120103c Wire Feed Welding Shielding Gases

Question 1

Question: State the primary purpose of a shielding gas.

Answer 1

Answer: The primary purpose is to prevent the molten weld metal from absorbing elements like oxygen and nitrogen from the atmospheric air.

Explanation: Shielding gases are used in welding to protect the weld area from atmospheric gases such as oxygen, nitrogen, and water vapor. This is crucial as these gases can cause defects in the weld.

Question 2

Question: 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

Answer: b) form harmful oxides and nitrides in the weld metal.

Explanation: Oxygen and nitrogen can adversely react with molten metal, forming oxides and nitrides that can compromise the integrity of the weld.

Question 3

Question: Which gas is the lightest?

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

Answer 3

Answer: a) hydrogen

Explanation: Hydrogen has the lowest specific gravity among common shielding gases, making it the lightest.

Question 4

Question: Argon and helium are:

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

Answer 4

Answer: b) inert gases.

Explanation: Both argon and helium are inert, meaning they do not react with other elements or compounds under typical welding conditions.

Question 5

Question: Where would you use pure argon shielding gas with GMAW?

Answer 5

Answer: Welding non-ferrous materials such as aluminum, magnesium, and their alloys.

Explanation: Pure argon is often used in welding non-ferrous metals because it helps in stable arc formation and better control of the weld pool.

Question 6

Question: What is carbon dioxide gas primarily used for?

Answer 6

Answer: Welding mild and low alloy steels.

Explanation: Carbon dioxide is commonly used for welding steels because it is cost-effective and provides deep penetration.

Question 7

Question: List three (3) factors to consider when selecting a gas for GMAW.

Answer 7

7. Any three (3) of the following are correct.
   a) base metal type and thickness
   b) filler metal type
   c) welding process
   d) cost of gas
   e) width and depth of penetration
   f) desired bead shape
   g) importance of spatter and post-weld cleanup
   h) joint design and positioning
   i) jigging and fixturing
   j) type of metal transfer
   k) speed of travel required

Explanation: The selection of a shielding gas in welding depends on several factors, including the type of metal being welded, the thickness of the material, the filler metal being used, and the specific welding process.

Question 8

Question: Is carbon dioxide a monatomic gas or a compound gas?

Answer 8

Answer: Compound gas.

Explanation: Carbon dioxide (CO2) is a compound gas made up of one carbon and two oxygen atoms, hence not monatomic.

Question 9

Question: 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, wide penetration pattern.

Answer 9

Answer: b) high weld metal loss in the form of spatter.

Explanation: Carbon dioxide can result in a higher loss of weld metal as spatter, which is a common issue with short-circuiting metal transfer.

Question 10

Question: Which modes of metal transfer are possible with GMAW using 0.9 mm (0.035”) 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

Answer: b) globular and short circuiting

Explanation: For 0.9 mm mild steel wire with CO2, globular and short-circuiting are the viable metal transfer modes.

Question 11

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

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

Answer 11

Answer: b) increase.

Explanation: Adding oxygen to argon increases the temperature of the molten metal, which can be beneficial in certain welding scenarios.

Question 12

Question: Compared to CO2, argon is an excellent shielding gas 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

Answer: a) spray metal transfer.

Explanation: Argon is preferred for its ability to facilitate spray metal transfer in GMAW, offering better control and cleaner welds.

Question 13

Question: 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

Answer: c) improve wetting action.

Explanation: The addition of oxygen to argon enhances the wetting action of the weld pool, leading to better bead quality.

Question 14

Question: 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

Answer: d) argon-helium-carbon dioxide

Explanation: The combination of argon, helium, and carbon dioxide is effective in producing low-crowned beads on stainless steel.

Question 15

Question: Draw a cross-section sketch of the bead shape and penetration obtained when using each gas:

a) argon

b}helium.

Answer 15

Answer: Figure 19 shows the correct sketches for argon and helium.

Explanation: This question refers to specific illustrations (Figure 19) demonstrating the bead shape and penetration for argon and helium.

Question 16

Question: 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 16

Answer: c) improved arc characteristics

Explanation: A mix of 75% argon and 25% CO2 improves the arc characteristics when welding carbon steel, offering a balance between cost and performance.

Question 17

Question: Name four (4) factors that can influence gas flow rates.

Answer 17

Answer: Any four of the following are correct:

a) type of shielding gas used
b) type and thickness of the material
c) position of welding
d) joint design
e) diameter of wire
f) size and shape of gas diffuser and nozzle
g) size of weld pool
h) presence of drafts or air currents
i) design of welding fixtures
j) nozzle to work distance
k) amount of welding current
l) welding speed
m) inclination of the gun

Explanation: These factors are crucial in determining the appropriate gas flow rate for welding, as they directly affect the welding process’s efficiency and quality.

Question 18

Question: 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 18

Answer: d) a mixture of argon and carbon dioxide

Explanation: A mixture of argon and CO2 is commonly used in Metal Core Arc Welding (MCAW) for its beneficial properties in the welding process.

Question 19

Question: 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 19

Answer: a) maintain a constant flow rate of gas.

Explanation: Flowmeters are used to ensure a consistent flow rate of shielding gas, which is critical for maintaining the quality and consistency of the weld.

Question 20

Question: The preferred method of measuring shielding gas supply is:
a) kilograms per square centimetre (pounds per square inch)
b) kilograms per minute (pounds per hour)
c) litres per minute (cubic feet per hour)
d) surface metres per minute (surface feet per hour)

Answer 20

Answer: c) litres per minute (cubic feet per hour).

Explanation: Measuring gas flow in litres per minute or cubic feet per hour is preferred for precision and consistency in the welding process.

Question 21

Question: 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 21

Answer: a) volume of shielding gas supplied.

Explanation: Flowmeters are calibrated to show the volume of gas being used, which is important for ensuring the correct amount of shielding gas is supplied during welding.

Question 22

Question: What can be done to avoid regulator 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 22

Answer: d) install a line heater or manifold system

Explanation: Regulator freeze-up, a common issue when using CO2 gas, can be prevented by installing a line heater or manifold system to maintain the gas at a usable temperature.

Question 23

Question: 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 23

Answer: b) frequency of use

Explanation: Before using a mini-bulk system, it’s important to consider how frequently it will be used to ensure it is a cost-effective and practical solution for the welding needs.