# Thread: ID change due to heating on a press fit polymer bearing

1. ## ID change due to heating on a press fit polymer bearing

I am in he process of writing a design calculator and would like some insight regarding the following:

Assembly: Polymer bearing press fit into a steel sleeve

For numbers sake:
Sleeve: 410SS (avg CTE of 5.7E-6 /°F)
Size: Ø10" x Ø9" x 6"
Polymer Bearing: Carbon filled PEEK (avg CTE of 24E-6 /°F)
Size: Ø9.013" x Ø8.5" x 6" (.013" interference fit, Ø8.5" must be cut for clearance to shaft)
Shaft: Ø8.5"; 410SS

Temperature range: 75°F to 275°F

Desired diametrical clearance at 275°F: .010" minimum

I am looking for a method to calculate the change in ID due to the temperature increase and the restriction of free growth. So far I have worked to the following:

ID=Shaft diameter + Clearance + Shaft Expansion + 2*Bearing Cross-section (Cx) Expansion + Differential Expansion of Bore to Bearing OD

Differential Expansion of Bore to Bearing: Bearing OD Expansion - Bore ID Expansion

The 2 parts that I am not comfortable with are the Bearing Cx and the differential expansion. Is this double dipping in the amount of expansion/contraction that the bearing will see? There is a certain amount of expansion that the Cx will see, but yet there is also thermal growth that is now restricted due to the interference fit and the difference in CTE's.

Thank you for any and all input/assistance
Richard

2. I am a new member so I am not sure how best to convey this information; but, on the suggested link there are some text errors that should be corrected in the portion of the calculations "For the Inner Body Subjected to External Pressure , Axial Force, torque and Rotation". (ie. in (13) thru (15) the word "internal" should be "external" and in (13) the equation is mislabeled as "radial stress" instead of "radial displacement".

3. Originally Posted by JAlberts
I am a new member so I am not sure how best to convey this information; but, on the suggested link there are some text errors that should be corrected in the portion of the calculations "For the Inner Body Subjected to External Pressure , Axial Force, torque and Rotation". (ie. in (13) thru (15) the word "internal" should be "external" and in (13) the equation is mislabeled as "radial stress" instead of "radial displacement".
Yes, the terminology is wrong and has been corrected.