Line B Exam (CAC-A and PAC)) Flashcards
To remember
What is the first line of eye protection during any procedure?
Eye protection. Specifically safety goggles with side shields.
The CSA W117.2 recommends number ____ lenses for welding helmets for currents up to 500 A.
12.
The CSA W117.2 recommends number 12 lenses for welding helmets for currents up to 500 A.
The CSA W117.2 recommends number ____ lenses for welding helmets for currents greater than 500 A.
14.
The CSA W117.2 recommends number 14 lenses for welding helmets for currents greater than 500 A.
Hearing protection for gouging is suggested. True or false.
False.
Gouging is a very noisy process, so appropriate hearing protection is REQUIRED for those those operating the equipment and persons in the immediate area.
What form of radiation does CAC-A produce?
Ultraviolet light (UV).
The high current open arc sends out large amounts of UV radiation and as a result, skin must be well protected.
Any worker within _______ distance of the gouging process must also wear UV radiation protection.
10m (33ft).
What alloys present the most common problems for respiratory reasons?
Stainless steels and copper alloys.
What coatings on metals create toxic fumes when CAC-A?
Corrosion resistant coatings such as cadmium plating releases dangerous fumes.
What reacts with ultra-violet light to form toxic gases?
Most cleaning solvents react with UV light to form toxic gases. Therefore, they should never be used within line of sight of the process. Another reason respiratory protection is highly suggested.
Power sources for CAC-A should have an open circuit voltage greater than______.
60 V.
Power sources for CAC-A should have an open circuit voltage greater 60 V, is higher than many other power sources.
How far can liquid metal be ejected during the gouging process?
6m (20ft).
During operation never point the torch towards yourself, others, or combustible materials.
How far should flammable materials be relocated before beginning the gouging process?
15m (50ft).
It is also important to have a designated fire watch person to remain on watch after completion of welding or cutting operations.
The operations of CAC-A should only take place is atmospheres containing less than ____% of the LEL (Lower Explosive Limit) of gases or vapors.
> 20%.
Testing for gases or vapors is done when?
Before and continuously during work.
What are the two commonly used abbreviations for air carbon arc cutting?
“CAC-A” (Carbon Arc Cutting - Air) and “ACC” (Air Arc Cutting).
The CAC-A process was developed to remove metal through…
…high temperature of the electric arc created between a carbon electrode and the workpiece.
What type of current is used in Carbon arc gouging?
CC (Constant Current).
–Provided they have a high open circuit voltage of at least 60V).
For carbon, steel, and stainless-steel applications, what polarity is used?
DCEP (Direct Current Electrode Positive)
For various base metals, what current and polarity is used?
AC (Alternating Current) and DCEN (Direct Current Electrode Negative).
The capacity of compressed air is supplied to the torch between _____-_____psi.
80-100 psi (55-690 kPa).
A medium torch uses about ___ litres/min.
700 litres/min (25 cfm).
When selecting equipment, capacity of the ‘what’ is an important factor.
The capacity of the compressor.
The minimum recommended OCV is ___V.
60 V.
The arc voltage should be ___V or higher.
28 V or higher.
Welding current and voltages depend on the _________ size and the type of cutting application.
Electrode size, cutting application.
A power source with a high current capacity having a ____% duty cycle rating is recommended for many CAC-A applications.
100% duty cycle rating.
If a power source CANNOT be operated at 100% duty cycle, the power source should have __________ __________ in the output circuit as a safeguard for the high current usage in CAC-A.
Overload Protection.
In industrial circumstances, a large ______-_______ ___________ rectifier unit that can handle extreme surges in current is commonly selected.
Three-phase transformer rectifier unit.
What type of power source is not recommended as they cannot produce sufficient current at 100% duty-cycle rating.
Single-phase welding power source.
Machine gouging with an automatic electrode feeder is typically done with what kind of power source?
Constant Voltage (CV) power source.
