R.P.McMurphy wrote:
Hi all, I need to heat a steel rod 12inches long and half and inch in
diameter up to around 40 degrees centigrade and keep it within 2degrees. It
will need to be kept constantly at this temperature. it can only be heated
at one end, the other end needs to be un cluttered.

Any suggestions how I can do this?

Cheers!


You need to provide more information...

I assume that the rod is solid?

I assume that the rod is suspended in free air?

I assume that there is no dynamic thermal load bearing? (i.e. nothing
randomly comes into contact)

I assume the environment is reasonably controlled? (i.e. not placed in a
draught)

I assume there's no limitation on the heating technology?

I assume that the environment is cooler than the rod - that we're
talking heating and not cooling!


If my assumptions are broadly correct, then I'd suggest machining two
bore holes , connected at the far end, and pump water or oil through
these channels, pre-heated to 40c. (pro: with an adequate sump of
pre-heated water/oil) this would provide good stability under differing
thermal loads and a good (flat) temperature gradient across the length
of the bar)

Another option is to machine a single hole, and insert a straight
heating element down the length of the hole. If temperature control is
vital, then make this a multi-stage element, each stage with some
thermal control to modulate power to each stage of the element (con:
difficult to maintain a stable temperature gradient across the length)

Another option, again requiring the machining of a single hole, is to
run a conductor to the far end of the rod (internally) and use the rod
itself as a heating element, passing a current through the internal
conductor to the far end and have the supply return at the near end.
Would also need an embedded temperature monitor (con: likely to be slow
to heat and have poor response to thermal loading)

The easiest option, of course, is to change the environment to present a
constant 40c around the bar, however, I'm guessing that this is not a
solution for your problem.

More info please!!!

Mike