Dross between shield and tip causing Z diving

[chadmjohn]

I'm running an everlast 50s with a machine torch on a custom table (not a major brand). I'm having issues with my THC (CandCNC / CommandCNC) diving at odd intervals and in every instance what I've found is dross build up between the tip and shield.

When cutting I have topside sparks projecting in the direction of the cut and I do get very good cuts, except for this instance.

The shield for this torch is one for the PM60 torches shown below. To me it's a strange design as the air holes on the perimeter of the shield are 're-directed' by the shield ring (I hope this makes sense). All other shields I've seen have the air holes pointing directly toward the material.

To be quite honest, the only reason I'm using this shield is for ohmic sensing. I was considering putting the shield in the lath and turning down the 'ring' around the bottom to allow the jets to hit the material. Any suggestions on if this would be better or worse would be appreciated.

Has anyone here had their THC dive due to build-up between the nozzle and the THC sensor tip / shield body?

20220906_140453.jpg (42.97 KiB) Viewed 1205 times

20220906_140453.jpg (42.97 KiB) Viewed 1205 times

[adbuch]

You could try coating your consumables with anti-spatter coating.
David

[chadmjohn]

Thanks. I do use welding anti-spatter and the table is tuned well. It will be cutting beautifully then suddenly crash, drag and only cut partially through. When I look, there is a lot of dross bridging the shield and tip. What I don't know is does this build up happen because of the crash or does the build up cause the crash???

[adbuch]

Perhaps try raising your cut height slightly to see if this helps.
David

[chadmjohn]

Here is a video I put together about the compressor setup. From the compressor head output, it goes through a fan driven heat exchanger. the fittings on the head are approximately 200F and when it exits the heat exchanger it is down to ambient temp, the water is then removed via an air water separator before it enters the tank.

On the way out of the tank it goes through a three stage air - water / oil separation (2 stages) and then a desiccant before going to a final air/water separator on the back of the plasma cutter. The desiccant stays blue and there is never even so much as a drop of water in the separator on the cutter.

I'd love to hear your input to help identify where this may be coming from.

[weldguy]

Looks like a robust air cleaning and drying setup. I don't expect that air quality has anything to do with dross accumulating between the nozzle and the shield. It is likely that the buildup happens during the piercing process, could try piercing higher and making sure that it is not piercing any longer than it needs to.

[tnbndr]

That is a very odd shield design. I would do some research to find another option.
In my opinion the buildup would be causing the crash as the machine would seek to increase voltage by lowering the torch, thus the crash.

[acourtjester]

From the image it looks like you have a DIY ohmic sensor touch, is it possible the pierce height could be too low. I would do some non fire G-code tests to check the actual pierce height.

[chadmjohn]

That is a very odd shield design. I would do some research to find another option.
In my opinion the buildup would be causing the crash as the machine would seek to increase voltage by lowering the torch, thus the crash.

I agree, but it's the ONLY thing I could find for a PT60 style machine torch used by my Everlast 50s. It's very strange to me that there are air holes above that 'disk' which essentially shoot air 'sideways' away from the nozzle. Maybe in some attempt to create a low pressure zone helping evacuate sparks?????

I'm about to chuck the entire cutter and get a hypertherm 45xp.

[chadmjohn]

From the image it looks like you have a DIY ohmic sensor touch, is it possible the pierce height could be too low. I would do some non fire G-code tests to check the actual pierce height.

I've tuned the pierce pretty well. The disk on the shield cap is .03" further out than the nozzle, so my pierce height is anywhere from .05 (which is .08 actual to the nozzle) to a .1 (which is .13 to the nozzle). This is at 40amps.

It's piercing 16g CRS, so it's almost instant and very little blowback.

It is possible that more height would help, I'll give it a shot and see. I tried to keep it low because I want the pierce marks (open paths) to be minimal. It may be that I need to put up with a bit larger pierce 'hole' for stability sake.

[TJS]

I get this too on my hypertherm duramax torch when piercing thick material 3/8" and up. Or it leaves a tail looking puddle and when the torch comes back I can see the DTCH work and lift up. I sometime baby sit it with a scraper and move the little tail out of the way. I am hearing people have used wiggle lead in in sheetcam to combat this problem. I have not tired it.

[ROKCRLER]

Remove the shield cap, its used for standoff cutting.
It looks the same as my SL60 on my Cutmaster 39.

[chadmjohn]

Remove the shield cap, its used for standoff cutting.
It looks the same as my SL60 on my Cutmaster 39.

It's not a drag shield, those have relief cuts and generally put the torch nozzle at .06" from the material for drag cutting. This is a nozzle shield, with a .03" protrusion meaning there is a .03" gap between material and shield when cutting at .06" standoff.

[ROKCRLER]

It's a deflector cap for the shield... At least on my hand torch.
I had to remove it when I had the hand torch on a table before machine torch as it would put the tip too far from the material.