Welding C

What is amperage used for in welding?

It is used as the heat setting and causes the parent metal to melt.

What does increased amperage result in?

Increased metal deposition rate and increased penetration.

What is arc blow in welding?

A condition encountered during DC welding only - where the arc becomes uncontrolled and moves from side to side.

Due to electric current being in the same direction for a prolonged period.

How can arc blow be prevented?

By changing ground clamp location, adjusting electrode angle, welding towards a heavy existing weld, or lowering current setting.

What is the function of the core in a welding transformer?

magnetic link between primary and secondary coils in welding transformer. Known as a moveable shunt can be moved to control amperage. It alters the link between transformer’s primary and secondary by coil.

What type of welding machine is used for SMAW?

Constant Current welding machine.

Constant Current vs Constant Voltage Welding Machine?

• Constant Current- welding machine used for shielded metal arc welding. (SMAW). And gas tungsten arc welding (GMAW). Relatively high open cct voltage to establish weld arc. Steep voltage curve.

• Constant Voltage- aka constant potential- used for wire process welding. Stable voltage but amperage changes. Almost flat volt-amp curve.

How many direction changes occur in an AC circuit for 60 cycle operation?

120 direction changes

What does 'duty cycle' refer to in welding machines?

The percentage of time within a 10-minute period a machine can operate at its maximum output before needing to cool.

• Duty Cycle- NEMA (National Electric Manufacturer’s Association) rates welding machines. Based on max output of machine over a 10 minute period. Expressed as % of the 10 minutes that you can run at max output before needing to allow it to cool down.

  • ex: 300A, 60% duty cycle means you can run at 300A for 6 minutes out of 10. Or you can run at 60% of 300A for the full 10 minutes!

What does an electron in welding refer to?

A negatively charged particle that moves from negative to positive.

What is inductance defined as?

The ability of a conductor to transfer current into a neighboring body without physical contact.

What is open circuit voltage?

• when welding machine is turned on for the first time, and no current flowing, you have open circuit voltage.

What is Electrical Resistance? How does it apply to welding?

• Resistance: property of electrical conductor to oppose current flow- causes energy to turn into heat. The electrode work gap offers resistance to current flow which creates the heat needed for welding.

Reverse Polarity vs Straight Polarity Welding

• Reverse polarity: DC welding circuit only.

  • electrode cable connected to positive terminal on welder.

  • deeper penetration

  • Slower rod melting

  • Narrower metal flow

  • 2/3 of arc associates with base metal (negative terminal)

  • You can test polarity by using any rod that has a 0 as its last digit, the arc is quiet sounds like bacon sizzling, minimal spatter, deep penetration.

• Straight Polarity: DC welding circuit only.

  • Electrode cable connected to negative terminal of welding machine.

  • electrode melts faster

  • 2/3 arc energy associates with electrode

  • Shallow penetration

  • Wider metal flow

  • Test polarity using any rod ending in 0 as its last digit, arc is loud hissing sound, produced more spatter, emits smoke fumes from arc.

What is the purpose of an inverter in welding?

To convert DC to AC

What is voltage sometimes called? What is it responsible for in welding?

• Voltage often called EMF (electromagnetic force).

  • responsible for:

    • Creating the arc: Arc starts at higher open circuit voltage around 50-100V. Once established, the voltage drops to arc voltage.

    • Maintaining the arc: During SMAW it drops to 17-40V.

    • Puddle fluidity/Flow: arc voltage directly affects width of weld bead and wetness of the puddle. More arc voltage is more puddle width and fluidity.

What is the volt/amp curve in welding?

• Volt/amp curve (output slope):

  • Graphical illustration indicating output of welding machine

  • steep/drooping volt/amp (constant current): SMAW or GTAW

  • Flat volt/amp (constant voltage): wire feeding processes.

  • Open circuit voltage usually plotted where graph meets vertical axis.

How is a magnetic field created with regards to a transformer?

When current flows through a coil wrapped around an iron core.

What is the typical open circuit voltage range to create an arc?

Around 50-100 volts.

How does arc voltage affect the weld puddle?

Higher arc voltage increases the width of the weld bead and fluidity of the puddle.

What are the Advantages/Disadvantages of an AC transformer in welding?

• AC Transformer

  • converts high voltage low current into low voltage high current for welding. Using more wraps on primary and fewer wraps on secondary coil. Via laminated steel core (induction)

  • Adv:

    • low cost, maintenance, operating

    • Quiet

    • No arc blow

  • Disadv:

    • not portable

    • AC output only

    • Limited selection of electrodes

    • SMAW only

What are the Advantages/Disadvantages of an AC-DC Transformer Rectifier in welding?

