WELDING OPERATIONS I - OD1651 - LESSON 1/TASK 1
(b) Procedure. Both the shielded metal-arc method and brazing
with oxyacetylene may be used for repair of cracks in cast iron
When using the shielded metal-arc method of
repair, a welding rod with a high nickel content of at least 50
to 60 percent must be used. Cracks in a cast iron engine block
must be properly prepared prior to welding, otherwise (after
cooling), the weld deposit shrinks, which pulls the crack
together and results in the formation of internal stress.
stress finally relieves itself by cracking due to continued
the steps that should be followed to eliminate this stress and
effectively repair the crack.
1 Drill a 1/8 inch diameter hole 1/4 inch beyond each end of
the crack as shown in figure 3, view A, on the previous page.
2 Clean and groove the crack and remove the "as cast" surface
or skin by grinding or machining.
3 Preheat the casting by baking or locally heating the
casting at 1000 Fahrenheit for a few minutes to remove all
(It is imperative that all moisture be removed,
otherwise the weld will not adhere to the base metal.)
4 Drill and tap a hole to receive a 1/4 inch bolt in the
center of the crack as shown in figure 3, view B.
tighten a bolt slightly deeper than the thickness of the base
metal. Stake the sides of the bolt with a center punch so that
it will not back out, and cut off the bolt as shown in figure 3,
5 Weld the crack using the backstep method shown in figure 3,
view D, and peen each bead with a round nose tool.
6 The minimum preheat and interpass temperature should not be
below 400 to 500 F when using a nickel rod, and the weld should
not be allowed to cool when applying more than one pass. If all
the impregnated oil or gas is not eliminated during preheating,
the first pass will usually be too porous and must be removed and
the weld repeated until a sound first pass is obtained.
7 Allow the completed weld to cool
asbestos blanket over the welded area.