Consumables

[Tonywish]

I fixed my THC problem but now I am having issues with consumables. It seems they are burning out rather quickly. Just how long should a tip and electrode last? I have a Thermal Dynamics A60 plasma and am cutting .125 steel 150ipm with cut height at .20 and pierce height at .19. Pierce delay is set at .500. Some of my projects are quite detailed. I have a water table and it does get to be a wet mess at times.

Any sugggestions??

Tony Wish

[jimcolt]

If you can provide more details.....material thickness, pictures of the worn consumables, why are you changing them...and the approximate life (starts and hours)....we could probably help.

Jim Colt

[Tonywish]

Jim,

Consumables last around 20 minutes. I can't get a good pix to send. The tip has a recessed hole where the orifice is and the electrode has the same thing where the silver material is at the end. The TD manual has much higher pierce and cut settings than the Hypotherm unit. I'm really struggling with this. Any help will be gratly appreciated.

Tony

[jimcolt]

The higher pierce and cut heights are due to the fact that the T-D unit is using unshielded consumables....higher piercing minimizes the chance of pierce splatter damaging the nozzle orifice....and higher cut height minimizes the chance of the nozzle contacting the plate during steady state cutting.

The nozzle (also known as a tip on many plasma's) is at positive electrical potential (same as the plate you are cutting) only for a few miliseconds at the beginning of each plasmastart cycle....as soon a the pilot arc establishes and transfers (starts cutting) the plate...the electronics in the power supply disconnect the positive connection tothe nozzle. So...during steady state cuttin the nozzle is electrically isolated...and its only function is to shape the arc with its orifice.

If the nozzle makes an electrical connection to the positive plate....such as when some molten metal blows back and creates a condutive path between the nozzle and the plate....the nozzle again becomes positive...and the plasma arc , instead of 100% passing through the orifice to the plate, splits off and travels through the copper nozzle to the conductive (molten metal) to the plate. This is called a "double arc"....and every time it occurs it causes erosion to the precision shape of the nozzle orifice. When the orifice is slanted or in any way out of round...the arc follows that shape, loses cutting power and cuts at an angle.

Shielded consumables (invented by Hypertherm in the mid 1980's) ad another part...the shield....between the nozzle and the plate. The shield is electricallyisolated at all times...and acts as an insulator between the plate and the nozzle. With a Hypertherm torch you can (after the pierce is complete) drag directly on the plate with no damage to the nozzle orifice....you cannot do that with an unshielded torch without affecting the nozzle life. At lower power levels, typically 40 amps and less...you can get away with dragging an unshielded nozzle as the lower power does not cause a much damage.

T-D has some shielded consumables....and while I understand they do not cut as well as the standard ones...they supposedly do have better life.

Jim

[bob49]

Jim, I'm a td owner cutmaster 82 and td boasts about there drag tips. so when a person is drag cutting does the pilot arc stay established until the tip raises off the plate? Ive noticed that while drag cutting (by hand) the nozzles do not keep there integrity very long. Bob

[jimcolt]

The pilot arc stays on only until the arc transfers to the plate. If the torch is close to the plate the pilot arc will stay on for a few miliseconds. On some torches (most T-D's....and Hypertherm's if you have the slector switch in the "continuous pilot mode") the pilot will refire if you pull the torch away from the plate or cut over a hole (like cutting expanded metal grating).

The Pilot Arc is what you see when you fire the torch in the air. It is a DC plasma arc that follows a path from the electrode to the nozzle...with the force of the air blowing the arc out through the nozzle orifice. The pilot arc is relatively low current (usually 5 to 15 amps, depending on torch design)....but if it is fired in the air for more than a few miliseconds at a time it will wear the nozzle orifice very rapidly.

With any torch....if the nozzle (tip) is exposed, expect shorter nozzle life when drag cutting....this issues gets much worse at amperages above 40. With the Hypertherm shielded consumables...the shield is electrically isolated from the nozzle...the nozzle cannot touch the plate (the shield touches the plate) and drag cutting can be done all the way to 200 Amps with no noticeable effect on the nozzle.

Jim Colt