HomeRoast Digest


Topic: Popper Heater Temp? (9 msgs / 157 lines)
1) From: David Westebbe
Has anybody ever measured the temperature of heater coils on a popper?  I'm
wondering what their temperature is with no air blowing over them.  I'm also
wondering what kind of air velocity is needed to make them 530 degrees,
which some claim is the hottest temp you would ever want in a roaster.
Maybe somebody with an IR thermometer could give it a try?
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2) From: Victor Blackwell
There is a very cheap way to tell the temp of the heating elements surface
temp.  Simple put some "Templac" on the surface.  When the Templac melts you
know the temp.  The Templac comes designed for just about any temperature in
this range.  I had a kit and the kit allowed me to work over a large temp
range.  Not very high tech or expensive.  NASA would not like this solution.
Vic

3) From: dewardh
David:
<Snip>
wondering what their temperature is with no air blowing over them.
Anyone who has ever burned one out has . . . just look up the melting point (or 
the sag temperature, perhaps a hundred or two degrees lower) of Nichrome . . .
Deward
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4) From: Victor Blackwell
A typical heater is made with an Inconel sheath material with a Nicrome coil
inside and magnesium oxide is used as a insulator between coil and sheath.
Hot water heating elements are copper with tin plating.  They run very cool
immersed in water.  Do not use in air as the watt/density is way to high.
Vic

5) From: AlChemist John
Sometime around 09:26 1/30/2003, dewardh typed:
<Snip>
Are there not different compositions of Nichrome that act differently?
--
John Nanci 
AlChemist at large
Roasting and Blending by Gestalt
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6) From: Victor Blackwell
I think you can find a definition of Nicrome in the machinist handbook.  I
am sure didling with the composition probably would change the electrical
resistance and/or melt down temps.
But the majoy controls for the heater manufacture is to use Nicrome wire of
differant diameters and total length of the wire coil.  Greater diameters or
lower # wire gauge lowers the resistance of the heater and longer length of
the wire will increase the resistance of the heater and will produce a
heater of lower wattage.  The trick is to get the proper balance between
wire diameter and length.  A further complication,  the resistance of the
wire will change with temperature.  So ohmic readings at room temp.  will
make one think the heater will draw more current and be of higher wattage.
But when the heater is energized the temp of the heater increases and
increases the resistance and the end wattage is lower than predided by room
temp. measurements.  So not good to change the characterisics of Nicrome,
that would be just another variable to deal with.
Nicrome is drawn through dies in its manufacture.  Thus changing the wire
diameter, but dies wear, the diameter increase lower the resistance per
foot.  So you need to monitor the diameters of the wire.  Before you start a
production run of coils and on going during the manufacturing process.  With
out these checks the heaters wattage can drift out of specs.
I think what we need to do is determine the ideal temp profile and design to
what we need.  Has this already been determined by someone?  Or maybe you
are working on this now?
Vic
<Snip>
.. . .
<Snip>
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7) From: Ken Mary
<Snip>
Are you talking about a burnout-proof heater? What are your design
objectives? One person's ideal is not necessarily another's.
--
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8) From: Ken Mary
<Snip>
Are you talking about a burnout-proof heater? What are your design
objectives? One person's ideal is not necessarily another's.
--
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9) From: Victor Blackwell
If I had the answer to my question above, I could answer you question below.
I am stuck in the middle.
I do have a patent of a heater that when it fails it will not rupture and
melt down.  But that is not the issue here.
Vic


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