Hi - new beek here.
my bees have effectively glued the trough caps shut with propolis 
thoughts on how I can remove the propolis so that I can get honey out?
Thank you
Tzipor
Hello and welcome to the Flow forum! 
How did the bees get to the caps? Any chance of a photo? I am guessing that you left your Flow super on over winter? Bees will propolize everything in sight over winter, so I would strongly recommend taking it off after July.
To answer your question more directly, propolis dissolves quite well in rubbing alcohol or ethanol, if you have that much propolis to remove. Assuming it is on the outside of the frames, I would apply it with a shop towel or a gauze pad - something that won’t shred when wet and used for rubbing. Those two solvents will not hurt the frames, which are made of food grade polypropylene. I would not use acetone though. You might not want to contaminate your honey with alcohol either, especially rubbing alcohol or even pure isopropanol if you can get that from your job… 
In that case, I would get a pair of pliers and gently but firmly grab the central moulding of the cap. You should then be able to use enough force to twist them off with those. They may break, as that central part is not very strong. If you need replacements, you can usually buy them from here and while you are at it, I would suggest a second Flow key, as it is much easier to open the frames using two keys at once (still only opening 20% of the frame at a time):
https://www.honeyflow.com/collections/spare-parts/products/flow-frame-caps-covers-and-tube-kit
If the propolis is inside the trough, you may have a bigger problem. I would lift the frames out and inspect the underside for a hole in one of the sections. If there is one, bees can get into the trough. More problematic is that any hole will leak honey into the hive when you harvest. You will then need to take the super off the hive and harvest over a drip tray.
Hope that helps!
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Thank you so much! I cleaned them today.
The bees didn’t get into the trough - they put propolis in the tiny space between the cap and the tube - from underneath. Very clever
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I use a pair of pliers when the plugs are tight with a bit of propolis. I just give a little twist. Works well.