Can I use thermal expansion to hold together materials?

In summary, the person is exploring the possibility of building a tesla turbine using old hard drive disks and a steel shaft. They are wondering if using a method commonly used in the injection molding and automobile industries, where parts are heated and cooled for an interference fit, would work for their application. They are seeking guidance on how to ensure a secure fit between the disks and the shaft without using glue.
  • #1
Cbrown92
8
0
Okay, I will give a quick run down of what I am 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 I am 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.
 
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  • #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.
 
  • #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
 
  • #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.
 

1. Can thermal expansion be used to hold together materials?

Yes, thermal expansion can be used to hold together materials by taking advantage of the physical property of materials expanding when heated and contracting when cooled. This can be used to create a secure bond between two materials without the need for adhesives or mechanical fasteners.

2. What types of materials can be held together using thermal expansion?

Thermal expansion can be used to hold together a variety of materials, including metals, plastics, ceramics, and composites. However, the materials must have similar coefficients of thermal expansion in order to create a strong bond.

3. How does thermal expansion hold materials together?

When two materials with similar coefficients of thermal expansion are heated, they will expand at the same rate and create a bond between them. As the materials cool, they will contract and remain tightly bonded together. This process can be repeated multiple times without weakening the bond.

4. Are there any limitations to using thermal expansion to hold materials together?

Yes, there are limitations to using thermal expansion to hold materials together. The materials must have similar coefficients of thermal expansion, and the bond may not be as strong as other methods such as welding or adhesive bonding. Additionally, extreme temperature changes can cause the materials to expand or contract too much, potentially weakening the bond.

5. What are some practical applications of using thermal expansion to hold materials together?

Thermal expansion can be used in a variety of applications, including the construction of bridges, pipelines, and buildings. It can also be used in the production of electronic devices, such as circuit boards, where materials need to be held together without the use of adhesives that could interfere with electrical connections.

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