Describe the electrode to power chart.
AC electrode = AC Power
AC electrode = DC Power
DC Electrode X AC Power
DC Electrode = DC Power
(Its because DC electrodes don’t have stabilizers)
As electrode diameter increases, amperage requirements __________.
Also increase.
To connect two power sources together, you must ensure…
They are to be connected in parallel.
You are to follow manufacturers directions.
That they are identical.
What will insufficient air supply cause?
Carbon build-up.
What gas can be used as an alternative to compressed air?
Nitrogen.
What gas should never be used as an alternative to compressed air?
Oxygen.
What is the biggest difference between the SMAW and CAC-A electrode holder is?
The air jet holes.
Where should the air jet holes be during the CAC-A process?
Between the electrode and workpiece.
The electrode holder should be checked for wear and damage ________.
Daily.
What is the most common cable size for CAC-A?
4/0
The electrode holder rotates ____ degrees.
360 degrees.
If the cable is not large enough, it will_________.
Overheat.
What does the CAC-A electrode holder cable contain?
It contains both an electrical cable and a compressed air supply hose.
What does the copper coating on a Direct Current electrode do?
It improves electrode life
Improves heat dissipation.
Maintains the electrode shape.
What are the three types of basic carbon-graphite cutting rods?
DC copper-coated
DC uncoated
AC copper-coated
What type of coated/uncoated electrode is used for cutting carbon steel, low-alloy steels, stainless steels, and cast iron?
DC copper-coated electrode.
Copper coated DC electrodes diameters come in sizes ranging from 5/32” (4mm) to _________
1” (25mm)
5/32” (4mm) to 1” (25mm)
Copper coated DC electrode lengths range from 12” (300mm) to _________
18” (450mm)
12” (300mm) to 18” (450mm)
a benefit to DC uncoated electrodes compared to coated electrodes is that they are…
Less expensive than coated electrodes.
Uncoated electrodes are mostly used for what kind of work?
Demolition work.
(Where precision isn’t a huge concern).
DC uncoated electrodes come in diameters _________ and smaller.
3/8” (10mm) and smaller.
What do AC copper coated electrodes contain that DC copper coated electrodes don’t?
Arc stabilizers.
AC copper coated electrode diameters range from 3/16” (5mm) to ________
1/2” (13mm)
3/16” (5mm) to 1/2” (13mm)
Which power polarity is preferred for AC copper-coated electrodes?
DCEN.
CAC-A electrodes come in how many basic shapes?
Four.
Pointed (or round), Flat, Jointed, Half Round
Which type of CAC-A electrode can be used for both AC or DCEN?
AC Copper coated electrodes.
What electrode type fits the following description?
Required with semi-automatic & automatic machines to permit continuous cutting.
Jointed electrode.
What electrode type fits the following description?
Can produce both a shallow and broad groove.
Half-round electrode.
What electrode type fits the following description?
Mainly used to make wide, rectangular, and shallow grooves.
Flat electrode
What electrode type fits the following description?
A good general-purpose solution for removing metal & maintaining a consistent tip size.
Round pointed electrode
Groove width is usually _______ larger than the electrode diameter.
1/8” (3.2 mm).
At what length should you replace an electrode?
2” (50mm)
Most CAC-A cutting is done ________.
Manually.
At what angle for cutting should the electrode be to the base metal?
Perpendicular (90 degrees to the base metal)
CAC-A is typically done with what travel angle technique.
A pushing angle technique.
What should you do if you don’t have enough air supply when gouging?
Decrease travel speed.
What is the appropriate electrode stick-out length?
4-6” (100-150 mm)
At what length from the electrode holder should the electrode be repositioned?
1 1/2-2” (38-50mm)
any closer and there is risk of damage to the torch head.
Why should you avoid continuously touching the electrode to the base metal during the CAC-A process?
It causing contamination.
Gouging in a vertical position is done in what direction?
