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From: (Alan Frisbie)
Newsgroups: rec.crafts.metalworking
Subject: Re: Welding with propane?
Date: 1 Feb 96 09:31:23 PST

In article <4eotmk$>, (Christopher Lau) writes:

> : You can use propane-air for silver brazing brass if the piece is small 
> : enough. That works, but I prefer to use MAPP gas and air for that.
>                                           ^^^^
> This has been bugging me for ages..  what the @#$^%! does MAPP mean anyways?

MAPP is a registered trademark for the stabilized liquefied 
mixture of methylacetylene (CH3:C:CH) and propadiene (CH2:C:CH2)
gases.   It is one of approximately 26 methylacetylene-propadiene
(MPS) gases marketed.

I am not an expert in any area of welding, but I do have
a textbook.   To quote from "Welding Principles and Applications":

   "Oxy MAPP combusts with a high-heat, high-temperature flame what
   works well for cuting, heating, brazing, and metallizing.

   The gases mixed to produce MAPP both have the same atomic
   composition.   This means that three carbon and four hydrogen
   atoms are present in each molecule of gas.    Molecules of each
   gas therefore have the same mass and size, even though they are
   shaped differently.   Because they are the same mass and size,
   the gas molecules form a stable mixture that remains uniformly
   mixed in the cylinder.   This stabilization of mixture assures a
   uniform and consistent flame for easier quality control.

   Oxy MAPP produces a neutral flame temperature of 5,301 degrees F
   (2,927 C) that yields a heat value of 517 Btu/cubic foot in the
   primary flame (vs 507 for acetylene) and  1,889 Btu/cubic foot in
   the secondary flame (vs 963 for acetylene).   The total heat
   value is 2,406 Btu/cubic foot (1470 for acetylene).   The
   difference between the temperature produced by a neutral
   oxyacetylene flame and a neutral oxy MAPP flame is only 288
   degrees F.   Both flames are well above the approximately 2,800
   degrees F temperature required to melt mild steel.   

   Although MAPP is not normally recommended for use in gas welding,
   it can be used sucessfully.   because the secondary flame of MAPP
   produces almost twice the heat of the acetylene flame, distortion
   is more of a problem with MAPP than with actylene.   Also, it is
   more difficult to melt the root of the joint using MAPP.   Because
   of the higher heat, the sides of a T-joint melt first.   This is
   not as much of a problem with other joint designs.

   All gases used as alternatives to acetylene are safer to use,
   store, and handle.   MAPP has each one of the safety features of
   the other fuel gases.   These safety features include shock
   stability, narrow explosive limits in air, no pressure
   limitation, and slow burning velocities.   Another safety
   advantage of MAPP is its smell.   The odor of MAPP can be
   detected when there is as little as 100 parts per million of the
   gas of 1/340 of its lower explosive limit in air.   By law,
   propane, natural gass, and propylene must have an odor added to
   them so that they can be detected at a concentration of 1/15 of
   their lower explosive limit in air.   The ability to detect even
   small leaks can save gas and avoide the possibility of
   explostions.   The foul odor of MAPP allows leaks to be found
   more than twenty-two times faster than acetylene leaks can be

I know this more than you asked, but one I started typing, I
couldn't stop.   :-)

> I've been using propylene (+oxygen) in my torch, is this the 
> same as MAPP??

No, but its heat and temperature characteristics are similar.
The book doesn't give any more details on propylene.

--  Alan E. Frisbie               Frisbie@Flying-Disk.Com
--  Flying Disk Systems, Inc.
--  4759 Round Top Drive          (213) 256-2575 (voice)
--  Los Angeles, CA 90065         (213) 258-3585 (FAX)

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