Thank you so much for leading me down memory lane! Worked for Universal for 7 years overall. Early 90's was in sales and visited the site many times.
Think of the normal process like making sand castles, the abrasive (different types and grades stored in those hoppers) are mixed with various clay and glass compounds with a tiny amount of temporary binder (dextrose) then when mixed water is added to make it damp (dissolves the binder and makes it sticky).
The damp mix is spread into very strong moulds but has to be evenly spread - a skilled job!, then pressed in the presses, it's then demoulded and the binder holds everything together although it's still fragile. The 'green' wheels are then dried, the magnetrons shown were indeed for microwave heating to dry some types of wheel more quickly, recall 8kW but could be wrong, was early days of microwaves.
When dry they were fired in the kilns, these were gas fired hence the enormous gas meter. Seem to recall they were loaded onto wheeled trucks to load and unload etc. During firing the glass and clay go through different phases and become fluid, so when cooled form a solid structure around and between the abrasive.
I remember the labs (started in R&D at another site and visited few times), the offices - got a massive bollocking from the MD once in one of those offices due to an extraordinarily high mobile phone bill, back in the days when you got charged if someone left a voice message then again when you listened to it!
In days gone by the kilns were tunnel type, and part of the kiln workers employment was to get 6 pints of beer a day to prevent dehydration.
During WW2 when sugar was rationed the workers would use the the binder in tea in place of sugar, so a bitter chemical was added (like the one to stop you biting your nails) to try to prevent this. Workers forged on, using it regardless and got used to the taste, continuing to use it after the war and rationing stopped apparently. The works had it's own rail yard back in the day for transporting the abrasive wheels.
So - thanks for prompting my brain to search back in the archives!!