I try to restore my IBM 9406 Model 600 AS/400 back to working order. To remove the failing power supply, I had to remove lots of things and I have now this major source dust here, the magnificent IBM 44H7756 fan assembly from the year 1997:
I’d guess it is for muffling the sound. A box made out of thin sheet metal (as this unit seems to be when assembled) can give quite a lot of sound. You can find different version of sound dampeners in older (and newer) products. I suppose companies working with acoustics could have somethig similar to sell.
I’d agree - so the thing to do, I think, is get all the old foam out, buy some sheets of acoustic damping foam, cut them to shape and stick them in. Those sheets seem to be sold variously as sound deadening, noise deadening, foam silencing, acoustic foam, acoustic material, and sold as panels, sheets, pads or kits. I’m pretty sure I bought some back in the day, and they worked well. Bare metal panels do vibrate and transmit noise very well.
As you say, it is quite obvious this is used to reduce noise (the server is pretty loud anyway).
I was wondering what was the reason for the foam to be destroyed like this? There is stark contract between the top part that seems to be outside of the main air flow and the rest which is crushing to pieces.
It’s true that many plastics deteriorate over time - I think through loss of plasticisers which are mildly volatile. Maybe that has something to do with it. (We’re told not to leave flexible power cords in contact with hard plastics for extended periods, because they will soften and deform the hard plastic.