• AC-DC Transformer Rectifier:

  • AC machine with added diode rectifier to convert to DC.

  • Silicon diodes mounted on heat sinks (made of copper or aluminum plates)

  • Adv:

    • AC and DC output

    • Full electrode selection

    • Choice of polarity

    • Few moving parts

    • CC or CV machines (can use CC with voltage sensing feeder for GMAW)

  • Disadv:

    • more costly

    • Arc blow if using DC

    • Not portable

    • Need clean, cool environment

What is an AC Alternator and some adv/disadv?

• AC Alternator:

  • useful for remote locations, essentially a small engine driven device that is fuel powered (generator)

  • Adv:

    • Portable

    • High Duty Cycle compared to transformer

    • No arc blow

    • Can also run power tools

  • Disadv:

    • high cost, operating, maintenance

    • Noise

    • Limited electrode selection

What is the difference between a Generator vs Alternator?

• A generator is spinning wire coils surrounded by magnets,

• while an alternator is a spinning magnet assembly surrounded by wires

An alternator is a generator, but a generator isn't necessarily an alternator.

An alternator is one type of generators. One that specifically makes alternating current (AC)

What are the Advantages/Disadvantages of an DC Output Alternator for welding?

• DC Output Alternator

  • Many engine driven welding power sources use the alternator design.

  • AC output is rectified to DC.

  • Adv:

    • Major - capability of producing AC and DC output at high duty cycle rating

    • Choice of polarity

    • Smoother arc than AC

    • Portable

    • Full choice of electrodes

    • Can also run power tools

  • Disadv:

    • High cost, maintenance, operating

    • Noisier

    • Arc blow if using DC

What are the Advantages/Disadvantages of an Inverter for Welding?

• Inverter

  • electronic circuit that can convert DC into AC. Output voltage and frequency can be adjusted sometimes.

  • Adv:

    • Excellent arc starting characteristics

    • Excellent output current control

    • Pulse current capability

    • May be CC or CV

    • small and lightweight

  • Disadv:

    • AC is noisy

    • needs clean environment

    • high cost

    • Arc blow with DC

    • electronics (fragile)

    • expensive repairs

How many standardized sizes are there for welding cables?

• 8 sizes standardized.

  • #4, #3, #2, #1, 1/0, 2/0, 3/0, 4/0.

  • #4 is smallest, 4/0 is largest.

  • Cable size needed is determined by amperage and the length of distance from the welding machine. Longer distances and higher amperages require a bigger cable to be used.

  • You should connect a whip (small cable) at the electrode section, it is meant to make welding more comfortable as a very thick cable can be awkward to weld with. If overheating, upsize the whip.

What is a whip in welding cables?

A small cable connected at the electrode section to make welding more comfortable.

• You should connect a whip (small cable) at the electrode section, it is meant to make welding more comfortable as a very thick cable can be awkward to weld with. If overheating, upsize the whip.

Welding Cable Connectors Overview

• Cable Connectors:

  • Sized by amperage ratings.

  • Quick connect type using male and female ends twist together and lock. Usually brass or copper

  • Lugs attach to machines, work clamps, tables. They are not insulated in order to make good electrical contact.

  • Ensure connector or lug sizing is correct for application or else it will overheat!

What are the two types of electrode holders (stingers)?

• 2 Types:

  • Alligator Jaw: clamps bare end of electrode in spring loaded jaw

  • Twist Head: bare end of electrode inserted into head, mechanical pressure tightens it into place as the head is twisted.

• Electrode current capacity must match the amps used and welding cable amp capacity.

• Holder is insulated to prevent stray arcs and for safety.

What is the importance of a clean work lead clamp connection?

It prevents accidental arcing and maintains stable welding arcs.

What are the types of Work Lead Clamps (Ground Connections) and applications for each?

• Work Lead Clamps (ground clamp)

  • Must have clean connection.

  • Types:

    • C Clamp: allows for secure connection on thick or bulky workpieces.

    • Spring Loaded Clamp: Easy change of location if needed, most common on general SMAW.

    • Magnetic Clamp: quick, secure attachment. Cannot use on non magnetic material like aluminum.

  • Poor connections can cause accidental arcing, (hard and brittle spots forming on workpiece)

  • Never place ground where it may pass through a part not designed for current flow.

  • A poor work lead connection creates resistance to current flow which generates heat, you may see unstable arcs or overheating of welding cables.

