Labyrinth/Housing Fit Question 2

[MechatroPro]

Hi everyone,
I'm tasked with preparing manufacturing drawings of a Co2 compressor labyrinth seals,
I have a question about the required Fit(clearance/interference Fit) of compressor labyrinth seals in housing.As you see in the attached picture, labyrinth seal has an interlocking feature which secures the laby inside housing, my question is about the required fit between faces 1 to 8 on its counterpart housing surfaces. to have a sense of the size,the overall section of the labyrinth fits inside a 33mmx24mm box.
figure 1 is the drawing i have, and fig 2 is only for clarification:

http://oi57.tinypic.com/2637xw1.jpg

I highly appreciate any input.

 

[MechatroPro]

I forgot to mention that these labyrinth seals are made of aluminum alloy.

 

[Tunalover]

I would look up "sliding fit" in Machinery's Handbook and call out the size tolerances required for the mating parts. There's an ANSI standard, I'm sure, that assigns tolerance nomenclature to the mating parts.


Tunalover

 

[Tmoose]

Is figure 1 complete? If it is, I don't see how the labyrinth is removable. Surfaces 2 thry 7 appear to form an interlocking shape. Like it would have to be cast in place

 

[MechatroPro]

Yes, figure 1 is part of the assembly drawing of the compressor and figure 2 is a simplified representation of the laby seal, and in both figures you see interlocking features on the laby and housing. It's not cast into the stationary part, How they fit the laby seal into place should be tricky, its my question too. Designing it with correct fit and tolerance, is another point of debate here.

 

[tbuelna]

The simple answer to your question is that the radial and axial fits should be sufficient to precisely locate the seal tips relative to the shaft gland surfaces under all operating conditions, so that leakage is minimized and no contact between the shaft and seal tips occurs. The radial/axial locating features of each component should be selected to minimize the effect of tolerance accumulations, but should not create an over-constrained condition in the assembly.

Having said that, the detailed design of high-performance labyrinth seals is actually quite complicated. To perform effectively the operating clearances must be extremely tight. To determine the optimum clearances, you must take into account factors such as thermal growth mismatch, shaft dynamics, and even the local fluid dynamics. Your sketch shows stepped diameters at the seal tips, which makes things even a bit more complicated.

Often, due to the difficulty in obtaining a satisfactory operating tip clearance because of factors such as tolerance accumulation, thermal mismatch, shaft dynamics, etc, a sacrificial or abradable coating is applied to the seal tip surfaces. After a few operating cycles, the coating is worn away to provide an optimum clearance.

Good luck to you.
Terry

 

[JJPellin]

These laby seals are built in two sections (half circles). They are rolled into place in these hook fits when the compressor case is split open (axial split machine). The manufacturer should have fit criteria for these laby seals. I have attached a sketch with the laby seal fits for the last compressor I worked on that uses these same sorts of hook fits. The laby seals in my machine have a cross-section that is approximately 1" by 1.5". But, the laby seal fits around the impeller eye in an Elliott 88M. My seals are approximately 30 inches in diameter when assembled. Note: The dimensions in the attached sketch are in inches.

Johnny Pellin