Use of Fixed Orifice to Limit Surge Flow
A
simple surge flow restriction orifice can be added to the wire feeder to
limit high gas surge at the weld start. (We have measured
surge peaks over 250 CFH in some applications which is much higher than the
level needed to avoid excess turbulence!) On the surface sounds like a
reasonable way to limit peak flow, but it creates other problems! The
restrictor is typically implemented in one of two ways:
The
surge limiting orifice can be sized to limit peak flow while still
controlling the steady state flow at the gas cylinder with a
regulator/flowmeter or regulator flowgauge or at
a pipeline gas supply drop using a flowmeter.
FIRST: Properly
sized this can work to reduce the undesirable effects of gas surge and
improve weld start quality. However even if sized correctly (we find most
are not) when welding stops, gas still builds in the delivery hose from gas
supply to feeder. Significant gas is still wasted when welding starts
(and the pressure in the hose reduces to the ~4 to 6 psi
needed to flow the steady state setting!) However rather
than
exit in a very short time with a high
gas surge rate it flows at higher than the steady state setting until the excess
gas stored in the delivery hose is gone!
Almost the same amount of gas
waste still occurs it just takes somewhat longer and is less obvious!
It requires an understanding of why the
surge existed in the first place (which is the increase in gas delivery
hose pressure when welding stops and reduction to that needed to flow the
steady state flow setting when it starts) to see that adding a surge orifice did not
change the cause! Many folks selling these devices just demonstrate
the reduced surge velocity and conclude your saving gas waste!
SECOND: We often find the orifice size selected
to limit peak surge flow is set too
low to fully purge the weld start area of moisture laden air. The high flow
surge that caused start problems is eliminated but moisture laden air is
still in the start area and causes similar weld start quality problems! Stauffer in his 1982 patent clearly defined this need
for this extra start gas, See what Stauffer
said.
Welders often can see this lack of extra start gas problem by observing poor starts.
They counter by drilling out the orifice
to “get more gas.” Unfortunately the smallest drill readily available
in a drill set in 1/16 inches--way to big!!
state flow rate.
The orifice is mounted at the gas inlet to a wire feeder.
Surge is reduced however with this approach there is not enough extra gas at the weld
start which creates a greater problem (defined in (b) above.)
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 proper purging the weld start area of
moisture laden air. 
by installing flowmeters at the wire feeders. These were connected by a hose
to a 50 psi shielding gas pipeline. Many of the flowmeters were model L-32
(shown at right) which are designed to read accurately at 50 psi, so the flow readings
are direct. 
