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Can I use thermal expansion to hold together materials?

  1. Jun 5, 2017 #1
    Okay, I will give a quick run down of what Im trying to do here. What I want to do is build a tesla turbine from old hard drive disks. Being that they're already rated for high RPM, it seems like a viable option. Now these disks are probably going to be aluminum and Im probably going to buy steel shaft for them to attach to.

    I know that metals like most anything else expand when heated and contract when cooled. My question is if I were to heat the aluminum disks to a few hundred degrees, and cool the shaft to say -100 degrees (Fahrenheit) ensuring the disks just BARELY side onto the shaft. When the shaft warms up and the disks cool down will the disks contract enough, and the shaft expand enough to hold itself rigidly in place without any glues?

    Any help or guidance on this would be a MASSIVE help.
     
  2. jcsd
  3. Jun 5, 2017 #2
    Essentially this method was used for a long time to mount the starter ring gear onto an automobile engine flywheel. Still may be, I don't know. However the diameter there was well over a foot, not sure how it would work for a small diameter shaft. I would expect some distortion of the aluminum disc.
     
  4. Jun 6, 2017 #3
    In the injection molding field, we used this concept (if I am understanding it correctly) to shut off between a mold face and a hot tip on a hot runner system. A hot runner system is essentially an area in the mold that is internally heated to keep the polymer flowing nicely. We actually design a several thousand's gap between the hot tip and the face of the mold so that when the hot runner system heats up, the tip thermally expands and shuts off against the inside face of the mold. Now we shoot plastic at anywhere from 5000psi to 35,000psi (generally), so the shutoff holds up against a lot of pressure. Not sure what your application will see but it's worth looking into in my opinion.

    Husky
     
  5. Jun 11, 2017 #4
    This is a very common method of assembly for all kinds of applications. Typically, the parts are sized for the intended interference fit at room temp, but remember that as soon as they come into contact with each other, the hot part starts cooling, and the cold part starts heating, so things can get very sticky very rapidly. If you can continue to apply heat during assembly, ie with a propane torch say, it will go much more smoothly. Its also best if you limit the distance the pieces have to move while being assembled, or don't require too tight a finished fit.
     
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