Scroll compressors - sharp corners at bottom of labyrinths 1

[sdra2]

I have had cause to look at a couple of stripped down scroll compressors (from two different manufacturers), and in both instances it was noticed that at the bottom of the labyrinth profiles, on both the stationary and moving part, there are sharp corners. By sharp, I mean almost non-existent, and certainly much less than you might expect from conventional machining processes.

Would anyone know why these things are engineered this way? Without knowing really what loads they see, I might have expected some kind of designed in fillet radius rather than a sharp corner. Is it related to performance, or to minimise the risk of clashing parts?

Thanks in advance.

 

[MintJulep]

The things work by maintaining very little clearance both radially and axially between the two halves of the scroll.

If there were a radius or chamfer where the spiral meets the disk then there would have to be a corresponding round-over or chamfer at the free edge of the spiral.

I would suspect that having such a feature would tend to build up a wedge of oil, causing more than desired inter-chamber leakage.

I suspect that the scrolls are rough cast, then finished by EDM.

 

[imok2]

Electrical Discharge Machining (or EDM) is a machining method primarily used for hard metals or those that would be impossible to machine with traditional techniques

 

[MintJulep]

So are you saying that you think the machining is not EDM?

 

[sdra2]

Cheers for the info chaps (yep, I'm from the UK).

Do these things not crack at the bottom of the labyrinths from fluctuating pressure and/or motion induced loads then? What I was really wondering, I suppose, is how on earth anyone could ever make any sort of analysis of these components with such sharp corners - how could anyone predict component life? Is there, in reality, little or no net load on the labyrinths? (I haven't managed to get my head around how these things are loaded yet).

Any input thankfully received. Thanks again.

 

[imok2]

"So are you saying that you think the machining is not EDM"?
I'm saying I didn't know what EDM was and maybe others didn't know either