120103c Flashcards
1
Q
State the primary purpose of a shielding gas
A
to protect the molten metal from atmosphere
2
Q
When O2 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
A
b) form harmful oxides and nitrides in the weld metal
3
Q
Which gas is the lightest?
a) hydrogen
b) argon
c) helium
d) O2
A
a) hydrogen
4
Q
Argon and helium are
a) reactive gasses
b) inert gasses
c) ionized gasses
d) non conductive gasses
A
b) inert gasses
5
Q
Where would you use pure argon shielding gas with GMAW?
A
welding non ferrous materials such as aluminum and magnesium and their alloys
6
Q
What is CO2 gas primarily used for?
A
welding low alloy steels
7
Q
What are 3 factors to consider when selecting a gas for GMAW
A
Any of the 3 are correct
base metal type & thickness
filler metal type
welding process
got of gas
width and dept of penetration
desired bead shape
importance of spatter and post weld cleanup
joint design and positioning
jigging and fixturing
type of metal transfer
speed of travel required
8
Q
Is CO2 Monatomic gas or a compound gas
A
compound gas
9
Q
A characteristic of CO2 shielding gas used with short circuiting metal transfer is:
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
A
b) high weld metal loss in the form of spatter
10
Q
which modes of metal transfer are possible with GMAW using .9mm (.035”) mild steel wire and CO2 shielding gas
A
short circuiting & globular
11
Q
The addition of O2 and argon causes the temp of the molten metal to
a) decrease
b) increase
c) stabilize
d) oxidize
A
b) increase
12
Q
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
A
a) spray metal transfer
13
Q
When 1% - 9% O2 is added to argon shielding gas it is to?
a) reduce spatter
b)increase the deposition rate
c) improve wetting action
d) reduce welding cost
A
c) improve wetting action
14
Q
Which of the following gas mixes tends to produce low-crowned weld beads on stainless steels?
a)helium - CO2
b) argon - CO2
c) nitrogen - CO2
d) argon - helium - CO2
A
d) argon - helium - CO2
15
Q
Draw a cross section sketch of the bead shape and penetration obtained when using each gas
a) argon
b) helium
A
Find pictures on page 36
16
Q
What is an advantage of using 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
A
c)improved arc characteristics
17
Q
Name 4 factors that can influence gas flow rates
A
Any 4 of the following are correct
type of shielding gas used
type and thickness of the material
position of 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
nozzle to work distance
amount of welding current
welding speed
inclination of the gun
18
Q
Which gas is generally used for shielding when using MCAW
a) argon only
b) no gas shielding with certain wires
c) O2 only
d) mixture of argon and CO2
A
d) mixture of argon and CO2
19
Q
The purpose of the flow metre 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
A
a) maintain a constant flow rate of gas
20
Q
The preferred method of measuring shielding gas supply is:
a) KG per square CM ( pounds per square inch)
b) KG per min (lb/hr)
c) L/Min ( cubic feet per hr)
d) surface metres per min ( surface feet per hour)
A
c) L/Min ( cubic feet per hr)
21
Q
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
A
a) volume of shielding gas supplied
22
Q
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
A
d) install a line heater or manifold system
23
Q
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
A
b) frequency of use
24
Q
What percentages of O2 and Nitrogen are in atmosphere (breathing air)
A
21% O2 78% Nitrogen
25
Is argon gas considered to have high or low thermal conductivity?
Argon has low thermal conductivity
26
When shielding gasses such as CO2 or O2 is heated these gasses tend to break down into their component atoms.
What is another term for this process?
dissociate into their component atoms
27
What are the 2 categories of oxidation potential for shielding gasses.
Reactive (active or oxidizing)
Inert ( non- reactive)
28
Why might you use a shielding gas which has had O2 added to it?
promote better wetting at the weld edges
minimizes undercut
29
Define Inert gases
Inert gasses are gases that do not combine chemically with the products in the weld zone
30
Aprox how much heavier is Argon than air?
Argon is 1.4X heavier than air.
31
List 4 Characteristics of Argon.
Any of the 4 below are correct.
- It has low thermal conductivity & ionization potential
- Argon promotes a spray arc transfer and has a stable arc that is easily started.
