|
MIG Shielding Gas Flow Rate Chart
The condensed CHART BELOW provides suggestions
for setting MIG Shielding Gas Flow Rates (Argon Mixtures and CO2.)
Note MIG Gas Flow is SET in CFH (cubic feet per hour) NOT in psi
(pounds per square inch.)
The basis for the recommendations is
documented with references and personal experiences.
CLICK
for FREE PDF of Chart with Expanded Nozzle Sizes and Information |
|
Click to See Video: MIG
Shielding Gas Flow Settings |
|
 We receive questions asking:
"What MIG shielding gas flow
rate should be used?" Sometimes asking: "What pressure should be set?"
This is understandable since even the
American Welding Societies 5 volume, 4000 page "Welding Handbook" has
everything you would want to know about MIG welding (GMAW) but very little shielding
gas flow rate recommendations! There are statements saying excess shielding
gas flow creates turbulence and pulls in oxygen and nitrogen creating
problems but no mention of what the maximum flow rate should be! We
have done the research and defined the maximum levels.
MIG shielding gas flow is set and measured
as cubic feet of gas per hour (CFH) NOT pressure in psi.
Unlike oxyfuel welding and cutting, MIG gas flow rates are very low.
The gas pressure in the hose going into a wire feeder/welder will typically
vary from 3 to 8 psi. Flow restrictions in the
MIG gun and gas passages vary when welding. This occurs as spatter builds in the
gun nozzle/ gas diffuser and the small gas passage in the gun cable is
bent, etc. Pressure must increase to offset these added restrictions. A method of "Automatic Flow Compensation" is built into all quality gas control systems to
maintain preset flow rates as these restrictions occur. |
|
MINIMUM FLOW RATES:
 A
number of factors determine the minimum shielding gas flow rate needed. The MIG gun
nozzle size is an important factor. Small ID nozzle sizes require less
flow to get quality shielding. Drafts are also very important as is
the type of weld joint.
In a low draft environment when
making a fillet weld the lowest suggested flows are usable. The
plates being welded help retain the shielding gas. Shielding is more
effective with the help of the gas retention at these low rates. The vertical member is also effective in
providing a natural block for drafts. |
|
TYPICAL FLOW RATE RANGE:
For butt welds there is no
vertical plate to help retain the shielding gas. In addition there is
nothing to help maintain the gas shield when drafts are encountered. Therefore the gas flow
rate needs to increase to assure quality gas shielding and proper weld
coverage. The range
shown in the table is typical of that used in industry (or that should be
used!) As wire size, welding current and the gun nozzle to work
distance are increased gas flow rates should increase. |
|
MAXIMUM SUGGESTED FLOW RATE:
In the presence of drafts, higher
flow rates can be used - up to a limit. It is important to avoid
creating Turbulent flow that will pull air into the shielding gas stream.
In 1893 Osborne Reynolds
defined the flow rates that establish smooth Laminar flow (needed for
quality MIG shielding) versus Turbulent flow that causes moisture laden
air to mix with the shielding gas stream. Using that information and
extensive tests The Welding Institute in the UK defined the maximum flow
rates to maintain Laminar flow. In a recent published article the manager of welding R&D for Praxair states;
"flow rates
in excess of 50 CFH cause atmospheric gases to be pulled into the gas
stream causing poor weld quality."
Click and see references numbers 3 & 4 on this web page. |
|
Reinforcing the maximum flow
rate values is unpublished research that defined flow rates needed to handle
drafts. In a 4 to 5 mph controlled draft using Argon based shielding
gas and a standard 5/8 inch diameter MIG gun nozzle, 45 CFH flow rate had
less internal weld porosity as measured by X-ray than 65 CFH flow rate. This
reinforces the need to keep flow rates below about 55 CFH with a 5/8 inch
nozzle. |
|
WIND SHIELD:
 When MIG welding, if drafts exceed about 4 to 5 mph, a wind shield or block must be used. In some cases that can
be as simple as positioning your body between the source of the draft and
the weld.
A simple wind shield can
be made from sheet metal and held to the work with small magnets.
During a "Best Practices" tour
in Japan of bridge fabricators we saw gas shielded MIG being used at a construction site
to butt weld large girder vertical seams. Simple flexible wind
shields were used that were moved as welding progressed.
If drafts are an issue, a
larger 3/4 inch ID nozzle and
increased shielding gas flow can be used up to the suggested maximum of 65 CFH BUT NO
HIGHER.
|
 Unfortunately some folks believe;
"If Some is Good,
More Must Be Better" when it comes to setting shielding gas
flow! We have often seen flowmeters with the ball pinned to the top of
the flow gauge tube. Measurements of commercial flowmeters show with
the needle valve opened fully flow rates will range from 125 to 150 CFH- far
too much for good shielding. Also a fabricator recently called and
said his welding gas distributor told him the 100 CFH flow rate they were
using was fine! It's NOT! |
|
 Another
problem with excess flow is the "Blast of Gas" that occurs at the weld start
with conventional gas control systems. We have measured peak flows at
the weld start in
excess of 250 CFH.
The graph on the left is from a
production operation where the gas flow rate at each weld start exceeded 75
CFH for 4 seconds. Osborne Reynolds defined that Turbulent flow takes
some time to return to Laminar flow even after the flow rate is reduced.
Therefore it is probable Turbulent flow existed for 6 or 7 seconds.
Note when the company installed our patented Gas Saver System
peak flow was reduced to under 90 CFH and it was over 75 CFH for only about a
second after the torch switch was pulled.
The GSS quickly provided enough
extra gas to purge the weld start area but at a flow rate that did not
create excess Turbulence.
The welder at this repair weld station immediately saw the benefit of the
GSS as his welds are all ultrasonically tested.
He was having significant problems with weld start porosity and knew the high starting gas
surge was a major cause. After 6 months using our patented
GSS
he said his porosity problems had been eliminated.
Note, it only takes about 2 1/2 % air being mixed into
the shielding gas stream to exceed the
2% Nitrogen
some sources indicate will cause weld porosity.
SEE DETAILS OF THIS APPLICATION. |
|
Received an Excellent
Question About How an Orifice or Needle Valve Can Set and Automatically
Adjust to the Proper
Pressure Drop to Maintain Consistent MIG Gas Flow?
The Answer is Detailed so a PDF was
Produced:
CLICK TO SEE THE ANSWER: |
|
 |
Purchase Flow Rate Limiter |
Purchase
Gas Saver System
|
|
|
Purchase
Training
Products |
Purchase Wire Feeding Aids |
|
| |
|
Purchase Replaceable Orifice Flow Control System |
|
