Are there specific
production instances where a switch to some extra gas at the start helped
Answer: Yes, the following
validate the need for some extra gas at the weld
bar joist manufacturer was using flow control orifices mounted at the wire
feeders. Argon/CO2 shielding
gas is supplied in a pipeline
through about 15 feet of gas delivery hose. The flow control orifice
established the flow at 45 CFH. However the welders wanted higher flow
rates with some even drilling out the orifice! The welding engineer wanted to avoid wasting
shielding gas. With this flow setting arrangement where control is mounted at
the feeder next to the gas solenoid there is insufficient extra gas provided at the weld start.
This lack of extra gas prevents to purging the weld start area
of moisture laden air.
A test was made to check weld performance and
potential shielding gas
savings using two cylinders of shielding gas on two adjacent welders instead
of their pipeline gas supply. One was set with their
standard flow control orifice system and a regulator providing a pressure
that matched their pipeline, 50 psi. The other with a
regulator/flowmeter (also of a 50 psi design) using a 15 foot
GSS without their flow control
orifice. Both steady state flows were set at 45 CFH. Since welders stand side
by side, it was easy to observe the weld start quality! Instantly the
welder using the
GSS noticed improved
starting. After about an hour with observably better results the
welding engineer suggested we lower the shielding
gas flow on the welder with the
GSS to 35 CFH! The same improved weld start quality
was observed and the welder was "happy." In
fact even though we lowered the steady-state flow to 35 CFH there was still
about the same controlled amount of extra gas available at the start (that
stored in the GSS
hose when welding stopped.) The higher start gas flow rate established by the
surge flow orifice in the
maintained the higher flow at the start.
This higher start flow rate quickly flooded and purged the weld start area of
moisture laden air.
It was this air that was casing
excess spatter and lack of shielding on all their other welders! After about 4 hours of observation it was obvious the spatter
at the weld start was less with the GSS.
We also measured a reduced use of shielding gas of 25%.
After several months of testing to check this one system during windy days etc,
this shop now has
GSS's installed on all 50 welders!
Bottom Line - - "Some extra
gas flow at the start is very beneficial." In addition, after about a year
of use their gas supplier called to see if their business had turned down since
they were using about 30% less gas- it had not!
Second Case: A review of the shielding gas
flow rates in a shop with 100 welders revealed the amount of excess gas flow
on each welder.
DETAILS: A shop with ~100 MIG welders tried to
reduce gas waste
by installing flowmeters with flow controsl at the wire feeders. These were connected by a gas
hose to a 50 psi shielding gas pipeline. Most of the flowmeters were model L-32
(shown at right) which is designed to read accurately at 50 psi inlet
pressure, so the flow readings
are direct and accurate.
As when mounting a flow control orifice at the wire
feeder, this approach eliminates the start surge flow but there is insufficient
extra gas available to purge air from the weld start area and
MIG gun nozzle. It is if you're starting in air! As expected,
the welders tried to compensate by increasing the steady state flow! However increasing the steady state flow can only partially help as a substitute for quickly needing extra gas at the weld start! it also wasted much more gas than moving the flowmeter to the wirefeeder reduced!
The following was observed:
~50% of the welders were set at ~50
to 55 CFH. None were found lower than that flow level.
~25% of the welders were set near the
top of the flowgauge, which for this model is 70 CFH.
The remaining ~25% had the flow ball
pinned to the top of the flow tube. In our Lab we have measured
flows with this model of 150 CFH when the needle valve is fully opened and
the float ball pinned to the top of the flow tube!
Trying to compensate for the lack of sufficient extra start gas, the welders
set the steady state flow far higher than needed. Any flow over 50 to
60 CFH is also pulling air into the gas stream and is counter productive! Therefore increasing the steady state flow to the average 60 to 70 CFH observed, increased gas usage far more than the observed decrease in initial gas surge!!