Plasma cut plate oriented vertically

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I don't currently have a plasma cutter but I was wondering if you can use one to cut a plate oriented vertically and how the resulting cut compares to a plate cut in the horizontal position.Any advice on this would be appreciated.Thanks,Chad
Reply:Yes you can.  The only difference I've noticed is that the dross on the back of thicker sections can sag a little more.
Reply:I have cut in virtually all positions.  Not a problem.  Be very safety conscious as Plasma Cutting blows sparks EVERYWHERE, just like O/A.
Reply:You can cut in any position with plasma....just be aware of where the molten metal and fumes are going. There is an effect on dross formation when cutting in any position but with the nozzle down and the plate horizontal. There are many applications with robotics and pipe cutting machines where the torch is manipulated in virtually all positions.Jim
Reply:Thanks, these replies help a lot.  FYI, I am trying to get some cost estimates together for doing some work related to improving the fatigue performance of some steel bridges that contain poorly performing details from a fatigue standpoint.  What would be required would involve drilling two 3/4" to 1" holes in a vertically oriented girder web plate (say 3/8" to 1/2" thick) and then using a plasma cutter to cut a single arc (semi circular) slot connnecting the two holes.  All work would be done from a snooper truck which would allow close access to all points of work and the plasma cutter could sit on the platform along with the worker and it could be powered by a Trailblazer sitting on the snooper truck.  Once the worker is in place at each location how long do you think it would take to set up, cut the two holes and a 10" long plasma cut slot joining the holes and do a little clean up (probably with just a flap disc)?  There would be many (as in possibly over 100) of identical details to perform this work on so it would be worthwhile to create some setup jigs to help perform the work efficiently and uniformly.  I have an estimate in my head but I'd like to get some more thoughts before I mention it so I can get some sort of independent verification of my estimate.Last edited by IrishBrewer; 10-30-2008 at 12:37 PM.Reason: Added clarification
Reply:???  Fatigue on bridge structural steel?Then the engineer(s) F'd up big time!To evaluate stress on a steel structure, no drilling is necessary.  Apply strain gauge(s), or otherwise instrument the structure, take measurements, engineers calculate and redesign repair/replacement/reinforcement, someone installs.Plasma will cut just fine on a vertical member (as mentioned).  The best laid schemes ... Gang oft agley ...
Reply:For what it is worth, even a newly designed steel bridge can still be controlled by fatigue as opposed to strength.  The difference is that today we have a better handle on this mode of failure so we can design for it and where possible, we do avoid troublesome details.  However there are times when we do have to use less than ideal details so we just have to make sure that the design fatigue stresses in those areas are kept sufficiently low. Not all bridges in existance today were built prior to the point in time where the profession had a good handle on which types of details were and were not prone to fatigue.  The bridges in question were built in the 50s and 60s and if they were built today would likely be much different.Also, we are investigating a loading case that is much more severe than a typical truck crossing the bridge.  The load in question is nearly five times the legal load and even though the bridge may be strong enough to carry the load, the life of the bridge may be comprimised by the heavier load due to fatigue.  We are looking at various methods, including the one I outlined above to make the questionable details behave better from a fatigue standpoint.  I just need to get a ballpark idea of the amount of time required for the plasma cutting and drilling for this method of improvement.
Reply:A single load event is not fatigue.  It would be yield.Or a low-cycle plastic deformation strain condition.Miner's Rule or the Coffin-Manson relationship.Hmmm, two 1" diameter holes and then connect the holes via a plasma cut arc?  Maybe five minutes per 'set' with an annular cutter on a mag drill and a 45+ amp plasma for the arc.  Hypertherm Powermax45 cut speed at 45 amps (max output) on 3/8 inch thick mild steel is listed at 40 ipm.  Move up to a 60 amp  Powermax1000 and the cut speed on that 3/8 inch thick mild steel is 63 ipm.  If the holes don't have to be super clean and you are just trying to 'make a hole', plasma cut the whole thing.  If all you need is the 'arc', skip the holes and just pierce cut the arc segment.  The best laid schemes ... Gang oft agley ...
Reply:Sounds too easy. If you are drilling the holes....then it sounds like you will edge start with the plasma. I would recomend a 60 to 80 Amp plasma (Hypertherm Powermax1000 or Powermax1250).....as these units are designed to operate off generator power.....and the torch is designed to drag cut...as well as easily be guided by a template. The template can be made from material (plastic or metalic...or even wood) of about 1/8" to 3/16" thickness.....and I have made them attachable with magnets for ease of use.I once did a job that involved 350 holes that had to be cut in steel (I-Beam style) joists in a commercial building.....the steel fab house had forgotten these holes....and so they had to be done in place after the steel was erected. All were done with magnetic monted templates and a 60 Amp hand plasma torch.....very little grinding was required.Just a note of caution: Air plasma cutting will leave a nitride hardened edge (due to 80% nitrogen content in air)....which could cause isues with weld porosity if you are rewelding directly on the cut edge. This nitride finish is usually about .005" thickness and can be removed with a grinder easily. If you use an oxygen plasma...there will not be any nitriding of the cut face...and minimal hardening.Jim Colt
Reply:Jim/Moon,Thanks for the additional comments.  Sounds like we should be able to zip right along with the plasma.  Jim - can most plasma cutters use different types of gas depending on what edge finish you are looking for?  Just curious - for this case, we would not need to weld at all, much less the cut edge.Moon, FYI, we are applying Miner's rule using the combined effects of normal traffic and the anticipated number of cycles of the BIG truck.  The big truck is not a one time deal.  At this time we are assuming 1000 passages in each direction (although the return direction will be more lightly loaded).  Even if the large vehicle does not induce a lot of fatigue damage, since these bridges were constructed using design codes that predated modern fatigue design provisions they may have fatigue issues even using standard loadings because we are dealing with Category E details.
Reply:My thoughts are that setup and relocation each time will be the major consideration.  So many time estimates are made on the machine operations but do not consider handling which is the big time killer.  Huge gains can be made by making all the operations done between each drilling and plasma cutting more efficient.  Lifting a mag drill up into position then taking it down is time consuming.. consider mounting the drill on a hinged arm of some sort that can swing into position, adjust, around then after, simply swing back out of the way while the plasma cut it done.
Reply:Most (95%) of hand held plasma systems cannot use oxygen as the plasma gas....they use air or nitrogen. Hypertherm has one hand held system...the Max200 that can use oxygen.....but it probably is overkill at 200 Amps for this application.....unless the nitrided edge is of issue.Jim
Reply:Originally Posted by jimcoltMost (95%) of hand held plasma systems cannot use oxygen as the plasma gas....they use air or nitrogen. Hypertherm has one hand held system...the Max200 that can use oxygen.....but it probably is overkill at 200 Amps for this application.....unless the nitrided edge is of issue.Jim