[Bulk] Re: [Bulk] Heat treating aluminum header?

[Karl G. Mueller]

Bill,

You're correct that aluminum has to be quenched, usually in some type of salt bath,
to be annealed. In the case of a header you are looking at a finished item with
various material thicknesses (flange). If you quench an item like this you will
induce stresses because part of the item (thin wall tubing) will cool of faster than the
heavier flange. I have used this method (electric oven) a lot to take the T6 hardness
out of 6061 aluminum.
I don't think that the heat from the exhaust is high enough to put the header in a 
continued annealed condition, but high enough to cause some artificial aging ???
Vibration and more so continuous flexing of the header with too much weight
(tuned pipe) on the end of it will cause it to break eventually.
I did not want to get to technical in my first post, just something  the average modeler
should be able to do. Not everybody has a Brinnell Hardness Scale at home :-).

Karl G. Mueller
kgamueller at rogers.com

  ----- Original Message ----- 
  From: Bill Glaze 
  To: discussion at nsrca.org 
  Sent: Thursday, September 08, 2005 9:50 AM
  Subject: [Bulk] Re: [Bulk] Heat treating aluminum header?


  This is getting to be a rather absorbing thread; at least for me.  I had always been taught that aluminum anneals like brass and copper; that is, opposite to steel.  I had been taught that to anneal aluminum, (or brass, as in cartridge cases, or copper, as in cold worked bullet jackets) that one heats the material, then chills it rapidly.  In fact, even with lead, which most people would think is, well, just lead, that lead in its pure state, or alloyed with the common metals, (tin, antimony, others) can be hardened.  In fact, by heating lead bullets in an oven to just below deformation temperatures, (just below where the bullets would begin to "slump") for an hour, then rapidly immersing them in cold water, I have been able to raise the Brinnell of the bullets from 9-10 to over 20.
  What I am wondering is if the aluminum headers are being hardened to brittleness by "work hardening" caused by minute vibrations, repeated thousands of times.
  Because the applied exhaust heat would, it seems, tend to put the aluminum in a continual annealing condition.
  I was in the aluminum window manufacturing business for many years.  We used several hardnesses of aluminum, and several different hardening processes; heat treating, artificial aging, artificial hardening, etc.
  Of course, when flying for United Airlines, in severe turbulence, I found myself hoping that the wing spars hadn't been work hardened to the brittleness stage!
  Sorry for the long posting, but, as I said, it is an extremely interesting thread.

  Bill Glaze

  Karl G. Mueller wrote:

    Jon,

    The problem with the aluminum being heated and cooled every time
    you run the engine acts like an artificial aging (hardening). In time the 
    material will get very brittle and therefore break very easy. Here is a little
    trick you can try that I know works: If you have a self cleaning electric oven
    at home, put the header in the oven run the cleaning cycle. Do that at night
    before you go to bed and the next morning you header will be annealed.
    It has to cool of slowly.This is the opposite process of hardening. This makes
    the aluminum more flexible and less prone to breakage.

    Karl G. Mueller
    kgamueller at rogers.com

      ----- Original Message ----- 
      From: JonLowe at aol.com 
      To: discussion at nsrca.org 
      Sent: Wednesday, September 07, 2005 8:39 PM
      Subject: [Bulk] Heat treating aluminum header?


      After many many flights, I had an aluminum header break for my OS 1.60.  I had it welded up by a very good welder, but the header broke again after one flight in an area removed from the weld, but close enough that it would have gotten pretty hot.  I suspect that the heat treat of the header got changed.  Any ideas on how to try to heat treat a second pipe that has benn welded to try to at least get more than one flight?  I've odered a new header, but it is not here yet.

      Thanks

      Jon Lowe
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