Lincoln Electric IM790 manual Shielding Gas, Making a Weld

B-5		OPERATION		B-5
	FIGURE B.5		FIGURE B.6

Gun Handle	Contact Tip
Gas Diffuser/
Contact Tip	Wire Electrode
Gas Nozzle

3/8" – 1/2" Contact Tip to Work Distance (CTWD)

Shielding Gas

When using the GMAW process, a cylinder of shield- ing gas, must be obtained. Refer to the ACCES- SORIES section for more information about selecting gas cylinders for use with the SP-175 Plus. Be sure to observe all cylinder handling and use precau- tions.

1.For CO2, open the cylinder very slowly. For argon- mixed gas, open cylinder valve slowly a fraction of a turn. When the cylinder pressure gauge pointer stops moving, open the valve fully.

2.If using a regulator with an adjustable flow meter, press the gun trigger and adjust the flow to give 15

– 20 cubic ft per hour (CFH) (7 – 10 I/min) [use 20 -– 25 CFH (10 – 12 I/min) when welding out of

position or in a drafty location for CO2]. For argon mixed gas, press the gun trigger to release gas pressure, and adjust the flow to give 25 – 30 CFH (12 – 14 I/min).

3.Keep the cylinder valve closed, except when using the SP-175 Plus. When finished welding:

a) Close the cylinder valve to stop gas flow.

b) Depress the gun trigger briefly to release the pressure in the gas hose.

c) Turn off the SP-175 Plus.

Making A Weld

1.See Recommended Processes And Equipment section for selection of welding wire and shielding gas and for range of metal thicknesses that can be welded.

2.See the Application Chart on the inside of wire feed section door for information on setting the SP-175 Plus controls.

3.Set the Voltage (“V”) and Wire Speed (“olo’”) con- trols to the settings suggested for the welding wire and base metal thickness being used.

4.Check that the polarity is correct for the welding wire being used and that the gas supply, if required, is turned on.

5.When using Innershield electrode, remove the gas nozzle and install the gasless nozzle. This will improve visibility of the arc and protect the gas dif- fuser from weld spatter. Refer to the MAINTE- NANCE section for details on nozzle replacement.

6.Refer to Figure B.7. Connect work clamp to metal to be welded. Work clamp must make good elec- trical contact to the workpiece. The workpiece must also be grounded as stated in “Arc Welding Safety Precautions” in the beginning of this manu- al.

7.Position gun over joint. End of wire may be lightly touching the work.

8.Lower welding helmet, close gun trigger, and begin welding. Hold the gun so the contact tip to work distance is about 3/8 inch (10 mm).

FIGURE B.7

GUN CABLE

WORKPIECE

ARC

WORK CLAMP

SP-175 PLUS