Thermal Expansion to Retain a Bolt

In summary, the conversation discussed the possibility of creating a secure connection between a 1" aluminum rod and a steel structure by drilling a hole and sliding the two pieces together while they are at different temperatures. It was mentioned that a 200°C temperature difference between the two metals would be necessary for a strong bond, and that restoring this difference once the pieces are in contact would be nearly impossible. The speaker also noted that the aluminum would need to be cooled to about 120°C for optimal results.
  • #1
christian everett
16
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I have 1" aluminum rod and I want to dril a hole in a steel structure for the bolt.

If I have a 1" drill and take .001" inches off of it at the machine shop, so that it is now 0.998 inches, there will have to be about a 200°C difference in temperature between the two articles (aluminum having a coefficeint of expansion of 17 x 10-6 and steel 11 x 10-6) which shouldn´t be a problem.

There will be some mechanical retention (a bolt passing though both structures), but I was wondering if I am able to slide them together before they cool off and/or heat up how secure would this retention be withiut the mechanical retention (say it´s just one inch of length where they meet).
 
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  • #2
I show aluminum at 0.000023 - so you would need to cool it to about 120C.

https://www.engineeringtoolbox.com/linear-thermal-expansion-d_1379.html

It would be a very firm connection. Since restoring that thermal difference would be nearly impossible once the metals were in contact, it would be permanent.
Of course, slide them together smoothly. Once they bind, that's it.
 
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1. What is thermal expansion and how does it relate to bolts?

Thermal expansion is the tendency of a substance to expand or contract when heated or cooled. This can have significant effects on bolts, as they are often subjected to changes in temperature. When a bolt is heated, it will expand, and when it cools, it will contract. This can cause issues with the integrity of the bolt and its connection.

2. How does thermal expansion affect bolted connections?

Thermal expansion can cause issues with bolted connections as the expansion and contraction of the bolt can lead to loosening or even failure of the connection. This is especially true if the temperature changes are significant or occur frequently.

3. What materials are most susceptible to thermal expansion?

Materials that have a high coefficient of thermal expansion, such as metals and plastics, are more susceptible to thermal expansion. However, all materials will expand and contract to some degree when subjected to temperature changes.

4. How can thermal expansion be accounted for in bolted connections?

To account for thermal expansion, engineers may use special bolts with a high temperature resistance or use materials with lower coefficients of thermal expansion for the bolt and the connected components. Additionally, proper torqueing techniques and the use of washers can help to reduce the effects of thermal expansion on bolted connections.

5. What are the potential consequences of not considering thermal expansion in bolted connections?

If thermal expansion is not properly considered in bolted connections, it can lead to loosening or failure of the connection, which can have serious consequences. This can result in structural instability, equipment malfunction, or even safety hazards. It is essential to account for thermal expansion to ensure the integrity and safety of bolted connections.

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