- Gas mixtures with more than 85% argon promote axial spray transfer when the current is set above a critical value called the transition current
Below the transition current metal transfer occurs in the short circuit or globular mode
- It is a monatomic gas (1 atom per molecule) and can not be dissolved in molten metal
-An arc shielded with argon results in a relatively narrow bead with deep capillary (finger like ) penetration
- the arc plasma has a high energy inner core and outer zone of less energy
32
Why is argon not used as a shielding gas on its own in its pure form?
Causes erratic arc and has a tendency to undercut along bead edges
33
What is argons primary use with GMAW.
welding non ferrous metals such as aluminum, magnesium, and copper ( or their alloys)
34
Look at page 7 image & understand it
35
How much denser (heavier) is helium than air.
Helium is .14X denser than air
36
Using helium as a shielding gas, what changes with the weld characteristics?
Produces a broader weld bead with more uniform penetration pattern as compared to using argon.
37
Helium as a shielding gas does not exhibit true axial spray transfer at any current level what effect does this have on the weld?
more spatter and rougher weld beads
38
What metals is helium used as a shielding gas for?
non-ferrous metals such as aluminium, magnesium & copper
39
Define reactive gases
Reactive gasses are compounds of gasses that tend to dissociate molecularly and recombine under certain conditions
40
Is CO2 a reactive compound? Y/N
Yes
41
In the heat of the weld what does CO2 have the ability to change into?
It can change into carbon monoxide (CO) and free O2, and then it recombines as it cools.
42
When CO2 dissociates into CO & O2 what does the arc do with the free O2?
It uses the free O2 to super heat the weld, creating a wetter, more fluid puddle.
43
What shielding gas is often used for short circuiting and globular modes of metal transfer?
CO2
44
What are 2 major concern when using the short circuit mode of metal transfer?
Spatter loss is high and has excessive post weld cleanup costs
45
What is another name for Globular Metal Transfer Mode?
Open arc
46
What are 3 risks when using open arc CO2 welding
- plastic cold shuts (lack of fusion)
- gas entrapment (porosity)
- internal cracking
47
A true spray arc can not be obtained with gas mixes that contain more than what percentage of CO2?
A) 20%
B) 8%
C) 50%
D) 15%
D) 15%
48
What type of metals primarily use CO2 as a shielding gas
mild and low alloy steels
49
What is currently the cheapest shielding gas?
CO2
50
What does adding O2 to shielding gas do to arc characteristics?
Improves arc stability
51
How much O2 is added to shielding gas to increase puddle fluidity?
a) <5%
b) <10%
c) <15%
d) <20%
b) <10%
52
How does O2 improve puddle fluidity?
The oxidizing nature of O2 breaks down the surface tension on molten metal and allows the puddle to wet out the edges of the weld bead
53
What weld characteristics change when you have better puddle fluidity?
Improves bead appearance and minimizes undercut
54
What shielding gas is excellent for GMAW
a) CO2
b) argon
c) CO2 & Argon
d) CO2 & O2
b) Argon
55
why would you add O2 to Argon as a shielding gas?
it allows the use of spray metal transfer, allows the hotter molten metal to blend nicely with the toes of the weld.
56
If you only used argon with GMAW process when welding carbon steel or SS, what would the negative characteristics of the weld be
Undercut due to lack of puddle fluidity
57
What percentage of O2 is added to Argon to improve puddle wetting and reduce the tendency to undercut?
a) 2-5%
b) 7-10%
c) 1-9%
d) 9-18%
c) 1-9%
58
If using an Argon - O2 mix of shielding gas, do the filler metals require added deoxidizers added? Y/N
Yes
59
Why would you not use an Argon - O2 shielding gas mix for welding mild steels?
The cost is to high
60
What is the widely used ratio of Argon to CO2 and what is the ratio known as?
a) 20% & 80%
b) 80% - 20%
c) 75% - 25%
d) 25% - 75%
c) 75% Argon - 25% O2
it is known as C25
61
What metals is C25 used as a shielding gas to weld?
mild and low alloy steels using GMAW
has a stable arc & good puddle control with little spatter
it can be used with lower voltage and current settings
62
What is the most common shielding gas ratio used with GMAW on carbon steel?