Downhill direction.
If it were uphill there would be spatter everywhere.
CAC-A can produce a thin _________ zone in high-carbon steels and cast irons.
Hardened
CAC-A can produce a thin hardened zone in high-carbon steels and cast irons.
How can hardened areas produced by CAC-A be removed?
By grinding.
How can one reduce the hardening effect that comes with CAC-A?
Pre-heating high-carbon steels and cast irons can reduce the hardening effect.
When a CAC-A torch moves quickly it has a lower heat input than compared to that of the oxy-fuel process. What is the result of such?
Minimal distortion.
What type of cause fits the following issue description?
A hard, irregular start.
A hard, irregular start is cause by the compressed air not being on prior to striking the arc.
What type of issue fits the following description?
Sputtering arc, with electrode slow to heat.
Sputtering arc, with the electrode slow to heat is due to a too low current.
What type of issue fits the following description?
Sputtering arc, with electrode heating rapidly.
Sputtering arc, with the electrode heating rapidly is due to the wrong polarity input.
What type of issue fits the following description?\
Intermittent (choppy, stop-start) gouging action.
Intermittent gouging action is due to the travel speed of the electrode being too slow.
What type of issue fits the following description?
Carbon deposit.
Carbon deposit is caused when the electrode touched the workpiece.
What type of issue fits the following description?
Irregular looking groove.
An irregular looking groove is most likely due to the unsteadiness of the operator. This is why operator comfort/ handling in important.
What type of issue fits the following description?
Slag adhering to edges.
Slag adhering to edges is due to having the wrong stickout, the air jets are not aligned with the carbon electrode, and/or the air pressure is too low.
For plasma arc cutting / gouging (PAC/PAG) for an arc current at approximately 20 A, what is the minimum and suggested lens shade?
Shade 5 and 5.
For plasma arc cutting / gouging (PAC/PAG) for an arc current from 20-100A, what is the minimum and suggested lens shade?
Shade 8 and 9.
For plasma arc cutting / gouging (PAC/PAG) for an arc current from 100-400A, what is the minimum and suggested lens shade?
Shade 9 and 12.
For plasma arc cutting / gouging (PAC/PAG) for an arc current from 400-800A, what is the minimum and suggested lens shade?
Shade 10 and 14.
What is a major benefit of PAC?
It can be done on any metal that conducts electricity.
What is plasma?
Plasma is an ionized gas which is created by super heating a gas (with the use a high voltage direct current) so much its molecules separate into ionized atoms.
Describe the PAC process.
It is the transformation of a gas into plasma (which is an ionized gas). The now ionized gas is then propelled at high speeds towards the cut area.
What type of polarity/current is typically used for plasma arc cutting?
Direct current electrode negative (DCEN)
The arc for the Plasma Arc Cutting process is started between the copper nozzle and what?
It is started between the copper nozzle and the ‘hafnium electrode.’
How hot can a plasma jet reach?
Over 30,000 Celsius (Approx. 54,000 Fahrenheit).
This is over 10x hotter than the oxy-acetylene flame.
How is plasma cutting different than oxy acetylene cutting?
Oxy-acetylene is a chemical process, where as PAC does not rely on a chemical reaction and can be used on any electrically conducive material.
To increase the life of internal components, the pilot arc often will shut off after ____ seconds.
Two seconds.
What will happen if any of these are present?
-An improperly assembled torch
-Insufficient gas pressure
-Incorrect line voltage
The pilot arc will not start.
What is the most common air used for manual plasma cutting?
Compressed air.
Just like CAC-A.
For low current applications, what may be used for cooling?
Gas cooling may be used.
For high current applications, what is used for cooling?
Water cooling is used.
For manual cutting, what is most commonly used to cool the torches.
Most manual cutting process use air-cooled torches.
What is the biggest difference between PAC and PAG?
