Shielded vs. Unshielded questions

[TrinityFabworks]

I finally picked up a machine torch for my miller 625 xtreme and had a couple of questions as I am new to all of this. I've been trying to read up on shielded and unshielded. The machine torch came with a shielded cap on it which my hand torch did not have. I was just wondering what advantages and disadvantages are for cutting shielded. I noticed that the actual tip is recessed a little bit behind the shielded tip. Does this mean that I need to change my retract and cut height to the distance of the actual tip? I'm sorry for all of the questions, I'm just a bit lost. Is it worth even using the shielded tip on it? Are you supposed to use different consumables with a shielded tip?

[plasmanewbie]

It's my understanding that the shielded version protects the nozzle from slag blow back during piercing and cutting and I have found this to be the case when cutting thicker materials that take a second or to to pierce. It works well. Yes,you want to maintain the same nozzle to work distance whether your shielded or un-shielded so make the adjustment to your heights.

[jimcolt]

The shield ( a Hypertherm patent (expired now) from the 1990's) was designed to allow long nozzle life when drag cutting with a plasma torch. If you drag a non shielded torch the nozzle (which during the cut is electrically floating, neither negative or positive ) takes the same electrical potential as the plate and work clamp (positive). When this occurs, some of the energy from the electrode (negative) splits off from the electrode and attaches to the nozzle, then jumps from the nozzle to the material being cut. This is called a double arc, it takes energy away from the cutting arc (slowing down the process) and dramatically shortens nozzle life. So a shield allows for drag cutting and template cutting with better performance and consumable life. Different shield designs were developed for machine cutting applications with height control....in this case the shield allowed for thicker piercing and better nozzle cooling / life. The newest technology shields have another feature (a current patent and only found on Hypertherm torches) called "conical flow" uses the inner shape of the shield and outer shape of the nozzle to inject the shield air cooling flow radially around the nozzle orifice and the cutting arc, this conical flow squeezes the arc and increases energy density, Faster cut speeds, squarer edges, less dross and better nozzle cooling are the results. Hope this helps, Jim Colt

[TrinityFabworks]

I was under the impression that the xt40 torches for the 625 xtreme's are manufactured by Hypertherm. In my case, would it be better to use it unshielded? I'm still confused if I am cutting at 1/16 above the plate to the shield tip, or to the tip of the nozzle? If it was to the tip of the shield that would only give me maybe 1/32 of an inch of clearance between the plate and the nozzle which I feel would cause more torch crashes. Am I missing something?

[TrinityFabworks]

Attached is a picture of what this torch looks like with the style of shield that mine currently has on it.

torch.jpg

[Ironken]

Take this for what its worth, I am kinda a noob....I believe the torch height must be set from the nozzle to plate. If your shield has any standoff, this will give you the wrong standoff when you Z probe. Do you have ohmic sensing?

[TrinityFabworks]

That's what I was thinking, I was just wondering since they have an offset (the 30 amp tips are even shorter than the 40 amp tips) which means that I would need to edit my post to have one for each. With the 30 amp tip installed, it would be further up in the shield than the cut height is supposed to be, so maybe I will just have to run without it.

[Ironken]

Would it be possible to machine the shield down to where the nozzle contacts the plate first? How are other guys using Miller machine torches on their CNC? Could you just run unshielded with a deflector?

[jimcolt]

Torch height (at least on a Hypertherm torch) is set from the frontmost part of the torch to the surface of the material. The voltage / height characteristics of any torch changes when the shield technology is used (again, on a Hypertherm at least), and requires different nozzle to surface specs. To make it as easy as possible...the parts and specs were developed to try to maintain a constant physical height difference from shielded to unshielded. I see no reason with a Hypertherm torch to run unshelded….if you do, expect slower speeds, more dross, shorter consumable life.

Also...the Miller torches used to be made by Hypertherm. That was terminated by Miller a number of years ago as a cost saving decision.....they purchase imported torches for their systems today. Jim Colt Hypertherm