We've (The SO is doing all the work) got about 10 sq.ft. of 1/2" thick foam rubber to remove on the apple packing line. It was bonded to steel with contact cement. We're scraping 1 sq.in. at a time, its going to take forever this way. Its inside the weight sizer and hard to get at.
Heat will make it let go. Can you use a heat gun or propane torch on the back side of the steel? Warming from the rubber side will not work as well. Rubber sure stinks if you get it charcoal hot, you just want to get it really warm, like sitting out on a really hot, sunny day. You should be able to peel the whole sheet off. Lacquer thinner should help clean up any residue.
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Heat or solvent, and when it softens up you use a 4" blade wallpaper scraper with an 18" handle to peel it up. Available at your local DIY center, about $8 for the tool and $3 for a half-dozen spare blades. Looks like a S/E Razor Blade Scraper on steroids, gives you the leverage and control you need.
But see if you can take the plate out, or disassemble the sizer and remove the chute overhead for easier access to scrape and re-line it - no matter what you do, working on it while it's still installed deep in the guts of a machine is going to be a ball buster. Been there, Done (stuff like) that, have the scars...
And this time you might want to pick a less aggressive cement - use the good cement to put a Burlap backing on the foam, then use the special Green Removable carpet adhesive (for commercial peel-up 2'x2' carpet squares) to attach it to the machine. Then it will come out again without nearly the fight.
Or put a Burlap backing on the foam for strength, and screw the foam sandwich to the machine, or wrap the burlap around the edges and Ty-rap it on the back side. Think! ;-) There is usually a way to make it easier the next time.
Tuluol. Or tuluene, whichever. Lacquer thinner evaporates too fast, and allows the contact cement to return to its original stickiness when it evaporates. Toluol keeps it softer longer, and less sticky. And it doesn't kill as many brain cells.
De-ice boots are glued to aircraft wings and props with contact cement. I changed tons of them in my younger days.