Measuring furnace temperature

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100model

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Hi everyone

Have you ever wondered how hot it is in a furnace that melts cast iron? I made a video about how I measured my furnace temperature using a "R" type wire pyrometer. One wire is pure platinium and the other wire is 90% platinium/ !0% Rodium. Both wires are welded together at one end and the other two ends are connected a millivolt meter recalibrated to read in Celsius. It will read up to 1770 C before the wire begins to melt. This wire is very expensive so it will not be on top of the shopping list for the home foundryman. [ame="http://youtu.be/h3YXRl2LGMk"]http://youtu.be/h3YXRl2LGMk [/ame]
 
Many of these older read outs have dip switches to allow the user to use other types of thermocouple wire. For example, if you are melting aluminum or brass, one can use type K (chromel-alumel) thermocouples which are considerably cheaper than platinum rhodium. Type K is good for ~2300F on an intermittent basis. In my work, we use tungsten rhenium couples which are good to over 3400F. If you use thermocouples, they must have an insulating sheath to protect them from the molten metal. Often they have a ceramic oxide coated over the wires to insulate them electrically, and a metal sheath to protect them from the environment. If the measuring junction gets contaminated with molten metal, is messes with the voltage-temperature characteristics of the couple and renders them inaccurate. I do a lot of Babbitt work at home and have an old digital readout with a type K couple. The sheath is made of stainless steel and somewhat bendable. While I am doing the preheat of the work with a propane torch, I can gauge the heating of the molten Babbitt (in a small Johnson gas fired forge) so I do not overheat it. For melting iron as 100model is doing, platinum rhodium is just abut the only game.
 
Way back in 1990s I had a US$150 Digital Thermocouple Pyrometer to check Molten Aluminium.
I had to find & confirm the best pour temperature into C.I. Gravity Cast molds. The C.I. molds must be heated to a temperature to avoid cold runs. Gus was no expert at Gravity Casting Aluminium.
Took an order for 300 Garage Air Compressors for Thailand and must have Auto Condensate Traps made of Aluminium.The traps were reversed engineered from Champion.The Aluminium Furnace was DIY and LPG fired.

Got lucky.Traps successfully made and worked. All 300 sets of Air Compressors shipped on time.No accidents hapened during casting.I took all safety precautions.No on-lookers. Just me and my trusted partner.

We had repeat orders. Looking back today.I won't do it again.

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