26 Joint
Cleaning Introduction
It is most important that the joint be clean. Any material
that will evolve gases when subjected to the heat of welding,
such as oil, grease, water, paint, rust, or scale, must be removed. Mill scale
or even crayon marks may cause trouble.
Cleanliness is particularly important when welding thin material at high speeds.
Methods of Cleaning
1. Flame-Cleaning -used to remove
rust, scale, and moisture is one of the most effective means of
eliminating porosity in submerged arc welding. Since there
is no radiant arc heat preceding the weld and speeds
are usually quite fast, flame cleaning is even more important than with open arc
processes. In some applications a heating
torch is mounted directly on the submerged arc welding machine. The
hottest section of the flame core should impinge on the
weld seam. The immediate weld area should be heated
to above 400o F to avoid condensing additional
moisture from gas combustion products in the joint.
2. Grinding - may be used to remove
mill scale or rust. Grinders can be manually guided or mounted on the
welding machine. (Protective glasses must be worn at
all times and it is a safety essential that the proper type
of grinding wheel be selected for the speed at which the wheel is to operate.)
3. Wire Brushing - is useful for removing
light rust and dirt only. Some types of paint can be removed by
wire brushing but generally paint remover, flame cleaning
or grinding is necessary. 4. Paint
Removers - should be applied to painted surfaces, the loose paint scraped off,
then wire brushed, and washed with a volatile
solvent. The hazards involved in using solvents should be recognized. Paint
can sometimes be removed by grinding but surfaces should
be carefully inspected to be sure paint has been
completely removed. 5. Sandblasting
or Shotblasting -readily removes heavy rust, mill scale and paint. Sheared edges
are not satisfactorily cleaned by this
method. (Adequate ventilation and eye protection must be provided for the
operators.) 6. Pickling
- may be used to remove mill scale and rust. The pickling bath should contain
inhibitors and a neutralizing rinse should
be used to prevent hydrogen absorption. 7.
Degreasing - used especially for cleaning cold formed parts.
