Thermally Insulating Driveshaft

[superpanda]

Hi,

We are conducting performance tests on a gearbox and one of the primary ways we do this is by accurately measuring the temperature while in operation. In a test environment we drive the gearbox with an electric motor connected with a steel driveshaft. This motor is having a small but measureable heating/cooling effect depending on the temperature differentials between the two. We want to isolate the motor from the gearbox for test purposes.

Can anyone suggest a material that would be sufficiently strong but also significantly limit the amount of thermal conductivity compared to steel? A composite like phenolic would be sufficiently strong for our purposes, but is there perhaps another material that could even further minimizes heat transfer from the motor to the gearbox and have similar mechanical properties? I considered a magnetic coupling and this is a possibility, but it presents its own challenges such as limited torque.

Thanks for any input

 

[btrueblood]

What are your size constraints and what peak torque is the shaft required to carry?

Mag couplings usually slip, which then generates heat also.

I have seen fiberglass and graphite fiber shafts for transmitting torque, both need to be somewhat larger in diameter than the equivalent steel tube shaft. They are pretty specialty items though, not like you can just order one up "off the shelf" (though if you are handy you could likely fabricate one from catalog-available structural tubing).

In comparison, stainless steel is about half the thermal conductivity as plain carbon steel, and titanium alloy Ti6Al4V another half of that which is about as low as metals get.

Can you use a hollow tube and cut down some thermal cross section that way? Why not just use a longer shaft? Or do you have requirements for torsional flexibility of the shaft?

 

[EdStainless]

A thin stainless shaft will greatly reduce thermal conduction issues.
What size/strength do you need?
There is cold worked SS tube in the market (for aerospace applications).

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[hendersdc]

An Oldham style coupling could work, you can easily find different materials such as plastic or rubber for the central floating portion. As btrueblood mentioned you will need to define your size and torque requirements for us to give you more than general options.

 

[CouplingGuru]

I would suggest a thermally insulated coupling. This is a common selection, most times it is referred to as an electrically insulated coupling. Depending on what your needs are most companies offer an electrically insulated option, the phenolic spacerss in and electrically insulated design also serve as a great thermal break for applications such as yours. We have done many to solve your exact problem.

When it comes to couplings we are always here to help.

http://WWW.PSCCOUPLINGS.COM

 

[superpanda]

Thanks for all the suggestions. I am going to try the isolated coupling. Rubber has a pretty low heat conductivity so I am thinking this will do nicely.

 

[dvd]

Dodge Paraflex couplings may be a pretty good choice -

Or[link

https://www.rexnord.com/ContentItem..._Omega-Elastomeric-Couplings_Catalog-pdf.aspx

] Rexnord Omega couplings[/url] - you can put the hubs outboard on the Omega couplings and get a nice separation between motor and reducer shafts.

 

[racookpe1978]

Even a pipe-type flange adapted with a rubber gasket will cut thermal transfer. A very little bit of energy will go through the bolts in the flange, but not much.

 

[lilliput1]

It would be better to use VFD to drive the motor at various rpm, first without the gearbox attached and measuring the power input at each rpm. Then do the same with the gearbox attached. Using the difference in power consumption you can readily calculate the efficiency of the gear box. Measuring temperature gain is tricky because of thermal storage and radiation heat transfer.