PAG uses tips specifically designed for gouging and shielding cap. This allows a higher standoff distance. The variety of tips also control the depth and width of the gouge.
What does plasma gouging not require unlike air carbon arc cutting?
Carbon electrodes.
Why is plasma arc gouging ideal for aluminum?
Because there is little carbon contamination.
Although aluminum oxide is created but can easily be grinded off.
What is considered a “consumable”?
An electrode is considered a consumable.
A swirl ring is considered a consumable.
A nozzle is considered a consumable.
A shielding cap is considered a consumable.
The power source must always be turned ___ when changing consumables.
Off.
Always have the power source turned off when doing any sort of repairs on a plasma cutting/gouging machine.
What is the most important part of the PAC system located in the torch head?
The electrode.
How do most electrode and nozzle assemblies direct the flow of gas from the nozzle?
In a swirling/spinning motion.
Most assemblies are designed to provide a spin or rotation to the gas when it flows from the nozzle.
Most assemblies in electrodes are designed to provide a spin or rotation to the gas when it flows from the nozzle. What is this part of the electrode called?
Swirl ring.
The electrode and nozzle combinations can be changed according to what?
The gasses used and the power settings of the unit.
In PAC, what makes up an electrode?
Most electrode designs have a self-centering copper tip with a tiny piece of hafnium embedded in the tip.
At what pitting depth at the end of the electrode should you replace it?
1\32” (0.8mm)
What is the purpose of the “nozzle?”
To focus the plasma jet.
What is a “shielding cap?”
A shielding cap protects the nozzle and sets the standoff. This piece should occasionally be replaced due to spatter buildup and heat damage.
What is “standoff?”
Standoff is the tip to work distance.
Are some shielding caps okay to be in direct contact with the surface of the workpiece?
Yes. This is a drag tip.
What is a “drag tip.”
A shielding cap designed to be in direct contact with the workpiece and dragged along the surface of the material.
At what distance should shielding caps without a drag tip be held from the surface of the workpiece?
1/8-1/4” (3-6mm)
All plasma arc torches require…?
A form of cooling and a shielding gas system.
What type of cooling is used for low current torches?
Gas cooling
Manual cutting torches that are designed fir operations at over 100 amperes typically use what form of cooling?
Water cooling.
Recirculating water is operated depending on the recommended what?
Recirculating water is operated at the recommended pressure and flow rate to provide enough cooling.
For water cooled systems, how does one prevent solid deposits in the passages?
By using only the manufacturer’s recommended coolant in the systems.
All PAC systems use what form of gas/air to create the plasma.
Compressed air/gas.
Determining plasma gas depends on what?
Plasma gas varies depending on the type of metal to be cut.
In what three ways can plasma gas be supplied?
Gas cylinders, manifold system, or a compressed air line system.
What is the most common plasma and shielding gas used for manual cutting?
Compressed air.
Although some combinations of compressed air, nitrogen, and argon can be used.
How does one determine what plasma gas and secondary gas to use for PAC systems that don’t use compressed air?
Through a manufacturer’s gas selection chart.
Name several things that gases for automated PAC systems depend on.
Type of metal/ thickness of metal.
Travel speed.
Design of cutting head.
Design of torch consumables.
What type of gas systems do most PAC systems use today?
Single-gas systems.
What is the benefit of using oxygen in single-gas PAC systems?
Oxygen is best for cutting carbon steels.
What is the benefit of using nitrogen in single-gas PAC systems?
Nitrogen is best for aluminum and stainless-steel alloys.
What is the benefit of using air in single-gas PAC systems?
Air is chosen for its convenience and is economy friendly.
What is the universal second choice for single-gas PAC systems?
Air.
How is the secondary gas in a PAC system determined?
Just like plasma gas, it is determined by the thickness of the metal to be cut.
What is dross also known as?
Slag.
Manual Machining is what type of power source?
Constant Current
Automatic machining is what kind of current?
Constant voltage.
