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A basic physics question for you to consider.


donkpow

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Things expand and contract with changes in temperature.

Let's set the example of a common and simple metal plate. It could be steel , aluminum, whatever. The plate is 1' square and 1" thick. There is a through hole directly in the center of the plate. The hole is 2" in diameter. 

The question: When the plate is heated or cooled significantly, how does the diameter of the hole change? Does the hole increase or decrease in size relative to the temperature of the plate?

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5 minutes ago, donkpow said:

Things expand and contract with changes in temperature.

Let's set the example of a common and simple metal plate. It could be steel , aluminum, whatever. The plate is 1' square and 1" thick. There is a through hole directly in the center of the plate. The hole is 2" in diameter. 

The question: When the plate is heated or cooled significantly, how does the diameter of the hole change? Does the hole increase or decrease in size relative to the temperature of the plate?

Yes, the hole changes.  it is not uncommon with interference fit parts to cool one part and heat the other to get them to go together easily and when they return to normal temp, they are tightly fitted. 

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Just now, jsharr said:

Yes, the hole changes.  it is not uncommon with interference fit parts to cool one part and heat the other to get them to go together easily and when they return to normal temp, they are tightly fitted. 

Thank you for the reiteration and expansion of the preface to the problem. I'm assuming you have people to do the actual answering of questions.

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2 minutes ago, donkpow said:

Thank you for the reiteration and expansion of the preface to the problem. I'm assuming you have people to do the actual answering of questions.

I am going to say the hole increases in size, as in my example, you heat the bearing being pressed onto an axle, and you cool the axle.    But I can see the issue you are asking.  If the steel plate expands, does it expand into the hole, making the hole smaller.  Now I am corn fused.

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Three things.

1 - it's not a plate it is a cube.

2 - the hole increases in diameter based on the heat.

3 - "when they return to normal temp, they are tightly fitted." but it won't return to its original diameter because expanded metal does not return to its original size.  It will always return to a slightly larger size. 

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3 minutes ago, Road Runner said:

I know that one method to remove a ring that doesn't want to come off is to put your hand in very warm or hot water to increase the size of the ring.  

I have witnessed a procedure that a coupling is made in steel tubing where freezing temperatures is used on a ferrule like coupler. The extremely cold coupler then slips over the ends of the two pieces of tubing and shrinks to make a leakproof joint.

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15 minutes ago, jsharr said:

Yes, the hole changes.  it is not uncommon with interference fit parts to cool one part and heat the other to get them to go together easily and when they return to normal temp, they are tightly fitted. 

Agreed. I've heated up engine heads to replace valve guides. As you also mentioned, it helps to cool down the valve guides also.

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Just now, donkpow said:

This misunderstanding on your part negates all possibility you producing  a correct answer.

Has no bearing on the physics.  My very first project in my very first engineering department had to do with corrugated sheets of SS expanding in a vacuum furnace.  Iv an example just like yours, a previous designer miscalculated the expansion rate of the sheets of SS used as refractory in the vacuum furnace and caused massive issues.  I was tasked with making sure that our expansion rates of the sheets in 2 dimensions matched our calculations.  Pins were used to attach the sheets and the expansion of the holes used to mount the corrugated sheets had to be measured as well.  After about 2000*F the sheets and the holes never returned to their original size.  With each heating the expansion was the same but the resulting cold size expansion was reducing.

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The hole in a piece of metal has an edge.  If the hole were to be forced to expand inwards (smaller diameter) then the metal in that edge would be compressing.  Since it's expanding due to heat it can't be compressing.  This forces the rest of the plate to expand outwards even more and the hole does not get smaller.  It gets larger.

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2 minutes ago, Kzoo said:

Has no bearing on the physics.  My very first project in my very first engineering department had to do with corrugated sheets of SS expanding in a vacuum furnace.  Iv an example just like yours, a previous designer miscalculated the expansion rate of the sheets of SS used as refractory in the vacuum furnace and caused massive issues.  I was tasked with making sure that our expansion rates of the sheets in 2 dimensions matched our calculations.  Pins were used to attach the sheets and the expansion of the holes used to mount the corrugated sheets had to be measured as well.  After about 2000*F the sheets and the holes never returned to their original size.  With each heating the expansion was the same but the resulting cold size expansion was reducing.

