Steel plates are commonly attached to each other with rivets, which are slipped into holes in the plates and rounded with hammers. The hotness of the rivets makes them easier to round over but their hotness has another advantage in providing a tight fit. What is it?
I know the heat expands the rivets, but wouldn't that make for a looser fit when they cooled?
Steel plates are commonly attached to each other with rivets, which are slipped into holes in the plates and rounded with hammers. The hotness of the rivets makes them easier to round over but their hotness has another advantage in providing a tight fit. What is it?
I know the heat expands the rivets, but wouldn't that make for a looser fit when they cooled?
* physics - jim, Sunday, September 20, 2009 at 7:39am
Consider the amount of contraction in cooling - in _both_ directions.
The cross-sectional contraction is a minor negative, but the rivet is much longer than its cross-section, so the contraction along its length is proportionally greater.
And, remembering that the rivet is holding two steel places together along its length, what does that contraction do?
If the contraction along the length of the rivet is proportionately greater, wouldn't that make for a fit that is even looser as the rivet tries to hold the two plates together?
Consider the amount of contraction in cooling - in _both_ directions.
The cross-sectional contraction is a minor negative, but the rivet is much longer than its cross-section, so the contraction along its length is proportionally greater.
And, remembering that the rivet is holding two steel places together along its length, what does that contraction do?
When the rivet goes in, let's say its length is L.
As it cools, it shortens a little, so its length is now L-delta(L).
But it's holding the two plates, so as it shortens, it pulls them together just a little, by the amount delta(L).
What you're thinking is that its cross-section narrows enough not to hold them at all. But the rivet doesn't hold them together by fitting _exactly_ into the hole; it hold them together by its head and tail. The head is pre-formed, and the tail is made by hitting the end of the cylinder that is poked through so that it expands to form, effectively, a new "head".
The Wikipedia page Rivet shows two rivets before they're installed. Then the tail is flattened out to hold the rivet in place. Then the contraction pulls the rivet to be shorter and the two plates closer together.
Thanks so much! That is exactly what I was thinking - the cross section would get narrower. I didn't know how a rivet worked. Looking at the pic and knowing the tail was also flattened out enabled me to "see" why you mentioned length. I wish the book wouldn't assume we know this stuff about equipment we have never used :-P. thanks again. I understood the peanut/calorie answer too. :-)
You're very welcome, Mary. Sometimes, just sometimes, a picture, or graph, or video, is worth much more than a thousand words.
You're correct that heating the rivets expands them, which might at first seem counterintuitive for achieving a tight fit. However, the advantage of hot rivets is not due to expansion and the subsequent cooling, but rather due to a specific property of the materials involved.
When the hot rivets are inserted into the holes and hammered, they create a very strong and secure joint between the steel plates. The heat helps in two ways:
1. The heat softens and ductilizes the rivets: As the rivets are heated, they become more malleable and can be more easily rounded with hammers. This deformation allows the rivets to tightly fill the holes and form a strong grip on the surrounding material, providing a tight fit.
2. The heat causes the rivets to contract upon cooling: Steel contracts when it cools down. As the hot rivets cool, they shrink and become smaller in size. This causes them to exert inward pressure on the steel plates, further enhancing the tightness of the joint. The contraction of the rivets compensates for any gaps or discrepancies in the hole sizes, ensuring a secure fit.
Overall, the combination of softening and deformation during the heating process, followed by cooling and contraction of the rivets, helps to create a tight and strong connection between the steel plates, even after the rivets have cooled down.