Electrode types (2 categories)

• 2 Categories:

  • Non Consumable:

    • Not to be consumed into weld puddle.

    • Ex: in GTAW (Gas Tungsten Arc Weld), the tungsten electrode only does the arc. If you are using a filler metal, it must be fed externally.

  • Consumable:

    • electrode is melted into weld puddle. Therefore, the electrode is also the filler metal.

    • Ex: in SMAW (shielded metal arc welding), you use these.

  • AWS (American Welding Society) and CSA (Canadian Standards Association) developed specs for carbon steel filler metals when using SMAW. This module is focused on carbon steel electrodes (aka mild steel).

AWS and CSA systems for classifying electrodes for mild stee:

• AWS Classification System for mild steel:

  • E6027 as an example.

    • E stands for Electrode.

    • First 2 digits (60) are minimum welded tensile strength of the weld material in PSI x 1000. This would be 60,000 psi. This may be 3 digits sometimes if the tensile strength needed is very high!

    • Third digit (2) indicates the satisfactory welding position applicable. This would be only Flat and Horizontal positions. This is the same as CSA standard.

      • 1- All positions

      • 2- Flat and Horizontal Fillets

      • 3- Flat only

      • 4- Flat, Overhead, Horizontal, Vertical Down

    • Fourth Digit (7) indicates the the type of flux coating and recommended type of current. This would be Iron Oxide, with AC or DC in either polarity. This is the same as CSA standard.

    • Recommended to read digits from back to front as the tensile strength rating may be in 3 digits sometimes!

• CSA Classification system for mild steel:

  • Standardized with AWS, meaning their code system is the exact same. The only difference is the units of the tensile strength rating.

  • AWS uses PSI, but the CSA system denotes in MPa (Mega Pascals).

  • The first 2 digits for the tensile strength rating would be Megapascals / 10.

• The last digit in both classification systems gives additional info about the electrode. Most common ones are

  • #0 =

    • Iron powder 0 - 10%

    • Deep Penetration

    • Easy to remove, thin slag

    • Bead appears flat with coarse ripples

    • Dynamic loads, fast freeze

  • #8 =

    • Iron powder 30 - 50%

    • Medium Penetration

    • Easy to remove, heavy slag

    • Bead appears smooth, concave, fine ripples.

    • Dynamic loads, low hydrogen weld desposits

What does the first digit in AWS electrode classification indicate?

The minimum welded tensile strength of the weld material in PSI x 1000.

What does the first digit in CSA electrode classification indicate?

The minimum welded tensile strength of the weld material in MPa / 10.

How should electrodes be stored to prevent moisture absorption?

In a hermetic seal and kept in an electrode holding oven.

Coated Electrodes - what is the diameter of the electrode based on?

Diameter of the core wire.

Coated Electrodes - what is the outer coating on the rod?

• Flux

• Flux ingredients are what differentiate operating characteristics for the weld deposit. This allows the weld to equal or exceed the parent material properties.

What do oxides do to a weld? How is it prevented?

• Oxides are low in tensile strength and ductility and reduce the base metal’s property. They are undesireable.

  • To prevent these from forming, the electrode provides and “automatic cleansing and deoxidizing” action. As the coating burns, it forms a gaseous atmosphere that surrounds and protects the molten end of the electrode and weld pool. Other ingredients from the coating form a slag to cover the deposited weld metal.

  • Other important functions:

    • improves weld appearance

    • easier arc striking

    • helps maintain stable arc and penetration depth

    • insulator for core wire

    • affects arc length and amperage

    • influences puddle fluidity and controls welding position that can be used.

What are the 6 materials used for coating electrodes? What does each one do?

• Materials:

  • Cellulose:

    • wood pulp product

    • forms CO2 and H2, protective gas over weld puddle

  • Rutile:

    • titanium dioxide and traces of iron

    • arc stabilizing and slag forming

  • Iron Oxide:

    • found in iron ore such as magnetite and hematite

    • slag forming

  • Iron Powder:

    • increase deposition rate to help increase weld speed by 50%.

  • Calcium Carbonate:

    • limestone

    • low hydrogen type - produces CO2 and protects metal, lowest hydrogen atmosphere in arc.

  • Potassium Silicate:

    • arc stabilizer and enhances binding of flux coating to core wire.

What is the role of slag in a weld?

• Slag Functions

  • Flux coating melts and forms a slag that covers the deposited weld material.

    • isolates oxygen and nitrogen from the weld until it has cooled to the point that they do not contribute to the weld making it hard and brittle.

