All you need is an inverter. As long as you keep the motor within 20% or so of its rated speed, you have have adequate torque and other operational characteristics. You can go even slower, but I personally like to keep it within 20%.

If you have three phase power, then I have a nice supply of inverters, could hook you up. If not, then you're not out of luck, they do make single phase inverters. ( Variable Frequency Drives. ) It would be probably more expensive to get a DC motor and drive than just an inverter. I promise you would love the machine after you put a speed drive on it. You might find yourself adjusting it constantly for different jobs, you you might find a happy medium and leave it, but either way the machine won't be in the dumpster.

I am unclear on how a sanding disc can explode? Are you talking about the steel plate upon which you attatch a sticky sandpaper sheet? yikes.