75% Argon - 25% O2
(C25)
63
Argon- Helium mixed shielding gas works on all metals but what metals is it primarily used for?
a) aluminum & alloys
b) copper & alloys
c) magnesium & alloys
d) all of the above
d) all of the above
64
With austenitic SS what shielding gas mix is used that produces a weld with a very low crown?
a) CO2 - Argon
b) Argon - O2
c) Helium - Argon - CO2
d) Helium - CO2
c) Helium - Argon - CO2
65
What is the GMAW shielding gas flow rate range?
a) 7L/ min to 23L/min
b) 12L/min to 30L/min
c) 2L/min to 10L/min
d) 0L/min - 10L/min
a) 7L/ min to 23L/min
66
Does the size and shape of the gas diffuser and the nozzle influence how effective the gas shielding is? Y/N
Yes
67
What does laminar flow mean?
Straight line
68
Explain what happens if the flow rate of shielding gas is to high?
it causes turbulence which draws in atmospheric air and possible contamination of the weld
69
Welding Carbon Steel with CO2 shielding gas what are 2 Advantages and 2 disadvantages ?
Advantages
- Low cost & readily available
- Deeper penetration and argon mixes
Disadvantages
- Spatter makes it look bad & increases post weld clean-up
- rougher bead appearance than argon mixes
70
Welding Carbon Steel with 75% Argon + 25% CO2 shielding gas what are an Advantage and disadvantage ?
Advantage
- Min spatter & smooth bead appearance
Disadvantage
- higher cost than CO2
71
Welding Stainless Steel with 90% Helium + 7.5% Argon + 2.5% CO2 shielding gas what is the main advantage of this mix?
Advantage
- No undercutting - low crown
72
When using AR+1%-5% O2 shielding gas what is the main advantage of this mix?
Good coalescence (fusion) and bead contour, min undercutting
73
When using AR+1-2% O2 shielding gas what is the main advantage of this mix?
- min undercutting
74
When welding Aluminum and using Argon what is the intended material thickness for best metal transfer and arc stability
0-1" thick
75
When welding Aluminum and using 35% Argon + 65% Helium what is the intended material thickness for best metal transfer and arc stability
1-3" thick
76
What is the main advantage using Argon when welding Magnesium?
Excellent cleaning action
77
What shielding gas is used as an oxidizer to weld Carbon, low alloy steels and SS
CO2
78
What shielding mix is used as an oxidizer for welding carbon , low alloy steels and SS out of position?
75% Argon + 25% CO2
79
FCAW process on Carbon Steel using 75% AR + 25% CO2 list 3 advantages
- Higher tensile and yield strengths
- primarily for out of position work
- improved arc characteristics
80
FCAW process on Carbon Steel using 75% AR + 25% CO2 what is a disadvantage
Gas mixes are more expensive than CO2
81
FCAW process on Carbon Steel using CO2 list 2 advantages
Deeper penetration
low cost
82
FCAW process on Carbon Steel using 75% AR + 25% CO2 list 2 disadvantages
more spatter than AR+CO2 mixes
generally a rougher bead appearance than argon mixes
83
What is the flow rate range for FCAW
a) 7L/ min to 23L/min
b) 14L/min to 23L/min
c) 2L/min to 10L/min
d) 0L/min - 10L/min
b) 14L/min to 23L/min
84
What do MCAW consumables always require?
auxiliary gas shield ( shielding gas)
85
What pressure range can a compressed cylinder contain
2000-6000 psi
86
All of the following are sold by volume except one. Which one is sold by weight?
Co2
Argon
Helium
Hydrogen
Nitrogen
CO2 is sold by weight
87
Cylinders containing liquids should be replaced in some applications if the pressure drops to approximately what psi?
200psi
88
How do you prevent a regulator or line from freezing on your supplied air bulk system?
Using an inline heater or having a heat lamp pointed on the regulator
89
How is the flow of shielding gas more accurately measured when using a flow metre.
a) by volume
b) by pressure
a) volume
90
Why are flow meters designed and calibrated for use with a specific gas?
Because gas density varies from gas to gas
91
Why are hoses generally made of plastic materials and not rubber?
The use of plastic hoses allows for compatibility with all gasses.
Rubber is incompatible with helium due to the pressure needed (>20psi) and it penetrates through the hose causing gas loss.
