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Freezing tri metal bearings with Liquid Nitrogen

General engine tech -- Drag Racing to Circle Track

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Re: Freezing tri metal bearings with Liquid Nitrogen

Post by Truckedup » Sat Sep 07, 2019 4:18 pm

englertracing wrote:
Sat Sep 07, 2019 1:17 pm
Truckedup wrote:
Sat Sep 07, 2019 1:11 pm
What kind of bike engine?
Aprilia sxv550
I looked at Images, it's a typical Italian vertical split casting with a two piece bearing pressed into the aluminum...That's different...
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Re: Freezing tri metal bearings with Liquid Nitrogen

Post by modok » Sat Sep 07, 2019 6:51 pm

Yeah i did a lot of head scratching the first time I came across it, but seems to work ok. Seamless bearings real nice, but half the bearings in the world have one seam and do ok, and having two seams isn't that different.
.0045 press should be ok.

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Re: Freezing tri metal bearings with Liquid Nitrogen

Post by 4sfed » Sat Sep 07, 2019 9:48 pm

modok wrote:
Sat Sep 07, 2019 1:09 am
Ok, good luck! :D

if the press fit is on the high end of sanity, might do you good to use a lube such as..... standard silver anti-sieze, or coating the parts in soot, are the best lubes i know of for steel in aluminum press fits.
I've had good luck with cutting oil for aluminum. I prevents aluminum from galling on a cutting tool, and does the same when pressing steel inserts into aluminum.

-jim

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Re: Freezing tri metal bearings with Liquid Nitrogen

Post by modok » Sun Sep 08, 2019 6:37 am

I can tell no difference using motor oil, gear oil, cutting oil or sunnen b200. Actually gear oil and b200 work slightly better than motor oil or cutting oil IMO. Of course there are many types of cutting oil. Some of the more waxy ones I use now might do better, haven't tried it.
And if it is or isn't for aluminum should not really matter in this case as the temperatures will NOT be high enough to activate the sulfer compounds.

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Re: Freezing tri metal bearings with Liquid Nitrogen

Post by Truckedup » Sun Sep 08, 2019 8:07 am

I can say from expereince that heating cast aluminim bike cases to 212 F will let a 3 inch diameter roller bearing with a .002 press fit fall out on it's own or a slight blow from a drift....There's been some disagreement on heating hotter than 230F or so and possible effects on the aluminum that is often heat treated.. But I know nothing about the cases being discussed here...
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Re: Freezing tri metal bearings with Liquid Nitrogen

Post by peejay » Sun Sep 08, 2019 8:42 am

Truckedup wrote:
Sun Sep 08, 2019 8:07 am
I can say from expereince that heating cast aluminim bike cases to 212 F will let a 3 inch diameter roller bearing with a .002 press fit fall out on it's own or a slight blow from a drift....There's been some disagreement on heating hotter than 230F or so and possible effects on the aluminum that is often heat treated.. But I know nothing about the cases being discussed here...
I was "told" that you don't have to worry about heat treat effects until you get to 350 and up.

I have used 250 because I know it's safe, that's less than the oil temperature gets a lot of times, and if the oil is that hot then the metal is hotter. So it wouldn't be doing anything worse than happens as a matter of course.

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Re: Freezing tri metal bearings with Liquid Nitrogen

Post by Rick! » Sun Sep 08, 2019 9:32 am

Doing some back of the napkin calcs using each material's coefficient of thermal expansion:

CTE (Coefficient of thermal expansion)

CTE Aluminum, assumed to be 356T6: 2.32E-5 inch/(inch•Rankine) or m/(m•K) if you like SI units

CTE Steel; most steels are very similar: 1.13E-5 inch/(inch•Rankine)
Ssince we are dealing with a temperature delta, you don't have to convert to Rankine, just use Fahrenheit.

The fundamental relationship is: Circumference Final = Circumference initial + Circumference x CTE x delta temperature
Turning it into a slightly easier form: Diameter(final) = Diameter(initial) x (1+CTE x deltaT) after getting rid of Pi in all the terms.

For the aluminum case:
The expanded diameter of the bearing bore using a 300F final temp and 68F starting temp and assuming the initial bore is Ø1.600": 1.6086"

The contracted diameter of the bearing, assuming the steel is the major component using a 68F starting point and -166F final temp with the OD the same as the bore: Ø1.600"→ 1.5982" Note that at -166F, the steel is well below its brittle transition temp and care is needed to prevent breakage if malletizing the bearing.

You can see steel doesn't shrink much. But you have almost .010" change to fit in the bearing now. Heating up the case might give another .0018" extra and using liquid N2 could shrink the bearing by another .0033". 300F is less than a typical bake oven for painting so that temp is ok if you don't dwell there long. At 400F, which is a paint oven temp, T6 Al parts will lose a little strength if exposed for an hour or so. 6061T6 can lose about 10% of its yield strength from what I've tested.

