GENERAL MAINTENANCE PROCEDURES (Continued)
1-79 REPAIR OR REPLACEMENT
Surface to be welded must be free from protective
coatings, dirt, grease, oil, foreign matter, and oxides.
Wire brushes and abrasives may be used to remove
protective coating and oxides, except that the final step
in removing oxides from aluminum and aluminum alloys
preferably should consist of chemical treatment taking
place as close as practical to the time of welding. Wire
brushes must have bristles of austenitic corrosion-
resistant steel. No deposit or residue must remain on
surface to be welded after cleaning operations.
Because a high percentage of steel parts used on the
engine are fabricated from 12 percent chromium
corrosion-resistant steels, which are characterized by
their susceptibility to air hardening, field repair of cracks
by fusion welding is a special problem. The high
temperatures at which fusion weld repairs are made and
the subsequent air cooling of the part, or parts, from
these temperatures usually result in an increase in
material hardness and a loss of ductility. Parts on which
fusion weld repairs have been made have a tendency to
crack because the steel structure becomes unstable,
brittle and highly stressed. The structure of the material
can be improved by reheating the parts and controlling
the cooling rate.
After welding, flux must be removed. If complete
removal is not practical, the assemblies should be
suitably treated to prevent corrosion by residual flux.
After the welding is completed, clean out any holes with
a rotary file, then polish with No. 400 Crocus Cloth
(E.64).
Components which are not highly stressed may be
repaired by fusion welding to restore the original
properties of such welded components through the use
of local heat treatment. The localized heat may be
applied by the neutral flame of an oxyacetylene torch.
Extend the stress relief one inch minimum beyond the
welded area. After the desired heat has been applied to
the component for the proper length of time, reduce
temperature gradually.
Inspect the weld for quality, uniformity, undercutting,
cracking and flux removal. Welds must blend into the
adjacent metal in gradual, smooth curves. Welds must
be sound, clean, free from foreign material, and from
internal and external defects that would adversely affect
the strength of the weld.
1-80 TESTING
Test of assemblies is detailed in Chapter 2 thru 10.
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