92
_____ _____ are electrically operated valves that control the flow of the shielding gas to the weld zone.
Solenoid valves
93
When O2 and N 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
b) form harmful oxides and nitrides in the weld metal
94
Which gas is the lightest
a) hydrogen
b) argon
c) helium
d) O2
a) hydrogen
95
Argon and helium are
a) reactive gases
b) inert gases
c) ionized gases
d) non-conductive gases
b) inert gases
96
Where would you use pure argon shielding gas with GMAW
non- ferrous materials such as aluminum, magnesium, and their alloys
97
What is CO2 gas primarily used for
mild steels or low alloy steels
98
List 3 factors to consider when selecting a gas for GMAW
Any of these are correct
base metal type and thickness
filler 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 filtering
type of metal transfer
speed of travel required
99
A characteristic of CO2 shielding gas used with short circuiting metal transfer is
a) a deep, narrow penetration pattern
b) high weld metal loss as spatter
c) excellent surface cleaning action
d) a shallow, wide penetration pattern
b) high weld metal loss as spatter
100
Which modes of metal transfer are possible with GMAW using .035" mild steel wire and CO2 shielding gas?
a) spray & globular
b) globular and short circuiting
c) short circuiting and pulse spray
d) spray and pulse spray
b) globular and short circuiting
101
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 circuiting metal transfer
d) low gas flow rates in globular transfer
a) spray metal transfer
102
When 1-9% O2 is added to argon shielding gas it is to
a) reduce spatter
b) increase the deposition rate
c) improve wetting action
d) reduce welding $$
c) improve wetting action
103
Which of the following gas mixes tends to produce low crowned weld beads on SS?
a) helium -CO2
b) Argon - CO2
c) N-Co2
d) Argon - Helium - CO2
d) Argon - Helium - CO2
104
Draw a cross secition of the bead shape and penetration obtained when using each gas.
Find the answer on page 36.
A) Argon
B) Helium
105
What is the advantage of Ising a 75% Argon + 25% CO2 mix on Carbon Steel
a) lower cost
b) deeper penetration
c) improved arc characteristics
d) argon is less dangerous when used in confined spaces
c) improved arc characteristics
106
Which gas is generally used for shielding when using MCAW
a) argon only
b) no gas shielding with certain wires
c) O2 only
d) a mix of argon + CO2
d) a mix of argon + CO2
107
The preferred method of measuring shielding gas supply is:
a) pounds per square inch
b) pounds per hour
c) cubic feet per hour
d) surface feet per hour
c) cubic feet per hour
108
Flow meters are calibrated to indicate
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
a) volume of shielding gas supplied
109
What must be considered before using a mini-bulk system?
a) cylinder rental costs
b) frequency of use
c) can not be used with argon gas
d) availability of an external evaporator unit
b) frequency of use
110
Which of the following would be a correct statement when performing MCAW with C25 gas mix
a) used primarily for out of position work
b) excellent penetration with short circuiting metal transfer
c) it exhibits more spatter than CO2
d) all of the above
a) used primarily for out of position work
111
Helium is used primarily as a shielding gas for which of the following metals
a) Aluminum and copper
b) mild steel and stainless steel
c) cast iron and cast steel
d) plain carbon steels and low alloy steels
a) Aluminum and copper
112
If pure argon is used for gas metal arc welding steel, it may cause the weld to have
a) undercut
b) a flat bead contour
c) reduced penetration
d) excess porosity
a) undercut
113
What is the main purpose of adding O2 (1-9%) to argon when welding
a) eliminates propriety
b) gives better penetration
c) allows weld metal to wet out on the edges min undercut
d) allows for a greater selection of filler wire to be used
c) allows weld metal to wet out on the edges min undercut
114
Which of the following gas blends will reduce high crowned weld beads on stainless steels
a) helium- CO2
b) argon - CO2
c) Nitrogen - CO2
d) helium - argon - CO2
d) helium - argon - CO2
115
What type of shielding gas would be referenced as a reactive gas
a) pure nitrogen
b) pure CO2
c) pure argon
c) pure argon
d) pure helium
b) pure CO2
116
Which type of shielding gas would have a low thermal conductivity
a) argon
b) helium
c) O2
d) CO2
a) argon
117
When there is a buildup of frost on the carbon dioxide flowmeter it is recommended that you
a) install a line heater
b) increase the gas flow
c) increase the inductance
d) increase the amperage
a) install a line heater
118
A very small percentage of O2 mixed with argon will
a) reduce the cost of shielding gas
b) increase puddle fluidity
c) create a toxic gas
d) oxidize the puddle
b) increase puddle fluidity
119
Which of the following will have an effect on the flow rate of shielding gasses
a) diameter of electrode, wire speed, climatic conditions
b) position of weld, thickness of material, polarity of current
c) type of material, diameter of rod, amount of current
d) type of gas, thickness and type of material, position of weld
d) type of gas, thickness and type of material, position of weld
120
Which shielding gas is used primarily for welding mild steel?