Changing the subject is not allowed. Sorry. :dontknow:

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Ahh coefficient of expansion. The part will expand when heated, and shrink when cooled (ask George Costanza :D)  Heating the part will enlarge the hole. For instance, wheels on a train are heated prior to pressing them onto the axle. Steel has a expansion rate of ≈6 µin/in/°F, for aluminum its ≈12  µin. I've done these calculations before, and measured parts at various temperatures. The physics check oot. We've also had to predict a diameter of a part post heat treat :wacko: this is not an exact science, and takes trial and error. Variation can occur depending where the part is in the oven. The part diameter tolerance is .0009"

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2 minutes ago, donkpow said:

Changing the subject is not allowed. Sorry. :dontknow:

Well, getting back to the original line, I think we now know it is best to be a hot blooded guy with a cool wife.  Am I correct?  The shrinking and growing really needs to be properly analyzed to fully understand this stuff.

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The hole expands in diameter, that's why nuts that can't be loosened from bolts are sometimes heated with a torch - quickly so the nut gets hot before the bolt does - loosening the nut.

Also, some parts are joined together by putting a hot part around a cold part and letting the hot part squeeze the cold part as it cools.

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1 hour ago, Kzoo said:

Three things.

1 - it's not a plate it is a cube.

2 - the hole increases in diameter based on the heat.

3 - "when they return to normal temp, they are tightly fitted." but it won't return to its original diameter because expanded metal does not return to its original size.  It will always return to a slightly larger size. 

aluminum wiring!  

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1 hour ago, Razors Edge said:

Well, getting back to the original line, I think we now know it is best to be a hot blooded guy with a cool wife.  Am I correct?  The shrinking and growing really needs to be properly analyzed to fully understand this stuff.

Now you just take this adolescence right back to the viagra thread!

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14 minutes ago, jsharr said:

Isn't that what makes aluminum wiring bad?  It gets hot, get biggened, cools down, gets smallened and things get loose and then FIRE!!!!!!! 

Because you have an alum wire and an alum connector that both expend and cool and return to different rates of their original size.  This results in additional heating next time its energized - repeating the process.

The coefficiency of expansion on aluminum is much higher than other metals.  30% difference between aluminum and copper.

Material Fractional expansion per degree C x10^-6 Fractional expansion per degree F x10^-6
Aluminum 24 13
Brass 19 11
Copper 17 9.4
Iron 12 6.7

 

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4 minutes ago, Kzoo said:

Because you have an alum wire and an alum connector that both expend and cool and return to different rates of their original size.  This results in additional heating next time its energized - repeating the process.

The coefficiency of expansion on aluminum is much higher than other metals.  30% difference between aluminum and copper.

Material Fractional expansion per degree C x10^-6 Fractional expansion per degree F x10^-6
Aluminum 24 13
Brass 19 11
Copper 17 9.4
Iron 12 6.7

 

Isn't that what I said? I did not know the biggening and smallening happened fasterly in some metals.  

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19 minutes ago, Philander Seabury said:

This was a good example because if you think about a donut, the hole gets smaller as the donut expands. So why is this different?  

Do doughnuts expand because they are getting hot or is most of the expansion due to the cooking of the dough?  I ask because the do not appear to shrink and crack as they cool enough to eat.

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11 hours ago, Kirby said:

Why would anyone want a plate with a hole in the middle?  My food would fall through.  :(

Most people who buy plates with holes in them do so in order insert their large toe into the hole.

10 hours ago, Philander Seabury said:

This was a good example because if you think about a donut, the hole gets smaller as the donut expands. So why is this different?  

The donut is not made of steel.

10 hours ago, Further said:

So....lets make the plate big, say 8' x 8' still an inch thick, still a 2" hole in the center.

Now we heat the area directly around the hole, maybe a 2" area around the hole, to 400 degree F. The main bulk of the plate doesn't heat up.

What does the hole do ?

The hole doesn't do anything, it is a hole.

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