Engineering / Physics Question
 

At what temperature (low) does it take to shrink a stainless steel bolt one mil from ambient temp?

I guess I didn't give enough info. Here is why:
• Machinery’s Handbook has coefficients of expansion for 41 different stainless steel alloys.
• Of the 41 alloys, the coefficients vary from 5.2 to 9.6 micro-inches per inch-°F of expansion.
• From there, you need to know the alloy, the length of the whatever that you are determining the amount of change, the starting temperature, and the end temperature.
• With a range of the coefficients being as wide as it is, roughly 52%, and the other information necessary the best that I can do is a very rough guess.

My best guess, and it is really a guess, is a minimum of a 50° change between T1 and T2. It is the length of the whatever that is the limiting factor here. If we are talking about something 36” long, then 1/1000” of expansion is easily achieved and the ΔT is not that great. If we are discussing 1½”, then the ΔT gets to be fairly large because the amount of length is fairly short.

This question comes about because I saw a product on the market that "freezes" a bolt to loosen it. I thought it was dumb but it did get me thinking - at what temp do you have to get to in order to actually shrink a bolt? I guess the answer is "It depends..."?

I know heavy equipment shops use liquid nitrogen to shrink bearings to install them. From what I have heard they will shrink so much that you have to hold them in place until they warm back up or they will fall out.

Common technique to press fit rifle barrels - heat the reciever, chill the barrel, pound 'em together. Quick googling found: http://www.eng-tips.com/viewthread.cfm?qid=148749&page=1

If the idea is to get a bolt to release from thermal contraction then it's the diameter you're trying to work with not the length.


Lets take a half inch diameter bolt and assume the median thermal range (7.4 micro inches/°F).

270°F change would yield .001" reduction in diameter. A 1 " diameter bolt would be twice that and a 1/4" bolt 1/2X that.

edit:fixed the missing zero for 270°

That idea is used in installing dry sleeves in aluminum blocks. They usually heat up the block, and dip the sleeves in liquid nitrogen so that the sleeves literally drop right in. Then once the temperature return back to normal you have a nice press fit. When i was building my dad's 951 motor, this was the method used by the shop who installed the sleeves.
As a side note, that product better freeze it really really fast. If the bolt is fastened to something like aluminum then it won't take long for the material around the bolt to catch up to the bolt's temperature. Also any temperature drop will shrink material, the question becomes more of how fast does it need to drop before the hole it's in catches up? And how much do you need it to shrink? .000001" or .001" or .1" (i don't think that last one is possible with most metals but you get the idea)
EDIT: Let me rephrase that last comment, i don't think it's possible with most metals and normal sized bolts.

It's easier to heat the surrounding metal to get your delta t than it would be to cool the bolt. I can see where you'd be reluctant to apply a lot of heat to surrounding metal sometimes, so there is some romance to the cooling, but I don't see how you're going to get several hundred degrees temperature differential with a bolt freezer.

I've been doing some research since receiving this email yesterday and was surprised at what I found.....besides using a penetrating oil here is a list of the "home remedies" I found online for removing a rusted nut/bolt in order of popularity.



1) Coca-Cola - I can only assume the acidity of the drink attacks the metal and subsequently, the rust.



2) Heat - Quite a few mechanics (and shade tree mechanics) suggest heating the bolt with a torch and then banging it with a hammer. Some suggested using WD-40 and then heating it up.



3) Transmission Fluid - OK, whatever...



4) Candle wax - This method is to melt candle wax over the bolt/nut and then hit it with a torch to help the wax melt and penetrate into the threads.



5) Freezing - I found three products on the market that are being marketed as "freezing" rust busters(Cold Shock, Loctite's Freeze & Release and the CRC product) The reviews for these products were mixed with some saying it worked great and others saying Heat worked better. One guy who sounded like he knew what he was talking about said heating the bolt and THEN freezing it worked best which makes sense.



My Conclusion: The overwhelmingly most popular method for removing rusted bolts/nuts was using a penetrating oil. There were numerous “home remedies” that ranged from the five mentioned above to obscure remedies like Apple Juice. The freezing method seems to rely on extreme cold(-70F) that can be pretty dangerous as frostbite and ‘cold burns” start happening at -20F with short exposures. I will try to find a can of one of these freezing products locally and see if they live up to their performance claims.

Older turbos used to be assembled by putting the shaft in the freezer and the cold side impeller in the oven at about 350 degrees. When both came to equilbrium the assembly was impossible to take apart without destroying it.

