Nelweld Operations and Service Manual
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Figure 2-2
shows typical ground and edge effect
patterns due to arc blow. These effects are less
noticeable where large masses of steel are present
such as in large beams, but relatively small
embedment plates can present difficulties.
Typically, there is a lack of weld fillet on the
periphery of the stud opposite the arc blow
direction that can adversely affect weld strength
and quality.
For example, a welding platen table may be
grounded at all 4 corners by 4 separate ground
cables bolted to the table and joined to the
welding system single ground wire by a bolted
connection. This in essence turns the entire
platen into a grounded mass and arc blow on a
small plate set onto the table is minimized. On
longer, rectangular plates a double ground (one at
each end on opposite edges of the plate provides a
good current flow pattern.
The ground connection does not have to
be a screw type “C” clamp, but can be fast
action spring clamps or lever action hold
down clamps mounted to the welding table and
connected to the stud welding system ground
cable(s).
Figure 2-2:
Effect of (A) welding near an edge, and (B)
ground connection on the distortion of magnetic field.
Frequently, a copper or steel plate larger than the
base plate to be welded with a center ground
bolted to the bottom will eliminate or minimize
arc blow effects. If a welding platen, table, or
surface is used for this purpose, it should be kept
clean by removing weld splatter, weld berries and
ferrule pieces so that the surface contacts the
weld plate cleanly and evenly to assure good
electrical contact and current flow. It may take
some time and trials to establish a good a current
flow
path
for
your
typical
base
plate
configuration, but the end result is a significant
increase in weld quality and consistency and
lower rejections and repair costs.
Weld Cables:
It is
not
recommended to leave
combination or ground cables in a circular or
coiled fashion during unit operation. Failure to
place cables as recommended below may result in
poor weld quality and the development of
dangerous electromagnetic fields.
Ceramic Ferrules:
These are also termed ceramic
arc shields. Ferrules serve several functions.
•
Contain the pool of molten metal and form it
into the fillet (flash) formed around the stud
periphery.
•
Control to a great extent the amount of arc
brightness seen and the quantity of sparks
expelled during the weld.
•
They are designed with specific vent patterns
so that when the arc is initiated, the flux in the
end of the stud is consumed and deoxidizes
the weld zone. Weld gasses are expelled
through the vents, thus preventing oxygen
from entering the weld area.
•
Style variations allow welds in many
positions and to plate edges, corners, etc.
CAUTION
Summary of Contents for Nelweld 4000
Page 58: ...Nelweld Operations and Service Manual 58 7 5 Declaration of Conformity...
Page 61: ...Nelweld Operations and Service Manual 61 8 2 Base and Side Cabinet Section...
Page 65: ...Nelweld Operations and Service Manual 65 8 4 Rear Cabinet Section...
Page 67: ...Nelweld Operations and Service Manual 67 8 5 Wiring Diagram...
