Method for fitting Aluminium fins into slots

[///]

Hi Picclock,
Your little problem has dragged me out from lurking and made me register as a member!

I believe you will find joy with shrink fitting as Bezalel has mentioned, but go in the reverse direction.
Machine the slots to size, then make the plates oversize(or whatever is easiest)
Throw the lot in the freezer for ?? time and all the metal will shrink. Your slots will get wider, the plates narrower.

Assemble the lot and as the Ali warms back up to room temperature, the slots will narrow and the plates widen.. they will be firmly attached, you will be surprised how strong this is, particularly with the surface area you will have in contact.

I have used this method to shrink fit many items over the years and it works a treat.

The thermal coefficient of expansion for Aluminium is 22.2^-6 M/M/degC, or, 12.3^-6 in/in/degF

Hope you give it a shot

Edit: Hmmm, the thicknesses of material you are working with may be a problem.
Play with this (very)rough spreadsheet I threw together and see what you think.
That shrink figure is for one item only... the slot or the sheet.. combine the two.
(rename the file from Therm.txt to Therm.xlsx)

View attachment Therm.txt

 

[bezalel2000]

Hi there /// wEc1

I like that method and a much safer solution - :bow:

Just no where near as much fun :big:

Bez

 

[Ken I]

@ KenI
Yes. If you bolt a stack together to some extent you make things worse. The number of junctions between the fins and the core increases, additionally you then have to thermally connect the assembled fins to the block. With fins in slots each fin has a direct connection to the block limited only by the joining method.

I meant that this was the whole thing - whatever you are going to machine on the opposites side (tapped holes and all) - you perform on the assembled block - obviously dodging the cross bolts.
You could replace the bolts with aluminium rivets into countersinks and machine flush. Rivet using a hot rod - the final contraction will secure.
It doesn't matter if you drill and tap across plates - it will still hold together.

I like Bezalel's casting idea.

A drawing of the complete assembly might help. (I'm thinking like this is an electronics heat sink - if its an engine underneath then I'm way off base.)

Ken

 

[picclock]

@ kenI
The reason for mounting to a solid block is that there is a pressure differential between the fin side and the interior, The interior structure of the block is also complex - for me anyway. I have spent around 3 weeks on both halves so far, with a bit more to go (I do work slowly though).

@ Bezalel
Casting the fins in position is a good idea, but with the fins attached I would have insufficient room to machine the interior of the block pieces.

@ ///
I don't think I could get the tolerances for that to work well, additionally it would tend to curve the block. If I could have got the tolerances that close I would just push fit them.

For the curious I will post pictures after the project is finished, although I suspect that it will not be very photogenic. I was testing one of the pressure containers in my conservatory, by filling with water and anti freeze and pumping it up to 300 psi to ensure its integrity. I left it at this pressure to see if it would weep for an hour or two. When I returned the pressure had risen to 950psi due to the heat from the sun expanding the fluid. Felt very afraid at that point Integrity was still good though that's something I would not want to repeat.

Need to sort out an aluminium sheet denter now ;D

Best Regards

picclock