Electrical heating of stainless steel bar

[VangelKukov]

Hello,
I would like to ask for help with a task. I need to be able to heat up stainless steel bar 1mm x 10mm x 1000mm up to 200 degrees Celsius homogeneously from its two ends leaving the central part free. I know you can heat up Ni-chrome alloys with electricity but the resistance of steel bar with this dimensions is low and I am afraid i will cause short circuit. Could someone give an advice on the subject. What method could be appropriate. Thank you so much for you help!!!

 

[itsmoked]

Look up induction heating.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Skogsgurra]

An easier way would be to use a transformer with a low voltage secondary. For that size and around 200 C, I think you can use any transformer with a few hundred VA and put a few turns of 6 or 10 mm² Cu as an extra secondary.

If you are in the cold part of the world, there may be guys with a thawing transformer (used to thaw frozen water pipes) in your neighbourhood. Talk to them.



Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[OperaHouse]

There are spot welding transformers ready made that might work well for this application. Been a while since I looked at the Harbor Freight ones. Seems these were 600-800W range. Add a controller and it could be interesting.

http://www.harborfreight.com/240-volt-spot-welder-61206.html

 

[iceworm]

I looked up 18-8 SS. Resistivity is 73 x 10^-6 ohm-cm. Temperature cooeficient is .00094 (degC^-1). At 200C that puts the resistance ~.09 ohms. (Here is where you carefully check my math - nothing says I didn't slip a decimal point - or two)

I have few clues as to the power input needed. That's a thermo problem - Have to ask one of them mechanicals. However, comparing to strip heaters, one might guess 500W --> which gives ~75A at 7V.

Pipe thaw machine is a good choice - they will definitely make the current, but they may not make the voltage. The few that I have used were in the 3V open circuit range. Spot welder looks really short duty cycle. The rewound xfm looks good, but I would save that one for the final after I knew the heat input required.

So, in my shop, limited funds (as in the kid's science fair project grade) I'd start with a welding machine. Currents are in the right range, easy to adjust the current, voltage range is (maybe) 80V OC, 25V normal load, fine at short circuit. Depending on what you need for duty cycle, an inexpensive 100A AC buzz-box (Harbor freight grade) might only be 1 minute in 10 minutes at 100A. Still that should get you the information to design exactly what you need. They you can come up with a clean, DC if needed, tailored, temperature feedback controlled, that exactly fits.

Keep in mind I have a couple of welding machines right handy. That is likely coloring my thinking.

Interesting science fair project. Let us know how it goes.

ice

Harmless flakes working together can unleash an avalanche of destruction

 

[jraef]

I'm with Keith, induction heating, more controllable. If this is just a one-off deal, you could probably do it with a simple induction hob / cook top (hot plate if you are an American).


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[ScottyUK]

The long slender shape doesn't lend itself induction heating unless a custom coil was produced. That could get expensive for one-off, and the small dimensions mean a fairly high frequency will be needed. Resistance heating should be ok - you'll get the usual cooler spots near the ends and any supports where heat is lost through conduction, if that is a problem.

 

[Skogsgurra]

Dimensions are like a 1 m tape measure. Not easy to heat inductively and keep straight (leaving central part free).

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.