Talk:Plasma cutting

Technical Details

The transistors used were initially MOSFETs, but are now increasingly using IGBTs. With paralleled MOSFETs, if one of the transistors activates prematurely it can lead to a cascading failure of one quarter of the inverter. A later invention, IGBTs, are not as subject to this failure mode. IGBTs can be generally found in high current machines where it is not possible to parallel sufficient MOSFET transistors.

I consider these technical details completely irrelevant for the article, and as such should be either completely removed or greatly simplified. In this form it is just confusing. There are certain set of requirements and many technical solutions exist that fulfil these requirements. It is a matter of manufacturer/engineering choice how actual implementation is done. — Preceding unsigned comment added by 2001:981:882F:1:805E:1F9B:6F4D:F98B (talk) 12:48, 14 March 2016 (UTC)

"I disagree. I found the information very useful indeed in designing my own circuit; I don't see the point of trying to make articles short by excluding information that some readers find extraneous - I found the information to be vitally useful to me. One of the reasons I loved the very old Encyclopedia Brittanica's before all the encyclopedia's started being dumbed down to save printing costs because it contained scholarly articles from true experts with a wealth of information; reading some of them was like attending a lecture at one of the finest universities in the world, and I always wished for more. I would love to see wikipedia go to much longer and more detailed articles on subjects." Synchro27 (talk) 04:38, 25 July 2017 (UTC)Charles Knouse

"I agree with you Synchro27, it's the kind of "details" I was looking for in this page. Wikipedia has been made for people wanting to understand how things work, the more information, the better it will be. I added this missing information to the page. Nestashi (talk) 18:08, 15 September 2019 (UTC)

I disagree with the previous comment. Some readers may be as interested in how the machine works, and how they’ve been upgraded. Especially if they’re on a quest to get the best budget unit. I wish there was even more technical data about the components and their lay out. 174.247.187.153 (talk) 02:54, 7 November 2023 (UTC)

Picture

It would be awesome to have a picture of plasma cutting in action taken through welding glass, showing what the operator sees. ―BenFrantzDale 04:02, 10 February 2006 (UTC)

Actually you see very little. The fire blows right through the material and there is near nothing to see on the front side---but a great blast of fire on the back side.

Photographing the welding /cutting in action is very difficult because of the lighting issues but I'll look for a photo of some cutting that is completed it is interesting as well. —Preceding unsigned comment added by Rvannatta (talk • contribs) 07:22, August 26, 2007 (UTC)

I might be able to provide some pictures of a plasma in action. All are pictures I took myself Devaes (talk) 08:39, 14 January 2008 (UTC)

I added some pictures, remove "reqphoto"?? Devaes (talk) 12:31, 14 January 2008 (UTC)

Added sore stuff which can be put in the article Devaes (talk) 14:46, 14 January 2008 (UTC)

Plasma cutting with a cnc machine

Plasma cutting with a cnc machine

Metal plasma?

jlj.ko The article implies that the metal is turned to plasma. From watching the process it seems much more plausible that the metal is primarily liquified (and maybe also vaporized) but that it is primarily the inert gas which is the plasma. ―BenFrantzDale 05:32, 14 February 2006 (UTC)

I corrected the intro to match my understanding which also matches the description found from the HowThingsWork.com link. ―BenFrantzDale 01:18, 16 February 2006 (UTC)

In plasma cutting process, metal is often "burned" with oxygen. For example when cutting mild steel, oxygen is used as main plasma gas. Oxygen react with steel - steel simply burns and changes to dust of oxides. 188.167.228.35 (talk) 06:05, 2 July 2016 (UTC)mato

References

Flow Rate; rambling

I'm skeptical of the 15,000 km/h flow rate quoted here and in some of the links. At very least it seems misleading. My sense is that one molecule of inert gas doesn't stay plasma for very long. The gas jet without plasma is fast, but ridiculously fast. My hunch, then, is that the heated gas and plasma may be ridiculously fast, but that the mass flow rate doesn't change when the arc is on versus off. In other words, if you heat flowing gas from ~300 K to ~30,000 K, it will move 100 times faster. ―BenFrantzDale 04:32, 16 February 2006 (UTC)

At 15,000 km/h, a flow with a 1 cm² cross section would go through 14.7 cubic feet per second (i.e., you could empty a scuba tank in 5.4 seconds). ―BenFrantzDale 04:32, 16 February 2006 (UTC)

1² cm cross section? Most nozzles are .020-.090 inches (~.0026 cm² to .041 cm²) Might yield more realistic calculations, plus the whole temperature thing.71.252.248.7 03:50, 1 September 2006 (UTC)

It's not a pure plasma. Only a portion of the gas passing through the nozzle is ionized. The flow rate DOES change, as the plasma reacts to the electric field in the torch and on the workpiece. - Toastydeath 04:24, 5 December 2006 (UTC)

To give an idea of the flow rate while plasma cutting: The flow of a Hypertherm plasma 260A for mild steel uses 42 l/min for the plasma gas (O2) and 104 l/min for the shield gas (air). The hole in the nozzle is about 2mm². Source: Hypertherm HPR260 manual. Devaes (talk) 08:36, 14 January 2008 (UTC)

