[Ashish B]

HI

I WANT TO FIT A BEARING OVER A SHAFT IN SHRINK FIT. (SHRINK FIT MEANS EITHER BY COOLING THE SHAFT...so that shaft gets undersize OR BY HEATING THE BEARING...so that it gets Oversize.)

I HAVE A CARBIDE SHAFT & I KEPT IT IN A FREEZER FOR A COMPLETE DAY. BUT STILL ITS SIZE DID NOT WENT UNDERSIZE.??

CAN ANYONE TELL ME THE PROPER WAY OF COOLING A SHAFT???

THANKS
ASHISH

[RICHARD ZASTROW]

Your carbide shaft may have a very small coefficent of expansion. The bearing may grow more for the same amount of heat. Make sure you do not heat the bearing beyond it's operating heat limit., the lube may "cook" out.

Dick Z

[mike_Kilroy]

I am no expert at all but remember my customers HEATING the outside piece and COOLING the inside piece and then putting them together.... oven and cooler full of dry ice. got best of both worlds then hurried to put together. so maybe do both? maybe do dry ice for colder temp?

[Ashish B]

Hey,
Thanks for the REPLY.

But Up to what temperature, the shaft (or bearing) should be cooled (or heated) to contract (or expand) by 0.015 mm??
Any IDEAS !

Thanks
Ashish

[jeffrey001]

For the bearing, just look at the spec for max temp.

For the shaft, freezer should be enough.

But you have to understand that when it will be the time to put the bearing in place, you'll have to be 100% ready with everything you need ready too, hammer, round pipe to place the bearing at full depth.

You will have only, maybe one second or two before bearing get back to it's original size when it make contact with the cold shaft, after that, it's too late.

It will be very difficult to remove the bearing if you get it wrong.

Just my tough.

Jeff

[RICHARD ZASTROW]

What diameter is the bearing bore? The max. operating temperature is usually listed in the bearing catalog eng./tech section.

SKF cautions: "Bearings should not be strongly heated and certainly not to temperatures above 110C (230F). Greased and sealed bearings should generally not heated."

Hope that helps.

Dick Z

[packrat]

There is a chart about half way down the page of this link, that shows the amount of change for temperature; 2. Mounting | NSK Global

[Ashish B]

Thanks,
FOR THAT SPECIAL PRECAUTION WHILE FITTING THEM IN SHRINK FIT. I REALLY HAVE TO KEEP EVERYTHING READY.

THE BEARING DIAMETER IS 6 MM.

Also i read the Special Instructions posted on the link & also downloaded the chart of temperature v/s the amount of expansion in the shaft.
Thanks


Also Guys, i read some where about Induction Heating process (which is normally used in Shrink Tool Holders) heats the piece externally & in a very quick time. I was wandering that is there any such process which cools down the shaft...(May be called as INDUCTION COOLING)...Any Ideas !

[HuFlungDung]

6mm is practically too small of a bearing to obtain enough expansion by heating to 110°C, since you only get about .01mm differential expansion of the diameter that it had at 0°C. If the room temperature parts have any interference by design, you'd need probably .02mm clearance to do a rather quick assembly, although .01mm might be enough if you had a very accurate guided assembly that holds the parts in perfect alignment.

The two parts will actually be surprisingly tight if the design has zero interference. Then you could use the heat to your advantage to make a quick assembly, yet still press the bearing on or off some more if it cools and stops in the wrong place.

[Ashish B]

I really like CNC Zone Dot Com because of the correct, wonderful, prompt guidance given by you. :rainfro::rainfro::rainfro:

I will go ahead as per your instructions.

Thanks
Ashish

[jhovel]

You can also buy"freezer spray" at bearing shops now. Squirting that on a surface will cool it down to -50deg C or more. Reasnably expensive option, but can be used easily rioght there on the press, with everything in place to push the parts together.
I've used the Locktite version a couple of times successfully for this purpose. You have to squirt the freezing fluid quite liberally though to make a real difference.
I
BTW: have very successfully used it for the actual purpose of the purchase: to reduce the size of broken off studs - drilled ready for an easy-out. MUCH easier that at room temperature!

[Ashish B]

Hi jhovel,

I really appreciate & salute for your opinion. :wee:

I was wandering about the same thing that how should i cool the shaft on assembly (as a contrast option to BEARING HEATING). And suddenly you came up what that opinion.You really made my made my dream come.:banana:

REALLY THANKFUL.
I WILL TAKE MY 1st SHRINK FIT Experiment & WILL LET KNOW EVERYONE THE RESULTS.

Thanks, Once Again.

[neilw20]

I used liquid nitrogen on a 12" shaft weighing 400Kg. That was fun!
Carbide is probably only 4.5 parts per million per degree C
Steel is about 10.5
It will be a challenge to measure the change in size on your 6mm shaft.
With liquid nitrogen at -196 degrees it will shrink about 5 microns. -- 0.005mm -- about 2 tenths.
The fridge might give you 1 micron.

[Ashish B]

Hi,

Any manufacturer's refrences/links which sell "FREEZER SPRAY" or "LIQUID NITROGEN"?

Also anyone has some videos of assembling the shaft or bearing. It would be really fruitful if I could see one...

neilw20, I agree your point. Probably the carbide shaft went undersize by 0.001 mm only...

[Ashish B]

Also want to know that does that FREEZER SPRAY / LIQUID NITROGEN leaves some residual substances on the shaft ( after evaporation of the spray) & which normally can lead to erosion, corrosion or increase in friction???

Thanks

[neilw20]

Probably no residue, but best to spray a bit on a perfect mirror surface and hold it to the light.

[Ashish B]

Gr8....That it doesn't leaves any residue on the assembly.


Also, Linear coefficient of some materials is as under -

Linear coefficient (In 10-6)
Aluminium 23
Brass 19
Diamond 1
Sapphire 5.3
Carbide 2.77
Stainless steel 17.3
Steel 12

As you can see that Stainless Steel has the greatest coefficient. So, does it mean that Stainless Steel will EXPAND..(when heated) OR COMPRESS (when cooled) 17.3 times more than DIAMOND (Diamond's coefficient is 1) ??

Also will there by any change in Coefficient if I use hardened Stainless Steel (50-55HRC) ??

Thanks
Ashish

[HuFlungDung]

The chart values are linear expansion values, so yes, some types of stainless will expand 17 times as much as diamond will. But it is only a comparison of the expansivities per inch of the material per degree C

As far as I know, only the austenitic type stainlesses (like Type 304 or 316) have those large expansivities. They are not hardenable. So you'd need to look up the coefficient for the type of stainless which you are dealing with.

[Ashish B]

Thanks for the reply !

Thanks for notifying me that only 304 & 316 material have that higher coefficient of expansion...:-) but not hardenable..
Also can anyone can give me a suitable grade having higher coefficient of expansion & can be hardened..


Also will they reduce it in size (after cooling) 17 times more than that of diamond.
Thanks
Ashish

[Ashish B]

Also, I will purchase 1 freezer spray & see how quickly it can cool a shaft..

Thanks
Ashish