WELD 110 Plasma Arc Cutting

8/10/2019 WELD 110 Plasma Arc Cutting

1/38

Plasma Arc Cutting

PAC
http://www.hypertherm.com/en/Products/Handheld_cutting/Systems/powermax105.jsphttp://www.hypertherm.com/en/Products/Handheld_cutting/Systems/powermax105.jsp


2/38

Objectives

Define plasma arc cutting (PAC).

Explain how a PAC cutter operates.

Identify the parts of a PAC cutter.

Explain advantages and disadvantages of thePAC system.

Identify materials that can be cut with thePAC.

Explain safety associated with using theplasma arc cutter.


3/38

History

The plasma-arc process had its origin almost 50 years ago,during the height of World War II.

Plasma cutting was accidentally discovered by an inventorwho was trying to develop a better welding process.

In an effort to improve the joining of aircraft materials, amethod of welding was developed that used a protectivebarrier of inert gas around an electric arc to protect theweld from oxidation.
http://www.google.com/url?sa=i&rct=j&q=&esrc=s&frm=1&source=images&cd=&cad=rja&docid=R3oi6P6Fje4X-M&tbnid=Jc5S8H4GfUp1cM:&ved=0CAUQjRw&url=http%3A%2F%2Fwww.ebay.com%2Fsch%2FWelders-%2F113743%2Fi.html&ei=SowSUvywN-imyQG2iIEw&bvm=bv.50768961,d.b2I&psig=AFQjCNFHBp3sf1SLhANO3lGpAww3uVrzKw&ust=1377033545790015


4/38

History

It was discovered that by restricting the opening through which theinert gas passed, the heat produced by the process was greatlyincreased.

At the same time, the smaller opening caused the flow of gas to speedup dramatically, ultimately blowing out a channel in the work.

The plasma-arc cutting process started seeing commercial use in thefirst few years of the sixties.

It was an extremely expensive process to undertake, and most cuttingwas performed by large burning services.
http://www.google.com/url?sa=i&rct=j&q=&esrc=s&frm=1&source=images&cd=&cad=rja&docid=KhA29_80cXOToM&tbnid=IO-nD-V-T1UsyM:&ved=0CAUQjRw&url=http%3A%2F%2Fwww.ebay.com%2Fbhp%2F220-stick-welder&ei=440SUo_oEKKbygHk7YA4&bvm=bv.50768961,d.b2I&psig=AFQjCNFHBp3sf1SLhANO3lGpAww3uVrzKw&ust=1377033545790015http://www.google.com/url?sa=i&rct=j&q=&esrc=s&frm=1&source=images&cd=&cad=rja&docid=KhA29_80cXOToM&tbnid=IO-nD-V-T1UsyM:&ved=0CAUQjRw&url=http%3A%2F%2Fwww.ebay.com%2Fbhp%2F220-stick-welder&ei=440SUo_oEKKbygHk7YA4&bvm=bv.50768961,d.b2I&psig=AFQjCNFHBp3sf1SLhANO3lGpAww3uVrzKw&ust=1377033545790015http://www.google.com/url?sa=i&rct=j&q=&esrc=s&frm=1&source=images&cd=&cad=rja&docid=g3uuNBdFaXZSfM&tbnid=cxoYGoD3eYOTdM:&ved=0CAUQjRw&url=http%3A%2F%2Fbeckmannag.com%2Fautomobilia%2Fv4-saab-frame-repair%2Fsaab-96-rocker-repair-tools-etc&ei=co0SUpuhIcWkyAHTn4BA&bvm=bv.50768961,d.b2I&psig=AFQjCNFHBp3sf1SLhANO3lGpAww3uVrzKw&ust=1377033545790015


5/38

4thState of Matter


6/38

Plasma

Plasma has two meanings.

The fluid portion of blood.

A state of matter that is found in the region of an electrical

discharge (arc).

Plasma created by an arc is an ionized gas that has both

electrons and positive ions whose charges are nearly equal

to each other.

Plasma is present in any electrical discharge.


7/38

Plasma

Plasma consists of charged particles that conduct the electrons acrossthe gap.

Both the glow of a neon tube and the bright fluorescent light bulb areexamples of low-temperature plasmas.

Plasma results when a gas is heated to a high enough temperature to

convert into positive and negative ions, neutral atoms, and negativeelectrons.

The temperature of an unrestricted arc is about 11,000F

The temperature created when the arc is concentrated to from a plasma isabout 23,000F.


8/38

Machines

Most, if not all, of the light portable plasma cutters are 110

volt machines.

Suited primarily for cutting sheetmetal and other light work.

The next level up are the 220 volt machines with 50 to 80amp output current.