    • dissolves impurities in weld and floats them to surface

    • controls shape and smoothness of bead

    • slows down the rate of cooling - improves weld quality.

  • Avoid trapping slag by removing slag from each weld bead before depositing another pass. Use chipping hammer or wire brush.

  • Heavy coated electrodes produce a heavier slag.

What is porosity in welding?

The presence of small pit holes indicating gases trapped in the weld.

What prevents trapping slag during welding?

Removing slag from each weld bead before depositing another pass.

What happens if the arc length is too short? What about too long?

• Too short : short circuit to plate, voltage drops to 0 and electrode sticks to the material. Need minimum 17 volts to maintain a stable arc.

• Too Long: Amperage drops since voltage is high, not enough penetration in weld. Flux coating not as effective since it’s not melting properly. Arc stops if way too long length since there won’t be enough voltage.

Why should you control Arc Length?

• Using shorter arc length is beneficial for root beads and fill passes for better penetration with narrower bead. Higher amperage and less voltage.

• Using longer arc length is beneficial for multi pass welds as you will get a wider bead with less penetration. Higher voltage and less amperage.

What is the recommended arc length for maintaining stable welding?

The arc length should be equal to 1 diameter of the core wire.

What role does flux coating play in consumable electrodes?

It protects the weld area from oxidation and contamination.

How does the diameter of an electrode affect welding?

It is determined by the thickness of the base material. Larger diameter electrodes are used for thicker materials, providing deeper penetration and faster deposition rates.

What factors determine the required cable size in welding?

The amperage and distance from the welding machine.

What is the effect of higher arc voltage on puddle fluidity?

More arc voltage increases the width and fluidity of the weld puddle.

What happens during arc initiation when using a high open circuit voltage?

The arc starts at a higher voltage and then drops dramatically to maintain the arc.

What steps must be taken to maintain electrode integrity?

Ensure they are packaged securely and stored in an appropriate environment.

Cracking vs Porosity in welds:

• Cracking -

  • hydrogen can dissolve into molten pool that enters the arc, this can crack the weld when it cools and solidifies.

• Porosity -

  • small pit holes.

  • Indicates that gases are trapped in the weld.

  • Start Porosity - porosity is more prevalent at the start of a weld.

  • Can be caused by too fast welding speed or too large of welding arc - coating did not heat enough to drive off moisture and gas shield not fully effective.

Electrodes with Low Hydrogen Deposits Flashcard - usage and storage.

• Electrodes with low hydrogen deposits

  • Lime Coated

  • designed for welding medium carbon and high carbon steels that crack from hydrogen absorption.

  • use this to weld steel with unknown weld properties. Reduces hydrogen induced cracking.

  • Packaged airtight (hermetic seal), and needs to be in electrode holding oven (rod oven) immediately after opening. This ensures minimum moisture content is maintained.

  • Oven should be 30-140C (50-250F) above ambient.

  • Can be re-baked for 1-2hr at 260-427C(500-800F).

Which electrode type does not need to be stored in an oven?

• Cellulose coated electrodes such as E4310 does not need to be in an oven. - moisture should be around 3-7%.

Electrode Negative is known as:

Straight Polarity (Or abbreviated as DCSP).

What term expresses the strength of a current of electricity?

Amperage

An AC transformer welding machine sounds like?

Buzz Box

Loose work lead connections using SMAW may cause:

arcing at work clamp

Magnetic work clamp vs spring work clamp - benefit?

Less likely to damage surface of material.

In CSA and AWS classification for SMAW mild steel electrodes - what does last digit mean?

major coating ingredient and recommended current for best results.

If base metal property unknown, which electrode is best to use?

E7018

Which of the following electrodes has cellulose coating?

E6010, E6013, E7014, E7018

E6010

Using a new hand held file - how can you estimate metal hardness?

If file bites metal easily, the metal is soft.

What term describes a material that shows no permanent distortion before failure?

Brittleness

What is the purpose of silicon controlled rectifiers?

Change AC to DC (used in converters apparently) - I don’t fully agree to this because SCRs can be used in inverters too..

Label the 4 electrode positions stated by AWS and CSA for electrode classification as the 3rd digit:

• 1- All positions

• 2- Flat and Horizontal Fillets

• 3- Flat only

• 4- Flat, Overhead, Horizontal, Vertical Down

What is core wire (wire stock) made from?

1010 carbon steel with carbon content of 0.05 to 0.15%

Different electrode properties come from the flux not the core wire