Need pointers for calculating 6061 shrink fit 4

[JimLou]

Hi! I'm new here, and a shade-tree mechanic.

My current project is to shrink fit a sleeve over a drive pulley hub. Both parts are 6061 T6. The hub has an I.D of 1.6" and an O.D. of 2.1". The sleeve will have an O.D. of 2.88" with 0.10" deep serpentine belt grooves in it.

In my copy of Machinery's Handbook are formulas for calculating the shrink fit allowance for steel and cast iron components, but not for aluminum.

Can someone please point me in the right direction? Thanks!

 

[JimLou]

Yep. You have accurately described the problem. And I understand what you're saying about the stress concentration as the base of the groove. I hope that the fine details like that are of such a minor nature that I don't have to worry about them.

My customer's main concern is that the mechanism will slip, but I think that's covered. Once I get down the the final dimensions I'll have to see what room I have for Dutch pins. I'm hoping that the metal they displace won't cause a problem, being in a relaticely high-stress location.

 

[IFRs]

Can you weld the parts together?

 

[JimLou]

Yes, I considered TIG welding them, but the HAZ will probably reach two of the six belt grooves. I'm afraid that in a -0 condition they would wear unacceptably. With the additional expense of heat treating the total would approach the cost of making a complete pulley.

 

[MikeHalloran]

The beauty of the Dutch pins is that you don't need a severe interference fit.



Mike Halloran
Pembroke Pines, FL, USA

 

[JimLou]

An update. Today we finished machining the collar to go over the hub. We had an interference fit of 0.0035". I had decided on .003 to .004, so I felt quite confident.

We chilled the hub to about 0F in a deep freeze and boiled the collar. That should have given an assembly clearance of .0045. We had excellent surface finish, so it should have worked.

The assembly started well, but about a third of the way on, of about an inch total, it got too tight to push by hand. I quickly put it in the press but it was too late. The next movement apparently galled the pieces, and the hub subsequently collapsed.

I knew I should have gotten some dry ice to chill the hub. Drat! So now we'll just machine a complete pulley.

Thanks for all the help, guys! Even though it didn't work out, it was a nice education.