These are portable from the standpoint that one person can put it

on a truck and take it to the job.
http://www.google.com/url?sa=i&rct=j&q=&esrc=s&frm=1&source=images&cd=&cad=rja&docid=t4KmGJKbleUX5M&tbnid=B9KKQh79pPg2lM:&ved=0CAUQjRw&url=http://www.northerntool.com/shop/tools/product_200336604_200336604&ei=Ro4SUom-AoGGyAGqt4BA&bvm=bv.50768961,d.b2I&psig=AFQjCNF-U2uGTniNjK2B5YzNHnUvANLaDA&ust=1377034167870696


9/38

How PAC works

Plasma cutters work by sending an electric arc through a gas that is passingthrough a constricted opening. The gas can be shop air, nitrogen, argon, oxygen. etc.

This elevates the temperature of the gas to the point that it enters a 4th stateof matter. Scientists call this additional state plasma. As the metal being cut is part of the

circuit, the electrical conductivity of the plasma causes the arc to transfer to thework.

The restricted opening (nozzle) the gas passes through causes it to squeeze byat a high speed. This high speed gas cuts through the molten metal.

The gas is also directed around the perimeter of the cutting area to shield thecut.


10/38

How a Plasma Cutter works

A complete plasma cutter consists of a

power supply,

a ground clamp,

and a hand torch.

The main function of the power supply is to convert the AC line voltageinto a user-adjustable regulated (continuous) DC current.

The hand torch contains a trigger for controlling the cutting, and anozzle through which the compressed air blows. An electrode is alsomounted inside the hand torch, behind the nozzle.
http://www.google.com/url?sa=i&rct=j&q=&esrc=s&frm=1&source=images&cd=&cad=rja&docid=t4KmGJKbleUX5M&tbnid=B9KKQh79pPg2lM:&ved=0CAUQjRw&url=http://www.northerntool.com/shop/tools/product_200336604_200336604&ei=Ro4SUom-AoGGyAGqt4BA&bvm=bv.50768961,d.b2I&psig=AFQjCNF-U2uGTniNjK2B5YzNHnUvANLaDA&ust=1377034167870696


11/38

PAC System


12/38

Operation

Initially, the electrode is in contact with(touches) the nozzle.

When the trigger is squeezed, DC current

flows through this contact. Next, compressed air starts trying to force its

way through the joint and out the nozzle.


13/38

Operation

Air moves the electrode back and establishes a fixed gap between itand the tip. The power supply automatically increases the voltage in order to maintain

a constant current through the joint - a current that is now going throughthe air gap and turning the air into plasma.

Finally, the regulated DC current is switched so that it no longer flowsthrough the nozzle but instead flows between the electrode and thework piece. This current and airflow continues until cutting is halted.


14/38

Starting the Arc

In many of today's better plasma cutters, apilot arc between the electrode and nozzle isused to ionize the gas and initially generate

the plasma prior to the arc transfer. Other methods that have been used are

touching the torch tip to the work to create aspark, and the use of a high-frequency startingcircuit.


15/38

PAC versus Oxy-Fuel

In general, fabricators consider oxy-fuel to be superior to

plasma for cutting steel when thicknesses exceed about 1/2

inch.

This is because of the slight bevel (4 to 6 degrees) in the cut

face that plasma produces. It is not noticeable in thinner

materials, but becomes more so as thicknesses increase.

Also, at thicknesses above 1/2 inch, plasma has no cutting

speed advantage over oxy-fuel.


16/38

PAC versus Oxy-Fuel

If you are planning to cut non-ferrous metals such as

stainless or aluminum, which cannot be cut by oxy-fuel,

consider a 50 to 80 amp, 220 volt plasma cutter.

Plasma cutting is by far the simplest and most economical

way to cut a variety of metal shapes accurately.

Plasma cutters can cut much finer, faster, and more

automatically than oxy-acetylene torches.


17/38

PAC Cutting Examples


18/38

Plasma Torch

A device depending on its design, which

allows the creation and control of the plasma

for welding and cutting processes.

Plasma torch supplies electrical energy to a

gas to change it into the high energy state of a

plasma


19/38

Torch Body

Made of a special plastic that is resistant to

high temperatures, ultraviolet light, and

impact.

Provides a good grip area and protects the

cable and hose connections to the head.

Torch body is available in a variety of lengths

and sizes.


20/38

Torch head

Torch head is attached to the torch body where the cables and hosesattach to the electrode tip, nozzle tip, and nozzle.

Torch and head may be connected at any angle such as 90, 75, 180(straight), or it can be flexible.

Because of the heat in the head produced by the arc, some provisions

for cooling the head and its internal parts must be made. Cooling for low power torches may be either by air or water.

High power torches must be liquid cooled.

It is possible to replace just the torch head on most torches if itbecomes worn or damaged.


21/38

Power switch

Manual power switch used to start and stop

the power source, gas, and cooling water.

Thumb switch on the torch body most often

used.

Foot control can be used.


