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Hi Scott, Here is a reprint of one of my past articles in the archives: There's several items that control how much cover gas flow is required while Mig or Tig welding. Lets start off with how a typical flow meter/gauge works. Gauges: There are two basic types of gauges: 1) flow meter:
A flow meter has two gauges on the manifold assymble: a) The high pressure gauge that reads tank pressure contents in PSI. b) The "caliberated" gas flow meter that controls cover gas flow measured in cubic feet hour (CFH). There are two basic typical flow meter configurations, square vertical dial, and round vertical dial. Both use a center steel ball to denote gas flow. Each side of one type of a typical "caliberated" square vertical flow meter is marked with a Argon flow scale, a Helium flow scale, a Carbon dioxide scale, and a Nitrogen scale. Why? Each cover gas has a different weight thus will flow more or less CFH when comparred another gas. This is why I used the term "calibrated" flow meter as it accurately reads and measures other types of gases. This will become useful when using a welding process that requires different types of a mixed cover gas, like Mig welding Aluminum. You can buy a premix gas cylinder (higher gas cost) that "maybe" be exactly what is required or mix your own gas with seperate pure gas cylinders (lower cost) that will always be what is required. One flow meter also can accurate measure 4 different types of gas and once again at a lower cost. The round verticle dial is read from the "calibrated" center dial and typicaly covers several different types of gases. This type of flow meter typicaly measures 5 to 200 CFH depending on the type of gas being metered. 2) Round flow gauge:
A typical round flow gauge has two gauges on a manifold assymble, however there are one gauge round flow gauges: a) The high pressure gauge that reads tank pressure contents in PSI. b) The "caliberated" gas flow meter gauge that controls cover gas flow measured in cubic feet hour (CFH). c) A one gauge round flow gauge only measures cover gas flow and not cylinder contents. This type of flow gauge is not as accurate as a flow meter and usually only measures one type of gas. I do have one dual round flow gauge that measures Argon and Carbon dioxide. This dual gauge is marked with AR numbers on the out side scale and the Co2 numbers on the inside scale. This type of gauge typicaly measures 0 to 30CFH.
What controls how much cover gas flow is needed?
When you do not get porosity with-in the weldment while welding! What normally happens while with low cover gas flow, is tiny gas bubbles form on the face of the weld from the oxygen thats allowed to enter the weld zone, called porosity. As the cover gas decreases the porosity travels deep with-in the molten puddle to the root of the weld. When this happens then the weld needs removed and rewelded. Notice as your grinding out the porosity filled weld of just how deep the porosity can penetrate. While welding carbon steel, you will notice the arc sputter then porosity form on the weld face then porosity proceeds thru out the weldment. While welding SS, you will notice alot of carbon forming on the weld face. As the cover gas decreases, porosity once agains forms on the face first then proceeds thru out the weldment. While welding Aluminum, the enitre weld will have porosity thru out almost 100% of the time. The torch cup size determines how the cover gas is spread over the weld. A #10 cup will spread a wider gas flow area than a #7 cup. How far the cup is held above the molten puddle at a given gas flow will determine adaquote gas coverage. A gas flow of 15CFH maybe adaquote gas coverage with a #10 cup while at a 1/4" arc length at 140amps, inside a shop but not outside. As the welding amperage increase so does cover gas flow rate as the heat pushs the cover gas away from the molten puddle. While 15cfh maybe adaquote at 150amps, 30cfh maybe needed at 225amps and 45cfh at 275amps. Hand and body positon around the torch will greatly influance gas flow rate needed. Welding inside with no external air current decreases gas flow rate. Clean weld joint preperation will take less cover gas than a dirty joint. AR or Co2 uses less cover gas than a HE mixed cover gas. A v-groove joint will take less cover gas than a butt weld joint. A weld joint using a chill bar or backing bar will use less cover gas than a open root weld. I'm sure I missed something else but I think this will help. And I bet you thought I was going to say, ahh just use 20cfh... LOL T_Bone
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