Conflicting statements

Can someone explain the following two apparently conflicting statements in the article: 1 "The HF Contact type typically found in budget machines uses a high-frequency, high-voltage spark to ionise the air through the torch head and initiate an arc. These require the torch to be in contact with the job material when starting, and so are not suitable for applications involving CNC cutting." 2 "Plasma cutters working near sensitive electronics, such as CNC hardware or computers, use the contact start method. The nozzle and electrode are in contact. The nozzle is the cathode, and the electrode is the anode. When the plasma gas begins to flow, the nozzle is blown forward." JSM Saudi Arabia —Preceding unsigned comment added by 212.118.128.246 (talk) 11:20, 4 November 2009 (UTC)

I agree, that makes little sense. The CNC HyperTherm unit I've used starts the arc without contact with the workpiece in a three step process. A high voltage spark briefly ionizes the air within the torch head. This makes the air conductive and allows the "pilot arc" to form. The pilot arc forms within the the torch head, with current flowing from the electrode to the nozzle inside the torch head. The pilot arc burns up the nozzle, a consumable part, while in this phase. The air then blows the plasma out the nozzle towards the work, providing a current path from the electrode to the work. When the control system senses current flowing from the electrode to the work, it cuts the electrical connection to the nozzle. Current then flows from the electrode to the work, and the arc forms outside the nozzle. Cutting can then proceed, without burning up the nozzle. Nozzle life is limited by the number of arc starts, not cutting time. --John Nagle (talk) 00:29, 29 September 2010 (UTC)

Thanks Nagle! I posted it on the wiki page, we are missing this important info, that's very well explained.Nestashi (talk) 18:13, 15 September 2019 (UTC)

Thickness of steel cut with a hand held plasma torch.

I use two hand held plasma torches and an automated CNC plasma in my shop. I've never seen a hand held plasma torch that can cut 2" thick steel plate. My cutting table is 6' x 12' and uses a Hypertherm 130HSD. The dimensions on this unit are about 4' x 4' and it weighs more than 300', the maximum thickness it can cut with edge start is 1 1/2" steel. This Wikipedia article has already been disseminated throughout the internet claiming that a hand held plasma can usually cut 2" thick steel, and a automated table system can usually cut 6" thick steel. I believe the author confused plasma cutting with acetylene cutting. —Preceding unsigned comment added by 216.212.106.154 (talk) 20:04, 3 February 2011 (UTC)

Not correct:

- Mechanised plasma http://www.kjellberg.de/Plasma-Cutting/Products/CNC-and-mechanised/FineFocus-series/FineFocus-1600.html cuts trough 160mm.

- Handheld plasma http://awp-p.com/awp2/pdf/prospekt_pas25-70w_en.pdf cuts trough 70mm.

You can actually cut trough any thickness with custom made torches. A FineFocus 1600 is actually two FineFocus 800 added together, if you add more you can increse the amperage and thus the thickness you can cut. Torches and consumables can be custom made for higher amperage. All you have to do is increase the cooling flow and increase diameter of the hole in the nozzle and shield. 195.26.2.117 (talk) 10:57, 25 February 2011 (UTC)

This article states that a hand held plasma can USUALLY cut 2" thick steel. And that a typical mechanized system can cut through 6" steel. What I am saying is that neither of those scenarios are usual or typical from the myriad of shops I've worked in. The handheld torch that cuts through 2" steel would be unwieldy. We can talk about custom plasma torches all day, but that is not how the article is worded. Usually means commonly and a hand held that cuts 2" steel is not common. The link you provided for the handheld that cuts 70mm is not working, so I cannot verify it. I am only talking from years of personal experience, however important that may be for Wikipedia. — Preceding unsigned comment added by 216.212.106.154 (talk) 18:52, 2 June 2011 (UTC)

Please post pictures or video of a hand held plasma torch cutting 2" thick steel. Also post some CNC plasmas cutting 6" thick steel. If it is typical and usual, you should have no problem locating some photographs.. — Preceding unsigned comment added by 64.139.81.85 (talk) 23:22, 16 June 2011 (UTC)

Eye safety

The article at present claims that the eye, and face, safety hazard for plasma cutting is the same as for arc welding. This is unsourced, and plasma equipment manufacturers do not claim this. The goggle tint is lighter and there is no requirement for a face shield. No doubt someone will now find a "source" in Google that the KillerTron 2000 50MW plasma-cutting deathray requires a tinfoil hat to be worn at all time. Yet in the general case, and where encylopedic coverage is so needed, for the type of hand-held plasma cutters used in industry it is wrong to describe them as equivalent to arc welding protection. Andy Dingley (talk) 19:35, 15 May 2016 (UTC)

someone tried to see what it would do on a finger. It's actually very dangerous especially when the finger is below the sheet to be cut: https://www.youtube.com/watch?v=GHLD8SPIDAU — Preceding unsigned comment added by Nestashi (talk • contribs) 18:24, 15 September 2019 (UTC)

"Plasma torches were once quite expensive" : why are they cheaper?

Anyone knows why they were so expensive just few years ago, and are much cheaper now? Nestashi (talk) 16:36, 15 September 2019 (UTC)