I am making a knife with a flat grind on it and I am using my 2x28 belt grinder 1/2hp. It is taking so much time just to get the bevel down to the center line. I need to know how to do a flat grind fast and also my knife is 1 1/2 inch thick
Blaze 36 grit belt around 5000 FPM will remove material quickly along with finger tips if you get sloppy. The little grinder you have will be slow just by design and one reason people go with a 2hp+ 2x72 with variable speed, they can eat steel surprisingly fast.
Don't be in too big a hurry. Grinding fast tends to equal ruined blades, when you're starting out. As John said, a 36 grit ceramic belt at high rpm will go through metal like a kid through cake. It's very easy to take off too much, too quickly. You may find it slow going on your grinder but it will help you develop good technique that will last forever.
For what it's worth I may do 60 to 100 passes on the belts to flat grind a medium size knife. It's not a fast process even on a 2 x 72". It's about controlled pressure and time. If too much heat is being generated try a fresh belt. Dan