We used this on the submarine once. Underway on strategic deterrent patrol, thousands of miles from anywhere, and desperate to get a bearing installed. One of the old chiefs knew that the process called for heating the one side and cooling the other, so we did our best: we put the hot-parts in the oven, all the way in the forward compartment of the submarine, and the cold-parts in the chill-box, right next to the galley. There's two watertight doors and 3 ladders between the oven and the work site. I have this striking mental image of the XO supervising a pair of mechanics with hot-gloves, speed-walking this thing through the missile compartment.

Nutty. I should write a book. ;)

what is the original size of the bolt?

The most common type of freeze can is one containing HCFC and are class II ozone depleters. Not as bad as Freon but still bad for the ozone.

The Montreal Protocal of which he US is a supporter limits the use of CFCs only to the cleaning of absolutely essential industries such as cleaning computer chips. Even thos restrictions are scheduled for rapid phase out.

Use of a HCFC to freeze a bolt would be against the rules established by the EPA to help the US comply with he Montreal Protcol. Use of CO2 gas for the same person would not be illegal but EPA tells me that if you filled a normal aerosl can with CO2 the pressure would be so high it would burst. To sell a can full of CO2 you would have to have much thicker can.

A downside to using freezing to loosen bolts is that freezing make metal brittle so they might snap when you tried to apply force.

So long thread short - I guess it doesn't matter, the idea just doesn't make sense for a product notion...

If water didn't expand when frozen, then life on earth wouldn't exist as we know it. Just thought I'd throw that in...

As posted, the diamter of the part is important to calculate.
Rule of thumb for carbon steel, about .0006" per inch of diameter per 100 degrees delta T.
Depending on the alloy of the stainless it could be more or less (usually less).
If the part is 1" in diameter, it will theoretically grow half as much than a 2" diameter part heated to the same teperature.
400 series stainless behaves itself, 300 series can do funny, unpredicted things. I've heated large diameter 304 and 316 pieces before only to have the bore collapse instead of grow. The heating technique makes all the difference. If the piece is large you need to heat the outside first and then the inside.

When trying to use temperature to remove a part (whether hot or cold) you need to make the temperature change as quickly as possible in order to ensure the heat or cold doesn't transfer to the other parts.
My favorite technique is to use either one or two rosebud torches. Cooling to remove a part is more difficult but I've used liquid N2 before with sucess. It has it's own dangers and must be handled carefully by qualified and intelligent people tho.


BTW, the very best high temperature anti-sieze compound I've found for most stainless alloys is milk of magnesia.

And how do you make your computer do the little "degree" O? Mine doan do that. I hafta speel it out ;)

Luby,

Applying cold/heat to a mechanical fastener is really not the best process for separating the two. Delta temperatures are the best way to assemble them by shrinking one and expanding the other in a close tolerance application. Are you just trying to remove rusted bolts? if you are, are you sure they are Cres steel? (stainless) if they are you must have galvanic corrosion from dissimilar materials. Write this down.. Aerokroil! without a doubt the best penetrating oil out there. Spray it on and wait awhile..if it doesn't release it, nothing will. It will be time to remove the nut with a nut splitter. The physical properties and linear expansion of materials is academic in this situation because there is no way to shield the heat from the adjacent part. A rosebud tip on an acetylene torch will work to shock the assemble like Sammy said. I have done this many times but have zero control on the thermal isolation of parts. Everything gets hot...Aerokroil... then heat and some moderate tapping to break the rust free. If that doesn't work...Nut splitter or grind it off.:mad:

Bob

Degrees C or F ;)

+1 Kroil

And you heat the outside item, not the inside item when trying to remove something stuck, or you make it harder.

Also, heating after applying penetrating may cause, uh, fire...

Lubemaster:

Try these formulas: http://www.ajdesigner.com/phpthermalexpansion/thermal_expansion_equation_relation_linear.php

or look here:
http://www.liquidnitrogenservices.com.au/Shrink%20Fitting.htm

Bear in mind that SS has a reputation as a lousy conductor of heat (or cold).

As others have noted, it is quite intersting to do a press fit by chillingthe internal part with Liquid Ntrogen. The part will literally swim inide its location until it warms up and expnads to it's final size.

daily use
 

SmileWavy
Nice vid of shink fit tooling. Ours is in constant use
http://www.haimer-usa.com/media/shrinking_DSL.mpg