anyone tried making a thermocouple?

[downsfish]

We've got several broken thermocouples and i was wondering about rebuilding them into something more user friendly for us. They're pretty long about 2' to four' and in different stages of disrepair, some have a stainless sheath and some have a ceramic sheath, some of the wires are in a ceramic tube which then goes into a ceramic sheath. I'm told we don't repair them anymore, sooo what have been your experiences with them?:)

[Fe-Wood]

Considering how cheep they are, why bother?

[Dragons lair]

Welded many of them yrs ago. So many sizes and types of junctions type and wire sizes
Way better to buy new.
Ken

[Thomas Dean]

I currently weld them on contract for a machine shop that is a vendor for a chemical plant. They are made of Inconel and Stellite. Finished they are 10 1/2"long. Welded up 12 of them and the machinist said "Be careful with them, that's $7,500.00 just in material." I normally do about 32+/-per year. He charges approx. $1300.00 each and the company scraps the old ones.... The Stellite is $60.00 per/inch for 1"dia, we weld 3" to the end of each bar.

[Fe-Wood]

well... maybe they aren't ALL so cheep:o
but the ones I use are:D

[Thomas Dean]

Yeah, just thought I would throw that one out there. I get paid REALLY good to make those weld too. just wish there were more to do. They also get 100% X-RAY after welding and then after final machine work.

[pkrankow]

I got a small spool of type J somewhere. I welded up a bunch in lab class, for my class and other classes. Was on a funny machine that looked like 2 carbon studs. The twist was held between and then close your eyes, trigger it, and done! I got about 3 ft left that was going to get tossed since it was too short for some reason. Never thought about what to do with it. I thinks its packed up with my protoboard.

Phil

[Dragons lair]

When I did them they ranged from 3/8 dia tubes to .0005 bare wire. Medical probes
were .010 tubes 10 feet long. For forgeing use a K type (cromel-alumel) with about .062 wire. I bought mine with the gage. For small ones you need a 80 power microscope and steady hands. Had a guy who butt welded .0005 wire he was huge. They were carbon arced with a flat car battery.
Ken

[Sweany]

Try a thermowell, thermowells protect the thermocouple

Thermowells and Head and Well Assemblies: Thermowells

[Charlotte]

Sensors, Thermocouple, PLC, Operator Interface, Data Acquisition, RTD was the source of the thermocouples we used when I was working.
Great short course on temp measurment if you read there info sections
Basically a type K thermocouple in a thermowell insulated with ceramic beads and an analoge temp readout is all you need. Doesn't have to bank breaking.
DO pay attention to the color codeing. In this field it is crucial!!!!
Thermo well= closed end pipe of heat/scale resistant material with a specalized electrical fixture featuring a ceramic insulator for connecting the thermocople.


PS My first industrail job was running gas fired annealing furnaces. When producing mechanical tube we used to insert Themocouples front and rear to manage the heat zones of the car type furnaces. We used to get five guys together to pull the thermowells out, not because they were heavy but because they would bend when red hot. We'd catch them with steel hooks to keep them straight. 30 ft long in some furnaces. Edited September 26, 2009 by Charlotte
PS

[Reinhard Schwaninger]

Use your car battery and a graphite rod from an old AA od D battery.
weld the end of the 2 wires together and you are in business.
This is what I did, when I built my pizza oven.

[RedLeg0811]

Unless you are talking about an R or S thermalcouple (3200deg), which is what Thomas Dean is talking about. You will want a K (2300 deg) $30. This will do almost everything you will want.