Re: ATM My underground Kiln.

[Dennis Rech <dennisrech@home.com>]

At 05:11 PM 4/23/01 -0400, Viper71049@aol.com wrote: 
>
> Hello, 
>
> Since about February my friend and i dug a 6ft hole and 6ft square for a
kiln
>
> all by 2 shovels! It took us that long because we were working only
weekends 
> and we are only 14yrs old. It is now complete and ready to melt glass. It
is 
> self annealing since the ground when closed with a lid can hold a lot of 
> heat. We test tried it by melting 100 aluminum cans into a sheet of
aluminum.
>
> It worked and now I think i can do some glass melting. I am going to need a 
> pyrometer(high temp. thermometer) and was wondering if anyone had one I
could
>
> buy off them? I am planning to melt glass blanks up to 12" for my friends 
> telescope as we do not have jobs. 
>
> Tony 


Hi Tony,
You can probably find better info on pyrometers in the pottery or metal
casting
websites. 
Three methods of measuring temperatures in the range of melting glass are:
1: Dissimilar metal probes.  For high temperatures in the 2000 degree F range
you can check with the pottery shops. They sell the thermocouples as
reasonably
priced as anyone. Unfortunately, metal probes tend to dissolve in molten glass
and/ or metals so you will be replacing them or rewelding them often. The
cheapest form of thermocouple is that  found in a gas furnace to verify that
the flame has lit. They are a few dollars at Home Depot and you will need a
cheap milliamp meter to measure the current flow. They are usually covered
with
stainless steel and hold up well.  
Your high school science class may have thermocouple wire that can be had
freely if you call it a science experiment. It will have known elctrical
characteristics for calibration purposes.  
2: Infra red guns. These are now getting very cheap (its relative, a few
hundred dollars). Talk your school science teacher into buying one. You just
aim and pull the trigger.  
3: The most practical is to make an optical comparator. The hotter anything is
the brighter it glows. You can make an optical pyrometer with a clear light
bulb, rheostat and voltmeter.  Basically, you hold the light bulb up and look
at the hot glowing object through it. Slowly turn up the dimmer until the
filament turns the same color as the object under test. Check the voltage (or
amperage).  You can calibrate the tester by noting the known book value
melting
points of aluminum, copper and steel samples under a gas welding torch and
plotting the curve of temperature vs. voltage.  
More info can be found in amateur foundry books. This is a method widely used
in industry. Best part is that you can be far away from the heat. Glass will
start melting at about twice the temperature of aluminum and even then its
more
like taffy than water.  
Safety note: What are you using for a mold?  If its plaster, pottery or cement
make sure that it has been baked free of hydroscopic water. Molds have been
known to explode when heated.
Dennis
Dennis Rech
Mirror-o-Matic

http://www.oblivion.net/~astro/mirror/