PLASMA ARC CUTTING PARTS & ELECTRICAL

I. Plasma Torch/Head/PowerSwitch

A. Plasma Torch

  • Device that allows the creation and control of the plasma for welding and or cutting processes by producing a narrow arc between the electrode and nozzle

B. Torch head

  • Attached to the torch body

  • Attachment angles for the torch and head are:

    • 90° (Popular for manual operations)

    • 75° (Popular for manual operations)

    • 180° (Straight, mainly used for machining)

    • (Or it can be flexible)

  • Low power torches are cooled with air or water

  • High power torches are liquid cooled

C. Power Switch

  • A handheld torch will have a manuel switch with a safety guard

  • Trigger is used to start and stop the power source, gas, and cooling water.

II. Important Plasma torch parts

A. Electrode tip

  • The electrical path for cutting current in torch body

  • Held on negative polarity

  • The tip is made of copper, coated with either

    • Tungsten

    • Hafnium-coated. tungsten

    • Or Hafnium cylinder embedded in the end

  • The material used is to help conduct the electrical current

  • Non-oxidizing gases (such as argon or nitrogen) must be used with tungsten tipped electrodes

  • Tungsten can oxidize quickly, resulting in failure of electrode

  • (At the tip of the electrode the plasma arc meets the air gas and forms the plasma at 40,000 degree Fahrenheit before passing through the tip (nozzle)

B. Swirl ring

  • Causes supplied shielding gas to spin in torch body around the electrode

  • Angled (Beveled) holes to circulate air counter clockwise

  • Lasts 15x. longer than electrode and nozzle tip

  • (Helps create the plasma arc, otherwise there wouldn’t be a great consistency)

C. Nozzle Insulator

  • Located between the electrode tip and the nozzle tip (the space is known as Electrical setback), providing air flow space, and ensuring arc is formed and directed for cutting.

D. Nozzle Tip

  • The nozzle tip has a small, cone-shaped narrow opening in the center.

  • The electrode setback space is where the electrical current forms the plasma

  • The close fitting parts provide the restriction of the gas in the presence of the electrical current

  • This part is consumable, meaning it will get worn out and has a short lifespan

  • As the diameter of the opening changes = the plasma jet action will be affected

    • (The sizes of the opening could change based on amperage levels)

  • When setback distance is changed = the arc voltage and current flow will change

  • As the nozzle and electrode wear = the gap will change and the machine voltage may adjust to continue making high quality cuts

E. Shield or nozzle (AKA: cup or deflector)

  • Made of ceramic or any other high temperature-resistant substance

  • Helps prevent internal electrical parts from shorting

  • Provides control of the shielding gas or water injection if they are used

  • A drag shield allows user to put the shield directly onto base metal and just drag along base metal while being cut (change or get new part if the center hole is no longer perfectly round)

  • (Must be placed on tight or plasma arc will not operate)

F. Water shroud

  • The water surrounding the nozzle tip, used to control the potential hazards and noise generated by the process.

G. Replacement parts

  • The electrode tip and nozzle are the two main priority parts that are easily replaced.

  • Other parts that must be inspected and changed are:

    • Shield

    • Swirl ring

    • O-ring

III. Hoses and Power cables

  • Some plasma arc cutting systems may require a number of power, control cables, gas, and cooling water hoses to connect power supply with torch.

  • However, only a power lead, torch lead, and work lead are needed

  • A cover is needed for these cables to prolong their lifespan

IV. Electrical of PAC
A. Voltage

  • The voltage for a PAC ranges from 50 to 200 volts compared to 18 volts to 45 volts for most types of welding

  • Higher voltage is required because the resistance of the gas increases as it is forced through the small opening

  • Although voltage is higher, the current (amperage) flow is much lower than it is with most other welding processes

B. Pilot arc

  • Using. higher levels of volts, arc can begin without touching the base metal

  • This is called a pilot arc for that reason

  • Once arc touches base metal, the high frequency turns off and the plasma arc is established. This is due to the fact that the circuit is coming from the ground and base metal. Established the plasma arc in this way, is called a complete circuit.

C. Postflow

  • After arc is done, the compressed air will still linger in the device for 10 seconds to cool off the consumable parts