## Heat Shrink Fit

## Heat Shrink Fit

(OP)

I am currently working on analyzing the capability of using shrink fit (Most likely with induction shrink fitting) to heat up a steel hub (1045 steel) so that it can slide onto a shaft. Using the tolerances from the tables obtained in the machinery handbook for a FN5 fit I have an estimated desired deformation of 0.0045. Ideally I would like to have the hub at around 1.1255" and the shaft at 1.125".

Using the formula shown below I should be able to calculate how much I need to heat up the hub, but I was wondering for nominal length L should I use the inner or outer diameter? Also if I were to use either option it would reach over 300 F. Isn't that value above the critical value before the material properties would change? Or is it 300 C and up that I need to worry about?

d = aL(Dt)

d = Total deformation desired (in or mm)

a = Coefficient of thermal expansion (in/in °F or mm/mm °C)

L = Nominal length of the part being heated (the diameter for a cylinder) (in or mm)

Dt = Temperature difference (°F or °C)

(http://www.inductionheating.jp/pdf/shrinkfit_calcs...)

Using the formula shown below I should be able to calculate how much I need to heat up the hub, but I was wondering for nominal length L should I use the inner or outer diameter? Also if I were to use either option it would reach over 300 F. Isn't that value above the critical value before the material properties would change? Or is it 300 C and up that I need to worry about?

d = aL(Dt)

d = Total deformation desired (in or mm)

a = Coefficient of thermal expansion (in/in °F or mm/mm °C)

L = Nominal length of the part being heated (the diameter for a cylinder) (in or mm)

Dt = Temperature difference (°F or °C)

(http://www.inductionheating.jp/pdf/shrinkfit_calcs...)

## RE: Heat Shrink Fit

For 2-4 thousandths interference fit, I have used liquid N2 successfully to cool the small diameter part. Again, much smaller temp difference than heating the larger diameter part that much.

## RE: Heat Shrink Fit

Brian

www.espcomposites.com

## RE: Heat Shrink Fit

## RE: Heat Shrink Fit

another day in paradise, or is paradise one day closer ?

## RE: Heat Shrink Fit

Ted

## RE: Heat Shrink Fit

I may have done this wrong but when I was using the FN tables in the machinery handbook for shrink fits it showed the Largest Tolerance for the hub would be 0.0012" while the smallest tolerance for the shaft would be 0.0025". That would give me a tightest fit on top of some clearance to get a reasonable value. I may be wrong on doing things this way but my calculations are very similar as the one in the link below.

http://docplayer.net/41324995-Shigley-s-mechanical...

The hub has an OD of 2" so it's not too big.

For now we are trying to avoid cold shrinking as the shaft is chrome coated steel so we want to avoid the possibility of cracking when it heats back up

## RE: Heat Shrink Fit

Nominal diameter 1.1250

Minimum interference: 1.1275 - 1.1262 = .0013

Maximum interference: 1.1283 - 1.1250 = .0033

Ted

## RE: Heat Shrink Fit

## RE: Heat Shrink Fit

Assuming all that works out though my main concern would be the hardness of the material. If the calculations are right the hub would be around 700F. The only way to safely assemble it would be to design a fixture as you mentioned then have someone carefully slide the shaft into the hub. Heat transfer would definitely be a problem but to retain the hardness won't we need to quench it as fast as possible?

## RE: Heat Shrink Fit

400 F is the tempering temperature of many steels over HRC 50, so wouldn't change the hardness much of softer steels

What is the interference fit supposed to accomplish? Transfer of torque, or resist axial forces ? Not release the shaft at 60,000 rpm?

## RE: Heat Shrink Fit

I used

d = aL(Dt)

d = 0.045

a = 6.1x10^-6in/in °F

L = 1.125"

Dt = Temperature difference (°F or °C)

The assembly will go into a steering cylinder so I think that's axial forces?

## RE: Heat Shrink Fit

1.125 inch heated 70 F to 400 F = .0022" diametral increase.

70 > 500F = darn close to 0.003"

## RE: Heat Shrink Fit

hopefully there's a step on the shaft so the hub can be quickly driven home (against the shoulder).

another day in paradise, or is paradise one day closer ?

## RE: Heat Shrink Fit

And with that type of fit variance you have to worry about yielding the hub that you are installing.

If it is one time creation you are better off getting the exact measurement after plating the shaft, then tolerance your hub accordingly.

It may seem counter intuitive but smaller parts are much more difficult to heat fit, because of the amount of interference require to hold and limited about of material growth from heating.

When it comes to couplings we are always here to help.

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