[TheForge] Annealing Aluminum

Thu Jul 29 19:14:52 EDT 2004

John,  The questions, at least for aluminum, was how accurate and how
repeatable.  I don't have any good information, or experience, about
measurements in or around "room temperature" i.e. from the freezer
temperature to you heating ducts say from -10 F to + 130 F.  These questions
always comes down to what is the "real temperature" and how close is my IR
temperature to that.  Also just what does the manufacture mean by 2 percent
accuracy.  Usually this means 2 percent of full scale -- not 2 percent of
what I am measuring.  (depends on the fine print, it can be stated multiple
ways)  The unit I think you have is for measurements from 0 F to 500 F.  2
percent of full scale would be 10 degree F, not  bad, but I would want to
use it to know if the kids had a fever.  I think that your unit would be
very useful for gauging tempering temperatures.

The high priced ($ 1000) Raytek units that Granger sells have a range that
goes from - 25 F to 1600 F which seem on the surface (pun intended) to be
really great for measuring the temperature of aluminum at 700 F for
annealing.  Problem is that this instrument has an adjustable emmisivity
from .3 to 1.  OK just what do I set my emmisivity to today?  In practice
you can use a sample of the same metal with the same surface finish and a
internal heating element and thermocouple to cross check for the actual
emmisivity, then set the IR instrument to the measured value.  Works in the
lab with nice surfaces, set ups and such -- but in the real world the
surface finish is always different, the alloy and color is always different
etc. etc.  In my experience on an industrial level just go stick the surface
with a two point and get your temperature measurement.  (This is a long way
from perfect too, but works well day to day.)

Dave Smucker
----- Original Message ----- 
From: "JOHN CHOBRDA" <jchob at verizon.net>
To: "'Sponsored by ABANA'" <theforge at mailman.qth.net>
Sent: Thursday, July 29, 2004 6:05 PM
Subject: RE: [TheForge] Annealing Aluminum

> Dave,
> Very interesting, but now I am very confused, how come I can measure
> my skin surface (sorta brown) HVAC duct (silver in color) inside of my
> freezer (painted white)with good results? Is it just the aluminum that is
> the culprit?
>
> John C.
>
> -----Original Message-----
> From: theforge-bounces at mailman.qth.net
> [mailto:theforge-bounces at mailman.qth.net] On Behalf Of David E. Smucker
> Sent: Thursday, July 29, 2004 4:27 PM
> To: Sponsored by ABANA
> Subject: Re: [TheForge] Annealing Aluminum
>
> John, I hate to throw cold water on you idea of using a IR to measure the
> temperature of aluminum but they don't work worth SH#T for measuring
> aluminum.  They are great for dark or black metal such as steel but god
> didn't intend for man to measure the temperature of a shinny surface like
> aluminum with IR.  (Works fine if you paint the metal black).  Alcoa spent
> millions over many years working to develop a good and reliable IR -- non
> contacting temperature measure for aluminum.  They would be very useful in
> hot rolling of aluminum.  They even tried 2 wave length units but never
came
> up with anything that could hold standards across a wide range of alloys
and
> surface condition.  Sure you could get to 10 to 20 percent accurate but
not
> anywhere the accuracy you could get on steel or black surfaces.
>
> For big chucks of metal (hot rolling, forging and extrusions) we mostly
used
> two point contact measurement.
>
> For the blacksmith the good old pine stick works well.
>
> Dave Smucker
> ----- Original Message ----- 
> From: "JOHN CHOBRDA" <jchob at verizon.net>
> To: <munlaw2 at hcsmail.com>; "'Sponsored by ABANA'"
<theforge at mailman.qth.net>
> Sent: Thursday, July 29, 2004 10:38 AM
> Subject: RE: [TheForge] Annealing Aluminum
>
>
> > Craig:
> > Or if you want to be more accurate, Granger Supply sells an IR
> > thermometer with a laser pointer for about $100.00 (it's guaranteed for
as
> > long as you own it). It's accurate to within 2%, and I love mine,
instead
> of
> > carrying around 6 or 7 different temple sticks I just point, press the
> > button, and I know the exact temperature.
> >
> > John C.
> >
> > -----Original Message-----
> > From: theforge-bounces at mailman.qth.net
> > [mailto:theforge-bounces at mailman.qth.net] On Behalf Of Ron Childers
> > Sent: Thursday, July 29, 2004 6:57 AM
> > To: 'Sponsored by ABANA'
> > Subject: RE: [TheForge] Annealing Aluminum
> >
> > Use a Temple stick.
> >
> > Ron C
> >
> >
> > On Wednesday, July 28, 2004, at 10:07 PM, Craig Schaefer wrote:
> >
> > > I need to anneal some small pieces of aluminum plate.   1/8 to 3/16
> > > thickness.  I do not know the alloy.  I have oxy/acetylene at my
> > > disposal.
> > > I know that heating to 650F and air cooling is a good rule of thumb,
> > > but how do I approximate 650F with the torch?
> > >
> > > CraigS
> > > Gresham, OR
> > >
> > >>
> > >
> > >
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