Welding Equipment & Maintenance Flashcards

Which power source output characteristic is normally used for SMAW?

Answer: Constant current (drooping)

SMAW uses constant current so amperage stays fairly stable as the welder's arc length changes.

A power source is rated at 300 A at a 60% duty cycle. What does this mean?

Answer: It can weld at 300 A for 6 minutes out of every 10 minutes

Duty cycle is the percentage of a 10-minute period a machine can run at rated output without overheating.

A machine is rated 200 A at 60% duty cycle. About what duty cycle is allowed at 150 A?

Answer: About 100%

Allowable duty cycle = (rated A / actual A)² × rated duty cycle = (200/150)² × 60 ≈ 107%, capped at 100%.

On a constant-voltage GMAW power source, what mainly controls welding current?

Answer: Wire feed speed

With CV output, raising wire feed speed raises the current the machine supplies to melt the wire.

In short-circuit GMAW, raising the inductance setting usually does what?

Answer: Slows the rate of current rise, giving a softer arc with less spatter

Inductance limits how fast current rises during each short circuit, which cuts spatter and makes the puddle more fluid.

What is the main purpose of open circuit voltage (OCV) on a welding power source?

Answer: To start and re-strike the arc

OCV is the voltage across the output terminals when no arc is burning, and it is needed to start the arc.

What is a key advantage of inverter-based power sources over conventional transformer-rectifier machines?

Answer: Smaller size, lighter weight, and better electrical efficiency

High-frequency switching lets inverters use much smaller transformers, which reduces weight and improves efficiency.

A crew must run welding leads much farther than usual at the same current. What cable change is correct?

Answer: Use a larger-diameter cable (smaller AWG number)

Longer runs increase resistance and voltage drop, so you need a larger conductor to carry the current properly.

A loose or corroded work (ground) clamp connection is most likely to cause what?

Answer: Erratic arc, voltage drop, and overheating at the connection

A poor work connection adds resistance, which causes heat, voltage loss, and an unstable arc.

Under AWS D1.1, at what minimum temperature must low-hydrogen SMAW electrodes be kept in a holding oven after removal from hermetically sealed containers?

Answer: 250°F (120°C)

D1.1 requires low-hydrogen electrodes to be stored in ovens held at 250°F (120°C) or higher.

Which drive roll type is generally recommended for feeding soft aluminum GMAW wire?

Answer: U-groove

U-groove rolls cradle soft aluminum wire without shaving or deforming it.

A GMAW wire feeder keeps 'birdnesting' at the drive rolls. Which is the most likely equipment cause?

Answer: A kinked, dirty, or wrong-size liner, or a clogged contact tip

Resistance downstream of the drive rolls makes the wire buckle and tangle at the feeder.

When should a GMAW contact tip normally be replaced?

Answer: When the bore is worn oval or spatter causes erratic feeding and arc wander

A worn or spatter-fouled tip transfers current poorly and lets the wire wander, which destabilizes the arc.

Which equipment setup is commonly used to feed aluminum wire reliably over longer distances in GMAW?

Answer: Push-pull gun or spool gun

Push-pull and spool guns shorten or assist the feed path, so soft aluminum wire doesn't buckle.

Above what working pressure should acetylene never be used?

Answer: 15 psig

Free acetylene becomes unstable and can decompose explosively above 15 psig.

Under OSHA 29 CFR 1910.253, oxygen cylinders in storage must be separated from fuel-gas cylinders by at least what?

Answer: 20 feet, or a noncombustible barrier at least 5 feet high with a 1/2-hour fire rating

OSHA requires 20 ft of separation or a 5-ft-high noncombustible barrier rated for at least 1/2 hour of fire resistance.

What is the main function of a flashback arrestor on an oxyfuel outfit?

Answer: To stop a flame front from traveling back into the hose, regulator, and cylinder

Flashback arrestors quench a reverse-traveling flame and usually include a check valve to prevent gas backflow.

Why should acetylene cylinders be stored and used upright, with withdrawal limited to about 1/7 of contents per hour?

Answer: To keep acetone from being drawn out of the cylinder

Acetylene is dissolved in acetone, and drawing gas too fast or from a horizontal cylinder pulls acetone into the regulator and torch.

What is the correct method to check oxyfuel or shielding gas connections for leaks?

Answer: Apply an approved leak-detection solution and watch for bubbles

Approved leak solutions show leaks safely, while flames and oil create fire or explosion hazards.

Before attaching a regulator to an oxygen cylinder, what practice is recommended?

Answer: Briefly crack the cylinder valve to blow out dust and debris, standing to the side

Cracking the valve clears contaminants that could ignite in high-pressure oxygen, and oil must never touch oxygen fittings.