22/38

Common Torch Parts

Parts of the torch

Electrode

Tip nozzle insulator

Nozzle tip

Nozzle guide

Nozzles and the metal partsare usually made out ofcopper, and they may beplated.

The plating of copper partswill help stay spatter-freelonger.


23/38

PAC


24/38

Electrode tip

Electrode tip is often made of copper electrode with atungsten tip attached.

Use of copper/tungsten tip has improved the quality ofwork they can produce.

By using copper, the heat generated at the tip can beconducted away faster.

Keeping the tip as cool as possible lengthens the life of thetip and allows for better quality cuts for a longer time.

Old torches you must grind the tungsten electrode


25/38

Nozzle Insulator

Located between the electrode tip and thenozzle tip

Provides the critical gap spacing and electrical

separation of the parts. The spacing between the electrode tip and

nozzle tip called the electrode setback is

critical to the proper operation.


26/38

Nozzle tip

Has a small, cone-shaped, constricting orifice in the center.

The electrode setback space, between the electrode tip and nozzle tip iswhere the electric current forms the plasma.

The preset close-fitting parts provide the restriction of the gas in the presenceof the electric current so the plasma can be generated.

The diameter of the constricting orifice and electrode setback are major

factors in the operation of the torch. As the diameter of the orifice changes, the plasma jet action will be affected.

When the setback distance is changed, the arc voltage and current flow willchange.


27/38

Nozzle

Sometimes call the cup.

Made of ceramic or any other high-

temperature resistant substance.

Helps prevent the internal electrical parts

from accidental shorting and provides control

of the shielding gas or water injection if they

are used.


28/38

Water shroud

Water shroud nozzle may be attached to some

torches.

Water surrounding nozzle tip is used to

control the potential hazards of light, fumes,

noise, or other pollutants produced.


29/38

Power Requirements

Requires a drooping arc voltage or constant current, direct

current, high-voltage, power supply.

Drooping arc voltage allows for a rapid start of the plasma

arc at the high open circuit voltage and more controlled

plasma arc aas the voltage rapidly droops.

Ranges from 50-200 volts closed circuit

Ranges from 150-400 volts open circuit.


30/38

Amperages

High voltage

Amperage range from 10-200 amps.

Some automated machines may have 1,000ampere capacities.

Higher the amperage capacity the faster and

thicker they will cut.


31/38

Cutting speeds

High cutting speeds are possible

Up to 300 inches per minute

25 feet a minute

mile an hour


32/38

Metals to be cut

Any material that is conductive can be cut using the PAC process.

In a few applications nonconductive materials can be coated with conductivematerial so that they can be cut.

Most popular materials cut Carbon steel up to 1

Stainless steel up to 4

Aluminum up to 6

Other metals commonly cut Copper

Nickel-alloys

High-strength, low alloy steels

Clad materials

Expanded metal


33/38

Starting Methods

Two methods are used to establish a current

path through the gas

High frequency alternating current

Momentary shorting


34/38

High frequency alternating current

Most common Uses a high frequency alternating current carried through the

conductor, the electrode and back from the nozzle tip.

High frequency current will ionize the gas and allow it to carry theinitial current to establish a pilot arc.

After the pilot arc has been started, the high frequency starting circuitcan be stopped.

When the torch is brought close enough to the work, the primary arcwill follow the pilot arc across the gap, and the main plasma is started.

Once the main plasma is started, the pilot arc power can be shut off.


35/38

Momentary shorting

Requires the electrode tip and nozzle tip to be

momentarily shorted together.

This is accomplished by automatically moving

them together and immediately separating

them again.


36/38

Safety

Electrical shock Because the open circuit voltage is much higher for this process than for any other,

extra caution must be taken.

The chance that a fatal shock could be received from this equipment is muchhigher than from any other welding equipment.

Moisture

Often water is used with PAC torches to cool the torch, improve the cuttingcharacteristics, or as a part of a water table.

Any time water is used its very important that there be no leaks or splashes.

The chance of electrical shock is greatly increased if there is no moisture on thefloors, cables, or equipment.


37/38

Safety

Noise Because the plasma stream is passing through the nozzle orifice at a high speed, a loud sound

is produced.

The sound level increases as the power level increases.

High levels of sound can have a cumulative effect on ones hearing.

Light PAC produces light radiation in all three spectrums.

Large quantity of visible light, if the eyes are unprotected, will cause night blindness. Most dangerous of the lights is ultraviolet. This light can cause burns to the skin and eyes.

Infrared can be felt as heat, and it is not as much a hazard.

Fumes PAC produces a large quantity of fumes that are potentially hazardous.

A specific means for removing them from the work space should be in place.


38/38

Safety

Gases

Some of the plasma gas mixtures includehydrogen.

Hydrogen is a flammable gas. Make sure that the system is leak-proof.

Sparks

Danger of accidental fire is present.

Use a fire watch person if excessive sparks arepresent.

Documents

WELD 110 Plasma Arc Cutting