a) CO2
b) N2
c) He
d) Ar
a) CO2
121
Inert gas welding flowmeters are calibrated in L/min, which measures?
a) volume flow of gas
b) capacity of gas
c) pressure of gas
d) density of gas
a) volume flow of gas
122
Which gas has the highest weight (specific gravity)?
a) hydrogen
b) helium
c) argon
d) nitrogen
c) argon
123
When using CO2 shielding gas with GMAW welding, the mode of metal transfer is
a) spray transfer
b) globular and plasma
c) short circuit and globular
d) pulsed current
c) short circuit and globular
124
MCAW carbon steels with pure CO2 shielding gas produce excellent quality welds and is commonly used T/F
False
125
It is recommended that liquid filled CO2 cylinders be changed out when the pressure gets below
a) 175 psi
b) 200 psi
c) 225 psi
d) 250 psi
b) 200 psi
126
Which of the following is correct about helium used as a shielding gas
a) it has a high thermal conductivity
b) it has a high ionization potential compared to Ar
c) it produces a broader weld bead than argon
d) all the above
d) all the above
127
What is the primary purpose of the shielding gas used for gas metal arc welding
a) reduce the carbon content in the weld metal
b) protect the weld from the atmospheric air
c) combines with weld metal to improve mechanical properties
d) increases the heat in the weld puddle to improve
b) protect the weld from the atmospheric air
128
Which shielding gas is commonly used with the FCAW process to weld carbon or stainless steel
a) N2 & CO2
b) Ar & N2
c) Ar & He
d) 75% Ar & 25% CO2
d) 75% Ar & 25% CO2
129
Which of the following would be a correct statement when performing FCAW with C25 gas mix
a) used primarily for out of position work
b) excellent penetration with short circuiting metal transfer
c) it exhibits more spatter than carbon dioxide gas
d) all of the above
a) used primarily for out of position work
130
Which of the following gases is sold by weight?
a) Ar
b) He
c) N2
d) CO2
d) CO2
131
The recommended way of measuring shielding gas flow is:
a) pounds per inch
b) pounds per hour
c) cubic feet per hour
d) surface feet per hour
c) cubic feet per hour
132
Which shielding gas is spray transfer NOT possible with
a) argon, O2 mix
b) 90% Ar & 10% CO2
c) pure Ar
d) Pure CO2
d) Pure CO2
133
What is another name for globular transfer when using CO2 as a shielding gas
a) open arc
b) CO2 arc
c) closed arc
d) extension arc
a) open arc
134
Which of the following GMAW modes would produce the most spatter
a) globular with CO2
b) Short circuiting with Ar&CO2
c) spray transfer
d) spray transfer, Ar&CO2
a) globular with CO2
135
Due to the heat of the arc when welding with CO2 it has the ability to separate from itself (dissociate) into which toxic gas?
a) chlorinated gas
b) CO
c) phosgene gas
d) phosphene gas
b) CO
136
What type of hose should be used with helium shielding gas
a) plastic
b) rubber
c) acetylene
d) O2
a) plastic
137
Helium is used primarily as a shielding gas for which of the following metals
a) Al & copper
b) mild steel and stainless steel
c) cast iron and cast steel
d) pain carbon steels and low alloy
a) Al & copper
138
A flow meter is calibrated for
a) all inert gases
b) fuel or non fuel gases
c) all gases used for GMAW
d) a specific type of gas
d) a specific type of gas
139
What is the most used regulator/flowmeter for shielding gas
a) floating ball type
b) dual gauge type
c) regulator type
d) 2 stage
a) floating ball type
140
When welding SS 1-9% O2 is added to Ar shielding gas
a) reduce spatter
b) increase deposition rates
c) improve the puddles wetting action
d) reduce cost
c) improve the puddles wetting action
141
What is the effect of O2 or N2 in the molten weld metal
a) strengthens the weld
b) harmful to the weld
c) increases the ductility of the weld
d) improves mechanical properties
b) harmful to the weld
