In order to maintain a high standard of workmanship in the
practice of arc-welding to steel castings, the following general
principles should be followed, but the precise technique will
of necessity vary according to the circumstances.
Surface condition.- The surfaces of the steel, it
is intended to weld should be cleaned and freed from all foreign
matter, otherwise poor penetration and unsound weld metal
The preparation for the welding of cracks should be of the
U or V types. When the latter is used, the included angle
should be not less than 70°C. Where cracks extend through
the section of the casting, the choice between single and
double preparation, U or V will be governed by (i) the thickness
of the casting; (ii) the location of the defect. In double
preparation, U or V the root of the U or V should be sufficiently
open to ensure complete penetration.
Electrodes.- The electrodes shall comply with Regulations
94 to 98 for Grade A castings. Electrodes for Grade
B and C castings should be agreed between the manufacturer
and the Inspecting Officer.
The electrode manufacturers recommendations for the
use of the electrode should be strictly followed.
Pre-heating.- Variations in composition, mass design,
and the extent of welding required make it impossible to lay
down specific rules to establish conditions under which pre-heating
should be applied.
When after consideration of each casting in the light of
the above variables it is deemed necessary to pre-heat, such
pre-heating should be carried out at a temperature of 150-300°C
Stress-relieving treatment.- When the welding is carried
out after the casting has received its normal heat treatment,
a further heat treatment may be considered necessary. This
treatment need be applied only in cases where welding has
been such as to induce either internal stresses which would
be detrimental to the casting, or locally hardened areas which
would cause difficulty in machining. Where this further heat
treatment is applied, the casting, where possible, should
not be allowed to go cold after welding, but should be charged
into a warm furnace and reheated to a suitable tempering temperature
which in general should be not less than 550°C (1022°F).
When considering the advisability of applying this further
treatment, its effect on the physical properties of the castings
should be borne in mind. If the treatment, or the welding
itself is such that the physical properties will be adversely
affected, the full heat treatment required to produce satisfactory
qualities should be substituted.