It took some research, but I got it!

Research:
1. See page 151 in this PDF: https://gis.townofbethlehem.org/maproom/tempMigrationFiles/S...

There it says: "The filter is equipped
with a demooning bar to prevent belt wrinkling due to
mooning of belt fastener or a sewn joint."

2. Also see page 153. There it says: "The belt
with the dried· cake then moves over a demooning bar for the
elimination of belt wrinkles."

3. Also see page 157, where it says: "The demooning bar
and Edge Track mechanisms are to provide automatic wrinklefree alignment of the filter belt."

4. Also see page 158, where it says: "Belt mooning should becheckedduring operation and corrected with the adjustment of the mooning bar."

Conclusion:
Now we know that with "belt mooning", they refer to a belt being wrinkled during runtime.
So, lets figure out some answers.

Answer:
De-mooning bar = Utsträckningsstång
– "Utslätningsstång" is probably not a correct description of what it is doing. If your customers de-mooning bar is the same as the one used in this cake machine, then the belt runs over it. Making "utsträckningsstång" a fine choice. And it is adjustable too, which makes sense.
– You could use other words for "bar". But it´s very likely round, as to not damage the belt, so "stång" should be fitting.

When it comes to "belt mooning" you just have to write something fitting depending on where it appear.

This was fun! I think I´ll answer more KudoZ-questions going forward.