Rate of Freeze-fitting shrinkage

[mechanicalhead]

Hi

I work for an excavator bucket manufacturing company and we do a lot of Freeze-fitting on the bushes. I have come across a continuous issue regarding the fitting of some of the bushes as we can't work out how the bushings behave when frozen i.e. how much they shrink by, using liquid Nitrogen. Most of the bushes are made out of phosphor bronze or steel

I was wondering if there is a way to predict/work out the shrinkage rate of such material over a given diameter and wall thickness so that we could work out the tolerances accordingly.

 

[TVP]

Lots of available information on this topic:

http://www.engineeringtoolbox.com/assembly-shrink-fits-d_951.html

http://www.ameritherm.com/PDFs/shrinkfitcalcs.pdf

http://www.tribology-abc.com/calculators/e6_2.htm

 

[Cockroach]

For sure, you're realling with a heat transfer and thermal strains.

Look at a first year course in statics, deformation for example, and you will come across the equation: d=a(T')L. Deformation is a function of temperature change and length of the member. The linear coefficient is a number particular to the material properties in question.

Good luck with it.

Regards,
Cockroach

 

[dhengr]

Search this Mech. forum for shrink-fit threads/discussions. Just a month or so ago there was quite a lengthy thread an the topic. thread404-312505 In part, the discussion had to do with, what happens if you cool a bushing, does the outside dia. shrink and the inside dia. expand, or shrink also? It has to do with volumetric change or length (circumferential) change due to temp. change. Or, vis-a-versa, if you heat the bushing. And, we seem to understand this better when we are just talking about a 12" long steel rod. Now, form this rod into a ring and do the same thought experiment. Look up Lame’s equations and shrink or press fits in any good Strength of Materials, Machine Design or Theory of Elasticity books. Another thread thread404-314076.