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Re: Torch Cutting Steel

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Both the air-arc and plasma arc are high temperature melting processes.  But the high temperature area is confined to a very small area.  Plasma arc can be used on carbon steel, stainless steels, and aluminum.  Air-arc and ox-acetylene can only be used effectively on carbon steels.  Ox-acetylene, as I mentioned in an earlier post, is a high temperature chemical reaction where the steel is oxidized. 

One of the most common methods in preparing J groove full pen welds is the use of air-arc.  The depth of penetration is easy to control.  It is probably the method of choice for back-gouging welds, and is appropriate for A572 steels.  The cut is a bit ragged in appearance.

Plasma arc is a very high temperature process and is not as easy to control as far as penetration.  If you are cutting a bevel for preparation for a full pen weld, the plasma arc or the ox-acetylene will work well.  When either of these methods are used in a track set up, the cuts look like they were performed with a saw.  The only relative disadvantage ox-acetylene has vs. plasma arc is that plasma arc has less of a kerf (the rounding effect on the opposite side of the cut).  

Many shops use plasma arc machines to cut holes for bolting.  On projects you will notice that they will not have the distinctive burr that you see on punched holes, and they take less time, depending on thickness, then drilled holes.

Any of these methods is appropriate for A572 steels.

Harold Sprague, PE
Krawinkler, Luth & Assoc.

-----Original Message-----
From:	Ron E. Campos
Sent:	Friday, June 26, 1998 9:12 AM
To:	'hsprague(--nospam--at)'
Subject:	RE: Torch Cutting Steel

In your response below to Mr. Serroels, you mention the possible use of air-arc and plasma arc for cutting steel.
Could you please comment further on the advantages and disadvantages of each - particularly the melting aspects.
What are your thoughts about backgouging E7018 welds and preparing joints (bevels) of ASTM A572-50 steel with a plasma arc?