Wire feed welding shielding gases

Question 1

state the primary purpose of a shielding gas

Answer 1

The primary purpose of a shielding gas is to prevent the molten weld metal from absorbing elements from atmospheric air such as oxygen and nitrogen.

Question 2

when oxygen and nitrogen from the atmosphere become mixed in the molten weld metal, they:

a) increase the tensile strength of the weld metal
b) form harmful oxides and nitrides in the weld metal
c) help increase the ductility of the weld zone.
d) increase the fracture toughness of the weld metal

Answer 2

b) form harmful oxides and nitrides in the weld metal

Question 3

Which gas is the lightest??

a) hydrogen
b) argon
c) helium
d) oxygen

Answer 3

a) hydrogen

Question 4

Argon and helium are:

a) reactive gases
b) inert gases
c) ionized gases
d) non-conductive gases

Answer 4

b) inert gases

Question 5

Where would you use pre argon shielding gas with GMAW

Answer 5

welding non-ferrous materials such as aluminum, magnesium and their alloys.

Question 6

What is carbon dioxide gas primarily used for?

Answer 6

welding mild and low alloy steels

Question 7

List three factors to consider when selecting a gas for GMAW

Answer 7

base metal type and thickness
filler metal type
welding process
cost of gas
width and depth of penetration
desired bead shape
importance of spatter and post-weld cleanup
joint design and positioning
jigging and fixturing
type of metal transfer

Question 8

Is carbon dioxide a monatomic gas or compound gas?

Answer 8

compound gas

Question 9

A characteristic of carbon dioxide shielding gas used with short-circuiting metal transfer is:

a) a deep, narrow penetration pattern
b) high weld metal loss in the form of spatter
c) excellent surface cleaning action
d) a shallow, wider penetration pattern

Answer 9

b) high weld metal loss in the form of spatter

Question 10

Which modes of metal transfer are possible with GMAW using 0.9mm (.035”) mild steel wire and carbon dioxide shielding gas?

a) spray and globular
b) globular and short circuiting
c) short circuiting and pulse spray
d) spray and pulse spray

Answer 10

b) globular and short circuiting

Question 11

The addition of oxygen to argon causes the temperature of the molten metal to:

a) decrease
b) increase
c) stabilize
d) oxidize

Answer 11

b) increase

Question 12

Compared to Co2, argon is an excellent shielding for GMAW because it promotes the use of:

a) spray metal transfer
b) globular metal transfer
c) short-circuit metal transfer
d) low gas flow rates in globular transfer

Answer 12

a) spray metal transfer

Question 13

When 1%-9% oxygen is added to argon shielding gas it is to:

a) reduce spatter
b) increase the deposition rate
c) improve wetting action
d) reduce welding costs

Answer 13

c) improve wetting action

Question 14

Which of the following gas mixes tends to produce low-crowned weld beads on stainless steels?

a) helium-carbon dioxide
b) argon-carbon dioxide
c) nitrogen-carbon dioxide
d) argon - helium -carbon dioxide

Answer 14

d) argon - helium -carbon dioxide

Question 15

What is an advantage of using a 75% argon + 25% CO2 gas mix on carbon steel?

a) lower cost
b) deeper penetration
c) improved arc characteristics
d) Argon is less dangerous when used in confined spaces

Answer 15

c) improved arc characteristics

Question 16

Name 4 factors that can influence gas flow rates.

Answer 16

type of shielding gas used
type and thickness of the material 
position of the welding
joint design
diameter of wire
size and shape of gas diffuser and nozzle
size of weld pool
presence of drafts or air currents
design of welding fixtures

Question 17

Which gas is generally used for shielding when using MCAW?

a) argon only
b) no gas shielding with certain wires
c) oxygen only
d) a mixture of argon and carbon dioxide

Answer 17

a) argon only

Question 18

The purpose of a flowmeter is to:

a) maintain a constant flow rate of gas
b) maintain a constant pressure of gas
c) maintain a post flow of gas
d) reduce source pressure to working pressure

Answer 18

a) maintain a constant flow rate of gas

Question 19

The preferred method of measuring shielding gas supply is:

a) kilograms per square centimetre
b) kilograms per minute
c) litres per minute
d) surface metres per minute

Answer 19

c) litres per minute

Question 20

Flowmeters are calibrated to indicate the:

a) volume of shielding gas supplied
b) capacity of the shielding gas cylinder
c) pressure of shielding gas supplied
d) density of shielding gas supplied

Answer 20

a) volume of shielding gas supplied

Question 21

What can be done to avoid regular freeze-up when using Co2 gas?

a) lower the gas flow rate
b) increase the working pressure of the regulator
c) cover the regulator body with insulating material
d) install a line heater or manifold system

Answer 21

d) install a line heater or manifold system

Question 22

What must be considered before using a mini-bulk system?

a) cylinder rental costs
b) frequency of use
c) cannot be used with argon gas
d) availability of an external evaporator unit.

Answer 22

b) frequency of use