Shrink-fit ceramics, steel 1

[FC2008]

Hi,
I'm looking at the possibility of connecting a cylinder made of Zirconia and a steel housing made of Inconel 625 by heating the steel housing.

The steel housing is a simple pipe with a outer diameter of 50mm. The Zirconia cylindre has a diameter of 40mm and is 40mm long.

The connection has to be strong enough so the Zirconia does not fall out. The system may experience relatively large temperature variations, let's say -50degC to 100degC.

Any information is greatly appreciated.
Thanks

 

[vpl]

I must be missing something here ... what's the inner diameter of the steel housing? As posted, your Zirconia cylinder will just slide in and out of the Inconel pipe.

Patricia Lougheed

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[FC2008]

Hm, I wrote that the pipe has an outer diameter of 50mm..The inner diameter of the pipe and the outer diameter of the zirconia are the "same"..

 

[robnew]

I would start by determining how much press fit you need. Decide how much force you want the zirconia to withstand without falling out. Use this force plus a safety factor and the coefficient of friction between the two materials to determine a surface pressure you need between the two parts. Calculate the deflection this surface pressure will cause in your two parts. This will give you the press fit needed without considering temperature variations. Add the dimensional changes your expected temperature variations will cause to the press fit and you have your answer. Next you should calculate the stresses when the temperature variation is making the press fit as tight as possible to be sure you are within acceptable limits. Don't forget manufacturing tolerances.

 

[moltenmetal]

robnew gives good advice, but probably means how much "interference" you need when saying "press fit". You should not even think about actually pressing the zirconia part into the metal part- you heat one and perhaps cool the other as you already plan, such that the metal part shrinks onto the zirconia part as it cools.

The zirconia has quite an enormous compressive strength as long as you take its brittleness into account. You need to carefully avoid stress concentrations in your design which might lead to cracks. At the hottest (or coldest) your parts will ever get in storage or service, the zirconia must still be held with sufficient compressive force inside the steel housing. The zirc part also must never be put into tension or it will break. Sudden transitions from hot to cold will be a worry.

 

[tomwalz]

Hard to beat Moltenmetals answer.

I am not sure I would bother trying to shrink the Zirconia since it is pretty thermally stable. Chilling it would speed up the assembly process.

Where moltenmetals talks about stress concentrations and tension I will talk about the need to have the mating surfaces match pretty close to exactly. Certainly both need to be smooth. The smoothness required will depend on the size of the pieces involved. Also the steel will need to shrink very uniformly.

Tom


Thomas J. Walz
Carbide Processors, Inc.

http://www.carbideprocessors.com

Good engineering starts with a Grainger Catalog.

 

[FC2008]

I will have to check the likelihood of rapid temperature drops. I have limited space, but have tried to design the steel part such that it shrinks uniformly.

I greatly appreciate your advice, thank you.