Plasma cutting sequence

Ignoramus28229 wrote:


PLASMA GAS SELECTION CHART Gas     Recommended For     Advantages     Disadvantages Air
* Carbon Steel * Stainless Steel
* Clean Fast Cut on C.S. * Affordable * Convenient
* Short Electrode Life * Nitriding on Cut Surface * Oxidation on S.S./ AL
Nitrogen
* Stainless Steel * Aluminum * Carbon Steel
* Excellent Cut on S.S./AL * Excellent Electrode Life * Affordable
* Nitriding on Cut Surface
Argon/Hydrogen
* Stainless Steel * Aluminum
* Excellent Cut Quality and Speed on Thicker Material (> 1/2 in.) * Less Smoke/Fumes
* Expensive * Not for C.S.
Oxygen
* Carbon Steel
* Clean Cut * No Surface Nitriding * Fast on C.S.
* Short Electrode Life * Oxidation on S.S./AL There are various types of torch cooling systems. Low-amp torches (150 amps or less) can be cooled by channeling a secondary gas through the torch. Higher-powered torches use water and require a cooling system with a reservoir, pump and heat exchanger. It's very important to use de-ionized water for cooling, since the coolant (water) may contact both negative and positive potentials inside the torch. Theory: Sequence of Operation
When an operator gives a start cut signal, the system energizes and a prepurge of gas lasting a few seconds will flow through the torch. This ensures that proper gas flow is available before an arc is struck. The initial arc, which ionizes a portion of the plasma gas, is generated by a high-voltage spark between the nozzle and the electrode. Current flows through the ionized gas (plasma) to the nozzle.
The gas flow pushes the arc out of the orifice where it reattaches to the outside of the nozzle, forming a J-shaped pilot arc. In some systems, the pilot arc is controlled by a timing circuit. Other systems have an arc transfer sensor to detect the current change (when the cutting arc takes over) and switch off the pilot circuit. Some systems also have an automatic restart pilot, which is useful when cutting grating or expanded metal. With automatic restart, the torch can cycle back and forth between "pilot" and "cut" modes as long as the start signal is present.
The pilot arc forms a "pathway" to the metal. If the torch is close enough to the workpiece, then the arc will transfer from the electrode, through the nozzle, to the metal. Once this transferred arc is established, it will continue as long as there is metal to transfer to. The constricted plasma jet concentrates the energy of the arc on a small area of the workpiece, heating it to melting temperature and blasting the molten material out of the cut.
When a stop signal is given (or the start-cut signal is shut off), the cutting arc stops and the gas continues to flow for a few seconds to cool the torch and torch parts. It also shields the electrode, preventing outside air from reacting with the electrode element as it cools. hay i hope this helps out some:-))
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I'd consider a ramp up and hold ... then ramp down (when trigger released)...
The ramps prevent surge currents that might bite the electronics and might punch holes through the metal...
I'd go to some of the sites - Hypertherm is a good site - see tech docs for how things work.
Martin
Martin H. Eastburn @ home at Lions' Lair with our computer lionslair at consolidated dot net NRA LOH & Endowment Member NRA Second Amendment Task Force Charter Founder IHMSA and NRA Metallic Silhouette maker & member http://lufkinced.com /
Ignoramus27153 wrote:

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There's an guy on ebay every once awhile selling plans to convent your welder to a plasma cutter. There like $3 plus shipping maybe there something useful in his plans I don't know. I thought I'd throw that out there.
His torch is made from PVC pipe which bring a smile to face every time I see his item for sale.

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