Substitute in the correct diameters of your bearing bore and bearing diameters and see if you have a snowball's chance of not breaking something.
YMMV

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Re: Freezing tri metal bearings with Liquid Nitrogen

Post by Truckedup » Sun Sep 08, 2019 10:17 am

One Factor is you don't know the actual aluminum alloy, does sand cast or die cast or forged or plate aluminum all expand the same? I believe it's a decision based on actual expereince, some of which has been expressed here....
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Re: Freezing tri metal bearings with Liquid Nitrogen

Post by Rick! » Sun Sep 08, 2019 12:32 pm

Truckedup wrote:
Sun Sep 08, 2019 10:17 am
One Factor is you don't know the actual aluminum alloy, does sand cast or die cast or forged or plate aluminum all expand the same? I believe it's a decision based on actual experience, some of which has been expressed here....
Since it's an engine case, one can safely assume it is not plate or forged aluminum. That leaves cast aluminum as the method of manufacture. Going one step further, it could be sand cast but that's not like that bike mfr to use. The case more than likely could be permanent mold IMO.
Knowing where the estimated press fit numbers end up after a simple calculation is very useful and is a fundamental engineering exercise. Since a lot of smart guys spent a lot of time measuring CTE, I have reasonable trust in the numbers. I've also done a little thermal/structural FE to doublecheck this sort of thing and it substantiates the basic thermal properties written in most books. Matweb is a good source for these kinds of material data.
Up above, I listed the CTE of 356T6 aluminum to be 2.32E-5 inch/(inch•Rankine) or m/(m•K), which is incorrect for BS units and correct for SI units.
That's my bad, that's a rookie error.
As before, the 1.600 diameter is an assumed number. The OP would need to use the actual dimensions for proper estimations.
CTE for cast 356T6 is 11.9E-6-12.9E-6 inch/inch•Rankine
CTE for A360 is 11.6E-6-12.7E-6 inch/inch•Rankine (typical engine case alloy with higher copper content)
CTE for A380T5 is 11.7E-6-12.6E-6 inch/inch•Rankine (typical engine case alloy with lower copper content - reduces white fuzz when exporting across the pond)

You could use a simple spreadsheet to calculate the values for the diameter change for each alloy and get the range of expansion. Average them and you have a good idea of how the case changes.

So, to correct my error above:
For the aluminum case using an average CTE of 12.0E-6 inch/(inch•Rankine):
The expanded diameter of the bearing bore using a 300F final temp and 68F starting temp and assuming the initial bore is Ø1.600" is about 1.6045"
Adding another 50*F to the case heating will add about another .001" to the bore diameter.

The contracted diameter of the bearing, assuming the steel is the major component using a 68F starting point and -166F final temp with the OD the same as the bore: Ø1.600"→ 1.599". Note that at -166F, the steel is well below its brittle transition temp and care is needed to prevent breakage if malletizing the bearing.

So, it looks like about 1.6045-1.599 = 0.0055" of space could be created without going exotic and using 300F and the average CTE of both metals (.0053" using minimum CTEs). The OP mentioned .0045" interference at room temp so it appears using regular methods is adequate. Looking at the hoop stress in the case from this press fit, it is pushing the elastic limits of the case but that can be reviewed in another thread.

If the actual case and bearing measurements after doing the math for heating and cooling still show a press fit is needed, I don't see much chance for success. It is also interesting to note that around 87% of the press fit is "absorbed" by the engine case due to the bore expanding. Squeezing the steel cylinder into the bore takes up the remaining press of 11% of the original .0045".

For the OP's original question on whether using liquid N2 is a viable method should be directed to a Cryo company such as Cryopro or 300 Below.
The heating (oven) and cooling (frozen CO2) I used with aircraft APU parts always resulted in the bearing dropping in and waiting for the housing to cool enough to properly retain the bearing. Ag parts require a bit less precision and copious amounts of heat due to large castings in order to create a successful assembly.

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Re: Freezing tri metal bearings with Liquid Nitrogen

Post by modok » Sun Sep 08, 2019 5:33 pm

Yeah there is little point in heating aluminum over.... depending on alloy, about 250F
Because the strength of the aluminum drops off more rapidly with increasing temp, so no matter how you look at it, it won't result in a better fit.
higher temps might reduce the amount of force required, BUt also increase the chances of damaging/distorting the bore, so no gain.

Of course since the bearing is a thinwall piece, there is little point in heating the aluminum at all IMO.
The bearing will need to be installed FAST to get it in there before the temps equalize, and that's just making it more complicated than it needs to be.

Time would be better spent on the THREE main important things, making sure the interference fit is RIGHT, chamfering the edges, and selecting an effective lubricant.
And of course making a good driver to support it on the way in, would be a fourth rule for this particular case.

next step MORe advanced IMO, is taking about the surface finish of the bore. a surface finish that works well with the lubricant can reduce friction 30%, maybe more, over and OLD surface that is glazed with misc. oxide and petroleum residue.

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